Forecast Discussions mentioning any of
"HRRR" "RAP" "RR" "RUC13" "RUC" received at GSD on 12/20/12
AREA FORECAST DISCUSSION
NWS DENVER/BOULDER CO
342 PM MST TUE DEC 18 2012
.SHORT TERM...MOUNTAIN WEB CAMS SHOW SNOW HAS DECREASED MOST AREAS
AS FLOW ALOFT BECOMES SOUTHWEST AHEAD OF APPROACHING TROUGH.
ELSEWHERE...MID AND HIGH LEVEL CLOUDS ON THE INCREASE AS MOISTURE
SPREADS INTO REGION. MODELS SIMILAR IN BRINGING TROUGH ACROSS
GREAT BASIN THIS EVENING WITH INCREASING MID LEVEL ASCENT AND
INSTABILITY. SHOULD BEGIN TO SEE SNOW INCREASE ONCE AGAIN...
ESPECIALLY AFTER MIDNIGHT WHEN 700 MB LOW MOVES INTO WESTERN
COLORADO AND FLOW ALOFT BECOMES WESTERLY. SHOULD SEE A GOOD SHOT
OF SNOW WITH THE INCREASING ASCENT AND FAVORABLE LAPSE RATES. WILL
ISSUE AN ADVISORY FOR SNOW FOR THE MOUNTAINS...BEGINNING AT
MIDNIGHT. ACROSS PLAINS...SURFACE LOW TO DEEPEN TONIGHT AHEAD THE
APPROACHING LOW WITH WINDS BECOMING NORTHERLY AFTER 06Z. AIRMASS
TO GRADUALLY MOISTEN AS DEEPER MOISTURE SPREADS INTO AREA.
BEGINNING TO SEE SOME ECHOES ACROSS LARIMER AND NORTHWESTERN WELD
COUNTIES. LATEST MODELS SHOW MOST OF THE SNOW DEVELOPING AFTER
06Z..THOUGH THE RAP HOLDING OFF UNTIL AFTER 09Z WHICH MAY BE A BIT
SLOW. AS WINDS BECOME NORTHERLY...SHOULD SEE SNOW COVERAGE
INCREASE AND BEGIN TO SPREAD SOUTH BY 12Z. UPPER LOW TO MOVE
ACROSS THE STATE DURING THE MORNING WITH GOOD QG VERTICAL
VELOCITIES AND INCREASING LAPSE RATES. LATEST MODELS HAVE BEEN
INDICATING LESS SNOW FOR THE PLAINS...BUT MAY BE OVERDONE GIVEN
THE MID LEVEL ASCENT. A FEW LOCATIONS COULD SEE SNOW FALL RATES OF
1/2 TO 1 INCH PER HOUR DURING THE PERIOD OF GREATEST ASCENT DURING
THE MORNING. WILL UPGRADE THE WINTER STORM WATCH TO A SNOW AND
BLOWING SNOW ADVISORY FOR MUCH OF THE PLAINS. WILL BEGIN THIS
HILITES AT 08Z...MAINLY TO ACCOUNT FOR THE MORNING RUSH. WILL ALSO
ISSUE A SNOW ADVISORY FOR THE FOOTHILLS BEGINNING AT 08Z AS
MODELS SHOW DEEP UPSLOPE TO AROUND 600 MB. ACROSS THE FAR EASTERN
PLAINS...BEST CHANCE FOR SNOW TO BE AROUND 15Z. THOUGH SNOW
AMOUNTS MAY BE A BIT LIGHT...THE GUSTY WINDS WILL PROVIDE FOR
BLIZZARD CONDITIONS FOR ZONES 46..47 AND 49 WITH LIMITED
VISIBILITES. WILL ISSUE A BLIZZARD WARNING FOR THOSE ZONES
BEGINNING AT 15Z. WILL ALSO INCLUDE ZONES 48..50..51 AS WELL AS
41. SOME ROAD CLOSURES WILL CERTAINLY BE POSSIBLE. ACROSS THE
MOUNTAINS...WILL CONTINUE THE ADVISORY THROUGH THE AFTERNOON. SNOW
WILL PROBABLY BE ON THE DECREASE AS MOISTURE AND DYNAMICS
DECREASE. TOTAL SNOW ACCUMULATIONS LOOK TO BE FROM 3 TO 8 INCHES
ACROSS THE PLAINS AND FOOTHILLS...HIGHEST NEAR THE WYOMING
BORDER. ACROSS THE MOUNTAINS...6 TO 14 INCHES CAN BE EXPECTED.
.LONG TERM...MODELS SHOW THE UPPER TROUGH AXIS OVER THE EASTERN
BORDER AT 00Z WEDNESDAY EVENING. STRONG NORTHWESTERLY FLOW ALOFT
IS PROGGED WEDNESDAY NIGHT. ON THURSDAY AND THURSDAY NIGHT...AN UPPER
RIDGE IS PROGGED TO MOVE ACROSS COLORADO WITH FAIRLY STRONG WEST-
NORTHWESTERLY FLOW ALOFT. THURSDAY NIGHT AND FRIDAY ARE PROGGED
TO HAVE FAIRLY WEAK ZONAL FLOW ALOFT. BY FRIDAY NIGHT...THE FLOW
ALFOT IS WEST-SOUTHWESTERLY IN DIRECTION. THE QG VERTICAL VELOCITY
FIELDS HAVE DOWNWARD SYNOPTIC SCALE ENERGY PROGGED FOR THE CWA
WEDNESDAY NIGHT INTO THURSDAY EVENING. THE REST OF THE THURSDAY
NIGHT THROUGH FRIDAY NIGHT...THE ENERGY IS BENIGN. THE LOW LEVEL
WIND AND PRESSURE FIELDS SHOW THE BOUNDARY LAYER FLOW TO BECOME
DOWNSLOPING EARLY WEDNESDAY EVENING. BY 06Z WEDNESDAY NIGHT...
WESTERLY WINDS PREVAIL OVER THE MOUNTAINS...FOOTHILLS AND WESTERN
PLAINS...WITH FAIRLY STRONG NORTHWESTERLIES THE FURTHER EAST TO GO
TO THE COLORADO BORDER. DOWNSLOPING IS PROGGED TO CONTINUE
THURSDAY AND FRIDAY...BUT AT LESSER SPEEDS. FOR MOISTURE...THERE
IS STILL SOME OVER THE EASTERN FORECAST AREA EARLY THURSDAY
EVENING...BUT ALL THE MODELS DRY THINGS OUT RAPIDLY AND BY 06Z
WEDNESDAY NIGHT...PRECIPATION SHOULD BE OVER EVERYWHERE. MOISTURE
IS QUITE SPARSE THURSDAY THROUGH FRIDAY NIGHT. THERE IS NO
MEASURABLE PRECIPITATION NOTED ON THE QPF FIELDS WEDNESDAY NIGHT
THROUGH FRIDAY NIGHT...ALL FIVE PERIODS. FOR POPS...WILL DECREASE
EVERYTHING RAPIDLY WEDNESDAY EVENING...THEN NO POPS FROM 06Z
WEDNESDAY NIGHT THROUGH FRIDAY. WILL LINGER SOME BLOWING SNOW OVER
APPROPRIATE AREAS WEDNESDAY NIGHT. AS FAR AS HIGHLIGHTS GO...
WILL GO WITH THE SHORT TERM FORECASTER. FOR TEMPERATURES...
THURSDAY HIGHS ARE 6-9 C WARMER THAN WEDNESDAY`S. MOS GUIDANCE
VALUES MAY BE TO HIGH...ESPECIALLY FIGURING WE WILL LIKELY HAVE A
SNOW COVER IN PLACE OVER MUCH OF THE CWA. FRIDAYS`S HIGH COME UP
ANOTHER 2-4 C FROM THURSDAY`S. FOR THE LATER DAYS...SATURDAY
THROUGH TUESDAY...MODELS HAVE WEST-SOUTHWESTERLY FLOW ALOFT OVER
THE CWA SATURDAY INTO MONDAY. THE ECMWF BRINGS AN UPPER TROUGH
ACROSS LATE MONDAY AND MONDAY NIGHT. THE GFS IS MUCH SLOWER WITH
THE SYSTEM. BOTH MODELS HAVE LITTLE MOISTURE OVER THE WEEKEND. BUT
BY SUNDAY NIGHT...MOISTURE IS ON THE INCREASE. BOTH MODELS DO
SHOW A PRETTY COLD AIRMASS TO MOVE INTO COLORADO WITH THE UPPER
TROUGH MONDAY OR TUESDAY...DEPENDING. THERE IS ALSO UPSLOPE FOR
THE PLAINS AND FOOTHILLS. WILL GO WITH MINOR POPS RIGHT NOW AND
CONTINUE TO WATCH THE EVOLUTION OF THIS FEATURE.
&&
.AVIATION...EASTERLY WINDS TO SHIFT TO THE NORTH AROUND 06Z AS A
COLD FRONT MOVES SOUTH ACROSS THE PLAINS. SHOULD SEE CEILINGS
GRADUALLY LOWER...WITH CEILINGS AROUND 6000 FEET POSSIBLE. NOT
EXPECTING SNOW TO DEVELOP UNTIL AFTER 06Z WITH MVFR CONDITIONS
BY 09Z. IFR CONDITIONS TO FROM 12Z TO 19Z DUE TO SNOW AND BLOWING
SNOW AS WELL AS LOW CEILINGS. SNOW TO DECREASE AFTER 19Z BUT GUSTY
WINDS TO CONTINUE. MVFR CONDITIONS TO PREVAIL WITH OCCASIONAL IFR
CONDITIONS. TOTAL SNOW ACCUMULATIONS OF 2 TO 4 INCHES
EXPECTED...MAINLY DURING THE 12Z TO 18Z TIME FRAME.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
BLIZZARD WARNING FROM 8 AM TO 8 PM MST WEDNESDAY FOR COZ041-
046>051.
WINTER WEATHER ADVISORY FROM 3 AM TO 5 PM MST WEDNESDAY FOR
COZ035-036.
WINTER WEATHER ADVISORY FROM 11 PM THIS EVENING TO 5 PM MST
WEDNESDAY FOR COZ031-033-034.
WINTER WEATHER ADVISORY FROM 3 AM TO 8 PM MST WEDNESDAY FOR
COZ038>040-042>045.
&&
$$
SHORT TERM...D-L
LONG TERM....RJK
AVIATION...D-L
AREA FORECAST DISCUSSION
NWS GRAND JUNCTION CO
258 PM MST TUE DEC 18 2012
.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY NIGHT)
ISSUED AT 218 PM MST TUE DEC 18 2012
THIS LATE AFTERNOON THE FORECAST AREA IS DIVIDED INTO TWO REGIMES
DIVIDED BY THE COLD FRONT LAYING ALONG THE ROAN-TAVAPUTS PLATEAU
INTO THE FLATTOPS. ALONG AND NORTH OF THE FRONT...HEAVY SNOW HAS
BEEN FALLING. STATE PATROL REPORTS AROUND 6 INCHES IN CRAIG THOUGH
ONLY HALF AND INCH IN VERNAL. CROSHO AND BUFFALO PARK SNOTELS REPORT 15
INCHES OF NEW SNOW. SOUTH OF THE FRONT SNOWFALL HAS BEEN MUCH MORE
SKETCHY...MAINLY ALONG SW FACING SLOPES.
A STRONG WEST TO EAST ORIENTED JET STREAK ALONG THE WYOMING
BORDER THIS MORNING HAS LIFTED OFF TO THE NE TODAY. IN RESPONSE
THE MID-UPPER FLOW HAS BACKED TO SSW TODAY PRODUCING WARM
ADVECTION. THIS WARM OVER-RUNNING HAS HELPED TO PRODUCE THE HEAVY
SNOWFALL ALONG THE STATIONARY FRONT. SOUTH OF THE
FRONT...AFTERNOON SURFACE TEMPERATURES CLIMBED SEVERAL DEGREES
ABOVE GUIDANCE. STRONG ISENTROPIC UPGLIDE WILL CONTINUE INTO THIS
EVENING. THIS STABILIZING PATTERN CAN BE SEEN ON RADAR WITH MTN
WAVE BANDING SEEN TO THE NORTH OF THE RADAR TRANSMITTER.
WET BULB ZERO AND 700MB TEMPS SUPPORT SNOW DOWN TO 4500FT SO ANY
SHOWERS WILL QUICKLY TURN TO SNOW.
THE UPPER LEVEL TROUGH MOTION...THROUGH THE GREAT BASIN TONIGHT...
HAS GOOD MODEL CONTINUITY. YET THE 18Z NAM AND RAP BOTH SUPPORT A
LATER FRONTAL ADVANCE HOWEVER...NOW INTO THE I-70 CORRIDOR AROUND
MIDNIGHT TONIGHT. THIS PUTS THE CENTRAL VALLEY WARNINGS IN DOUBT
BUT DOES NOT REMOVE THE POTENTIAL TO GET UP TO 6 INCHES OF
SNOWFALL THERE. BASED ON THIS AND IN COORDINATION WITH THE SLC
OFFICE... HAVE KEPT THE WARNINGS IN PLACE AND SLOWED THE WORDING
TO EMPHASIZE THE PERIOD BETWEEN MIGHT AND SUNRISE.
THE SOUTHERN ZONES TOO WILL SEE IMPRESSIVE FRONTAL FORCING AFTER
MIDNIGHT INTO WEDNESDAY MORNING. IN THE COLD SECTOR OF THE STORM
LATE TONIGHT THROUGH WEDNESDAY...700MB TEMPERATURES WILL DROP
RIGHT THROUGH THE DENDRITIC CRYSTAL GROWTH REGIME TO -17C BY
WEDNESDAY AFTERNOON. THIS WILL VERY EFFICIENTLY EEK OUT ALL
AVAILABLE MOISTURE. ONLY NW-FACING SLOPES WILL CONTINUE THROUGH
WEDNESDAY AFTERNOON WITH ALL SHOWERS SHUTTING DOWN BY SUNSET. A
VERY COLD NIGHT IS IN STORE FOR WEDNESDAY NIGHT.
.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY) ISSUED AT 430 AM
MST TUE DEC 18 2012
DRIER NORTHWESTERLY FLOW ALOFT OVERHEAD WEDNESDAY NIGHT AS THE STORM
SYSTEM CONTINUES TO MOVE EAST. A RIDGE OF HIGH PRESSURE WILL MOVE
EAST OVER THE REGION AND REMAIN DOMINATE DURING THE END OF THE WEEK.
WITH SNOW ON THE GROUND...THE COLD AIR MASS BEHIND THE FRONT AND HIGH
PRESSURE EXPECT VALLEY INVERSIONS. TEMPERATURES SHOULD REMAIN COLD
IN THE VALLEYS. THEREFORE WENT BELOW GUIDANCE FOR THESE LOCATIONS.
THE COLDEST MORNING SHOULD BE THURSDAY WHICH SHOULD ALSO BE THE
COLDEST OF THE SEASON. BY THE END OF THE WEEK TEMPERATURES SHOULD BE
MODIFIED SLIGHTLY BUT THIS WILL BE A SLOW PROCESS DUE TO THE
PREVIOUSLY MENTIONED RIDGE OF HIGH PRESSURE.
THE RIDGE WILL SLIDE EASTWARD ALLOWING THE NEXT STORM SYSTEM INTO
THE AREA BY MONDAY ALTHOUGH THE TIMING AND PLACEMENT VARIES BETWEEN
MODELS. INCREASED THE PRECIPITATION FORECAST SLIGHTLY TO HIGHLIGHT
THAT A STORM IS ON THE HORIZON. THAT SAID THERE ARE MANY VARIABLES
STILL NOT WORKED OUT YET SO MUCH UNCERTAINTY WITH TIMING AND
STRENGTH.
&&
.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 1030 AM MST TUE DEC 18 2012
WIDESPREAD MODERATE TO STRONG MECHANICAL TURBULENCE EXPECTED THIS
EVENING ALONG AND NORTH OF AREA RIDGES AND MTNS. WRN COLORADO TAF
SITES...DETERIORATING CONDITIONS TONIGHT WITH LOWERING CIGS AFTER
03Z...BECOMING WIDESPREAD IFR FOR ALL TAF SITES AFTER 06Z.
WIDESPREAD 1 1/2SM -SN BR CIGS VV002 IS EXPECTED INTO WEDNESDAY MORNING.
AREAS OF MODERATE SN OVER NW COLORADO TODAY WILL SPREAD
SOUTHWARD OVERNIGHT.
&&
.GJT WATCHES/WARNINGS/ADVISORIES...
CO...WINTER STORM WARNING UNTIL NOON MST WEDNESDAY FOR COZ003-006>008-
011-014-020-022-023.
WINTER STORM WARNING UNTIL 6 AM MST WEDNESDAY FOR COZ001-002.
WINTER STORM WARNING UNTIL 6 PM MST WEDNESDAY FOR COZ004-005-009-
010-012-013-017>019.
WINTER WEATHER ADVISORY UNTIL NOON MST WEDNESDAY FOR COZ021.
UT...WINTER STORM WARNING UNTIL NOON MST WEDNESDAY FOR UTZ025.
WINTER WEATHER ADVISORY UNTIL 6 AM MST WEDNESDAY FOR UTZ024.
WINTER STORM WARNING UNTIL 8 AM MST WEDNESDAY FOR UTZ027.
WINTER STORM WARNING UNTIL 6 AM MST WEDNESDAY FOR UTZ023.
WINTER WEATHER ADVISORY UNTIL 8 AM MST WEDNESDAY FOR UTZ029.
WINTER STORM WARNING UNTIL 6 PM MST WEDNESDAY FOR UTZ028.
&&
$$
SHORT TERM...JOE
LONG TERM...AS
AVIATION...PF/JOE
AREA FORECAST DISCUSSION
NWS DENVER/BOULDER CO
949 PM MST MON DEC 17 2012
.UPDATE...
&&
.SHORT TERM...NO CHANGES NEEDED THIS EVENING. WELL ORGANIZED
SHOWER BAND WILL DROP SOUTH ACROSS OUR AREA OVER THE NEXT 6 HOURS.
A LITTLE BIT OF THIS WAS GETTING EAST OF THE MOUNTAINS IN WYOMING
WITH A BRIEF SHOWER AT CHEYENNE...BUT STRONGER DESCENT OFF OF THE
HIGHER MOUNTAINS OF THE FRONT RANGE WILL LIKELY REDUCE THIS AS THE
BAND DROPS SOUTHWARD. CURRENT LOW POPS FOR LARIMER COUNTY IS ALL
WE HAVE ON THE PLAINS AND THAT LOOKS FINE. FOR THE MOUNTAINS THIS
BAND WILL ENHANCE SNOWFALL FOR A FEW HOURS AS IT
PASSES...AMOUNTS IN THE FORECAST LOOK PRETTY GOOD.
&&
.AVIATION...VFR WITH SOUTH WINDS THROUGH TUESDAY MORNING...WINDS
BECOMING MORE EASTERLY AND POSSIBLY EVEN NORTHEAST BY LATE TUESDAY
AFTERNOON WITH A SLIGHT CHANCE OF CEILINGS LOWERING ENOUGH FOR
INSTRUMENT APPROACHES TO KDEN IN THE LATE AFTERNOON. MORE LIKELY
THESE CONDITIONS WILL WAIT UNTIL EVENING WITH SNOW DEVELOPING
AFTER MIDNIGHT TUESDAY NIGHT.
&&
.PREV DISCUSSION... /ISSUED 334 PM MST MON DEC 17 2012/
SHORT TERM...WEB CAMS SHOWING SNOW ACROSS MOUNTAINS
CONTINUING...THOUGH A BIT IMPROVEMENT IN THE LAST FEW HOURS. ALSO
SOME GUSTS AROUND 50 MPH ALONG THE DIVIDE...WHICH HAS BEEN
CREATING AREAS OF BLOWING AND DRIFTING SNOW. LATEST SNOTEL OBS
SUGGESTING ABOUT 6 INCHES OF SNOW HAD FALLEN ACROSS ZONE 31 IN THE
LAST 6 HOURS...WITH PERHAPS 2 TO 4 INCHES FOR ZONES 33 AND 34.
ACROSS FOOTHILLS AND ALONG URBAN CORRIDOR...WESTERLY WINDS GUSTING
IN THE 30-40 MPH RANGE MOST AREAS. STRONG PACIFIC JET STILL
EXPECTED TO MOVE ACROSS NORTHERN COLORADO DURING THE EVENING AND
OVERNIGHT WITH STRONGER WINDS LOWERING TO NEAR MOUNTAIN TOP. MODEL
CROSS SECTIONS INDICATING INCREASING LAPSE RATES ALONG WITH MID
LEVEL ASCENT. SHOULD SEE MOUNTAIN SNOW BEGIN TO INCREASE AGAIN
DURING THE EVENING AS THE LIFT INCREASES. LOCAL SNOW MODEL STILL
YIELDING ROUGHLY 5-10 INCHES ACROSS ZONE 31 TONIGHT...WITH AROUND
4-8 INCHES FOR ZONES 33 AND 34. THIS LOOKS REASONABLE BUT MAY NEED
TO ADD A FEW INCHES FOR THE DYNAMICS. FEEL CURRENT WARNING FOR
ZONE 31 AND ADVISORY FOR 33 STILL ON TRACK. BUT WILL ALSO INCLUDE
ZONE 34 IN THE ADVISORY...THOUGH AMOUNTS MAY NOT MEET CRITERIA
THERE WILL BE SUFFICIENT BLOWING SNOW. ACROSS PLAINS SHOULD SEE
WINDS BEGIN TO DECOUPLE THOUGH WILL REMAIN A BIT GUSTY NEAR THE
FOOTHILLS. LATEST RUC SHOWS SOME LIGHT PRECIP ACROSS ZONE 38 THIS
EVENING...STILL LOOKS REASONABLE WITH THE APPROACHING LIFT. ON
TUESDAY...FLOW ALOFT WEAKENS A BIT AS THE JET CORE HEADS EAST AND
BECOMES MORE SOUTHWEST AS AN UPPER TROUGH APPROACHES THE GREAT
BASIN. WILL STILL BE A BIT GUSTY ACROSS THE RIDGES. SOUTHWEST FLOW
NOT FAVORABLE FOR DECENT MOUNTAIN SNOWFALL. MID LEVEL QG ACENT
ALSO DECREASES. WOULD EXPECT SNOW TO CONTINUE WITH FAIRLY GOOD
MOISTURE...BUT SHOULD BE LIGHT. WILL NOT EXTEND HILITES BEYOND
12Z. ACROSS PLAINS...SURFACE WINDS TO BECOME EASTERLY WITH THE
DEVELOPMENT OF AN ANTICYCLONE. LATEST GFS AND ECMWF SHOWS SOME
LIGHT QPF DURING THE AFTERNOON...MAY BE A BIT OVERDONE AS LOW
LEVEL STILL LOOK DRY.
LONG TERM...MODELS CONTINUE TO ADVERTISE A SIGNIFICANT WINTER
WEATHER EVENT ACROSS THE FORECAST AREA ON WEDNESDAY. FROM TUESDAY
EVENING THROUGH WEDNESDAY EVENING AN UPPER TROUGH WILL BE MOVING
OVER THE STATE WHILE A SURFACE LOW OVER SOUTHEAST COLORADO
UNDERGOES STRONG CYCLOGENESIS. A STRONG COLD FRONT WILL MOVE OVER
NORTHERN COLORADO...INCLUDING THE MOUNTAINS...TUESDAY EVENING.
UPSLOPE WINDS WILL THEN CONTINUE THROUGH THE PRE-DAWN HOURS AND
STRENGTHEN THROUGH THE DAY WEDNESDAY. THE UPPER TROUGH WILL
CONTAIN PLENTY OF DYNAMICS ACCORDING TO THE Q-G DIAGNOSTICS
PACKAGE. THE PRESENCE OF THE STRONG UPPER LEVEL JET OVER THE PAST
FEW DAYS MAKE THE MODEL SOLUTIONS VERY BELIEVABLE. THE NAM QPF
AMOUNTS ARE A FAIR AMOUNT HIGHER THAN THE GFS AND ECMWF SOLUTIONS
CONCERNING HOW MUCH SNOW WE GET ON WEDNESDAY. ALL MODELS AGREE
QUITE A BIT OF WIND DEVELOPING. WITH THE THREAT OF SIGNIFICANT
BLOWING SNOW BECAUSE OF THE WIND...WILL ISSUE A WINTER STORM WATCH
ACROSS THE PLAINS. SNOW AMOUNTS OF 3 TO 6 INCHES WILL BE TOO LIGHT
IF THE NAM IS RIGHT. WIND GUSTS OF 25 TO 40 MPH MIGHT BE COMMON AT
THE HEIGHT OF THE STORM. PERIODS OF SNOW WILL BE ONGOING IN THE
MOUNTAINS DUE TO THE DYNAMICS OVER THE STATE.
THE UPPER TROUGH WILL BE MOVING EAST OF COLORADO BY WEDNESDAY
EVENING WHICH WILL BRING A RAPID END TO THE SNOW EVENT. LINGERING
SHOWERS IN THE EVENING WILL COME TO AN END OVERNIGHT. FOR THE
PERIOD THURSDAY THROUGH SUNDAY...STRONG UPPER RIDGING WILL BE OVER
THE STATE WITH DRY WEATHER FROM THE MOUNTAINS EASTWARD WITH
TEMPERATURES TRENDING TOWARD SEASONAL NORMALS.
EARLY NEXT WEEK LOOKS LIKE ANOTHER TROUGH MAY BE APPROACHING THE
STATE IF THE ECMWF IS CORRECT. FOR THE TIME BEING WILL JUST
MENTION AN INCREASING CHANCE OF SNOW IN THE MOUNTAINS AS THE STATE
COMES UNDER THE SOUTHWESTERLY FLOW AHEAD OF THE TROUGH.
AVIATION...WESTERLY WINDS TO CONTINUE ACROSS THE DENVER
AREA THROUGH 02Z...WITH SOME GUSTS TO TO 35 KTS. WINDS TO DECREASE
AT DEN AND APA AND BECOME SOUTHWESTERLY DURING THE EVENING BUT
SHOULD REMAIN WESTERLY AND GUSTY AT BJC. AFTER 15Z TUESDAY...
MODELS SHOW THE DEVELOPMENT OF AN ANTICYCLONE IN THE DENVER
AREA...WITH WIND BECOMING EASTERLY. VFR TO CONTINUE WITH NO
PRECIPITATION EXPECTED.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM LATE TUESDAY NIGHT THROUGH WEDNESDAY
AFTERNOON FOR COZ038>051.
WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY FOR COZ033-034.
WINTER STORM WARNING UNTIL 5 AM MST TUESDAY FOR COZ031.
&&
$$
SHORT TERM...D-L
LONG TERM....DANKERS
AVIATION/UPDATE...GIMMESTAD
AREA FORECAST DISCUSSION
NWS DES MOINES IA
345 AM CST TUE DEC 18 2012
...SIGNIFICANT WINTER STORM TO IMPACT THE MIDWEST AND PLAINS
WEDNESDAY AND THURSDAY...
.SHORT TERM /TODAY/...
LOW CLOUDS CONTINUE OVER MUCH OF THE AREA THIS MORNING DUE TO
STRATUS THAT HAS DEVELOPED OVER THE PAST 24 TO 36 HOURS WITH HIGH
PRESSURE OFF TO EAST AND WEAK LOW PRESSURE ALOFT. ANOTHER WAVE IS
CURRENTLY DROPPING SOUTHEAST AND IS LOCATED NEAR THE SOUTH DAKOTA
AND NEBRASKA BORDER THIS MORNING. A WARM FRONT IS DEVELOPING OVER
IOWA NOW AND AT H850-H700 FORCING IS INCREASING ACROSS NORTHWEST
IOWA NOW WITH LIGHT SNOW BEGINNING TO SHOW UP ON RADAR. THE AREA IS
LIFTING TO THE EAST WITH TIME AND SHOULD AFFECT MAINLY FOLKS ALONG
AND NORTH OF HIGHWAY 20 WITH SOME LIGHT PRECIPITATION POSSIBLE TO
HIGHWAY 30. RIGHT ALONG THE IA AND MN BORDER UP TO AN INCH OF SNOW
MAY FALL THROUGH MIDDAY BEFORE THE WEAK SYSTEM AND FORCING MOVES
EAST. OVER THE SOUTH THE BACK EDGE OF THE STRATUS EXTENDS TO NEAR
OMAHA BUT IS ERODING ON THE SOUTH EDGE AS WARM AIR ADVECTION
INCREASES EARLY TODAY. BY THE NOON HOUR THERE WILL BE SOME BREAKS
ACROSS THE SOUTH WHICH SHOULD HELP PUSH AFTERNOON HIGHS BACK INTO
THE LOWER 40S. ACROSS THE NORTH THE CLOUDS WILL HOLD ON LONGER AND
KEEP HIGHS IN THE MID 30S. WINDS WILL BE LIGHT ACROSS THE REGION
TODAY FROM THE SOUTHEAST AND THEN SWITCHING TO THE NORTHWEST BY
AFTERNOON AND EVENING.
.LONG TERM /TONIGHT THROUGH MONDAY/...
MAIN FOCUS IS ON THE MAJOR WINTER STORM TO IMPACT CENTRAL IOWA
WEDNESDAY NIGHT AND THURSDAY. THE STORM IS JUST COMING ONSHORE NOW
AND WILL PUSH INTO THE AREA WEDNESDAY NIGHT AND THURSDAY. SOUNDINGS
SHOW THE WEST SATURATING QUICKLY WEDNESDAY AFTERNOON THEN MOISTURE
SPREADS EAST/NORTHEASTWARD. COLD AIR WRAPS QUICKLY INTO THIS
SYSTEM SO PRECIP SHOULD QUICKLY CHANGE OVER TO SNOW CWA WIDE BY
EVENING. SNOW RATIOS WILL BE FAIRLY HIGH WITH THIS SYSTEM AS WELL
GIVEN THE AMOUNT OF COLD AIR. FORCING IS VERY IMPRESSIVE WITH THIS
SYSTEM AND THIS WILL PRODUCE HIGHER PRECIP RATES. THE EURO AND GFS
DO BOTH HAVE A BAND OF HIGHER QPF IN THE CORRIDOR OF BETTER FORCING
FROM ROUGHLY WATERLOO TO AUDUBON SO I TRIED TO ADJUST SNOWFALL IN
THIS AREA.
I WAS LOOKING AT WHETHER OR NOT TO KICK TO WATCH UP A NOTCH TO A
BLIZZARD WATCH GIVEN THE STRONG NORTH WINDS THAT WILL ACCOMPANY THIS
STORM. SUSTAINED WINDS OF 30 TO 40 MPH ARE QUITE LIKELY WITH SOME
POTENTIAL OF GUSTS 40+ MPH. AT THIS POINT HOWEVER WE HAVE NO SNOW
ON THE GROUND AND I RECALL THAT TO GET REDUCED VISIBILITY FOR A
SUSTAINED PERIOD OF TIME THERE SHOULD BE SOME EXISTING SNOW COVER.
HOWEVER...I DO EXPECT SNOW TO BEGIN IN EARNEST IN THE EVENING AND
THE STRONGEST WINDS TO NOT IMPACT THE AREA UNTIL BETWEEN 09Z AND 12Z
SO WITH 6 TO 9 HOURS OF SNOWFALL PRIOR TO THE ONSET OF THE WIND...WE
SHOULD HAVE A SUFFICIENT BLANKET ON THE GROUND. CONFIDENCE BETWEEN
OFFICES STILL NOT HIGH ENOUGH TO GO BLIZZARD WATCH AS WE ARE STILL
TRYING TO DEFINE WHERE THE HEAVIEST SNOW BAND WILL SET UP. AS A
RESULT WE WILL LEAVE THE WATCH A WINTER STORM WATCH AND HAVE A LOOK
AT ONE MORE MODEL RUN BEFORE MAKING THAT DECISION.
FOR THE REMAINDER OF THE EXTENDED I GENERALLY LOWERED TEMPS IN
ANTICIPATION OF A SNOW PACK THAT WILL KEEP TEMPS LOWER. MOST OF THE
REMAINDER OF THE EXTENDED LOOKS QUIET WITH TEMPS SLOWLY RECOVERING.
THERE IS POTENTIAL FOR ANOTHER SYSTEM TO AFFECT THE AREA NEXT
TUESDAY INTO WEDNESDAY BUT WITH MODEL DISCREPANCIES AND THE
IMPENDING STORM THIS WEEK...I HAVE JUST PLACED POPS IN THE GRIDS
DURING THE TIMEFRAME MOST LIKELY TO SEE PRECIP.
&&
.AVIATION...18/06Z
SOMEWHAT LOW CONFIDENCE THIS SET WITH VARIABLE CONDITIONS STATEWIDE
AT 0530Z...MVFR/IFR EAST DOWN TO IFR/LIFR WEST. WEAK FRONTAL
BOUNDARY THROUGH CENTRAL IA BECOMING SOMEWHAT DIFFUSE THAN NOTED
EARLIER. LATEST RAP SEEMS TO HAVE BEST HANDLE ON REALITY RIGHT NOW
WITH HIGHER LOW LEVEL MOISTURE AND WILL BE FOLLOWED FOR GUIDANCE.
THIS RESULTS IN IFR CONDITIONS OVER MOST LOCATIONS OVERNIGHT AS LOW
LEVEL MOISTURE REMAINS TRAPPED IN LIGHT SELY WINDS. CONDITIONS
SHOULD IMPROVE SOMEWHAT BY MIDDAY CENTRAL AND SOUTH BUT MAY REMAIN
AT LEAST MVFR NORTH...NORTH OF FRONTAL BOUNDARY WHERE THERE COULD
ALSO BE SOME LIGHT SNOW EARLY THIS MORNING. WINDS WILL ALSO
INCREASE SOMEWHAT BY TUE AFTERNOON...BUT NOT AS MUCH AS PREVIOUSLY
ANTICIPATED.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM WEDNESDAY AFTERNOON THROUGH THURSDAY
AFTERNOON FOR ADAIR-ADAMS-APPANOOSE-AUDUBON-BLACK HAWK-BOONE-
BREMER-BUTLER-CALHOUN-CARROLL-CASS-CLARKE-CRAWFORD-DALLAS-DAVIS-
DECATUR-FRANKLIN-GREENE-GRUNDY-GUTHRIE-HAMILTON-HARDIN-JASPER-LUCAS-
MADISON-MAHASKA-MARION-MARSHALL-MONROE-POLK-POWESHIEK-RINGGOLD-SAC-
STORY-TAMA-TAYLOR-UNION-WAPELLO-WARREN-WAYNE-WEBSTER-WRIGHT
&&
$$
SHORT TERM...DONAVON
LONG TERM...COGIL
AVIATION...SMALL
AREA FORECAST DISCUSSION
NWS DES MOINES IA
1135 PM CST MON DEC 17 2012
...SIGNIFICANT WINTER STORM TO IMPACT THE MIDWEST AND PLAINS
WEDNESDAY AND THURSDAY...
.SHORT TERM /TONIGHT/...
LOW PRESSURE OVER NORTHEAST WYOMING WILL SHIFT EAST ACROSS SOUTH
DAKOTA AND NEBRASKA AND REACH NORTHWEST IOWA LATE TONIGHT. AN
ASSOCIATED UPPER LEVEL SHORT WILL SPREAD INCREASING QG FORCING
ACROSS CENTRAL IOWA. IN ADDITION...STRONG THETA-E ADVECTION WILL
ARRIVE AFTER MIDNIGHT THROUGH CENTRAL AND NORTHWEST IOWA. THE BEST
COMBINATION OF FORCING IS OVER CENTRAL IA NEAR DES MOINES AND AMES
BETWEEN 3 AM TO 6 AM HOWEVER THE DEEPER MOISTURE WILL BE FARTHER
NORTH. TYPICALLY THIS TIME OF YEAR FORCING TRUMPS DEEP MOISTURE
THEREFORE CERTAINLY SHOULD HAVE PRECIPITATION FARTHER SOUTH THAN
WHAT MOST MODEL GUIDANCE PRECIPITATION FIELDS WOULD SUGGEST. WARM
ADVECTION IN THE LOW LEVELS IS EXPECTED AS WELL OVERNIGHT RESULTING
IN NON-DIURNAL TEMPERATURES. THIS COULD SWITCH PRECIPITATION TYPE TO
RAIN ON THE SOUTHERN FRINGES. NOT CONFIDENT IN POTENTIAL OF FREEZING
RAIN WITH UNCERTAINTY IN ARRIVAL OF WARMER AIR ALOFT...THOUGH CAN
NOT TOTALLY DISCOUNT. POTENTIAL AS WELL FOR POCKETS OF LOWER
VISIBILITIES DUE TO FOG THOUGH LOW LEVEL WARM ADVECTION SHOULD LIMIT
AREAL COVERAGE OF VISIBILITIES BELOW 2SM.
.LONG TERM /TUESDAY THROUGH MONDAY/...
WILL SEE SOME LINGERING POPS IN THE NORTH ON TUESDAY MORNING AS THE
SYSTEM GRADUALLY DEPARTS TO THE EAST. SOME LIGHT ACCUMULATIONS WILL
STILL BE POSSIBLE AROUND MASON CITY BEFORE MIDDAY BUT PCPN IS
EXPECTED TO END BY MIDDAY. THE WEATHER WILL BE TRANQUIL FROM TUESDAY
AFTERNOON INTO EARLY WEDNESDAY MORNING BEFORE MAJOR SYSTEM BEGINS TO
AFFECT THE FORECAST AREA.
THIS MAJOR STORM IS CURRENTLY OFF THE WEST COAST AND WILL COME
ASHORE LATE TONIGHT INTO TUESDAY. THEREFORE...THERE IS LITTLE
RESOLUTION OF THE SYSTEM BY THE UPPER AIR NETWORK WHICH IS LIKELY
CAUSING SOME OF THE DIFFERENCES SEEN IN THE MODEL RUNS. INITIALLY
ON WEDNESDAY...RIDGE AXIS WILL BE IN PLACE ACROSS THE NORTHEAST WITH
RELATIVELY QUITE WEATHER. HOWEVER...BY MIDDAY...FORCING WILL
RAPIDLY INCREASE AS ISENTROPIC LIFT BEGINS IN EARNEST. STRONG
FRONTOGENETICAL FORCING ALSO ARRIVES ACROSS CENTRAL INTO NORTHERN
IOWA BY LATE AFTERNOON WHICH WILL LIKELY ENHANCE PCPN RATES IN THOSE
LOCATIONS. PCPN WILL BREAK OUT DURING THE AFTERNOON AND INCREASE IN
BOTH COVERAGE AND INTENSITY AS THE AFTERNOON PROGRESSES. SNOW IS
EXPECTED ALONG AND NORTH OF AN ATLANTIC TO WATERLOO LINE WITH A BAND
OF MIXED PCPN OF 50 MILES WIDE OR SO SOUTH OF THE SNOW. RAIN IS
EXPECTED ALONG THE MISSOURI BORDER AS READINGS REMAIN ABOVE
FREEZING.
CONDITIONS DETERIORATE RAPIDLY ON WEDNESDAY NIGHT AS COLD ADVECTION
INTENSIFIES ACROSS THE STATE. UPPER SYSTEM WILL EJECT FROM SOUTHERN
PLAINS AND RACE NORTHEAST TO NEAR QUINCY ILLINOIS BY DAYBREAK.
SYSTEM WILL BE DEEPENING AND BECOMING NEGATIVELY TILTED WITH TIME AS
SURFACE LOW STRENGTHENS. PCPN ACRS THE FORECAST AREA WILL BECOME
ALL SNOW BY MIDNIGHT AS COLD AIR IS DRAWN SOUTHWARD. WINDS ARE
LIKELY TO BECOME A VERY SERIOUS ISSUE AFTER MIDNIGHT AND CERTAINLY
BY DAYBREAK ON THURSDAY. 925MB WINDS WILL BE NEAR OR EVEN SLIGHTLY
ABOVE 50KTS WITH MOS OUTPUT SHOWING SUSTAINED WINDS OF 30KTS IN MANY
LOCATIONS IN CENTRAL IOWA. THIS EVENT MAY BECOME MORE OF A BLIZZARD
INTO THURSDAY MORNING AS THE WINDS INCREASE AND WILL HAVE TO BE
MONITORED CLOSELY. SNOW ON WEDNESDAY NIGHT WILL BE HEAVIEST IN THE
EVENING AS MID LEVEL FORCING IS MAXIMIZED. SOME CONVECTIVE SNOW
WILL BE POSSIBLE AS WELL WITH NEGATIVE EPV ACROSS MUCH OF THE STATE
WITH DECENT MID LEVEL LAPSE RATES. CONDITIONS WILL BE POOR ON
THURSDAY MORNING WITH VERY STRONG WINDS DESPITE THE SNOWFALL
ENDING. GIVEN ALL OF THIS...HAVE ISSUED A WINTER STORM WATCH FOR
MUCH OF CENTRAL IOWA FROM MIDDAY WEDNESDAY INTO THURSDAY FOR THE
POTENTIAL OF HEAVY SNOWFALL AND VERY STRONG WINDS. AN UPGRADE TO
BLIZZARD WATCH MAY BE NEEDED SHOULD FORECAST WINDS REMAIN STRONG OR
INCREASE.
THE WEATHER BEYOND THURSDAY IS RELATIVELY QUIET WITH LITTLE CHANGE
IN THE FORECAST. MAIN CONCERN IS THAT TEMPERATURES WOULD BE TOO
WARM GIVEN THE FRESH SNOW COVER ACROSS THE AREA.
&&
.AVIATION...18/06Z
SOMEWHAT LOW CONFIDENCE THIS SET WITH VARIABLE CONDITIONS STATEWIDE
AT 0530Z...MVFR/IFR EAST DOWN TO IFR/LIFR WEST. WEAK FRONTAL
BOUNDARY THROUGH CENTRAL IA BECOMING SOMEWHAT DIFFUSE THAN NOTED
EARLIER. LATEST RAP SEEMS TO HAVE BEST HANDLE ON REALITY RIGHT NOW
WITH HIGHER LOW LEVEL MOISTURE AND WILL BE FOLLOWED FOR GUIDANCE.
THIS RESULTS IN IFR CONDITIONS OVER MOST LOCATIONS OVERNIGHT AS LOW
LEVEL MOISTURE REMAINS TRAPPED IN LIGHT SELY WINDS. CONDITIONS
SHOULD IMPROVE SOMEWHAT BY MIDDAY CENTRAL AND SOUTH BUT MAY REMAIN
AT LEAST MVFR NORTH...NORTH OF FRONTAL BOUNDARY WHERE THERE COULD
ALSO BE SOME LIGHT SNOW EARLY THIS MORNING. WINDS WILL ALSO
INCREASE SOMEWHAT BY TUE AFTERNOON...BUT NOT AS MUCH AS PREVIOUSLY
ANTICIPATED.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM WEDNESDAY AFTERNOON THROUGH THURSDAY
AFTERNOON FOR ADAIR-ADAMS-APPANOOSE-AUDUBON-BLACK HAWK-BOONE-
BREMER-BUTLER-CALHOUN-CARROLL-CASS-CLARKE-CRAWFORD-DALLAS-DAVIS-
DECATUR-FRANKLIN-GREENE-GRUNDY-GUTHRIE-HAMILTON-HARDIN-JASPER-LUCAS-
MADISON-MAHASKA-MARION-MARSHALL-MONROE-POLK-POWESHIEK-RINGGOLD-SAC-
STORY-TAMA-TAYLOR-UNION-WAPELLO-WARREN-WAYNE-WEBSTER-WRIGHT
&&
$$
SHORT TERM...DONAVON
LONG TERM...COGIL
AVIATION...SMALL
AREA FORECAST DISCUSSION
NWS QUAD CITIES IA IL
1123 PM CST MON DEC 17 2012
.AVIATION...
STRATUS AND PATCHY FOG WILL LIKELY REMAIN IN PLACE OVERNIGHT...WITH
INTERVALS OF PARTIAL CLEARING POSSIBLE. LIGHT SNOW OR FLURRIES MAY
IMPACT CID...DBQ POSSIBLY TOWARD DAWN TUESDAY UNTIL MID DAY. LINGERING
LOW LEVEL MOISTURE AND LIGHT WINDS WILL CONTINUE IFR AND POSSIBLE
LIFR CONDITIONS DUE TO LOW CIGS AND POSSIBLY FOG THROUGH THE
LATE MORNING...MAINLY AT DBQ AND POSSIBLY AT CID TERMINALS. BRL AND
MLI TERMINALS ARE MORE FAVORED FOR MVFR CONDITIONS. A FAST MOVING
LOW PRESSURE SYSTEM MOVING OUT OF THE ROCKIES WILL PASS NEAR
HIGHWAY 30 CORRIDOR TUESDAY AFTERNOON WITH VFR CONDITIONS AND
PARTLY CLOUDY SKIES AT BRL...MLI AND PROBABLY CID TERMINALS. DBQ
TERMINAL SHOULD IMPROVE TO MVFR BY LATE TUESDAY AFTERNOON.
NICHOLS
&&
.PREV DISCUSSION... /ISSUED 905 PM CST MON DEC 17 2012/
UPDATE...
ONLY MINOR CHANGES TO OVERNIGHT PACKAGE. ANALYSIS AND VERIFICATION
CONFIRMS A COLDER TREND WITH A SOUTHEAST SLIDE IN SURFACE LOW
TRACK ON AMERICAN SOLUTIONS. 00Z NAM ANALYSIS SUGGESTS STILL
PLAYING CATCH UP WHICH HAS BEEN COMMON FOR A WHILE WITH THIS MODEL.
WILL BE SENDING OUT UPDATED WSW...OR WINTER STORM WATCH PRODUCT
SHORTLY WITH MENTION OF HIGHER WINDS GUSTING UP TO NEAR 50 MPH ON
BACK SIDE AND BLIZZARD TO NEAR BLIZZARDS SUPPORTED PER LOCAL STUDIES
AND TECHNIQUES. THE LOCAL IMPACTS OF WHERE THESE CONDITIONS ARE TO
OCCUR STILL TOO UNCERTAIN TO ASSESS IF AND EVEN HOW MUCH OF THE
FORECAST COULD BE IMPACTED...THIS IS LIKELY STILL 12-24 HOURS AWAY.
WHAT IS CERTAIN IS THE STRONG WINDS WITH THE SNOW AND CERTAIN NEAR
BLIZZARD CONDITIONS TO POSSIBLY BLIZZARD CONDITIONS IN THE COLD
DEFORMATION ZONE IN RURAL AND OPEN AREAS AT A MINIMUM. THE UPDATED
WSW PRODUCT SHOULD BE OUT WITHIN THE NEXT HALF HOUR.
NICHOLS
PREV DISCUSSION...
SYNOPSIS...
LIGHT WINDS AND LINGERING LOW LEVEL MOISTURE HAS KEPT LOW CLOUDS AND
LIGHT FOG IN PLACE TODAY ACROSS THE FORECAST AREA. AS A RESULT...
TEMPERATURES HAVE STRUGGLED TO CLIMB...HAVING ONLY REACHED THE UPPER
20S NORTH TO MID 30S SOUTH THIS AFTERNOON. MSAS ANALYSIS INDICATED A
RIDGE OF HIGH PRESSURE REACHED FROM TX TO MN...FLANKED BY LOW
PRESSURE MOVING ALONG A COLD FRONT IN NORTHERN KY TO THE SE...AND A
LEE TROUGH REACHING FROM NORTHERN MT TO EASTERN CO. IN THE UPPER
LEVELS...A TROUGH AXIS REACHED FROM THE EASTERN DAKOTAS TO THE MO
BOOTHEEL REGION. UPSTREAM...12Z ANALYSIS INDICATED A 160 KT JET AT
300 MT MOVING IN THE STRONG...NEARLY ZONAL FLOW...ACROSS NORTHERN CA
INTO THE GREAT BASIN REGION. AN UPPER LOW WAS OFF THE NORTHERN BC
COAST WITH A TROUGH AXIS EXTENDING S-SW INTO THE PACIFIC.
SHORT TERM...TONIGHT AND TUESDAY...
DEVELOPING ACTIVE PATTERN WILL SEND ANOTHER ROUND OF PRECIPITATION
THROUGH THE REGION TONIGHT INTO EARLY TUESDAY. FORECAST CHALLENGES
CENTER ON THIS PRECIPITATION LATE TONIGHT INTO TUESDAY...ALONG WITH
LOW CLOUDS AND FOG.
LATEST VISIBLE SATELLITE IMAGES SHOW AN AREA OF CLOUDS OVER NORTH
CENTRAL MO INTO SOUTHERN IA...SLOWLY MIGRATING EASTWARD WITH THE
UPPER LEVEL TROUGH. AS THIS EXTENDS EASTWARD INTO THE SOUTHERN THIRD
OF THE FORECAST AREA AROUND SUNSET...THERE WILL BE A POTENTIAL FOR
THICKENING OF THE FOG THAT HAS LINGERED OVER SE IA AND ADJACENT
AREAS OF MO AND IL THIS EVENING. BASED ON LATEST RAP LOW LEVEL
MOISTURE FIELDS...STRATUS WILL LIKELY REMAIN IN PLACE THROUGH THE
NIGHT OVER THE REMAINDER OF THE FORECAST AREA...AND LIKELY FILL BACK
IN ANY HOLES THAT DEVELOP ACROSS THE SOUTH. WILL GO WITH PATCHY FOG
WORDING FOR NOW AND MONITOR THE SOUTH THIS EVENING FOR POSSIBLE
UPDATES TO MORE DENSE OR WIDESPREAD COVERAGE. A STRIKE AGAINST FOG
TONIGHT WILL BE THE INCOMING SUBSIDENCE BEHIND THE UPPER LEVEL WAVE
AND INCREASING WINDS TOWARD MORNING AS A SURFACE LOW APPROACHES.
AS SEEN TODAY...CLOUDS...LINGERING MOISTURE AND WEAK WINDS WILL
LIMIT DIURNAL TEMPERATURE CURVES AND HAVE KEPT MINS CLOSE TO CURRENT
DEWPOINTS...FROM THE MID 20S NORTH TO LOWER 30S SOUTH.
THE FOCUS THEN TURNS TO AN IMPULSE IN THE FAST ZONAL FLOW ALOFT THAT
WAS MOVING ACROSS CENTRAL ID AT MIDDAY. MODELS DEVELOP THIS INTO A
CLIPPER LIKE LOW PRESSURE SYSTEM AS THE ENERGY MOVES OVER THE LEE
TROUGH TONIGHT. THIS FAST MOVING LOW DEVELOPS OVER NEB LATE
TONIGHT...THEN HEADS EASTWARD OVER THE FORECAST AREA DURING THE
DAY TUESDAY. HAVE GENERALLY FOLLOWED A BLEND OF THE GFS/ECMWF AND
GEM WITH THIS FEATURE...WHICH DEVELOPS A NW TO SE ORIENTED WARM
ADVECTION WING OF LIGHT SNOW OVER THE CENTRAL PART OF THE FORECAST
AREA BETWEEN 06Z AND 12Z AND HAVE KEPT CHANCE POPS THERE. THE
POTENTIAL FOR LIGHT SNOW OR FLURRIES SHOULD THEN SHIFT TO THE FAR
NORTH AND NORTHEAST BY AFTERNOON AS THE LOW MOVES TOWARD CHICAGO.
WITH LIMITED MOISTURE AND RAPID PROGRESSION...SNOWFALL AMOUNTS
SHOULD BE WELL BELOW AN INCH IN MOST LOCATIONS WITH THE BEST CHANCES
OF A LIGHT COATING NORTH OF THE HIGHWAY 30 CORRIDOR. HAVE TRENDED
SOME PARTIAL CLEARING FROM SW TO NE IN THE AFTERNOON...BUT THIS MAY
END UP BEING TOO OPTIMISTIC DUE TO THE LINGERING MOISTURE AND
CYCLONIC FLOW THROUGH THE AFTERNOON. BRISK WESTERLY WINDS IN THE FAR
SOUTH MAY ALLOW TEMPERATURES TO REACH THE UPPER 40S...WHILE HIGHS IN
THE NORTH ARE KEPT IN THE UPPER 30S.
SHEETS
LONG TERM...TUESDAY NIGHT THROUGH NEXT MONDAY...
ALL LONG TERM FCST ENERGY INTO HANDLING MIDWEEK STORM SYSTEM...WITH
THE WEEKEND LOOKING IN BETWEEN SYSTEMS AND RATHER BENIGN/SEASONABLE
ANYWAY THROUGH EARLY MONDAY. ASSESSING THE LATEST 12Z MEDIUM RANGE
MODEL RUNS AS WELL AS THE NAM...SURPRISINGLY GOOD AGREEMENT WITH
GENERAL SFC LOW AND MID LEVEL LOW PATHS BUT WITH SOME TRACKING
SPEED AND STRENGTH VARIANCES. THIS TAKING INTO ACCOUNT BULK OF WAVE
ENERGY THAT WILL DRIVE THE STORM STILL OFF THE PACIFIC NORTHWEST
COAST AND SOUTH OF THE GULF OF AK. ALL MODELS BUT THE 12Z ECMWF THAT
IS. WHILE THE OTHERS HAVE TRENDED FURTHER NORTH AND WEST WITH THEIR
LATEST 12Z RUNS WHICH MAKE FOR MORE OF A PRECIP TYPE/AMOUNT CHALLENGE
FOR THE DVN CWA...THE CONSISTENT ECMWF WOULD STILL IMPACT MOST OF THE
LOCAL FCST AREA WITH A QUICKER SWITCH OVER TO SNOW AND MORE AREAS
STARTING OFF AS SNOW TO BEGIN WITH. THE ENSEMBLE SFC LOW TRACK OF
THE 12Z GFS/NAM/UKMET/GEM ALL HOOK THE DEVELOPING LOW FROM THE OK
PANHANDLE ON WED UP THROUGH NORTHEAST MO/WEST CENTRAL IL LATE WED
NIGHT...TO A NORTH CENTRAL IL POSITION BY THU MORNING...AND THEN
BOMB IT OUT ACRS LOWER MI INTO THU EVENING. THE 12Z EURO MAINTAINS
A TRACK FURTHER TO THE SOUTHEAST OF THE ENSEMBLE PATH...SOUTHWEST MO
TO NEAR THE STL AREA BY THU MORNING AND THEN OFF TO WEST CENTRAL
INDIANA BY EARLY THU AFTERNOON. THE ENSEMBLE OF SOLUTIONS BESIDES THE
ECMWF WOULD GENERALLY SUGGEST MUCH OF THE SOUTHEAST HALF TO TWO
THIRDS OF THE FCST AREA TO BE RAIN OR EVEN EXPERIENCE SOME
CONVECTION THROUGH MIDNIGHT WED NIGHT...WHILE THE NORTHWEST THIRD
MIXES AND DYNAMICALLY COOLS INTO WET ACCUMULATING SNOW AFTER 03Z
THU. AS DEF ZONE CONTINUES TO FORM AND LLVL COLD CONVEYOR IN-WRAPS
AND INCREASES...THESE MODELS GENERALLY SUGGEST THE SWITCH OVER TO
WET SNOW TO CONTINUE FROM WEST-NORTHWEST TO THE EAST AFTER MIDNIGHT
AND INTO EARLY THU MORNING ACRS THE DVN CWA. 3-7 INCHES POSSIBLE BY
12Z THU ALONG AND WEST OF A LINE FROM SIGOURNEY IA...TO EAST OF
CEDAR RAPIDS AND TO WEST OF DBQ. SOME ADDITIONAL ACCUMS OF 1-2
INCHES IN THESE AREAS POSSIBLE THROUGH 18Z THU...BUT BULK OF
ACCUMULATING SNOW TO SWITCH EASTWARD ACRS THE REST OF THE CWA WITH 3-
6 INCHES POSSIBLE ALONG AND NORTH OF A LINE FROM MT PLEASANT IA...TO
THE QUAD CITIES..AND TO STERLING IL.
WHILE THE NORTHWEST THIRD AND NORTH CENTRAL PORTIONS OF THE DVN CWA
MAY EVENTUALLY GET 4-8+ INCHES BY THU EVENING...THE ENSEMBLES MINUS
THE ECMWF SUGGEST THE HIGHEST SNOWFALL TOTALS OF 8-12+ INCHES OCCUR
WEST AND NORTH OF THE DVN CWA ACRS SOUTH CENTRAL IA...UP THROUGH
NORTHEASTERN IA INTO SW/CENTRAL WI. EXTENT OF BOMBING CYCLONE TO THE
EAST STILL INDICATED BY BULK OF THE MODEL RUNS TO DRIVE VERY STRONG
NORTH BECOMING NORTHWEST WINDS LATE WED NIGHT AND ESPECIALLY ON
THU...SUSTAINED 25 TO 35 MPH WITH GUSTS TO AT LEAST 45 MPH. GRAVITY
WAVE PHENOMENA WEST OF RAPIDLY DEEPENING CYCLONE COULD ALSO PRODUCE
ISOLATED GUSTS OVER 50 MPH AT MAX DEEPENING STAGE ON THU. THUS WHERE
ACCUMULATING SNOWS OCCUR...NEAR BLIZZARD OR BLIZZARD CONDITIONS VERY
POSSIBLE. BACK TO THE ECMWF...IT/S TRACK WOULD MEAN MORE OF A DIRECT
HIT UPON THE LOCAL AREA AND HIGHER SNOW AMOUNTS FURTHER EAST AND
SOUTH...ESPECIALLY TAKING INTO ACCOUNT SOME FUJI-WARA EFFECT OF
SECONDARY VORT INTERACTING IN TROF BASE AND ENHANCING DEF ZONE SNOWS
ACRS THE LOCAL AREA ON THU. DESPITE ONGOING MODEL UNCERTAINTY AND
THE SYSTEM TO BE BETTER SAMPLED FOR THE 00Z RUNS TONIGHT AND
ESPECIALLY 12Z TUE...WILL ISSUE A WINTER STORM WATCH FOR ROUGHLY THE
NORTHWEST HALF OF THE DVN CWA FOR WED NIGHT AND THU GIVING A NOD
SOMEWHAT TO THE ENSEMBLE TRACK. THE STRONG WINDS LOOK TO BE A LARGE
IMPACT EVEN FOR ADVISORY LEVEL OR SLIGHTLY LESS SNOW AMOUNTS. DO FEEL
THE CWA WILL HAVE TO EVENTUALLY BE DIVIDED INTO WINTER STORM WARNING
AND ADVISORY AREAS...BUT WHERE AN WHEN STILL UP IN THE AIR. A
WATCHFUL EYE WILL ALSO NEED TO BE OPEN FOR TRENDS ON THE NEXT 1-2
MODEL RUNS BACK CLOSER TO THE CONSISTENT ECMWF...WHICH WOULD THEN
WARRANT THE NEED OF EXPANDING THE WATCH SOUTH AND EAST. ..12..
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...WINTER STORM WATCH FROM WEDNESDAY EVENING THROUGH THURSDAY
AFTERNOON FOR BENTON-BUCHANAN-CEDAR-CLINTON-DELAWARE-
DUBUQUE-HENRY IA-IOWA-JACKSON-JEFFERSON-JOHNSON-JONES-
KEOKUK-LINN-LOUISA-MUSCATINE-SCOTT-VAN BUREN-WASHINGTON.
IL...WINTER STORM WATCH FROM WEDNESDAY EVENING THROUGH THURSDAY
AFTERNOON FOR JO DAVIESS-ROCK ISLAND.
MO...NONE.
&&
$$
NICHOLS
AREA FORECAST DISCUSSION
NWS TOPEKA KS
930 PM CST WED DEC 19 2012
.UPDATE...
ALTERATIONS TO THE FORECAST WILL BE MADE BASED ON LATEST TRENDS AND
MODEL OUTPUT. THE OVERALL TRANSITION TO WINTRY PRECIPITATION IS A
BIT SLOWER THAN EARLIER RUNS PROGGED. LAST SEVERAL RAP RUNS AND
THE 18Z AND 0Z NAM SUGGEST THE PERSISTENT SNOW IN NORTH CENTRAL
KANSAS WILL WANE IN THE NEXT FEW HOURS AND ANOTHER AREA STRENGTHEN
JUST TO ITS SOUTHWEST AND ROTATE CLOCKWISE AS THE UPPER TROF TAKES
ON A NEGATIVE TILT AND MEETS WITH SLANTWISE AND BIT OF UPRIGHT
INSTABILITY. TAPERED BACK TOTALS IN THE NORTH A LITTLE WITH THIS
IN MIND. LOCALLY HIGHER AMOUNTS IN THE MANHATTAN TO LAWRENCE TO
HIAWATHA REGION ARE POSSIBLE IF THE CONVECTIVE ELEMENTS PERSIST.
65
&&
.DISCUSSION...
A VERY POTENT AND SIGNIFICANT WINTER STORM SET TO IMPACT THE AREA
WEDNESDAY NIGHT INTO THURSDAY MORNING...BRINGING PERIODS OF HEAVY
SNOW AND VERY STRONG WINDS. NEAR BLIZZARD CONDITIONS WILL BE LIKELY
ACROSS ALL OF NORTH CENTRAL...NORTHEAST...AND EAST CENTRAL KANSAS.
SHORT TERM FORECAST (TONIGHT THROUGH TOMORROW)...
AT 22Z A SURFACE TROUGH WAS UNDERGOING LEE SIDE CYCLOGENESIS IN FAR
NORTHWEST OKLAHOMA. THE STRONG PRESSURE GRADIENT ON THE NORTHERN AND
WESTERN EDGE OF THE LOW IS PRODUCING STRONG WINDS ACROSS WESTERN
NEBRASKA AND WESTERN KANSAS. RADAR TRENDS INDICATE THAT
PRECIPITATION HAS COMMENCED ACROSS CENTRAL AND SOUTHERN NEBRASKA AND
SURFACE OBS INDICATE THE SNOW LINE AT THIS POINT RUNS FROM KRDK TO
KGCK. AS THE SURFACE LOW DEEPENS AND MOVES TO THE EAST THE
FREEZING LINE WILL SHIFT TO THE SOUTHEAST WITH IT. BANDED
PRECIPITATION ACROSS NORTHERN KANSAS AND CENTRAL NEBRASKA LOOKS TO
BE IN RESPONSE TO STRONG ISENTROPIC ASCENT ALONG WITH GOOD 850 TO
700 MB FRONTOGENETICAL LIFT. ALOFT RAP ANALYSIS INDICATES THE
STRONG MID LEVEL TROUGH IS CURRENTLY OVER THE GREAT
DIVIDE...PUSHING INTO THE CENTRAL HIGH PLAINS. AS THIS TROUGH
PUSHES EASTWARD IT WILL CONTINUE TO DEEPEN TO AROUND 536 DM OVER
WESTERN MISSOURI OVERNIGHT. AS THIS MID/UPPER TROUGH COMES THROUGH
THE AREA A VERY STRONG PV ANOMALY WILL GLIDE JUST SOUTH OF THE
AREA...INDICATING THE BEST MID/UPPER ASCENT JUST NORTH OF THE PV
ANOMALY CENTER.
MODELS HAVE BEEN FAIRLY CONSISTENT REGARDING THE SCENARIO FOR
WEDNESDAY NIGHT INTO THURSDAY. THE PREVIOUSLY MENTIONED SURFACE
TROUGH IS EXPECTED TO REMAIN STEADY STATE OR POSSIBLY EVEN DEEPEN A
BIT AS IT MOVES ACROSS NORTHERN OKLAHOMA. IT WILL TAKE A TURN TO THE
NORTH AND MOVE NORTHEAST ALONG INTERSTATE 44 OVERNIGHT. STRONG
TRANSPORT VECTORS BOTH AT THE SURFACE AND AT 850 MB WILL BRING A
GOOD AMOUNT OF MOISTURE INTO THE EASTERN FLANK OF THE STRONG LOW
LEVEL CYCLONE. THE WARM/MOIST CONVEYOR BELT WILL TRANSPORT THE
MOISTURE AROUND THE NORTHERN FLANK OF THE LOW LEVEL CYCLONE AND
INTRODUCE IT TO THE COLD AIR ON THE NORTHWESTERN AND WESTERN SIDE OF
THE LOW LEVEL TROUGH. THE BETTER/DEEPER MOISTURE WILL ALSO DEFINE A
DECENT WARM SECTOR...WHICH WILL TAKE SHAPE MAINLY ALONG AND EAST OF
THE KANSAS TURNPIKE THIS EVENING. BETWEEN ROUGHLY 00Z AND 06Z THE
AREA SOUTH AND EAST OF THE KANSAS TURNPIKE WILL LIKELY EXPERIENCE A
PERIOD OF RAIN...WITH SOME THUNDERSTORMS. WITH 500 TO 1000 J/KG OF
MU CAPE RESIDING IN THE WARM SECTOR A FEW OF THE THUNDERSTORMS COULD
BECOME STRONG...ESPECIALLY GIVEN THE VERY STRONG DEEP LAYER SHEAR.
AS THE COLD AIR QUICKLY SHIFTS EASTWARD LIQUID PRECIPITATION WILL
QUICKLY CHANGE OVER TO SNOW...WITH POTENTIALLY A BRIEF PERIOD OF
SLEET IN THE TRANSITION PERIOD. THIS TRANSITION WILL LIKELY OCCUR
AROUND KMHK AROUND 05Z...WITH A CHANGE OVER AT KTOP AND KLWC BETWEEN
07Z AND 08Z. NAM CROSS SECTIONS INDICATE A FEW AREAS WITH CONVECTIVE
INSTABILITY RESIDING ALONG THE INTERSTATE 70 CORRIDOR BETWEEN 09Z
AND 12Z. THIS IS THE TIME PERIOD TARGETED AS THE PERIOD OF HEAVIEST
SNOW ACROSS THE FAR EASTERN PORTION OF THE STATE. ACROSS NORTH
CENTRAL KANSAS GOOD MID LEVEL FRONTOGENESIS AND THE AFOREMENTIONED
PV ANOMALY WILL BE THE PRIMARY MODES OF LIFT. ALTHOUGH THE OVERALL
LIFT FROM THIS SYSTEM WILL BE QUITE ROBUST ITS PROGRESSIVE NATURE
WILL HELP KEEP SNOW AMOUNTS TO A MANAGEABLE 4 TO 6 INCHES ALONG AND
NORTH OF HIGHWAY INTERSTATE 70 AND IN THE 1 TO 3 INCH RANGE ALONG
AND SOUTH OF INTERSTATE 35. EXPECT THE HEAVY SNOW TO COME TO AN END
BY 12Z ACROSS THE ENTIRE AREA...WITH LINGERING SNOW LIKELY COMING TO
AN END BY 15Z THURSDAY.
AGGRAVATING THE PERIL OF THIS SYSTEM ARE THE VERY STRONG WINDS
ASSOCIATED WITH THE LOW LEVEL CYCLONE. MODELS CONTINUE TO INDICATE
SURFACE WINDS BEING SUSTAINED AT 30 TO 40 MPH. 925 MB WINDS ARE ALSO
PROGGED TO BE IN THE 50 TO 60 KT RANGE...WITH 850 MB WINDS REACHING
70 KTS. DEEP MIXING WILL LIKELY NOT OCCUR...BUT WITH LOW LEVEL WINDS
BEING SO STRONG ITS CONCEIVABLE THAT 50 MPH GUSTS WILL BE POSSIBLE
IN CONCURRENCE WITH THE MODERATE TO HEAVY SNOW. THE COMBINATION OF
THESE FACTORS WILL BRING NEAR BLIZZARD CONDITIONS TO ALMOST THE
ENTIRE AREA...WITH AREAS RECEIVING THE HEAVIEST SNOW HAVING THE MOST
LIMITED VISIBILITIES. CONSIDERATION OF AN UPGRADE TO BLIZZARD
WARNING WAS MADE HOWEVER THE EXPECTED SHORT DURATION OF THE
CONDITIONS (ON THE ORDER OF 3 TO 5 HOURS) PRECLUDED THAT UPGRADE.
THE CONSISTENCY OF THE MODELS TO THIS POINT HAVE BEEN GOOD...BUT THE
18Z RUN OF THE NAM CAME IN MUCH MORE ROBUST REGARDING THE
PRECIPITATION OUTPUT AND WIND FORECAST. WILL CONTINUE TO MONITOR THE
EVOLUTION OF THIS SYSTEM AND PROVIDE UPDATES AS NECESSARY.
JL
THURSDAY...
SNOW WILL LINGER IN EXTREME KANSAS THROUGH MID MORNING WITH VERY
STRONG WINDS GUSTING TO 45 MPH OR GREATER IN FAR EASTERN KANSAS AS
WELL. THE SNOW SHOULD END BY 9 AM OR SO...WITH WINDS GRADUALLY
DECREASING AFTER THAT POINT AS WELL. THE EXTENT OF BLOWING SNOW
WILL DEPEND ON TOTAL ACCUMULATIONS...BUT EXPECT ANY LOCATION WITH
MORE THAN 2 INCHES OF SNOW TO SEE QUITE A BIT OF BLOWING WITH SOME
DRIFTING...AND THOSE AREAS THAT SEE CLOSER TO 5 OR 6 INCHES OF
SNOW CAN EXPECT SOME PRETTY SUBSTANTIAL BLOWING AND DRIFTING. WITH
THE TREND TOWARD A SLIGHTLY LATER END TIME FOR THE SNOW...EXPECT
THE MORNING COMMUTE TO BE RATHER DIFFICULT.
THURSDAY NIGHT THROUGH MONDAY...
STILL EXPECT A RATHER BENIGN WEATHER PATTERN THROUGH THIS PERIOD
AND HAVE NOT MADE MANY CHANGES TO THE FORECAST GIVEN THE HIGH
IMPACT WEATHER PRESENT IN THE SHORT TERM. MADE SOME ADJUSTMENTS TO
THE TEMPERATURES BASED ON EXPECTED SNOW COVER AS BOTH HIGH AND LOW
TEMPS IN THE NORTHERN FORECAST AREA COULD BE QUITE A BIT COOLER
THAN THE MODEL CONSENSUS. FRIDAY MORNING...AND EVEN SATURDAY
MORNING...COULD BE QUITE COLD AS HIGH PRESSURE BUILDS INTO THE
AREA WITH LIGHT WINDS...CLEAR SKIES...AND SNOW COVER.
MONDAY NIGHT THROUGH WEDNESDAY...
THERE REMAINS PLENTY OF UNCERTAINTY REGARDING A POTENTIAL STORM
SYSTEM DURING THIS PERIOD NEAR OR JUST AFTER CHRISTMAS DAY. THE
OPERATIONAL ECMWF AND GFS HAVE COME BACK INTO AGREEMENT IN TERMS
OF PLACING THE FORECAST OFFICE ON THE COLD SIDE OF A POTENT STORM
SYSTEM. TIMING WOULD SUGGEST THAT THE BULK OF PRECIP POTENTIAL
WOULD COME ON THE NIGHT OF THE 25TH INTO THE 26TH. HAVE MAINTAINED
CHANCES FOR SNOW ACROSS THE AREA DURING THIS TIME FRAME AND WILL
CONTINUE TO MONITOR THE PROGRESSION OF THIS STORM SYSTEM. THE TAKE
AWAY POINT AT THIS TIME IS THAT THE POTENTIAL FOR ACCUMULATING
WINTER PRECIPITATION EXISTS...BUT IS BY NO MEANS A GUARANTEE AT
THIS TIME AS THE ENERGY IS CURRENTLY OVER EASTERN RUSSIA AND
SIGNIFICANT CHANGES TO THE FORECAST ARE POSSIBLE IN THE NEXT FEW
DAYS. STAY TUNED.
BARJENBRUCH
&&
.AVIATION...
ONLY A FEW CHANGES TO THE PREVIOUS FORECASTS. DETERIORATION ON
TRACK OVER THE NEXT SEVERAL HOURS WITH WINTER STORM WINDING UP.
INCLUDED A BRIEF WINDOW OF MIXED PRECIP AS THE COLD AIR
SURGES IN. VLIFR STILL SEEMS ON TARGET AFTER 06Z...BUT DID DELAY
ITS ONSET AND KEPT IFR GOING A BIT LONGER BASED ON LATEST
GUIDANCE. STOUT NORTHWEST WINDS SHOULD PERSIST THROUGH MUCH OF
THURSDAY.
65
&&
.TOP WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING UNTIL 9 AM CST THURSDAY FOR KSZ011-012-024-
026-038-039.
WINTER STORM WARNING UNTIL 6 AM CST THURSDAY FOR KSZ008>010-
020>023-034>036.
WINTER WEATHER ADVISORY UNTIL 9 AM CST THURSDAY FOR KSZ040-055-
056-058-059.
WINTER WEATHER ADVISORY UNTIL 6 AM CST THURSDAY FOR KSZ037-054.
&&
$$
AREA FORECAST DISCUSSION
NWS TOPEKA KS
545 PM CST WED DEC 19 2012
...UPDATE TO AVIATION...
.DISCUSSION...
A VERY POTENT AND SIGNIFICANT WINTER STORM SET TO IMPACT THE AREA
WEDNESDAY NIGHT INTO THURSDAY MORNING...BRINGING PERIODS OF HEAVY
SNOW AND VERY STRONG WINDS. NEAR BLIZZARD CONDITIONS WILL BE LIKELY
ACROSS ALL OF NORTH CENTRAL...NORTHEAST...AND EAST CENTRAL KANSAS.
SHORT TERM FORECAST (TONIGHT THROUGH TOMORROW)...
AT 22Z A SURFACE TROUGH WAS UNDERGOING LEE SIDE CYCLOGENESIS IN FAR
NORTHWEST OKLAHOMA. THE STRONG PRESSURE GRADIENT ON THE NORTHERN AND
WESTERN EDGE OF THE LOW IS PRODUCING STRONG WINDS ACROSS WESTERN
NEBRASKA AND WESTERN KANSAS. RADAR TRENDS INDICATE THAT
PRECIPITATION HAS COMMENCED ACROSS CENTRAL AND SOUTHERN NEBRASKA AND
SURFACE OBS INDICATE THE SNOW LINE AT THIS POINT RUNS FROM KRDK TO
KGCK. AS THE SURFACE LOW DEEPENS AND MOVES TO THE EAST THE
FREEZING LINE WILL SHIFT TO THE SOUTHEAST WITH IT. BANDED
PRECIPITATION ACROSS NORTHERN KANSAS AND CENTRAL NEBRASKA LOOKS TO
BE IN RESPONSE TO STRONG ISENTROPIC ASCENT ALONG WITH GOOD 850 TO
700 MB FRONTOGENETICAL LIFT. ALOFT RAP ANALYSIS INDICATES THE
STRONG MID LEVEL TROUGH IS CURRENTLY OVER THE GREAT
DIVIDE...PUSHING INTO THE CENTRAL HIGH PLAINS. AS THIS TROUGH
PUSHES EASTWARD IT WILL CONTINUE TO DEEPEN TO AROUND 536 DM OVER
WESTERN MISSOURI OVERNIGHT. AS THIS MID/UPPER TROUGH COMES THROUGH
THE AREA A VERY STRONG PV ANOMALY WILL GLIDE JUST SOUTH OF THE
AREA...INDICATING THE BEST MID/UPPER ASCENT JUST NORTH OF THE PV
ANOMALY CENTER.
MODELS HAVE BEEN FAIRLY CONSISTENT REGARDING THE SCENARIO FOR
WEDNESDAY NIGHT INTO THURSDAY. THE PREVIOUSLY MENTIONED SURFACE
TROUGH IS EXPECTED TO REMAIN STEADY STATE OR POSSIBLY EVEN DEEPEN A
BIT AS IT MOVES ACROSS NORTHERN OKLAHOMA. IT WILL TAKE A TURN TO THE
NORTH AND MOVE NORTHEAST ALONG INTERSTATE 44 OVERNIGHT. STRONG
TRANSPORT VECTORS BOTH AT THE SURFACE AND AT 850 MB WILL BRING A
GOOD AMOUNT OF MOISTURE INTO THE EASTERN FLANK OF THE STRONG LOW
LEVEL CYCLONE. THE WARM/MOIST CONVEYOR BELT WILL TRANSPORT THE
MOISTURE AROUND THE NORTHERN FLANK OF THE LOW LEVEL CYCLONE AND
INTRODUCE IT TO THE COLD AIR ON THE NORTHWESTERN AND WESTERN SIDE OF
THE LOW LEVEL TROUGH. THE BETTER/DEEPER MOISTURE WILL ALSO DEFINE A
DECENT WARM SECTOR...WHICH WILL TAKE SHAPE MAINLY ALONG AND EAST OF
THE KANSAS TURNPIKE THIS EVENING. BETWEEN ROUGHLY 00Z AND 06Z THE
AREA SOUTH AND EAST OF THE KANSAS TURNPIKE WILL LIKELY EXPERIENCE A
PERIOD OF RAIN...WITH SOME THUNDERSTORMS. WITH 500 TO 1000 J/KG OF
MU CAPE RESIDING IN THE WARM SECTOR A FEW OF THE THUNDERSTORMS COULD
BECOME STRONG...ESPECIALLY GIVEN THE VERY STRONG DEEP LAYER SHEAR.
AS THE COLD AIR QUICKLY SHIFTS EASTWARD LIQUID PRECIPITATION WILL
QUICKLY CHANGE OVER TO SNOW...WITH POTENTIALLY A BRIEF PERIOD OF
SLEET IN THE TRANSITION PERIOD. THIS TRANSITION WILL LIKELY OCCUR
AROUND KMHK AROUND 05Z...WITH A CHANGE OVER AT KTOP AND KLWC BETWEEN
07Z AND 08Z. NAM CROSS SECTIONS INDICATE A FEW AREAS WITH CONVECTIVE
INSTABILITY RESIDING ALONG THE INTERSTATE 70 CORRIDOR BETWEEN 09Z
AND 12Z. THIS IS THE TIME PERIOD TARGETED AS THE PERIOD OF HEAVIEST
SNOW ACROSS THE FAR EASTERN PORTION OF THE STATE. ACROSS NORTH
CENTRAL KANSAS GOOD MID LEVEL FRONTOGENESIS AND THE AFOREMENTIONED
PV ANOMALY WILL BE THE PRIMARY MODES OF LIFT. ALTHOUGH THE OVERALL
LIFT FROM THIS SYSTEM WILL BE QUITE ROBUST ITS PROGRESSIVE NATURE
WILL HELP KEEP SNOW AMOUNTS TO A MANAGEABLE 4 TO 6 INCHES ALONG AND
NORTH OF HIGHWAY INTERSTATE 70 AND IN THE 1 TO 3 INCH RANGE ALONG
AND SOUTH OF INTERSTATE 35. EXPECT THE HEAVY SNOW TO COME TO AN END
BY 12Z ACROSS THE ENTIRE AREA...WITH LINGERING SNOW LIKELY COMING TO
AN END BY 15Z THURSDAY.
AGGRAVATING THE PERIL OF THIS SYSTEM ARE THE VERY STRONG WINDS
ASSOCIATED WITH THE LOW LEVEL CYCLONE. MODELS CONTINUE TO INDICATE
SURFACE WINDS BEING SUSTAINED AT 30 TO 40 MPH. 925 MB WINDS ARE ALSO
PROGGED TO BE IN THE 50 TO 60 KT RANGE...WITH 850 MB WINDS REACHING
70 KTS. DEEP MIXING WILL LIKELY NOT OCCUR...BUT WITH LOW LEVEL WINDS
BEING SO STRONG ITS CONCEIVABLE THAT 50 MPH GUSTS WILL BE POSSIBLE
IN CONCURRENCE WITH THE MODERATE TO HEAVY SNOW. THE COMBINATION OF
THESE FACTORS WILL BRING NEAR BLIZZARD CONDITIONS TO ALMOST THE
ENTIRE AREA...WITH AREAS RECEIVING THE HEAVIEST SNOW HAVING THE MOST
LIMITED VISIBILITIES. CONSIDERATION OF AN UPGRADE TO BLIZZARD
WARNING WAS MADE HOWEVER THE EXPECTED SHORT DURATION OF THE
CONDITIONS (ON THE ORDER OF 3 TO 5 HOURS) PRECLUDED THAT UPGRADE.
THE CONSISTENCY OF THE MODELS TO THIS POINT HAVE BEEN GOOD...BUT THE
18Z RUN OF THE NAM CAME IN MUCH MORE ROBUST REGARDING THE
PRECIPITATION OUTPUT AND WIND FORECAST. WILL CONTINUE TO MONITOR THE
EVOLUTION OF THIS SYSTEM AND PROVIDE UPDATES AS NECESSARY.
JL
THURSDAY...
SNOW WILL LINGER IN EXTREME KANSAS THROUGH MID MORNING WITH VERY
STRONG WINDS GUSTING TO 45 MPH OR GREATER IN FAR EASTERN KANSAS AS
WELL. THE SNOW SHOULD END BY 9 AM OR SO...WITH WINDS GRADUALLY
DECREASING AFTER THAT POINT AS WELL. THE EXTENT OF BLOWING SNOW
WILL DEPEND ON TOTAL ACCUMULATIONS...BUT EXPECT ANY LOCATION WITH
MORE THAN 2 INCHES OF SNOW TO SEE QUITE A BIT OF BLOWING WITH SOME
DRIFTING...AND THOSE AREAS THAT SEE CLOSER TO 5 OR 6 INCHES OF
SNOW CAN EXPECT SOME PRETTY SUBSTANTIAL BLOWING AND DRIFTING. WITH
THE TREND TOWARD A SLIGHTLY LATER END TIME FOR THE SNOW...EXPECT
THE MORNING COMMUTE TO BE RATHER DIFFICULT.
THURSDAY NIGHT THROUGH MONDAY...
STILL EXPECT A RATHER BENIGN WEATHER PATTERN THROUGH THIS PERIOD
AND HAVE NOT MADE MANY CHANGES TO THE FORECAST GIVEN THE HIGH
IMPACT WEATHER PRESENT IN THE SHORT TERM. MADE SOME ADJUSTMENTS TO
THE TEMPERATURES BASED ON EXPECTED SNOW COVER AS BOTH HIGH AND LOW
TEMPS IN THE NORTHERN FORECAST AREA COULD BE QUITE A BIT COOLER
THAN THE MODEL CONSENSUS. FRIDAY MORNING...AND EVEN SATURDAY
MORNING...COULD BE QUITE COLD AS HIGH PRESSURE BUILDS INTO THE
AREA WITH LIGHT WINDS...CLEAR SKIES...AND SNOW COVER.
MONDAY NIGHT THROUGH WEDNESDAY...
THERE REMAINS PLENTY OF UNCERTAINTY REGARDING A POTENTIAL STORM
SYSTEM DURING THIS PERIOD NEAR OR JUST AFTER CHRISTMAS DAY. THE
OPERATIONAL ECMWF AND GFS HAVE COME BACK INTO AGREEMENT IN TERMS
OF PLACING THE FORECAST OFFICE ON THE COLD SIDE OF A POTENT STORM
SYSTEM. TIMING WOULD SUGGEST THAT THE BULK OF PRECIP POTENTIAL
WOULD COME ON THE NIGHT OF THE 25TH INTO THE 26TH. HAVE MAINTAINED
CHANCES FOR SNOW ACROSS THE AREA DURING THIS TIME FRAME AND WILL
CONTINUE TO MONITOR THE PROGRESSION OF THIS STORM SYSTEM. THE TAKE
AWAY POINT AT THIS TIME IS THAT THE POTENTIAL FOR ACCUMULATING
WINTER PRECIPITATION EXISTS...BUT IS BY NO MEANS A GUARANTEE AT
THIS TIME AS THE ENERGY IS CURRENTLY OVER EASTERN RUSSIA AND
SIGNIFICANT CHANGES TO THE FORECAST ARE POSSIBLE IN THE NEXT FEW
DAYS. STAY TUNED.
BARJENBRUCH
&&
.AVIATION...
ONLY A FEW CHANGES TO THE PREVIOUS FORECASTS. DETERIORATION ON
TRACK OVER THE NEXT SEVERAL HOURS WITH WINTER STORM WINDING UP.
INCLUDED A BRIEF WINDOW OF MIXED PRECIP AS THE COLD AIR
SURGES IN. VLIFR STILL SEEMS ON TARGET AFTER 06Z...BUT DID DELAY
ITS ONSET AND KEPT IFR GOING A BIT LONGER BASED ON LATEST
GUIDANCE. STOUT NORTHWEST WINDS SHOULD PERSIST THROUGH MUCH OF
THURSDAY.
65
&&
.TOP WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING UNTIL 9 AM CST THURSDAY FOR KSZ011-012-024-
026-038-039.
WINTER STORM WARNING UNTIL 6 AM CST THURSDAY FOR KSZ008-009-020-
021-034.
WINTER STORM WARNING UNTIL 6 AM CST THURSDAY FOR KSZ010-022-023-
035-036.
WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO 9 AM CST
THURSDAY FOR KSZ040-055-056-058-059.
WINTER WEATHER ADVISORY UNTIL 6 AM CST THURSDAY FOR KSZ037-054.
&&
$$
AREA FORECAST DISCUSSION
NWS PITTSBURGH PA
1031 PM EST WED DEC 19 2012
.SYNOPSIS...
HIGH PRESSURE WILL BRING DRY WEATHER OVERNIGHT INTO EARLY
THURSDAY. A STRONG LOW PRESSURE SYSTEM WILL MOVE ACROSS THE GREAT
LAKES THURSDAY INTO FRIDAY AND INTO THE NORTHEAST BY THE WEEKEND.
THIS SYSTEM WILL BRING SHOWERS WITH GUSTY WINDS THURSDAY...RAIN
CHANGING TO SNOW THURSDAY NIGHT...AND BLUSTERY CONDITIONS WITH
ACCUMULATING SNOW FRIDAY INTO SATURDAY.
&&
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
A SECOND EVENING UPDATE HAS BEEN ISSUED TO UPGRADE THE WINTER
STORM WATCH TO A WARNING FOR THE MD/WV/PA RIDGES. NO OTHER CHANGES
IN THE NEAR TERM.
THE LATEST RAP MID-LEVEL ANALYSIS INDICATES A 500MB TROUGH AXIS
CENTERED ACROSS THE FRONT RANGE WITH MORE OF A ZONAL FLOW ACROSS
THE UPPER OHIO VALLEY IN ADVANCED OF THIS FEATURE. AN 850MB THERMAL RIDGE
IS BUILDING INTO THE OHIO VALLEY WITH A TIGHTENED THERMAL
GRADIENT CURRENTLY BISECTING THE CWA. AT THE SURFACE...A 1021MB
HIGH IS CENTERED ACROSS WV/OH.
TONIGHT...THE SURFACE HIGH WILL SLOWLY SHIFT EASTWARD WITH WAA
ENSUING AS THE 850MB FLOW SHIFTS TO SOUTHERLY. SKIES WILL
GENERALLY BE MOSTLY CLOUDY OVERNIGHT AS LINGERING AREAS OF
STRATOCU CONTINUE TO MOVE ACROSS THE REGION AND UPPER LEVEL
MOISTURE BEGINS TO ADVECT INTO THE AREA. WITH WAA ENSUING
OVERNIGHT...SFC TEMPS WILL DECREASE VERY LITTLE OVERNIGHT...WITH
LOWS RANGING FROM THE LOWER 30S ACROSS THE I-80 CORRIDOR AND
EASTERN RIDGES TO THE UPPER 30S IN EASTERN OHIO.
&&
.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
THE LATEST MODEL RUN CONSENSUS CONTINUES TO INDICATE THE DEEP MID-
LEVEL TROUGH SWINGING ACROSS THE PLAINS AND QUICKLY CLOSING OFF. ITS
ASSOCIATED SURFACE CYCLONE WILL STRENGTHEN AS IT MOVES INTO THE
GREAT LAKES ON THURSDAY. MODELS HAVE BEEN FAIRLY CONSISTENT IN
SHOWING A TIGHT PRESSURE GRADIENT SETTING UP ACROSS THE OHIO
VALLEY ON THURSDAY AND SHOWERS WITH THIS SYSTEM BEGINNING TO PUSH
IN FROM THE WEST AFTER 18Z. MOMENTUM TRANSFER FROM GFS/NAM MODEL
SOUNDINGS INDICATE 30 TO 40 MPH WINDS MIXING DOWN THURSDAY
AFTERNOON. AT THIS TIME...STILL LOOKS TO BE JUST BELOW ADVISORY
CRITERIA WITH BETTER WIND GUSTS TO THE WEST AND CLOSER TO THE LOW.
WITH SHOWERS MOVING ACROSS THE AREA...A QUARTER TO A HALF OF AN
INCH OF RAINFALL IS FORECAST ACROSS THE AREA ON THURSDAY.
THE LOW WILL SHIFT INTO THE EASTERN GREAT LAKES ON THURSDAY
NIGHT...USHERING A COLD FRONT ACROSS THE AREA BETWEEN 00Z AND
09Z. RAIN AHEAD OF THE FRONT WILL QUICKLY TURN OVER TO SNOW
WITH A SHOT OF STRONG CAA BEHIND THE FRONT. WITH THE QUICK
CHANGEOVER...A QUICK INCH OR TWO OF SNOWFALL WILL BE POSSIBLE
DEPENDING ON THE AMOUNT OF MOISTURE AND THE TIME THAT IT TAKES FOR
A DRY SLOT TO MOVE INTO THE AREA BEHIND THE FRONT.
THE SURFACE LOW WILL SHIFT FURTHER NORTHEASTWARD INTO UPSTATE NY
ON FRIDAY...ALLOWING FOR CAA TO CONTINUE AND FOR THE LOW-LEVEL
FLOW TO SHIFT FROM WEST TO NORTHWESTERLY BY THE AFTERNOON HOURS.
THERE IS STILL SOME UNCERTAINTY IN HOW THE DRY SLOT EARLY IN THE
DAY WILL BE RESOLVED. DEPENDING ON THE INTERACTION OF THE DRY AIR
WITH TROWAL WRAPPING IN AROUND SYSTEM AND ALSO HOW A CYCLONIC
FETCH WITH AN UPSTREAM LINK TO MICHIGAN WILL SERVE TO BRING SNOW
SHOWERS AND BLUSTERY CONDITIONS EARLY IN THE DAY STILL MAKE FOR
SOME UNCERTAINTY IN QPF/SNOW AMOUNTS IN THE 06Z-16Z PERIOD ON
FRIDAY. HOWEVER...AFTER 16Z...THE 850MB FLOW SHIFTS TO MORE
NORTHWESTERLY AND THE COLUMN SATURATES THROUGH THE DENDRITIC
GROWTH ZONE...MAKING UPSLOPING AND LAKE EFFECT MUCH MORE
FAVORABLE. WITH THIS IN MIND...THE WINTER STORM WATCH HAS BEEN
UPGRADED TO A WARNING FOR THE RIDGES OF WV/MD/PA. THERE IS STILL
SOME UNCERTAINTY IN LAKE EFFECT DURATION AND THUS A WATCH REMAINS
FOR LOCATIONS ALONG THE I-80 CORRIDOR.
THERE ARE TWO BIG QUESTIONS IN REGARDS TO HOW THIS EVENT WILL
UNFOLD...HOW STRONG WILL THE WINDS BE ON FRIDAY...AND WILL
SNOW/BLOWING SNOW WITH WINDS LEAD TO BLIZZARD CONDITIONS FOR
THE RIDGES. GFS/NAM MIXED LAYER WINDS INDICATE THE POTENTIAL OF
REACHING MARGINAL CRITERIA FOR A WIND ADVISORY ON FRIDAY. IN
REGARDS TO BLIZZARD CONDITIONS FOR THE RIDGES...WINDS GUSTING TO
45 MPH AT TIMES...ALONG WITH DRIER SNOW AS SNOW-TO-LIQUID RATIOS
INCREASING TO 15-20:1 DURING THE DAY WILL LEAD TO BLOWING SNOW
ACROSS MUCH OF THE AREA...ESPECIALLY THE EASTERN RIDGES. AT THIS
TIME...WENT WITH A WINTER STORM WARNING WITH NEAR BLIZZARD
CONDITIONS MENTIONED FOR THE HIGHER ELEVATIONS. THIS IS IN
CONSIDERATION THAT THERE COULD BE A FUTURE UPGRADE...BUT AT THIS
TIME CONFIDENCE IN A TIME WINDOW OF WHEN VISIBILITIES BELOW A
QUARTER OF A MILE COUPLED WITH WINDS GUSTING TO 35 MPH WOULD OCCUR
IS NOT HIGH ENOUGH TO WARRANT A BLIZZARD WARNING.
UPSLOPE AND LAKE EFFECT SNOWS WILL LIKELY PEAK FRIDAY AFTERNOON
AND OVERNIGHT INTO EARLY SATURDAY...WITH 6 TO 10 INCHES ACROSS THE
LAKE EFFECT ZONES AND 8 TO 14 FOR THE RIDGES MAKING FOR
TREACHEROUS CONDITIONS. ELSEWHERE...2-5 INCHES ACROSS THE AREA
WITH BLOWING SNOW WILL ALSO CONTRIBUTE TO IMPACTING TRAVEL.
SNOWFALL RATES WILL BEGIN TO DECREASE IN INTENSITY ON SATURDAY AS
INVERSION HEIGHTS LOWER AND THE SURFACE LOW LIFTS FURTHER
NORTHEASTWARD OF THE AREA.
FOR TEMPS...WAA ADVECTION IN A SOUTHERLY FLOW AHEAD OF THE LOW
WILL ALLOW FOR TEMPS TO WARM TO 10-15 DEGREES ABOVE NORMAL AHEAD
OF THE COLD FRONT ON THURSDAY. IN THE WAKE OF THE FRONT...WITH 850
TEMPS COOLING TO AROUND -8C...EXPECT TEMPS TO BE AROUND 5 DEGREES
BELOW NORMAL WITH BLUSTERY CONDITIONS FOR FRIDAY AND SATURDAY.
&&
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
BLEND OF RECENT GFS AND ECMWF MODEL OUTPUT SHOWS HIGH PRESSURE
SHOULD PROMOTE MAINLY DRY SEASONABLY COLD CONDITIONS SUNDAY AND
MONDAY.
THERE CONTINUES TO BE UNCERTAINTY REGARDING THE WEATHER FOR
CHRISTMAS DAY AND WEDNESDAY AS GFS AND ECMWF DIFFER ON EVOLUTION
DETAILS OF INCOMING LOW PRESSURE SYSTEMS. AT THIS JUNCTURE DEFERRED
TO HPC SOLUTIONS WHICH SUPPORTED IDEA THAT THERE CAN BE
PRECIPITATION MOVING ACROSS THE UPPER OHIO VALLEY CHRISTMAS DAY AND
WEDNESDAY.
REGARDING TEMPERATURES...ALSO CONCURRED WITH HPC WITH PREFERENCE TO
COLDER ECMWF MOS...WHICH SHOWED LOWS AND HIGHS STRADDLING THE
FREEZING POINT. SO NOT SURPRISINGLY FORECAST FOR CHRISTMAS DAY AND
WEDNESDAY HAS A CHANCE OF RAIN AS WELL AS A CHANCE OF SNOW.
&&
.AVIATION /03Z THURSDAY THROUGH MONDAY/...
MODEL TIME HEIGHT SECTIONS INDICATE STRATOCUMULUS SHOULD BECOME
GRADUALLY ERADICATED AS SOUTHEASTERLY DOWNSLOPE FLOW FROM THE
RIDGES STARTS TO BECOME STRONGER OVERNIGHT. THIS WILL LEAVE US
WITH A PERIOD OF INCREASING HIGH CLOUDS AND LOW PRECIPITATION
CHANCES AS THE LOW LEVELS ARE DRIED DUE TO DOWNSLOPING. A STRONGER
PRESSURE GRADIENT SHOULD GRADUALLY INCREASE SOUTHEASTERLY FLOW
WITH GUSTS MATERIALIZING BY NOON ON THURSDAY. AS A COLD FRONT
ADVANCES EASTWARD...CIGS/VIS SHOULD QUICKLY DETERIORATE ON MONDAY
EVENING AS MODERATE RAIN SHOWERS WITH LOW CIGS AND GUSTY SSE WINDS
BECOME COMMON AT ALL SITES. FRIES
.OUTLOOK.../THURSDAY NIGHT THROUGH MONDAY/...
PASSAGE OF STRONG LOW PRESSURE SYSTEM AND ITS COLD FRONT THURSDAY
EVENING WILL PROMOTE IFR RAIN SHOWERS AND WIND GUSTS TO 40 KTS.
ENSUING COLD WESTERLY WINDS WILL PROMOTE PERIODS OF IFR RESTRICTIONS
IN SNOW SHOWERS LATE THURSDAY NIGHT INTO SATURDAY AFTERNOON. SURFACE
WINDS CAN CONTINUE TO GUST AT TIMES OVER 35 KTS.
ENSUING HIGH PRESSURE SHOULD PROMOTE IMPROVEMENT TO VFR SUNDAY AND
MONDAY.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...WINTER STORM WARNING FROM 11 AM FRIDAY TO 7 PM EST SATURDAY
FOR MDZ001.
OH...NONE.
PA...WINTER STORM WATCH FROM LATE THURSDAY NIGHT THROUGH SATURDAY
EVENING FOR PAZ007>009-015-016.
WINTER STORM WARNING FROM 11 AM FRIDAY TO 7 PM EST SATURDAY
FOR PAZ074-076.
WV...WINTER STORM WARNING FROM 11 AM FRIDAY TO 7 PM EST SATURDAY
FOR WVZ023-041.
&&
$$
AREA FORECAST DISCUSSION
NWS PITTSBURGH PA
755 PM EST WED DEC 19 2012
.SYNOPSIS...
HIGH PRESSURE WILL BRING DRY WEATHER TONIGHT INTO EARLY THURSDAY.
A STRONG COLD FRONT WILL MOVE ACROSS THE AREA THURSDAY AFTERNOON
AND EVENING BRINGING SHOWERS TO THE REGION. MUCH COLDER AIR WILL
MOVE IN BEHIND THE FRONT WITH SNOW SHOWERS AND GUSTY WINDS LATE
THURSDAY NIGHT THROUGH SATURDAY EVENING.
&&
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
AN EVENING UPDATE HAS BEEN ISSUED TO ACCOUNT FOR THE LATEST TRENDS
IN TEMPS AND SKY GRIDS OVERNIGHT.
THE LATEST RAP MID-LEVEL ANALYSIS INDICATES A 500MB TROUGH AXIS
CENTERED ACROSS THE FRONT RANGE WITH MORE OF A ZONAL FLOW ACROSS
THE UPPER OHIO VALLEY IN ADVANCED OF THIS FEATURE. AN 850MB THERMAL RIDGE
IS BUILDING INTO THE OHIO VALLEY WITH A TIGHTENED THERMAL
GRADIENT CURRENTLY BISECTING THE CWA. AT THE SURFACE...A 1021MB
HIGH IS CENTERED ACROSS WV/OH.
TONIGHT...THE SURFACE HIGH WILL SLOWLY SHIFT EASTWARD WITH WAA
ENSUING AS THE 850MB FLOW SHIFTS TO SOUTHERLY. SKIES WILL
GENERALLY BE MOSTLY CLOUDY OVERNIGHT AS LINGERING AREAS OF
STRATOCU CONTINUE TO MOVE ACROSS THE REGION AND UPPER LEVEL
MOISTURE BEGINS TO ADVECT INTO THE AREA. WITH WAA ENSUING
OVERNIGHT...TEMPS WILL DECREASE VERY LITTLE OVERNIGHT...WITH LOWS
RANGING FROM THE LOWER 30S ACROSS THE I-80 CORRIDOR AND EASTERN
RIDGES TO THE UPPER 30S IN EASTERN OHIO.
&&
.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
LOW PRESSURE WL TRACK NEWD TO THE GREAT LAKES RGN THU INTO FRI. A
COLD FRONT WL MOV E ACRS THE AREA LATE THURSDAY INTO THURSDAY EVE.
MOST OF THE MOISTURE IS PRE FRONTAL. EXPECT A BAND OF SHOWERS TO
MOVE THROUGH AHEAD OF THE FRONT. GUSTY WINDS OF 30-40 MPH ARE
EXPECTED. SHOULD BE JUST BELOW WIND ADVISORY CRITERIA BUT WL HAVE
TO MONITOR.
ATTENTION THEN TURNS TO COLD AIR MOVING IN BEHIND THE FRONT...AND
SNOW SHOWERS. WRAP AROUND MOISTURE BEHIND THE LOW WL BRING SNOW
SHOWERS TO THE ENTIRE AREA. THE HEAVIEST SNOW SHOULD BE LOCATED IN
THE HIGHER TERRAIN...WITH GOOD UPSLOPE FLOW AND OMEGA. KEPT WINTER
STORM WATCH AS IS IN THAT AREA...WITH MENTION OF NEAR BLIZZARD
CONDITIONS. WL MONITOR THIS SITUATION AS WELL TO SEE IF BLIZZARD
HEADLINES WOULD EVENTUALLY BE NEEDED. THE SECOND AREA OF HEAVIER
SNOW WL BE SE OF LAKE ERIE...WHERE LAKE ENHANCEMENT COMBINED WITH
THE WRAP AROUND SYNOPTIC MOISTURE SHOULD BRING DECENT SNOWFALL. NO
SGFNT CAPPING INVERSION EITHER WHICH SHOULD HELP BRING HEAVIER
SNOWFALL RATES. WENT WITH A WINTER STORM WATCH IN THIS AREA AS
WELL WITH THE POTENTIAL FOR HEAVY SNOW AND GUSTY WINDS. THIS
INCLUDES THE I 80 CORRIDOR. ELSEWHERE...EXPECT BELOW WARNING
CRITERIA SNOWFALL...ALTHOUGH ADVISORIES WL LIKELY BE NEEDED AS THE
EVENT NEARS. PCPN SHOULD BEGIN TO WIND DOWN SAT EVE AS DEEPER
MOISTURE MOVES OUT AND HIGH PRES TRIES TO NUDGE EWD.
&&
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
BLEND OF RECENT GFS AND ECMWF MODEL OUTPUT SHOWS HIGH PRESSURE
SHOULD PROMOTE MAINLY DRY SEASONABLY COLD CONDITIONS SUNDAY AND
MONDAY.
THERE CONTINUES TO BE UNCERTAINTY REGARDING THE WEATHER FOR
CHRISTMAS DAY AND WEDNESDAY AS GFS AND ECMWF DIFFER ON EVOLUTION
DETAILS OF INCOMING LOW PRESSURE SYSTEMS. AT THIS JUNCTURE DEFERRED
TO HPC SOLUTIONS WHICH SUPPORTED IDEA THAT THERE CAN BE
PRECIPITATION MOVING ACROSS THE UPPER OHIO VALLEY CHRISTMAS DAY AND
WEDNESDAY.
REGARDING TEMPERATURES...ALSO CONCURRED WITH HPC WITH PREFERENCE TO
COLDER ECMWF MOS...WHICH SHOWED LOWS AND HIGHS STRADDLING THE
FREEZING POINT. SO NOT SURPRISINGLY FORECAST FOR CHRISTMAS DAY AND
WEDNESDAY HAS A CHANCE OF RAIN AS WELL AS A CHANCE OF SNOW.
&&
.AVIATION /01Z THURSDAY THROUGH MONDAY/...
MODEL TIME HEIGHT SECTIONS INDICATE STRATOCUMULUS SHOULD BECOME
GRADUALLY ERADICATED AS SOUTHEASTERLY DOWNSLOPE FLOW FROM THE
RIDGES STARTS TO BECOME STRONGER OVERNIGHT. THIS WILL LEAVE US
WITH A PERIOD OF INCREASING HIGH CLOUDS AND LOW PRECIPITATION
CHANCES AS THE LOW LEVELS ARE DRIED DUE TO DOWNSLOPING. A STRONGER
PRESSURE GRADIENT SHOULD GRADUALLY INCREASE SOUTHEASTERLY FLOW
WITH GUSTS MATERIALIZING BY NOON ON THURSDAY. AS A COLD FRONT
ADVANCES EASTWARD...CIGS/VIS SHOULD QUICKLY DETERIORATE ON MONDAY
EVENING AS MODERATE RAIN SHOWERS WITH LOW CIGS AND GUSTY SSE WINDS
BECOME COMMON AT ALL SITES. FRIES
.OUTLOOK.../THURSDAY NIGHT THROUGH MONDAY/...
PASSAGE OF STRONG LOW PRESSURE SYSTEM AND ITS COLD FRONT THURSDAY
EVENING WILL PROMOTE IFR RAIN SHOWERS AND WIND GUSTS TO 40 KTS.
ENSUING COLD WESTERLY WINDS WILL PROMOTE PERIODS OF IFR RESTRICTIONS
IN SNOW SHOWERS LATE THURSDAY NIGHT INTO SATURDAY AFTERNOON. SURFACE
WINDS CAN CONTINUE TO GUST AT TIMES OVER 35 KTS.
ENSUING HIGH PRESSURE SHOULD PROMOTE IMPROVEMENT TO VFR SUNDAY AND
MONDAY.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...WINTER STORM WATCH FROM LATE THURSDAY NIGHT THROUGH SATURDAY
EVENING FOR MDZ001.
OH...NONE.
PA...WINTER STORM WATCH FROM LATE THURSDAY NIGHT THROUGH SATURDAY
EVENING FOR PAZ007>009-015-016-074-076.
WV...WINTER STORM WATCH FROM LATE THURSDAY NIGHT THROUGH SATURDAY
EVENING FOR WVZ023-041.
&&
$$
AREA FORECAST DISCUSSION
NWS PITTSBURGH PA
757 AM EST TUE DEC 18 2012
.SYNOPSIS...
SHOWERS WILL END TODAY AS LOW PRESSURE EXITS TO THE NORTHEAST.
HIGH PRESSURE WILL FOLLOW WITH DRY MILD CONDITIONS WEDNESDAY.
LOW PRESSURE COMING FROM CALIFORNIA WILL STRENGTHEN AS IT PICKS
UP COLDER AIR CROSSING THE PLAINS...TO PROVIDE US WITH SHOWERS
THURSDAY...BLUSTERY CONDITIONS FRIDAY... AND A COLDER WEEKEND.
&&
.NEAR TERM /THROUGH TONIGHT/...
BLEND OF RECENT SURFACE RADAR AND SATELLITE DATA COUPLED WITH
RECENT RAP AND SREF MODEL OUTPUT SHOWS SHOWERS DECREASING WEST TO
EAST ACROSS THE UPPER OHIO VALLEY THIS MORNING AND PRETTY MUCH
ENDING THIS AFTERNOON.
NAM MODEL PROFILES SHOW CLOUDS CAN LINGER
INTO TONIGHT. SURFACE WINDS WILL BE FROM THE WEST WITH GUSTS UP
TO 25 MPH.
FORECASTED TEMPERATURES TODAY WILL BE FAIRLY STEADY...BASED ON
RECENT RAP AND SREF MODEL OUTPUT. LOWS TONIGHT WILL BE MAINLY IN
THE LOWER 30S...WHICH IS STILL NEARLY 10 DEGREES WARMER THAN
NORMAL.
&&
.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
THAT BUILDING HIGH PRES WL PROVIDE FOR A DRY WEDNESDAY WITH WARM
ADVECTION DRIVING TEMPS FURTHER ABOVE THE SEASONAL AVERAGES. WARM
READINGS CAN BE EXPECTED INTO THURSDAY AS THAT ADVCTN REGIME
STRENGTHENS IN ADVN OF LOW PRES DEEPENING/DIGGING TWD THE GREAT
LAKES.
RAIN CHCS ARE ALSO ON THE RISE IN THE THURSDAY FORECAST AND THE
POPS INCRS TO CATEGORICAL NMBRS BY AFTN HAS BEEN
MAINTAINED...ALTHOUGH TIMING HAS BEEN ADJUSTED FORWARD BASED ON
THE LATEST DETERMINISTIC MDL TRENDS. IN ADDITION...THE TIGHTENING
PRES GRADIENT WL STRENGTHEN THE WIND FIELD...AND ADVISORY-LVL
GUSTS ARE POSSIBLE...ESPECIALLY OVR THE RIDGE ZONES. THE HAZARDOUS
WEATHER OUTLOOK HAS BEEN UPDATED FOR THAT POTENTIAL...WHICH WL
PERSIST INTO FRIDAY AS THE LOW DIGS ACRS THE ERN LAKES.
FINALLY...STRONG COLD ADVCTN FOLLOWING FRONTAL PASSAGE IS EXPECTED
TO CHANGE RAIN SHOWERS TO SNOW ON THURSDAY NGT...AND SOME LIGHT
ACCUMULATION WL BE POSSIBLE THROUGH FRIDAY. THE BTR CHC OF THAT
POTENTIAL IS FOR COUNTIES IN LEE OF THE LAKES...AND FOR THE RIDGE
ZONES.
SHORT TERM TEMPERATURES WERE FORECAST USING A BLEND OF THE WARMER GUIDANCE.
&&
.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
MODEL DIFFERENCES ARE INDICATED BY FRIDAY NIGHT...WITH THE GFS
SHOWING THE MATURE LOW MOVING OFFSHORE MORE QUICKLY THAN THE
ECMWF. SPEED OF THE DEPARTING LOW WILL DETERMINE HOW LONG
FAVORABLE FETCH WILL PERSIST OFF LAKE ERIE. FOR NOW...HAVE GONE
WITH SLOW DECLINE IN POPS THROUGH THE WEEKEND. EXPECT LITTLE
RECOVERY IN TEMPERATURES...WITH HIGHS A COUPLE OF DEGREES BELOW
NORMAL.
&&
.AVIATION /13Z TUESDAY THROUGH SATURDAY/...
SHOWERS AND RESTRICTIONS WILL CONTINUE FOR MUCH OF THE MORNING
BEFORE A GRADUAL IMPROVEMENT IN BOTH CIGS AND VSBYS IS EXPECTED.
IFR CLOUD DECK SHOULD BEGIN TO LIFT...WITH BETTER MIXING AS THE
COLD FRONT AND LOW SHIFT NORTHEASTWARD. BUFKIT SOUNDINGS SUGGEST THAT
MID LEVEL SUBSIDENCE WILL HELP TO SCATTER OUT THE CLOUD DECK LATE
TODAY. WHILE CONFIDENCE IN THIS ISN`T EXTREMELY HIGH...AND WILL
DEPEND ON THE UPPER LEVEL FLOW...TRIED TO HINT AT THIS
IMPROVEMENT.
WINDS OUT AHEAD OF AND SOUTH OF THE LOW WILL GENERALLY REMAIN E-SE
SHIFTING TO SW-W BY MORNING. WINDS SHOULD INCREASE TO 10KTS WITH
GUSTS TO 20KTS POSSIBLE FOR THE REMAINDER OF TUESDAY.
.OUTLOOK.../TONIGHT THROUGH SATURDAY/...
GUIDANCE SUGGESTS A RETURN OF SOME RESTRICTIONS IN COLD POOL
STRATOCUMULUS TUESDAY NIGHT/WEDNESDAY MORNING...ESPECIALLY NORTH
OF I-80. OTHERWISE...VFR EXPECTED IN HIGH PRESSURE BEFORE YET
ANOTHER LOW PRESSURE SYSTEM APPROACHES THURSDAY AFTERNOON.
RESTRICTIONS WILL THEN BE PROBABLE FROM THURSDAY ONWARD WITH THIS
STRONGER LOW PRESSURE/COLD FRONT PASSAGE. STRONG WIND GUSTS MAY
ALSO BE OF CONCERN THURSDAY NIGHT/FRIDAY.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...NONE.
OH...NONE.
PA...NONE.
WV...NONE.
&&
$$
AREA FORECAST DISCUSSION
NWS GAYLORD MI
1045 PM EST WED DEC 19 2012
.SYNOPSIS...
ISSUED AT 406 PM EST WED DEC 19 2012
QUIET WEATHER WILL CONTINUE THROUGH THIS EVENING...AS HIGH PRESSURE
DRIFTS OVERHEAD...PROVIDING MOSTLY CLOUDY SKIES AND MILD
TEMPERATURES.
THE WEATHER WILL DRAMATICALLY CHANGE ACROSS THE GREAT LAKES EARLY
THURSDAY MORNING AND FRIDAY...AS A STRONG WINTER STORM ORGANIZING
OVER THE CENTRAL PLAINS...LIFTS INTO THE GREAT LAKES REGION.
SIGNIFICANT SNOWFALL AND GUSTY WINDS ARE EXPECTED ACROSS NORTHERN
MICHIGAN INTO SATURDAY. CONDITIONS WILL GRADUALLY IMPROVE THROUGH
THE WEEKEND...AS HIGH PRESSURE AGAIN MAKES ITS APPROACH.
&&
.UPDATE...
ISSUED AT 1045 PM EST WED DEC 19 2012
LEADING EDGE OF SNOW SHIELD HAS REACHED FAR SRN WISCONSIN LATE
THIS EVENING. THIS GENERALLY MATCHES WELL WITH THE LATEST RUC13
AND NAM40. FURTHER UPSTREAM...THUNDERSNOW HAS BEEN REPORTED IN
PORTIONS OF IOWA AND NW MISSOURI WITHIN AN AREA OF VERY STRONG
700-500 MB DIV-Q AND IMPRESSIVE UPPER FORCING FROM JET COUPLING.
CLOSER TO HOME...LOW CLOUDS APPEAR TO BE ENTRENCHED ACROSS OUR
CWA...AND HAVE INCREASED CLOUD COVER A BIT FOR THE BALANCE OF THE
NIGHT. BUT MORE IMPORTANTLY...MAINTENANCE OF LOW CLOUDS/MOISTURE
MAY ALLOW FOR SNOW TO BEGIN SLIGHTLY AHEAD OF THE TIMING SUGGESTED
BY THE SHORT TERM MODELS DESPITE THE DEVELOPMENT OF DRIER EASTERLY
LOW LEVEL FLOW OVERNIGHT. THUS...WILL MAINTAIN THE TIMING OF SNOW
ARRIVAL AS PROVIDED BY THE GOING FORECAST...WHICH IS JUST SLIGHTLY
AHEAD OF THAT PROVIDED BY THE LATEST RUC AND NAM. CERTAINLY THE
VAST MAJORITY OF SNOW AND RESULTING IMPACTS FROM THIS UPCOMING
STORM WILL HOLD OFF UNTIL AFTER SUNRISE...BUT SW SECTIONS OF OUR
CWA WILL LIKELY SEE AROUND AN INCH OF NEW WHITE STUFF BY DAYBREAK...
WITH LESS THAN AN INCH ACROSS THE REST OF OUR CWA. STAY TUNED!
UPDATE ISSUED AT 700 PM EST WED DEC 19 2012
RESIDUAL LOW CLOUDS APPEAR TO BE INCREASING ACROSS NW LWR MICHIGAN THIS
EVENING...LIKELY EXPANDING UNDER THE WELL-ESTABLISHED INVERSION AS
THE BOUNDARY LAYER COOLS WITH SUNSET. STILL SUSPECT THIS INCREASE
IN LOW CLOUDS WILL BE SHORT-LIVED AS DRIER EASTERLY FLOW BECOMES
ESTABLISHED LATER THIS EVENING IN ADVANCE OF THE DEVELOPING STORM
SYSTEM NOW CENTERED OVER THE CENTRAL PLAINS. HOWEVER...MID/HIGH
CLOUDS WILL QUICKLY REPLACE ANY BREAK IN THE LOW CLOUDS BY LATE
EVENING...SO OVERALL SKY CONDITIONS TONIGHT WILL BE MAINLY CLOUDY.
LATEST RUC13 IS STILL SHOWING THE ARRIVAL OF WIDESPREAD SNOW
RANGING FROM AROUND 09Z IN OUR FAR SW CWA TO AROUND 12Z FOR ERN
UPR AND FAR NRN/NE LWR MICHIGAN...WITH SNOW BECOMING HEAVY AT
TIMES AFTER SUNRISE. THIS IS A BIT LATER THAN THE CURRENT FORECAST
SUGGESTS. START TIME HINGES...AT LEAST IN PART...ON IF AND TO WHAT
EXTEND LOW LEVEL MOISTURE/CLOUDS CAN BE SCOURED OUT THIS EVENING
BY DRIER EAST FLOW. IF LOW LEVEL MOISTURE REMAINS IN PLACE...START
TIME OF SNOW MAY VERY WELL BE EARLIER AS DEPICTED IN THE GOING
FORECAST. WILL KEEP A CLOSE EYE ON THIS THRU THE EVENING AND
ADJUST CLOUDS/WX/POP AS NECESSARY.
&&
.SHORT TERM...(TONIGHT)
ISSUED AT 406 PM EST WED DEC 19 2012
CURRENT OVERVIEW: WEAK HIGH PRESSURE IN CONTROL OF THE REGION/S
WEATHER TODAY WHICH...DUE TO IT/S WEAK NATURE...HAS ALLOWED STRATUS
AND STRATOCUMULUS TO PERSIST THROUGHOUT NORTHERN MICHIGAN FOR MUCH
OF TODAY. SURFACE MAP SHOWS LOW PRESSURE GRADUALLY CONGEALING OVER
THE PANHANDLES OF TX/OK WITH IMPRESSIVE BAROCLINIC LEAF SIGNATURE IN
WV/IR IMAGERY.
FORECAST CONCERNS CENTER AROUND CLOUD TRENDS...AND THEN TIMING THE
ARRIVAL OF SNOW LATER TONIGHT. ST/STCU WILL LIKELY NOT BE IN ANY
HURRY TO GO ANYWHERE THIS EVENING GIVEN SOME WEAK LAKE SUPPORT...AND
NO INTRODUCTION OF MEANINGFULLY-DRIER AIR. WHILE SOME BREAKS ARE
LIKELY...TIMING/LOCATING THEM WOULD BE FRUITLESS...AND...WITH HIGH
CLOUDS INCREASING BY MID/LATE EVENING AHEAD OF OUR APPROACHING
WINTER STORM...WILL GO WITH MOSTLY CLOUDY WORDING THROUGH THE
EVENING...TRANSITIONING TO CLOUDY OVERNIGHT.
AS FOR PRECIPITATION ONSET...GUIDANCE IS IN GOOD AGREEMENT THAT
INITIAL WARM ADVECTION SURGE WILL HOLD OFF UNTIL AFTER
MIDNIGHT...BUT STILL WITH A RANGE OF ABOUT 6 HOURS. IN THESE
SCENARIOS...WITH A DEEP SOUTHEAST FLOW AT PRECIP ONSET...TEND TO
SIDE WITH THE SLOWER EDGE OF THE GUIDANCE ENVELOPE. OF COURSE...THE
ANTECEDENT AIRMASS IS NOT ALL THAT DRY...HOWEVER...SO WHILE I/LL
LEAN SLOWER...I STILL THINK MOST SPOTS FROM CVX-GLR-OSC SOUTH AND
WEST WILL SEE FLAKES IN THE AIR BY DAYBREAK. WE/LL HAVE TO WATCH
ALONG THE IMMEDIATE LAKE HURON COAST...WHERE A LLEVEL WARM LAYER MAY
BE DEEP ENOUGH TO ALLOW PRECIPITATION TO START AS A MIX /OR ALL
RAIN/. NO ICING EXPECTED. AS FOR SNOW TOTALS...EXPECT 1-2" BY
DAYBREAK OVER THE FAR SOUTHWEST /NEAR MBL/ WITH NO MORE THAN A
COATING FROM CVX TO GLR.
NOTE! FOR MOST LOCATIONS SAVE THE FAR SOUTHWEST...TRAVEL CONDITIONS
MAY NOT BE ALL THAT BAD AT DAYBREAK THURSDAY. PLEASE CONSIDER...
HOWEVER...THAT QUICKLY DETERIORATING CONDITIONS ARE EXPECTED
THURSDAY /SEE BELOW/.
.LONG TERM...(THURSDAY THROUGH WEDNESDAY)
ISSUED AT 406 PM EST WED DEC 19 2012
...HIGH IMPACT WINTER STORM THURSDAY THROUGH FRIDAY...
WATER VAPOR IMAGERY...OVERLAID WITH 12Z RAOB ANALYSIS...LENDS MUCH
CONFIDENCE TO NOW MULTI-DAY MODEL TRENDS OF A HIGH IMPACT WINTER
WEATHER EVENT ACROSS MUCH OF THE NORTH WOODS THURSDAY AND FRIDAY.
SHORTWAVE NO DOUBT LOOKS IMPRESSIVE AS IT BEGINS ITS EJECTION OUT OF
THE SOUTHWEST CONUS...WITH EXCELLENT PACIFIC "PINEAPPLE" CONNECTION
AND BURGEONING WESTERN GULF OF MEXICO MOISTURE ADVECTION OUT FRONT
OF IT (AS EVIDENCE BY DEWPOINTS SURGING INTO THE 60S OVER NORTHEAST
TEXAS ON GUSTY SOUTH WINDS). ATTENDANT UPPER JET CORE MEANS BUSINESS
...WITH CONUS RAOB H25/H30 NETWORK SHOWING CORRIDOR OF 120+ KNOT
WINDS EXTENDING FROM THE MID ATLANTIC ALL THE WAY BACK INTO THE
DESERT SOUTHWEST...WITH EMBEDDED 145+ KNOT JET MAX ARCHING INTO THE
SOUTHWEST LAKES. THIS JET WILL HELP EJECTING WAVE QUICKLY TAKE ON A
NEGATIVE TILT AS IT REACHES THE MID MISSISSIPPI VALLEY REGION EARLY
THURSDAY ...ON ITS WAY TO CLOSING OFF AS IT CROSSES THE SOUTHERN
LAKES OVERNIGHT THURSDAY. SURFACE REFLECTION WILL INITIALLY LEAD ITS
MID LEVEL PARENT...STEADILY DEEPENING (REACHING SUB 990MBS LEVELS)
AS IT PIVOTS NORTHEAST TO VICINITY SOUTHERN LAKE MICHIGAN BY
THURSDAY EVENING. SYSTEM OCCLUDES THERE ON AFTER...WITH SURFACE LOW
TUCKING UNDER ITS MID LEVEL LIKENESS. THIS TRACK UP THROUGH SOUTHERN
LAKE MICHIGAN AND ACROSS SOUTHERN MICHIGAN/THE THUMB PLACES MUCH OF
OUR AREA IN THE CROSS-HAIRS OF A SIGNIFICANT WINTER WEATHER
EVENT...WITH HEAVY SNOW AND VERY GUSTY WINDS LEADING TO THE
DEVELOPMENT OF EXTREMELY HAZARDOUS CONDITIONS EARLY
THURSDAY...CONTINUING RIGHT THROUGH FRIDAY. SOUNDS PRETTY
CLEAR-CUT...BUT SAID TRACK (DRY SLOT ISSUES?)...ABOVE NORMAL LAKE
HURON WATER TEMPERATURES...AND ANTECEDENT RATHER "MILD" AIRMASS
STILL MAKES EXACT PRECIP TYPE AND TIMING OF CHANGEOVERS A FORMIDABLE
CHALLENGE...ESPECIALLY FOR THE SOUTHEAST THIRD OF OUR AREA.
INHERITED FORECASTERS HAVE LAID A SOLID FOUNDATION ON ALL THE
ABOVE...WITH FORECASTS/WARNINGS AND STATEMENTS/WEB BRIEFINGS ALL
HIGHLIGHTING THIS HIGH IMPACT EVENT. THUS...MOST CHALLENGING PART OF
THE FORECAST REMAINS TRYING TO FIGURE EXACT DEMARCATION OF RAIN/SNOW
LINE AND WHAT TO DO WITH INHERITED WINTER STORM WATCH THAT STRADDLES
THIS DIVISION.
HIGH CONFIDENCE PORTION OF THE FORECAST: AS MENTIONED BY OVERNIGHT
FORECAST...STORM STRUCTURE SHOULD BE A "CLASSIC" ONE...AS IS QUITE
OFTEN SEEN WITH THESE PANHANDLE-HOOK SYSTEMS. LEAD ISENTROPIC/FGEN
DRIVEN PRECIP SHIELD EARLY THURSDAY WILL GIVE WAY TO INTENSE DEEP
LAYER -DIVQ/UPPER LEVEL DIVERGENCE AXIS AND INCREASINGLY WELL
ESTABLISHED TROWAL AS CYCLONIC PORTION OF WARM CONVEYOR BELT WRAPS
BACK ACROSS NORTHERN MICHIGAN LATER THURSDAY INTO EARLY FRIDAY. FGEN
SIGNATURE FOCUSES ALONG THE NORTHWEST QUADRANT OF SYSTEM LATER
THURSDAY...WITH WARM SIDE RESPONSE TARGETING NORTHWEST LOWER AND
EASTERN UPPER MICHIGAN. GOOD -EPV SIGNATURE...SUGGESTING CONVECTIVE
SNOW BURSTS (THUNDERSNOW?) AND POSSIBILITY FOR ENHANCED VERY HEAVY
SNOW BANDS EMBEDDED WITHING BROADER SNOW SHIELD. MOISTURE FOR ALL
THE ABOVE REMAINS ABUNDANT...WITH PWAT VALUES NEARING AN INCH OVER
THE FAR SOUTHERN LAKES...AND EXCEEDING 0.5 INCHES OVER NORTHERN
MICHIGAN...WHICH IS REACHING NEAR 2 STANDARD DEVIATIONS ABOVE NORMAL
FOR DECEMBER. HPC/MODEL PRECIP GRAPHICS AGREE...TARGETING NORTHERN
MICHIGAN WITH STORM TOTAL LIQUID EQUIVALENTS IN EXCESS OF AN INCH
BY THE END OF FRIDAY.
LINGERING UNCERTAINTIES AND WHAT CAN GO WRONG SCENARIO: WHILE ABOVE
NEARLY SET IN STONE...EXACT PRECIP TYPES...SNOW-LIQUID RATIOS...AND
POSSIBLE DRY-SLOT ISSUES REMAIN A FORMIDABLE CHALLENGE. AS FEARED...
LATEST 12Z NAM-WRF AND GFS FITS PATTERN RECOGNITION OF SUCH A
WRAPPED-UP SYSTEM TRENDING A TOUCH NORTHWEST THAN EARLIER PROGGED.
COMBINE THIS WITH INITIAL STRONG EAST FLOW COMING OFF THE ABOVE
NORMAL LAKE HURON WATERS AND ANTECEDENT RATHER MILD MID DECEMBER
TEMPERATURES...AND RAIN SEEMS LIKE A GIVEN FOR AT LEAST SOME OF OUR
SOUTHEAST COUNTIES. USING LATEST NAM-WRF AND GFS 0-6KM MAX TEMP
PROGS AND FORECAST RAOBS NOW SUGGEST THIS DEMARCATION SPREADING AS
FAR WEST AS A HARRISVILLE TO HOUGHTON LAKE LINE DURING THE
AFTERNOON...WITH EVEN SOME MIX POSSIBLE A TOUCH FURTHER NORTHWEST.
MOST OTHER GUIDANCE NOT QUITE AS AGGRESSIVE SPREADING RAIN AS FAR
INLAND... ALTHOUGH ALL ARE ON BOARD WITH PREDOMINATELY LIQUID ACROSS
BOTH IOSCO AND ARENAC COUNTIES...AS WELL AS THE IMMEDIATE COASTLINE
AREAS OF ALCONA COUNTY...UNTIL LATER THURSDAY NIGHT. HARD NOT TO GO
WITH THE MAJORITY...BUT ALSO HARD TO COMPLETELY IGNORE PAST HISTORY
AND PATTERN RECOGNITION. UNFORTUNATELY...FORECAST WILL BY NO MEANS
MIMIC REALITY AS THESE EXACT DETAILS WILL NOT BE REALIZED TO THE
EVENT ACTUALLY UNFOLDS. WILL TAKE A "BEST GUESS"...KEEPING
PREDOMINATELY RAIN WHERE THE MAJORITY AGREE...BUT SPREADING MIX
RAIN/SNOW WORDING A TOUCH FURTHER INLAND...STRETCHING FROM ABOUT
ROGER CITY DOWN TO MANISTEE (NOT TOO WORRIED ABOUT SLEET WITH LITTLE
SUPPORT FOR SURFACE BASED COLD LAYER BELOW ELEVATED WARM NOSE). OF
COURSE...SNOW-TO-LIQUID RATIOS CONTINGENT ON THE ABOVE...AS WELL AS
THE FACT DGZ REMAINS FAIRLY ELEVATED DURING THE EVENT EVEN WHERE ALL
SNOW IS EXPECTED. REALLY LIKE PREVIOUS FORECAST IDEA OF TRENDING
MODEL DEPICTED SNOW/LIQUID RATIOS DOWN...AND WILL MAKE ONLY SUBTLE
CHANGES TO THOSE INHERITED. LASTLY...DRY SLOT ISSUES. IT WILL BE A
CLOSE CALL FOR AREAS DOWN NEAR SAGINAW BAY...ESPECIALLY IF LAST
SECOND NORTHWEST TREND IS REALIZED. WILL NOT GO THIS ROUTE JUST
YET...BUT DEFINITELY COULD SEE PRECIP WOUND DOWN FOR A PERIOD OF
TIME THURSDAY EVENING ACROSS THE FAR SOUTHEAST.
SNOWFALL AMOUNTS: DESPITE SOMEWHAT LOW SNOW-TO-LIQUID RATIOS...
ESPECIALLY ACROSS NORTHERN LOWER...SIMPLE MAGNITUDE OF DYNAMICS AND
AVAILABLE MOISTURE SUPPORTS SNOWFALL AMOUNTS POSSIBLY APPROACHING A
FOOT FOR AREAS ALONG AND NORTHWEST OF A LINE EXTENDING FROM ROGERS
CITY TO CADILLAC...WITH SOME LOCALLY HIGHER AMOUNTS IN FAVORED NNW
FLOW AREAS AS LAKE ENHANCEMENT AUGMENTS TROWAL DRIVEN SNOWS LATER
THURSDAY NIGHT INTO FRIDAY. IN ADDITION...POTENTIAL FOR HIGH
INTENSITY (ONE TO TWO INCH PER HOUR?) ELEVATED CONVECTIVE DRIVEN
SNOW BANDS COULD LEAD TO LOCALLY HIGHER AMOUNTS. SNOWFALL TOTALS
SHOULD FALL OF RAPIDLY FURTHER SOUTHEAST...WITH PERHAPS JUST A FEW
INCHES NEAR SAGINAW BAY GIVEN LATER CHANGEOVER AND DECAYING TROWAL
DYNAMICS BY THE TIME CHANGEOVER OCCURS. LITTLE DOUBT EXACT GRADIENT
SHOWN IN FORECAST WILL CHANGE AS EVENT UNFOLDS.
HEADLINES...INHERITED WINTER STORM WARNING IS A NO-BRAINER...WITH
SAID HEAVY SNOW AMOUNTS AND INCREASINGLY GUSTY WINDS...ESPECIALLY BY
LATE THURSDAY NIGHT AND FRIDAY. WIND GUSTS COULD EASILY EXCEED
30MPH...WITH EVEN HIGHER GUSTS ALONG THE IMMEDIATE LAKE MICHIGAN
SHORELINE. PROGS CONCUR...WITH STRONG NNW FLOW LOW LEVEL JET CENTER
OVER LAKE MICHIGAN BY EARLY FRIDAY. NEAR WHITEOUT CONDITIONS IN
BLOWING AND DRIFTING SNOW IS DEFINITELY PLAUSIBLE...ESPECIALLY IN
UNSHELTERED AREAS. HAVE TOSSED AROUND THE BLIZZARD IDEA...BUT PAST
HISTORY SHOWS GETTING TRUE BLIZZARD CONDITIONS IS AWFULLY TOUGH.
WILL LET WINTER STORM WARNING SPEAK FOR ITSELF...WITH NEAR BLIZZARD
CONDITIONS MENTIONED WITHIN THE TEXT. AS FOR THE REMAINING
WATCH...TOUCH CALL BASED ON RAIN/SNOW ISSUE...BUT WILL UPGRADE
NORTHWEST TIER OF WATCH COUNTIES TO A WARNING...STRESSING HIGHEST
SNOW TOTALS OVER THE NORTHWEST CORNER OF EACH. REST OF THE WATCH
WILL FALL UNDER AN ADVISORY...HIGHLIGHTING INITIAL AND END EVENT
SNOW BURST. AS FOR A LIST OF EXPECTED IMPACTS FROM THIS
SYSTEM...PLEASE REFER TO OUR WARNING AND ADVISORY PRODUCTS.
MSB
SATURDAY AND SUNDAY...INGREDIENTS ARE CONTINUING TO LOOK DISMAL
FOR LAKE EFFECT SNOW BEHIND THE DEPARTING STORM SYSTEM. LOW
MOISTURE...850MB TEMPERATURES ONLY AROUND -5C...WHICH PUT DELTA T/S
ONLY AT 11C. THE BEST CHANCE APPEARS TO BE EARLY SUNDAY
MORNING...WHEN 850MB TEMPERATURES BEGIN TO DROP AHEAD OF A WEAK
SHORTWAVE WITH SYNOPTIC-SCALE QG FORCING...HIGHER MOISTURE
AMOUNTS...DELTA T/S OF AROUND 14C. WINDS WILL BE NORTHERLY DURING
THIS OPTIMAL TIMEFRAME...WHICH WOULD IMPACT MAINLY WHITEFISH POINT
TO WESTERN MACKINAC COUNTY AND THEN LEELANAU...BENZIE AND MANISTEE
COUNTIES IN NORTHERN LOWER. STILL DON/T EXPECT MUCH ACCUMULATIONS
FROM ANY LAKE EFFECT SNOW THAT DEVELOPS SATURDAY THROUGH LATE SUNDAY
NIGHT.
CHRISTMAS EVE...ECMWF AND GFS HAVE COME TO AGREEMENT ON A SHORTWAVE
MOVING THROUGH THE GREAT LAKES REGION MONDAY AFTERNOON AND INTO THE
EVENING HOURS...POSSIBLY GENERATING SOME MINOR SNOW ACCUMULATIONS
ACROSS NORTHERN MICHIGAN. THERE COULD ALSO BE SOME LOCALIZED LAKE
ENHANCED SNOW WITH 850MB TEMPS NEAR -14C...BRINGING DELTA T/S TO
NEAR 20C.
TUESDAY AND WEDNESDAY...TEMPERATURES MAY REACH SINGLE DIGITS OVER
INTERIOR PORTIONS OF NORTHERN LOWER MICHIGAN TUESDAY AND WEDNESDAY
MORNING...AS COLD ARCTIC AIR FILTERS IN FROM BETWEEN A SURFACE HIGH
PRESSURE RIDGING INTO THE GREAT LAKES REGION FROM WESTERN CANADA AND
A FORECAST DEVELOPING STORM SYSTEM OVER THE SOUTHERN PLAINS. I HAVE
USED THE COLDER ECMWF FOR TEMPERATURES TUESDAY AND WEDNESDAY.
INCREASED CLOUDINESS TUESDAY AHEAD OF THE AFOREMENTIONED POTENTIALLY
STRONG STORM SYSTEM THAT MAY IMPACT THE GREAT LAKES REGION WEDNESDAY
AND INTO THURSDAY.
TJL
&&
.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1045 PM EST WED DEC 19 2012
MVFR/LOW VFR CIGS WILL PERSIST OVERNIGHT AS SHALLOW LOW LEVEL
MOISTURE HAS AND WILL REMAIN STUCK BELOW THE INVERSION. CONDITIONS
WILL QUICKLY DETERIORATE TO IFR BEFORE DAYBREAK AS WIDESPREAD SNOW
SPREADS SW TO NE ACROSS ALL NRN LWR MICHIGAN TAF SITES...BECOMING
HEAVY DURING THE MORNING AND CONTINUING THRU THURSDAY NIGHT. SOME
RAIN WILL MIX WITH THE SNOW AT APN THANKS TO MODIFIED LOW LEVEL
TEMPS ALONG THE LAKE HURON SHORELINE WITH EASTERLY WINDS. LIGHT
WINDS THIS EVENING WILL BECOME EAST OVERNIGHT AND QUICKLY
STRENGTHEN ON THURSDAY...WITH GUSTS TO 30 TO 35 KTS EXPECTED.
WINDS WILL SHIFT TO THE NE AND EVENTUALLY NORTH ACROSS NW LWR
MICHIGAN (PLN/TVC/MBL) THURSDAY AFTERNOON AND NIGHT AS THE LOW
CENTER TRACKS FROM SW LWR MICHIGAN THRU SAGINAW BAY.
&&
.MARINE...
ISSUED AT 406 PM EST WED DEC 19 2012
THE CALM BEFORE THE STORM. LIGHT WINDS ARE EXPECTED THROUGH
MUCH OF TONIGHT WITH HIGH PRESSURE IN CONTROL. HOWEVER...APPROACHING
STRONG LOW PRESSURE WILL BRING A RAPID INCREASE IN SPEEDS BY SUNRISE
THURSDAY...WITH VERY STRONG WINDS LIKELY THROUGH THE DAY ON FRIDAY
AS THE LOW PASSES. GALE FORCE SPEEDS ARE EXPECTED ACROSS MOST OF THE
WATERS...WITH THE POSSIBILITY OF A FEW STORM FORCE GUSTS ON THE LAKE
MICHIGAN NEARSHORE WATERS LATER THURSDAY NIGHT INTO FRIDAY. MORE
TRANQUIL CONDITIONS ARE EXPECTED LATER INTO THE WEEKEND AS WEAK HIGH
PRESSURE GRADUALLY WORKS BACK OVER THE WATERS.
&&
.APX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER STORM WARNING FROM 7 AM THURSDAY TO 7 PM EST FRIDAY FOR
MIZ008-015>029-031>034.
WINTER WEATHER ADVISORY FROM 7 AM THURSDAY TO 7 PM EST FRIDAY
FOR MIZ030-035-041.
LH...GALE WARNING FROM 1 PM THURSDAY TO 7 AM EST SATURDAY FOR
LHZ345>349.
LM...GALE WARNING FROM 1 PM THURSDAY TO 7 AM EST SATURDAY FOR LMZ323-
341-342-344>346.
LS...GALE WARNING FROM 1 PM THURSDAY TO 7 AM EST SATURDAY FOR LSZ321-
322.
&&
$$
UPDATE...MR
SYNOPSIS...TL
SHORT TERM...JA
LONG TERM...MB/TL
AVIATION...MR
MARINE...MB
AREA FORECAST DISCUSSION
NWS MARQUETTE MI
945 PM EST WED DEC 19 2012
.UPDATE...
ISSUED AT 944 PM EST WED DEC 19 2012
THE 00Z NAM AND RUC RUNS INDICATE THAT THE HEAVIER SNOW MAY BE A
LITTLE LATER TO ARRIVE...ESPECIALLY CLOSER TO LAKE SUPERIOR WHERE
INITIAL DRY AIR WILL NEED TO BE OVERCOME. WITH A TRACK SO FAR
SOUTH...THIS WOULD TEND TO MAKE SENSE. ALTHOUGH THE OVERALL STORM
TOTAL SNOWFALL FORECAST HAS NOT CHANGED...WILL DELAY THE ARRIVAL OF
SNOW FOR A FEW HOURS THU MORNING.
IT SHOULD BE NOTED THAT MANY PLACES IN UPPER MICHIGAN WILL NOT HAVE
MUCH OR ANY SNOW EARLY THURSDAY MORNING. HOWEVER...CONDITIONS WILL
RAPIDLY DETERIORATE DURING THE DAY AS THE SNOW SPREADS NORTH AND THE
NE WINDS INCREASE.
ISSUED AT 831 PM EST WED DEC 19 2012
NO MAJOR CHANGES TO THE GOING FORECAST THIS EVENING AS THE AFTERNOON
PACKAGE HAS THE SITUATION WELL IN HAND. LOW PRESSURE JUST NORTH OF
OKC IS STILL EXPECTED TO MOVE RAPIDLY NE TONIGHT TO A POSITION NEAR
CHICAGO BY NOON THURSDAY. WIDESPREAD SNOW IN THE DEFORMATION AXIS TO
THE N AND NW OF THE LOW WILL RAPIDLY MOVE NE AS WELL. THE LATEST
RUNS OF THE RUC AGREES WITH THE NAM AND SREF MEMBERS IN SHOWING THE
SNOW DEVELOPING AROUND 09Z AT MNM...THEN RAPIDLY SPREADING NORTHWARD
IN THE MORNING TO MQT BY 12Z AND CMX SOON AFTER. WITH THE
STRENGTHENING F-GEN MOVING OVER THE AREA ASSOCIATED WITH THE
DEVELOPING TROWAL /AND ASSOCIATED LOWER STABILITY/...EXPECT SNOW TO
FALL HEAVY AT TIMES ESPECIALLY ACROSS THE SOUTH AND EAST DURING THE
DAY. AS SUCH...HAVE OPTED TO INCLUDE SNOWFALL RATES OF 1-2 INCHES
PER HOUR IN THE WARNING AREAS TO HIGHLIGHT THIS SPECIFIC CONCERN.
OTHERWISE...THE ONLY OTHER CONCERN THAT WILL NEED TO MONITORED IS
THE POTENTIAL FOR HIGHER SNOW AMOUNTS IN GOGEBIC COUNTY DUE TO THE
SUSTAINED N-NE WIND. LATEST RUC RUNS INDICATE SNOW BECOMING HEAVIER
BY LATE MORNING AS THE BETTER MOISTURE WRAPS WESTWARD INTO FAR
WESTERN UPPER MI. IF THIS TREND CONTINUES WITH THE 00Z RUNS...THE
MID SHIFT MAY NEED TO OPT FOR A WARNING HERE AS WELL. STILL
EXPECTING THE WINDS TO INCREASE LATER THU INTO THU NIGHT. IN
FACT...AREAS NEAR LAKE SUPERIOR NEAR AND EAST OF MARQUETTE WILL
LIKELY SEE SIGNIFICANT BLOWING/DRIFTING THU NIGHT INTO FRI MORNING
AS THE SNOW TRANSITIONS TO A LESS DENSE LAKE EFFECT. NWP SUGGEST
45-50KT 925MB WINDS...AND THERE IS A CONCERN THAT BLIZZARD CRITERIA
COULD TECHNICALLY BE MET EARLY FRI MORNING. WILL NOT MAKE ANY
HEADLINE ADJUSTMENTS...BUT IT IS QUITE POSSIBLE THAT THE WORST
CONDITIONS OF THE ENTIRE EVENT FOR AREAS NEAR LAKE SUPERIOR WILL BE
THU NIGHT INTO FRIDAY MORNING.
UPDATED WINTER STATEMENT ALREADY OUT.
&&
.SHORT TERM...(THIS EVENING THROUGH THURSDAY)
ISSUED AT 441 PM EST WED DEC 19 2012
HEADLINES ARE OUT FOR ALL OF UPR MICHIGAN. SNOW BEGINS LATE TONIGHT
OVER SOUTH AND SPREADS ACROSS REST OF CWA ON THURSDAY. NOW WE WAIT.
WV LOOP/12Z RAOBS SHOW TWO PRIMARY UPPER LEVEL FEATURES. STRONG
SHORTWAVE TROUGH/PV ANAMOLY EMERGING ON TO THE SOUTHERN PLAINS
WHILE SHORTWAVE TROUGH IN THE NORTHERN STREAM IS DIGGING ACROSS
DAKOTAS. LEE SIDE CYCLOGENESIS WELL UNDERWAY NEAR TX/OK PANHANDLE.
SOUTHERN STREAM PV ANAOMOLY MAIN WX MAKER TO START. WAVE HEADS INTO
OK AND SOUTHERN MO TONIGHT WITH A 995MB SFC LOW NEARING SAINT LOUIS
MO BY 12Z ON THURSDAY. JET STREAK DIGGING INTO BASE OF TROUGH FM
WY TO KS AND INCREASING DIVERGENCE ALOFT RESULTS IN DEEPENING SFC
LOW BLO 990MB AS IT REACHES CHICAGO/SOUTHERN TIP OF LK MICHIGAN
18Z-24Z. FURTHER DEEPENING OF MID-LEVEL LOW THEN EXPECTED ON
THURSDAY NIGHT AS THE NORTHERN STREAM WAVE BEGIN TO INTERACT WITH
THE SOUTHERN STREAM ONE. THIS SHOULD ALLOW LAKE ENHANCED SNOW TO
LINGER LONGER ALONG LK SUPERIOR INTO FRIDAY.
BACK TO TONIGHT...LGT SNOW BEGINS TO SPREAD INTO FAR SOUTH CWA AFT
09Z TONIGHT THEN REACHES LK MICHIGAN TO IMT LINE AROUND 12Z THU.
INTIALLY SNOW WILL BE DRIVEN BY DIVERGENCE ALOFT FM JET STREAK
LIFTING INTO ONTARIO. LATER THU MORNING THROUGH THU AFTN...SOUTHERLY
WINDS AHEAD OF SFC-H85 LOW INCREAS GULF MOISTURE INTO AREA WITH
PERSISTENT ISENTROPIC ASCENT NOTED ON 290-305K SFCS /H9-H6/.
FRONTOGENESIS RAMPS UP WITH STEADY SURGE OF H8-H7 FRONTOGENESIS
SWEEPING ACROSS SCNTRL AND EASTERN CWA. STRONGEST/PERSISTENT FN/FS
VECTOR CONVERGENCE FAVORS CORRIDOR FROM MNM-ISQ-ERY TO SEE HEAVY
SNOW THROUGH MUCH OF AFTN. PIVOT POINT FOR SNOW SEEMS TO FAVOR LUCE
COUNTY FOR MOST PROLONGED PERIOD OF HEAVIER SNOW. RATES UP TO 2
INCHES/HOUR POSSIBLE AS ADDITIONAL FORCING IS PROVIDED BY 925-850MB
THETA-E ADVECTION. MEANWHILE OVER CNTRL AND WEST CWA MODERATE SNOW
SHOULD STEADILY LIFT NORTH ON THURSDAY MORNING AND SHOULD BE OVER
ALL AREAS BY MIDDAY. WILD CARD IN CNTRL CWA IS AREA OF H7-H5
FRONTOGENESIS THAT KEEPS SHOWING UP FROM MQT-IMT. SEEMS THAT
NAM/GFS/ECMWF/GEM-REGIONAL ALL PICK UP ON THIS ENHANCING FEATURE.
RESULT IS INCREASE IN MODELED QPF FM GFS/GEM-REGIONAL/ECMWF WHICH
NOW LOOKS A BIT CLOSER TO WETTER NAM IDEA. ALREADY ADDED DICKINSON
TO ONGOING WARNINGS ON EARLIER UPDATE. HIGHER TERRAIN OF MARQUETTE
AND BARAGA COUNTIES ALSO WILL BEGIN TO SEE POTENTIAL FOR INCREASED
SNOW AMOUNTS COMPARED TO LOWER ELEVATIONS BY LATE THURSDAY AFTN DUE
TO INCREASING NORTHEAST WINDS/UPSLOPE LIFTING.
ACROSS WESTERN TIER...SYNOPTIC SNOW WILL NOT FALL AS HEAVY AS IN THE
CNTRL AND EASTERN CWA. ULTIMATELY...TOTAL SNOW AMOUNTS WILL BE
BOOSTED OVER HIGHER TERRAIN OF WEST DUE TO LK ENHANCED/LK EFFECT
SNOW LATER THURSDAY NIGHT INTO FRIDAY. MORE ON THAT IN THE LONG TERM
DISCUSSION.
OVERALL...OTHER THAN ADDITION OF DICKINSON TO ORIGINAL WARNING AND
INCLUDING WESTERN CWA IN ADVY...THEME OF GOING FORECAST ISSUED ON
MID SHIFT IS STILL ON TRACK. EXPECT 12-15HR SYNOPTIC SNOW TOTALS
ENDING AROUND 7 PM EST THURSDAY OF 3-6 INCHES OVER WESTERN THIRD OF
CWA /IRONWOOD AND HOUGHTON/ WITH 6 TO 10 INCHES OVR REST OF CWA.
WIDESPREAD SYNOPTIC PORTION OF THE STORM CONTINUES ON THURSDAY NIGHT
OVER EASTERN CWA...BUT WILL WANE OVER THE SOUTH. BLOWING SNOW
BECOMES MORE SIGNIFICANT JUST BEYOND THE SCOPE OF THE SHORT TERM.
MODELS COMING INTO EVEN BETTER AGREEMENT TODAY JUST ADDS FURTHER
CONFIDENCE TO THE FORECAST. SO NOW WE WAIT.
.LONG TERM...(THURSDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 441 PM EST WED DEC 19 2012
THURSDAY NIGHT...MODELS WERE IN GOOD OVERALL AGREEMENT...TAKING
THE MID LEVEL LOW FROM NRN INDIANA TO THE SRN END OF LAKE HURON BY
12Z/FRI. AT 00Z/FRI...THE NAM INDICATED A BAND OF STRONG 700-500 MB
FGEN AND TROWAL FEATURE OVER CNTRL UPPER MI WHICH IS EXPECTED TO
SHIFT INTO THE ERN CWA DURING THE EVENING WHICH MAY HELP TO ENHANCE
SNOWFALL RATES BTWN 00Z-06Z OVER THE EAST HALF. AS THE STRONGER
FGEN...AND 700-300 MB QVECTOR CONV OVER NRN LAKE HURON INTO NRN LOWER
MI SHIFT STEADILY TO THE NE...THE SYNOPTIC SCALE LIFT AND PCPN WILL
ALSO WEAKEN. ADDITIONAL OVERALL SYNOPTIC SNOWFALL AMOUNTS OF 1 TO 3
INCHES ARE LIKELY..MAINLY DURING THE EVENING. SO...THE ADVISORIES AND
WARNINGS OVER THE SRN TIER OF COUNTIES WILL END AT 06Z.
850 MB TEMPS TO AROUND -10C OVER LAKE SUPERIOR COMBINED WITH 950-925
WINDS INTO THE 40-50 KT RANGE WILL LEAD TO SIGNIFICANT LAKE
ENHANCEMENT AND OROGRAPHIC BOOST TO SNOWFALL AMOUNTS. THE GREATEST
AMOUNTS WOULD BE EXPECTED IN THE HIGHER TERRAIN WEST OF MARQUETTE
WHERE ADDITIONAL SNOWFALL AMOUNTS OF 8 INCHES ARE EXPECTED WITH EVEN
LOCALLY HIGHER AMOUNTS POSSIBLE. LOCALLY GREATER SNOWFALL AMOUNTS ARE ALSO
EXPECTED ESPECIALLY NEAR IRONWOOD/WAKEFIELD THAT MAY EVENTUALLY PUSH
SNOW TOTALS INTO THE WARNING CATEGORY. HOWEVER...CONFIDENCE IN HEAVY
SNOWFALL AMOUNTS OVER THE WEST IS LOWER.
FRIDAY...MID LEVEL RIDGING AND ASSOCIATED QVECTOR
DIVERGENCE/SUBSIDENCE WITH LOWERING INVERSION HEIGHTS/STRONG 850-700
MB DRYING WILL SPREAD FROM WEST TO EAST BRINGING AN END TO ANY
SIGNIFICANT SNOWFALL RATES OVER THE WEST DURING THE MORNING AND
CNTRL/EAST BY EARLY AFTERNOON. SO...GOING WARNING/ADVY ENDING TIMES
LOOK ON TRACK. ADDITIONAL AMOUNTS OF A FEW INCHES WILL STILL BE
POSSIBLE...MAINLY NORTH CENTRAL AND EAST.
FRIDAY NIGHT INTO SATURDAY...WITH 850 MB TEMPS AROUND -8C AND LINGERING
MOISTURE OVER THE ERN PORTION LAKE SUPERIOR SOME LINGERING SCT -SHSN
MAY BE POSSIBLE OVER THE EAST WHICH SHOULD END EARLY SATURDAY
MORNING. OTHERWISE...LOOK FOR DECREASING CLOUDS WITH TEMPS CLOSER TO
SEASONAL AVERAGES...LOWS IN THE TEENS AND LOWER 20S AND HIGHS IN THE
MID TO UPPER 20S.
SUN-WED...SOME LIGHT LES MAY BE POSSIBLE SUNDAY AS ARCTIC HIGH PRES
OVER CNTRL CANADA PUSHES A COLD FRONT THROUGH THE AREA.
HOWEVER...WITH GENERALLY LIGHT ACYC NRLY WINDS...KEPT MODEL
CONSENSUS SLIGHT CHANCE POPS. THE GFS AND ECMWF SUGGEST THAT A WEAK
SHORTWAVE TROUGH MOVING FROM THE NRN PLAINS INTO THE WRN GREAT LAKES
COULD ALSO BRING SOME LIGHT SNOW TO THE REGION. SOME LIGHT LES MAY
ALSO BE POSSIBLE WITH NE LOW LEVEL FLOW.
&&
.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)
ISSUED AT 631 PM EST WED DEC 19 2012
INITIAL MVFR CIGS HAVE MOVED INTO WESTERN UPPER MICHIGAN THIS AFTN
AHEAD OF THE MAIN SYSTEM WHICH WILL IMPACT THE AREA THURSDAY. WINDS
SHOULD STAY GENERALLY LIGHT TONIGHT AS THE MAIN SYSTEM STAYS WELL TO
OUR SOUTHWEST. SNOW WILL MOVE INTO THE AREA THU MORNING...LIKELY
STARTING AT IWD AND SAW AROUND 10Z AND CMX SEVERAL HOURS LATER. SNOW
SHOULD BECOME HEAVY AT SAW BY MID-LATE MORNING WITH VSBYS LIKELY
BELOW AIRPORT MINIMUMS DURING THE AFTN DUE TO SN/BLSN. IWD AND CMX
WILL BE FARTHER FROM THE SYSTEM...AND AS SUCH THESE SITES WILL NOT
SEE THE SNOW FALL AS HEAVY...BUT LIFR CONDITIONS STILL LIKELY THU.
NE WINDS WILL INCREASE DURING THE DAY AS THE LOW MOVES INTO SRN
LOWER MI AND GUST AT TIMES TO 25 KT. CONTINUED WINDY WITH HEAVY SNOW
ESPECAILLY AT SAW THROUGH FRIDAY MORNING.
&&
.MARINE...(FOR THE 4 PM LAKE SUPERIOR FORECAST ISSUANCE)
ISSUED AT 441 PM EST WED DEC 19 2012
WINDS LESS THAN 20 KTS CURRENTLY WILL QUICKLY GIVE WAY TO STRONGER
WINDS ON THURSDAY AS LOW PRESSURE MOVES TOWARD SOUTHERN LK MICHIGAN.
AS DEEPENING LOW PRESSURE MOVES INTO LOWER MI BY LATER THU...EXPECT
N TO NE GALES TO DEVELOP OVER ALL BUT FAR WESTERN LAKE SUP BY THU
EVENING. GALE WARNINGS CONTINUE FOR THESE AREAS FOR WINDS AS HI
40-45 KTS UNTIL THE STRONGER WINDS DIMINISH W-E FRI INTO FRI EVENING
AS THE LO SHIFTS FARTHER EAST. FOR THE WEEKEND...EXPECT GENERALLY
N-NW WINDS NO HIER THAN 25 KTS OR SO WITH A WEAKER PRES GRADIENT
DOMINATING.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
UPPER MICHIGAN...
WINTER WEATHER ADVISORY FROM 7 AM EST /6 AM CST/ THURSDAY TO 10
AM EST /9 AM CST/ FRIDAY FOR MIZ002-009-084.
WINTER STORM WARNING FROM 7 AM THURSDAY TO 1 PM EST FRIDAY FOR
MIZ005>007-014-085.
WINTER WEATHER ADVISORY FROM 10 AM THURSDAY TO 10 AM EST FRIDAY
FOR MIZ001-003.
WINTER WEATHER ADVISORY FROM 7 AM THURSDAY TO 1 PM EST FRIDAY
FOR MIZ004.
WINTER STORM WARNING FROM 6 AM THURSDAY TO MIDNIGHT CST THURSDAY
NIGHT FOR MIZ011.
WINTER WEATHER ADVISORY FROM 6 AM THURSDAY TO MIDNIGHT CST
THURSDAY NIGHT FOR MIZ010.
WINTER STORM WARNING FROM 7 AM THURSDAY TO 7 AM EST FRIDAY FOR
MIZ013.
WINTER STORM WARNING FROM 3 AM THURSDAY TO MIDNIGHT CST THURSDAY
NIGHT FOR MIZ012.
LAKE SUPERIOR...
GALE WARNING FROM 7 PM THURSDAY TO 10 PM EST FRIDAY FOR
LSZ249>251-266-267.
GALE WARNING FROM 7 PM THURSDAY TO 4 PM EST FRIDAY FOR LSZ244-
245-248-265.
GALE WARNING FROM 7 PM THURSDAY TO 1 PM EST FRIDAY FOR LSZ264.
GALE WARNING FROM 7 PM THURSDAY TO 11 AM EST FRIDAY FOR LSZ243-
263.
LAKE MICHIGAN...
GALE WARNING FROM 1 PM THURSDAY TO 7 PM EST FRIDAY FOR LMZ248-
250.
GALE WARNING FROM 1 PM THURSDAY TO 4 PM EST FRIDAY FOR LMZ221.
&&
$$
UPDATE...MRD
SHORT TERM...JLA
LONG TERM...JLB
AVIATION...MRD
MARINE...JLA
AREA FORECAST DISCUSSION
NWS MARQUETTE MI
834 PM EST WED DEC 19 2012
.UPDATE...
ISSUED AT 831 PM EST WED DEC 19 2012
NO MAJOR CHANGES TO THE GOING FORECAST THIS EVENING AS THE AFTERNOON
PACKAGE HAS THE SITUATION WELL IN HAND. LOW PRESSURE JUST NORTH OF
OKC IS STILL EXPECTED TO MOVE RAPIDLY NE TONIGHT TO A POSITION NEAR
CHICAGO BY NOON THURSDAY. WIDESPREAD SNOW IN THE DEFORMATION AXIS TO
THE N AND NW OF THE LOW WILL RAPIDLY MOVE NE AS WELL. THE LATEST
RUNS OF THE RUC AGREES WITH THE NAM AND SREF MEMBERS IN SHOWING THE
SNOW DEVELOPING AROUND 09Z AT MNM...THEN RAPIDLY SPREADING NORTHWARD
IN THE MORNING TO MQT BY 12Z AND CMX SOON AFTER. WITH THE
STRENGTHENING F-GEN MOVING OVER THE AREA ASSOCIATED WITH THE
DEVELOPING TROWAL /AND ASSOCIATED LOWER STABILITY/...EXPECT SNOW TO
FALL HEAVY AT TIMES ESPECIALLY ACROSS THE SOUTH AND EAST DURING THE
DAY. AS SUCH...HAVE OPTED TO INCLUDE SNOWFALL RATES OF 1-2 INCHES
PER HOUR IN THE WARNING AREAS TO HIGHLIGHT THIS SPECIFIC CONCERN.
OTHERWISE...THE ONLY OTHER CONCERN THAT WILL NEED TO MONITORED IS
THE POTENTIAL FOR HIGHER SNOW AMOUNTS IN GOGEBIC COUNTY DUE TO THE
SUSTAINED N-NE WIND. LATEST RUC RUNS INDICATE SNOW BECOMING HEAVIER
BY LATE MORNING AS THE BETTER MOISTURE WRAPS WESTWARD INTO FAR
WESTERN UPPER MI. IF THIS TREND CONTINUES WITH THE 00Z RUNS...THE
MID SHIFT MAY NEED TO OPT FOR A WARNING HERE AS WELL. STILL
EXPECTING THE WINDS TO INCREASE LATER THU INTO THU NIGHT. IN
FACT...AREAS NEAR LAKE SUPERIOR NEAR AND EAST OF MARQUETTE WILL
LIKELY SEE SIGNIFICANT BLOWING/DRIFTING THU NIGHT INTO FRI MORNING
AS THE SNOW TRANSITIONS TO A LESS DENSE LAKE EFFECT. NWP SUGGEST
45-50KT 925MB WINDS...AND THERE IS A CONCERN THAT BLIZZARD CRITERIA
COULD TECHNICALLY BE MET EARLY FRI MORNING. WILL NOT MAKE ANY
HEADLINE ADJUSTMENTS...BUT IT IS QUITE POSSIBLE THAT THE WORST
CONDITIONS OF THE ENTIRE EVENT FOR AREAS NEAR LAKE SUPERIOR WILL BE
THU NIGHT INTO FRIDAY MORNING.
UPDATED WINTER STATEMENT ALREADY OUT.
&&
.SHORT TERM...(THIS EVENING THROUGH THURSDAY)
ISSUED AT 441 PM EST WED DEC 19 2012
HEADLINES ARE OUT FOR ALL OF UPR MICHIGAN. SNOW BEGINS LATE TONIGHT
OVER SOUTH AND SPREADS ACROSS REST OF CWA ON THURSDAY. NOW WE WAIT.
WV LOOP/12Z RAOBS SHOW TWO PRIMARY UPPER LEVEL FEATURES. STRONG
SHORTWAVE TROUGH/PV ANAMOLY EMERGING ON TO THE SOUTHERN PLAINS
WHILE SHORTWAVE TROUGH IN THE NORTHERN STREAM IS DIGGING ACROSS
DAKOTAS. LEE SIDE CYCLOGENESIS WELL UNDERWAY NEAR TX/OK PANHANDLE.
SOUTHERN STREAM PV ANAOMOLY MAIN WX MAKER TO START. WAVE HEADS INTO
OK AND SOUTHERN MO TONIGHT WITH A 995MB SFC LOW NEARING SAINT LOUIS
MO BY 12Z ON THURSDAY. JET STREAK DIGGING INTO BASE OF TROUGH FM
WY TO KS AND INCREASING DIVERGENCE ALOFT RESULTS IN DEEPENING SFC
LOW BLO 990MB AS IT REACHES CHICAGO/SOUTHERN TIP OF LK MICHIGAN
18Z-24Z. FURTHER DEEPENING OF MID-LEVEL LOW THEN EXPECTED ON
THURSDAY NIGHT AS THE NORTHERN STREAM WAVE BEGIN TO INTERACT WITH
THE SOUTHERN STREAM ONE. THIS SHOULD ALLOW LAKE ENHANCED SNOW TO
LINGER LONGER ALONG LK SUPERIOR INTO FRIDAY.
BACK TO TONIGHT...LGT SNOW BEGINS TO SPREAD INTO FAR SOUTH CWA AFT
09Z TONIGHT THEN REACHES LK MICHIGAN TO IMT LINE AROUND 12Z THU.
INTIALLY SNOW WILL BE DRIVEN BY DIVERGENCE ALOFT FM JET STREAK
LIFTING INTO ONTARIO. LATER THU MORNING THROUGH THU AFTN...SOUTHERLY
WINDS AHEAD OF SFC-H85 LOW INCREAS GULF MOISTURE INTO AREA WITH
PERSISTENT ISENTROPIC ASCENT NOTED ON 290-305K SFCS /H9-H6/.
FRONTOGENESIS RAMPS UP WITH STEADY SURGE OF H8-H7 FRONTOGENESIS
SWEEPING ACROSS SCNTRL AND EASTERN CWA. STRONGEST/PERSISTENT FN/FS
VECTOR CONVERGENCE FAVORS CORRIDOR FROM MNM-ISQ-ERY TO SEE HEAVY
SNOW THROUGH MUCH OF AFTN. PIVOT POINT FOR SNOW SEEMS TO FAVOR LUCE
COUNTY FOR MOST PROLONGED PERIOD OF HEAVIER SNOW. RATES UP TO 2
INCHES/HOUR POSSIBLE AS ADDITIONAL FORCING IS PROVIDED BY 925-850MB
THETA-E ADVECTION. MEANWHILE OVER CNTRL AND WEST CWA MODERATE SNOW
SHOULD STEADILY LIFT NORTH ON THURSDAY MORNING AND SHOULD BE OVER
ALL AREAS BY MIDDAY. WILD CARD IN CNTRL CWA IS AREA OF H7-H5
FRONTOGENESIS THAT KEEPS SHOWING UP FROM MQT-IMT. SEEMS THAT
NAM/GFS/ECMWF/GEM-REGIONAL ALL PICK UP ON THIS ENHANCING FEATURE.
RESULT IS INCREASE IN MODELED QPF FM GFS/GEM-REGIONAL/ECMWF WHICH
NOW LOOKS A BIT CLOSER TO WETTER NAM IDEA. ALREADY ADDED DICKINSON
TO ONGOING WARNINGS ON EARLIER UPDATE. HIGHER TERRAIN OF MARQUETTE
AND BARAGA COUNTIES ALSO WILL BEGIN TO SEE POTENTIAL FOR INCREASED
SNOW AMOUNTS COMPARED TO LOWER ELEVATIONS BY LATE THURSDAY AFTN DUE
TO INCREASING NORTHEAST WINDS/UPSLOPE LIFTING.
ACROSS WESTERN TIER...SYNOPTIC SNOW WILL NOT FALL AS HEAVY AS IN THE
CNTRL AND EASTERN CWA. ULTIMATELY...TOTAL SNOW AMOUNTS WILL BE
BOOSTED OVER HIGHER TERRAIN OF WEST DUE TO LK ENHANCED/LK EFFECT
SNOW LATER THURSDAY NIGHT INTO FRIDAY. MORE ON THAT IN THE LONG TERM
DISCUSSION.
OVERALL...OTHER THAN ADDITION OF DICKINSON TO ORIGINAL WARNING AND
INCLUDING WESTERN CWA IN ADVY...THEME OF GOING FORECAST ISSUED ON
MID SHIFT IS STILL ON TRACK. EXPECT 12-15HR SYNOPTIC SNOW TOTALS
ENDING AROUND 7 PM EST THURSDAY OF 3-6 INCHES OVER WESTERN THIRD OF
CWA /IRONWOOD AND HOUGHTON/ WITH 6 TO 10 INCHES OVR REST OF CWA.
WIDESPREAD SYNOPTIC PORTION OF THE STORM CONTINUES ON THURSDAY NIGHT
OVER EASTERN CWA...BUT WILL WANE OVER THE SOUTH. BLOWING SNOW
BECOMES MORE SIGNIFICANT JUST BEYOND THE SCOPE OF THE SHORT TERM.
MODELS COMING INTO EVEN BETTER AGREEMENT TODAY JUST ADDS FURTHER
CONFIDENCE TO THE FORECAST. SO NOW WE WAIT.
.LONG TERM...(THURSDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 441 PM EST WED DEC 19 2012
THURSDAY NIGHT...MODELS WERE IN GOOD OVERALL AGREEMENT...TAKING
THE MID LEVEL LOW FROM NRN INDIANA TO THE SRN END OF LAKE HURON BY
12Z/FRI. AT 00Z/FRI...THE NAM INDICATED A BAND OF STRONG 700-500 MB
FGEN AND TROWAL FEATURE OVER CNTRL UPPER MI WHICH IS EXPECTED TO
SHIFT INTO THE ERN CWA DURING THE EVENING WHICH MAY HELP TO ENHANCE
SNOWFALL RATES BTWN 00Z-06Z OVER THE EAST HALF. AS THE STRONGER
FGEN...AND 700-300 MB QVECTOR CONV OVER NRN LAKE HURON INTO NRN LOWER
MI SHIFT STEADILY TO THE NE...THE SYNOPTIC SCALE LIFT AND PCPN WILL
ALSO WEAKEN. ADDITIONAL OVERALL SYNOPTIC SNOWFALL AMOUNTS OF 1 TO 3
INCHES ARE LIKELY..MAINLY DURING THE EVENING. SO...THE ADVISORIES AND
WARNINGS OVER THE SRN TIER OF COUNTIES WILL END AT 06Z.
850 MB TEMPS TO AROUND -10C OVER LAKE SUPERIOR COMBINED WITH 950-925
WINDS INTO THE 40-50 KT RANGE WILL LEAD TO SIGNIFICANT LAKE
ENHANCEMENT AND OROGRAPHIC BOOST TO SNOWFALL AMOUNTS. THE GREATEST
AMOUNTS WOULD BE EXPECTED IN THE HIGHER TERRAIN WEST OF MARQUETTE
WHERE ADDITIONAL SNOWFALL AMOUNTS OF 8 INCHES ARE EXPECTED WITH EVEN
LOCALLY HIGHER AMOUNTS POSSIBLE. LOCALLY GREATER SNOWFALL AMOUNTS ARE ALSO
EXPECTED ESPECIALLY NEAR IRONWOOD/WAKEFIELD THAT MAY EVENTUALLY PUSH
SNOW TOTALS INTO THE WARNING CATEGORY. HOWEVER...CONFIDENCE IN HEAVY
SNOWFALL AMOUNTS OVER THE WEST IS LOWER.
FRIDAY...MID LEVEL RIDGING AND ASSOCIATED QVECTOR
DIVERGENCE/SUBSIDENCE WITH LOWERING INVERSION HEIGHTS/STRONG 850-700
MB DRYING WILL SPREAD FROM WEST TO EAST BRINGING AN END TO ANY
SIGNIFICANT SNOWFALL RATES OVER THE WEST DURING THE MORNING AND
CNTRL/EAST BY EARLY AFTERNOON. SO...GOING WARNING/ADVY ENDING TIMES
LOOK ON TRACK. ADDITIONAL AMOUNTS OF A FEW INCHES WILL STILL BE
POSSIBLE...MAINLY NORTH CENTRAL AND EAST.
FRIDAY NIGHT INTO SATURDAY...WITH 850 MB TEMPS AROUND -8C AND LINGERING
MOISTURE OVER THE ERN PORTION LAKE SUPERIOR SOME LINGERING SCT -SHSN
MAY BE POSSIBLE OVER THE EAST WHICH SHOULD END EARLY SATURDAY
MORNING. OTHERWISE...LOOK FOR DECREASING CLOUDS WITH TEMPS CLOSER TO
SEASONAL AVERAGES...LOWS IN THE TEENS AND LOWER 20S AND HIGHS IN THE
MID TO UPPER 20S.
SUN-WED...SOME LIGHT LES MAY BE POSSIBLE SUNDAY AS ARCTIC HIGH PRES
OVER CNTRL CANADA PUSHES A COLD FRONT THROUGH THE AREA.
HOWEVER...WITH GENERALLY LIGHT ACYC NRLY WINDS...KEPT MODEL
CONSENSUS SLIGHT CHANCE POPS. THE GFS AND ECMWF SUGGEST THAT A WEAK
SHORTWAVE TROUGH MOVING FROM THE NRN PLAINS INTO THE WRN GREAT LAKES
COULD ALSO BRING SOME LIGHT SNOW TO THE REGION. SOME LIGHT LES MAY
ALSO BE POSSIBLE WITH NE LOW LEVEL FLOW.
&&
.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)
ISSUED AT 631 PM EST WED DEC 19 2012
INITIAL MVFR CIGS HAVE MOVED INTO WESTERN UPPER MICHIGAN THIS AFTN
AHEAD OF THE MAIN SYSTEM WHICH WILL IMPACT THE AREA THURSDAY. WINDS
SHOULD STAY GENERALLY LIGHT TONIGHT AS THE MAIN SYSTEM STAYS WELL TO
OUR SOUTHWEST. SNOW WILL MOVE INTO THE AREA THU MORNING...LIKELY
STARTING AT IWD AND SAW AROUND 10Z AND CMX SEVERAL HOURS LATER. SNOW
SHOULD BECOME HEAVY AT SAW BY MID-LATE MORNING WITH VSBYS LIKELY
BELOW AIRPORT MINIMUMS DURING THE AFTN DUE TO SN/BLSN. IWD AND CMX
WILL BE FARTHER FROM THE SYSTEM...AND AS SUCH THESE SITES WILL NOT
SEE THE SNOW FALL AS HEAVY...BUT LIFR CONDITIONS STILL LIKELY THU.
NE WINDS WILL INCREASE DURING THE DAY AS THE LOW MOVES INTO SRN
LOWER MI AND GUST AT TIMES TO 25 KT. CONTINUED WINDY WITH HEAVY SNOW
ESPECAILLY AT SAW THROUGH FRIDAY MORNING.
&&
.MARINE...(FOR THE 4 PM LAKE SUPERIOR FORECAST ISSUANCE)
ISSUED AT 441 PM EST WED DEC 19 2012
WINDS LESS THAN 20 KTS CURRENTLY WILL QUICKLY GIVE WAY TO STRONGER
WINDS ON THURSDAY AS LOW PRESSURE MOVES TOWARD SOUTHERN LK MICHIGAN.
AS DEEPENING LOW PRESSURE MOVES INTO LOWER MI BY LATER THU...EXPECT
N TO NE GALES TO DEVELOP OVER ALL BUT FAR WESTERN LAKE SUP BY THU
EVENING. GALE WARNINGS CONTINUE FOR THESE AREAS FOR WINDS AS HI
40-45 KTS UNTIL THE STRONGER WINDS DIMINISH W-E FRI INTO FRI EVENING
AS THE LO SHIFTS FARTHER EAST. FOR THE WEEKEND...EXPECT GENERALLY
N-NW WINDS NO HIER THAN 25 KTS OR SO WITH A WEAKER PRES GRADIENT
DOMINATING.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
UPPER MICHIGAN...
WINTER WEATHER ADVISORY FROM 7 AM EST /6 AM CST/ THURSDAY TO 10
AM EST /9 AM CST/ FRIDAY FOR MIZ002-009-084.
WINTER STORM WARNING FROM 7 AM THURSDAY TO 1 PM EST FRIDAY FOR
MIZ005>007-014-085.
WINTER WEATHER ADVISORY FROM 10 AM THURSDAY TO 10 AM EST FRIDAY
FOR MIZ001-003.
WINTER WEATHER ADVISORY FROM 7 AM THURSDAY TO 1 PM EST FRIDAY
FOR MIZ004.
WINTER STORM WARNING FROM 6 AM THURSDAY TO MIDNIGHT CST THURSDAY
NIGHT FOR MIZ011.
WINTER WEATHER ADVISORY FROM 6 AM THURSDAY TO MIDNIGHT CST
THURSDAY NIGHT FOR MIZ010.
WINTER STORM WARNING FROM 7 AM THURSDAY TO 7 AM EST FRIDAY FOR
MIZ013.
WINTER STORM WARNING FROM 3 AM THURSDAY TO MIDNIGHT CST THURSDAY
NIGHT FOR MIZ012.
LAKE SUPERIOR...
GALE WARNING FROM 7 PM THURSDAY TO 10 PM EST FRIDAY FOR
LSZ249>251-266-267.
GALE WARNING FROM 7 PM THURSDAY TO 4 PM EST FRIDAY FOR LSZ244-
245-248-265.
GALE WARNING FROM 7 PM THURSDAY TO 1 PM EST FRIDAY FOR LSZ264.
GALE WARNING FROM 7 PM THURSDAY TO 11 AM EST FRIDAY FOR LSZ243-
263.
LAKE MICHIGAN...
GALE WARNING FROM 1 PM THURSDAY TO 7 PM EST FRIDAY FOR LMZ248-
250.
GALE WARNING FROM 1 PM THURSDAY TO 4 PM EST FRIDAY FOR LMZ221.
&&
$$
UPDATE...MRD
SHORT TERM...JLA
LONG TERM...JLB
AVIATION...MRD
MARINE...JLA
AREA FORECAST DISCUSSION
NWS GAYLORD MI
700 PM EST WED DEC 19 2012
.SYNOPSIS...
ISSUED AT 406 PM EST WED DEC 19 2012
QUIET WEATHER WILL CONTINUE THROUGH THIS EVENING...AS HIGH PRESSURE
DRIFTS OVERHEAD...PROVIDING MOSTLY CLOUDY SKIES AND MILD
TEMPERATURES.
THE WEATHER WILL DRAMATICALLY CHANGE ACROSS THE GREAT LAKES EARLY
THURSDAY MORNING AND FRIDAY...AS A STRONG WINTER STORM ORGANIZING
OVER THE CENTRAL PLAINS...LIFTS INTO THE GREAT LAKES REGION.
SIGNIFICANT SNOWFALL AND GUSTY WINDS ARE EXPECTED ACROSS NORTHERN
MICHIGAN INTO SATURDAY. CONDITIONS WILL GRADUALLY IMPROVE THROUGH
THE WEEKEND...AS HIGH PRESSURE AGAIN MAKES ITS APPROACH.
&&
.UPDATE...
ISSUED AT 700 PM EST WED DEC 19 2012
RESIDUAL LOW CLOUDS APPEAR TO BE INCREASING ACROSS NW LWR MICHIGAN THIS
EVENING...LIKELY EXPANDING UNDER THE WELL-ESTABLISHED INVERSION AS
THE BOUNDARY LAYER COOLS WITH SUNSET. STILL SUSPECT THIS INCREASE
IN LOW CLOUDS WILL BE SHORT-LIVED AS DRIER EASTERLY FLOW BECOMES
ESTABLISHED LATER THIS EVENING IN ADVANCE OF THE DEVELOPING STORM
SYSTEM NOW CENTERED OVER THE CENTRAL PLAINS. HOWEVER...MID/HIGH
CLOUDS WILL QUICKLY REPLACE ANY BREAK IN THE LOW CLOUDS BY LATE
EVENING...SO OVERALL SKY CONDITIONS TONIGHT WILL BE MAINLY CLOUDY.
LATEST RUC13 IS STILL SHOWING THE ARRIVAL OF WIDESPREAD SNOW
RANGING FROM AROUND 09Z IN OUR FAR SW CWA TO AROUND 12Z FOR ERN
UPR AND FAR NRN/NE LWR MICHIGAN...WITH SNOW BECOMING HEAVY AT
TIMES AFTER SUNRISE. THIS IS A BIT LATER THAN THE CURRENT FORECAST
SUGGESTS. START TIME HINGES...AT LEAST IN PART...ON IF AND TO WHAT
EXTEND LOW LEVEL MOISTURE/CLOUDS CAN BE SCOURED OUT THIS EVENING
BY DRIER EAST FLOW. IF LOW LEVEL MOISTURE REMAINS IN PLACE...START
TIME OF SNOW MAY VERY WELL BE EARLIER AS DEPICTED IN THE GOING
FORECAST. WILL KEEP A CLOSE EYE ON THIS THRU THE EVENING AND
ADJUST CLOUDS/WX/POP AS NECESSARY.
&&
.SHORT TERM...(TONIGHT)
ISSUED AT 406 PM EST WED DEC 19 2012
CURRENT OVERVIEW: WEAK HIGH PRESSURE IN CONTROL OF THE REGION/S
WEATHER TODAY WHICH...DUE TO IT/S WEAK NATURE...HAS ALLOWED STRATUS
AND STRATOCUMULUS TO PERSIST THROUGHOUT NORTHERN MICHIGAN FOR MUCH
OF TODAY. SURFACE MAP SHOWS LOW PRESSURE GRADUALLY CONGEALING OVER
THE PANHANDLES OF TX/OK WITH IMPRESSIVE BAROCLINIC LEAF SIGNATURE IN
WV/IR IMAGERY.
FORECAST CONCERNS CENTER AROUND CLOUD TRENDS...AND THEN TIMING THE
ARRIVAL OF SNOW LATER TONIGHT. ST/STCU WILL LIKELY NOT BE IN ANY
HURRY TO GO ANYWHERE THIS EVENING GIVEN SOME WEAK LAKE SUPPORT...AND
NO INTRODUCTION OF MEANINGFULLY-DRIER AIR. WHILE SOME BREAKS ARE
LIKELY...TIMING/LOCATING THEM WOULD BE FRUITLESS...AND...WITH HIGH
CLOUDS INCREASING BY MID/LATE EVENING AHEAD OF OUR APPROACHING
WINTER STORM...WILL GO WITH MOSTLY CLOUDY WORDING THROUGH THE
EVENING...TRANSITIONING TO CLOUDY OVERNIGHT.
AS FOR PRECIPITATION ONSET...GUIDANCE IS IN GOOD AGREEMENT THAT
INITIAL WARM ADVECTION SURGE WILL HOLD OFF UNTIL AFTER
MIDNIGHT...BUT STILL WITH A RANGE OF ABOUT 6 HOURS. IN THESE
SCENARIOS...WITH A DEEP SOUTHEAST FLOW AT PRECIP ONSET...TEND TO
SIDE WITH THE SLOWER EDGE OF THE GUIDANCE ENVELOPE. OF COURSE...THE
ANTECEDENT AIRMASS IS NOT ALL THAT DRY...HOWEVER...SO WHILE I/LL
LEAN SLOWER...I STILL THINK MOST SPOTS FROM CVX-GLR-OSC SOUTH AND
WEST WILL SEE FLAKES IN THE AIR BY DAYBREAK. WE/LL HAVE TO WATCH
ALONG THE IMMEDIATE LAKE HURON COAST...WHERE A LLEVEL WARM LAYER MAY
BE DEEP ENOUGH TO ALLOW PRECIPITATION TO START AS A MIX /OR ALL
RAIN/. NO ICING EXPECTED. AS FOR SNOW TOTALS...EXPECT 1-2" BY
DAYBREAK OVER THE FAR SOUTHWEST /NEAR MBL/ WITH NO MORE THAN A
COATING FROM CVX TO GLR.
NOTE! FOR MOST LOCATIONS SAVE THE FAR SOUTHWEST...TRAVEL CONDITIONS
MAY NOT BE ALL THAT BAD AT DAYBREAK THURSDAY. PLEASE CONSIDER...
HOWEVER...THAT QUICKLY DETERIORATING CONDITIONS ARE EXPECTED
THURSDAY /SEE BELOW/.
.LONG TERM...(THURSDAY THROUGH WEDNESDAY)
ISSUED AT 406 PM EST WED DEC 19 2012
...HIGH IMPACT WINTER STORM THURSDAY THROUGH FRIDAY...
WATER VAPOR IMAGERY...OVERLAID WITH 12Z RAOB ANALYSIS...LENDS MUCH
CONFIDENCE TO NOW MULTI-DAY MODEL TRENDS OF A HIGH IMPACT WINTER
WEATHER EVENT ACROSS MUCH OF THE NORTH WOODS THURSDAY AND FRIDAY.
SHORTWAVE NO DOUBT LOOKS IMPRESSIVE AS IT BEGINS ITS EJECTION OUT OF
THE SOUTHWEST CONUS...WITH EXCELLENT PACIFIC "PINEAPPLE" CONNECTION
AND BURGEONING WESTERN GULF OF MEXICO MOISTURE ADVECTION OUT FRONT
OF IT (AS EVIDENCE BY DEWPOINTS SURGING INTO THE 60S OVER NORTHEAST
TEXAS ON GUSTY SOUTH WINDS). ATTENDANT UPPER JET CORE MEANS BUSINESS
...WITH CONUS RAOB H25/H30 NETWORK SHOWING CORRIDOR OF 120+ KNOT
WINDS EXTENDING FROM THE MID ATLANTIC ALL THE WAY BACK INTO THE
DESERT SOUTHWEST...WITH EMBEDDED 145+ KNOT JET MAX ARCHING INTO THE
SOUTHWEST LAKES. THIS JET WILL HELP EJECTING WAVE QUICKLY TAKE ON A
NEGATIVE TILT AS IT REACHES THE MID MISSISSIPPI VALLEY REGION EARLY
THURSDAY ...ON ITS WAY TO CLOSING OFF AS IT CROSSES THE SOUTHERN
LAKES OVERNIGHT THURSDAY. SURFACE REFLECTION WILL INITIALLY LEAD ITS
MID LEVEL PARENT...STEADILY DEEPENING (REACHING SUB 990MBS LEVELS)
AS IT PIVOTS NORTHEAST TO VICINITY SOUTHERN LAKE MICHIGAN BY
THURSDAY EVENING. SYSTEM OCCLUDES THERE ON AFTER...WITH SURFACE LOW
TUCKING UNDER ITS MID LEVEL LIKENESS. THIS TRACK UP THROUGH SOUTHERN
LAKE MICHIGAN AND ACROSS SOUTHERN MICHIGAN/THE THUMB PLACES MUCH OF
OUR AREA IN THE CROSS-HAIRS OF A SIGNIFICANT WINTER WEATHER
EVENT...WITH HEAVY SNOW AND VERY GUSTY WINDS LEADING TO THE
DEVELOPMENT OF EXTREMELY HAZARDOUS CONDITIONS EARLY
THURSDAY...CONTINUING RIGHT THROUGH FRIDAY. SOUNDS PRETTY
CLEAR-CUT...BUT SAID TRACK (DRY SLOT ISSUES?)...ABOVE NORMAL LAKE
HURON WATER TEMPERATURES...AND ANTECEDENT RATHER "MILD" AIRMASS
STILL MAKES EXACT PRECIP TYPE AND TIMING OF CHANGEOVERS A FORMIDABLE
CHALLENGE...ESPECIALLY FOR THE SOUTHEAST THIRD OF OUR AREA.
INHERITED FORECASTERS HAVE LAID A SOLID FOUNDATION ON ALL THE
ABOVE...WITH FORECASTS/WARNINGS AND STATEMENTS/WEB BRIEFINGS ALL
HIGHLIGHTING THIS HIGH IMPACT EVENT. THUS...MOST CHALLENGING PART OF
THE FORECAST REMAINS TRYING TO FIGURE EXACT DEMARCATION OF RAIN/SNOW
LINE AND WHAT TO DO WITH INHERITED WINTER STORM WATCH THAT STRADDLES
THIS DIVISION.
HIGH CONFIDENCE PORTION OF THE FORECAST: AS MENTIONED BY OVERNIGHT
FORECAST...STORM STRUCTURE SHOULD BE A "CLASSIC" ONE...AS IS QUITE
OFTEN SEEN WITH THESE PANHANDLE-HOOK SYSTEMS. LEAD ISENTROPIC/FGEN
DRIVEN PRECIP SHIELD EARLY THURSDAY WILL GIVE WAY TO INTENSE DEEP
LAYER -DIVQ/UPPER LEVEL DIVERGENCE AXIS AND INCREASINGLY WELL
ESTABLISHED TROWAL AS CYCLONIC PORTION OF WARM CONVEYOR BELT WRAPS
BACK ACROSS NORTHERN MICHIGAN LATER THURSDAY INTO EARLY FRIDAY. FGEN
SIGNATURE FOCUSES ALONG THE NORTHWEST QUADRANT OF SYSTEM LATER
THURSDAY...WITH WARM SIDE RESPONSE TARGETING NORTHWEST LOWER AND
EASTERN UPPER MICHIGAN. GOOD -EPV SIGNATURE...SUGGESTING CONVECTIVE
SNOW BURSTS (THUNDERSNOW?) AND POSSIBILITY FOR ENHANCED VERY HEAVY
SNOW BANDS EMBEDDED WITHING BROADER SNOW SHIELD. MOISTURE FOR ALL
THE ABOVE REMAINS ABUNDANT...WITH PWAT VALUES NEARING AN INCH OVER
THE FAR SOUTHERN LAKES...AND EXCEEDING 0.5 INCHES OVER NORTHERN
MICHIGAN...WHICH IS REACHING NEAR 2 STANDARD DEVIATIONS ABOVE NORMAL
FOR DECEMBER. HPC/MODEL PRECIP GRAPHICS AGREE...TARGETING NORTHERN
MICHIGAN WITH STORM TOTAL LIQUID EQUIVALENTS IN EXCESS OF AN INCH
BY THE END OF FRIDAY.
LINGERING UNCERTAINTIES AND WHAT CAN GO WRONG SCENARIO: WHILE ABOVE
NEARLY SET IN STONE...EXACT PRECIP TYPES...SNOW-LIQUID RATIOS...AND
POSSIBLE DRY-SLOT ISSUES REMAIN A FORMIDABLE CHALLENGE. AS FEARED...
LATEST 12Z NAM-WRF AND GFS FITS PATTERN RECOGNITION OF SUCH A
WRAPPED-UP SYSTEM TRENDING A TOUCH NORTHWEST THAN EARLIER PROGGED.
COMBINE THIS WITH INITIAL STRONG EAST FLOW COMING OFF THE ABOVE
NORMAL LAKE HURON WATERS AND ANTECEDENT RATHER MILD MID DECEMBER
TEMPERATURES...AND RAIN SEEMS LIKE A GIVEN FOR AT LEAST SOME OF OUR
SOUTHEAST COUNTIES. USING LATEST NAM-WRF AND GFS 0-6KM MAX TEMP
PROGS AND FORECAST RAOBS NOW SUGGEST THIS DEMARCATION SPREADING AS
FAR WEST AS A HARRISVILLE TO HOUGHTON LAKE LINE DURING THE
AFTERNOON...WITH EVEN SOME MIX POSSIBLE A TOUCH FURTHER NORTHWEST.
MOST OTHER GUIDANCE NOT QUITE AS AGGRESSIVE SPREADING RAIN AS FAR
INLAND... ALTHOUGH ALL ARE ON BOARD WITH PREDOMINATELY LIQUID ACROSS
BOTH IOSCO AND ARENAC COUNTIES...AS WELL AS THE IMMEDIATE COASTLINE
AREAS OF ALCONA COUNTY...UNTIL LATER THURSDAY NIGHT. HARD NOT TO GO
WITH THE MAJORITY...BUT ALSO HARD TO COMPLETELY IGNORE PAST HISTORY
AND PATTERN RECOGNITION. UNFORTUNATELY...FORECAST WILL BY NO MEANS
MIMIC REALITY AS THESE EXACT DETAILS WILL NOT BE REALIZED TO THE
EVENT ACTUALLY UNFOLDS. WILL TAKE A "BEST GUESS"...KEEPING
PREDOMINATELY RAIN WHERE THE MAJORITY AGREE...BUT SPREADING MIX
RAIN/SNOW WORDING A TOUCH FURTHER INLAND...STRETCHING FROM ABOUT
ROGER CITY DOWN TO MANISTEE (NOT TOO WORRIED ABOUT SLEET WITH LITTLE
SUPPORT FOR SURFACE BASED COLD LAYER BELOW ELEVATED WARM NOSE). OF
COURSE...SNOW-TO-LIQUID RATIOS CONTINGENT ON THE ABOVE...AS WELL AS
THE FACT DGZ REMAINS FAIRLY ELEVATED DURING THE EVENT EVEN WHERE ALL
SNOW IS EXPECTED. REALLY LIKE PREVIOUS FORECAST IDEA OF TRENDING
MODEL DEPICTED SNOW/LIQUID RATIOS DOWN...AND WILL MAKE ONLY SUBTLE
CHANGES TO THOSE INHERITED. LASTLY...DRY SLOT ISSUES. IT WILL BE A
CLOSE CALL FOR AREAS DOWN NEAR SAGINAW BAY...ESPECIALLY IF LAST
SECOND NORTHWEST TREND IS REALIZED. WILL NOT GO THIS ROUTE JUST
YET...BUT DEFINITELY COULD SEE PRECIP WOUND DOWN FOR A PERIOD OF
TIME THURSDAY EVENING ACROSS THE FAR SOUTHEAST.
SNOWFALL AMOUNTS: DESPITE SOMEWHAT LOW SNOW-TO-LIQUID RATIOS...
ESPECIALLY ACROSS NORTHERN LOWER...SIMPLE MAGNITUDE OF DYNAMICS AND
AVAILABLE MOISTURE SUPPORTS SNOWFALL AMOUNTS POSSIBLY APPROACHING A
FOOT FOR AREAS ALONG AND NORTHWEST OF A LINE EXTENDING FROM ROGERS
CITY TO CADILLAC...WITH SOME LOCALLY HIGHER AMOUNTS IN FAVORED NNW
FLOW AREAS AS LAKE ENHANCEMENT AUGMENTS TROWAL DRIVEN SNOWS LATER
THURSDAY NIGHT INTO FRIDAY. IN ADDITION...POTENTIAL FOR HIGH
INTENSITY (ONE TO TWO INCH PER HOUR?) ELEVATED CONVECTIVE DRIVEN
SNOW BANDS COULD LEAD TO LOCALLY HIGHER AMOUNTS. SNOWFALL TOTALS
SHOULD FALL OF RAPIDLY FURTHER SOUTHEAST...WITH PERHAPS JUST A FEW
INCHES NEAR SAGINAW BAY GIVEN LATER CHANGEOVER AND DECAYING TROWAL
DYNAMICS BY THE TIME CHANGEOVER OCCURS. LITTLE DOUBT EXACT GRADIENT
SHOWN IN FORECAST WILL CHANGE AS EVENT UNFOLDS.
HEADLINES...INHERITED WINTER STORM WARNING IS A NO-BRAINER...WITH
SAID HEAVY SNOW AMOUNTS AND INCREASINGLY GUSTY WINDS...ESPECIALLY BY
LATE THURSDAY NIGHT AND FRIDAY. WIND GUSTS COULD EASILY EXCEED
30MPH...WITH EVEN HIGHER GUSTS ALONG THE IMMEDIATE LAKE MICHIGAN
SHORELINE. PROGS CONCUR...WITH STRONG NNW FLOW LOW LEVEL JET CENTER
OVER LAKE MICHIGAN BY EARLY FRIDAY. NEAR WHITEOUT CONDITIONS IN
BLOWING AND DRIFTING SNOW IS DEFINITELY PLAUSIBLE...ESPECIALLY IN
UNSHELTERED AREAS. HAVE TOSSED AROUND THE BLIZZARD IDEA...BUT PAST
HISTORY SHOWS GETTING TRUE BLIZZARD CONDITIONS IS AWFULLY TOUGH.
WILL LET WINTER STORM WARNING SPEAK FOR ITSELF...WITH NEAR BLIZZARD
CONDITIONS MENTIONED WITHIN THE TEXT. AS FOR THE REMAINING
WATCH...TOUCH CALL BASED ON RAIN/SNOW ISSUE...BUT WILL UPGRADE
NORTHWEST TIER OF WATCH COUNTIES TO A WARNING...STRESSING HIGHEST
SNOW TOTALS OVER THE NORTHWEST CORNER OF EACH. REST OF THE WATCH
WILL FALL UNDER AN ADVISORY...HIGHLIGHTING INITIAL AND END EVENT
SNOW BURST. AS FOR A LIST OF EXPECTED IMPACTS FROM THIS
SYSTEM...PLEASE REFER TO OUR WARNING AND ADVISORY PRODUCTS.
MSB
SATURDAY AND SUNDAY...INGREDIENTS ARE CONTINUING TO LOOK DISMAL
FOR LAKE EFFECT SNOW BEHIND THE DEPARTING STORM SYSTEM. LOW
MOISTURE...850MB TEMPERATURES ONLY AROUND -5C...WHICH PUT DELTA T/S
ONLY AT 11C. THE BEST CHANCE APPEARS TO BE EARLY SUNDAY
MORNING...WHEN 850MB TEMPERATURES BEGIN TO DROP AHEAD OF A WEAK
SHORTWAVE WITH SYNOPTIC-SCALE QG FORCING...HIGHER MOISTURE
AMOUNTS...DELTA T/S OF AROUND 14C. WINDS WILL BE NORTHERLY DURING
THIS OPTIMAL TIMEFRAME...WHICH WOULD IMPACT MAINLY WHITEFISH POINT
TO WESTERN MACKINAC COUNTY AND THEN LEELANAU...BENZIE AND MANISTEE
COUNTIES IN NORTHERN LOWER. STILL DON/T EXPECT MUCH ACCUMULATIONS
FROM ANY LAKE EFFECT SNOW THAT DEVELOPS SATURDAY THROUGH LATE SUNDAY
NIGHT.
CHRISTMAS EVE...ECMWF AND GFS HAVE COME TO AGREEMENT ON A SHORTWAVE
MOVING THROUGH THE GREAT LAKES REGION MONDAY AFTERNOON AND INTO THE
EVENING HOURS...POSSIBLY GENERATING SOME MINOR SNOW ACCUMULATIONS
ACROSS NORTHERN MICHIGAN. THERE COULD ALSO BE SOME LOCALIZED LAKE
ENHANCED SNOW WITH 850MB TEMPS NEAR -14C...BRINGING DELTA T/S TO
NEAR 20C.
TUESDAY AND WEDNESDAY...TEMPERATURES MAY REACH SINGLE DIGITS OVER
INTERIOR PORTIONS OF NORTHERN LOWER MICHIGAN TUESDAY AND WEDNESDAY
MORNING...AS COLD ARCTIC AIR FILTERS IN FROM BETWEEN A SURFACE HIGH
PRESSURE RIDGING INTO THE GREAT LAKES REGION FROM WESTERN CANADA AND
A FORECAST DEVELOPING STORM SYSTEM OVER THE SOUTHERN PLAINS. I HAVE
USED THE COLDER ECMWF FOR TEMPERATURES TUESDAY AND WEDNESDAY.
INCREASED CLOUDINESS TUESDAY AHEAD OF THE AFOREMENTIONED POTENTIALLY
STRONG STORM SYSTEM THAT MAY IMPACT THE GREAT LAKES REGION WEDNESDAY
AND INTO THURSDAY.
TJL
&&
.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)
ISSUED AT 700 PM EST WED DEC 19 2012
RESIDUAL MVFR CLOUDS WILL GRADUALLY DISSIPATE BY LATE EVENING AS DRIER
LOW LEVEL EASTERLY FLOW BEGINS ACROSS MICHIGAN WELL IN ADVANCE OF
THE DEVELOPING STORM SYSTEM CURRENTLY CENTERED OVER THE CENTRAL
PLAINS. THESE LOW CLOUDS WILL QUICKLY BE REPLACED WITH INCREASING
MID/HIGH CLOUDS AND EVENTUALLY INCREASING LOW CLOUDS OVERNIGHT.
CONDITIONS WILL QUICKLY DETERIORATE TO IFR BEFORE DAYBREAK AS
WIDESPREAD SNOW SPREADS SW TO NE ACROSS NRN LWR MICHIGAN...
BECOMING HEAVY DURING THE MORNING AND CONTINUING THRU THURSDAY
EVENING. LIGHT WINDS THIS EVENING WILL BECOME EASTERLY OVERNIGHT AND
QUICKLY STRENGTHEN ON THURSDAY...WITH GUSTS TO 30 KTS EXPECTED.
&&
.MARINE...
ISSUED AT 406 PM EST WED DEC 19 2012
THE CALM BEFORE THE STORM. LIGHT WINDS ARE EXPECTED THROUGH
MUCH OF TONIGHT WITH HIGH PRESSURE IN CONTROL. HOWEVER...APPROACHING
STRONG LOW PRESSURE WILL BRING A RAPID INCREASE IN SPEEDS BY SUNRISE
THURSDAY...WITH VERY STRONG WINDS LIKELY THROUGH THE DAY ON FRIDAY
AS THE LOW PASSES. GALE FORCE SPEEDS ARE EXPECTED ACROSS MOST OF THE
WATERS...WITH THE POSSIBILITY OF A FEW STORM FORCE GUSTS ON THE LAKE
MICHIGAN NEARSHORE WATERS LATER THURSDAY NIGHT INTO FRIDAY. MORE
TRANQUIL CONDITIONS ARE EXPECTED LATER INTO THE WEEKEND AS WEAK HIGH
PRESSURE GRADUALLY WORKS BACK OVER THE WATERS.
&&
.APX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER STORM WARNING FROM 7 AM THURSDAY TO 7 PM EST FRIDAY FOR
MIZ008-015>029-031>034.
WINTER WEATHER ADVISORY FROM 7 AM THURSDAY TO 7 PM EST FRIDAY
FOR MIZ030-035-041.
LH...GALE WARNING FROM 1 PM THURSDAY TO 7 AM EST SATURDAY FOR
LHZ345>349.
LM...GALE WARNING FROM 1 PM THURSDAY TO 7 AM EST SATURDAY FOR LMZ323-
341-342-344>346.
LS...GALE WARNING FROM 1 PM THURSDAY TO 7 AM EST SATURDAY FOR LSZ321-
322.
&&
$$
UPDATE...MR
SYNOPSIS...TL
SHORT TERM...JA
LONG TERM...MB/TL
AVIATION...MR
MARINE...MB
AREA FORECAST DISCUSSION...UPDATED
NWS TWIN CITIES/CHANHASSEN MN
814 PM CST WED DEC 19 2012
.UPDATE...
MINOR BUT IMPORTANT CHANGES TO THE FORECAST THIS EVENING. SEVERAL
RUNS OF THE RAP ALONG WITH THE 20/00Z NAM INDICATE LIKELY POPS A
LITTLE FARTHER WEST OVERNIGHT AND EARLY THURSDAY MORNING THAN WE
CURRENTLY HAVE IN THE GRIDS. THIS WOULD MAKE SNOW MORE LIKELY OVER
MUCH OF THE WESTERN AND NORTHERN METRO AS WELL AS AREAS TO THE
SOUTHWEST TOWARDS NEW ULM. THE 00Z NAM CONTINUES THE TREND OF THE
18Z NAM AND BRINGS NEARLY A TENTH OF AN INCH OF QPF TO THE
AFOREMENTIONED AREAS. VERIFICATION ON THE 6HR QPF FROM THE 18Z NAM
ENDING AT 00Z WAS QUITE IMPRESSIVE ON THE AREAL COVERAGE. AN UPDATED
FORECAST HAS BEEN SENT WITH SNOW LIKELY FOR THE WESTERN AND
NORTHERN METRO ON SOUTHWEST WITH AROUND AN INCH OF ACCUMULATION
OVERNIGHT. TWO TO 3 INCHES STILL LOOK OKAY FOR THE SOUTHEAST
METRO.
&&
.DISCUSSION... /ISSUED AT 409 PM CST WED DEC 19 2012/
TONIGHT AND THURSDAY...MAJOR WINTER STORM TO IMPACT NEBRASKA...
IOWA...WISCONSIN AND ILLINOIS. MINNESOTA TO REMAIN JUST ON THE
FRINGES...AND THAT INCLUDES THE WFO MPX CWFA. SFC LOW TO TRACK
FROM THE TX/OK PANHANDLES TO KANSAS CITY TO CHICAGO TO DETROIT
TNGT THRU FRI MRNG. WHAT WILL HELP KEEP THIS STORM SHUNTED TO THE
S...AND KEEP THE SIGNIFICANT SNOW AMOUNTS OVER FAR SE MN INTO
CENTRAL WI...IS AN APPROACHING CDFNT FROM THE NW TNGT THRU TMRW.
THE NAM IS STILL MOST BULLISH WITH SNOWFALL AMOUNTS COMPARED TO
OTHER MODELS...AND THE OTHER CERTAINTY IS THAT THERE WILL BE SHARP
GRADIENTS IN THE SNOW AMOUNTS NOT ONLY FROM THE TWIN CITIES SOUTH-
AND EASTWARD...BUT EVEN WITHIN INDIVIDUAL COUNTIES IN THE WINTER
STORM AND BLIZZARD WARNING AREAS. PATCHES OF BLUE SKY THIS AFTN
WILL BE REPLACED BY EXTENSIVE CLOUD COVER TNGT AS THE STORM SYSTEM
APCHS. SNOW WILL COMMENCE CLOSE TO MIDNIGHT...THEN INCREASE
SIGNIFICANTLY DURG THE EARLY MRNG HOURS. THE HEAVIEST AMOUNTS WILL
BE IN FAR SERN AND ERN PORTIONS OF THE CWFA WHERE 5-9 INCHES OF
SNOW ARE EXPECTED. THE AMOUNTS THEN DROP OFF TO A TIER OF 3-6
INCHES THEN 1-3 INCHES FROM BALSALM LAKE TO THE TWIN CITIES TO NEW
ULM. NORTH OF THAT LINE...LITTLE TO NO SNOWFALL IS EXPECTED WITH
THIS SYSTEM. THE SNOW WILL TAPER OFF DURG THE DAY THU AS THE
SYSTEM PASSES TO THE SE OF THE AREA...BUT A VERY TIGHT PRES
GRADIENT ALONG WITH TIGHT H5 VORTICITY PACKING WITHIN STRONG
SUBSIDENCE ON THE BACKSIDE OF THIS SYSTEM WILL PRODUCE STRONG NNW
WINDS MUCH OF THE DAY THU. THIS WILL RESULT IN BLIZZARD CONDITIONS
OVER FAR SERN MN INTO SW WI...WITH NEAR- BLIZZARD CONDITIONS FROM
BLUE EARTH TO RED WIND MN...AND ELLSWORTH TO CHIPPEWA FALLS WI.
WINDS WILL BEGIN TO SETTLE DOWN BY THE EVENING HOURS BUT WITH THE
TIMING OF THIS SYSTEM CRITICAL TO THE BLOWING SNOW...THERE IS THE
POSSIBILITY THAT THE WINTER STORM WARNINGS AND/OR BLIZZARD
WARNINGS MAY NEED TO BE ADJUSTED IN TIME AND AREA AS THE EVENTS
UNFOLD. THE MAIN CERTAINTY IS THAT THE PRECIPITATION WILL COME AS
SNOW...WITH NO RAIN AHEAD OF IT FOR THE MPX COVERAGE AREA...WITH
TEMPERATURES DROPPING TO AROUND 10 IN NW PORTIONS OF THE COVERAGE
AREA...TO THE LOW-MID 20S IN W-CENTRAL WI. FOR HIGHS ON THU...
TEMPS WILL RANGE FROM THE TEENS TO MID 20S W TO E.
THURSDAY NIGHT THROUGH SATURDAY...CONDITIONS WILL IMPROVE THU
NIGHT INTO FRI AS THE POTENT STORM SYSTEM EXITS INTO THE GREAT
LAKES. THAT SAID...MUCH COLDER AIR WILL MOVE IN ON ITS BACKSIDE
WHILE A DEEP EXTENSIVE RIDGE SETS UP OVER THE CENTRAL CONUS FRI-
SAT. SKIES WILL BECOME PARTLY TO MOSTLY CLEAR STARTING FRI AND
LASTING INTO THE WEEKEND WITH HIGH PRES DOMINATING. HIGHS WILL
DROP TO THE MID TEENS TO MID 20S FRI-SAT...WITH LOWS DROPPING TO
THE SINGLE DIGITS ABOVE AND BELOW ZERO.
SATURDAY NIGHT THROUGH TUESDAY...DEEP RIDGING WILL CONTINUE INTO
SUN THE WEAKEN MON AS A CUTOFF LOW SWINGS THRU CENTRAL-SOUTHEAST
CANADA. A WEAK CDFNT WILL APPROACH MON INTO TUE...POSSIBLY
BRINGING ENOUGH ENERGY TO PRODUCE SNOW SHOWERS AND/OR LIGHT SNOW
MON NIGHT THRU TUE NIGHT. THIS SYSTEM IS TOO WEAK AND TOO QUICK TO
PRODUCE ANYTHING SIGNIFICANT BUT SOME LIGHT SNOW CANNOT BE RULED
OUT SO HAVE INCLUDED 20-30 POPS AT THAT TIME. THE COLD AIR WILL
REMAIN ENTRENCHED OVER THE REGION WITH HIGHS IN THE MID TEENS TO
MID 20S...AND LOWS IN THE SINGLE DIGITS TO MID TEENS.
&&
.AVIATION... /00Z TAF ISSUANCE/
A STRONG STORM SYSTEM WILL DEVELOP AND MOVE ACROSS IOWA INTO
SOUTHERN WISCONSIN. THE BEST CHANCE FOR HEAVY SNOW WILL BE AT KEAU
LATER TONIGHT AND LASTING THROUGH TOMORROW. STRONG NORTHWEST WINDS
OF 20G30KTS ARE POSSIBLE ON THURSDAY...WITH VFR CONDITIONS ACROSS
THE WEST DURING THE AFTERNOON.
KMSP...
FORECAST GUIDANCE SHOWS SNOW DEVELOPING LATER THIS EVENING AT
KMSP...AND INCREASING IN INTENSITY OVERNIGHT. KMSP WILL BE CLOSE
TO THE CUT OFF OF HEAVY SNOW TO THE SOUTHEAST...AND LIGHT SNOW
SHOWERS TO THE NORTHWEST. THEREFORE DID NOT HAVE THE CONFIDENCE TO
LOWER VISBYS BELOW 1MI AT THIS TIME.
/OUTLOOK FOR KMSP/
FRI...VFR. WINDS NW AT 10KTS.
SAT...VFR. WINDS SE AT 5 TO 10KTS.
SUN...VFR. WINDS NE AT 5 TO 10KTS.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...WINTER STORM WARNING UNTIL 6 PM CST THURSDAY FOR FARIBAULT-
GOODHUE-MARTIN-RICE-WASECA.
WINTER WEATHER ADVISORY UNTIL 6 PM CST THURSDAY FOR BLUE EARTH-
DAKOTA-LE SUEUR-SCOTT-WASHINGTON-WATONWAN.
BLIZZARD WARNING UNTIL 6 PM CST THURSDAY FOR FREEBORN-STEELE.
WI...WINTER STORM WARNING UNTIL 6 PM CST THURSDAY FOR CHIPPEWA-DUNN-
EAU CLAIRE-PEPIN-PIERCE.
WINTER WEATHER ADVISORY UNTIL 6 PM CST THURSDAY FOR BARRON-RUSK-
ST. CROIX.
&&
$$
RAH/JPC/JRB
AREA FORECAST DISCUSSION
NWS OMAHA/VALLEY NE
846 PM CST WED DEC 19 2012
.UPDATE...
EVENING UPDATE.
WINTER STORM SYSTEM CONTINUES TO AFFECT THE REGION THIS EVENING.
HAD SOME REPORTS OF THUNDER AND LIGHTNING IN THE OMAHA METRO AREA
WITH SLANTWISE CONVECTION. FARTHER SOUTH...UPRIGHT CONVECTION WAS
OCCURRING. SNOW HAS BEEN FAIRLY WET SO FAR...BUT BLOWING AND
DRIFTING SNOW WILL INCREASE AS COLDER AIR MOVES IN AND WIND
INCREASES. DID NOT CHANGE FORECAST SNOW AMOUNTS MUCH. THE
DEFORMATION ZONE EXTENDED FROM SOUTH CENTRAL NEBRASKA OVER INTO
IOWA AS OF 845 PM.
00Z UPPER AIR CHARTS SHOWED THE FOLLOWING. AT 300 MB...THERE WAS
SOMEWHAT OF A COUPLED JET STRUCTURE WITH A 90 KNOT JEX MAX FROM
NORTHEAST SOUTH DAKOTA INTO NORTHERN MINNESOTA AND ANOTHER OF
135 KNOTS FROM SOUTHERN NEW MEXICO INTO WEST TEXAS. 500 MB CHART
SHOWED A HEIGHT FALL CENTER ESTIMATED AT AROUND 160 METERS IN THE
TEXAS PANHANDLE. 850 MB LOW WAS OVER KANSAS WEST OF TOPEKA AND
TOPEKA HAD AN 850 DEWPOINT OF 8. SO PLENTY OF MOISTURE TO WORK
WITH.
MILLER
&&
.PREV DISCUSSION... /ISSUED 546 PM CST WED DEC 19 2012/
AVIATION...
00Z TAFS FOR KOMA...KLNK...KOFK.
MODERATE SNOW AND POSSIBLE PERIODS OF HEAVY SNOW WILL IMPACT KOMA
AND KLNK THROUGH AT LEAST 08Z THEN TAPER OFF. THIS WILL PRODUCE
IFR OR LOWER CONDITIONS. SNOW SHOULD BE LESS AT KOFK BUT STILL IFR
AT TIMES. INCREASING WINDS WILL LEAD TO SOME BLOWING SNOW AND
LOWER VISIBILITIES. SNOW SHOULD GRADUALLY END AT KOFK BY AROUND
09Z AND THEN FOR KOMA AND KLNK BY 12Z...WITH CONDITONS BECOMING
VFR AFTER THAT.
MILLER
PREV DISCUSSION... /ISSUED 344 PM CST WED DEC 19 2012/
SHORT TERM...TONIGHT THROUGH SATURDAY.
.BLIZZARD TO IMPACT MUCH OF EASTERN NEBRASKA/WESTERN IOWA...
OBVIOUS CONCERN/FOCUS IN THE SHORT TERM WILL BE THE DEVELOPING
BLIZZARD WHICH WILL AFFECT MOST OF THE SOUTHEAST 2/3RDS OR SO OF
THE FORECAST AREA TONIGHT.
AFTERNOON SATELLITE SHOWED DEEP UPPER TROUGH FROM WY THROUGH CO
WITH STRONG POTENTIAL VORTICITY MAX ALONG CO/NM BORDER. AS
THROUGH/PV MAX TRACK EAST TONIGHT...MID LEVEL FLOW FORECAST TO
CLOSE OFF JUST TO OUR SSE WITH RESULTANT FRONTOGENESIS PROVIDING
STRONG LIFT. ALTHOUGH A GOOD PART OF THIS LIFT IS IN DENDRITIC
LAYER...SOME OCCURS EARLY THIS EVENING BELOW THAT LEVEL.
HOWEVER...CROSS SECTIONS SHOWED FOLDING OF THETA SURFACES
INDICATING UPRIGHT OR AT LEAST SLANT-WISE CONVECTIVE BANDS
POSSIBLE AIDING IN 1+ INCH SNOW RATES. ALSO A FEW INSTANCES OF
LIGHTNING HAVE BEEN REPORTED BOTH W OF LNK AND NE OF OMAHA.
12Z GFS/NAM HAVE INCREASED QPF NOW IN 1 INCH RANGE ALONG I80 INTO
WRN IA...ALTHOUGH ECMWF WAS LESS. USING A BLEND WOULD STILL
PROVIDE A BAND OF 7-9+ INCHES OF SNOW IN THE 00Z-12Z PERIOD USING
SNOW TO LIQUID RATIOS OF 13 TO 1 WEST TO AROUND 10-1 EAST THIS
EVENING AND 14-1 OR SO AFTER 06Z...USED A BIT LOWER RATIOS ACROSS
FAR SE. FORECAST SOUNDINGS INDICATED A RAIN/SLEET MIX POSSIBLE TO
BEGIN EVENT FAR SERN ZONES THROUGH 03Z. LATEST RAP FORECAST
SOUNDINGS ALSO FORECAST 65-75 KT WINDS SEVERAL K FEET ABOVE THE
SURFACE SPREADING FM FNB-FBY WITH SPEEDS AT THAT LEVEL IN 55-65KT
RANGE AT LNK/OMA TAPERING TO 45-50 AT KOFK. THUS DYNAMIC MIXING OF
SOME THESE WINDS DOWN TONIGHT SHOULD PROVIDE GUSTS THAT COULD
EXCEED 45-50KTS... ESPECIALLY SERN ZONES.
BLOWING/DRIFTING SNOW SHOULD LINGER THURSDAY MORNING ALTHOUGH HOW
WIDESPREAD BLIZZARD VISIBILITIES ARE MAINTAINED IS A QUESTION.
NONETHELESS...FELT RISK WAS GREAT ENOUGH WITH INITIAL LATE MORNING
ISSUANCE TO KEEP ERN 2/3RDS OR SO OF BLIZZARD AREA VALID THROUGH
18Z...AND THIS WAS CONTINUED IN AFTERNOON PACKAGE. SOME BLOWING
SNOW COULD LINGER ACROSS FAR ERN ZONES AFTER 18Z BUT WOULD EXPECT
VSBYS IMPROVING ENOUGH SO NO HEADLINE PAST THAT TIME. NO OTHER
WEATHER EXPECTED IN SHORT TERM WITH CLEARING AFTERNOON SKIES
LIKELY LASTING THROUGH SATURDAY.
LITTLE CHANGES TO TONIGHTS LOWS BUT WOULD EXPECT WITH FRESH SNOW
COVER MUCH OF THE AREA RECOVERY WILL BE TOUGH AND THUS REDUCED
DIURNAL RANGE. FRESH SNOW AND LIGHT WINDS SHOULD ALLOW MANY TEMPS
TO BE ON OR BELOW THE COLD SIDE OF GUIDANCE THU NGT/FRIDAY.
ALTHOUGH CONTINUED WARM ADVECTION COULD KEEP READINGS UP FRI NGT
AND ALLOW A BIT MORE RECOVERY SATURDAY...KEPT TEMPS NEAR COOLER
MAV MANY AREAS.
CHERMOK
LONG TERM...SATURDAY NIGHT THROUGH WEDNESDAY
A WEAK COLD FRONT MOVES THROUGH SATURDAY NIGHT WITH HIGH PRESSURE
BUILDING IN FOR SUNDAY AND SUNDAY NIGHT. SURFACE LOW PRESSURE OVER
THE ROCKIES MONDAY CONTINUES TO ORGANIZE AND DEVELOP OVER THE
SOUTHERN PLAINS. A MID LEVEL WAVE MOVES THROUGH THE PLAINS MONDAY
NIGHT THROUGH TUESDAY NIGHT. WITHIN THE LONG WAVE...THERE IS SOME
STRONGER ENERGY OVER THE NORTHERN PLAINS. SINCE THE FORECAST AREA IS
WELL AWAY FROM THE ENERGY IN THE NORTH AND THE MAIN STORM SYSTEM TO
OUR SOUTH...WE HAVE A CHANCE FOR LIGHT SNOW AND FLURRIES WITH THE
WAVE. THE TEMPERATURES ARE VERY COLD ALOFT...SO IT SHOULD BE EASY
TO GET LIGHT SNOW AND FLURRIES...THUS THERE MAY BE SOME LIGHT
ACCUMULATIONS. AT THIS TIME THE ORGANIZED PRECIPITATION IS ACROSS
KANSAS AND MISSOURI OVER THE CHRISTMAS HOLIDAY.
TEMPERATURES WILL REMAIN BELOW NORMAL THROUGH THE EXTENDED.
ZAPOTOCNY
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...BLIZZARD WARNING UNTIL NOON CST THURSDAY FOR NEZ015-033-034-044-
045-051>053-066>068-090>093.
BLIZZARD WARNING UNTIL 6 AM CST THURSDAY FOR NEZ050-065-078-088-
089.
WINTER STORM WARNING UNTIL 6 AM CST THURSDAY FOR NEZ032-042-043.
WINTER WEATHER ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR NEZ016-
030.
WINTER WEATHER ADVISORY UNTIL 6 AM CST THURSDAY FOR NEZ017-018-
031.
IA...BLIZZARD WARNING UNTIL NOON CST THURSDAY FOR IAZ043-055-056-069-
079-080-090-091.
&&
$$
99/99
AREA FORECAST DISCUSSION
NWS OMAHA/VALLEY NE
546 PM CST WED DEC 19 2012
.AVIATION...
00Z TAFS FOR KOMA...KLNK...KOFK.
MODERATE SNOW AND POSSIBLE PERIODS OF HEAVY SNOW WILL IMPACT KOMA
AND KLNK THROUGH AT LEAST 08Z THEN TAPER OFF. THIS WILL PRODUCE
IFR OR LOWER CONDITIONS. SNOW SHOULD BE LESS AT KOFK BUT STILL IFR
AT TIMES. INCREASING WINDS WILL LEAD TO SOME BLOWING SNOW AND
LOWER VISIBILITIES. SNOW SHOULD GRADUALLY END AT KOFK BY AROUND
09Z AND THEN FOR KOMA AND KLNK BY 12Z...WITH CONDITONS BECOMING
VFR AFTER THAT.
MILLER
&&
.PREV DISCUSSION... /ISSUED 344 PM CST WED DEC 19 2012/
SHORT TERM...TONIGHT THROUGH SATURDAY.
..BLIZZARD TO IMPACT MUCH OF EASTERN NEBRASKA/WESTERN IOWA...
OBVIOUS CONCERN/FOCUS IN THE SHORT TERM WILL BE THE DEVELOPING
BLIZZARD WHICH WILL AFFECT MOST OF THE SOUTHEAST 2/3RDS OR SO OF
THE FORECAST AREA TONIGHT.
AFTERNOON SATELLITE SHOWED DEEP UPPER TROUGH FROM WY THROUGH CO
WITH STRONG POTENTIAL VORTICITY MAX ALONG CO/NM BORDER. AS
THROUGH/PV MAX TRACK EAST TONIGHT...MID LEVEL FLOW FORECAST TO
CLOSE OFF JUST TO OUR SSE WITH RESULTANT FRONTOGENESIS PROVIDING
STRONG LIFT. ALTHOUGH A GOOD PART OF THIS LIFT IS IN DENDRITIC
LAYER...SOME OCCURS EARLY THIS EVENING BELOW THAT LEVEL.
HOWEVER...CROSS SECTIONS SHOWED FOLDING OF THETA SURFACES
INDICATING UPRIGHT OR AT LEAST SLANT-WISE CONVECTIVE BANDS
POSSIBLE AIDING IN 1+ INCH SNOW RATES. ALSO A FEW INSTANCES OF
LIGHTNING HAVE BEEN REPORTED BOTH W OF LNK AND NE OF OMAHA.
12Z GFS/NAM HAVE INCREASED QPF NOW IN 1 INCH RANGE ALONG I80 INTO
WRN IA...ALTHOUGH ECMWF WAS LESS. USING A BLEND WOULD STILL
PROVIDE A BAND OF 7-9+ INCHES OF SNOW IN THE 00Z-12Z PERIOD USING
SNOW TO LIQUID RATIOS OF 13 TO 1 WEST TO AROUND 10-1 EAST THIS
EVENING AND 14-1 OR SO AFTER 06Z...USED A BIT LOWER RATIOS ACROSS
FAR SE. FORECAST SOUNDINGS INDICATED A RAIN/SLEET MIX POSSIBLE TO
BEGIN EVENT FAR SERN ZONES THROUGH 03Z. LATEST RAP FORECAST
SOUNDINGS ALSO FORECAST 65-75 KT WINDS SEVERAL K FEET ABOVE THE
SURFACE SPREADING FM FNB-FBY WITH SPEEDS AT THAT LEVEL IN 55-65KT
RANGE AT LNK/OMA TAPERING TO 45-50 AT KOFK. THUS DYNAMIC MIXING OF
SOME THESE WINDS DOWN TONIGHT SHOULD PROVIDE GUSTS THAT COULD
EXCEED 45-50KTS... ESPECIALLY SERN ZONES.
BLOWING/DRIFTING SNOW SHOULD LINGER THURSDAY MORNING ALTHOUGH HOW
WIDESPREAD BLIZZARD VISIBILITIES ARE MAINTAINED IS A QUESTION.
NONETHELESS...FELT RISK WAS GREAT ENOUGH WITH INITIAL LATE MORNING
ISSUANCE TO KEEP ERN 2/3RDS OR SO OF BLIZZARD AREA VALID THROUGH
18Z...AND THIS WAS CONTINUED IN AFTERNOON PACKAGE. SOME BLOWING
SNOW COULD LINGER ACROSS FAR ERN ZONES AFTER 18Z BUT WOULD EXPECT
VSBYS IMPROVING ENOUGH SO NO HEADLINE PAST THAT TIME. NO OTHER
WEATHER EXPECTED IN SHORT TERM WITH CLEARING AFTERNOON SKIES
LIKELY LASTING THROUGH SATURDAY.
LITTLE CHANGES TO TONIGHTS LOWS BUT WOULD EXPECT WITH FRESH SNOW
COVER MUCH OF THE AREA RECOVERY WILL BE TOUGH AND THUS REDUCED
DIURNAL RANGE. FRESH SNOW AND LIGHT WINDS SHOULD ALLOW MANY TEMPS
TO BE ON OR BELOW THE COLD SIDE OF GUIDANCE THU NGT/FRIDAY.
ALTHOUGH CONTINUED WARM ADVECTION COULD KEEP READINGS UP FRI NGT
AND ALLOW A BIT MORE RECOVERY SATURDAY...KEPT TEMPS NEAR COOLER
MAV MANY AREAS.
CHERMOK
LONG TERM...SATURDAY NIGHT THROUGH WEDNESDAY
A WEAK COLD FRONT MOVES THROUGH SATURDAY NIGHT WITH HIGH PRESSURE
BUILDING IN FOR SUNDAY AND SUNDAY NIGHT. SURFACE LOW PRESSURE OVER
THE ROCKIES MONDAY CONTINUES TO ORGANIZE AND DEVELOP OVER THE
SOUTHERN PLAINS. A MID LEVEL WAVE MOVES THROUGH THE PLAINS MONDAY
NIGHT THROUGH TUESDAY NIGHT. WITHIN THE LONG WAVE...THERE IS SOME
STRONGER ENERGY OVER THE NORTHERN PLAINS. SINCE THE FORECAST AREA IS
WELL AWAY FROM THE ENERGY IN THE NORTH AND THE MAIN STORM SYSTEM TO
OUR SOUTH...WE HAVE A CHANCE FOR LIGHT SNOW AND FLURRIES WITH THE
WAVE. THE TEMPERATURES ARE VERY COLD ALOFT...SO IT SHOULD BE EASY
TO GET LIGHT SNOW AND FLURRIES...THUS THERE MAY BE SOME LIGHT
ACCUMULATIONS. AT THIS TIME THE ORGANIZED PRECIPITATION IS ACROSS
KANSAS AND MISSOURI OVER THE CHRISTMAS HOLIDAY.
TEMPERATURES WILL REMAIN BELOW NORMAL THROUGH THE EXTENDED.
ZAPOTOCNY
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...BLIZZARD WARNING UNTIL NOON CST THURSDAY FOR NEZ015-090>093.
BLIZZARD WARNING UNTIL 6 AM CST THURSDAY FOR NEZ050-065-078-088-
089.
BLIZZARD WARNING UNTIL NOON CST THURSDAY FOR NEZ033-034-044-045-
051>053-066>068.
WINTER STORM WARNING UNTIL 6 AM CST THURSDAY FOR NEZ032-042-043.
WINTER WEATHER ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR NEZ016-
030.
WINTER WEATHER ADVISORY UNTIL 6 AM CST THURSDAY FOR NEZ017-018-
031.
IA...BLIZZARD WARNING UNTIL NOON CST THURSDAY FOR IAZ043-055-056-069-
079-080-090-091.
&&
$$
99/99
AREA FORECAST DISCUSSION
NWS NORTH PLATTE NE
1136 PM CST MON DEC 17 2012
.AVIATION...
VISUAL FLIGHT RULES FOR KLBF TERMINAL THROUGH 19/06Z WEDNESDAY.
THE LOW STRATUS NEAR KONL WILL CONTINUE TO MOVE SLOWLY EAST
OVERNIGHT AS A SURFACE LOW CURRENTLY NEAR KVTN MOVES EAST NORTHEAST
INTO SOUTHEASTERN SOUTH DAKOTA TOWARD 12Z. THIS WILL BRING A
BACKING WIND TO THE NORTHWEST NEAR 10KTS FOR KVTN...ALONG WITH THE
POTENTIAL FOR MVFR CEILINGS IN WRAP AROUND FROM 10Z-14Z. LATEST
NAM AND RAP MODELS FAVOR A CEILING AOA 3500 FEET WHICH IS WHAT
GOING FORECAST HAS. OTHERWISE SCATTERED CLOUD HEIGHTS AOA 8 KFT
WITH INCREASING MID/HIGH CLOUDS TOWARD 00Z/19TH AS UPSTREAM WINTER
STORM TAKES AIM ON THE CENTRAL ROCKIES.
&&
.PREV DISCUSSION... /ISSUED 349 PM CST MON DEC 17 2012/
DISCUSSION...
THE STORM OF INTEREST IS RAPIDLY APPROACHING THE PACIFIC NORTHWEST COAST.
MODELS AND TIMING TOOLS INDICATE THE DISTURBANCE IS MOVING EAST
SOUTHEAST AT 30KTS AND WILL CONTINUE SO THROUGH WEDNESDAY NIGHT.
SOME MODEL SOLNS ARE SOUTH...NORTH...WETTER AND DRIER. THE ECMWF
HAS BEEN THE MOST CONSISTENT FOCUSING THE BEST FORCING ACROSS SWRN
NEB SOUTH OF INTERSTATE 80. THE GFS...NAM AND GEM HAVE BEEN
WOBBLING NORTH AND SOUTH. THE ECM IS ALSO ABOUT 6 HOURS SLOWER
THAN THE OTHER MODELS AND SHOWS THE DRIEST BOUNDARY LAYER MOISTURE
AND PRODUCES THE LEAST QPF. THE GFS ENSEMBLE H700MB LOW TRACK AND
QPF IS A REASONABLE COMPROMISE IN TERMS OF TIMING AND CAPTURING
AREAS SOUTH OF NEBRASKA HIGHWAY 2 WITH SNOW.
THE FEATURE OF INTEREST APPEARS TO BE VERY STRONG BUT FAST MOVING
MID LEVEL FRONTOGENESIS AND DEFORMATION ALONG AND JUST NORTH OF
THE H700MB LOW. IT IS STRONGLY TILTED POSITIVELY. THIS SHOULD
PRODUCE A RELATIVELY NARROW BAND OF LIGHT TO MODERATE SNOW. THE
NAM IS SHOWING HEAVY SNOW AS TEMPERATURES ARE VERY FAVORABLE FOR
GROWTH AND THE DENDRITIC LAYER WILL BE DESCENDING AS COLD AIR
FILLS IN BEHIND THE H7 LOW. THE QUICK MOTION OF THE STORM MAKES
HEAVY SNOW LESS LIKELY.
ONE THING ALL MODELS AGREE ON ARE WIND SPEEDS. A NRN STREAM
DISTURBANCE MOVING THROUGH THE NRN PLAINS TUESDAY WILL TAP SOME
ARCTIC AIR AND THIS WILL DROP SOUTH WEDNESDAY MORNING AND GET
CAUGHT UP IN THE SFC CYCLONE. WIND SPEEDS WEDNESDAY AFTN SHOULD
INCREASE TO 15 TO 25 MPH WITH SPEEDS APPROACHING 30 MPH ACROSS FAR
SWRN NEB. MOST OF THE SNOW SHOULD BE OVER BY TIME THE WINDS COME
UP BUT THATS PERFECT FOR BLOWING SNOW.
THURSDAY THROUGH SATURDAY...A ZONAL FLOW TAKES OVER ALOFT PRODUCING
CLEAR SKIES A GRADUAL MODERATION IN TEMPERATURES. THE WEATHER MAY
BE QUIET IN NEBRASKA BUT A LARGE UPPER LEVEL RIDGE WILL BUILD
ACROSS ALASKA SUPPORTING THE DEVELOPMENT OF A VERY LARGE ARCTIC
HIGH PRESSURE SYSTEM. THIS HIGH WILL EVENTUALLY DROP SOUTH AND THE
MODELS ARE HAVING TROUBLE TIMING THE EVENTUAL ARCTIC FRONTAL
PASSAGE INTO NEBRASKA. TODAYS MODEL RUNS SUGGEST THE FRONT WILL
DROP IN MONDAY...A DAY OR SO LATER THAN YESTERDAYS MODEL SOLNS. SO
THERE IS A CHANCE OF SNOW MONDAY FOR UPSLOPE CONDITIONS.
OTHERWISE THE FCST IS STRAIGHT FORWARD. THE ARCTIC DRAPE ACROSS
NORTHEAST NEBRASKA WHILL REMAIN IN PLACE TONIGHT THROUGH 14Z
TUESDAY ACCORDING TO THE RUC. SFC LOW PRESSURE WILL DROP SOUTHEAST
ALONG THE FRONT TONIGHT. IT MAY EVEN REMAIN ON TUESDAY BUT THATS
NOT INDICATED BY ANY MODEL. THE TANDEM EFFECT OF THE NRN STREAM
LOW AND THE LOW DROPPING THROUGH NEB TONIGHT SHOULD LIFT THE
ARCTIC FRONT AND CLOUDS NORTH TUESDAY.
&&
.LBF WATCHES/WARNINGS/ADVISORIES...WINTER STORM WATCH FROM WEDNESDAY
MORNING THROUGH WEDNESDAY EVENING FOR NEZ058-069>071.
&&
$$
SHORT TERM/EXTENDED...NWS
AVIATION...ROBERG
AREA FORECAST DISCUSSION
NWS BUFFALO NY
746 AM EST TUE DEC 18 2012
.SYNOPSIS...
LOW PRESSURE WILL LIFT ACROSS NEW YORK THIS MORNING AND THEN EXIT
INTO SOUTHERN NEW ENGLAND THIS AFTERNOON. RAIN WILL CONTINUE THIS
MORNING...THEN TAPER OFF FROM WEST TO EAST THIS AFTERNOON...ENDING
AS SNOW ACROSS HIGHER TERRAIN AND EAST OF LAKE ONTARIO. HIGH
PRESSURE WILL BRING FAIR AND MILD WEATHER MID WEEK BEFORE A STRONGER
SYSTEM BRINGS RAIN ON THURSDAY AND MORE WINTRY WEATHER AND WIND TO
THE REGION BY FRIDAY.
&&
.NEAR TERM /THROUGH TONIGHT/...
AT 700 AM...A WEAK AREA OF LOW PRESSURE WAS CENTERED ACROSS
CENTRAL NEW YORK. EVEN THOUGH THE SURFACE LOW IS ONLY 998 MB...IT
IS FAIRLY WELL DEVELOPED ALOFT AND CLOSED OFF TO 700 MB WITH A
SHARP 500 MB TROF TO THE WEST. ASSOCIATED WITH THIS LOW IS A LARGE
AREA OF RAIN ACROSS WESTERN NEW YORK. THE MAIN FOCUS FOR LIFT WITH
THIS IS WARM AIR ADVECTION WRAPPING AROUND THE 850MB LOW IN A
TROWAL- LIKE FEATURE ON THE BACK SIDE OF THE LOW.
OVERALL MODEL GUIDANCE HAS A GOOD HANDLE ON THIS...THOUGH A
CONSENSUS OF THE 00Z NAM/RGEM AND THE 21Z SREF TENDS TO BE A BIT TOO
SLOW IN ENDING RAIN EAST OF LAKE ONTARIO WHEN COMPARED WITH
RADAR TRENDS. THE HRRR SEEMS TO HAVE A GOOD HANDLE ON THIS
FEATURE. QPF FORECAST HAVE BEEN GOOD...WITH ADDITIONAL RAIN LIKELY
TO AVERAGE AROUND A QUARTER INCH TODAY...WITH AN ADDITIONAL TENTH
OR SO EAST OF LAKE ONTARIO TONIGHT. RAIN WILL SLOWLY END FROM WEST
TO EAST...TAPERING OFF WEST OF ROCHESTER AROUND EARLY
AFTERNOON...AND ENDING LATE AFTERNOON BETWEEN ROCHESTER AND SYRACUSE.
OUTSIDE OF THE NOTABLY DREARY CONDITIONS ACROSS THE REGION...THIS
SYSTEM WILL NOT HAVE A MAJOR IMPACT ON MOST OF WESTERN NEW
YORK...SINCE PRECIPITATION SHOULD FALL PRIMARILY AS RAIN. THIS
SAID...COLDER AIR MOVING IN FROM THE WEST THIS AFTERNOON WILL CAUSE
RAIN TO MIX WITH AND CHANGE TO SNOW ACROSS HIGHER TERRAIN IN THE
SOUTHERN TIER...EXTENDING INTO THE BOSTON HILLS. EXPECT A SLIGHTLY
LATER CHANGEOVER EAST OF LAKE ONTARIO...AGAIN HIGHER TERRAIN SUCH AS
THE TUG HILL TRANSITIONING FIRST. COLDER AIR WILL CONTINUE TO WORK
IN THIS EVENING...WHEN MOST LINGERING PRECIPITATION SHOULD FALL
PRIMARILY AS SNOW.
ONE IMPORTANT NOTE IN TERMS OF PRECIPITATION TYPE IS THAT BECAUSE
THIS IS SYNOPTIC INSTEAD OF LAKE EFFECT...OUR USUAL -6C AT 850MB
RAIN/SNOW LINE WILL NOT APPLY. NAM/GFS BUFKIT FORECAST SOUNDINGS
BOTH SUPPORT A CHANGEOVER ONCE 850MB TEMPERATURES REACH ABOUT
-3C...WHICH SEEMS REASONABLE CONSIDERING THIS WILL BE IN THE
NORTHWESTERN SECTOR OF THE LOW. USED A CONSENSUS OF THE
SREF/RGEM/NAM TO TIME THIS...WHICH IS A BIT SLOWER THAN THE 00Z NAM
WHICH SEEMS TO BE ON THE COLDEST END OF GUIDANCE.
OTHERWISE...DRIER AIR WILL WORK IN FROM THE WEST THIS EVENING...WITH
A PARTIAL CLEARING FROM BUFFALO TO ROCHESTER. EXPECT MINIMAL
ACCUMULATIONS OF AN INCH OR LESS IN WESTERN PORTIONS OF THE
SOUTHERN TIER THIS AFTERNOON...AND THIS MAINLY ACROSS HIGHER
TERRAIN. SOME MODELS SUGGEST LIGHT QPF IN THE SOUTHERN TIER THIS
EVENING...BUT EXPECT NO ADDITIONAL ACCUMULATION THIS EVENING.
THERE WILL BE MORE MOISTURE EAST OF LAKE ONTARIO...WHICH IS CLOSER
TO THE UPPER LOW. THUS EXPECT SLIGHTLY MORE SIGNIFICANT AMOUNTS
EAST OF LAKE ONTARIO...WHERE A GENERAL 1 TO 3 INCHES THROUGH
TONIGHT.
TEMPERATURES WILL HOLD STEADY OR SLOWLY DROP TODAY...AS THE FLOW
BECOMES MORE NORTHWESTERLY. MORNING HIGHS IN THE LOWER 40S CAN BE
EXPECTED IN MOST LOCATIONS. TONIGHT WILL BE COOLER...BUT LINGERING
WINDS AND CLOUD COVER SHOULD KEEP TEMPERATURES TOO DRASTICALLY...MAINLY
IN THE LOWER 30S.
&&
.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
LINGERING LIGHT SNOW SHOWERS POSSIBLE EAST OF LAKE ONTARIO WEDNESDAY
MORNING...BEFORE MOISTURE PULLS EASTWARD. HIGH PRESSURE BOTH AT THE
SURFACE AND ALOFT WILL THEN BUILD IN FOR THE REMAINDER OF THE DAY
AND MAINTAIN ITSELF ACROSS THE REGION THROUGH WEDNESDAY NIGHT. THIS
WILL RESULT IN A PERIOD OF QUIET CONDITIONS...BEFORE WE DEAL WITH
THE SIGNIFICANT STORM SYSTEM IN THE LONGER TERM. MODEL CROSS
SECTIONS WOULD SUGGEST A FAIR AMOUNT OF SUNSHINE DEVELOPING
WEDNESDAY...ALTHOUGH A HINT OF SOME LAKE CLOUDINESS PERSISTING
SOUTHEAST OF THE LAKES IN A GENERAL NORTHWEST FLOW. TEMPERATURES
WILL STILL BE MILD FOR MID DECEMBER...WITH HIGHS IN THE LOWER 40S
ACROSS THE LOWER ELEVATIONS AND UPPER 30S FOR THE HIGHER TERRAIN.
HIGH PRESSURE WILL BEGIN TO SHIFT EAST OF THE AREA WEDNESDAY NIGHT
ALLOWING A STRENGTHENING WARM AIR ADVECTION PATTERN TO SET UP. THERE
SHOULD BE A GRADUALLY WEST TO EAST INCREASE IN CLOUD COVER
OVERNIGHT. TEMPERATURES LIKELY TO REMAIN IN THE 30S OR EVEN RISE
ACROSS THE WEST WITH 20S FARTHER TO THE EAST.
BY THURSDAY...OUR ATTENTION TURNS TO A SIGNIFICANT STORM SYSTEM THAT
WILL BE PROGRESSING EAST ACROSS THE NATION. A MODEL CONSENSUS
CONTINUES TO FAVOR A DEEPENING CENTRAL ILLINOIS TO SOUTHERN MICHIGAN
SURFACE LOW TRACK. THIS FORECAST TRACK WOULD EASILY PLACE WESTERN
AND CENTRAL NEW YORK IN THE WARM AIR IN ADVANCE OF THE MID LATITUDE
CYCLONE...SUPPORTING A RAIN EVENT WITHIN THE INITIAL THETA-E AND
ISENTROPIC ASCENT SURGE THURSDAY AFTERNOON AND THURSDAY EVENING. THE
DEEP SOUTHERLY FLOW WILL RESULT IN A MILD DAY THURSDAY WITH HIGHS IN
THE 50S ACROSS THE LOWER ELEVATIONS AND 40S ELSEWHERE.
AS THE SOUTHERN STREAM PV ANOMALY ATTEMPTS TO TAKE ON A NEGATIVE
TILT THURSDAY NIGHT...SHARPLY COLDER AIR WILL BE USHERED IN BEHIND
THE SURFACE COLD FRONT. IMPRESSIVE WIND FIELDS WITHIN THE MID LEVEL
DRY SLOT WILL MATERIALIZE IN WAKE OFF THE FRONT...WITH A POTENTIAL
SHORT PERIOD OF HIGH WINDS. THE DRY SLOT WILL ALSO DIMINISH THE RAIN
RAPIDLY BEHIND THE FRONT. WE MAY SEE SNOW DEVELOP AS EARLY AS LATE
THURSDAY NIGHT ACROSS THE FAR WEST...ESPECIALLY THE HIGHER
ELEVATIONS OF THE SOUTHERN TIER.
&&
.LONG TERM /FRIDAY THROUGH MONDAY/...
FRIDAY THE PRIMARY SURFACE LOW IS FORECAST TO TRACK OVER OR JUST
NORTH OF LAKE ONTARIO. MODEL DIFFERENCES STILL REVOLVE AROUND HOW
MUCH SECONDARY CYCLOGENESIS WILL TAKE PLACE ON THE TRIPLE POINT OF
THE LOW ALONG THE EAST COAST FRIDAY. THE ECMWF REMAINS THE MOST
AGGRESSIVE...ALLOWING THIS SECONDARY LOW TO TAKE OVER BY MIDDAY
FRIDAY...THEN MAKE A LOOP THROUGH WESTERN NEW ENGLAND AND BACK INTO
NORTHERN NEW YORK FRIDAY NIGHT. THE GFS AND CANADIAN GEM ALSO HAVE
SOME SECONDARY CYCLOGENESIS...BUT A LITTLE WEAKER AND SLOWER...WHICH
ALLOWS THE SURFACE LOW TO LIFT INTO SOUTHERN QUEBEC FRIDAY NIGHT AND
ALSO ALLOWS IT TO PULL OUT FASTER OVER THE WEEKEND...WHILE THE ECMWF
HANGS THE SURFACE LOW AND MID LEVEL CLOSED LOW BACK LONGER.
THE DETAILS OF THE SYNOPTIC EVOLUTION AND TRACK WILL PLAY AN
IMPORTANT ROLE IN WHERE THE HEAVIEST SNOW WILL BE...AND IT WILL
PROBABLY STILL BE A FEW DAYS BEFORE WE HAVE A MORE PRECISE MODEL
CONSENSUS GIVEN THE COMPLEXITY OF THE PATTERN EVOLUTION. IN A
GENERAL SENSE...EXPECT SNOW DEVELOPING FROM WEST TO EAST FRIDAY
MORNING AS THE WRAP AROUND/COMMA HEAD ARRIVES. SNOW SHOULD CONTINUE
FRIDAY THROUGH MUCH OF SATURDAY...WITH INTENSITY DEPENDING ON
EXACTLY WHERE THE MID LEVEL CUTOFF AND SURFACE LOW END UP STALLING.
IT IS LOOKING MORE AND MORE LIKELY WE WILL SEE AT LEAST SOME
ACCUMULATING SNOW EVERYWHERE...WITH CURRENT INDICATIONS SUGGESTING
THE HEAVIEST WILL BE SOUTHEAST OF THE LAKES AND ACROSS HIGHER
TERRAIN WITH SOME HELP FROM LAKE ENHANCEMENT AND UPSLOPE FLOW.
FROM SUNDAY INTO EARLY NEXT WEEK THE AREA WILL REMAIN UNDER THE
INFLUENCE OF THE CUTOFF UPPER LEVEL LOW...ALTHOUGH TO WHAT EXTENT
STILL DEPENDS ON WHERE IT ENDS UP STALLING. FOR NOW WILL JUST RUN
WITH A CHANCE OF SNOW SHOWERS EVERYWHERE...WITH THE BEST CHANCES
SOUTHEAST OF THE LAKES WITH SOME NORTHWEST FLOW LAKE EFFECT.
TEMPERATURES WILL BE BACK TO WHERE THEY SHOULD BE FOR THIS TIME OF
YEAR OVER THE WEEKEND...AND MAYBE EVEN BELOW AVERAGE IF THE COLDER
ECMWF SOLUTION VERIFIES.
&&
.AVIATION /13Z TUESDAY THROUGH SATURDAY/...
LOW PRESSURE ACROSS CENTRAL NEW YORK AT 12Z WILL SLOWLY LIFT TO THE
NORTHEAST. THERE IS LOTS OF LOW LEVEL MOISTURE AND RAIN ASSOCIATED
WITH THIS LOW...WITH LOW CIGS AND VSBY MAINLY DEPENDENT ON
LOCALIZED FLOWS. AHEAD OF THE LOW...A SE FLOW HAS DOWNSLOPED...AND
KEPT CONDITIONS MAINLY VFR. HOWEVER...NOW ALL TAF SITES ARE IN A
NORTHERLY FLOW TO THE NORTH OF THE SYSTEM...WITH WIDESPREAD IFR OR
LOWER CONDITIONS. HOWEVER...DRIER AIR SITS JUST TO THE WEST...SO AS
WINDS BECOME MORE WESTERLY AND INCREASE...CIGS SHOULD START IMPROVING FROM
W-E THIS MORNING AND INTO THIS AFTERNOON...WITH MAINLY MVFR CONDITIONS
LIKELY BY LATE AFTERNOON.
RAIN WILL TAPER OFF FROM WEST TO EAST AS WELL...BUT WILL PROBABLY
MIX WITH OR TURN TO SNOW AT JHW/ART. MINIMAL ACCUMULATIONS ARE
POSSIBLE AT ART.
DRIER AIR WILL CONTINUE TO BUILD INTO THE REGION TONIGHT...WITH LIFTING
CIGS AND A GRADUAL IMPROVEMENT TO VFR EXPECTED.
OUTLOOK...
WEDNESDAY...MAINLY VFR.
THURSDAY...DETERIORATING TO MVFR WITH SHOWERS LIKELY IN THE
AFTERNOON.
THURSDAY NIGHT...MVFR WITH RAIN SHOWERS CHANGING TO SNOW. GUSTY WINDS.
FRIDAY...IFR WITH SNOW LIKELY. GUSTY WINDS.
SATURDAY...MVFR/IFR SNOW SHOWERS LIKELY.
&&
.MARINE...
WEAK LOW PRESSURE EXITING TO THE EAST WILL RESULT IN A NORTHWESTERLY
FLOW DEVELOPING THIS AFTERNOON AND TONIGHT. WHILE THE LOW IS QUITE
WEAK...THE GRADIENT BETWEEN THIS AND HIGH PRESSURE TO THE WEST SHOULD
BE ENOUGH TO PRODUCE SMALL CRAFT CONDITIONS ON THE WATERS. THESE
WILL LAST LONGEST ON EASTERN LAKE ONTARIO...WHERE THE FLOW WILL BE
STRONGEST AND MOST CONDUCIVE TO WAVE BUILDING.
AFTER THIS...HIGH PRESSURE WILL BUILD ACROSS THE WATERS WEDNESDAY
NIGHT.
A STRONGER STORM SYSTEM IS FORECAST TO MOVE INTO THE VICINITY OF THE
LOWER LAKES BY THURSDAY AND FRIDAY. THIS WILL BRING A PERIOD OF
STRONGER WINDS...AND GREATER WAVE HEIGHTS. THIS SYSTEM HAS THE
POTENTIAL TO BRING GALE FORCE WINDS...DEPENDING ON THE TRACK AND
STRENGTH.
&&
.BUF WATCHES/WARNINGS/ADVISORIES...
NY...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR LEZ040-041.
SMALL CRAFT ADVISORY FROM 1 PM THIS AFTERNOON TO NOON
EST WEDNESDAY FOR LOZ043.
SMALL CRAFT ADVISORY FROM 1 PM THIS AFTERNOON TO 5 AM EST
WEDNESDAY FOR LOZ042.
SMALL CRAFT ADVISORY FROM 3 PM THIS AFTERNOON TO 6 PM EST
WEDNESDAY FOR LOZ044-045.
&&
$$
SYNOPSIS...APFFEL
NEAR TERM...APFFEL
SHORT TERM...TMA
LONG TERM...HITCHCOCK
AVIATION...APFFEL
MARINE...APFFEL/TMA
AREA FORECAST DISCUSSION
NWS GRAND FORKS ND
944 AM CST TUE DEC 18 2012
.DISCUSSION...
ADJUSTED POPS/WX FOR A SLOWER PROGRESSION OF THE PRECIP BAND
THROUGH THE CWA. RADAR HAS SOME LIGHT RETURNS FROM DEVILS LAKE
BASIN TO SHEYENNE VALLEY...BUT WEB CAMS AND SFC OBS SHOW NOT MUCH
IS REACHING THE GROUND YET. VALLEY CITY AND COOPERSTOWN OBS
SHOWING SOME 1/4MI VIS...BUT THIS IS FAIRLY PATCHY AND THINK IT
WILL BE SHORT LIVED SO WILL COVER WITH NOWCASTS AND NOT INCLUDE AN
ADVISORY. BETTER RADAR RETURNS AND CHANCES FOR ACCUMULATING SNOW
ARE FURTHER WEST NEAR THE SFC TROUGH AXIS. NAM AND RAP ARE IN
PRETTY GOOD AGREEMENT ON BRINGING MEASURABLE PRECIP INTO THE
WESTERN COUNTIES DURING THE LATE MORNING/EARLY AFTERNOON...AND
INTO THE RED RIVER VALLEY DURING THE 21Z TO 00Z TIME FRAME.
RAISED HIGHS A COUPLE OF DEGREES IN THE SOUTHWESTERN CWA AS SOME
LOCATIONS HAVE ALREADY HIT THEIR AFTERNOON HIGH OF 25. DO NOT
THINK THEY WILL WARM A LARGE AMOUNT DUE TO EXTENSIVE CLOUD
COVER...BUT THINK THEY SHOULD CONTINUE TO RISE A FEW DEGREES TO
TOP OUT IN THE UPPER 20S.
&&
.AVIATION...
EXPECT MAINLY IFR CONDITIONS TO PERSIST THROUGH THE PERIOD...WITH
LIGHT SNOW OVERSPREADING THE AREA FROM WEST TO EAST TODAY. THE MVFR
CIGS IN THE EASTERN TAF SITES WILL FALL INTO THE IFR RANGE DURING
THE LATE MORNING AND EARLY AFTERNOON. WINDS SHOULD REMAIN
LIGHT...UNDER 10KT GENERALLY FROM THE SE.
&&
.PREV DISCUSSION... /ISSUED 244 AM CST TUE DEC 18 2012/
SHORT TERM...
THE MAIN CHALLENGE WILL BE LIGHT SNOW BAND THAT WILL MOVE FROM
WEST TO EAST TODAY AND TONIGHT. MODELS ARE IN GOOD AGREEMENT WITH
THIS LIGHT SNOW...WITH SLIGHT TIMING DIFFERENCES. IT SEEMS THE
SLIGHTLY SLOWER PROGRESSION OF THE LIGHT SNOW IS PREFERRED...WITH
THE LATEST RUNS PICKING UP ON THIS.
FOR TODAY AND TONIGHT...EXPECT AN AREA OF ISENTROPIC LIFT AND DEEPER
LAYERED SATURATION TO MOVE SLOWLY FROM WEST TO EAST THROUGH THE
DAY. THE BEST THREAT FOR ACCUMULATING SNOW SHOULD OCCUR IN THE RED
RIVER VALLEY...WHERE UP TO AN INCH OR PERHAPS A BIT MORE IS
POSSIBLE THROUGH TONIGHT. AN UPPER LEVEL TROUGH SHOULD MOVE INTO
CENTRAL ND AROUND 00Z WED...AND THIS SHOULD ENHANCE LARGER SCALE
LIFT PER Q VECTOR AND OMEGA FIELDS. THERE WILL ALSO BE A WEAK BAND
OF MID LEVEL FGEN THAT WILL ALSO HELP VERTICAL MOTION AND SNOW
PRODUCTION. WINDS WILL REMAIN FAIRLY LIGHT FROM THE SOUTHEAST...SO
NO BLOWING SNOW ISSUES AT ALL TO WORRY ABOUT. TEMPS SHOULD WARM
SOME TODAY FROM WEAK LOW LEVEL WAA AND WON/T FALL TOO MUCH
OVERNIGHT WITH COLDER AIR JUST NORTH OF THE CANADIAN BORDER.
ON WED...EXPECT SOME LINGERING LIGHT SNOW ACROSS THE NORTH...WITH
FLURRIES POSSIBLE IN ALL AREAS BY EVENING. LOW LEVEL COLD AIR
ADVECTION WILL MOVE INTO THE NW BY AFTERNOON...AND TEMPS COULD
FALL SOME HERE BY AFTERNOON...WITH NORTHERLY WINDS INCREASING SOME
IN ALL AREAS BY 00Z THU.
ON THU...EXPECT A DRY AND COOL DAY WITH SFC HIGH PRESSURE CONTROLLING
THE WEATHER PATTERN. THERE SHOULD BE SOME SUNSHINE BY THE
AFTERNOON WITH DRIER AIR AND SUBSIDENCE ADVECTING IN FROM THE
NORTH. TEMPS SHOULD BE IN THE SINGLE DIGITS ABOVE NORTH TO AROUND
10 IN MOST OTHER AREAS.
LONG TERM (FRI-MON)...
MODELS IN GOOD AGREEMENT IN THE EXTENDED TIME FRAME WITH OVERALL DRY
WEATHER EXPECTED. UPPER LEVEL RIDGE WILL BRING THE QUIET PATTERN TOT
THE REGION THOUGH CANADIAN HIGH PRESSURE AT THE SFC WILL KEEP A COLD
AIR MASS ANCHORED ACROSS THE NORTHERN PLAINS. THIS WILL GIVE BELOW
NORMAL TEMPS THROUGH THE PERIOD. THE RIDGE WILL SLOWLY GIVE WAY TO
SOUTHWEST FLOW ALOFT AND BRING A CHC OF -SN FOR CHRISTMAS EVE.
&&
.FGF WATCHES/WARNINGS/ADVISORIES...
ND...NONE.
MN...NONE.
&&
$$
JR
AREA FORECAST DISCUSSION
NWS BISMARCK ND
619 AM CST TUE DEC 18 2012
.DISCUSSION...QUICK UPDATE TO RAISE POPS IN THE SOUTH CENTRAL THIS
MORNING. BAND OF SNOW FROM BEULAH AND CENTER SOUTHEAST THROUGH
BISMARCK TO CANNONBALL...LINTON AND STRASBURG CONTINUES TO SLIDE
SOUTHEAST AND COULD DUMP UP TO AN INCH OF SNOW EARLY THIS MORNING.
LATEST RAP SHOWS THE BAND HOLDING TOGETHER AS IT MOVES ACROSS
SOUTH CENTRAL NORTH DAKOTA SO RAISED POPS TO LIKELY ALONG AND
EAST OF THIS BAND. OTHERWISE NO UPDATES OTHER THAN TO POPULATE
WITH THE LATEST SENSIBLE WEATHER.
&&
.AVIATION...LOW PRESSURE OVER SOUTHWEST SASKATCHEWAN AT 12 UTC
WITH A WARM FRONT EXTENDING INTO WESTERN NORTH DAKOTA. THE SURFACE
LOW WILL MOVE INTO NORTHWEST NORTH DAKOTA THIS MORNING AND INTO
NORTHEAST NORTH DAKOTA BY MID EVENING...LIFTING INTO SOUTHERN
MANITOBA BY 12 UTC WEDNESDAY. CURRENTLY...IFR CEILINGS OVER
CENTRAL NORTH DAKOTA INCLUDING MINOT BISMARCK AND JAMESTOWN.
CEILINGS ARE EXPECTED TO IMPROVE AT BISMARCK AND MINOT BY MID TO
LATE MORNING AND AT JAMESTOWN BY EARLY AFTERNOON AS THE SURFACE
LOW TRACKS ACROSS NORTHERN NORTH DAKOTA AND A DRIER WESTERLY
SURFACE FLOW MOVES WEST TO EAST ACROSS THE LOCAL AREA. MVFR-IFR
CEILINGS WILL LINGER AT OR JUST NORTH OF WILLISTON AND MINOT
TODAY...THEN DROP SOUTH LATER TONIGHT AS THE SURFACE LOW MOVES
EAST AND FLOW TURNS MORE NORTHWEST. THERE WILL BE ISOLATED TO
SCATTERED SNOW SHOWERS TODAY...MOST PREVALENT ACROSS THE NORTH.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
TWH
AREA FORECAST DISCUSSION
NWS WILMINGTON OH
914 PM EST WED DEC 19 2012
.SYNOPSIS...
A POTENT AND DEEP LOW PRESSURE SYSTEM WILL MOVE QUICKLY FROM
OKLAHOMA THIS EVENING INTO SOUTHERN LOWER MICHIGAN BY THURSDAY
NIGHT. THIS SYSTEM WILL BRING A POTPOURRI OVER WEATHER TO OHIO
VALLEY...INCLUDING A BAND OF MODERATE RAIN SHOWERS AND A FEW
THUNDERSTORMS WITH GUSTY WINDS ON THURSDAY...FOLLOWED BY A STRONG
COLD FRONT AND RAPID TEMPERATURE DROP LATE THURSDAY AFTERNOON AND
EVENING...WITH A CONTINUED INCREASE IN STRONG WIND GUSTS THURSDAY
NIGHT AND LINGERING INTO MUCH OF FRIDAY. IN ADDITION...SNOW AND
SNOW SHOWERS WILL WRAP THROUGH INDIANA AND OHIO WITH LIGHT
ACCUMULATIONS...AND WHEN COMBINED WITH THE PLUNGING
TEMPERATURES...STRONG WINDS...AND REDUCED VISIBILITIES...TRAVEL
CONDITIONS ARE EXPECTED TO DETERIORATE THURSDAY NIGHT AND INTO
FRIDAY. WINDS WILL DECREASE AND SNOW SHOWERS WILL END FRIDAY
NIGHT...WITH A QUIET PERIOD IN STORE FOR THE WEEKEND.
&&
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
THIS IS A QUIET PERIOD FOR THE WFO ILN FORECAST AREA...AS WEAK
HIGH PRESSURE YIELDS TO THE DEEPENING STORM IN THE SOUTHERN
PLAINS. BKN-OVC CIRRUS SHIELD WILL CONTINUE TO THICKEN OVERNIGHT
WHILE LIGHT/VARIABLE FLOW UNDER THE WEAK RIDGE AXIS TURNS EASTERLY
AND SLOWLY INCREASES THROUGH THE NIGHT IN RESPONSE TO THE
APPROACHING STORM. THIS SHOULD KEEP TEMPS A TICK ABOVE
GUIDANCE...BUT DID LOWER THE TEMPS FROM THE PREVIOUS FORECAST A
FEW DEGREES.
WITH RADAR SHOWING A FEW SHOWERS FLIRTING WITH OUR WESTERN
COUNTIES...RAISED POPS TO CHANCE THERE THIS EVENING INTO THE
OVERNIGHT.
&&
.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/...
ALL THE FOCUS TODAY IS ON THE RAPIDLY DEEPENING LOW PRESSURE AND
ITS IMPACT ON THE FORECAST AREA ON THURSDAY AND FRIDAY. INHERITED
A FORECAST FROM PREVIOUS SHIFTS THAT ALREADY HAD MUCH OF THE GIST
OF WHAT WILL UNFOLD - THUS WE FOCUSED ON ADDING DETAIL WHERE WE
COULD AND GET HEADLINE DECISIONS MADE. THERE ARE NO SIGNIFICANT
CHANGES IN THE FORECAST ITSELF BASED ON TODAY/S DATA.
GOES WATER VAPOR IMAGERY AND 19.12Z RAOBS CLEARLY SHOW THE POTENT
SHORTWAVE TROUGH ABOUT TO INDUCE RAPIDLY DEEPENING SURFACE CYCLONE
OVER THE SRN PLAINS. KFGZ/KABQ RAOBS BOTH HAD MORE THAN 100M
HEIGHT FALLS /500MB/ WHILE AIRCRAFT SOUTH OF THESE STATIONS
SAMPLED AN INTENSE 150-170KT JET STREAK /250MB/ THAT SEEMS TO HAVE
BEEN UNDER-INITIALIZED BY ALL DETERMINISTIC MODEL SOLNS BY A GOOD
20KTS. A CLASSIC MID-WINTER SYSTEM...SATELLITE PRESENTATION IS
ALREADY IMPRESSIVE AND RAP ANALYSIS /19Z/ ALREADY HAS THE
TROPOPAUSE FOLD /1.5 PV SURFACE/ DOWN TO 650MB OVER NRN NM. 996MB
CYCLONE IS ALREADY DEEPENING IN THE OKLAHOMA PANHANDLE AND
GUIDANCE IS NOW TIGHTLY CLUSTERED IN A VERY TYPICAL DECEMBER TRACK
THROUGH MISSOURI AND OVER THE CHICAGO METRO AREA TOWARD DETROIT BY
LATE THURSDAY NIGHT...WITH BLIZZARD CONDITIONS TO THE LEFT OF THE
TRACK AND AMPLE CONVECTION/WINDS IN THE WARM SECTOR.
IT IS IMPORTANT TO NOTE THAT FOR THE WFO ILN CWA...THERE CONTINUES
TO BE A LESSENING MODEL SIGNAL FOR A DAMAGING /HIGH WIND WARNING/ WIND
EVENT. DPROG/DT OVER ABOUT THE LAST DAYS WORTH OF DAY HAS TRENDED
TO AN EARLIER DEEPENING...AND HIGHER MINIMUM PRESSURE WHEN THE LOW
TRACKS ACROSS SOUTHERN MICHIGAN...WITH LATEST DATA SUGGESTING
MODEST FILLING WILL BE OCCURRING THURSDAY NIGHT WITH PRESSURES
BOTTOMING OUT NEAR 984MB NEAR CHICAGO. THIS MODEST CHANGE
DECREASES TO SOME DEGREE THE ISALLOBARIC COMPONENT...AND HAS
ALLOWED THE 925MB/850MB LAYERED WIND MAX TO DROP OUT OF ALARMING
RANGE THAT WOULD HAVE OTHERWISE PROMPTED A HIGH WIND WATCH OR
WARNING. THAT BEING SAID...WE TAKE FROM THE WIND...BUT NOW HAVE
ADDED A LITTLE MORE SNOW BASED ON NOW-AGREED-UPON SECONDARY PV
ANOMALY THAT WILL WRAP SOUTHEAST THROUGH THE BASE OF THE UPPER
TROUGH LATER ON THURSDAY NIGHT...THAT SHOULD BRING A RATHER
CONCENTRATED PERIOD OF LIGHT SNOW/SNOW SHOWERS TO AREAS NORTH OF
I-70 THURSDAY NIGHT INTO FRIDAY. SO IMPACTS WILL STILL BE
SIGNIFICANT WITH THIS SYSTEM...PROBABLY MORE SO FROM ICY
ROADS/WINTER TRAVEL ISSUES THAN FROM WIND DAMAGE/POWER
OUTAGES...ALTHOUGH WITH ANTICIPATED GUSTS TO 45-50MPH OR A LITTLE
HIGHER...ISOLATED POWER OUTAGES AND MINOR/NUISANCE TREE DAMAGE IS
STILL EXPECTED.
DETAILS ON IT ALL...WITH THE TIGHT CLUSTERING OF THE NWP MODEL
SUITE CONFIDENCE IS HIGH IN MOST ASPECTS OF THIS FORECAST. VERY
STRONG/DEEP LAYERED FORCING IMMEDIATELY DOWNSTREAM OF THE PV
CURRENTLY IN NM WILL INDUCE A VERY STRONG MOISTURE TRANSPORT FEED
LATER TONIGHT WHICH WILL MANIFEST AS A ELONGATED/LARGE AREA OF
SHOWERS AND EMBEDDED THUNDERSTORMS RAPIDLY MOVING FROM MS VALLEY
INTO THE OHIO VALLEY LATE. THINK THIS SPREADS ACROSS THE WESTERN
AREAS JUST AFTER SUNRISE WITH BEST POTENTIAL OF THUNDER WEST OF
I-71 WHERE MUCAPE IS THE HIGHEST. ALL AREAS GET A GOOD 1/2 INCH OF
RAIN IT APPEARS WITH THIS ACTIVITY WHICH SHIFTS QUICKLY THROUGH
THE FORECAST AREA BY MID AFTERNOON.
A 60-65KT SOUTHERLY LOW LEVEL JET WILL BE DRIVING THIS
ACTIVITY...AND MAY PRESENT A WIND ISSUE AT THE SURFACE...BUT WARM
ADVECTION WIND EVENTS TOUGH TO REALIZE GIVEN INVERTED THERMAL
PROFILES...DEEP LAYERED OMEGA...AND THICK CLOUDS...SO THINK
MORNING/AFTN WILL BE WINDY...BUT NOT WIND ADVISORY
LEVELS...PROBABLY 20/25 GUST 35/40 MPH. PERHAPS A LITTLE STRONGER
IN HEAVIER REFLECTIVITY CORES WITH PASSING SHOWERS...BUT WE CHOSE
TO HOLD OFF ON A WIND ADVISORY FOR THE DAYLIGHT HOURS.
WIND POTENTIAL GOES UP MARKEDLY AS THE COLD FRONT PLOWS INTO
WESTERN AREAS AROUND 21Z AND MARCHES ACROSS THE CWA EFFECTIVELY IN
ABOUT 4-5 HOURS TIME. THERE IS LOW CONFIDENCE IN A FINE LINE OF
SHOWERS ALONG THIS BOUNDARY - AND IF IT OCCURS - THERE IS SHALLOW
SB BUOYANCY /SHOWN VERY NICELY IN 19.12Z BUFR SOUNDINGS FROM NAM-
WRF/ THAT THIS LINE COULD PRODUCE BRIEF HIGH WIND GUSTS.
HOWEVER...BUOYANCY IS SO SHALLOW THAT CHARGE SEPARATION SEEMS
IMPOSSIBLE AND THUNDER WILL BE A STRETCH...SO DECIDED TO GET WIND
ADVISORY GOING AT 21Z ALL AREAS IN CASE THE FRONT CAN TRANSPORT
STRONG GUSTS TO THE SURFACE VIA THIS MECHANISM. IN THE WAKE OF THE
FRONT...LAPSE RATES STEEPEN VERY QUICKLY AND WITH A PSEUDO-DRY
SLOT /THOUGH LOW LEVEL MOISTURE WILL STILL BE AMPLE/...THERE IS
REMAINING INSTABILITY WITH STRONG GUST POTENTIAL IN THE HOURS
FOLLOWING THE FRONT DESPITE DEEPER LAYER STRONG WINDS WILL HAVE
YET TO ARRIVE. WIND POTENTIAL CONTINUES INTO THE OVERNIGHT AS
19.12Z NAM/GFS/ARW-WRF ALL BRING 55-60KT 925-850MB LAYERED WIND
MAX SOUTHEAST FROM THE BACKSIDE OF THE LOW RIGHT THROUGH THE HEART
OF THE CWA. WITH COLD ADVECTION...RAPID PRESSURE RISES...AND
STEEPENING LAPSE RATES...CONTINUED ADVISORY LEVEL WINDS AND GUSTS
ARE EXPECTED AREA-WIDE. THE MOST CONCERNING AREA FOR HIGHER END
GUSTS CONTINUES TO BE ACROSS WEST-CENTRAL OHIO IN THE HIGHER
TERRAIN AREAS AND WEST TO THE INDIANA BORDER WHERE SOME 55 MPH
GUSTS COULD BE SEEN. ANOTHER BIG CHANGE FROM YESTERDAY IS THE
LINGERING OF STRONG WINDS NOW INTO THE AFTERNOON HOURS ON
FRIDAY...AND WHILE AMPLE LOW LEVEL MOISTURE AND OMEGA IS SEEN NEAR
THE SURFACE WHICH WILL HELP TEMPER GUSTS...EVEN CONSERVATIVE MOMENTUM
TRANSPORT /MIXING/ TECHNIQUES SUGGEST LOW-END WIND ADVISORY WINDS
WILL BE POSSIBLE MOST AREAS AT LEAST INTO THE MID AFTERNOON...AND
PARTICULARLY NORTH OF THE OHIO RIVER.
IN TERMS OF SNOW...THE TEMP DROP IN THE WAKE OF THE COLD FRONT IS
FAST AND IMPRESSIVE...AND MAY INDUCE RAPID ROAD FREEZING AND ICING
EVEN IN THE DRY SLOT EARLY THURSDAY EVENING. LATER IN THE
EVENING...SECONDARY PV WRAPS SOUTHEASTWARD /ACCOMPANIED BY LOW
LEVEL WIND MAX MENTIONED ABOVE/ AND SPREADS GOOD FORCING FOR UVM
INTO AREAS NORTH OF I-70 WHERE SNOW/SNOW SHOWERS WILL BE ABUNDANT.
SEE A NICE LITTLE STRIPE OF 1-2 INCHES OF SNOW ACROSS WCNTL INTO
CNTL OH...SO DECIDED TO BE SIMPLE AND COMBINE THE THREATS OF
STRONG WINDS/SNOW/REDUCED VISIBILITIES/ICY ROADS INTO A WINTER
WEATHER ADVISORY. SNOW AMOUNTS WON/T BE SIGNIFICANT...BUT COMING
OUT OF A LONG TERM WARM PERIOD...PAVEMENT SUBSURFACES ARE
ATYPICALLY WARM. WITH VERY COLD AIR AND PERSISTENT SNOW
SHOWERS/STRONG WINDS REMOVING THIS WARMTH FROM THE SKIN SURFACE OF
THE PAVEMENT...SETUP IS SUCH THAT ROADS COULD BECOME EXTREMELY
SLIPPERY IN THE WINTER WX ADVISORY AREA ESP LATER THURS NIGHT INTO
MUCH OF FRIDAY WHERE SNOW IS PERSISTENT. COMBINED WITH RAPID VSBY
CHANGES IN SNOW SHOWERS...THESE SITUATIONS CAN BE SNEAKY-
DANGEROUS...ESPECIALLY CONSIDERING THE MILD WINTER THUS FAR. DON/T
SEE A SIGNAL IN THE DATA FOR SNOW RATIOS AS DIFFERENT THAN CLIM0 -
MUCH OF LIFT/SATURATIONS REMAINS BELOW THE DENDRITIC GROWTH ZONES
AND COBB RATIOS FROM A WEALTH OF SOURCES ARE ALL FROM 8:1 TO 11:1
FOR MOST OF THE PERIOD. LOWEST CONFIDENCE IN WINTER WX ADVISORY
CONDITIONS IN AROUND CMH METRO...BUT DIDN/T WANT TO GET CUTE AT
THIS MOMENT AND TRY TO BE TOO FINE GIVEN INHERENT UNCERTAINTIES.
ISSUED THE WIND ADVISORY FOR AREAS IN THE SOUTH NOT EXPECTED TO
SEE SIGNIFICANT ENOUGH SNOW FOR TRAVEL ISSUES...BUT EVEN IN THESE
AREAS CANNOT RULE OUT A PERIOD OF SLIPPERY TRAVEL AS MAIN WAVE
TRAVERSES THE AREA FRIDAY NIGHT INTO FRIDAY MORNING WITH THE
STRONG WINDS AND COLD TEMPS AND WARM ROAD SURFACES CAUSING
SLIPPERY TRAVEL. FUTURE SHIFTS MAY NEED TO CONSIDER EXPANSION OF
THE WINTER WEATHER ADVISORY IF SNOW SHOWERS ARE MORE WIDESPREAD OR
CONTAIN HEAVIER RATES THAN CURRENTLY ANTICIPATED.
CONDITIONS RAPIDLY IMPROVE FRIDAY EVENING AS WINDS DECREASE AND
SYSTEM PULLS OUT.
&&
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
THE LONG TERM WILL START OFF WITH SOME LINGERING CLOUDS AND A
POSSIBLE FLURRY SATURDAY MORNING BEHIND THE DEPARTING STORM SYSTEM.
CLOUDS SHOULD BE OUT OF THE AREA BY SATURDAY NIGHT AS HIGH PRESSURE
EXTENDS ACROSS THE AREA. WENT BELOW THE MODEL CONSENSUS FOR FORECAST
HIGHS ON SATURDAY ACROSS THE NORTH WHERE CLOUDS AND REMNANT SNOW
COVER WILL KEEP TEMPERATURES DOWN. WENT BELOW THE MODEL CONSENSUS
FOR THE WHOLE AREA SATURDAY NIGHT WITH HIGH PRESSURE AND DECREASING
WINDS HELPING TO PRODUCE FAVORABLE CONDITIONS FOR RADIATIONAL
COOLING.
SUNDAY WILL BE A TRANSITION DAY AS THE HIGH SHIFTS EAST OF THE AREA
AND WEAK LOW PRESSURE APPROACHES FROM THE WEST. ON SUNDAY
NIGHT...CLOUD COVER WILL INCREASE AHEAD OF THIS WEAK LOW AS MOISTURE
GETS DRAWN NORTHWARD INTO THE OHIO VALLEY. MODELS ARE IN FAIR
AGREEMENT ON BRINGING LIGHT PRECIPITATION TO THE FORECAST AREA
SOMETIME BETWEEN EARLY MONDAY MORNING AND EARLY MONDAY
AFTERNOON...DEPENDING ON WHICH MODEL YOU LOOK AT. THIS TIMING WILL
PROBABLY HELP TO DETERMINE PRECIPITATION TYPE. GFS HAS THE COLDEST
AND QUICKEST ARRIVAL OF PRECIPITATION...ALLOWING FOR A PARTIAL MIX
OF RAIN AND SNOW ACROSS MUCH OF THE AREA FOR THIS EVENT. THE
ECMWF/CANADIAN MODELS ARE TOO WARM ALOFT FOR ANY SNOW...HOWEVER
BRING LIGHT RAIN INTO THE AREA WHEN TEMPERATURES ARE NEAR FREEZING
AT THE SURFACE. THEREFORE...THIS PARTICULAR TIME PERIOD WILL NEED
ADJUSTING AS THE TIME DRAWS NEARER. REGARDLESS IT DOES APPEAR THAT
QPF AMOUNTS WILL BE LIGHT FOR THIS LOW WITH NO ACCUMULATION OF ANY
SNOW EXPECTED IF ANY MIX DOES OCCUR.
AFTER A FAIR WEATHER DAY ON CHRISTMAS...THE ATTENTION TURNS TO
CHRISTMAS NIGHT INTO WEDNESDAY AS A VIGOROUS LOW PRESSURE SYSTEM
APPROACHES OUR REGION. MODELS ARE STILL SHIFTING WITH TIMING AND
LOCATION FOR THIS LOW BETWEEN RUNS. HOWEVER...IT DOES APPEAR ONE WAY
OR ANOTHER THAT PRECIPITATION WILL OCCUR. BUMPED UP POPS TO 50
PERCENT. COULD HAVE GONE HIGHER FOR POPS IF THERE WERE NOT STILL
TIMING DIFFERENCES AMONGST THE MODELS.
&&
.AVIATION /02Z THURSDAY THROUGH MONDAY/...
FLIGHT CONDITIONS START OUT IN DECENT SHAPE WITH WEAK HIGH
PRESSURE MOVING IN. OTHER THAN MVFR CEILINGS AT LCK...EXPECT
VFR AT OTHER SITES UNDER HIGH THIN CLOUDS.
WEATHER WILL CHANGE FOR THE WORSE ON THURSDAY DUE TO A POWERFUL
COLD FRONT TRAILING GREAT LAKES LOW PRESSURE. SHOWERS WILL DEVELOP
AT ALL SITES BY MID AFTERNOON. MVFR CONDITIONS WILL OCCUR BY THE
END OF THE FORECAST AS THE FRONT ENTERS THE AREA. WINDS WILL BE A
PROBLEM WITH GUSTS OVER 30 KNOTS OUT OF THE SOUTH TO SOUTHWEST.
SNOW WILL MIX IN AT CVG AFTER 00Z FRIDAY AS COLDER AIR WORKS IN.
&&
.ILN WATCHES/WARNINGS/ADVISORIES...
OH...WINTER WEATHER ADVISORY FROM 4 PM THURSDAY TO 4 PM EST FRIDAY
FOR OHZ026-034-035-042>046-051>056-060>062.
WIND ADVISORY FROM 4 PM THURSDAY TO 4 PM EST FRIDAY FOR
OHZ063>065-070>074-077>082-088.
KY...WIND ADVISORY FROM 4 PM THURSDAY TO 4 PM EST FRIDAY FOR
KYZ089>100.
IN...WINTER WEATHER ADVISORY FROM 4 PM THURSDAY TO 4 PM EST FRIDAY
FOR INZ050-058-059.
WIND ADVISORY FROM 4 PM THURSDAY TO 4 PM EST FRIDAY FOR INZ066-
073>075-080.
&&
$$
SYNOPSIS...BINAU
NEAR TERM...BINAU/CONIGLIO
SHORT TERM...BINAU
LONG TERM...LATTO
AVIATION...CONIGLIO
AREA FORECAST DISCUSSION
NWS WILMINGTON OH
641 PM EST WED DEC 19 2012
.SYNOPSIS...
A POTENT AND DEEP LOW PRESSURE SYSTEM WILL MOVE QUICKLY FROM
OKLAHOMA THIS EVENING INTO SOUTHERN LOWER MICHIGAN BY THURSDAY
NIGHT. THIS SYSTEM WILL BRING A POTPOURRI OVER WEATHER TO OHIO
VALLEY...INCLUDING A BAND OF MODERATE RAIN SHOWERS AND A FEW
THUNDERSTORMS WITH GUSTY WINDS ON THURSDAY...FOLLOWED BY A STRONG
COLD FRONT AND RAPID TEMPERATURE DROP LATE THURSDAY AFTERNOON AND
EVENING...WITH A CONTINUED INCREASE IN STRONG WIND GUSTS THURSDAY
NIGHT AND LINGERING INTO MUCH OF FRIDAY. IN ADDITION...SNOW AND
SNOW SHOWERS WILL WRAP THROUGH INDIANA AND OHIO WITH LIGHT
ACCUMULATIONS...AND WHEN COMBINED WITH THE PLUNGING
TEMPERATURES...STRONG WINDS...AND REDUCED VISIBILITIES...TRAVEL
CONDITIONS ARE EXPECTED TO DETERIORATE THURSDAY NIGHT AND INTO
FRIDAY. WINDS WILL DECREASE AND SNOW SHOWERS WILL END FRIDAY
NIGHT...WITH A QUIET PERIOD IN STORE FOR THE WEEKEND.
&&
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
THIS IS A QUIET PERIOD FOR THE WFO ILN FORECAST AREA...AS WEAK
HIGH PRESSURE YIELDS TO THE DEEPENING STORM IN THE SOUTHERN
PLAINS. BKN-OVC CIRRUS SHIELD WILL CONTINUE TO THICKEN OVERNIGHT
WHILE LIGHT/VARIABLE FLOW UNDER THE WEAK RIDGE AXIS TURNS EASTERLY
AND SLOWLY INCREASES THROUGH THE NIGHT IN RESPONSE TO THE
APPROACHING STORM. THIS SHOULD KEEP TEMPS A TICK ABOVE
GUIDANCE...BUT DID LOWER THE TEMPS FROM THE PREVIOUS FORECAST A
FEW DEGREES.
&&
.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/...
ALL THE FOCUS TODAY IS ON THE RAPIDLY DEEPENING LOW PRESSURE AND
ITS IMPACT ON THE FORECAST AREA ON THURSDAY AND FRIDAY. INHERITED
A FORECAST FROM PREVIOUS SHIFTS THAT ALREADY HAD MUCH OF THE GIST
OF WHAT WILL UNFOLD - THUS WE FOCUSED ON ADDING DETAIL WHERE WE
COULD AND GET HEADLINE DECISIONS MADE. THERE ARE NO SIGNIFICANT
CHANGES IN THE FORECAST ITSELF BASED ON TODAY/S DATA.
GOES WATER VAPOR IMAGERY AND 19.12Z RAOBS CLEARLY SHOW THE POTENT
SHORTWAVE TROUGH ABOUT TO INDUCE RAPIDLY DEEPENING SURFACE CYCLONE
OVER THE SRN PLAINS. KFGZ/KABQ RAOBS BOTH HAD MORE THAN 100M
HEIGHT FALLS /500MB/ WHILE AIRCRAFT SOUTH OF THESE STATIONS
SAMPLED AN INTENSE 150-170KT JET STREAK /250MB/ THAT SEEMS TO HAVE
BEEN UNDER-INITIALIZED BY ALL DETERMINISTIC MODEL SOLNS BY A GOOD
20KTS. A CLASSIC MID-WINTER SYSTEM...SATELLITE PRESENTATION IS
ALREADY IMPRESSIVE AND RAP ANALYSIS /19Z/ ALREADY HAS THE
TROPOPAUSE FOLD /1.5 PV SURFACE/ DOWN TO 650MB OVER NRN NM. 996MB
CYCLONE IS ALREADY DEEPENING IN THE OKLAHOMA PANHANDLE AND
GUIDANCE IS NOW TIGHTLY CLUSTERED IN A VERY TYPICAL DECEMBER TRACK
THROUGH MISSOURI AND OVER THE CHICAGO METRO AREA TOWARD DETROIT BY
LATE THURSDAY NIGHT...WITH BLIZZARD CONDITIONS TO THE LEFT OF THE
TRACK AND AMPLE CONVECTION/WINDS IN THE WARM SECTOR.
IT IS IMPORTANT TO NOTE THAT FOR THE WFO ILN CWA...THERE CONTINUES
TO BE A LESSENING MODEL SIGNAL FOR A DAMAGING /HIGH WIND WARNING/ WIND
EVENT. DPROG/DT OVER ABOUT THE LAST DAYS WORTH OF DAY HAS TRENDED
TO AN EARLIER DEEPENING...AND HIGHER MINIMUM PRESSURE WHEN THE LOW
TRACKS ACROSS SOUTHERN MICHIGAN...WITH LATEST DATA SUGGESTING
MODEST FILLING WILL BE OCCURRING THURSDAY NIGHT WITH PRESSURES
BOTTOMING OUT NEAR 984MB NEAR CHICAGO. THIS MODEST CHANGE
DECREASES TO SOME DEGREE THE ISALLOBARIC COMPONENT...AND HAS
ALLOWED THE 925MB/850MB LAYERED WIND MAX TO DROP OUT OF ALARMING
RANGE THAT WOULD HAVE OTHERWISE PROMPTED A HIGH WIND WATCH OR
WARNING. THAT BEING SAID...WE TAKE FROM THE WIND...BUT NOW HAVE
ADDED A LITTLE MORE SNOW BASED ON NOW-AGREED-UPON SECONDARY PV
ANOMALY THAT WILL WRAP SOUTHEAST THROUGH THE BASE OF THE UPPER
TROUGH LATER ON THURSDAY NIGHT...THAT SHOULD BRING A RATHER
CONCENTRATED PERIOD OF LIGHT SNOW/SNOW SHOWERS TO AREAS NORTH OF
I-70 THURSDAY NIGHT INTO FRIDAY. SO IMPACTS WILL STILL BE
SIGNIFICANT WITH THIS SYSTEM...PROBABLY MORE SO FROM ICY
ROADS/WINTER TRAVEL ISSUES THAN FROM WIND DAMAGE/POWER
OUTAGES...ALTHOUGH WITH ANTICIPATED GUSTS TO 45-50MPH OR A LITTLE
HIGHER...ISOLATED POWER OUTAGES AND MINOR/NUISANCE TREE DAMAGE IS
STILL EXPECTED.
DETAILS ON IT ALL...WITH THE TIGHT CLUSTERING OF THE NWP MODEL
SUITE CONFIDENCE IS HIGH IN MOST ASPECTS OF THIS FORECAST. VERY
STRONG/DEEP LAYERED FORCING IMMEDIATELY DOWNSTREAM OF THE PV
CURRENTLY IN NM WILL INDUCE A VERY STRONG MOISTURE TRANSPORT FEED
LATER TONIGHT WHICH WILL MANIFEST AS A ELONGATED/LARGE AREA OF
SHOWERS AND EMBEDDED THUNDERSTORMS RAPIDLY MOVING FROM MS VALLEY
INTO THE OHIO VALLEY LATE. THINK THIS SPREADS ACROSS THE WESTERN
AREAS JUST AFTER SUNRISE WITH BEST POTENTIAL OF THUNDER WEST OF
I-71 WHERE MUCAPE IS THE HIGHEST. ALL AREAS GET A GOOD 1/2 INCH OF
RAIN IT APPEARS WITH THIS ACTIVITY WHICH SHIFTS QUICKLY THROUGH
THE FORECAST AREA BY MID AFTERNOON.
A 60-65KT SOUTHERLY LOW LEVEL JET WILL BE DRIVING THIS
ACTIVITY...AND MAY PRESENT A WIND ISSUE AT THE SURFACE...BUT WARM
ADVECTION WIND EVENTS TOUGH TO REALIZE GIVEN INVERTED THERMAL
PROFILES...DEEP LAYERED OMEGA...AND THICK CLOUDS...SO THINK
MORNING/AFTN WILL BE WINDY...BUT NOT WIND ADVISORY
LEVELS...PROBABLY 20/25 GUST 35/40 MPH. PERHAPS A LITTLE STRONGER
IN HEAVIER REFLECTIVITY CORES WITH PASSING SHOWERS...BUT WE CHOSE
TO HOLD OFF ON A WIND ADVISORY FOR THE DAYLIGHT HOURS.
WIND POTENTIAL GOES UP MARKEDLY AS THE COLD FRONT PLOWS INTO
WESTERN AREAS AROUND 21Z AND MARCHES ACROSS THE CWA EFFECTIVELY IN
ABOUT 4-5 HOURS TIME. THERE IS LOW CONFIDENCE IN A FINE LINE OF
SHOWERS ALONG THIS BOUNDARY - AND IF IT OCCURS - THERE IS SHALLOW
SB BUOYANCY /SHOWN VERY NICELY IN 19.12Z BUFR SOUNDINGS FROM NAM-
WRF/ THAT THIS LINE COULD PRODUCE BRIEF HIGH WIND GUSTS.
HOWEVER...BUOYANCY IS SO SHALLOW THAT CHARGE SEPARATION SEEMS
IMPOSSIBLE AND THUNDER WILL BE A STRETCH...SO DECIDED TO GET WIND
ADVISORY GOING AT 21Z ALL AREAS IN CASE THE FRONT CAN TRANSPORT
STRONG GUSTS TO THE SURFACE VIA THIS MECHANISM. IN THE WAKE OF THE
FRONT...LAPSE RATES STEEPEN VERY QUICKLY AND WITH A PSEUDO-DRY
SLOT /THOUGH LOW LEVEL MOISTURE WILL STILL BE AMPLE/...THERE IS
REMAINING INSTABILITY WITH STRONG GUST POTENTIAL IN THE HOURS
FOLLOWING THE FRONT DESPITE DEEPER LAYER STRONG WINDS WILL HAVE
YET TO ARRIVE. WIND POTENTIAL CONTINUES INTO THE OVERNIGHT AS
19.12Z NAM/GFS/ARW-WRF ALL BRING 55-60KT 925-850MB LAYERED WIND
MAX SOUTHEAST FROM THE BACKSIDE OF THE LOW RIGHT THROUGH THE HEART
OF THE CWA. WITH COLD ADVECTION...RAPID PRESSURE RISES...AND
STEEPENING LAPSE RATES...CONTINUED ADVISORY LEVEL WINDS AND GUSTS
ARE EXPECTED AREA-WIDE. THE MOST CONCERNING AREA FOR HIGHER END
GUSTS CONTINUES TO BE ACROSS WEST-CENTRAL OHIO IN THE HIGHER
TERRAIN AREAS AND WEST TO THE INDIANA BORDER WHERE SOME 55 MPH
GUSTS COULD BE SEEN. ANOTHER BIG CHANGE FROM YESTERDAY IS THE
LINGERING OF STRONG WINDS NOW INTO THE AFTERNOON HOURS ON
FRIDAY...AND WHILE AMPLE LOW LEVEL MOISTURE AND OMEGA IS SEEN NEAR
THE SURFACE WHICH WILL HELP TEMPER GUSTS...EVEN CONSERVATIVE MOMENTUM
TRANSPORT /MIXING/ TECHNIQUES SUGGEST LOW-END WIND ADVISORY WINDS
WILL BE POSSIBLE MOST AREAS AT LEAST INTO THE MID AFTERNOON...AND
PARTICULARLY NORTH OF THE OHIO RIVER.
IN TERMS OF SNOW...THE TEMP DROP IN THE WAKE OF THE COLD FRONT IS
FAST AND IMPRESSIVE...AND MAY INDUCE RAPID ROAD FREEZING AND ICING
EVEN IN THE DRY SLOT EARLY THURSDAY EVENING. LATER IN THE
EVENING...SECONDARY PV WRAPS SOUTHEASTWARD /ACCOMPANIED BY LOW
LEVEL WIND MAX MENTIONED ABOVE/ AND SPREADS GOOD FORCING FOR UVM
INTO AREAS NORTH OF I-70 WHERE SNOW/SNOW SHOWERS WILL BE ABUNDANT.
SEE A NICE LITTLE STRIPE OF 1-2 INCHES OF SNOW ACROSS WCNTL INTO
CNTL OH...SO DECIDED TO BE SIMPLE AND COMBINE THE THREATS OF
STRONG WINDS/SNOW/REDUCED VISIBILITIES/ICY ROADS INTO A WINTER
WEATHER ADVISORY. SNOW AMOUNTS WON/T BE SIGNIFICANT...BUT COMING
OUT OF A LONG TERM WARM PERIOD...PAVEMENT SUBSURFACES ARE
ATYPICALLY WARM. WITH VERY COLD AIR AND PERSISTENT SNOW
SHOWERS/STRONG WINDS REMOVING THIS WARMTH FROM THE SKIN SURFACE OF
THE PAVEMENT...SETUP IS SUCH THAT ROADS COULD BECOME EXTREMELY
SLIPPERY IN THE WINTER WX ADVISORY AREA ESP LATER THURS NIGHT INTO
MUCH OF FRIDAY WHERE SNOW IS PERSISTENT. COMBINED WITH RAPID VSBY
CHANGES IN SNOW SHOWERS...THESE SITUATIONS CAN BE SNEAKY-
DANGEROUS...ESPECIALLY CONSIDERING THE MILD WINTER THUS FAR. DON/T
SEE A SIGNAL IN THE DATA FOR SNOW RATIOS AS DIFFERENT THAN CLIM0 -
MUCH OF LIFT/SATURATIONS REMAINS BELOW THE DENDRITIC GROWTH ZONES
AND COBB RATIOS FROM A WEALTH OF SOURCES ARE ALL FROM 8:1 TO 11:1
FOR MOST OF THE PERIOD. LOWEST CONFIDENCE IN WINTER WX ADVISORY
CONDITIONS IN AROUND CMH METRO...BUT DIDN/T WANT TO GET CUTE AT
THIS MOMENT AND TRY TO BE TOO FINE GIVEN INHERENT UNCERTAINTIES.
ISSUED THE WIND ADVISORY FOR AREAS IN THE SOUTH NOT EXPECTED TO
SEE SIGNIFICANT ENOUGH SNOW FOR TRAVEL ISSUES...BUT EVEN IN THESE
AREAS CANNOT RULE OUT A PERIOD OF SLIPPERY TRAVEL AS MAIN WAVE
TRAVERSES THE AREA FRIDAY NIGHT INTO FRIDAY MORNING WITH THE
STRONG WINDS AND COLD TEMPS AND WARM ROAD SURFACES CAUSING
SLIPPERY TRAVEL. FUTURE SHIFTS MAY NEED TO CONSIDER EXPANSION OF
THE WINTER WEATHER ADVISORY IF SNOW SHOWERS ARE MORE WIDESPREAD OR
CONTAIN HEAVIER RATES THAN CURRENTLY ANTICIPATED.
CONDITIONS RAPIDLY IMPROVE FRIDAY EVENING AS WINDS DECREASE AND
SYSTEM PULLS OUT.
&&
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
THE LONG TERM WILL START OFF WITH SOME LINGERING CLOUDS AND A
POSSIBLE FLURRY SATURDAY MORNING BEHIND THE DEPARTING STORM SYSTEM.
CLOUDS SHOULD BE OUT OF THE AREA BY SATURDAY NIGHT AS HIGH PRESSURE
EXTENDS ACROSS THE AREA. WENT BELOW THE MODEL CONSENSUS FOR FORECAST
HIGHS ON SATURDAY ACROSS THE NORTH WHERE CLOUDS AND REMNANT SNOW
COVER WILL KEEP TEMPERATURES DOWN. WENT BELOW THE MODEL CONSENSUS
FOR THE WHOLE AREA SATURDAY NIGHT WITH HIGH PRESSURE AND DECREASING
WINDS HELPING TO PRODUCE FAVORABLE CONDITIONS FOR RADIATIONAL
COOLING.
SUNDAY WILL BE A TRANSITION DAY AS THE HIGH SHIFTS EAST OF THE AREA
AND WEAK LOW PRESSURE APPROACHES FROM THE WEST. ON SUNDAY
NIGHT...CLOUD COVER WILL INCREASE AHEAD OF THIS WEAK LOW AS MOISTURE
GETS DRAWN NORTHWARD INTO THE OHIO VALLEY. MODELS ARE IN FAIR
AGREEMENT ON BRINGING LIGHT PRECIPITATION TO THE FORECAST AREA
SOMETIME BETWEEN EARLY MONDAY MORNING AND EARLY MONDAY
AFTERNOON...DEPENDING ON WHICH MODEL YOU LOOK AT. THIS TIMING WILL
PROBABLY HELP TO DETERMINE PRECIPITATION TYPE. GFS HAS THE COLDEST
AND QUICKEST ARRIVAL OF PRECIPITATION...ALLOWING FOR A PARTIAL MIX
OF RAIN AND SNOW ACROSS MUCH OF THE AREA FOR THIS EVENT. THE
ECMWF/CANADIAN MODELS ARE TOO WARM ALOFT FOR ANY SNOW...HOWEVER
BRING LIGHT RAIN INTO THE AREA WHEN TEMPERATURES ARE NEAR FREEZING
AT THE SURFACE. THEREFORE...THIS PARTICULAR TIME PERIOD WILL NEED
ADJUSTING AS THE TIME DRAWS NEARER. REGARDLESS IT DOES APPEAR THAT
QPF AMOUNTS WILL BE LIGHT FOR THIS LOW WITH NO ACCUMULATION OF ANY
SNOW EXPECTED IF ANY MIX DOES OCCUR.
AFTER A FAIR WEATHER DAY ON CHRISTMAS...THE ATTENTION TURNS TO
CHRISTMAS NIGHT INTO WEDNESDAY AS A VIGOROUS LOW PRESSURE SYSTEM
APPROACHES OUR REGION. MODELS ARE STILL SHIFTING WITH TIMING AND
LOCATION FOR THIS LOW BETWEEN RUNS. HOWEVER...IT DOES APPEAR ONE WAY
OR ANOTHER THAT PRECIPITATION WILL OCCUR. BUMPED UP POPS TO 50
PERCENT. COULD HAVE GONE HIGHER FOR POPS IF THERE WERE NOT STILL
TIMING DIFFERENCES AMONGST THE MODELS.
&&
.AVIATION /00Z THURSDAY THROUGH MONDAY/...
FLIGHT CONDITIONS START OUT IN DECENT SHAPE WITH WEAK HIGH
PRESSURE MOVING IN. OTHER THAN MVFR CEILINGS AT LCK...EXPECT
VFR AT OTHER SITES UNDER HIGH THIN CLOUDS.
WEATHER WILL CHANGE FOR THE WORSE ON THURSDAY DUE TO A POWERFUL
COLD FRONT TRAILING GREAT LAKES LOW PRESSURE. SHOWERS WILL DEVELOP
AT ALL SITES BY MID AFTERNOON. MVFR CONDITIONS WILL OCCUR BY THE
END OF THE FORECAST AS THE FRONT ENTERS THE AREA. WINDS WILL BE A
PROBLEM WITH GUSTS OVER 30 KNOTS OUT OF THE SOUTH TO SOUTHWEST.
SNOW WILL MIX IN AT CVG AFTER 00Z FRIDAY AS COLDER AIR WORKS IN.
&&
.ILN WATCHES/WARNINGS/ADVISORIES...
OH...WINTER WEATHER ADVISORY FROM 4 PM THURSDAY TO 4 PM EST FRIDAY
FOR OHZ026-034-035-042>046-051>056-060>062.
WIND ADVISORY FROM 4 PM THURSDAY TO 4 PM EST FRIDAY FOR
OHZ063>065-070>074-077>082-088.
KY...WIND ADVISORY FROM 4 PM THURSDAY TO 4 PM EST FRIDAY FOR
KYZ089>100.
IN...WINTER WEATHER ADVISORY FROM 4 PM THURSDAY TO 4 PM EST FRIDAY
FOR INZ050-058-059.
WIND ADVISORY FROM 4 PM THURSDAY TO 4 PM EST FRIDAY FOR INZ066-
073>075-080.
&&
$$
SYNOPSIS...BINAU
NEAR TERM...BINAU
SHORT TERM...BINAU
LONG TERM...LATTO
AVIATION...CONIGLIO
AREA FORECAST DISCUSSION
NWS STATE COLLEGE PA
459 PM EST TUE DEC 18 2012
.SYNOPSIS...
BRISK AND DRIER CONDITIONS WILL PREVAIL ACROSS THE COMMONWEALTH
TONIGHT. SOME LAKE EFFECT SNOW SHOWERS AND FLURRIES WILL AFFECT
NORTHWEST SECTIONS. A MOISTURE LIMITED UPPER AIR DISTURBANCE AND
ASSOCIATED WEAK SURFACE LOW PRESSURE WILL PRODUCE SOME LIGHT SNOW
SHOWERS FROM EASTERN OHIO THROUGH THE LAUREL HIGHLANDS EARLY
WEDNESDAY MORNING...RESULTING IN A LIGHT COATING OF SNOW IN SOME
LOCATIONS. OTHERWISE...DRY CONDITIONS WILL PREVAIL UNTIL THURSDAY
AS A RIDGE OF HIGH PRESSURE DRIFTS ACROSS THE REGION ON WEDNESDAY.
ANOTHER SIGNIFICANT LOW PRESSURE SYSTEM AND ASSOCIATED COLD FRONT
WILL IMPACT THE LOCAL WEATHER WITH RAIN...FOLLOWED BY SNOW SHOWERS
AND GUSTY WEST TO NORTHWEST WINDS LATE THIS WEEK INTO THE WEEKEND.
&&
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
21Z RADAR LOOP SHOWING RAIN/SNOW SHOWERS RAPIDLY DIMINISHING FROM
WEST TO EAST ACROSS THE AREA...AS UPPER LVL TROF AND ASSOC
DEFORMATION BAND/DEEP LYR MOISTURE SHIFTS EAST. BASED ON LATEST
RADAR TRENDS AND RAP OUTPUT...WILL REMOVE MENTION OF PRECIP OVR
THE N MTNS BY ARND 00Z. GUSTY WEST WINDS CONTINUE TO BUFFET AREA
AS OF 21Z. HOWEVER...EXPECT THEM TO SUBSIDE OVERNIGHT AS SFC
RIDGING BUILDS INTO THE AREA.
NEXT UPSTREAM SHORTWAVE...OVR CHICAGO AT 21Z...WILL TRACK INTO
WESTERN PA LATE TONIGHT...WITH ASSOCIATED WEAK SFC LOW PRESSURE
PUSHING INTO EASTERN OHIO BEFORE GETTING ABSORBED INTO THE STRONG
PRESSURE GRADIENT ACROSS THE REGION. THIS COULD PRODUCE SOME
TRACE TO COATING AMOUNTS OF SNOW ACROSS THE LAUREL HIGHLANDS LATE
TONIGHT. LITTLE IF ANY ACCUMS EXPECTED THIS EVENING OVER WARREN
AND MCKEAN COUNTIES. SOME UNCERTAINTY WITH REGARDS TO PTYPE...AS
LYR OF MOISTURE WILL BE RELATIVELY SHALLOW AND MAY NOT BE DEEP
ENOUGH TO SUPPORT ICE CRYSTALS. WILL REEVALUATE THIS EVENING AND
MAY MENTION THE POSSIBILITY OF FZDZ/DZ IN ADDITION TO SHSN.
SOME PARTIAL CLEARING REACHING INTO THE WEST CENTRAL MOUNTAINS
AND LAURELS THIS EVENING...THEN CLOUDS INCREASE AGAIN LATER ON AS
THE AFOREMENTIONED DISTURBANCE APPROACHES. MIN TEMPS WILL BE
TRICKY AS A RESULT OVER THE WEST...BUT EXPECT READINGS TO FALL
BELOW FREEZING FROM THE LAURELS NORTHWARD TO THE NORTHWEST
MOUNTAINS AND EASTWARD THROUGH THE ENDLESS MOUNTAIN REGION. LOWS
FROM THE CENTRAL MOUNTAINS TO THE LOWER SUSQ ARE LIKELY TO BE IN
THE L/M 30S.
&&
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
SHORTWAVE RIDGING ALOFT AND BUILDING SFC HIGH PRESSURE WILL
PROVIDE A DECENT DAY ACROSS CENTRAL PA ON WEDNESDAY...AFTER ANY
AM -SHSN/-FZDZ DISSIPATE WITH THE EXIT OF THE WEAKENING LO PRE
SYSTEM.
PARTLY TO MOSTLY CLOUDY SKIES CENTRAL AND NW AREAS...AND MOSTLY SUNNY
SKIES ARE EXPECTED IN THE SOUTHEAST. VERTICAL MIXING UP TO 2-3
KFT AGL...COMBINED WITH THE TAIL END OF THE 925-850MB THERMAL
TROUGH AND NW FLOW ALOFT WILL YIELD 10-15 KT NW WINDS FOR THE
MIDDAY AND AFTERNOON HOURS. HIGH TEMPS SHOULD REACH THE UPPER 30S
TO LOWER 40S OVER THE MOUNTAINS...AND APPROACH 50F THROUGH THE
LOWER AND MIDDLE SUSQ RIVER VALLEY AIDED BY DOWNSLOPING FLOW. THIS
WILL STILL BE NEARLY 10F ABOVE NORMAL FOR THIS TIME OF YEAR.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
***ACTIVE WINTER PATTERN IN STORE LATE THIS WEEK INTO THE WEEKEND***
A SPLIT FLOW UPPER TROUGH ALIGNED ALONG THE FRONT RANGE OF THE
ROCKIES WITH A VERY POTENT SRN STREAM SHORT WAVE OVER THE FOUR
CORNERS REGION WILL EJECT OUT INTO THE CENTRAL/SRN PLAINS AND REACH
THE MID MS VLY BY 12Z THU. THE SRN STREAM TROUGH WILL DEEPEN AND
INTENSIFY WHILE ATTEMPTING TO PHASE WITH THE NRN STREAM FEATURE.
THIS WILL ALLOW A LEE SURFACE WAVE TO DEVELOP NEAR THE TX/OK
PANHANDLES...WITH INTENSIFICATION EXPECTED AS IT TRACKS ENEWD THRU
MO INTO CENTRAL IL BY THE END OF DAY2. THE SURFACE LOW WILL COMPLETE
CYCLOGENESIS ON DAY 3...CONTINUING TO DEEPEN AS IT LIFTS NEWD AND
OCCLUDES NEAR THE THUMB OF LOWER MI. WITH THE EXCEPTION OF THE
NAM...THE 18/12Z MODELS HAVE SHIFTED WEST...A BIT SLOWER...WITH
THE SFC LOW FCST TO TRACK NEWD FROM OKLAHOMA INTO THE GREAT LAKES
REGION. MEANWHILE...ITS ASSOCIATED POWERFUL/SHARP COLD FRONT WILL
SWEEP EWD AND CROSS THE APPLCHNS THUR NIGHT AND REACH THE MID-
ATL/SOUTHEAST COAST BY 12Z FRI. A TRIPLE POINT/SECONDARY LOW WILL
FORM OVER THE VA PIEDMONT AND TRACK NEWD TOWARD THE
POCONOS/CATSKILLS...AS THE MID-UPPER TROUGH GOES NEGATIVE TILT.
THE DEEP LOW EVENTUALLY BECOMES VERTICALLY STACKED INVOF UPSTATE
NY BY 00Z SAT.
INTENSE MID LEVEL HEIGHT FALLS...ON THE ORDER OF 200-250 M IN 12
HR...WILL SHIFT EWD FROM THE OH VLY ACROSS CENTRAL PA THUR NIGHT.
THE EXIT REGION OF A 100KT JET MAX ROUNDING THE BASE OF THE UPPER
LOW/MID LEVEL HEIGHT FALL CENTER WILL PROVIDE AMPLE LG SCALE
LIFT/DIVERGENCE ALOFT...WHILE VERY STRONG +3-5 SIGMA /50-60KT/ SLY
850MB LLJ WILL DRAW A NARROW RIBBON OF MODEST PWATS NWD ALONG THE
SHARP COLD FRONTAL BOUNDARY. THE DEEP-LAYER FORCING AND STRONG
DYNAMICS WILL SUPPORT A BAND OF MODERATE FRONTAL PCPN...WHICH MAY
TAKE ON THE FORM OF A NARROW COLD-FRONTAL RAIN BAND /NCFRB/. DAY 3
QPF AMTS RANGE BTWN 0.50-0.75 INCHES...WITH A MAX AROUND 1 INCH
INTO ERN PA NEAR THE TRIPLE POINT LOW TRACK. A BLEND OF
NAM/GFS/SREF HR THERMAL PROFILES ALLOWS FOR A PTYPE CHANGEOVER
FROM RAIN TO SNOW ON THE BACKSIDE OF THE FRONTAL PCPN BAND...AS
STRONG DYNAMIC COOLING AND LLVL CAA RAPIDLY DROPS TEMPS IN THE COLUMN.
THIS SUGGESTS A LGT SNOW ACCUM IS POSSIBLE LATE THU NIGHT INTO
EARLY FRI...ESPECIALLY OVR THE N-CNTRL AND NERN ZONES. IN
ADDITION...A LOW PROB FOR -FZRA WILL EXIST OVR THE NRN MTNS EARLY
THU AT THE ONSET OF PCPN...AS STG LLVL NE AGEO WINDS KEEPS COLD AIR
ENTRENCHED ALONG AND EAST OF THE ALLEGHENIES. THERE ARE STRONG
INDICATIONS FOR CAD ON THU...SO DESPITE THE STG WAA TEMPS MAY
STRUGGLE TO GET MUCH ABOVE 40F ESP IN THE NRN TIER. WILL BE A
TRICKY TEMP FCST...WITH HIGHS POSSIBLY OCCURRING JUST AFTER
FROPA/WIND SHIFT AND BEFORE THE COLD AIR RUSHES IN FROM THE WEST.
THE MID-LATE DECEMBER PATTERN STABILIZES TO SOME EXTENT HEADING
INTO THE WEEKEND...AS THE DEEP SFC/UPPER SYSTEM SHOULD PROVE SLOW
TO EXIT NRN NEW ENGLAND AND THE CANADIAN MARITIMES WORKING INTO
BLOCKED HIGH LATITUDE FLOW. THIS WILL OPEN THE DOOR FOR A
PERSISTENT...SEASONABLY COLD AND BLUSTERY NW FLOW TO MAINTAIN NEAR
TO BELOW NORMAL TEMPERATURES THROUGH THE WEEKEND AND PERHAPS INTO
EARLY NEXT WEEK. MORE IMPORTANTLY...THIS WILL LIKELY LEAD TO A
PROTRACTED LAKE EFFECT SNOW EVENT FROM FRIDAY-SUNDAY...WITH
SIGNIFICANT SNOW ACCUMULATIONS POSSIBLE OVER THE NW MTNS AND
ALLEGHENY RIDGES/LAUREL HIGHLANDS. WILL CONTINUE TO MENTION THE
HEAVY LAKE EFFECT SNOW THREAT IN THE HWO WITH ABOVE AVG
CONFIDENCE.
THE BROAD CYCLONIC FLOW ALOFT/LAKE EFFECT SNOW REGIME SHOULD LOSE
ITS GRIP ON THE AREA BY EARLY NEXT WEEK. THE 18/12Z ECENS AND
GEFS SHOW A TROUGH DEVELOPING IN THE NATIONS MIDSECTION WHICH
SHOULD FORCE HEIGHTS TO RISE DOWNSTREAM. A PACIFIC SYSTEM IS FCST
TO EMERGE INTO THE CENTRAL US NEXT TUE WHERE SRN PLAINS
CYCLOGENESIS/GULF INFLOW/DEVELOPING PCPN COULD OCCUR TUCKED
UNDERNEATH A MID-HIGHER LATITUDE DOME OF COLDER HIGH PRESSURE TO
THE NORTH. THIS SYSTEM MAY BRING A WINTRY MIXTURE OF PCPN TO THE
REGION AROUND DEC 26TH /NEXT WED/ AS IT LIFTS NEWD THRU THE LWR
MS/TN/OH VLYS AND INTO THE NORTHEAST STATES.
&&
.AVIATION /22Z TUESDAY THROUGH SUNDAY/...
VFR CONDS WILL PREVAIL ACROSS THE LOWER SUSQ...WITH MVFR CONDS
ACROSS THE CENTRAL MOUNTAINS. WESTERN AND NORTHERN HIGH TERRAIN
WILL MVFR TO LCL IFR DUE TO UPSLOPE FLOW AND SCT -SHSN. COLD AIR
AND NORTHWESTERLY FLOW WILL MAINTAIN SNOW SHOWERS AT BFD AND JST
INTO EARLY TONIGHT...FOLLOWED BY SOME IMPROVEMENT TO MVFR LATE.
GUSTY NW WINDS UP TO 35KTS POSSIBLE EARLY TONIGHT...BEFORE
GRADUALLY SUBSIDING. UPPER AIR DISTURBANCE WILL SPREAD MVFR CIGS
AND SCT -SHSN INTO THE LAUREL HIGHLANDS AND VCNTY KJST EARLY
FRIDAY MORNING.
OUTLOOK...
WED...BREEZY NW WIND. MVFR AND -SHSN/FLURRIES POSS NRN AND
WESTERN MTNS...AND MAINLY VFR ELSEWHERE.
THU...RAIN SHOWERS LIKELY. MAINLY VFR WITH MVFR POSS LATE.
FRI...TURNING COLDER. RAIN/SNOW SHOWERS BECOMING ALL SNOW...ESP
NW IN IFR/MVFR. BREEZY WEST WINDS RETURN.
SAT...BREEZY. LAKE EFFECT SNOWS IN NW MTNS WITH MVFR/IFR
CONDITIONS. MVFR POSS CENTRAL. VFR SE.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...DEVOIR
NEAR TERM...DEVOIR/FITZGERALD
SHORT TERM...DEVOIR
LONG TERM...STEINBUGL
AVIATION...DEVOIR/RXR
AREA FORECAST DISCUSSION
NWS STATE COLLEGE PA
743 AM EST TUE DEC 18 2012
.SYNOPSIS...
LOW PRESSURE WILL TRACK NORTHEAST ACROSS SOUTHWESTERN NEW YORK AND
THE FINGER LAKES REGION THIS MORNING. A SOUTHWARD TRAILING COLD
FRONT WILL PUSH EAST ACROSS THE STATE THROUGH EARLY THIS AFTERNOON.
BRISK WEST WINDS AND DRIER AIR WILL FOLLOW THIS FRONT ACROSS THE
CENTRAL AND EASTERN VALLEYS...WHILE RAIN SHOWERS CHANGE TO
OCCASIONAL SNOW SHOWERS ACROSS THE NORTHERN AND WESTERN MOUNTAINS.
A RIDGE OF HIGH PRESSURE WILL DRIFT ACROSS THE REGION ON WEDNESDAY
ACCOMPANIED BY FAIR WEATHER. ANOTHER SIGNIFICANT LOW PRESSURE SYSTEM
AND ATTENDANT COLD FRONT WILL IMPACT THE LOCAL WEATHER WITH
RAIN...FOLLOWED BY SNOW SHOWERS AND GUSTY WEST TO NORTHWEST WINDS
LATE THIS WEEK.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
430 AM UPDATE...
997 MB SFC LOW WAS LOCATED NEAR KBFD AND MOVING NORTHEAST. A FEW
MID/UPPER LEVEL VORT CENTERS INVOF OF THIS LOW WERE HELPING TO
PRODUCE AREAS OF STEADIER LIGHT TO MDT RAIN ACROSS...AND ABOUT 50NM
INLAND FROM THE SE SHORE OF LAKE ERIE.
THE COLD FRONT TRAILING SOUTH FROM THE LOW WILL MOVE STEADILY EAST
ACROSS THE REGION THIS MORNING...EXITING THE SUSQ VALLEY BY EARLY
THIS AFTERNOON.
AREAS OF FOG NEAR AND JUST TO THE NE OF A SFC WARM FRONT /THAT WAS
LIFTING SLOWLY NEWRD ACROSS THE SUSQ VALLEY/ WILL PERSIST THROUGH
ABOUT 13Z. THE DENSE FOG ADVISORY...PREVIOUSLY IN EFFECT UNTIL 11Z
TODAY...WAS RECENTLY CANCELLED.
VSBYS WILL LIKELY DIP TO BETWEEN 1/4 AND 1/2SM AT TIMES THROUGH
ABOUT 13Z...BUT WIDESPREAD DENSE FOG IS NOT LIKELY AS THE LIGHT AND
VARIABLE WINDS QUICKLY FRESHEN TO 10-15 KTS FROM THE WEST-SOUTHWEST
JUST AHEAD OF THE CFRONT THIS MORNING.
LATEST RUC AND SREF GUIDANCE SHOWS THE RAIN SHOWERS BECOMING/STAYING
ISOLATED TO SCATTERED ACROSS MUCH OF CENTRAL AND SERN PENN...WHILE
THE MORE FREQUENT RAIN SHOWERS CHANGE TO MAINLY SNOW SHOWERS AFTER
15Z AS THE FREEZING LEVEL QUICKLY DESCENDS FROM SVRL KFT AGL...DOWN
TO NEAR THE SFC FOR THE MIDDAY AND AFTERNOON HOURS.
A FEW INTERVALS OF SUNSHINE DEVELOPING THROUGH THE LIFTING STRATO CU
CLOUD BASES WILL HELP TO BOOST TEMPS INTO THE 40S AND LOWER 50S
THROUGHOUT THE CENTRAL AND SE VALLEY FOR A MIDDAY HIGH BEFORE LLVL
COLD ADVECTION STRENGTHENS TO TRIM TEMPS GRADUALLY DOWNWARD FROM 18Z
ON.
A LIGHT COATING OF SNOW /TO PERHAPS ONE INCH/ COULD ACCUMULATE ON
THE RIDGE TOPS OF THE LAURELS AND NW MTNS LATER THIS AFTERNOON AND
EVENING AS TEMPS DIP INTO THE LOWER 30S.
IN ADDITION...WEST TO NORTHWEST WINDS WILL INCREASE LATE THIS
MORNING AND SHOULD GUST BETWEEN 30-35 MPH THIS AFTERNOON.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
WEST-NORTHWEST WINDS WILL STAY GUSTY THIS EVENING WITH SNOW SHOWERS
DIMINISHING...BEFORE THE BASE OF THE SUBSIDENCE INVERSION GRADUALLY
LOWERS. THE RELATIVELY SHALLOW AND WARM CLOUD TEMPS OF -3C TO -6C
WILL SUPPORT JUST SOME LIGHT SNOW GRAINS OR PATCHY FREEZING DRIZZLE
ACROSS THE WESTERN MTNS TONIGHT.
ELSEWHERE PARTLY TO MOSTLY CLOUDY SKIES WILL BE FOUND ACROSS THE
CENTRAL RIDGE AND VALLEY REGION...AND SUSQ VALLEY.
MIN TEMPS TONIGHT WILL VARY FROM THE U20S TO AROUND 32F ACROSS THE
MTNS...TO THE LOWER AND MID 30S ELSEWHERE.
A RIDGE OF HIGH PRESSURE AT THE SFC AND ALOFT WILL DRIFT EAST ACROSS
THE STATE WEDNESDAY...ACCOMPANIED BY PARTLY...TO MOSTLY CLOUDY SKIES
CENTRAL AN NW...AND MOSTLY SUNNY SKIES IN THE SOUTHEAST.
VERTICAL MIXING UP TO 2-3 KFT AGL...COMBINED WITHE THE TAIL END OF
THE 925-850MB THERMAL TROUGH AND NW FLOW ALOFT WILL YIELD 10-15 KT
NW WINDS FOR THE MIDDAY AND AFTERNOON HOURS.
MAX TEMPS IN THE U30S TO LOWER 40S ACROSS THE MTNS...AND NEAR 50F
THROUGHOUT THE LOWER AND MIDDLE SUSQ VALLEY...WILL BE NEARLY 10F
ABOVE NORMAL.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
MEDIUM RANGE MODEL AND ENSEMBLE GUIDANCE REMAINS IN PRETTY GOOD
AGREEMENT WITH RESPECT TO THE LARGE SCALE PATTERN FROM THE SECOND
HALF OF THE WEEK THROUGH THE WEEKEND. A DEEPENING CYCLONE WILL MOVE
OUT OF THE MID-MS VALLEY INTO THE GREAT LAKES BY 00Z FRI...AND THEN
OCCLUDE INTO NORTHERN NEW ENGLAND AS IT SLOWS AMID AMPLIFYING FLOW.
THE GFS/GEFS REMAIN A BIT QUICKER THAN THE ECMWF/ECENS WITH THE
PROGRESSION OF THIS SYSTEM...INCLUDING THE TRAILING/SHARP COLD
FRONT. IT APPEARS SECONDARY SFC WAVE DEVELOPMENT IS LKLY ALONG THE
COLD FRONT INVOF NJ AS EMPHASIZED MORE-SO BY THE DETERMINISTIC
/NON-NCEP/ OPER ECMWF AND CANADIAN GEM. STG SLY LLJ +3-4SD AHEAD OF
THE COLD FRONT WILL TRANSPORT ABOVE NORMAL MSTR/PWAT NWD ALONG THE
FRONT. DIFFLUENT FLOW ALOFT ASSOC WITH 100KT SWLY UPPER JET ALONG
WITH STG HEIGHT FALL CENTER CROSSING THE LWR LAKES WILL SUPPORT A
BAND OF MOD FRONTAL RAINS. DESPITE STG SLY FLOW/WAA JUST OFF THE
DECK...MESO MODEL DATA INDICATES MUCH OF THE CWA /ESP THE NRN MTNS/
MAY BE CAD IN RESPONSE TO STG LLVL AGEO WINDS OUT OF THE ENE. HAVE
NOT LOOKED CLOSELY BUT THE LG SCALE PATTERN DOES SEEM TO SUPPORT A
LOW-TOPPED NCFRB. MAY ALSO NEED TO WATCH FOR STG PRES FALL/RISE
COUPLET WHICH MAY LEAD TO A BRIEF PERIOD OF POST-FRONTAL HIGH
WINDS/GUSTS.
COLD AIR WILL RUSH INTO THE AREA IN THE WAKE OF A SHARP COLD
FROPA...AND MAY CATCH-UP TO THE BACKSIDE OF THE DEPARTING
SYNOPTIC PCPN SHIELD...CHANGING RAIN OVER THE SNOW AT THE END OF
THE EVENT. THIS KIND OF DETAIL WILL NEED TO BE RESOLVED AT SHORTER
RANGES. A PROLONGED PERIOD OF SEASONABLY COLD AND BLUSTERY
NORTHWEST/CYCLONIC FLOW WILL PREVAIL FROM FRIDAY INTO THE UPCOMING
WEEKEND...WHICH WILL SUPPORT A PROLONGED PERIOD OF LAKE
EFFECT/UPSLOPE SNOW EVENT OVER THE NORTHWEST MTNS AND LAUREL
HIGHLANDS. THERE ARE STRONG INDICATIONS FROM THE MODELS AND
ENSEMBLES THAT SEVERAL INCHES OF SNOW IS POSSIBLE - IF NOT LKLY -
PARTICULARLY IN THE NW MTNS. WILL NEED TO ADD THIS WINTER WX
THREAT INTO THE HWO...WITH MEDIUM TO RELATIVELY HIGH CONFIDENCE
EVEN AT THIS RANGE.
SEASONABLY COLD...WINTERTIME TEMPERATURES SHOULD PERSIST INTO EARLY
NEXT WEEK. EVEN THOUGH TEMPS WILL BE NEAR NORMAL...IT WILL FEEL
MUCH COLDER GIVEN THE MILD DECEMBER THUS FAR. CYCLONIC FLOW ALOFT
SHOULD LOSE ITS GRIP ON THE NERN CONUS BY EARLY NEXT WEEK...AS
GEFS AND ECENS BOTH SHOW A TROUGH DEVELOPING OVER THE CENTRAL U.S.
BY CHRISTMAS DAY.
&&
.AVIATION /13Z TUESDAY THROUGH SATURDAY/...
LOW PRESSURE WILL TRACK NORTHEAST ACROSS SOUTHWESTERN NEW YORK AND
THE FINGER LAKES REGION THIS MORNING. THIS WILL KEEP MAINLY IFR
CONDITIONS ACROSS CENTRAL PA FOR SEVERAL MORE HOURS. A STEADIER
RAIN WILL IMPACT KBFD WHILE SCATTERED TO NUMEROUS SHOWERS AND
AREAS OF DRIZZLE SLIDE ACROSS REMAINDER OF NORTHERN AND CENTRAL
MTNS. WINDS WILL TURN WESTERLY THROUGH MID MORNING.
A COLD FRONT WILL CROSS THE STATE EARLY TODAY...WHICH WILL BRING
CHANGES. WESTERLY WINDS WILL PICK UP THIS AFTERNOON...GUSTING UP
TO 35-40 MPH. WITH DOWNSLOPE COMPONENT TO THE WIND...THE LOWER
SUSQ WILL SEE CONDITIONS IMPROVE TO VFR. CENTRAL MTNS WILL IMPROVE
TO MVFR...BUT WESTERN AND NORTHERN HIGHER TERRAIN WILL REMAIN IFR
AS COLD POOL ALOFT MOVES THROUGH IN ADDITION TO FORCED UPSLOPE
FLOW OF COOL/MOIST AIR AT LOW LEVELS TO KEEP LOW CLOUDS IN PLACE.
PRECIP WILL TURN TO SNOW SHOWERS BY LATE MORNING FROM KBFD-
KJST...AND LOCAL RESTRICTIONS WILL BE LIKELY.
EXPECT PARTIAL CLEARING ACROSS THE RIDGE AND VALLEY REGION OF PA
TONIGHT. THE COLD AIR AND NORTHWESTERLY FLOW SHOULD ALLOW FOR
BANDS OF LAKE ENHANCED SNOW AT BFD AND JST INTO EARLY
TONIGHT...FOLLOWED BY SOME IMPROVEMENT TO MVFR LATE. GUSTY NW
WINDS UP TO 35KTS POSSIBLE EARLY TONIGHT...BEFORE GRADUALLY
SUBSIDING.
OUTLOOK...
WED...BREEZY NW WIND. MVFR POSS NRN AND WESTERN MTNS...AND MAINLY VFR
ELSEWHERE.
THU...RAIN SHOWERS LIKELY. MAINLY VFR WITH MVFR POSS LATE.
FRI...TURNING COLDER. RAIN/SNOW SHOWERS BECOMING ALL SNOW...ESP
NW IN IFR/MVFR. BREEZY WEST WINDS RETURN.
SAT...BREEZY. LAKE EFFECT SNOWS IN NW MTNS WITH MVFR/IFR
CONDITIONS. MVFR POSS CENTRAL. VFR SE.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...LAMBERT
NEAR TERM...LAMBERT
SHORT TERM...LAMBERT
LONG TERM...LAMBERT/STEINBUGL
AVIATION...RXR
AREA FORECAST DISCUSSION
NWS STATE COLLEGE PA
445 AM EST TUE DEC 18 2012
.SYNOPSIS...
LOW PRESSURE WILL TRACK NORTHEAST ACROSS SOUTHWESTERN NEW YORK AND
THE FINGER LAKES REGION THIS MORNING. A SOUTHWARD TRAILING COLD
FRONT WILL PUSH EAST ACROSS THE STATE THROUGH EARLY THIS AFTERNOON.
BRISK WEST WINDS AND DRIER AIR WILL FOLLOW THIS FRONT ACROSS THE
CENTRAL AND EASTERN VALLEYS...WHILE RAIN SHOWERS CHANGE TO
OCCASIONAL SNOW SHOWERS ACROSS THE NORTHERN AND WESTERN MOUNTAINS.
A RIDGE OF HIGH PRESSURE WILL DRIFT ACROSS THE REGION ON WEDNESDAY
ACCOMPANIED BY FAIR WEATHER. ANOTHER SIGNIFICANT LOW PRESSURE SYSTEM
AND ATTENDANT COLD FRONT WILL IMPACT THE LOCAL WEATHER WITH
RAIN...FOLLOWED BY SNOW SHOWERS AND GUSTY WEST TO NORTHWEST WINDS
LATE THIS WEEK.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
430 AM UPDATE...
997 MB SFC LOW WAS LOCATED NEAR KBFD AND MOVING NORTHEAST. A FEW
MID/UPPER LEVEL VORT CENTERS INVOF OF THIS LOW WERE HELPING TO
PRODUCE AREAS OF STEADIER LIGHT TO MDT RAIN ACROSS...AND ABOUT 50NM
INLAND FROM THE SE SHORE OF LAKE ERIE.
THE COLD FRONT TRAILING SOUTH FROM THE LOW WILL MOVE STEADILY EAST
ACROSS THE REGION THIS MORNING...EXITING THE SUSQ VALLEY BY EARLY
THIS AFTERNOON.
AREAS OF FOG NEAR AND JUST TO THE NE OF A SFC WARM FRONT /THAT WAS
LIFTING SLOWLY NEWRD ACROSS THE SUSQ VALLEY/ WILL PERSIST THROUGH
ABOUT 13Z. THE DENSE FOG ADVISORY...PREVIOUSLY IN EFFECT UNTIL 11Z
TODAY...WAS RECENTLY CANCELLED.
VSBYS WILL LIKELY DIP TO BETWEEN 1/4 AND 1/2SM AT TIMES THROUGH
ABOUT 13Z...BUT WIDESPREAD DENSE FOG IS NOT LIKELY AS THE LIGHT AND
VARIABLE WINDS QUICKLY FRESHEN TO 10-15 KTS FROM THE WEST-SOUTHWEST
JUST AHEAD OF THE CFRONT THIS MORNING.
LATEST RUC AND SREF GUIDANCE SHOWS THE RAIN SHOWERS BECOMING/STAYING
ISOLATED TO SCATTERED ACROSS MUCH OF CENTRAL AND SERN PENN...WHILE
THE MORE FREQUENT RAIN SHOWERS CHANGE TO MAINLY SNOW SHOWERS AFTER
15Z AS THE FREEZING LEVEL QUICKLY DESCENDS FROM SVRL KFT AGL...DOWN
TO NEAR THE SFC FOR THE MIDDAY AND AFTERNOON HOURS.
A FEW INTERVALS OF SUNSHINE DEVELOPING THROUGH THE LIFTING STRATO CU
CLOUD BASES WILL HELP TO BOOST TEMPS INTO THE 40S AND LOWER 50S
THROUGHOUT THE CENTRAL AND SE VALLEY FOR A MIDDAY HIGH BEFORE LLVL
COLD ADVECTION STRENGTHENS TO TRIM TEMPS GRADUALLY DOWNWARD FROM 18Z
ON.
A LIGHT COATING OF SNOW /TO PERHAPS ONE INCH/ COULD ACCUMULATE ON
THE RIDGE TOPS OF THE LAURELS AND NW MTNS LATER THIS AFTERNOON AND
EVENING AS TEMPS DIP INTO THE LOWER 30S.
IN ADDITION...WEST TO NORTHWEST WINDS WILL INCREASE LATE THIS
MORNING AND SHOULD GUST BETWEEN 30-35 MPH THIS AFTERNOON.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
WEST-NORTHWEST WINDS WILL STAY GUSTY THIS EVENING WITH SNOW SHOWERS
DIMINISHING...BEFORE THE BASE OF THE SUBSIDENCE INVERSION GRADUALLY
LOWERS. THE RELATIVELY SHALLOW AND WARM CLOUD TEMPS OF -3C TO -6C
WILL SUPPORT JUST SOME LIGHT SNOW GRAINS OR PATCHY FREEZING DRIZZLE
ACROSS THE WESTERN MTNS TONIGHT.
ELSEWHERE PARTLY TO MOSTLY CLOUDY SKIES WILL BE FOUND ACROSS THE
CENTRAL RIDGE AND VALLEY REGION...AND SUSQ VALLEY.
MIN TEMPS TONIGHT WILL VARY FROM THE U20S TO AROUND 32F ACROSS THE
MTNS...TO THE LOWER AND MID 30S ELSEWHERE.
A RIDGE OF HIGH PRESSURE AT THE SFC AND ALOFT WILL DRIFT EAST ACROSS
THE STATE WEDNESDAY...ACCOMPANIED BY PARTLY...TO MOSTLY CLOUDY SKIES
CENTRAL AN NW...AND MOSTLY SUNNY SKIES IN THE SOUTHEAST.
VERTICAL MIXING UP TO 2-3 KFT AGL...COMBINED WITHE THE TAIL END OF
THE 925-850MB THERMAL TROUGH AND NW FLOW ALOFT WILL YIELD 10-15 KT
NW WINDS FOR THE MIDDAY AND AFTERNOON HOURS.
MAX TEMPS IN THE U30S TO LOWER 40S ACROSS THE MTNS...AND NEAR 50F
THROUGHOUT THE LOWER AND MIDDLE SUSQ VALLEY...WILL BE NEARLY 10F
ABOVE NORMAL.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
MEDIUM RANGE MODEL AND ENSEMBLE GUIDANCE REMAINS IN PRETTY GOOD
AGREEMENT WITH RESPECT TO THE LARGE SCALE PATTERN FROM THE SECOND
HALF OF THE WEEK THROUGH THE WEEKEND. A DEEPENING CYCLONE WILL MOVE
OUT OF THE MID-MS VALLEY INTO THE GREAT LAKES BY 00Z FRI...AND THEN
OCCLUDE INTO NORTHERN NEW ENGLAND AS IT SLOWS AMID AMPLIFYING FLOW.
THE GFS/GEFS REMAIN A BIT QUICKER THAN THE ECMWF/ECENS WITH THE
PROGRESSION OF THIS SYSTEM...INCLUDING THE TRAILING/SHARP COLD
FRONT. IT APPEARS SECONDARY SFC WAVE DEVELOPMENT IS LKLY ALONG THE
COLD FRONT INVOF NJ AS EMPHASIZED MORE-SO BY THE DETERMINISTIC
/NON-NCEP/ OPER ECMWF AND CANADIAN GEM. STG SLY LLJ +3-4SD AHEAD OF
THE COLD FRONT WILL TRANSPORT ABOVE NORMAL MSTR/PWAT NWD ALONG THE
FRONT. DIFFLUENT FLOW ALOFT ASSOC WITH 100KT SWLY UPPER JET ALONG
WITH STG HEIGHT FALL CENTER CROSSING THE LWR LAKES WILL SUPPORT A
BAND OF MOD FRONTAL RAINS. DESPITE STG SLY FLOW/WAA JUST OFF THE
DECK...MESO MODEL DATA INDICATES MUCH OF THE CWA /ESP THE NRN MTNS/
MAY BE CAD IN RESPONSE TO STG LLVL AGEO WINDS OUT OF THE ENE. HAVE
NOT LOOKED CLOSELY BUT THE LG SCALE PATTERN DOES SEEM TO SUPPORT A
LOW-TOPPED NCFRB. MAY ALSO NEED TO WATCH FOR STG PRES FALL/RISE
COUPLET WHICH MAY LEAD TO A BRIEF PERIOD OF POST-FRONTAL HIGH
WINDS/GUSTS.
COLD AIR WILL RUSH INTO THE AREA IN THE WAKE OF A SHARP COLD
FROPA...AND MAY CATCH-UP TO THE BACKSIDE OF THE DEPARTING
SYNOPTIC PCPN SHIELD...CHANGING RAIN OVER THE SNOW AT THE END OF
THE EVENT. THIS KIND OF DETAIL WILL NEED TO BE RESOLVED AT SHORTER
RANGES. A PROLONGED PERIOD OF SEASONABLY COLD AND BLUSTERY
NORTHWEST/CYCLONIC FLOW WILL PREVAIL FROM FRIDAY INTO THE UPCOMING
WEEKEND...WHICH WILL SUPPORT A PROLONGED PERIOD OF LAKE
EFFECT/UPSLOPE SNOW EVENT OVER THE NORTHWEST MTNS AND LAUREL
HIGHLANDS. THERE ARE STRONG INDICATIONS FROM THE MODELS AND
ENSEMBLES THAT SEVERAL INCHES OF SNOW IS POSSIBLE - IF NOT LKLY -
PARTICULARLY IN THE NW MTNS. WILL NEED TO ADD THIS WINTER WX
THREAT INTO THE HWO...WITH MEDIUM TO RELATIVELY HIGH CONFIDENCE
EVEN AT THIS RANGE.
SEASONABLY COLD...WINTERTIME TEMPERATURES SHOULD PERSIST INTO EARLY
NEXT WEEK. EVEN THOUGH TEMPS WILL BE NEAR NORMAL...IT WILL FEEL
MUCH COLDER GIVEN THE MILD DECEMBER THUS FAR. CYCLONIC FLOW ALOFT
SHOULD LOSE ITS GRIP ON THE NERN CONUS BY EARLY NEXT WEEK...AS
GEFS AND ECENS BOTH SHOW A TROUGH DEVELOPING OVER THE CENTRAL U.S.
BY CHRISTMAS DAY.
&&
.AVIATION /10Z TUESDAY THROUGH SATURDAY/...
THE HEAVIEST SHOWERS SHOWERS CONTINUE TO MOVE EASTWARD...WITH MAINLY
AREAS OF LIGHT RAIN/DRIZZLE IN CENTRAL PA AT THIS TIME.
LOW PRESSURE NEAR KYNG WILL CONTINUE TO TRACK NORTHEAST...AND INTO
THROUGH WESTERN AND CENTRAL NEW YORK STATE LATE THIS MORNING.
WIDESPREAD IFR TO LIFR CIGS...WITH MVFR TO IFR VSBYS WILL CONTINUE
THROUGH THE MID MORNING HOURS BEFORE A COLD FRONT CROSSES THE STATE
AND BRINGS SOME IMPROVEMENT TO CIGS AND VSBYS ACRS THE CENTRAL AND
ERN VALLEYS DURING THE MIDDAY AND AFTERNOON HOURS AS THE LLVL FLOW
SHIFTS TO WESTERLY.
THE WEST WINDS WILL GUST BETWEEN 28-33KTS DURING THE LATE MORNING
AND AFTERNOON HOURS TODAY.
POOR IFR TO LIFR FLYING CONDITIONS AND UNSETTLED WEATHER CONTINUES
ACRS THE WESTERN AND NRN MTNS FOR MUCH OF TODAY AS THE ORTHOGONAL
FLOW OF COLDER/MOIST AIR ASCENDS THE RIDGES. A CHANGEOVER FROM RAIN
TO SNOW IS EXPECTED FROM KJST TO KFIG AND KBFD LATE THIS MORNING.
EXPECT PARTIAL CLEARING ACROSS THE RIDGE AND VALLEY REGION OF PENN
TONIGHT. THE COLD AIR AND NORTHWESTERLY FLOW SHOULD ALLOW FOR BANDS
OF LAKE ENHANCED SNOW AT BFD AND JST INTO EARLY TONIGHT...FOLLOWED
BY SOME IMPROVEMENT TO MVFR LATE. GUSTY NW WINDS UP TO 35KTS
POSSIBLE EARLY TONIGHT...BEFORE GRADUALLY SUBSIDING.
OUTLOOK...
WED...BREEZY NW WIND. MVFR POSS NRN AND WESTERN MTNS...AND MAINLY VFR
ELSEWHERE.
THU...RAIN SHOWERS LIKELY. MAINLY VFR WITH MVFR POSS LATE.
FRI...TURNING COLDER. RAIN/SNOW SHOWERS BECOMING ALL SNOW...ESP
NW. BREEZY WEST WINDS RETURN.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...LAMBERT
NEAR TERM...LAMBERT
SHORT TERM...LAMBERT
LONG TERM...LAMBERT/STEINBUGL
AVIATION...LAMBERT/RXR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NWS RAPID CITY SD
1051 PM MST MON DEC 17 2012
.AVIATION...06Z TAFS
MVFR CIGS/IFR VSBY WILL BE FOUND ACROSS THE AREA WITH SCATTERED
SNOW SHOWERS...MAINLY FROM THE BLACK HILLS INTO CENTRAL SOUTH
DAKOTA. LIFR CIGS/VSBY WITH STRATUS/FZFG OVER CENTRAL SOUTH
DAKOTA WILL LINGER THROUGH THE NIGHT ALONG AND EAST A LINE FROM
KHEI-KPHP-KVTN. CONDITIONS WILL FROM WEST TO EAST LATE TONIGHT.
&&
.PREV DISCUSSION... /ISSUED 705 PM MST MON DEC 17 2012/
DISCUSSION...CURRENT SURFACE MAP SHOWS WARM FRONT ACROSS EASTERN
MONTANA INTO FAR WESTERN SOUTH DAKOTA...WITH WEAK LOW ALONG THE
FRONT NEAR THE BLACK HILLS. BAND OF CONVECTIVE SNOW HAS DEVELOPED
FROM NEAR GILLETTE TO THE NORTHERN BLACK HILLS. 18Z NAM/00Z RUC
SPREAD THIS CONVECTIVE SNOW ACROSS NORTHWEST SOUTH DAKOTA
OVERNIGHT. 00Z RAP IS GIVING 0.25-0.50 INCHES OF QPF ACROSS
NORTHWEST SOUTH DAKOTA OVERNIGHT...WITH UP TO 6 INCHES OF SNOW.
18Z NAM A LITTLE MORE REALISTIC WITH NARROW BAND OF 1-2 INCHES OF
SNOW. 00Z NAM IS COMING IN AND KEEPS THE ACCUMULATING SNOW
CONFINED TO THE BLACK HILLS.
FORECAST UPDATED TO INCREASE POPS THROUGH EARLY TUESDAY MORNING.
WILL LIMIT SNOWFALL ACCUMULATIONS TO 1-2 INCHES...MAINLY OVER THE
NORTHERN BLACK HILLS AND PLAINS JUST NORTH OF THE BLACK HILLS.
WITH EASTERLY WINDS ACROSS THE EASTERN PORTION OF THE FORECAST
AREA...LOW STRATUS/FZFG HAS BEEN MOVING WESTWARD. AS WARM FRONT
SHIFTS EAST OVERNIGHT...STRATUS/FOG WILL BEGIN TO DISSIPATE FROM
WEST TO EAST.
PREV DISCUSSION... /ISSUED 248 PM MST MON DEC 17 2012/
DISCUSSION...UPPER LEVEL ANALYSIS HAS FLAT RIDGE ACROSS THE
SOUTHWEST CONUS WITH WEAK TROFFING ACROSS THE PACIFIC NORTHWEST.
21Z SURFACE ANALYSIS PLACES LOW OVER SOUTHERN ALBERTA WHILE A
STATIONERY BOUNDARY BISECTS THE CWA. TEMPERATURES ARE IN THE 20S
AND LOWER 30S NORTH OF THE BOUNDARY...AND IN THE UPPER 30S AND 40S
SOUTH.
FOR TONIGHT...WEAK UPPER RIDGE PUSHES EAST TONIGHT AS THE ALBERTA
SURFACE LOW SLIDES INTO SOUTHERN SASKATCHEWAN. STATIONERY BOUNDARY
SLOWLY LIFTS NORTHEAST AS WESTERLY BOUNDARY LAYER FLOW INCREASES.
SHOULD BE A BREEZY NIGHT FOR MANY WESTERN AREAS WHERE BOUNDARY
LAYER REMAINS COUPLED. SOME FOG MAY REDEVELOP ACROSS CENTRAL
PORTIONS OF SOUTH DAKOTA THIS EVENING...BEFORE BOUNDARY FINALLY
LIFTS TO THE NORTH. LOWS WILL VARY FROM THE LOW TEENS IN DEEPER
DECOUPLED AREAS...TO THE 20S WHERE ATMOSPHERE STAYS COUPLED. WEAK
ENERGY CROSSING THE NORTHERN TIER MAY PRODUCE SOME SNOW SHOWERS
ACROSS NORTHWEST SOUTH DAKOTA THIS EVENING.
ON TUESDAY...TEMPERATURES WILL BE COOLER AS WEAK UPPER RIDGE
PUSHES EAST AND WESTERN TROF MOVES INTO THE NORTHERN ROCKIES.
HIGHS WILL BE CLOSER TO AVERAGE...IN THE 30S TO AROUND 40 DEGREES.
UPPER TROF DIGS INTO THE CENTRAL AND SOUTHERN ROCKIES TUESDAY
NIGHT WITH SURFACE LOW DEVELOPING OVER SOUTHERN COLORADO. LIGHT
WESTERLY FLOW WILL CONTINUE OVER THE AREA WITH LOWS FALLING INTO
THE TEENS AND 20S.
FOR WEDNESDAY...SURFACE LOW MOVES EAST ALONG THE KANSAS/OKLAHOMA
BORDER AS BASE OF UPPER TROF MOVES INTO WESTERN KANSAS. BROAD
AREA OF PRECIP WILL SLIDE ACROSS SOUTHEASTERN WYOMING INTO WESTERN
NEBRASKA...AND POSSIBLY GRAZE THE VERY SOUTHERN EDGE OF THE
FORECAST AREA. SOME OF THE MODEL GUIDANCE KEEPS PRECIP JUST TO THE
SOUTH OF THE AREA...SO WILL CONTINUE LOW POPS ACROSS FAR SOUTHERN
SOUTH DAKOTA. SYSTEM SHIFTS EAST WEDNESDAY NIGHT AS SURFACE RIDGE
SLIDES INTO THE AREA. TEMPERATURES WILL REMAIN CLOSE TO SEASONAL
AVERAGES.
EXTENDED...AN UPPER LEVEL RIDGE OF HIGH PRESSURE WILL BUILD OVER THE
INTERMOUNTAIN WEST ON THURSDAY...AS THE UPPER LEVEL TROF SHIFTS EAST
OF THE GREAT PLAINS. A FAIRLY FLAT RIDGE WILL THEN BECOME CENTERED
OVER THE NORTHERN PLAINS THROUGH THE WEEKEND...RESULTING IN A NEARLY
ZONAL FLOW PATTERN AND DRY WEATHER. EXPECT SLIGHTLY WARMER THAN
NORMAL TEMPERATURES THROUGH THE EXTENDED PERIOD WITH AN EXCEPTION
OVER THE NORTHEASTERN PART OF THE FORECAST AREA WHERE THE GFS
CONTINUES TO SHOW COOLER AIR BACKING INTO THE REGION. EXTENDED
MODELS SHOW ANOTHER UPPER TROUGH BRINGING A CHANCE OF SNOW TO PARTS
OF THE AREA ON MONDAY...BUT THEY STILL DIFFER GREATLY IN THE
STRENGTH AND PLACEMENT OF THE SURFACE LOW.
&&
.UNR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
WY...NONE.
&&
$$
SHORT TERM...07
LONG TERM....WFO UNR
AVIATION...07
AREA FORECAST DISCUSSION
NWS FORT WORTH TX
647 PM CST WED DEC 19 2012
.UPDATE...
HAVE UPDATED THE FORECAST TO INCLUDE HIGHER POPS ACROSS ROUGHLY
THE EASTERN HALF OF THE AREA. 0Z SOUNDING AND MORE RECENT ACARS
DATA SHOWS VERY IMPRESSIVE DYNAMIC LIFT IS OCCURRING OVER THE AREA
RIGHT NOW. THE CAP HAS BEEN ESSENTIALLY ERODED AND PARCELS JUST
ABOVE THE SURFACE ARE CONDITIONALLY UNSTABLE. MOISTURE REMAINS A
LIMITING FACTOR...BUT GIVEN THE DYNAMIC SUPPORT FOR LIFT AND THE
STRONG CONVERGENCE ALONG THE FRONTAL BOUNDARY...WE SHOULD SEE
CONVECTION FIRE ALONG THE FRONT AS IT REACHES A GAINESVILLE TO DFW
TO LAMPASAS LINE. CONVECTION WILL LIKELY FILL INTO A BROKEN OR
SOLID LINE ALONG THE FRONT AS IT MOVES THROUGH THE EASTERN ZONES
WHERE WE HAVE BUMPED UP POPS TO 40 PERCENT. SEVERE THREAT IS A BIT
AMBIGUOUS GIVEN LIMITED INSTABILITY VALUES...BUT SHEAR WILL BE
STRONG AND STORMS ALONG THE FRONT MAY BRING STRONG WINDS ALOFT
DOWN TO THE SURFACE. TR.92
&&
.AVIATION...
A DRYLINE STRETCHES FROM A DEEP SURFACE LOW OVER NORTHERN OK
SOUTHWARD TO JUST WEST OF NORTH TEXAS. AHEAD OF THE
BOUNDARY...SOUTH WINDS HAVE DECREASED WITH THE SETTING SUN TO
MAINLY IN THE 15-20 KT RANGE. WE SHOULD SEE THE DRYLINE MAKE A
PUSH TO THE EAST THIS EVENING AS A STRONG UPPER LOW MIGRATES EAST
ACROSS THE PLAINS. WILL CONTINUE WITH THE WIND SHIFT TO THE WEST
IN THE METROPLEX AT 04Z AND WACO AT 05Z...WITH SUSTAINED SPEEDS
INCREASING TO AROUND 20KTS. A STRONG COLD FRONT CURRENTLY DRIVING
SOUTHEAST THROUGH WESTERN OK AND NORTHWEST TX WILL QUICKLY FOLLOW
THE DRYLINE...BRINGING MORE OF A NORTHWESTERLY COMPONENT TO THE
SURFACE WINDS AND EVEN HIGHER SPEEDS. WILL INDICATE FROPA AT 06Z
AND KEEP AN EYE ON THE BOUNDARY AS IT APPROACHES THIS EVENING.
THERE COULD BE A FEW ISOLATED SHOWERS WITH THE FRONT BUT AT THIS
TIME IT APPEARS THAT THE BEST POTENTIAL FOR PRECIP WILL BE WELL
EAST OF THE TAF SITES.
FOR DFW...CROSS WIND ISSUES WILL BE PREVALENT THROUGH MOST OF THE
NIGHT. WINDS WILL REMAIN GUSTY DURING THE DAY THURSDAY BUT SHOULD
BE AROUND 10KT LESS THAN THE UPCOMING OVERNIGHT PERIOD. WINDS WILL
SUBSIDE THURSDAY EVENING AS HIGH PRESSURE BUILDS IN FROM THE WEST.
30
&&
.PREV UPDATE...
.UPDATE...
HAVE EXPIRED THE WIND ADVISORY THAT WAS IN EFFECT OVER THE SOUTH
CENTRAL ZONES. ANOTHER WIND ADVISORY REMAINS IN EFFECT FOR ALL OF
NORTH TEXAS FOR THE STRONG NORTHWEST WINDS BEHIND THE FRONT
TONIGHT. THESE WINDS TONIGHT WILL BE STRONGER THAN TODAY...WITH
GUSTS OVER THE NORTHWEST ZONES LIKELY PUSHING 45-50 MPH...TAPERING
DOWN TO 35-40 MPH GUSTS OVER THE SOUTHEAST ZONES. OTHERWISE HAVE
PULLED THE RED FLAG WARNING EARLY AS WINDS HAVE DIMINISHED WITH
THE LOSS OF HEATING.
NO OTHER SIGNIFICANT CHANGES TO THE FORECAST...BUT MADE SOME
UPDATES TO THE HOURLY GRIDS TO SHOW THE SHARP CHANGES WITH THE
DRY LINE AND COLD FRONT LATER TONIGHT.
OF NOTE IS THE HRRR DEVELOPING RAIN ALONG THE FRONT FARTHER TO THE
WEST...POSSIBLE AFFECTING THE I-35 CORRIDOR THIS EVENING. MAY HAVE
TO PULL THE POPS BACK TO THE WEST...BUT WILL AWAIT THE FULL 0Z
FWD SOUNDING AND LOOK OVER A FEW MORE THINGS BEFORE TOUCHING THE
POP FORECAST. A PRELIM LOOK AT THE 0Z SOUNDING DOES SHOW THE CAP
HAS BEEN LIFTED AND REMOVED FROM THE AREA.
TR.92
&&
.SHORT TERM...
DESPITE PERSISTENT CLOUD COVER AND THE WEAK DECEMBER SUN...THE
DROUGHT-PARCHED GROUND ALLOWED TEMPS TO SOAR TO RECORD HIGHS AT
BOTH DFW AND WACO. THIS OCCURRED WITH DUE SOUTH WINDS AND
AFTERNOON DEW POINTS NEAR 60F. (DFW SET ITS RECORD BEFORE NOON.)
DESPITE CONSIDERABLE LIFT WITH THIS POTENT STORM SYSTEM...MOISTURE
REMAINS VERY SHALLOW. THERE WILL BE A BRIEF WINDOW FOR CONVECTION
IN FAR EASTERN ZONES...WITH THE FLOW QUICKLY VEERING THIS EVENING.
DRIER AIR HAS MIXED TO THE SURFACE IN FAR WESTERN ZONES...BUT THE
DRYLINE REMAINS TO THE WEST. AT 3 PM...ABILENE (KABI) HAD A DEW
POINT OF 47 WHILE 50 MILES TO THE WEST IN SWEETWATER (KSWW) THE
DEW POINT WAS 19. BLOWING DUST CONTINUES ACROSS THE HIGH PLAINS OF
WEST TEXAS...WHERE WINDS HAVE GUSTED TO 60 MPH. A COLD FRONT HAS
NOW ENTERED THE PANHANDLE AND WILL CONTINUE DRIVING SOUTH. THE
DRYLINE WILL REACH THE I-35 THIS EVENING...WITH THE FRONT QUICKLY
OVERTAKING IT. THE ENTIRE CWA WILL BE UNDER A WIND ADVISORY BY THE
06-12Z (MIDNIGHT-6 AM CST) TIME FRAME. SUSTAINED WIND SPEEDS WILL
OCCASIONALLY TOP 30 MPH...WITH PEAK GUSTS IN EXCESS OF 40 MPH.
LIGHT WINDS THURSDAY NIGHT WILL ALLOW TEMPERATURES TO PLUMMET
AREAWIDE. A HARD FREEZE WILL OCCUR FRIDAY MORNING...WITH LOWS
DIPPING INTO THE TEENS IN LOW-LYING AND OTHER OUTLYING AREAS.
25
&&
.LONG TERM...
GUIDANCE CONTINUES TO SUGGEST A WEAK SHORTWAVE WILL SWING THROUGH
THE SOUTHERN PLAINS CHRISTMAS EVE...WELL IN ADVANCE OF THE STORM
SYSTEM STILL IN THE NORTH PACIFIC. THIS WILL FORCE A WEAK FRONTAL
BOUNDARY INTO NORTH TEXAS...BUT THE ARCTIC PUSH WILL NOT OCCUR
UNTIL TUESDAY NIGHT. THE POTENTIAL REMAINS FOR LINGERING
PRECIPITATION WELL BEHIND THE ARCTIC INTRUSION...SUPPORTED BY BOTH
THE ECMWF AND CANADIAN. THE OPERATIONAL GFS IS CURRENTLY LESS
FAVORABLE...BUT ENSEMBLE MEMBER SPREAD REMAINS TOO LARGE TO HAVE
CONFIDENCE IN ONE SINGLE SOLUTION. THE AFTERNOON PACKAGE ENDS
PRECIPITATION DURING CHRISTMAS DAY WELL BEFORE TEMPERATURES ARE
COLD ENOUGH TO SUPPORT SNOW.
25
&&
FIRE WEATHER DANGER IS EXPECTED TO BE VERY HIGH ACROSS ALL OF
NORTH AND CENTRAL TEXAS THURSDAY...WITH SLIGHTLY LOWER FIRE
WEATHER DANGER ON FRIDAY.
ON THURSDAY...WINDS ARE EXPECTED TO REMAIN OUT OF THE NORTHWEST AT
20 TO 25 MPH WITH GUSTS TO 35 MPH. AFTERNOON RELATIVE HUMIDITY
VALUES WILL FALL BELOW 25 PERCENT FOR ALL OF NORTH TEXAS...WITH
AFTERNOON RH VALUES FALLING TO 15 PERCENT WEST OF INTERSTATE 35.
THE COMBINATION OF WINDS AND LOW RH MAKES IT NEARLY CERTAIN TO
VERIFY RED FLAG WARNING CONDITIONS ACROSS ALL OF NORTH TX
TOMORROW. WE DID NOT ISSUE A FIRE WEATHER WATCH TODAY THOUGH
BECAUSE HIGH TEMPERATURES ON THURSDAY ARE ONLY EXPECTED TO TOP OUT
IN THE MID 50S. THESE COOL TEMPERATURES WILL HELP KEEP FUEL
TEMPERATURES DOWN WHICH DOES NOT SUPPORT ERRATIC OR CRITICAL FIRE
BEHAVIOR BECAUSE LOW FUEL TEMPERATURES WILL MAKE IT HARDER TO
START AND SPREAD GRASS FIRES. REGARDLESS...FIRE WEATHER DANGER
WILL REMAIN VERY HIGH...AND OUTDOOR BURNING IS NOT RECOMMENDED.
CAVANAUGH
&&
.PRELIMINARY POINT TEMPS/POPS...
DALLAS-FT. WORTH, TX 35 53 27 59 34 / 10 0 0 0 0
WACO, TX 37 57 23 61 32 / 20 0 0 0 5
PARIS, TX 37 51 26 57 30 / 30 0 0 0 5
DENTON, TX 32 51 21 60 31 / 10 0 0 0 0
MCKINNEY, TX 35 52 22 58 30 / 20 0 0 0 0
DALLAS, TX 36 52 28 59 36 / 20 0 0 0 0
TERRELL, TX 38 51 28 57 32 / 30 0 0 0 0
CORSICANA, TX 40 53 25 59 33 / 30 0 0 0 0
TEMPLE, TX 38 56 25 60 32 / 20 0 0 0 5
MINERAL WELLS, TX 31 54 24 62 28 / 5 0 0 0 5
&&
.FWD WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY UNTIL 6 AM CST THURSDAY FOR TXZ091>093-100>104-
115>120-129>133-141.
WIND ADVISORY FROM MIDNIGHT TONIGHT TO 9 AM CST THURSDAY FOR
TXZ094-095-105>107-121>123-134-135-142>148-156>162-174-175.
&&
$$
AREA FORECAST DISCUSSION
NWS FORT WORTH TX
603 PM CST WED DEC 19 2012
.UPDATE...
HAVE EXPIRED THE WIND ADVISORY THAT WAS IN EFFECT OVER THE SOUTH
CENTRAL ZONES. ANOTHER WIND ADVISORY REMAINS IN EFFECT FOR ALL OF
NORTH TEXAS FOR THE STRONG NORTHWEST WINDS BEHIND THE FRONT
TONIGHT. THESE WINDS TONIGHT WILL BE STRONGER THAN TODAY...WITH
GUSTS OVER THE NORTHWEST ZONES LIKELY PUSHING 45-50 MPH...TAPERING
DOWN TO 35-40 MPH GUSTS OVER THE SOUTHEAST ZONES. OTHERWISE HAVE
PULLED THE RED FLAG WARNING EARLY AS WINDS HAVE DIMINISHED WITH
THE LOSS OF HEATING.
NO OTHER SIGNIFICANT CHANGES TO THE FORECAST...BUT MADE SOME
UPDATES TO THE HOURLY GRIDS TO SHOW THE SHARP CHANGES WITH THE
DRY LINE AND COLD FRONT LATER TONIGHT.
OF NOTE IS THE HRRR DEVELOPING RAIN ALONG THE FRONT FARTHER TO THE
WEST...POSSIBLE AFFECTING THE I-35 CORRIDOR THIS EVENING. MAY HAVE
TO PULL THE POPS BACK TO THE WEST...BUT WILL AWAIT THE FULL 0Z
FWD SOUNDING AND LOOK OVER A FEW MORE THINGS BEFORE TOUCHING THE
POP FORECAST. A PRELIM LOOK AT THE 0Z SOUNDING DOES SHOW THE CAP
HAS BEEN LIFTED AND REMOVED FROM THE AREA.
TR.92
&&
.AVIATION...
A DRYLINE STRETCHES FROM A DEEP SURFACE LOW OVER NORTHERN OK
SOUTHWARD TO JUST WEST OF NORTH TEXAS. AHEAD OF THE
BOUNDARY...SOUTH WINDS HAVE DECREASED WITH THE SETTING SUN TO
MAINLY IN THE 15-20 KT RANGE. WE SHOULD SEE THE DRYLINE MAKE A
PUSH TO THE EAST THIS EVENING AS A STRONG UPPER LOW MIGRATES EAST
ACROSS THE PLAINS. WILL CONTINUE WITH THE WIND SHIFT TO THE WEST
IN THE METROPLEX AT 04Z AND WACO AT 05Z...WITH SUSTAINED SPEEDS
INCREASING TO AROUND 20KTS. A STRONG COLD FRONT CURRENTLY DRIVING
SOUTHEAST THROUGH WESTERN OK AND NORTHWEST TX WILL QUICKLY FOLLOW
THE DRYLINE...BRINGING MORE OF A NORTHWESTERLY COMPONENT TO THE
SURFACE WINDS AND EVEN HIGHER SPEEDS. WILL INDICATE FROPA AT 06Z
AND KEEP AN EYE ON THE BOUNDARY AS IT APPROACHES THIS EVENING.
THERE COULD BE A FEW ISOLATED SHOWERS WITH THE FRONT BUT AT THIS
TIME IT APPEARS THAT THE BEST POTENTIAL FOR PRECIP WILL BE WELL
EAST OF THE TAF SITES.
FOR DFW...CROSS WIND ISSUES WILL BE PREVALENT THROUGH MOST OF THE
NIGHT. WINDS WILL REMAIN GUSTY DURING THE DAY THURSDAY BUT SHOULD
BE AROUND 10KT LESS THAN THE UPCOMING OVERNIGHT PERIOD. WINDS WILL
SUBSIDE THURSDAY EVENING AS HIGH PRESSURE BUILDS IN FROM THE WEST.
30
&&
.SHORT TERM...
DESPITE PERSISTENT CLOUD COVER AND THE WEAK DECEMBER SUN...THE
DROUGHT-PARCHED GROUND ALLOWED TEMPS TO SOAR TO RECORD HIGHS AT
BOTH DFW AND WACO. THIS OCCURRED WITH DUE SOUTH WINDS AND
AFTERNOON DEW POINTS NEAR 60F. (DFW SET ITS RECORD BEFORE NOON.)
DESPITE CONSIDERABLE LIFT WITH THIS POTENT STORM SYSTEM...MOISTURE
REMAINS VERY SHALLOW. THERE WILL BE A BRIEF WINDOW FOR CONVECTION
IN FAR EASTERN ZONES...WITH THE FLOW QUICKLY VEERING THIS EVENING.
DRIER AIR HAS MIXED TO THE SURFACE IN FAR WESTERN ZONES...BUT THE
DRYLINE REMAINS TO THE WEST. AT 3 PM...ABILENE (KABI) HAD A DEW
POINT OF 47 WHILE 50 MILES TO THE WEST IN SWEETWATER (KSWW) THE
DEW POINT WAS 19. BLOWING DUST CONTINUES ACROSS THE HIGH PLAINS OF
WEST TEXAS...WHERE WINDS HAVE GUSTED TO 60 MPH. A COLD FRONT HAS
NOW ENTERED THE PANHANDLE AND WILL CONTINUE DRIVING SOUTH. THE
DRYLINE WILL REACH THE I-35 THIS EVENING...WITH THE FRONT QUICKLY
OVERTAKING IT. THE ENTIRE CWA WILL BE UNDER A WIND ADVISORY BY THE
06-12Z (MIDNIGHT-6 AM CST) TIME FRAME. SUSTAINED WIND SPEEDS WILL
OCCASIONALLY TOP 30 MPH...WITH PEAK GUSTS IN EXCESS OF 40 MPH.
LIGHT WINDS THURSDAY NIGHT WILL ALLOW TEMPERATURES TO PLUMMET
AREAWIDE. A HARD FREEZE WILL OCCUR FRIDAY MORNING...WITH LOWS
DIPPING INTO THE TEENS IN LOW-LYING AND OTHER OUTLYING AREAS.
25
&&
.LONG TERM...
GUIDANCE CONTINUES TO SUGGEST A WEAK SHORTWAVE WILL SWING THROUGH
THE SOUTHERN PLAINS CHRISTMAS EVE...WELL IN ADVANCE OF THE STORM
SYSTEM STILL IN THE NORTH PACIFIC. THIS WILL FORCE A WEAK FRONTAL
BOUNDARY INTO NORTH TEXAS...BUT THE ARCTIC PUSH WILL NOT OCCUR
UNTIL TUESDAY NIGHT. THE POTENTIAL REMAINS FOR LINGERING
PRECIPITATION WELL BEHIND THE ARCTIC INTRUSION...SUPPORTED BY BOTH
THE ECMWF AND CANADIAN. THE OPERATIONAL GFS IS CURRENTLY LESS
FAVORABLE...BUT ENSEMBLE MEMBER SPREAD REMAINS TOO LARGE TO HAVE
CONFIDENCE IN ONE SINGLE SOLUTION. THE AFTERNOON PACKAGE ENDS
PRECIPITATION DURING CHRISTMAS DAY WELL BEFORE TEMPERATURES ARE
COLD ENOUGH TO SUPPORT SNOW.
25
&&
.FIRE WEATHER...
FIRE WEATHER DANGER IS EXPECTED TO BE VERY HIGH ACROSS ALL OF
NORTH AND CENTRAL TEXAS THURSDAY...WITH SLIGHTLY LOWER FIRE
WEATHER DANGER ON FRIDAY.
ON THURSDAY...WINDS ARE EXPECTED TO REMAIN OUT OF THE NORTHWEST AT
20 TO 25 MPH WITH GUSTS TO 35 MPH. AFTERNOON RELATIVE HUMIDITY
VALUES WILL FALL BELOW 25 PERCENT FOR ALL OF NORTH TEXAS...WITH
AFTERNOON RH VALUES FALLING TO 15 PERCENT WEST OF INTERSTATE 35.
THE COMBINATION OF WINDS AND LOW RH MAKES IT NEARLY CERTAIN TO
VERIFY RED FLAG WARNING CONDITIONS ACROSS ALL OF NORTH TX
TOMORROW. WE DID NOT ISSUE A FIRE WEATHER WATCH TODAY THOUGH
BECAUSE HIGH TEMPERATURES ON THURSDAY ARE ONLY EXPECTED TO TOP OUT
IN THE MID 50S. THESE COOL TEMPERATURES WILL HELP KEEP FUEL
TEMPERATURES DOWN WHICH DOES NOT SUPPORT ERRATIC OR CRITICAL FIRE
BEHAVIOR BECAUSE LOW FUEL TEMPERATURES WILL MAKE IT HARDER TO
START AND SPREAD GRASS FIRES. REGARDLESS...FIRE WEATHER DANGER
WILL REMAIN VERY HIGH...AND OUTDOOR BURNING IS NOT RECOMMENDED.
CAVANAUGH
&&
.PRELIMINARY POINT TEMPS/POPS...
DALLAS-FT. WORTH, TX 37 53 27 59 34 / 10 0 0 0 0
WACO, TX 38 57 23 61 32 / 5 0 0 0 5
PARIS, TX 37 51 26 57 30 / 20 0 0 0 5
DENTON, TX 32 51 21 60 31 / 10 0 0 0 0
MCKINNEY, TX 39 52 22 58 30 / 10 0 0 0 0
DALLAS, TX 38 52 28 59 36 / 10 0 0 0 0
TERRELL, TX 40 51 28 57 32 / 10 0 0 0 0
CORSICANA, TX 40 53 25 59 33 / 10 0 0 0 0
TEMPLE, TX 38 56 25 60 32 / 5 0 0 0 5
MINERAL WELLS, TX 31 54 24 62 28 / 5 0 0 0 5
&&
.FWD WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY UNTIL 6 AM CST THURSDAY FOR TXZ091>093-100>104-
115>120-129>133-141.
WIND ADVISORY FROM MIDNIGHT TONIGHT TO 9 AM CST THURSDAY FOR
TXZ094-095-105>107-121>123-134-135-142>148-156>162-174-175.
&&
$$
/
AREA FORECAST DISCUSSION
NWS LA CROSSE WI
1129 PM CST MON DEC 17 2012
.SHORT TERM...TONIGHT THROUGH THURSDAY
303 PM CST MON DEC 17 2012
MAIN FORECAST CONCERNS ARE ON BRIEF LIGHT SNOW EVENT TOMORROW AND
THE POSSIBLE WINTER STORM LATE WEDNESDAY INTO THURSDAY.
CURRENTLY AS OF 21Z...WATER VAPOR LOOP AND RAP 500MB HEIGHT ANALYSIS
SHOWED TROUGHING FROM THE GULF OF ALASKA TO OFF THE PACIFIC
NORTHWEST...A RELATIVELY POTENT SHORTWAVE CROSSING THE NORTHERN
ROCKIES...A WEAK NORTH TO SOUTH ORIENTED SHORTWAVE OVER THE FAR
EASTERN DAKOTAS AND A WEAK RIDGE SANDWICHED IN-BETWEEN THESE
SHORTWAVES. MID LEVEL CLOUDS WERE ASSOCIATED AHEAD OF THE DAKOTAS
SHORTWAVE...WITH A FEW FLURRIES FALLING OUT OF THESE OVER SOUTHWEST
MINNESOTA AND NORTHWEST IOWA. OVER THE FORECAST AREA...STRATUS
PERSISTS...BURIED UNDERNEATH A SUBSIDENCE INVERSION SEEN ON THE 12Z
MPX...GRB AND DVN SOUNDINGS. HAVING LIGHT WINDS ASSOCIATED WITH HIGH
PRESSURE AT THE SURFACE COMBINED WITH BEING AT THE BOTTOM OF THE
DAYLIGHT CYCLE HAS NOT HELPED EITHER TO GET RID OF THE STRATUS.
TEMPERATURES AS A RESULT HAVE NOT CLIMBED A WHOLE LOT FROM MORNING
LOWS. THE STRATUS ACTUALLY EXTENDS WEST ALL THE WAY INTO THE CENTRAL
DAKOTAS. FARTHER WEST...LEE TROUGHING HAS FORMED DOWNSTREAM OF THE
NORTHERN ROCKIES SHORTWAVE...ALSO AIDED BY A 130KT JET NEAR THE
TROPOPAUSE ON THE SOUTH SIDE OF THE SHORTWAVE. THERE HAS BEEN QUITE
A BIT OF PRECIPITATION ACROSS THE NORTHERN ROCKIES AS WELL AS THE
UPPER JET DRIVES IN PACIFIC MOISTURE.
TONIGHT AND TUESDAY...FOCUS IS ON THAT NORTHERN ROCKIES SHORTWAVE.
MODELS ARE IN REALLY GOOD AGREEMENT BRING THE SHORTWAVE INTO
SOUTHERN SOUTH DAKOTA BY 06Z...NEAR SIOUX CITY IOWA BY 12Z...NEAR
DUBUQUE BY 18Z AND CHICAGO BY 00Z. THIS TRACK IS A BIT FARTHER SOUTH
THAN SUGGESTED OVER THE PAST FEW DAYS...WITH PERHAPS THE CANADIAN
AND ECMWF DOING THE BEST JOB ON IT. THE SHORTWAVE AND THE ASSOCIATED
UPPER JET SOUTH OF IT ARE STRONG ENOUGH THAT OUT OF THE CURRENT LEE
TROUGHING A SURFACE LOW IS SUGGESTED TO DEVELOP. THIS LOW OF COURSE
ENDS UP TRACKING WITH THE SHORTWAVE...RESULTING IN A LOW TO
MID-LEVEL FRONTOGENESIS ZONE ON THE NORTH SIDE OF IT. MOISTURE
INITIALLY IS LIMITED...NOTED BY THE CURRENT LACK OF MID-CLOUDS
ACROSS MUCH OF THE PLAINS. HOWEVER...AS WE GO THROUGH TONIGHT...
CONDENSATION PRESSURE DEFICITS ON THE 285-290K SURFACES DECREASE AS
THE LIFT HELPS TO SATURATE THE MID-LEVELS OF THE ATMOSPHERE. SHOULD
SEE A BAND OF LIGHT SNOW BREAK OUT ACROSS SOUTH DAKOTA INTO SOUTHERN
MINNESOTA AND NORTHERN IOWA BY LATE TONIGHT...ON THE NORTH SIDE OF
THE LOW. PERHAPS SOME OF THIS SNOW SQUEAKS INTO WESTERN PORTIONS OF
THE FORECAST AREA TOWARDS 12Z. WITH THE TREND FARTHER SOUTH WITH THE
SHORTWAVE TRACK...HAVE LEANED THE FORECAST MORE TOWARDS THE 17.12Z
GFS/ECMWF IDEA VERSUS THE FARTHER NORTH BUT TRENDING SOUTH 17.12Z
NAM FOR TUESDAY. THE FRONTOGENESIS BAND OF SNOW SHOULD AFFECT MAINLY
I-90 SOUTH AND RAISED PRECIPITATION CHANCES TOWARDS 60 IN THIS AREA.
LIMITED MOISTURE NOTED BY MIXING RATIOS OF 2-3 G/KG ON THE 285-290K
SURFACES WILL KEEP QPF AMOUNTS DOWN TO AT MOST A 0.10 OF AN INCH
TOTAL LIQUID EQUIVALENT. THE LIFT IS PRIMARILY CENTERED BELOW THE
DENDRITIC GROWTH ZONE...KEEPING SNOW TO WATER RATIOS DOWN NEAR 10 TO
1...THUS ONLY UP TO AN INCH OF SNOW IS ANTICIPATED. CONCERN THOUGH
IS THAT THE SNOW IS COMING AT MORNING COMMUTE TIME...SO HAVE ISSUED
AN SPS TO ACCOUNT FOR THIS. PLENTY OF CLOUDS LOOK TO PERSIST THROUGH
THIS PERIOD THUS AGAIN TEMPERATURES IMPACTED BY ADVECTION. WITH THE
FARTHER SOUTH TRACK OF THE LOW...HAVE COOLED HIGHS DOWN FOR TUESDAY.
TUESDAY NIGHT THROUGH THURSDAY...ALL ATTENTION IS ON THE WINTER
STORM POTENTIAL...WHICH RELATES TO THE CURRENT TROUGH OFF THE
PACIFIC NORTHWEST. THAT TROUGH IS COMPOSED OF 2 PARTS...A POTENT
SHORTWAVE NEAR 42N 140 W...AND A COLD SHORTWAVE NEAR THE NORTHERN
BRITISH COLUMBIA COAST. 500MB TEMPS WERE AROUND -40C WITH THE COLD
SHORTWAVE...AND JUST AHEAD OF IT OVER NORTHERN BRITISH COLUMBIA
850MB TEMPS ARE IN THE -15 TO -25C RANGE. THE IDEA SHOWN FOR THE
PAST MANY DAYS IS THAT THESE TWO PARTS ARE EVENTUALLY GOING TO PHASE
UP AFTER CROSSING THE WESTERN U.S....RESULTING IN A DEEPENING WINTER
STORM FROM THE CENTRAL PLAINS INTO THE GREAT LAKES. THE QUESTION HAS
BEEN WHERE DOES THE PHASING OCCUR WITH RESPECT TO OUR LONGITUDE TO
HELP DETERMINE THE EXACT TRACK AND SPEED. THE ANSWER STILL IS NOT
THERE YET...HOWEVER...THE DETERMINISTIC MODEL SPREAD IS SHRINKING
AND SHOULD CONTINUE TO DO SO OVER THE NEXT FEW DAYS AS THE TROUGH
COMES INTO THE WESTERN U.S.. WITH THE 17.12Z MODEL GUIDANCE...TRACK
SPREAD RANGES FROM THE NORTHWEST SOLUTION OF THE NAM TO THE
SOUTHEAST SOLUTION OF THE ECMWF. THE GFS...UKMET AND CANADIAN LIE
IN-BETWEEN. THE NAM HAS BEEN TRENDING SOUTHEAST...THE GFS NORTHWEST
AND THE CANADIAN/ECMWF STAYING FAIRLY CLOSE. THE FORECAST FOLLOWS A
BLEND OF THE GFS...CANADIAN AND ECMWF SCENARIOS SINCE THESE SEEM TO
BE THE MOST LIKELY TO OCCUR GIVEN TRENDS. FOR WHAT ITS WORTH...THE
PAST 4 SREF RUNS ARE VERY CONSISTENT ON A FARTHER NORTHWEST TRACK
CLOSE TO OR EVEN MORE NORTHWEST THAN THE NAM. NEEDLESS TO SAY...
STILL PLENTY OF UNCERTAINTY.
SOME DETAILS...TUESDAY NIGHT INTO WEDNESDAY MORNING SHOULD STAY DRY
AS WE ARE IN-BETWEEN SYSTEMS. BIG QUESTION MARK IS IF WE CAN CLEAR.
MOST MODELS SAY WE CAN...BUT HAVING SNOW ON TUESDAY COMBINED WITH
MODELS NOT DOING THE GREATEST ON THE CURRENT STRATUS YIELDS A MORE
PESSIMISTIC VIEW. AS SUCH...HAVE INCREASED CLOUD COVER AND FURTHER
INCREASES MAY BE NECESSARY. AS THE STORM SYSTEM DEEPENS IN THE
SOUTHERN PLAINS ON WEDNESDAY...A BAND OF FRONTOGENESIS
DEVELOPS/STRENGTHENS UP INTO OUR REGION. THE GFS AND CANADIAN
PRODUCE PRECIPITATION IN THE AFTERNOON AS THEY ARE QUICKER TO
SATURATE THE LOW LEVELS AND TO BRING IN THE FORCING...COMPARED TO
THE ECMWF/NAM/UKMET. HARD TO SAY WHICH GROUP MAY BE MORE CORRECT AT
THIS POINT...THOUGH THE MORE CONSISTENT SIGNAL HAS BEEN TO WAIT
UNTIL WEDNESDAY EVENING TO BRING THE PRECIPITATION IN. THUS...FOR
NOW JUST INCLUDED 20-40 PERCENT CHANCES FROM I-90 SOUTH FOR THE
AFTERNOON. THE MAJORITY OF THE FORECAST AREA SHOULD SEE
PRECIPITATION WEDNESDAY NIGHT INTO THURSDAY MORNING...NO MATTER WHAT
MODEL SOLUTION IS FOLLOWED. IF THERE IS ANYWHERE OF CONCERN DURING
THIS PERIOD THAT MAY NOT SEE PRECIPITATION IT IS OUR FAR NORTHWEST
AS INDICATED BY THE ECMWF. THUS...HIGHEST CHANCES UP AT OR NEAR 100
ARE CONFINED TO THE SOUTHEAST HALF. PRECIPITATION SHOULD START TO
DIMINISH THURSDAY AFTERNOON AS THE SYSTEM HEADS OFF INTO LOWER
MICHIGAN.
IMPACTS/CONCERNS TO WORRY ABOUT WITH THIS WINTER STORM INCLUDE:
1. HEAVY SNOW...PRETTY GOOD MODEL CONSENSUS EXISTS THAT THE TIME
PERIOD WOULD BE WEDNESDAY NIGHT INTO THURSDAY MORNING. EXACT
PLACEMENT OF HEAVIEST SNOW IS STILL UNCERTAIN...BUT FOLLOWING THE
AFOREMENTIONED GFS/ECMWF/CANADIAN BLEND PLACES IT IN THE
SOUTHEASTERN HALF OF THE FORECAST AREA. WITH MAYBE 100 MB OF
DENDRITIC GROWTH AT MOST AND FAIRLY HIGH UP SAY BETWEEN
550-650MB...THE SNOW TO WATER RATIOS SHOULD BE TYPICAL...IN THE
10-15 TO 1 RANGE.
2. MIXED PRECIPITATION TYPES...MODEL CONSENSUS HAS BEEN TO KEEP THE
SYSTEM OFF TO OUR SOUTHEAST...KEEPING OUR AREA IN THE DEEPER COLD
AIR AND THUS SNOW AS THE MAJORITY PRECIPITATION TYPE. HOWEVER...THE
GFS SUGGESTS THAT IF THE SYSTEM CAN WRAP UP ENOUGH...EVEN GRANT AND
CLAYTON COUNTIES COULD END UP WITH SLEET OR RAIN FOR A TIME.
3. BLOWING SNOW/WIND...AS THE SYSTEM DEEPENS ON ITS WAY UP THROUGH
ILLINOIS WEDNESDAY NIGHT AND BEGINS TO PULL AWAY FROM THE AREA ON
THURSDAY...THE PRESSURE GRADIENT TIGHTENS...CAUSING NORTHWEST WINDS
TO INCREASE. THESE WINDS COULD EASILY REACH THE 15-25KT RANGE WITH
HIGHER GUSTS. COMBINING THESE WITH FALLING OR ALREADY ON THE GROUND
SNOW WOULD YIELD BLOWING SNOW...ESPECIALLY ACROSS NORTHEAST IOWA
WHICH HAS THE MOST EXPOSED TERRAIN.
WITH THE NARROWING MODEL SPREAD...ENOUGH CONFIDENCE EXISTED EARLIER
TODAY TO ISSUE A WINTER STORM WATCH FOR ABOUT THE SOUTHEASTERN HALF
OF THE FORECAST AREA. NOTE THAT THE WATCH AREA MAY NOT END UP BEING
THE FINAL WARNING AREA...THUS THE PHRASE WATCH. FURTHER REFINEMENTS
MAY OCCUR...ESPECIALLY ONCE CONFIDENCE INCREASES ENOUGH TO CHANGE
THE WATCHES TO ADVISORIES/WARNINGS.
.LONG TERM...THURSDAY NIGHT THROUGH MONDAY
303 PM CST MON DEC 17 2012
MAIN FORECAST CONCERNS ARE TEMPERATURES THROUGH FORECAST PERIOD.
THE DETERMINISTIC 17.12Z GFS/ECMWF/GEM ARE IN GOOD AGREEMENT WITH
UPPER LEVEL TROUGH OVER THE NORTHEASTERN UNITED STATES AND UPPER
LEVEL RIDGE OVER THE EASTERN ROCKY MOUNTAINS THROUGH 18Z
SATURDAY...THEN THE MODELS BEGIN TO DIVERGE ON STRENGTH OF THE
UPPER LEVEL TROUGH OVER THE NORTHEASTERN UNITED STATES AND UPPER
LEVEL RIDGE OVER THE ROCKY MOUNTAINS. THE 17.12Z ECMWF IS MORE
AMPLIFIED WITH THE UPPER LEVEL TROUGH SATURDAY NIGHT INTO MONDAY
THAN THE 17.12Z GFS/GEM. IF THIS OCCURS...THE UPPER MIDWEST AND
GREAT LAKES REGION WILL REMAIN UNDER NORTHERLY FLOW ALOFT AND A
COLDER AIRMASS WILL FILTER INTO THE AREA. THIS WILL HAVE IMPACTS
ON TEMPERATURES...ESPECIALLY SATURDAY NIGHT INTO MONDAY. THE
17.12Z GFS INDICATES WEST TO EAST ZONAL FLOW ACROSS THE UNITED
STATES AND SLIGHTLY WARMER TEMPERATURES THAN THE 17.12Z ECMWF.
THIS WOULD RESULT IN NEAR NORMAL TEMPERATURES ACROSS FORECAST
AREA. AT THIS TIME...WILL CONTINUE WITH A CONSENSUS BLEND OF
TEMPERATURES...BASED ON THE LOW CONFIDENCE OF UPPER LEVEL FLOW
PATTERN AFTER 18Z SATURDAY.
NO REAL INDICATION OF ANY PRECIPITATION OCCURRING AS THE UPPER
FLOW PATTERN PROGGED IS MOSTLY SUBSIDENT...FAVORING HIGH PRESSURE
AT THE SURFACE.
&&
.AVIATION...THROUGH 06Z WEDNESDAY
1129 PM CST MON DEC 17 2012
EXTENSIVE STRATUS STILL REMAINS ACROSS THE REGION...BUT THERE WERE
HOLES WHERE CEILINGS ROSE INTO THE VFR CATEGORY. MODEL SOUNDINGS
CONTINUE TO SHOW MOISTURE TRAPPED UNDER THE INVERSION WITH THE LOW
STRATUS CONTINUING. HOWEVER...BASED ON METARS WILL LIKELY SEE
HOLES WITH VFR CONDITIONS FOR A SHORT TIME. THIS VERY DIFFICULT TO
TIME IN THE TAFS AND WILL KEEP A TEMPO GROUP TO ACCOUNT FOR THIS.
OTHERWISE...CEILINGS WILL BE IN THE IFR TO LOWER END VFR CATEGORY. NEXT
SYSTEM THEN MOVES ACROSS IOWA...WITH SNOW BREAKING OUT TUESDAY
MORNING BETWEEN 12Z-15Z. 18.00Z GFS AND NAM SHOWING MAIN BAND TO
MOVE JUST SOUTH OF THE TAF SITES...BUT STILL LOOKS LIKE 2-3 MILE
VISIBILITIES IN THE LIGHT SNOW INTO THE AFTERNOON HOURS. EXPECT
CEILINGS IN THE IFR TO LOWER MVFR IN THE SNOW...RISING TO MVFR
AFTER THE SNOW ENDS AND THROUGH THE END OF THE TAF PERIOD.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
303 PM CST MON DEC 17 2012
WI...WINTER STORM WATCH FROM WEDNESDAY EVENING THROUGH THURSDAY
AFTERNOON FOR WIZ034-041>044-053>055-061.
MN...WINTER STORM WATCH FROM WEDNESDAY EVENING THROUGH THURSDAY
AFTERNOON FOR MNZ096.
IA...WINTER STORM WATCH FROM WEDNESDAY EVENING THROUGH THURSDAY
AFTERNOON FOR IAZ010-011-019-029-030.
&&
$$
SHORT TERM...AJ
LONG TERM...DTJ/AJ
AVIATION...RABERDING
AREA FORECAST DISCUSSION
NWS PEACHTREE CITY GA
358 AM EST THU DEC 20 2012
.SHORT TERM /TODAY THROUGH FRIDAY NIGHT/...
PRIMARY CONCERNS ARE TIMING OF PRECIP ONSET AND END TODAY/TONIGHT
...CHC FOR SEVERE CONVECTION THIS AFTERNOON AND EXTENT AND INTENSITY
OF WIND EVENT TONIGHT THROUGH FRI NIGHT. WAA SHRA IN ADVANCE OF
SHORT WAVE ALREADY APPROACHING STATE LINE IN WC GA THIS MORNING.
LATEST RAP ANALYSIS SHOWS ONLY WEAK ELEVATED INSTABILITY EXTENDING
INTO SW 1/3RD OF ALABAMA AND NO LIGHTNING OBSERVED IN THE LAST FEW
HOURS. HAVE DELAYED ONSET OF OF SHRA TO 09-10Z AND SLT CHC TSRA
UNTIL 12Z. 00Z MODEL PROGS IN FAIR AGREEMENT THOUGH AGAIN THE NAM
IS THE MOST AGGRESSIVE WITH LOW LEVEL MOISTURE AND SBCAPE. 06Z NAM
HAS SBCAPE 250-400 J/KG SOUTH OF CSG TO MCN LINE WITH NO SBCAPE TO
THE NORTH. 00Z GFS AND ECMWF KEEP SBCAPE LESS THAN 200 J/KG ACROSS
ALL OF CWA. WILL HAVE TO WATCH MIDDLE GA CLOSE. VERY STRONG LOW
LEVEL VERTICAL WIND SHEAR /0-1KM BULK SHEAR NEAR 50KTS/ ALLOWS 06Z
NAM TO PROG 1.5-2.0 VALUES OF SIG TOR PARAMETER AT 00Z.
EXPERIMENTAL HIGH SHEAR-LOW CAPE SHERB PARAMETER FROM 06Z NAM ONLY
HAS 0.8-1.2 OVER MIDDLE GA. MAIN POINT IS IT WILL NOT TAKE MUCH
INSTABILITY TO PRODUCE BRIEF MESOVORTICES CAPABLE OF WIND DAMAGE
OR A BRIEF TORNADO ...SIMILAR TO WHAT WE SAW MONDAY. TOTAL
RAINFALL WILL NOT BE TOO HIGH WITH AMOUNTS OF 0.5-1.0 INCHES.
SYSTEM WILL MOVE OUT QUICKLY TAKING PRECIP WITH IT. VERY STRONG
PRESSURE GRADIENT AND STRONG VERTICAL CAA AND RESULTING DEEP MIXING
ALLOWS FOR SIGNIFICANT WIND EVENT OVER MUCH OF CWA WITH GUSTS TO
35-40 MPH AND 45+ MPH IN MOUNTAINS. COULD BEGIN LATE THIS AFTERNOON
IN THE WAKE OF PRECIP BUT APPEARS BEST PRESSURE GRADIENT WILL SET UP
AROUND 22Z-00Z. GUIDANCE FOR WIND SPEEDS NOT TOO FAR OFF BUT COULD
GO A LITTLE HIGHER IF SYSTEM INTENSIFIES OR MIXING IS MORE THAN
FCST. IN EXPOSED/HIGHER TERRAIN AREAS OF NE GA...WILL SEE STRONG
WINDS PERSIST. 1-2KM AGL WINDS NOT EXPECTED TO WEAKEN MUCH OVER NE
GA UNTIL AFTER 12Z SAT. HAVE ADJUSTED ADVISORIES APPROPRIATELY AND
BROKE OUT NE GA COUNTIES INTO ITS OWN SEGMENT THROUGHOUT THE EVENT.
SNELSON
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
AN H5 RIDGE BUILDS INTO THE REGION SATURDAY BRINGING DRIER AND MORE
STABLE AIR ALONG WITH A WARMING TREND. THIS RIDGE WILL BE SHORT
LIVED AS THE FLOW FLATTENS TO VERY PROGRESSIVE ZONAL FLOW BY SUNDAY.
THE FIRST SHORT WAVE IN A SERIES OF SHORT WAVES WILL MOVE ACROSS THE
CWA LATE SUNDAY AND INTO MONDAY. FROM THIS POINT TIMING OF THE SHORT
WAVES WILL BE TRICKY AS THE FLOW IS FAST AND THE MODELS APPEAR TO BE
HAVING A DIFFICULT TIME MAINTAINING CONTINUITY WITH IN THEMSELVES.
WILL GO WITH CHANCE POPS BEGINNING SUNDAY NIGHT AND CONTINUE POPS
THROUGH THE LONG TERM...FAVORING HIGHER POPS TOWARD MID WEEK AS BOTH
MODELS SHOWING A SIGNIFICANT SYSTEM MOVING ACROSS THE CWA.
17
&&
.AVIATION...06Z UPDATE...
MAIN AVIATION WX CONCERNS ARE ONSET OF IFR CIGS AND PRECIP TODAY
AND LIKELIHOOD OF TSRA THIS AFTERNOON. HIGH CONFIDENCE/QUICK
MOVING RAIN EVENT TODAY. EXPECT RAPID LOWERING OF CLOUDS AFTER 12Z
WITH MVFR CIGS BY 15Z WITH LIGHT RAIN AND NEAR IFR CIGS LIKELY
AROUND 17-19Z AS NEAR SOLID AREA OF MODERATE RAIN BEGINS. TSRA
CANT BE RULED OUT BUT INSTABILITY APPEARS TOO LOW TO MENTION IN
NORTH GA TAFS. HAVE ADDED TEMPO TSRA TO CSG AND MCN TAFS 18-22Z
WHERE INSTABILITY SHOULD BE SUFFICIENT FOR SOME EMBEDDED TS. SE
WINDS WILL BECOME SW AROUND 19-21Z AND THEN WEST 23-01Z AS FRONT
MOVES IN. SPEEDS WILL ALSO INCREASE SIGNIFICANTLY WITH FROPA.
GUSTS OF 23-26KT SHOULD PERSIST THROUGH AT LEAST 06Z FRI.
//ATL CONFIDENCE...06Z UPDATE...
LOW CONFIDENCE ON WHETHER IFR CIGS WILL DEVELOP TODAY.
HIGH CONFIDENCE ON ALL OTHER ELEMENTS.
SNELSON
&&
.PRELIMINARY POINT TEMPS/POPS...
ATHENS 61 32 48 25 / 100 40 0 0
ATLANTA 60 30 46 28 / 100 20 0 0
BLAIRSVILLE 54 27 41 19 / 100 20 0 0
CARTERSVILLE 58 28 45 24 / 100 20 0 0
COLUMBUS 68 33 52 30 / 100 20 0 0
GAINESVILLE 59 30 45 26 / 100 20 0 0
MACON 69 34 51 26 / 100 40 0 0
ROME 57 27 46 24 / 100 20 0 0
PEACHTREE CITY 63 29 48 25 / 100 20 0 0
VIDALIA 75 40 53 32 / 100 90 0 0
&&
.FFC WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY FROM 6 PM THIS EVENING TO 7 PM EST FRIDAY FOR THE
FOLLOWING ZONES: BALDWIN...BANKS...BARROW...BARTOW...BIBB...
BLECKLEY...BUTTS...CARROLL...CATOOSA...CHATTAHOOCHEE...
CHATTOOGA...CHEROKEE...CLARKE...CLAYTON...COBB...COWETA...
CRAWFORD...CRISP...DADE...DEKALB...DODGE...DOOLY...DOUGLAS...
EMANUEL...FAYETTE...FLOYD...FORSYTH...GLASCOCK...GORDON...
GREENE...GWINNETT...HALL...HANCOCK...HARALSON...HARRIS...HEARD...
HENRY...HOUSTON...JACKSON...JASPER...JEFFERSON...JOHNSON...
JONES...LAMAR...LAURENS...MACON...MADISON...MARION...
MERIWETHER...MONROE...MONTGOMERY...MORGAN...MURRAY...MUSCOGEE...
NEWTON...NORTH FULTON...OCONEE...OGLETHORPE...PAULDING...PEACH...
PIKE...POLK...PULASKI...PUTNAM...ROCKDALE...SCHLEY...SOUTH
FULTON...SPALDING...STEWART...SUMTER...TALBOT...TALIAFERRO...
TAYLOR...TELFAIR...TOOMBS...TREUTLEN...TROUP...TWIGGS...UPSON...
WALKER...WALTON...WARREN...WASHINGTON...WEBSTER...WHEELER...
WHITFIELD...WILCOX...WILKES...WILKINSON.
WIND ADVISORY FROM 6 PM THIS EVENING TO 7 AM EST SATURDAY FOR
THE FOLLOWING ZONES: DAWSON...FANNIN...GILMER...LUMPKIN...
PICKENS...TOWNS...UNION...WHITE.
&&
$$
SHORT TERM...SNELSON
LONG TERM....17
AVIATION...SNELSON
AREA FORECAST DISCUSSION
NWS DES MOINES IA
346 AM CST THU DEC 20 2012
...LIFE THREATENING BLIZZARD CONDITIONS TO IMPACT IOWA TONIGHT
THROUGH THURSDAY AFTERNOON...
.SHORT TERM /TODAY/...
CURRENT SITUATION HAS LONG WAVE TROUGH MOVING THROUGH CENTRAL PLAINS
WITH NOTED PV ANOMALY ACROSS ERN OK/KS. VERY STRONG FORCING
STILL EXISTS BACK INTO DEFORMATION ZONE AND IS MAINLY KINEMATIC
BY THIS POINT WITH THETA-E ADVECTION MAX NOW LIFTING OFF TO THE
NORTH AND EAST. HOWEVER JUST TO THE EAST INTO CENTRAL IA
FRONTOGENETICAL FORCING IS STILL EVIDENT AND LIKELY DRIVING ENHANCED
PRECIP WHERE DES MOINES OBS CONTINUE TO FLOAT AROUND 1/4 TO 1/2SM.
LATEST RAP CONTINUES TO DEPICT NEGATIVE H5/H6 THETA-E LAPSE RATES
AND EPV IN DENDRITIC GROWTH ZONE SO SEE NO REASON TO CHANGE CURRENT
AMOUNTS WITH LOW STATIC STABILITY CONTINUING TO REALIZE FORCING AND
PRODUCE MODERATE TO HEAVY SNOW FOR AT LEAST THE NEXT SEVERAL HOURS.
RAIN/SNOW LINE APPEARS TO BE IN FAR SERN IA AND SHOULD CONTINUE
ADVANCING SOUTH AND EAST THROUGH 12Z WHEN ENTIRE FORECAST AREA
SHOULD BE ALL SNOW. STORM TOTALS MAY STILL REACH 14 INCHES IN A FEW
SPOTS OF CENTRAL IA.
.LONG TERM /TONIGHT THROUGH WEDNESDAY/...
FOR TONIGHT...WE WILL STILL BE DEALING WITH BLOWING SNOW AND REDUCED
VISIBILITIES MAINLY OVER THE EASTERN CWA BUT CONDITIONS WILL BE
IMPROVING THROUGH THE EVENING. WITH THE FRESH SNOWPACK...CLEARING
SKIES AND DIMINISHING WIND...TEMPS WILL BE QUITE COLD TONIGHT AND I
EXPECT TEMPS TO BE COLDER THAN WHAT GUIDANCE SUGGESTS THROUGH AT
LEAST FRIDAY.
OTHER THAN COLDER TEMPS THROUGH FRIDAY THE EXTENDED THROUGH MONDAY
LOOKS RATHER QUIET WITH SLOWLY MODERATING TEMPERATURES.
MONDAY NIGHT THROUGH WEDNESDAY THE MODELS ARE STILL IN SUBSTANTIAL
DISAGREEMENT ON THE HANDLING OF A SHORT WAVE MOVING ACROSS THE AREA
THROUGH CHRISTMAS DAY. THE EURO AND CANADIAN ARE ARE MORE SIMILAR
WITH A LITTLE DEEPER AND SLOWER WAVE WITH A SURFACE LOW ACROSS THE
SOUTHERN PLAINS. THE GFS HAS A WEAKER WAVE AND IT IS FASTER AND
FURTHER NORTH WITH IT AND THE SURFACE LOW IS ALSO MUCH WEAKER AND
FURTHER NORTH. FOR NOW THERE WAS LITTLE CHANGE MADE TO THE GOING
FORECAST UNTIL MODEL CONSENSUS BECOMES BETTER ALIGNED.
&&
.AVIATION...20/06Z
MODERATE TO HEAVY SNOW HAS FALLEN ACROSS MUCH OF CNTRL IA EXCEPT IN
THE KOTM AREA. THE SNOW WILL CONTINUE MUCH OF THE NEXT 6 HOURS WITH
SNOW BEGINNING AT KOTM BY AROUND 09Z. WINDS WILL SIGNIFICANTLY
INCREASE OVERNIGHT INTO THURSDAY...ESPECIALLY BETWEEN 12-18Z. EXPECT
WIDESPREAD BLIZZARD/LIFR CONDITIONS THROUGH MUCH OF THURSDAY WITH
WIND GUSTS IN EXCESS OF 45 KTS AT TIMES. CONDITIONS WILL IMPROVE
LATE THURSDAY INTO THE EVENING AS THE GUSTS DIMINISH.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
BLIZZARD WARNING UNTIL 6 PM CST THURSDAY FOR BLACK HAWK-BREMER-
BUTLER-CERRO GORDO-CLARKE-DECATUR-FRANKLIN-GRUNDY-HAMILTON-
HANCOCK-HARDIN-JASPER-LUCAS-MAHASKA-MARION-MARSHALL-POLK-
POWESHIEK-STORY-TAMA-WARREN-WAYNE-WINNEBAGO-WORTH-WRIGHT.
BLIZZARD WARNING UNTIL NOON CST THURSDAY FOR ADAIR-ADAMS-AUDUBON-
BOONE-CALHOUN-CARROLL-CASS-CRAWFORD-DALLAS-GREENE-GUTHRIE-
HUMBOLDT-MADISON-POCAHONTAS-RINGGOLD-SAC-TAYLOR-UNION-WEBSTER.
WINTER STORM WARNING UNTIL NOON CST THURSDAY FOR EMMET-KOSSUTH-
PALO ALTO.
BLIZZARD WARNING FROM MIDNIGHT TONIGHT TO 6 PM CST THURSDAY FOR
APPANOOSE-DAVIS-MONROE-WAPELLO.
&&
$$
SHORT TERM...BSS
LONG TERM...FAB
AVIATION...DONAVON
AREA FORECAST DISCUSSION
NWS TOPEKA KS
319 AM CST THU DEC 20 2012
.DISCUSSION...
THE STORM SYSTEM SEEMS TO BE PROGRESSING AS FORECASTED WITH A WIDE
BAND OF MODERATE TO HEAVY SNOW AND WINDS GUSTING OVER 45 MPH MOVING
INTO THE EASTERN HALF OF THE AREA. 08Z WATER VAPOR SHOWS THE UPPER
LOW NEARLY OVER EMP CONTINUING TO LIFT NORTHEAST. MEANWHILE SFC OBS
SHOW THE SFC LOW MOVING NORTHEAST THROUGH CENTRAL MO AND DEEPENING.
THE STORM IS ON TRACK TO BE OUT OF THE AREA BY 9 AM. SO MAIN CONCERN
TODAY IS THE WINDS AND WHETHER WE WILL NEED A SEPARATE WIND ADVISORY
ONCE THE SNOW ENDS. LATEST NAM AND RAP PROGS SHOW WINDS SUBSIDING
ONCE THE BAND OF SNOW PASSES TO THE EAST AND CNK IS ALREADY TRENDING
WEAKER...SO THE CURRENT WINTER WEATHER HEADLINES LOOK TO COVER THE
WINDS. THE PLAN IS TO DOWNGRADE THE WARNING TO A WINTER WEATHER
ADVISORY AS THE BACK EDGE OF HEAVIER SNOW MOVES EAST TO ACCOUNT FOR
THE WINDS AND BLOWING SNOW...AND KEEP THE ORIGINAL EXPIRATION TIMES
FOR NOW.
THINGS SHOULD CLEAR OUT QUICKLY TODAY...BUT STRONG WINDS AND TEMPS
REMAINING BELOW FREEZING SHOULD MAKE IT FEEL PRETTY RAW. UPPER LEVEL
RIDGING DEVELOPS AND PERSISTS OVER THE CENTRAL PLAINS INTO THE
WEEKEND WITH DRY WEATHER EXPECTED. PREVIOUS FORECAST TEMPS FOR
FRIDAY AND SATURDAY SEEM TO BE IN THE BALL PARK EXPECTING SOME SNOW
COVER INITIALLY...SO HAVE NOT MADE MANY CHANGES.
THE FORECAST FOR NEXT WEEK CONTINUES TO BE UNCERTAIN AS THE ECMWF
HAS EXHIBITED POOR CONTINUITY FROM RUN TO RUN. THE GFS HAS STARTED
TO SHOW SOME CONSISTENCY...BUT THERE REMAINS SOME VARIATION IN THE
TRACK OF THE STORM SYSTEM FOR CHRISTMAS. THINK THE ECMWF HAS TRENDED
FURTHER SOUTH DUE TO AN ARCTIC INTRUSION FROM THE NORTH WHICH WOULD
BRING SOME VERY COLD AND DRY SOUTH SOUTH INTO THE PLAINS. IT IS
INTERESTING TO NOTE THAT THE GEM SEEMS TO BE IN THE GFS CAMP OF A
DEEPENING SYSTEM AND A CHANCE FOR SNOW. OPTED TO KEEP A 30 PERCENT
CHANCE FOR SNOW MAINLY FOR CHRISTMAS DAY AND TUESDAY NIGHT UNTIL
THERE IS BETTER CONSISTENCY FROM RUN TO RUN. ALSO TRENDED TEMPS
COOLER FOR NEXT WEEK WITH BOTH THE ECMWF AND GFS SHOWING COLD AIR
ADVECTION THROUGH THE PERIOD.
WOLTERS
&&
.AVIATION...
CONFIDENCE IN THE SPECIFICS OF THE NEXT SEVERAL HOURS IS NOT HIGH.
IT APPEARS SEVERAL PERIODS OF PRECIP...MAINLY SNOW...WILL AFFECT
THE TERMINALS WITH AT LEAST MODERATE SNOW DROPPING CONDITIONS TO
LIFR...THOUGH MANY LOCATIONS THAT HAVE RECEIVED SUCH SNOW THIS
EVENING HAVE NOT EXPERIENCED SUCH CONDITIONS. WILL BACK OFF FROM
EARLIER FORECAST OF VLIFR. THE WINDOW FOR MIXED PRECIP REMAINS
SMALL WITH ALL SNOW BY 07Z ANTICIPATED. STRONG WINDS WILL BE THE
RULE THROUGH NEARLY 0Z DESPITE THE STORM EXITING.
65
&&
.TOP WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING UNTIL 6 AM CST EARLY THIS MORNING FOR
KSZ010-022-023-036.
WINTER STORM WARNING UNTIL 9 AM CST THIS MORNING FOR KSZ011-012-
024-026-038-039.
WINTER WEATHER ADVISORY UNTIL 6 AM CST EARLY THIS MORNING FOR
KSZ008-009-020-021-034-035-037-054.
WINTER WEATHER ADVISORY UNTIL 9 AM CST THIS MORNING FOR
KSZ040-055-056-058-059.
&&
$$
AREA FORECAST DISCUSSION
NWS TOPEKA KS
1142 PM CST WED DEC 19 2012
...UPDATE TO AVIATION...
.UPDATE...
ALTERATIONS TO THE FORECAST WILL BE MADE BASED ON LATEST TRENDS AND
MODEL OUTPUT. THE OVERALL TRANSITION TO WINTRY PRECIPITATION IS A
BIT SLOWER THAN EARLIER RUNS PROGGED. LAST SEVERAL RAP RUNS AND
THE 18Z AND 0Z NAM SUGGEST THE PERSISTENT SNOW IN NORTH CENTRAL
KANSAS WILL WANE IN THE NEXT FEW HOURS AND ANOTHER AREA STRENGTHEN
JUST TO ITS SOUTHWEST AND ROTATE CLOCKWISE AS THE UPPER TROF TAKES
ON A NEGATIVE TILT AND MEETS WITH SLANTWISE AND BIT OF UPRIGHT
INSTABILITY. TAPERED BACK TOTALS IN THE NORTH A LITTLE WITH THIS
IN MIND. LOCALLY HIGHER AMOUNTS IN THE MANHATTAN TO LAWRENCE TO
HIAWATHA REGION ARE POSSIBLE IF THE CONVECTIVE ELEMENTS PERSIST.
65
&&
.DISCUSSION...
A VERY POTENT AND SIGNIFICANT WINTER STORM SET TO IMPACT THE AREA
WEDNESDAY NIGHT INTO THURSDAY MORNING...BRINGING PERIODS OF HEAVY
SNOW AND VERY STRONG WINDS. NEAR BLIZZARD CONDITIONS WILL BE LIKELY
ACROSS ALL OF NORTH CENTRAL...NORTHEAST...AND EAST CENTRAL KANSAS.
SHORT TERM FORECAST (TONIGHT THROUGH TOMORROW)...
AT 22Z A SURFACE TROUGH WAS UNDERGOING LEE SIDE CYCLOGENESIS IN FAR
NORTHWEST OKLAHOMA. THE STRONG PRESSURE GRADIENT ON THE NORTHERN AND
WESTERN EDGE OF THE LOW IS PRODUCING STRONG WINDS ACROSS WESTERN
NEBRASKA AND WESTERN KANSAS. RADAR TRENDS INDICATE THAT
PRECIPITATION HAS COMMENCED ACROSS CENTRAL AND SOUTHERN NEBRASKA AND
SURFACE OBS INDICATE THE SNOW LINE AT THIS POINT RUNS FROM KRDK TO
KGCK. AS THE SURFACE LOW DEEPENS AND MOVES TO THE EAST THE
FREEZING LINE WILL SHIFT TO THE SOUTHEAST WITH IT. BANDED
PRECIPITATION ACROSS NORTHERN KANSAS AND CENTRAL NEBRASKA LOOKS TO
BE IN RESPONSE TO STRONG ISENTROPIC ASCENT ALONG WITH GOOD 850 TO
700 MB FRONTOGENETICAL LIFT. ALOFT RAP ANALYSIS INDICATES THE
STRONG MID LEVEL TROUGH IS CURRENTLY OVER THE GREAT
DIVIDE...PUSHING INTO THE CENTRAL HIGH PLAINS. AS THIS TROUGH
PUSHES EASTWARD IT WILL CONTINUE TO DEEPEN TO AROUND 536 DM OVER
WESTERN MISSOURI OVERNIGHT. AS THIS MID/UPPER TROUGH COMES THROUGH
THE AREA A VERY STRONG PV ANOMALY WILL GLIDE JUST SOUTH OF THE
AREA...INDICATING THE BEST MID/UPPER ASCENT JUST NORTH OF THE PV
ANOMALY CENTER.
MODELS HAVE BEEN FAIRLY CONSISTENT REGARDING THE SCENARIO FOR
WEDNESDAY NIGHT INTO THURSDAY. THE PREVIOUSLY MENTIONED SURFACE
TROUGH IS EXPECTED TO REMAIN STEADY STATE OR POSSIBLY EVEN DEEPEN A
BIT AS IT MOVES ACROSS NORTHERN OKLAHOMA. IT WILL TAKE A TURN TO THE
NORTH AND MOVE NORTHEAST ALONG INTERSTATE 44 OVERNIGHT. STRONG
TRANSPORT VECTORS BOTH AT THE SURFACE AND AT 850 MB WILL BRING A
GOOD AMOUNT OF MOISTURE INTO THE EASTERN FLANK OF THE STRONG LOW
LEVEL CYCLONE. THE WARM/MOIST CONVEYOR BELT WILL TRANSPORT THE
MOISTURE AROUND THE NORTHERN FLANK OF THE LOW LEVEL CYCLONE AND
INTRODUCE IT TO THE COLD AIR ON THE NORTHWESTERN AND WESTERN SIDE OF
THE LOW LEVEL TROUGH. THE BETTER/DEEPER MOISTURE WILL ALSO DEFINE A
DECENT WARM SECTOR...WHICH WILL TAKE SHAPE MAINLY ALONG AND EAST OF
THE KANSAS TURNPIKE THIS EVENING. BETWEEN ROUGHLY 00Z AND 06Z THE
AREA SOUTH AND EAST OF THE KANSAS TURNPIKE WILL LIKELY EXPERIENCE A
PERIOD OF RAIN...WITH SOME THUNDERSTORMS. WITH 500 TO 1000 J/KG OF
MU CAPE RESIDING IN THE WARM SECTOR A FEW OF THE THUNDERSTORMS COULD
BECOME STRONG...ESPECIALLY GIVEN THE VERY STRONG DEEP LAYER SHEAR.
AS THE COLD AIR QUICKLY SHIFTS EASTWARD LIQUID PRECIPITATION WILL
QUICKLY CHANGE OVER TO SNOW...WITH POTENTIALLY A BRIEF PERIOD OF
SLEET IN THE TRANSITION PERIOD. THIS TRANSITION WILL LIKELY OCCUR
AROUND KMHK AROUND 05Z...WITH A CHANGE OVER AT KTOP AND KLWC BETWEEN
07Z AND 08Z. NAM CROSS SECTIONS INDICATE A FEW AREAS WITH CONVECTIVE
INSTABILITY RESIDING ALONG THE INTERSTATE 70 CORRIDOR BETWEEN 09Z
AND 12Z. THIS IS THE TIME PERIOD TARGETED AS THE PERIOD OF HEAVIEST
SNOW ACROSS THE FAR EASTERN PORTION OF THE STATE. ACROSS NORTH
CENTRAL KANSAS GOOD MID LEVEL FRONTOGENESIS AND THE AFOREMENTIONED
PV ANOMALY WILL BE THE PRIMARY MODES OF LIFT. ALTHOUGH THE OVERALL
LIFT FROM THIS SYSTEM WILL BE QUITE ROBUST ITS PROGRESSIVE NATURE
WILL HELP KEEP SNOW AMOUNTS TO A MANAGEABLE 4 TO 6 INCHES ALONG AND
NORTH OF HIGHWAY INTERSTATE 70 AND IN THE 1 TO 3 INCH RANGE ALONG
AND SOUTH OF INTERSTATE 35. EXPECT THE HEAVY SNOW TO COME TO AN END
BY 12Z ACROSS THE ENTIRE AREA...WITH LINGERING SNOW LIKELY COMING TO
AN END BY 15Z THURSDAY.
AGGRAVATING THE PERIL OF THIS SYSTEM ARE THE VERY STRONG WINDS
ASSOCIATED WITH THE LOW LEVEL CYCLONE. MODELS CONTINUE TO INDICATE
SURFACE WINDS BEING SUSTAINED AT 30 TO 40 MPH. 925 MB WINDS ARE ALSO
PROGGED TO BE IN THE 50 TO 60 KT RANGE...WITH 850 MB WINDS REACHING
70 KTS. DEEP MIXING WILL LIKELY NOT OCCUR...BUT WITH LOW LEVEL WINDS
BEING SO STRONG ITS CONCEIVABLE THAT 50 MPH GUSTS WILL BE POSSIBLE
IN CONCURRENCE WITH THE MODERATE TO HEAVY SNOW. THE COMBINATION OF
THESE FACTORS WILL BRING NEAR BLIZZARD CONDITIONS TO ALMOST THE
ENTIRE AREA...WITH AREAS RECEIVING THE HEAVIEST SNOW HAVING THE MOST
LIMITED VISIBILITIES. CONSIDERATION OF AN UPGRADE TO BLIZZARD
WARNING WAS MADE HOWEVER THE EXPECTED SHORT DURATION OF THE
CONDITIONS (ON THE ORDER OF 3 TO 5 HOURS) PRECLUDED THAT UPGRADE.
THE CONSISTENCY OF THE MODELS TO THIS POINT HAVE BEEN GOOD...BUT THE
18Z RUN OF THE NAM CAME IN MUCH MORE ROBUST REGARDING THE
PRECIPITATION OUTPUT AND WIND FORECAST. WILL CONTINUE TO MONITOR THE
EVOLUTION OF THIS SYSTEM AND PROVIDE UPDATES AS NECESSARY.
JL
THURSDAY...
SNOW WILL LINGER IN EXTREME KANSAS THROUGH MID MORNING WITH VERY
STRONG WINDS GUSTING TO 45 MPH OR GREATER IN FAR EASTERN KANSAS AS
WELL. THE SNOW SHOULD END BY 9 AM OR SO...WITH WINDS GRADUALLY
DECREASING AFTER THAT POINT AS WELL. THE EXTENT OF BLOWING SNOW
WILL DEPEND ON TOTAL ACCUMULATIONS...BUT EXPECT ANY LOCATION WITH
MORE THAN 2 INCHES OF SNOW TO SEE QUITE A BIT OF BLOWING WITH SOME
DRIFTING...AND THOSE AREAS THAT SEE CLOSER TO 5 OR 6 INCHES OF
SNOW CAN EXPECT SOME PRETTY SUBSTANTIAL BLOWING AND DRIFTING. WITH
THE TREND TOWARD A SLIGHTLY LATER END TIME FOR THE SNOW...EXPECT
THE MORNING COMMUTE TO BE RATHER DIFFICULT.
THURSDAY NIGHT THROUGH MONDAY...
STILL EXPECT A RATHER BENIGN WEATHER PATTERN THROUGH THIS PERIOD
AND HAVE NOT MADE MANY CHANGES TO THE FORECAST GIVEN THE HIGH
IMPACT WEATHER PRESENT IN THE SHORT TERM. MADE SOME ADJUSTMENTS TO
THE TEMPERATURES BASED ON EXPECTED SNOW COVER AS BOTH HIGH AND LOW
TEMPS IN THE NORTHERN FORECAST AREA COULD BE QUITE A BIT COOLER
THAN THE MODEL CONSENSUS. FRIDAY MORNING...AND EVEN SATURDAY
MORNING...COULD BE QUITE COLD AS HIGH PRESSURE BUILDS INTO THE
AREA WITH LIGHT WINDS...CLEAR SKIES...AND SNOW COVER.
MONDAY NIGHT THROUGH WEDNESDAY...
THERE REMAINS PLENTY OF UNCERTAINTY REGARDING A POTENTIAL STORM
SYSTEM DURING THIS PERIOD NEAR OR JUST AFTER CHRISTMAS DAY. THE
OPERATIONAL ECMWF AND GFS HAVE COME BACK INTO AGREEMENT IN TERMS
OF PLACING THE FORECAST OFFICE ON THE COLD SIDE OF A POTENT STORM
SYSTEM. TIMING WOULD SUGGEST THAT THE BULK OF PRECIP POTENTIAL
WOULD COME ON THE NIGHT OF THE 25TH INTO THE 26TH. HAVE MAINTAINED
CHANCES FOR SNOW ACROSS THE AREA DURING THIS TIME FRAME AND WILL
CONTINUE TO MONITOR THE PROGRESSION OF THIS STORM SYSTEM. THE TAKE
AWAY POINT AT THIS TIME IS THAT THE POTENTIAL FOR ACCUMULATING
WINTER PRECIPITATION EXISTS...BUT IS BY NO MEANS A GUARANTEE AT
THIS TIME AS THE ENERGY IS CURRENTLY OVER EASTERN RUSSIA AND
SIGNIFICANT CHANGES TO THE FORECAST ARE POSSIBLE IN THE NEXT FEW
DAYS. STAY TUNED.
BARJENBRUCH
&&
.AVIATION...
CONFIDENCE IN THE SPECIFICS OF THE NEXT SEVERAL HOURS IS NOT HIGH.
IT APPEARS SEVERAL PERIODS OF PRECIP...MAINLY SNOW...WILL AFFECT
THE TERMINALS WITH AT LEAST MODERATE SNOW DROPPING CONDITIONS TO
LIFR...THOUGH MANY LOCATIONS THAT HAVE RECEIVED SUCH SNOW THIS
EVENING HAVE NOT EXPERIENCED SUCH CONDITIONS. WILL BACK OFF FROM
EARLIER FORECAST OF VLIFR. THE WINDOW FOR MIXED PRECIP REMAINS
SMALL WITH ALL SNOW BY 07Z ANTICIPATED. STRONG WINDS WILL BE THE
RULE THROUGH NEARLY 0Z DESPITE THE STORM EXITING.
65
&&
.TOP WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING UNTIL 9 AM CST THURSDAY FOR KSZ011-012-024-
026-038-039.
WINTER STORM WARNING UNTIL 6 AM CST THURSDAY FOR KSZ008>010-
020>023-034>036.
WINTER WEATHER ADVISORY UNTIL 9 AM CST THURSDAY FOR KSZ040-055-
056-058-059.
WINTER WEATHER ADVISORY UNTIL 6 AM CST THURSDAY FOR KSZ037-054.
&&
$$
AREA FORECAST DISCUSSION
NWS PITTSBURGH PA
252 AM EST THU DEC 20 2012
.SYNOPSIS...
HIGH PRESSURE WILL BRING DRY WEATHER OVERNIGHT INTO EARLY
THURSDAY. A STRONG LOW PRESSURE SYSTEM WILL MOVE ACROSS THE GREAT
LAKES THURSDAY INTO FRIDAY AND INTO THE NORTHEAST BY THE WEEKEND.
THIS SYSTEM WILL BRING SHOWERS WITH GUSTY WINDS THURSDAY...RAIN
CHANGING TO SNOW THURSDAY NIGHT...AND BLUSTERY CONDITIONS WITH
ACCUMULATING SNOW FRIDAY INTO SATURDAY.
&&
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
UPDATE TO LOWER MIN TEMPS OVERNIGHT.
THE LATEST RAP MID-LEVEL ANALYSIS INDICATES A 500MB TROUGH AXIS
CENTERED ACROSS THE FRONT RANGE WITH MORE OF A ZONAL FLOW ACROSS
THE UPPER OHIO VALLEY IN ADVANCED OF THIS FEATURE. AN 850MB THERMAL RIDGE
IS BUILDING INTO THE OHIO VALLEY WITH A TIGHTENED THERMAL
GRADIENT CURRENTLY BISECTING THE CWA. AT THE SURFACE...A 1021MB
HIGH IS CENTERED ACROSS WV/OH.
TONIGHT...THE SURFACE HIGH WILL SLOWLY SHIFT EASTWARD WITH WAA
ENSUING AS THE 850MB FLOW SHIFTS TO SOUTHERLY. SKIES WILL
GENERALLY BE MOSTLY CLOUDY OVERNIGHT AS LINGERING AREAS OF
STRATOCU CONTINUE TO MOVE ACROSS THE REGION AND UPPER LEVEL
MOISTURE BEGINS TO ADVECT INTO THE AREA. WITH WAA ENSUING
OVERNIGHT...SFC TEMPS WILL DECREASE VERY LITTLE OVERNIGHT...WITH
LOWS RANGING FROM THE LOWER 30S ACROSS THE I-80 CORRIDOR AND
EASTERN RIDGES TO THE UPPER 30S IN EASTERN OHIO.
&&
.SHORT TERM /6 AM THIS MORNING THROUGH SATURDAY/...
THE LATEST MODEL RUN CONSENSUS CONTINUES TO INDICATE THE DEEP MID-
LEVEL TROUGH SWINGING ACROSS THE PLAINS AND QUICKLY CLOSING OFF. ITS
ASSOCIATED SURFACE CYCLONE WILL STRENGTHEN AS IT MOVES INTO THE
GREAT LAKES ON THURSDAY. MODELS HAVE BEEN FAIRLY CONSISTENT IN
SHOWING A TIGHT PRESSURE GRADIENT SETTING UP ACROSS THE OHIO
VALLEY ON THURSDAY AND SHOWERS WITH THIS SYSTEM BEGINNING TO PUSH
IN FROM THE WEST AFTER 18Z. MOMENTUM TRANSFER FROM GFS/NAM MODEL
SOUNDINGS INDICATE 30 TO 40 MPH WINDS MIXING DOWN THURSDAY
AFTERNOON. AT THIS TIME...STILL LOOKS TO BE JUST BELOW ADVISORY
CRITERIA WITH BETTER WIND GUSTS TO THE WEST AND CLOSER TO THE LOW.
WITH SHOWERS MOVING ACROSS THE AREA...A QUARTER TO A HALF OF AN
INCH OF RAINFALL IS FORECAST ACROSS THE AREA ON THURSDAY.
THE LOW WILL SHIFT INTO THE EASTERN GREAT LAKES ON THURSDAY
NIGHT...USHERING A COLD FRONT ACROSS THE AREA BETWEEN 00Z AND
09Z. RAIN AHEAD OF THE FRONT WILL QUICKLY TURN OVER TO SNOW
WITH A SHOT OF STRONG CAA BEHIND THE FRONT. WITH THE QUICK
CHANGEOVER...A QUICK INCH OR TWO OF SNOWFALL WILL BE POSSIBLE
DEPENDING ON THE AMOUNT OF MOISTURE AND THE TIME THAT IT TAKES FOR
A DRY SLOT TO MOVE INTO THE AREA BEHIND THE FRONT.
THE SURFACE LOW WILL SHIFT FURTHER NORTHEASTWARD INTO UPSTATE NY
ON FRIDAY...ALLOWING FOR CAA TO CONTINUE AND FOR THE LOW-LEVEL
FLOW TO SHIFT FROM WEST TO NORTHWESTERLY BY THE AFTERNOON HOURS.
THERE IS STILL SOME UNCERTAINTY IN HOW THE DRY SLOT EARLY IN THE
DAY WILL BE RESOLVED. DEPENDING ON THE INTERACTION OF THE DRY AIR
WITH TROWAL WRAPPING IN AROUND SYSTEM AND ALSO HOW A CYCLONIC
FETCH WITH AN UPSTREAM LINK TO MICHIGAN WILL SERVE TO BRING SNOW
SHOWERS AND BLUSTERY CONDITIONS EARLY IN THE DAY STILL MAKE FOR
SOME UNCERTAINTY IN QPF/SNOW AMOUNTS IN THE 06Z-16Z PERIOD ON
FRIDAY. HOWEVER...AFTER 16Z...THE 850MB FLOW SHIFTS TO MORE
NORTHWESTERLY AND THE COLUMN SATURATES THROUGH THE DENDRITIC
GROWTH ZONE...MAKING UPSLOPING AND LAKE EFFECT MUCH MORE
FAVORABLE. WITH THIS IN MIND...THE WINTER STORM WATCH HAS BEEN
UPGRADED TO A WARNING FOR THE RIDGES OF WV/MD/PA. THERE IS STILL
SOME UNCERTAINTY IN LAKE EFFECT DURATION AND THUS A WATCH REMAINS
FOR LOCATIONS ALONG THE I-80 CORRIDOR.
THERE ARE TWO BIG QUESTIONS IN REGARDS TO HOW THIS EVENT WILL
UNFOLD...HOW STRONG WILL THE WINDS BE ON FRIDAY...AND WILL
SNOW/BLOWING SNOW WITH WINDS LEAD TO BLIZZARD CONDITIONS FOR
THE RIDGES. GFS/NAM MIXED LAYER WINDS INDICATE THE POTENTIAL OF
REACHING MARGINAL CRITERIA FOR A WIND ADVISORY ON FRIDAY. IN
REGARDS TO BLIZZARD CONDITIONS FOR THE RIDGES...WINDS GUSTING TO
45 MPH AT TIMES...ALONG WITH DRIER SNOW AS SNOW-TO-LIQUID RATIOS
INCREASING TO 15-20:1 DURING THE DAY WILL LEAD TO BLOWING SNOW
ACROSS MUCH OF THE AREA...ESPECIALLY THE EASTERN RIDGES. AT THIS
TIME...WENT WITH A WINTER STORM WARNING WITH NEAR BLIZZARD
CONDITIONS MENTIONED FOR THE HIGHER ELEVATIONS. THIS IS IN
CONSIDERATION THAT THERE COULD BE A FUTURE UPGRADE...BUT AT THIS
TIME CONFIDENCE IN A TIME WINDOW OF WHEN VISIBILITIES BELOW A
QUARTER OF A MILE COUPLED WITH WINDS GUSTING TO 35 MPH WOULD OCCUR
IS NOT HIGH ENOUGH TO WARRANT A BLIZZARD WARNING.
UPSLOPE AND LAKE EFFECT SNOWS WILL LIKELY PEAK FRIDAY AFTERNOON
AND OVERNIGHT INTO EARLY SATURDAY...WITH 6 TO 10 INCHES ACROSS THE
LAKE EFFECT ZONES AND 8 TO 14 FOR THE RIDGES MAKING FOR
TREACHEROUS CONDITIONS. ELSEWHERE...2-5 INCHES ACROSS THE AREA
WITH BLOWING SNOW WILL ALSO CONTRIBUTE TO IMPACTING TRAVEL.
SNOWFALL RATES WILL BEGIN TO DECREASE IN INTENSITY ON SATURDAY AS
INVERSION HEIGHTS LOWER AND THE SURFACE LOW LIFTS FURTHER
NORTHEASTWARD OF THE AREA.
FOR TEMPS...WAA ADVECTION IN A SOUTHERLY FLOW AHEAD OF THE LOW
WILL ALLOW FOR TEMPS TO WARM TO 10-15 DEGREES ABOVE NORMAL AHEAD
OF THE COLD FRONT ON THURSDAY. IN THE WAKE OF THE FRONT...WITH 850
TEMPS COOLING TO AROUND -8C...EXPECT TEMPS TO BE AROUND 5 DEGREES
BELOW NORMAL WITH BLUSTERY CONDITIONS FOR FRIDAY AND SATURDAY.
&&
.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
BLEND OF RECENT GFS AND ECMWF MODEL OUTPUT SHOWS HIGH PRESSURE
SHOULD PROMOTE MAINLY DRY SEASONABLY COLD CONDITIONS SUNDAY AND
MONDAY.
THERE CONTINUES TO BE UNCERTAINTY REGARDING THE WEATHER FOR
CHRISTMAS DAY AND WEDNESDAY AS GFS AND ECMWF DIFFER ON EVOLUTION
DETAILS OF INCOMING LOW PRESSURE SYSTEMS. AT THIS JUNCTURE DEFERRED
TO HPC SOLUTIONS WHICH SUPPORTED IDEA THAT THERE CAN BE
PRECIPITATION MOVING ACROSS THE UPPER OHIO VALLEY CHRISTMAS DAY AND
WEDNESDAY.
REGARDING TEMPERATURES...ALSO CONCURRED WITH HPC WITH PREFERENCE TO
COLDER ECMWF MOS...WHICH SHOWED LOWS AND HIGHS STRADDLING THE
FREEZING POINT. SO NOT SURPRISINGLY FORECAST FOR CHRISTMAS DAY AND
WEDNESDAY HAS A CHANCE OF RAIN AS WELL AS A CHANCE OF SNOW.
&&
.AVIATION /08Z THURSDAY THROUGH MONDAY/...
COUPLE OF EARLY RESTRICTIONS TO DEAL WITH FOR FORECAST PERIOD. LIFR
CIGS AND VIS WITH FZFG AT FKL AND DUJ. EXPECT THESE CONDITIONS TO
REMAIN FOR THE FIRST 2 TO 3 HOURS OF THE FORECAST. AFTER THIS
TIME...SFC WINDS WILL BEGIN TO INCREASE AND A CIRRUS CLOUD DECK WILL
OVERSPREAD THE AREA. EXPECT A GENERAL VFR FOR THE REST OF THE PORTS
THROUGH THE MORNING. THE FIRST CONCERN FOLLOWING DAWN WILL BE THE
RAPIDLY INTENSIFYING SURFACE WINDS IN RESPONSE TO A TIGHTENING
SURFACE PRESSURE GRADIENT AROUND A DEEPENING MIDWEST LOW. WINDS WILL
INCREASE FROM WEST TO EAST WITH SOUTHEASTERLY GUSTS OF 20 TO 25 KTS
IN THE MORNING AND GUSTS OF 30 TO 35KTS IN THE AFTERNOON. MVFR/IFR
RESTRICTIONS WITH CLOUDS AND RAIN WILL MOVE IN QUICKLY FROM THE WEST
DURING THE AFTERNOON HOURS.
.OUTLOOK.../THURSDAY NIGHT THROUGH MONDAY/...
PASSAGE OF STRONG LOW PRESSURE SYSTEM AND ITS COLD FRONT THURSDAY
EVENING WILL PROMOTE IFR RAIN SHOWERS AND WIND GUSTS TO 40 KTS.
ENSUING COLD WESTERLY WINDS WILL PROMOTE PERIODS OF IFR RESTRICTIONS
IN SNOW SHOWERS LATE THURSDAY NIGHT INTO SATURDAY AFTERNOON. SURFACE
WINDS CAN CONTINUE TO GUST AT TIMES OVER 35 KTS.
ENSUING HIGH PRESSURE SHOULD PROMOTE IMPROVEMENT TO VFR SUNDAY AND
MONDAY.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...WINTER STORM WARNING FROM 11 AM FRIDAY TO 7 PM EST SATURDAY
FOR MDZ001.
OH...NONE.
PA...WINTER STORM WATCH FROM LATE TONIGHT THROUGH SATURDAY EVENING
FOR PAZ007>009-015-016.
WINTER STORM WARNING FROM 11 AM FRIDAY TO 7 PM EST SATURDAY
FOR PAZ074-076.
WV...WINTER STORM WARNING FROM 11 AM FRIDAY TO 7 PM EST SATURDAY
FOR WVZ023-041.
&&
$$
AREA FORECAST DISCUSSION
NWS PITTSBURGH PA
1157 PM EST WED DEC 19 2012
.SYNOPSIS...
HIGH PRESSURE WILL BRING DRY WEATHER OVERNIGHT INTO EARLY
THURSDAY. A STRONG LOW PRESSURE SYSTEM WILL MOVE ACROSS THE GREAT
LAKES THURSDAY INTO FRIDAY AND INTO THE NORTHEAST BY THE WEEKEND.
THIS SYSTEM WILL BRING SHOWERS WITH GUSTY WINDS THURSDAY...RAIN
CHANGING TO SNOW THURSDAY NIGHT...AND BLUSTERY CONDITIONS WITH
ACCUMULATING SNOW FRIDAY INTO SATURDAY.
&&
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
UPDATE TO INCLUDE THE MENTION OF PATCHY DENSE FOG IN NORTHWEST
PA AND EASTERN OHIO.
THE LATEST RAP MID-LEVEL ANALYSIS INDICATES A 500MB TROUGH AXIS
CENTERED ACROSS THE FRONT RANGE WITH MORE OF A ZONAL FLOW ACROSS
THE UPPER OHIO VALLEY IN ADVANCED OF THIS FEATURE. AN 850MB THERMAL RIDGE
IS BUILDING INTO THE OHIO VALLEY WITH A TIGHTENED THERMAL
GRADIENT CURRENTLY BISECTING THE CWA. AT THE SURFACE...A 1021MB
HIGH IS CENTERED ACROSS WV/OH.
TONIGHT...THE SURFACE HIGH WILL SLOWLY SHIFT EASTWARD WITH WAA
ENSUING AS THE 850MB FLOW SHIFTS TO SOUTHERLY. SKIES WILL
GENERALLY BE MOSTLY CLOUDY OVERNIGHT AS LINGERING AREAS OF
STRATOCU CONTINUE TO MOVE ACROSS THE REGION AND UPPER LEVEL
MOISTURE BEGINS TO ADVECT INTO THE AREA. WITH WAA ENSUING
OVERNIGHT...SFC TEMPS WILL DECREASE VERY LITTLE OVERNIGHT...WITH
LOWS RANGING FROM THE LOWER 30S ACROSS THE I-80 CORRIDOR AND
EASTERN RIDGES TO THE UPPER 30S IN EASTERN OHIO.
&&
.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
THE LATEST MODEL RUN CONSENSUS CONTINUES TO INDICATE THE DEEP MID-
LEVEL TROUGH SWINGING ACROSS THE PLAINS AND QUICKLY CLOSING OFF. ITS
ASSOCIATED SURFACE CYCLONE WILL STRENGTHEN AS IT MOVES INTO THE
GREAT LAKES ON THURSDAY. MODELS HAVE BEEN FAIRLY CONSISTENT IN
SHOWING A TIGHT PRESSURE GRADIENT SETTING UP ACROSS THE OHIO
VALLEY ON THURSDAY AND SHOWERS WITH THIS SYSTEM BEGINNING TO PUSH
IN FROM THE WEST AFTER 18Z. MOMENTUM TRANSFER FROM GFS/NAM MODEL
SOUNDINGS INDICATE 30 TO 40 MPH WINDS MIXING DOWN THURSDAY
AFTERNOON. AT THIS TIME...STILL LOOKS TO BE JUST BELOW ADVISORY
CRITERIA WITH BETTER WIND GUSTS TO THE WEST AND CLOSER TO THE LOW.
WITH SHOWERS MOVING ACROSS THE AREA...A QUARTER TO A HALF OF AN
INCH OF RAINFALL IS FORECAST ACROSS THE AREA ON THURSDAY.
THE LOW WILL SHIFT INTO THE EASTERN GREAT LAKES ON THURSDAY
NIGHT...USHERING A COLD FRONT ACROSS THE AREA BETWEEN 00Z AND
09Z. RAIN AHEAD OF THE FRONT WILL QUICKLY TURN OVER TO SNOW
WITH A SHOT OF STRONG CAA BEHIND THE FRONT. WITH THE QUICK
CHANGEOVER...A QUICK INCH OR TWO OF SNOWFALL WILL BE POSSIBLE
DEPENDING ON THE AMOUNT OF MOISTURE AND THE TIME THAT IT TAKES FOR
A DRY SLOT TO MOVE INTO THE AREA BEHIND THE FRONT.
THE SURFACE LOW WILL SHIFT FURTHER NORTHEASTWARD INTO UPSTATE NY
ON FRIDAY...ALLOWING FOR CAA TO CONTINUE AND FOR THE LOW-LEVEL
FLOW TO SHIFT FROM WEST TO NORTHWESTERLY BY THE AFTERNOON HOURS.
THERE IS STILL SOME UNCERTAINTY IN HOW THE DRY SLOT EARLY IN THE
DAY WILL BE RESOLVED. DEPENDING ON THE INTERACTION OF THE DRY AIR
WITH TROWAL WRAPPING IN AROUND SYSTEM AND ALSO HOW A CYCLONIC
FETCH WITH AN UPSTREAM LINK TO MICHIGAN WILL SERVE TO BRING SNOW
SHOWERS AND BLUSTERY CONDITIONS EARLY IN THE DAY STILL MAKE FOR
SOME UNCERTAINTY IN QPF/SNOW AMOUNTS IN THE 06Z-16Z PERIOD ON
FRIDAY. HOWEVER...AFTER 16Z...THE 850MB FLOW SHIFTS TO MORE
NORTHWESTERLY AND THE COLUMN SATURATES THROUGH THE DENDRITIC
GROWTH ZONE...MAKING UPSLOPING AND LAKE EFFECT MUCH MORE
FAVORABLE. WITH THIS IN MIND...THE WINTER STORM WATCH HAS BEEN
UPGRADED TO A WARNING FOR THE RIDGES OF WV/MD/PA. THERE IS STILL
SOME UNCERTAINTY IN LAKE EFFECT DURATION AND THUS A WATCH REMAINS
FOR LOCATIONS ALONG THE I-80 CORRIDOR.
THERE ARE TWO BIG QUESTIONS IN REGARDS TO HOW THIS EVENT WILL
UNFOLD...HOW STRONG WILL THE WINDS BE ON FRIDAY...AND WILL
SNOW/BLOWING SNOW WITH WINDS LEAD TO BLIZZARD CONDITIONS FOR
THE RIDGES. GFS/NAM MIXED LAYER WINDS INDICATE THE POTENTIAL OF
REACHING MARGINAL CRITERIA FOR A WIND ADVISORY ON FRIDAY. IN
REGARDS TO BLIZZARD CONDITIONS FOR THE RIDGES...WINDS GUSTING TO
45 MPH AT TIMES...ALONG WITH DRIER SNOW AS SNOW-TO-LIQUID RATIOS
INCREASING TO 15-20:1 DURING THE DAY WILL LEAD TO BLOWING SNOW
ACROSS MUCH OF THE AREA...ESPECIALLY THE EASTERN RIDGES. AT THIS
TIME...WENT WITH A WINTER STORM WARNING WITH NEAR BLIZZARD
CONDITIONS MENTIONED FOR THE HIGHER ELEVATIONS. THIS IS IN
CONSIDERATION THAT THERE COULD BE A FUTURE UPGRADE...BUT AT THIS
TIME CONFIDENCE IN A TIME WINDOW OF WHEN VISIBILITIES BELOW A
QUARTER OF A MILE COUPLED WITH WINDS GUSTING TO 35 MPH WOULD OCCUR
IS NOT HIGH ENOUGH TO WARRANT A BLIZZARD WARNING.
UPSLOPE AND LAKE EFFECT SNOWS WILL LIKELY PEAK FRIDAY AFTERNOON
AND OVERNIGHT INTO EARLY SATURDAY...WITH 6 TO 10 INCHES ACROSS THE
LAKE EFFECT ZONES AND 8 TO 14 FOR THE RIDGES MAKING FOR
TREACHEROUS CONDITIONS. ELSEWHERE...2-5 INCHES ACROSS THE AREA
WITH BLOWING SNOW WILL ALSO CONTRIBUTE TO IMPACTING TRAVEL.
SNOWFALL RATES WILL BEGIN TO DECREASE IN INTENSITY ON SATURDAY AS
INVERSION HEIGHTS LOWER AND THE SURFACE LOW LIFTS FURTHER
NORTHEASTWARD OF THE AREA.
FOR TEMPS...WAA ADVECTION IN A SOUTHERLY FLOW AHEAD OF THE LOW
WILL ALLOW FOR TEMPS TO WARM TO 10-15 DEGREES ABOVE NORMAL AHEAD
OF THE COLD FRONT ON THURSDAY. IN THE WAKE OF THE FRONT...WITH 850
TEMPS COOLING TO AROUND -8C...EXPECT TEMPS TO BE AROUND 5 DEGREES
BELOW NORMAL WITH BLUSTERY CONDITIONS FOR FRIDAY AND SATURDAY.
&&
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
BLEND OF RECENT GFS AND ECMWF MODEL OUTPUT SHOWS HIGH PRESSURE
SHOULD PROMOTE MAINLY DRY SEASONABLY COLD CONDITIONS SUNDAY AND
MONDAY.
THERE CONTINUES TO BE UNCERTAINTY REGARDING THE WEATHER FOR
CHRISTMAS DAY AND WEDNESDAY AS GFS AND ECMWF DIFFER ON EVOLUTION
DETAILS OF INCOMING LOW PRESSURE SYSTEMS. AT THIS JUNCTURE DEFERRED
TO HPC SOLUTIONS WHICH SUPPORTED IDEA THAT THERE CAN BE
PRECIPITATION MOVING ACROSS THE UPPER OHIO VALLEY CHRISTMAS DAY AND
WEDNESDAY.
REGARDING TEMPERATURES...ALSO CONCURRED WITH HPC WITH PREFERENCE TO
COLDER ECMWF MOS...WHICH SHOWED LOWS AND HIGHS STRADDLING THE
FREEZING POINT. SO NOT SURPRISINGLY FORECAST FOR CHRISTMAS DAY AND
WEDNESDAY HAS A CHANCE OF RAIN AS WELL AS A CHANCE OF SNOW.
&&
.AVIATION /06Z THURSDAY THROUGH MONDAY/...
MODEL TIME HEIGHT SECTIONS INDICATE STRATOCUMULUS SHOULD BECOME
GRADUALLY ERADICATED AS SOUTHEASTERLY DOWNSLOPE FLOW FROM THE
RIDGES STARTS TO BECOME STRONGER OVERNIGHT. THIS WILL LEAVE US
WITH A PERIOD OF INCREASING HIGH CLOUDS AND LOW PRECIPITATION
CHANCES AS THE LOW LEVELS ARE DRIED DUE TO DOWNSLOPING. A STRONGER
PRESSURE GRADIENT SHOULD GRADUALLY INCREASE SOUTHEASTERLY FLOW
WITH GUSTS MATERIALIZING BY NOON ON THURSDAY. AS A COLD FRONT
ADVANCES EASTWARD...CIGS/VIS SHOULD QUICKLY DETERIORATE ON MONDAY
EVENING AS MODERATE RAIN SHOWERS WITH LOW CIGS AND GUSTY SSE WINDS
BECOME COMMON AT ALL SITES. FRIES
.OUTLOOK.../THURSDAY NIGHT THROUGH MONDAY/...
PASSAGE OF STRONG LOW PRESSURE SYSTEM AND ITS COLD FRONT THURSDAY
EVENING WILL PROMOTE IFR RAIN SHOWERS AND WIND GUSTS TO 40 KTS.
ENSUING COLD WESTERLY WINDS WILL PROMOTE PERIODS OF IFR RESTRICTIONS
IN SNOW SHOWERS LATE THURSDAY NIGHT INTO SATURDAY AFTERNOON. SURFACE
WINDS CAN CONTINUE TO GUST AT TIMES OVER 35 KTS.
ENSUING HIGH PRESSURE SHOULD PROMOTE IMPROVEMENT TO VFR SUNDAY AND
MONDAY.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...WINTER STORM WARNING FROM 11 AM FRIDAY TO 7 PM EST SATURDAY
FOR MDZ001.
OH...NONE.
PA...WINTER STORM WATCH FROM LATE THURSDAY NIGHT THROUGH SATURDAY
EVENING FOR PAZ007>009-015-016.
WINTER STORM WARNING FROM 11 AM FRIDAY TO 7 PM EST SATURDAY
FOR PAZ074-076.
WV...WINTER STORM WARNING FROM 11 AM FRIDAY TO 7 PM EST SATURDAY
FOR WVZ023-041.
&&
$$
AREA FORECAST DISCUSSION
NWS GAYLORD MI
229 AM EST THU DEC 20 2012
.SYNOPSIS...
ISSUED AT 406 PM EST WED DEC 19 2012
QUIET WEATHER WILL CONTINUE THROUGH THIS EVENING...AS HIGH PRESSURE
DRIFTS OVERHEAD...PROVIDING MOSTLY CLOUDY SKIES AND MILD
TEMPERATURES.
THE WEATHER WILL DRAMATICALLY CHANGE ACROSS THE GREAT LAKES EARLY
THURSDAY MORNING AND FRIDAY...AS A STRONG WINTER STORM ORGANIZING
OVER THE CENTRAL PLAINS...LIFTS INTO THE GREAT LAKES REGION.
SIGNIFICANT SNOWFALL AND GUSTY WINDS ARE EXPECTED ACROSS NORTHERN
MICHIGAN INTO SATURDAY. CONDITIONS WILL GRADUALLY IMPROVE THROUGH
THE WEEKEND...AS HIGH PRESSURE AGAIN MAKES ITS APPROACH.
&&
.UPDATE...
ISSUED AT 224 AM EST THU DEC 20 2012
FORECAST TIMING OF INITIAL BAND OF LIGHT TO MODERATE SNOWS ACROSS
WISCONSIN AND SW LOWER MICHIGAN IS ON TRACK. WHILE INITIALLY
FIGHTING DRY LOW/MID LEVEL AIR...SHOULD SEE SNOWS BREAK OUT BY
DAYBREAK THROUGH MOST OF NRN LOWER. NO CHANGES WERE MADE.
UPDATE ISSUED AT 1045 PM EST WED DEC 19 2012
LEADING EDGE OF SNOW SHIELD HAS REACHED FAR SRN WISCONSIN LATE
THIS EVENING. THIS GENERALLY MATCHES WELL WITH THE LATEST RUC13
AND NAM40. FURTHER UPSTREAM...THUNDERSNOW HAS BEEN REPORTED IN
PORTIONS OF IOWA AND NW MISSOURI WITHIN AN AREA OF VERY STRONG
700-500 MB DIV-Q AND IMPRESSIVE UPPER FORCING FROM JET COUPLING.
CLOSER TO HOME...LOW CLOUDS APPEAR TO BE ENTRENCHED ACROSS OUR
CWA...AND HAVE INCREASED CLOUD COVER A BIT FOR THE BALANCE OF THE
NIGHT. BUT MORE IMPORTANTLY...MAINTENANCE OF LOW CLOUDS/MOISTURE
MAY ALLOW FOR SNOW TO BEGIN SLIGHTLY AHEAD OF THE TIMING SUGGESTED
BY THE SHORT TERM MODELS DESPITE THE DEVELOPMENT OF DRIER EASTERLY
LOW LEVEL FLOW OVERNIGHT. THUS...WILL MAINTAIN THE TIMING OF SNOW
ARRIVAL AS PROVIDED BY THE GOING FORECAST...WHICH IS JUST SLIGHTLY
AHEAD OF THAT PROVIDED BY THE LATEST RUC AND NAM. CERTAINLY THE
VAST MAJORITY OF SNOW AND RESULTING IMPACTS FROM THIS UPCOMING
STORM WILL HOLD OFF UNTIL AFTER SUNRISE...BUT SW SECTIONS OF OUR
CWA WILL LIKELY SEE AROUND AN INCH OF NEW WHITE STUFF BY DAYBREAK...
WITH LESS THAN AN INCH ACROSS THE REST OF OUR CWA. STAY TUNED!
UPDATE ISSUED AT 700 PM EST WED DEC 19 2012
RESIDUAL LOW CLOUDS APPEAR TO BE INCREASING ACROSS NW LWR MICHIGAN THIS
EVENING...LIKELY EXPANDING UNDER THE WELL-ESTABLISHED INVERSION AS
THE BOUNDARY LAYER COOLS WITH SUNSET. STILL SUSPECT THIS INCREASE
IN LOW CLOUDS WILL BE SHORT-LIVED AS DRIER EASTERLY FLOW BECOMES
ESTABLISHED LATER THIS EVENING IN ADVANCE OF THE DEVELOPING STORM
SYSTEM NOW CENTERED OVER THE CENTRAL PLAINS. HOWEVER...MID/HIGH
CLOUDS WILL QUICKLY REPLACE ANY BREAK IN THE LOW CLOUDS BY LATE
EVENING...SO OVERALL SKY CONDITIONS TONIGHT WILL BE MAINLY CLOUDY.
LATEST RUC13 IS STILL SHOWING THE ARRIVAL OF WIDESPREAD SNOW
RANGING FROM AROUND 09Z IN OUR FAR SW CWA TO AROUND 12Z FOR ERN
UPR AND FAR NRN/NE LWR MICHIGAN...WITH SNOW BECOMING HEAVY AT
TIMES AFTER SUNRISE. THIS IS A BIT LATER THAN THE CURRENT FORECAST
SUGGESTS. START TIME HINGES...AT LEAST IN PART...ON IF AND TO WHAT
EXTEND LOW LEVEL MOISTURE/CLOUDS CAN BE SCOURED OUT THIS EVENING
BY DRIER EAST FLOW. IF LOW LEVEL MOISTURE REMAINS IN PLACE...START
TIME OF SNOW MAY VERY WELL BE EARLIER AS DEPICTED IN THE GOING
FORECAST. WILL KEEP A CLOSE EYE ON THIS THRU THE EVENING AND
ADJUST CLOUDS/WX/POP AS NECESSARY.
&&
.SHORT TERM...(TONIGHT)
ISSUED AT 406 PM EST WED DEC 19 2012
CURRENT OVERVIEW: WEAK HIGH PRESSURE IN CONTROL OF THE REGION/S
WEATHER TODAY WHICH...DUE TO IT/S WEAK NATURE...HAS ALLOWED STRATUS
AND STRATOCUMULUS TO PERSIST THROUGHOUT NORTHERN MICHIGAN FOR MUCH
OF TODAY. SURFACE MAP SHOWS LOW PRESSURE GRADUALLY CONGEALING OVER
THE PANHANDLES OF TX/OK WITH IMPRESSIVE BAROCLINIC LEAF SIGNATURE IN
WV/IR IMAGERY.
FORECAST CONCERNS CENTER AROUND CLOUD TRENDS...AND THEN TIMING THE
ARRIVAL OF SNOW LATER TONIGHT. ST/STCU WILL LIKELY NOT BE IN ANY
HURRY TO GO ANYWHERE THIS EVENING GIVEN SOME WEAK LAKE SUPPORT...AND
NO INTRODUCTION OF MEANINGFULLY-DRIER AIR. WHILE SOME BREAKS ARE
LIKELY...TIMING/LOCATING THEM WOULD BE FRUITLESS...AND...WITH HIGH
CLOUDS INCREASING BY MID/LATE EVENING AHEAD OF OUR APPROACHING
WINTER STORM...WILL GO WITH MOSTLY CLOUDY WORDING THROUGH THE
EVENING...TRANSITIONING TO CLOUDY OVERNIGHT.
AS FOR PRECIPITATION ONSET...GUIDANCE IS IN GOOD AGREEMENT THAT
INITIAL WARM ADVECTION SURGE WILL HOLD OFF UNTIL AFTER
MIDNIGHT...BUT STILL WITH A RANGE OF ABOUT 6 HOURS. IN THESE
SCENARIOS...WITH A DEEP SOUTHEAST FLOW AT PRECIP ONSET...TEND TO
SIDE WITH THE SLOWER EDGE OF THE GUIDANCE ENVELOPE. OF COURSE...THE
ANTECEDENT AIRMASS IS NOT ALL THAT DRY...HOWEVER...SO WHILE I/LL
LEAN SLOWER...I STILL THINK MOST SPOTS FROM CVX-GLR-OSC SOUTH AND
WEST WILL SEE FLAKES IN THE AIR BY DAYBREAK. WE/LL HAVE TO WATCH
ALONG THE IMMEDIATE LAKE HURON COAST...WHERE A LLEVEL WARM LAYER MAY
BE DEEP ENOUGH TO ALLOW PRECIPITATION TO START AS A MIX /OR ALL
RAIN/. NO ICING EXPECTED. AS FOR SNOW TOTALS...EXPECT 1-2" BY
DAYBREAK OVER THE FAR SOUTHWEST /NEAR MBL/ WITH NO MORE THAN A
COATING FROM CVX TO GLR.
NOTE! FOR MOST LOCATIONS SAVE THE FAR SOUTHWEST...TRAVEL CONDITIONS
MAY NOT BE ALL THAT BAD AT DAYBREAK THURSDAY. PLEASE CONSIDER...
HOWEVER...THAT QUICKLY DETERIORATING CONDITIONS ARE EXPECTED
THURSDAY /SEE BELOW/.
.LONG TERM...(THURSDAY THROUGH WEDNESDAY)
ISSUED AT 406 PM EST WED DEC 19 2012
...HIGH IMPACT WINTER STORM THURSDAY THROUGH FRIDAY...
WATER VAPOR IMAGERY...OVERLAID WITH 12Z RAOB ANALYSIS...LENDS MUCH
CONFIDENCE TO NOW MULTI-DAY MODEL TRENDS OF A HIGH IMPACT WINTER
WEATHER EVENT ACROSS MUCH OF THE NORTH WOODS THURSDAY AND FRIDAY.
SHORTWAVE NO DOUBT LOOKS IMPRESSIVE AS IT BEGINS ITS EJECTION OUT OF
THE SOUTHWEST CONUS...WITH EXCELLENT PACIFIC "PINEAPPLE" CONNECTION
AND BURGEONING WESTERN GULF OF MEXICO MOISTURE ADVECTION OUT FRONT
OF IT (AS EVIDENCE BY DEWPOINTS SURGING INTO THE 60S OVER NORTHEAST
TEXAS ON GUSTY SOUTH WINDS). ATTENDANT UPPER JET CORE MEANS BUSINESS
...WITH CONUS RAOB H25/H30 NETWORK SHOWING CORRIDOR OF 120+ KNOT
WINDS EXTENDING FROM THE MID ATLANTIC ALL THE WAY BACK INTO THE
DESERT SOUTHWEST...WITH EMBEDDED 145+ KNOT JET MAX ARCHING INTO THE
SOUTHWEST LAKES. THIS JET WILL HELP EJECTING WAVE QUICKLY TAKE ON A
NEGATIVE TILT AS IT REACHES THE MID MISSISSIPPI VALLEY REGION EARLY
THURSDAY ...ON ITS WAY TO CLOSING OFF AS IT CROSSES THE SOUTHERN
LAKES OVERNIGHT THURSDAY. SURFACE REFLECTION WILL INITIALLY LEAD ITS
MID LEVEL PARENT...STEADILY DEEPENING (REACHING SUB 990MBS LEVELS)
AS IT PIVOTS NORTHEAST TO VICINITY SOUTHERN LAKE MICHIGAN BY
THURSDAY EVENING. SYSTEM OCCLUDES THERE ON AFTER...WITH SURFACE LOW
TUCKING UNDER ITS MID LEVEL LIKENESS. THIS TRACK UP THROUGH SOUTHERN
LAKE MICHIGAN AND ACROSS SOUTHERN MICHIGAN/THE THUMB PLACES MUCH OF
OUR AREA IN THE CROSS-HAIRS OF A SIGNIFICANT WINTER WEATHER
EVENT...WITH HEAVY SNOW AND VERY GUSTY WINDS LEADING TO THE
DEVELOPMENT OF EXTREMELY HAZARDOUS CONDITIONS EARLY
THURSDAY...CONTINUING RIGHT THROUGH FRIDAY. SOUNDS PRETTY
CLEAR-CUT...BUT SAID TRACK (DRY SLOT ISSUES?)...ABOVE NORMAL LAKE
HURON WATER TEMPERATURES...AND ANTECEDENT RATHER "MILD" AIRMASS
STILL MAKES EXACT PRECIP TYPE AND TIMING OF CHANGEOVERS A FORMIDABLE
CHALLENGE...ESPECIALLY FOR THE SOUTHEAST THIRD OF OUR AREA.
INHERITED FORECASTERS HAVE LAID A SOLID FOUNDATION ON ALL THE
ABOVE...WITH FORECASTS/WARNINGS AND STATEMENTS/WEB BRIEFINGS ALL
HIGHLIGHTING THIS HIGH IMPACT EVENT. THUS...MOST CHALLENGING PART OF
THE FORECAST REMAINS TRYING TO FIGURE EXACT DEMARCATION OF RAIN/SNOW
LINE AND WHAT TO DO WITH INHERITED WINTER STORM WATCH THAT STRADDLES
THIS DIVISION.
HIGH CONFIDENCE PORTION OF THE FORECAST: AS MENTIONED BY OVERNIGHT
FORECAST...STORM STRUCTURE SHOULD BE A "CLASSIC" ONE...AS IS QUITE
OFTEN SEEN WITH THESE PANHANDLE-HOOK SYSTEMS. LEAD ISENTROPIC/FGEN
DRIVEN PRECIP SHIELD EARLY THURSDAY WILL GIVE WAY TO INTENSE DEEP
LAYER -DIVQ/UPPER LEVEL DIVERGENCE AXIS AND INCREASINGLY WELL
ESTABLISHED TROWAL AS CYCLONIC PORTION OF WARM CONVEYOR BELT WRAPS
BACK ACROSS NORTHERN MICHIGAN LATER THURSDAY INTO EARLY FRIDAY. FGEN
SIGNATURE FOCUSES ALONG THE NORTHWEST QUADRANT OF SYSTEM LATER
THURSDAY...WITH WARM SIDE RESPONSE TARGETING NORTHWEST LOWER AND
EASTERN UPPER MICHIGAN. GOOD -EPV SIGNATURE...SUGGESTING CONVECTIVE
SNOW BURSTS (THUNDERSNOW?) AND POSSIBILITY FOR ENHANCED VERY HEAVY
SNOW BANDS EMBEDDED WITHING BROADER SNOW SHIELD. MOISTURE FOR ALL
THE ABOVE REMAINS ABUNDANT...WITH PWAT VALUES NEARING AN INCH OVER
THE FAR SOUTHERN LAKES...AND EXCEEDING 0.5 INCHES OVER NORTHERN
MICHIGAN...WHICH IS REACHING NEAR 2 STANDARD DEVIATIONS ABOVE NORMAL
FOR DECEMBER. HPC/MODEL PRECIP GRAPHICS AGREE...TARGETING NORTHERN
MICHIGAN WITH STORM TOTAL LIQUID EQUIVALENTS IN EXCESS OF AN INCH
BY THE END OF FRIDAY.
LINGERING UNCERTAINTIES AND WHAT CAN GO WRONG SCENARIO: WHILE ABOVE
NEARLY SET IN STONE...EXACT PRECIP TYPES...SNOW-LIQUID RATIOS...AND
POSSIBLE DRY-SLOT ISSUES REMAIN A FORMIDABLE CHALLENGE. AS FEARED...
LATEST 12Z NAM-WRF AND GFS FITS PATTERN RECOGNITION OF SUCH A
WRAPPED-UP SYSTEM TRENDING A TOUCH NORTHWEST THAN EARLIER PROGGED.
COMBINE THIS WITH INITIAL STRONG EAST FLOW COMING OFF THE ABOVE
NORMAL LAKE HURON WATERS AND ANTECEDENT RATHER MILD MID DECEMBER
TEMPERATURES...AND RAIN SEEMS LIKE A GIVEN FOR AT LEAST SOME OF OUR
SOUTHEAST COUNTIES. USING LATEST NAM-WRF AND GFS 0-6KM MAX TEMP
PROGS AND FORECAST RAOBS NOW SUGGEST THIS DEMARCATION SPREADING AS
FAR WEST AS A HARRISVILLE TO HOUGHTON LAKE LINE DURING THE
AFTERNOON...WITH EVEN SOME MIX POSSIBLE A TOUCH FURTHER NORTHWEST.
MOST OTHER GUIDANCE NOT QUITE AS AGGRESSIVE SPREADING RAIN AS FAR
INLAND... ALTHOUGH ALL ARE ON BOARD WITH PREDOMINATELY LIQUID ACROSS
BOTH IOSCO AND ARENAC COUNTIES...AS WELL AS THE IMMEDIATE COASTLINE
AREAS OF ALCONA COUNTY...UNTIL LATER THURSDAY NIGHT. HARD NOT TO GO
WITH THE MAJORITY...BUT ALSO HARD TO COMPLETELY IGNORE PAST HISTORY
AND PATTERN RECOGNITION. UNFORTUNATELY...FORECAST WILL BY NO MEANS
MIMIC REALITY AS THESE EXACT DETAILS WILL NOT BE REALIZED TO THE
EVENT ACTUALLY UNFOLDS. WILL TAKE A "BEST GUESS"...KEEPING
PREDOMINATELY RAIN WHERE THE MAJORITY AGREE...BUT SPREADING MIX
RAIN/SNOW WORDING A TOUCH FURTHER INLAND...STRETCHING FROM ABOUT
ROGER CITY DOWN TO MANISTEE (NOT TOO WORRIED ABOUT SLEET WITH LITTLE
SUPPORT FOR SURFACE BASED COLD LAYER BELOW ELEVATED WARM NOSE). OF
COURSE...SNOW-TO-LIQUID RATIOS CONTINGENT ON THE ABOVE...AS WELL AS
THE FACT DGZ REMAINS FAIRLY ELEVATED DURING THE EVENT EVEN WHERE ALL
SNOW IS EXPECTED. REALLY LIKE PREVIOUS FORECAST IDEA OF TRENDING
MODEL DEPICTED SNOW/LIQUID RATIOS DOWN...AND WILL MAKE ONLY SUBTLE
CHANGES TO THOSE INHERITED. LASTLY...DRY SLOT ISSUES. IT WILL BE A
CLOSE CALL FOR AREAS DOWN NEAR SAGINAW BAY...ESPECIALLY IF LAST
SECOND NORTHWEST TREND IS REALIZED. WILL NOT GO THIS ROUTE JUST
YET...BUT DEFINITELY COULD SEE PRECIP WOUND DOWN FOR A PERIOD OF
TIME THURSDAY EVENING ACROSS THE FAR SOUTHEAST.
SNOWFALL AMOUNTS: DESPITE SOMEWHAT LOW SNOW-TO-LIQUID RATIOS...
ESPECIALLY ACROSS NORTHERN LOWER...SIMPLE MAGNITUDE OF DYNAMICS AND
AVAILABLE MOISTURE SUPPORTS SNOWFALL AMOUNTS POSSIBLY APPROACHING A
FOOT FOR AREAS ALONG AND NORTHWEST OF A LINE EXTENDING FROM ROGERS
CITY TO CADILLAC...WITH SOME LOCALLY HIGHER AMOUNTS IN FAVORED NNW
FLOW AREAS AS LAKE ENHANCEMENT AUGMENTS TROWAL DRIVEN SNOWS LATER
THURSDAY NIGHT INTO FRIDAY. IN ADDITION...POTENTIAL FOR HIGH
INTENSITY (ONE TO TWO INCH PER HOUR?) ELEVATED CONVECTIVE DRIVEN
SNOW BANDS COULD LEAD TO LOCALLY HIGHER AMOUNTS. SNOWFALL TOTALS
SHOULD FALL OF RAPIDLY FURTHER SOUTHEAST...WITH PERHAPS JUST A FEW
INCHES NEAR SAGINAW BAY GIVEN LATER CHANGEOVER AND DECAYING TROWAL
DYNAMICS BY THE TIME CHANGEOVER OCCURS. LITTLE DOUBT EXACT GRADIENT
SHOWN IN FORECAST WILL CHANGE AS EVENT UNFOLDS.
HEADLINES...INHERITED WINTER STORM WARNING IS A NO-BRAINER...WITH
SAID HEAVY SNOW AMOUNTS AND INCREASINGLY GUSTY WINDS...ESPECIALLY BY
LATE THURSDAY NIGHT AND FRIDAY. WIND GUSTS COULD EASILY EXCEED
30MPH...WITH EVEN HIGHER GUSTS ALONG THE IMMEDIATE LAKE MICHIGAN
SHORELINE. PROGS CONCUR...WITH STRONG NNW FLOW LOW LEVEL JET CENTER
OVER LAKE MICHIGAN BY EARLY FRIDAY. NEAR WHITEOUT CONDITIONS IN
BLOWING AND DRIFTING SNOW IS DEFINITELY PLAUSIBLE...ESPECIALLY IN
UNSHELTERED AREAS. HAVE TOSSED AROUND THE BLIZZARD IDEA...BUT PAST
HISTORY SHOWS GETTING TRUE BLIZZARD CONDITIONS IS AWFULLY TOUGH.
WILL LET WINTER STORM WARNING SPEAK FOR ITSELF...WITH NEAR BLIZZARD
CONDITIONS MENTIONED WITHIN THE TEXT. AS FOR THE REMAINING
WATCH...TOUCH CALL BASED ON RAIN/SNOW ISSUE...BUT WILL UPGRADE
NORTHWEST TIER OF WATCH COUNTIES TO A WARNING...STRESSING HIGHEST
SNOW TOTALS OVER THE NORTHWEST CORNER OF EACH. REST OF THE WATCH
WILL FALL UNDER AN ADVISORY...HIGHLIGHTING INITIAL AND END EVENT
SNOW BURST. AS FOR A LIST OF EXPECTED IMPACTS FROM THIS
SYSTEM...PLEASE REFER TO OUR WARNING AND ADVISORY PRODUCTS.
MSB
SATURDAY AND SUNDAY...INGREDIENTS ARE CONTINUING TO LOOK DISMAL
FOR LAKE EFFECT SNOW BEHIND THE DEPARTING STORM SYSTEM. LOW
MOISTURE...850MB TEMPERATURES ONLY AROUND -5C...WHICH PUT DELTA T/S
ONLY AT 11C. THE BEST CHANCE APPEARS TO BE EARLY SUNDAY
MORNING...WHEN 850MB TEMPERATURES BEGIN TO DROP AHEAD OF A WEAK
SHORTWAVE WITH SYNOPTIC-SCALE QG FORCING...HIGHER MOISTURE
AMOUNTS...DELTA T/S OF AROUND 14C. WINDS WILL BE NORTHERLY DURING
THIS OPTIMAL TIMEFRAME...WHICH WOULD IMPACT MAINLY WHITEFISH POINT
TO WESTERN MACKINAC COUNTY AND THEN LEELANAU...BENZIE AND MANISTEE
COUNTIES IN NORTHERN LOWER. STILL DON/T EXPECT MUCH ACCUMULATIONS
FROM ANY LAKE EFFECT SNOW THAT DEVELOPS SATURDAY THROUGH LATE SUNDAY
NIGHT.
CHRISTMAS EVE...ECMWF AND GFS HAVE COME TO AGREEMENT ON A SHORTWAVE
MOVING THROUGH THE GREAT LAKES REGION MONDAY AFTERNOON AND INTO THE
EVENING HOURS...POSSIBLY GENERATING SOME MINOR SNOW ACCUMULATIONS
ACROSS NORTHERN MICHIGAN. THERE COULD ALSO BE SOME LOCALIZED LAKE
ENHANCED SNOW WITH 850MB TEMPS NEAR -14C...BRINGING DELTA T/S TO
NEAR 20C.
TUESDAY AND WEDNESDAY...TEMPERATURES MAY REACH SINGLE DIGITS OVER
INTERIOR PORTIONS OF NORTHERN LOWER MICHIGAN TUESDAY AND WEDNESDAY
MORNING...AS COLD ARCTIC AIR FILTERS IN FROM BETWEEN A SURFACE HIGH
PRESSURE RIDGING INTO THE GREAT LAKES REGION FROM WESTERN CANADA AND
A FORECAST DEVELOPING STORM SYSTEM OVER THE SOUTHERN PLAINS. I HAVE
USED THE COLDER ECMWF FOR TEMPERATURES TUESDAY AND WEDNESDAY.
INCREASED CLOUDINESS TUESDAY AHEAD OF THE AFOREMENTIONED POTENTIALLY
STRONG STORM SYSTEM THAT MAY IMPACT THE GREAT LAKES REGION WEDNESDAY
AND INTO THURSDAY.
TJL
&&
.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1045 PM EST WED DEC 19 2012
MVFR/LOW VFR CIGS WILL PERSIST OVERNIGHT AS SHALLOW LOW LEVEL
MOISTURE HAS AND WILL REMAIN STUCK BELOW THE INVERSION. CONDITIONS
WILL QUICKLY DETERIORATE TO IFR BEFORE DAYBREAK AS WIDESPREAD SNOW
SPREADS SW TO NE ACROSS ALL NRN LWR MICHIGAN TAF SITES...BECOMING
HEAVY DURING THE MORNING AND CONTINUING THRU THURSDAY NIGHT. SOME
RAIN WILL MIX WITH THE SNOW AT APN THANKS TO MODIFIED LOW LEVEL
TEMPS ALONG THE LAKE HURON SHORELINE WITH EASTERLY WINDS. LIGHT
WINDS THIS EVENING WILL BECOME EAST OVERNIGHT AND QUICKLY
STRENGTHEN ON THURSDAY...WITH GUSTS TO 30 TO 35 KTS EXPECTED.
WINDS WILL SHIFT TO THE NE AND EVENTUALLY NORTH ACROSS NW LWR
MICHIGAN (PLN/TVC/MBL) THURSDAY AFTERNOON AND NIGHT AS THE LOW
CENTER TRACKS FROM SW LWR MICHIGAN THRU SAGINAW BAY.
&&
.MARINE...
ISSUED AT 406 PM EST WED DEC 19 2012
THE CALM BEFORE THE STORM. LIGHT WINDS ARE EXPECTED THROUGH
MUCH OF TONIGHT WITH HIGH PRESSURE IN CONTROL. HOWEVER...APPROACHING
STRONG LOW PRESSURE WILL BRING A RAPID INCREASE IN SPEEDS BY SUNRISE
THURSDAY...WITH VERY STRONG WINDS LIKELY THROUGH THE DAY ON FRIDAY
AS THE LOW PASSES. GALE FORCE SPEEDS ARE EXPECTED ACROSS MOST OF THE
WATERS...WITH THE POSSIBILITY OF A FEW STORM FORCE GUSTS ON THE LAKE
MICHIGAN NEARSHORE WATERS LATER THURSDAY NIGHT INTO FRIDAY. MORE
TRANQUIL CONDITIONS ARE EXPECTED LATER INTO THE WEEKEND AS WEAK HIGH
PRESSURE GRADUALLY WORKS BACK OVER THE WATERS.
&&
.APX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER STORM WARNING FROM 7 AM THIS MORNING TO 7 PM EST FRIDAY
FOR MIZ008-015>029-031>034.
WINTER WEATHER ADVISORY FROM 7 AM THIS MORNING TO 7 PM EST
FRIDAY FOR MIZ030-035-041.
LH...GALE WARNING FROM 1 PM THIS AFTERNOON TO 7 AM EST SATURDAY FOR
LHZ345>349.
LM...GALE WARNING FROM 1 PM THIS AFTERNOON TO 7 AM EST SATURDAY FOR
LMZ323-341-342-344>346.
LS...GALE WARNING FROM 1 PM THIS AFTERNOON TO 7 AM EST SATURDAY FOR
LSZ321-322.
&&
$$
UPDATE...SD
SYNOPSIS...TL
SHORT TERM...JA
LONG TERM...MB/TL
AVIATION...MR
MARINE...MB
AREA FORECAST DISCUSSION
NWS MARQUETTE MI
1235 AM EST THU DEC 20 2012
.UPDATE...
ISSUED AT 944 PM EST WED DEC 19 2012
THE 00Z NAM AND RUC RUNS INDICATE THAT THE HEAVIER SNOW MAY BE A
LITTLE LATER TO ARRIVE...ESPECIALLY CLOSER TO LAKE SUPERIOR WHERE
INITIAL DRY AIR WILL NEED TO BE OVERCOME. WITH A TRACK SO FAR
SOUTH...THIS WOULD TEND TO MAKE SENSE. ALTHOUGH THE OVERALL STORM
TOTAL SNOWFALL FORECAST HAS NOT CHANGED...WILL DELAY THE ARRIVAL OF
SNOW FOR A FEW HOURS THU MORNING.
IT SHOULD BE NOTED THAT MANY PLACES IN UPPER MICHIGAN WILL NOT HAVE
MUCH OR ANY SNOW EARLY THURSDAY MORNING. HOWEVER...CONDITIONS WILL
RAPIDLY DETERIORATE DURING THE DAY AS THE SNOW SPREADS NORTH AND THE
NE WINDS INCREASE.
ISSUED AT 831 PM EST WED DEC 19 2012
NO MAJOR CHANGES TO THE GOING FORECAST THIS EVENING AS THE AFTERNOON
PACKAGE HAS THE SITUATION WELL IN HAND. LOW PRESSURE JUST NORTH OF
OKC IS STILL EXPECTED TO MOVE RAPIDLY NE TONIGHT TO A POSITION NEAR
CHICAGO BY NOON THURSDAY. WIDESPREAD SNOW IN THE DEFORMATION AXIS TO
THE N AND NW OF THE LOW WILL RAPIDLY MOVE NE AS WELL. THE LATEST
RUNS OF THE RUC AGREES WITH THE NAM AND SREF MEMBERS IN SHOWING THE
SNOW DEVELOPING AROUND 09Z AT MNM...THEN RAPIDLY SPREADING NORTHWARD
IN THE MORNING TO MQT BY 12Z AND CMX SOON AFTER. WITH THE
STRENGTHENING F-GEN MOVING OVER THE AREA ASSOCIATED WITH THE
DEVELOPING TROWAL /AND ASSOCIATED LOWER STABILITY/...EXPECT SNOW TO
FALL HEAVY AT TIMES ESPECIALLY ACROSS THE SOUTH AND EAST DURING THE
DAY. AS SUCH...HAVE OPTED TO INCLUDE SNOWFALL RATES OF 1-2 INCHES
PER HOUR IN THE WARNING AREAS TO HIGHLIGHT THIS SPECIFIC CONCERN.
OTHERWISE...THE ONLY OTHER CONCERN THAT WILL NEED TO MONITORED IS
THE POTENTIAL FOR HIGHER SNOW AMOUNTS IN GOGEBIC COUNTY DUE TO THE
SUSTAINED N-NE WIND. LATEST RUC RUNS INDICATE SNOW BECOMING HEAVIER
BY LATE MORNING AS THE BETTER MOISTURE WRAPS WESTWARD INTO FAR
WESTERN UPPER MI. IF THIS TREND CONTINUES WITH THE 00Z RUNS...THE
MID SHIFT MAY NEED TO OPT FOR A WARNING HERE AS WELL. STILL
EXPECTING THE WINDS TO INCREASE LATER THU INTO THU NIGHT. IN
FACT...AREAS NEAR LAKE SUPERIOR NEAR AND EAST OF MARQUETTE WILL
LIKELY SEE SIGNIFICANT BLOWING/DRIFTING THU NIGHT INTO FRI MORNING
AS THE SNOW TRANSITIONS TO A LESS DENSE LAKE EFFECT. NWP SUGGEST
45-50KT 925MB WINDS...AND THERE IS A CONCERN THAT BLIZZARD CRITERIA
COULD TECHNICALLY BE MET EARLY FRI MORNING. WILL NOT MAKE ANY
HEADLINE ADJUSTMENTS...BUT IT IS QUITE POSSIBLE THAT THE WORST
CONDITIONS OF THE ENTIRE EVENT FOR AREAS NEAR LAKE SUPERIOR WILL BE
THU NIGHT INTO FRIDAY MORNING.
UPDATED WINTER STATEMENT ALREADY OUT.
&&
.SHORT TERM...(THIS EVENING THROUGH THURSDAY)
ISSUED AT 441 PM EST WED DEC 19 2012
HEADLINES ARE OUT FOR ALL OF UPR MICHIGAN. SNOW BEGINS LATE TONIGHT
OVER SOUTH AND SPREADS ACROSS REST OF CWA ON THURSDAY. NOW WE WAIT.
WV LOOP/12Z RAOBS SHOW TWO PRIMARY UPPER LEVEL FEATURES. STRONG
SHORTWAVE TROUGH/PV ANAMOLY EMERGING ON TO THE SOUTHERN PLAINS
WHILE SHORTWAVE TROUGH IN THE NORTHERN STREAM IS DIGGING ACROSS
DAKOTAS. LEE SIDE CYCLOGENESIS WELL UNDERWAY NEAR TX/OK PANHANDLE.
SOUTHERN STREAM PV ANAOMOLY MAIN WX MAKER TO START. WAVE HEADS INTO
OK AND SOUTHERN MO TONIGHT WITH A 995MB SFC LOW NEARING SAINT LOUIS
MO BY 12Z ON THURSDAY. JET STREAK DIGGING INTO BASE OF TROUGH FM
WY TO KS AND INCREASING DIVERGENCE ALOFT RESULTS IN DEEPENING SFC
LOW BLO 990MB AS IT REACHES CHICAGO/SOUTHERN TIP OF LK MICHIGAN
18Z-24Z. FURTHER DEEPENING OF MID-LEVEL LOW THEN EXPECTED ON
THURSDAY NIGHT AS THE NORTHERN STREAM WAVE BEGIN TO INTERACT WITH
THE SOUTHERN STREAM ONE. THIS SHOULD ALLOW LAKE ENHANCED SNOW TO
LINGER LONGER ALONG LK SUPERIOR INTO FRIDAY.
BACK TO TONIGHT...LGT SNOW BEGINS TO SPREAD INTO FAR SOUTH CWA AFT
09Z TONIGHT THEN REACHES LK MICHIGAN TO IMT LINE AROUND 12Z THU.
INTIALLY SNOW WILL BE DRIVEN BY DIVERGENCE ALOFT FM JET STREAK
LIFTING INTO ONTARIO. LATER THU MORNING THROUGH THU AFTN...SOUTHERLY
WINDS AHEAD OF SFC-H85 LOW INCREAS GULF MOISTURE INTO AREA WITH
PERSISTENT ISENTROPIC ASCENT NOTED ON 290-305K SFCS /H9-H6/.
FRONTOGENESIS RAMPS UP WITH STEADY SURGE OF H8-H7 FRONTOGENESIS
SWEEPING ACROSS SCNTRL AND EASTERN CWA. STRONGEST/PERSISTENT FN/FS
VECTOR CONVERGENCE FAVORS CORRIDOR FROM MNM-ISQ-ERY TO SEE HEAVY
SNOW THROUGH MUCH OF AFTN. PIVOT POINT FOR SNOW SEEMS TO FAVOR LUCE
COUNTY FOR MOST PROLONGED PERIOD OF HEAVIER SNOW. RATES UP TO 2
INCHES/HOUR POSSIBLE AS ADDITIONAL FORCING IS PROVIDED BY 925-850MB
THETA-E ADVECTION. MEANWHILE OVER CNTRL AND WEST CWA MODERATE SNOW
SHOULD STEADILY LIFT NORTH ON THURSDAY MORNING AND SHOULD BE OVER
ALL AREAS BY MIDDAY. WILD CARD IN CNTRL CWA IS AREA OF H7-H5
FRONTOGENESIS THAT KEEPS SHOWING UP FROM MQT-IMT. SEEMS THAT
NAM/GFS/ECMWF/GEM-REGIONAL ALL PICK UP ON THIS ENHANCING FEATURE.
RESULT IS INCREASE IN MODELED QPF FM GFS/GEM-REGIONAL/ECMWF WHICH
NOW LOOKS A BIT CLOSER TO WETTER NAM IDEA. ALREADY ADDED DICKINSON
TO ONGOING WARNINGS ON EARLIER UPDATE. HIGHER TERRAIN OF MARQUETTE
AND BARAGA COUNTIES ALSO WILL BEGIN TO SEE POTENTIAL FOR INCREASED
SNOW AMOUNTS COMPARED TO LOWER ELEVATIONS BY LATE THURSDAY AFTN DUE
TO INCREASING NORTHEAST WINDS/UPSLOPE LIFTING.
ACROSS WESTERN TIER...SYNOPTIC SNOW WILL NOT FALL AS HEAVY AS IN THE
CNTRL AND EASTERN CWA. ULTIMATELY...TOTAL SNOW AMOUNTS WILL BE
BOOSTED OVER HIGHER TERRAIN OF WEST DUE TO LK ENHANCED/LK EFFECT
SNOW LATER THURSDAY NIGHT INTO FRIDAY. MORE ON THAT IN THE LONG TERM
DISCUSSION.
OVERALL...OTHER THAN ADDITION OF DICKINSON TO ORIGINAL WARNING AND
INCLUDING WESTERN CWA IN ADVY...THEME OF GOING FORECAST ISSUED ON
MID SHIFT IS STILL ON TRACK. EXPECT 12-15HR SYNOPTIC SNOW TOTALS
ENDING AROUND 7 PM EST THURSDAY OF 3-6 INCHES OVER WESTERN THIRD OF
CWA /IRONWOOD AND HOUGHTON/ WITH 6 TO 10 INCHES OVR REST OF CWA.
WIDESPREAD SYNOPTIC PORTION OF THE STORM CONTINUES ON THURSDAY NIGHT
OVER EASTERN CWA...BUT WILL WANE OVER THE SOUTH. BLOWING SNOW
BECOMES MORE SIGNIFICANT JUST BEYOND THE SCOPE OF THE SHORT TERM.
MODELS COMING INTO EVEN BETTER AGREEMENT TODAY JUST ADDS FURTHER
CONFIDENCE TO THE FORECAST. SO NOW WE WAIT.
.LONG TERM...(THURSDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 441 PM EST WED DEC 19 2012
THURSDAY NIGHT...MODELS WERE IN GOOD OVERALL AGREEMENT...TAKING
THE MID LEVEL LOW FROM NRN INDIANA TO THE SRN END OF LAKE HURON BY
12Z/FRI. AT 00Z/FRI...THE NAM INDICATED A BAND OF STRONG 700-500 MB
FGEN AND TROWAL FEATURE OVER CNTRL UPPER MI WHICH IS EXPECTED TO
SHIFT INTO THE ERN CWA DURING THE EVENING WHICH MAY HELP TO ENHANCE
SNOWFALL RATES BTWN 00Z-06Z OVER THE EAST HALF. AS THE STRONGER
FGEN...AND 700-300 MB QVECTOR CONV OVER NRN LAKE HURON INTO NRN LOWER
MI SHIFT STEADILY TO THE NE...THE SYNOPTIC SCALE LIFT AND PCPN WILL
ALSO WEAKEN. ADDITIONAL OVERALL SYNOPTIC SNOWFALL AMOUNTS OF 1 TO 3
INCHES ARE LIKELY..MAINLY DURING THE EVENING. SO...THE ADVISORIES AND
WARNINGS OVER THE SRN TIER OF COUNTIES WILL END AT 06Z.
850 MB TEMPS TO AROUND -10C OVER LAKE SUPERIOR COMBINED WITH 950-925
WINDS INTO THE 40-50 KT RANGE WILL LEAD TO SIGNIFICANT LAKE
ENHANCEMENT AND OROGRAPHIC BOOST TO SNOWFALL AMOUNTS. THE GREATEST
AMOUNTS WOULD BE EXPECTED IN THE HIGHER TERRAIN WEST OF MARQUETTE
WHERE ADDITIONAL SNOWFALL AMOUNTS OF 8 INCHES ARE EXPECTED WITH EVEN
LOCALLY HIGHER AMOUNTS POSSIBLE. LOCALLY GREATER SNOWFALL AMOUNTS ARE ALSO
EXPECTED ESPECIALLY NEAR IRONWOOD/WAKEFIELD THAT MAY EVENTUALLY PUSH
SNOW TOTALS INTO THE WARNING CATEGORY. HOWEVER...CONFIDENCE IN HEAVY
SNOWFALL AMOUNTS OVER THE WEST IS LOWER.
FRIDAY...MID LEVEL RIDGING AND ASSOCIATED QVECTOR
DIVERGENCE/SUBSIDENCE WITH LOWERING INVERSION HEIGHTS/STRONG 850-700
MB DRYING WILL SPREAD FROM WEST TO EAST BRINGING AN END TO ANY
SIGNIFICANT SNOWFALL RATES OVER THE WEST DURING THE MORNING AND
CNTRL/EAST BY EARLY AFTERNOON. SO...GOING WARNING/ADVY ENDING TIMES
LOOK ON TRACK. ADDITIONAL AMOUNTS OF A FEW INCHES WILL STILL BE
POSSIBLE...MAINLY NORTH CENTRAL AND EAST.
FRIDAY NIGHT INTO SATURDAY...WITH 850 MB TEMPS AROUND -8C AND LINGERING
MOISTURE OVER THE ERN PORTION LAKE SUPERIOR SOME LINGERING SCT -SHSN
MAY BE POSSIBLE OVER THE EAST WHICH SHOULD END EARLY SATURDAY
MORNING. OTHERWISE...LOOK FOR DECREASING CLOUDS WITH TEMPS CLOSER TO
SEASONAL AVERAGES...LOWS IN THE TEENS AND LOWER 20S AND HIGHS IN THE
MID TO UPPER 20S.
SUN-WED...SOME LIGHT LES MAY BE POSSIBLE SUNDAY AS ARCTIC HIGH PRES
OVER CNTRL CANADA PUSHES A COLD FRONT THROUGH THE AREA.
HOWEVER...WITH GENERALLY LIGHT ACYC NRLY WINDS...KEPT MODEL
CONSENSUS SLIGHT CHANCE POPS. THE GFS AND ECMWF SUGGEST THAT A WEAK
SHORTWAVE TROUGH MOVING FROM THE NRN PLAINS INTO THE WRN GREAT LAKES
COULD ALSO BRING SOME LIGHT SNOW TO THE REGION. SOME LIGHT LES MAY
ALSO BE POSSIBLE WITH NE LOW LEVEL FLOW.
&&
.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1229 AM EST THU DEC 20 2012
MVFR TO IFR CIGS CONTINUE ACROSS THE WESTERN HALF OF UPPER MICHIGAN
AHEAD OF THE DEVELOPING STORM SYSTEM OVER THE PLAINS. EXPECT THESE
CLOUDS TO SPREAD EAST THROUGH THE OVERNIGHT AND AFFECT SAW.
THE BIG STORY IS THE DEVELOPING STORM OVER THE PLAINS. SNOW HAS
SPREAD INTO SRN WI AND EXPECT THIS SNOW TO MOVE NORTH INTO UPPER MI
THU MORNING. THE SNOW WILL FIRST REACH IWD AROUND SUNRISE...SAW
AROUND 15Z...THEN SPREAD WEST TO CMX. IFR CONDITIONS WILL SOON
FOLLOW AS THE SNOW AND NE WINDS INCREASE. CONDITIONS WILL BE WORST
AT SAW WHERE CONDITIONS WILL LIKELY BE BELOW AIRPORT MINIMUMS THU
AFTN/NIGHT DUE TO HVY SNOW AND BLOWING SNOW. CMX AND IWD WILL ALSO
BE LIFR. CMX HAS A CHANCE TO SEE VSBYS BELOW 1/2SM LATE THU AFTN
INTO THU NIGHT DUE TO THE STRONG WINDS CREATING BLOWING SNOW. IWD
LOOKS TO BE FAR ENOUGH AWAY FROM THE DEEP MOISTURE AND STRONG WINDS
TO ALLOW VSBYS TO STAY ABOVE 1/2SM ON THU.
&&
.MARINE...(FOR THE 4 PM LAKE SUPERIOR FORECAST ISSUANCE)
ISSUED AT 441 PM EST WED DEC 19 2012
WINDS LESS THAN 20 KTS CURRENTLY WILL QUICKLY GIVE WAY TO STRONGER
WINDS ON THURSDAY AS LOW PRESSURE MOVES TOWARD SOUTHERN LK MICHIGAN.
AS DEEPENING LOW PRESSURE MOVES INTO LOWER MI BY LATER THU...EXPECT
N TO NE GALES TO DEVELOP OVER ALL BUT FAR WESTERN LAKE SUP BY THU
EVENING. GALE WARNINGS CONTINUE FOR THESE AREAS FOR WINDS AS HI
40-45 KTS UNTIL THE STRONGER WINDS DIMINISH W-E FRI INTO FRI EVENING
AS THE LO SHIFTS FARTHER EAST. FOR THE WEEKEND...EXPECT GENERALLY
N-NW WINDS NO HIER THAN 25 KTS OR SO WITH A WEAKER PRES GRADIENT
DOMINATING.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
UPPER MICHIGAN...
WINTER WEATHER ADVISORY FROM 7 AM EST /6 AM CST/ THIS MORNING TO
10 AM EST /9 AM CST/ FRIDAY FOR MIZ002-009-084.
WINTER STORM WARNING FROM 7 AM THIS MORNING TO 1 PM EST FRIDAY
FOR MIZ005>007-014-085.
WINTER WEATHER ADVISORY FROM 10 AM THIS MORNING TO 10 AM EST
FRIDAY FOR MIZ001-003.
WINTER WEATHER ADVISORY FROM 7 AM THIS MORNING TO 1 PM EST
FRIDAY FOR MIZ004.
WINTER STORM WARNING FROM 6 AM THURSDAY TO MIDNIGHT CST THURSDAY
NIGHT FOR MIZ011.
WINTER WEATHER ADVISORY FROM 6 AM THURSDAY TO MIDNIGHT CST
THURSDAY NIGHT FOR MIZ010.
WINTER STORM WARNING FROM 7 AM THIS MORNING TO 7 AM EST FRIDAY
FOR MIZ013.
WINTER STORM WARNING FROM 3 AM THURSDAY TO MIDNIGHT CST THURSDAY
NIGHT FOR MIZ012.
LAKE SUPERIOR...
GALE WARNING FROM 7 PM THIS EVENING TO 10 PM EST FRIDAY FOR
LSZ249>251-266-267.
GALE WARNING FROM 7 PM THIS EVENING TO 4 PM EST FRIDAY FOR
LSZ244-245-248-265.
GALE WARNING FROM 7 PM THIS EVENING TO 1 PM EST FRIDAY FOR
LSZ264.
GALE WARNING FROM 7 PM THIS EVENING TO 11 AM EST FRIDAY FOR
LSZ243-263.
LAKE MICHIGAN...
GALE WARNING FROM 1 PM THIS AFTERNOON TO 7 PM EST FRIDAY FOR
LMZ248-250.
GALE WARNING FROM 1 PM THIS AFTERNOON TO 4 PM EST FRIDAY FOR
LMZ221.
&&
$$
UPDATE...MRD
SHORT TERM...JLA
LONG TERM...JLB
AVIATION...MRD
MARINE...JLA
AREA FORECAST DISCUSSION
NWS OMAHA/VALLEY NE
1121 PM CST WED DEC 19 2012
.AVIATION...
06Z TAFS FOR KOMA...KLNK...KOFK.
BAND OF MODERATE TO HEAVY SNOW WILL CONTINUE TO MOVE EAST ACROSS
THE AREA OVERNIGHT. BACK EDGE WAS GETTING CLOSE TO KOFK AT 05Z AND
THINK CONDITIONS WILL GRADUALLY IMPROVE THERE OVERNIGHT WITH VFR
CONDITIONS BY AROUND 12Z OR 13Z. IFR OR LOWER CEILINGS AND VSBYS
WILL CONTINUE AT KLNK AND KOMA FOR SEVERAL MORE HOURS AND STRONG
WINDS WILL CAUSE BLOWING SNOW. THINK CONDITIONS SHOULD TREND
TOWARD VFR AT KLNK TOWARD MID MORNING AND SHOULD TREND TOWARD VFR
AT KOMA TOWARD LATE MORNING. WINDS WILL SLOWLY DECREASE THROUGH
THE REST OF THE DAY THURSDAY.
MILLER
&&
.PREV DISCUSSION... /ISSUED 846 PM CST WED DEC 19 2012/
UPDATE...
EVENING UPDATE.
WINTER STORM SYSTEM CONTINUES TO AFFECT THE REGION THIS EVENING.
HAD SOME REPORTS OF THUNDER AND LIGHTNING IN THE OMAHA METRO AREA
WITH SLANTWISE CONVECTION. FARTHER SOUTH...UPRIGHT CONVECTION WAS
OCCURRING. SNOW HAS BEEN FAIRLY WET SO FAR...BUT BLOWING AND
DRIFTING SNOW WILL INCREASE AS COLDER AIR MOVES IN AND WIND
INCREASES. DID NOT CHANGE FORECAST SNOW AMOUNTS MUCH. THE
DEFORMATION ZONE EXTENDED FROM SOUTH CENTRAL NEBRASKA OVER INTO
IOWA AS OF 845 PM.
00Z UPPER AIR CHARTS SHOWED THE FOLLOWING. AT 300 MB...THERE WAS
SOMEWHAT OF A COUPLED JET STRUCTURE WITH A 90 KNOT JEX MAX FROM
NORTHEAST SOUTH DAKOTA INTO NORTHERN MINNESOTA AND ANOTHER OF
135 KNOTS FROM SOUTHERN NEW MEXICO INTO WEST TEXAS. 500 MB CHART
SHOWED A HEIGHT FALL CENTER ESTIMATED AT AROUND 160 METERS IN THE
TEXAS PANHANDLE. 850 MB LOW WAS OVER KANSAS WEST OF TOPEKA AND
TOPEKA HAD AN 850 DEWPOINT OF 8. SO PLENTY OF MOISTURE TO WORK
WITH.
MILLER
PREV DISCUSSION... /ISSUED 344 PM CST WED DEC 19 2012/
SHORT TERM...TONIGHT THROUGH SATURDAY.
BLIZZARD TO IMPACT MUCH OF EASTERN NEBRASKA/WESTERN IOWA...
OBVIOUS CONCERN/FOCUS IN THE SHORT TERM WILL BE THE DEVELOPING
BLIZZARD WHICH WILL AFFECT MOST OF THE SOUTHEAST 2/3RDS OR SO OF
THE FORECAST AREA TONIGHT.
AFTERNOON SATELLITE SHOWED DEEP UPPER TROUGH FROM WY THROUGH CO
WITH STRONG POTENTIAL VORTICITY MAX ALONG CO/NM BORDER. AS
THROUGH/PV MAX TRACK EAST TONIGHT...MID LEVEL FLOW FORECAST TO
CLOSE OFF JUST TO OUR SSE WITH RESULTANT FRONTOGENESIS PROVIDING
STRONG LIFT. ALTHOUGH A GOOD PART OF THIS LIFT IS IN DENDRITIC
LAYER...SOME OCCURS EARLY THIS EVENING BELOW THAT LEVEL.
HOWEVER...CROSS SECTIONS SHOWED FOLDING OF THETA SURFACES
INDICATING UPRIGHT OR AT LEAST SLANT-WISE CONVECTIVE BANDS
POSSIBLE AIDING IN 1+ INCH SNOW RATES. ALSO A FEW INSTANCES OF
LIGHTNING HAVE BEEN REPORTED BOTH W OF LNK AND NE OF OMAHA.
12Z GFS/NAM HAVE INCREASED QPF NOW IN 1 INCH RANGE ALONG I80 INTO
WRN IA...ALTHOUGH ECMWF WAS LESS. USING A BLEND WOULD STILL
PROVIDE A BAND OF 7-9+ INCHES OF SNOW IN THE 00Z-12Z PERIOD USING
SNOW TO LIQUID RATIOS OF 13 TO 1 WEST TO AROUND 10-1 EAST THIS
EVENING AND 14-1 OR SO AFTER 06Z...USED A BIT LOWER RATIOS ACROSS
FAR SE. FORECAST SOUNDINGS INDICATED A RAIN/SLEET MIX POSSIBLE TO
BEGIN EVENT FAR SERN ZONES THROUGH 03Z. LATEST RAP FORECAST
SOUNDINGS ALSO FORECAST 65-75 KT WINDS SEVERAL K FEET ABOVE THE
SURFACE SPREADING FM FNB-FBY WITH SPEEDS AT THAT LEVEL IN 55-65KT
RANGE AT LNK/OMA TAPERING TO 45-50 AT KOFK. THUS DYNAMIC MIXING OF
SOME THESE WINDS DOWN TONIGHT SHOULD PROVIDE GUSTS THAT COULD
EXCEED 45-50KTS... ESPECIALLY SERN ZONES.
BLOWING/DRIFTING SNOW SHOULD LINGER THURSDAY MORNING ALTHOUGH HOW
WIDESPREAD BLIZZARD VISIBILITIES ARE MAINTAINED IS A QUESTION.
NONETHELESS...FELT RISK WAS GREAT ENOUGH WITH INITIAL LATE MORNING
ISSUANCE TO KEEP ERN 2/3RDS OR SO OF BLIZZARD AREA VALID THROUGH
18Z...AND THIS WAS CONTINUED IN AFTERNOON PACKAGE. SOME BLOWING
SNOW COULD LINGER ACROSS FAR ERN ZONES AFTER 18Z BUT WOULD EXPECT
VSBYS IMPROVING ENOUGH SO NO HEADLINE PAST THAT TIME. NO OTHER
WEATHER EXPECTED IN SHORT TERM WITH CLEARING AFTERNOON SKIES
LIKELY LASTING THROUGH SATURDAY.
LITTLE CHANGES TO TONIGHTS LOWS BUT WOULD EXPECT WITH FRESH SNOW
COVER MUCH OF THE AREA RECOVERY WILL BE TOUGH AND THUS REDUCED
DIURNAL RANGE. FRESH SNOW AND LIGHT WINDS SHOULD ALLOW MANY TEMPS
TO BE ON OR BELOW THE COLD SIDE OF GUIDANCE THU NGT/FRIDAY.
ALTHOUGH CONTINUED WARM ADVECTION COULD KEEP READINGS UP FRI NGT
AND ALLOW A BIT MORE RECOVERY SATURDAY...KEPT TEMPS NEAR COOLER
MAV MANY AREAS.
CHERMOK
LONG TERM...SATURDAY NIGHT THROUGH WEDNESDAY
A WEAK COLD FRONT MOVES THROUGH SATURDAY NIGHT WITH HIGH PRESSURE
BUILDING IN FOR SUNDAY AND SUNDAY NIGHT. SURFACE LOW PRESSURE OVER
THE ROCKIES MONDAY CONTINUES TO ORGANIZE AND DEVELOP OVER THE
SOUTHERN PLAINS. A MID LEVEL WAVE MOVES THROUGH THE PLAINS MONDAY
NIGHT THROUGH TUESDAY NIGHT. WITHIN THE LONG WAVE...THERE IS SOME
STRONGER ENERGY OVER THE NORTHERN PLAINS. SINCE THE FORECAST AREA IS
WELL AWAY FROM THE ENERGY IN THE NORTH AND THE MAIN STORM SYSTEM TO
OUR SOUTH...WE HAVE A CHANCE FOR LIGHT SNOW AND FLURRIES WITH THE
WAVE. THE TEMPERATURES ARE VERY COLD ALOFT...SO IT SHOULD BE EASY
TO GET LIGHT SNOW AND FLURRIES...THUS THERE MAY BE SOME LIGHT
ACCUMULATIONS. AT THIS TIME THE ORGANIZED PRECIPITATION IS ACROSS
KANSAS AND MISSOURI OVER THE CHRISTMAS HOLIDAY.
TEMPERATURES WILL REMAIN BELOW NORMAL THROUGH THE EXTENDED.
ZAPOTOCNY
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...BLIZZARD WARNING UNTIL NOON CST THURSDAY FOR NEZ015-033-034-044-
045-051>053-066>068-090>093.
BLIZZARD WARNING UNTIL 6 AM CST THURSDAY FOR NEZ050-065-078-088-
089.
WINTER STORM WARNING UNTIL 6 AM CST THURSDAY FOR NEZ032-042-043.
WINTER WEATHER ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR NEZ016-
030.
WINTER WEATHER ADVISORY UNTIL 6 AM CST THURSDAY FOR NEZ017-018-
031.
IA...BLIZZARD WARNING UNTIL NOON CST THURSDAY FOR IAZ043-055-056-069-
079-080-090-091.
&&
$$
AREA FORECAST DISCUSSION
NWS WILMINGTON OH
1257 AM EST THU DEC 20 2012
.SYNOPSIS...
A POTENT AND DEEP LOW PRESSURE SYSTEM WILL MOVE QUICKLY FROM
OKLAHOMA THIS EVENING INTO SOUTHERN LOWER MICHIGAN BY THURSDAY
NIGHT. THIS SYSTEM WILL BRING A POTPOURRI OVER WEATHER TO OHIO
VALLEY...INCLUDING A BAND OF MODERATE RAIN SHOWERS AND A FEW
THUNDERSTORMS WITH GUSTY WINDS ON THURSDAY...FOLLOWED BY A STRONG
COLD FRONT AND RAPID TEMPERATURE DROP LATE THURSDAY AFTERNOON AND
EVENING...WITH A CONTINUED INCREASE IN STRONG WIND GUSTS THURSDAY
NIGHT AND LINGERING INTO MUCH OF FRIDAY. IN ADDITION...SNOW AND
SNOW SHOWERS WILL WRAP THROUGH INDIANA AND OHIO WITH LIGHT
ACCUMULATIONS...AND WHEN COMBINED WITH THE PLUNGING
TEMPERATURES...STRONG WINDS...AND REDUCED VISIBILITIES...TRAVEL
CONDITIONS ARE EXPECTED TO DETERIORATE THURSDAY NIGHT AND INTO
FRIDAY. WINDS WILL DECREASE AND SNOW SHOWERS WILL END FRIDAY
NIGHT...WITH A QUIET PERIOD IN STORE FOR THE WEEKEND.
&&
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
THIS IS A QUIET PERIOD FOR THE WFO ILN FORECAST AREA...AS WEAK
HIGH PRESSURE YIELDS TO THE DEEPENING STORM IN THE SOUTHERN
PLAINS. BKN-OVC CIRRUS SHIELD WILL CONTINUE TO THICKEN OVERNIGHT
WHILE LIGHT/VARIABLE FLOW UNDER THE WEAK RIDGE AXIS TURNS EASTERLY
AND SLOWLY INCREASES THROUGH THE NIGHT IN RESPONSE TO THE
APPROACHING STORM. THIS SHOULD KEEP TEMPS A TICK ABOVE
GUIDANCE...BUT DID LOWER THE TEMPS FROM THE PREVIOUS FORECAST A
FEW DEGREES.
WITH RADAR SHOWING A FEW SHOWERS FLIRTING WITH OUR WESTERN
COUNTIES...RAISED POPS TO CHANCE THERE THIS EVENING INTO THE
OVERNIGHT.
&&
.SHORT TERM /6 AM THIS MORNING THROUGH FRIDAY NIGHT/...
ALL THE FOCUS TODAY IS ON THE RAPIDLY DEEPENING LOW PRESSURE AND
ITS IMPACT ON THE FORECAST AREA ON THURSDAY AND FRIDAY. INHERITED
A FORECAST FROM PREVIOUS SHIFTS THAT ALREADY HAD MUCH OF THE GIST
OF WHAT WILL UNFOLD - THUS WE FOCUSED ON ADDING DETAIL WHERE WE
COULD AND GET HEADLINE DECISIONS MADE. THERE ARE NO SIGNIFICANT
CHANGES IN THE FORECAST ITSELF BASED ON TODAY/S DATA.
GOES WATER VAPOR IMAGERY AND 19.12Z RAOBS CLEARLY SHOW THE POTENT
SHORTWAVE TROUGH ABOUT TO INDUCE RAPIDLY DEEPENING SURFACE CYCLONE
OVER THE SRN PLAINS. KFGZ/KABQ RAOBS BOTH HAD MORE THAN 100M
HEIGHT FALLS /500MB/ WHILE AIRCRAFT SOUTH OF THESE STATIONS
SAMPLED AN INTENSE 150-170KT JET STREAK /250MB/ THAT SEEMS TO HAVE
BEEN UNDER-INITIALIZED BY ALL DETERMINISTIC MODEL SOLNS BY A GOOD
20KTS. A CLASSIC MID-WINTER SYSTEM...SATELLITE PRESENTATION IS
ALREADY IMPRESSIVE AND RAP ANALYSIS /19Z/ ALREADY HAS THE
TROPOPAUSE FOLD /1.5 PV SURFACE/ DOWN TO 650MB OVER NRN NM. 996MB
CYCLONE IS ALREADY DEEPENING IN THE OKLAHOMA PANHANDLE AND
GUIDANCE IS NOW TIGHTLY CLUSTERED IN A VERY TYPICAL DECEMBER TRACK
THROUGH MISSOURI AND OVER THE CHICAGO METRO AREA TOWARD DETROIT BY
LATE THURSDAY NIGHT...WITH BLIZZARD CONDITIONS TO THE LEFT OF THE
TRACK AND AMPLE CONVECTION/WINDS IN THE WARM SECTOR.
IT IS IMPORTANT TO NOTE THAT FOR THE WFO ILN CWA...THERE CONTINUES
TO BE A LESSENING MODEL SIGNAL FOR A DAMAGING /HIGH WIND WARNING/ WIND
EVENT. DPROG/DT OVER ABOUT THE LAST DAYS WORTH OF DAY HAS TRENDED
TO AN EARLIER DEEPENING...AND HIGHER MINIMUM PRESSURE WHEN THE LOW
TRACKS ACROSS SOUTHERN MICHIGAN...WITH LATEST DATA SUGGESTING
MODEST FILLING WILL BE OCCURRING THURSDAY NIGHT WITH PRESSURES
BOTTOMING OUT NEAR 984MB NEAR CHICAGO. THIS MODEST CHANGE
DECREASES TO SOME DEGREE THE ISALLOBARIC COMPONENT...AND HAS
ALLOWED THE 925MB/850MB LAYERED WIND MAX TO DROP OUT OF ALARMING
RANGE THAT WOULD HAVE OTHERWISE PROMPTED A HIGH WIND WATCH OR
WARNING. THAT BEING SAID...WE TAKE FROM THE WIND...BUT NOW HAVE
ADDED A LITTLE MORE SNOW BASED ON NOW-AGREED-UPON SECONDARY PV
ANOMALY THAT WILL WRAP SOUTHEAST THROUGH THE BASE OF THE UPPER
TROUGH LATER ON THURSDAY NIGHT...THAT SHOULD BRING A RATHER
CONCENTRATED PERIOD OF LIGHT SNOW/SNOW SHOWERS TO AREAS NORTH OF
I-70 THURSDAY NIGHT INTO FRIDAY. SO IMPACTS WILL STILL BE
SIGNIFICANT WITH THIS SYSTEM...PROBABLY MORE SO FROM ICY
ROADS/WINTER TRAVEL ISSUES THAN FROM WIND DAMAGE/POWER
OUTAGES...ALTHOUGH WITH ANTICIPATED GUSTS TO 45-50MPH OR A LITTLE
HIGHER...ISOLATED POWER OUTAGES AND MINOR/NUISANCE TREE DAMAGE IS
STILL EXPECTED.
DETAILS ON IT ALL...WITH THE TIGHT CLUSTERING OF THE NWP MODEL
SUITE CONFIDENCE IS HIGH IN MOST ASPECTS OF THIS FORECAST. VERY
STRONG/DEEP LAYERED FORCING IMMEDIATELY DOWNSTREAM OF THE PV
CURRENTLY IN NM WILL INDUCE A VERY STRONG MOISTURE TRANSPORT FEED
LATER TONIGHT WHICH WILL MANIFEST AS A ELONGATED/LARGE AREA OF
SHOWERS AND EMBEDDED THUNDERSTORMS RAPIDLY MOVING FROM MS VALLEY
INTO THE OHIO VALLEY LATE. THINK THIS SPREADS ACROSS THE WESTERN
AREAS JUST AFTER SUNRISE WITH BEST POTENTIAL OF THUNDER WEST OF
I-71 WHERE MUCAPE IS THE HIGHEST. ALL AREAS GET A GOOD 1/2 INCH OF
RAIN IT APPEARS WITH THIS ACTIVITY WHICH SHIFTS QUICKLY THROUGH
THE FORECAST AREA BY MID AFTERNOON.
A 60-65KT SOUTHERLY LOW LEVEL JET WILL BE DRIVING THIS
ACTIVITY...AND MAY PRESENT A WIND ISSUE AT THE SURFACE...BUT WARM
ADVECTION WIND EVENTS TOUGH TO REALIZE GIVEN INVERTED THERMAL
PROFILES...DEEP LAYERED OMEGA...AND THICK CLOUDS...SO THINK
MORNING/AFTN WILL BE WINDY...BUT NOT WIND ADVISORY
LEVELS...PROBABLY 20/25 GUST 35/40 MPH. PERHAPS A LITTLE STRONGER
IN HEAVIER REFLECTIVITY CORES WITH PASSING SHOWERS...BUT WE CHOSE
TO HOLD OFF ON A WIND ADVISORY FOR THE DAYLIGHT HOURS.
WIND POTENTIAL GOES UP MARKEDLY AS THE COLD FRONT PLOWS INTO
WESTERN AREAS AROUND 21Z AND MARCHES ACROSS THE CWA EFFECTIVELY IN
ABOUT 4-5 HOURS TIME. THERE IS LOW CONFIDENCE IN A FINE LINE OF
SHOWERS ALONG THIS BOUNDARY - AND IF IT OCCURS - THERE IS SHALLOW
SB BUOYANCY /SHOWN VERY NICELY IN 19.12Z BUFR SOUNDINGS FROM NAM-
WRF/ THAT THIS LINE COULD PRODUCE BRIEF HIGH WIND GUSTS.
HOWEVER...BUOYANCY IS SO SHALLOW THAT CHARGE SEPARATION SEEMS
IMPOSSIBLE AND THUNDER WILL BE A STRETCH...SO DECIDED TO GET WIND
ADVISORY GOING AT 21Z ALL AREAS IN CASE THE FRONT CAN TRANSPORT
STRONG GUSTS TO THE SURFACE VIA THIS MECHANISM. IN THE WAKE OF THE
FRONT...LAPSE RATES STEEPEN VERY QUICKLY AND WITH A PSEUDO-DRY
SLOT /THOUGH LOW LEVEL MOISTURE WILL STILL BE AMPLE/...THERE IS
REMAINING INSTABILITY WITH STRONG GUST POTENTIAL IN THE HOURS
FOLLOWING THE FRONT DESPITE DEEPER LAYER STRONG WINDS WILL HAVE
YET TO ARRIVE. WIND POTENTIAL CONTINUES INTO THE OVERNIGHT AS
19.12Z NAM/GFS/ARW-WRF ALL BRING 55-60KT 925-850MB LAYERED WIND
MAX SOUTHEAST FROM THE BACKSIDE OF THE LOW RIGHT THROUGH THE HEART
OF THE CWA. WITH COLD ADVECTION...RAPID PRESSURE RISES...AND
STEEPENING LAPSE RATES...CONTINUED ADVISORY LEVEL WINDS AND GUSTS
ARE EXPECTED AREA-WIDE. THE MOST CONCERNING AREA FOR HIGHER END
GUSTS CONTINUES TO BE ACROSS WEST-CENTRAL OHIO IN THE HIGHER
TERRAIN AREAS AND WEST TO THE INDIANA BORDER WHERE SOME 55 MPH
GUSTS COULD BE SEEN. ANOTHER BIG CHANGE FROM YESTERDAY IS THE
LINGERING OF STRONG WINDS NOW INTO THE AFTERNOON HOURS ON
FRIDAY...AND WHILE AMPLE LOW LEVEL MOISTURE AND OMEGA IS SEEN NEAR
THE SURFACE WHICH WILL HELP TEMPER GUSTS...EVEN CONSERVATIVE MOMENTUM
TRANSPORT /MIXING/ TECHNIQUES SUGGEST LOW-END WIND ADVISORY WINDS
WILL BE POSSIBLE MOST AREAS AT LEAST INTO THE MID AFTERNOON...AND
PARTICULARLY NORTH OF THE OHIO RIVER.
IN TERMS OF SNOW...THE TEMP DROP IN THE WAKE OF THE COLD FRONT IS
FAST AND IMPRESSIVE...AND MAY INDUCE RAPID ROAD FREEZING AND ICING
EVEN IN THE DRY SLOT EARLY THURSDAY EVENING. LATER IN THE
EVENING...SECONDARY PV WRAPS SOUTHEASTWARD /ACCOMPANIED BY LOW
LEVEL WIND MAX MENTIONED ABOVE/ AND SPREADS GOOD FORCING FOR UVM
INTO AREAS NORTH OF I-70 WHERE SNOW/SNOW SHOWERS WILL BE ABUNDANT.
SEE A NICE LITTLE STRIPE OF 1-2 INCHES OF SNOW ACROSS WCNTL INTO
CNTL OH...SO DECIDED TO BE SIMPLE AND COMBINE THE THREATS OF
STRONG WINDS/SNOW/REDUCED VISIBILITIES/ICY ROADS INTO A WINTER
WEATHER ADVISORY. SNOW AMOUNTS WON/T BE SIGNIFICANT...BUT COMING
OUT OF A LONG TERM WARM PERIOD...PAVEMENT SUBSURFACES ARE
ATYPICALLY WARM. WITH VERY COLD AIR AND PERSISTENT SNOW
SHOWERS/STRONG WINDS REMOVING THIS WARMTH FROM THE SKIN SURFACE OF
THE PAVEMENT...SETUP IS SUCH THAT ROADS COULD BECOME EXTREMELY
SLIPPERY IN THE WINTER WX ADVISORY AREA ESP LATER THURS NIGHT INTO
MUCH OF FRIDAY WHERE SNOW IS PERSISTENT. COMBINED WITH RAPID VSBY
CHANGES IN SNOW SHOWERS...THESE SITUATIONS CAN BE SNEAKY-
DANGEROUS...ESPECIALLY CONSIDERING THE MILD WINTER THUS FAR. DON/T
SEE A SIGNAL IN THE DATA FOR SNOW RATIOS AS DIFFERENT THAN CLIM0 -
MUCH OF LIFT/SATURATIONS REMAINS BELOW THE DENDRITIC GROWTH ZONES
AND COBB RATIOS FROM A WEALTH OF SOURCES ARE ALL FROM 8:1 TO 11:1
FOR MOST OF THE PERIOD. LOWEST CONFIDENCE IN WINTER WX ADVISORY
CONDITIONS IN AROUND CMH METRO...BUT DIDN/T WANT TO GET CUTE AT
THIS MOMENT AND TRY TO BE TOO FINE GIVEN INHERENT UNCERTAINTIES.
ISSUED THE WIND ADVISORY FOR AREAS IN THE SOUTH NOT EXPECTED TO
SEE SIGNIFICANT ENOUGH SNOW FOR TRAVEL ISSUES...BUT EVEN IN THESE
AREAS CANNOT RULE OUT A PERIOD OF SLIPPERY TRAVEL AS MAIN WAVE
TRAVERSES THE AREA FRIDAY NIGHT INTO FRIDAY MORNING WITH THE
STRONG WINDS AND COLD TEMPS AND WARM ROAD SURFACES CAUSING
SLIPPERY TRAVEL. FUTURE SHIFTS MAY NEED TO CONSIDER EXPANSION OF
THE WINTER WEATHER ADVISORY IF SNOW SHOWERS ARE MORE WIDESPREAD OR
CONTAIN HEAVIER RATES THAN CURRENTLY ANTICIPATED.
CONDITIONS RAPIDLY IMPROVE FRIDAY EVENING AS WINDS DECREASE AND
SYSTEM PULLS OUT.
&&
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
THE LONG TERM WILL START OFF WITH SOME LINGERING CLOUDS AND A
POSSIBLE FLURRY SATURDAY MORNING BEHIND THE DEPARTING STORM SYSTEM.
CLOUDS SHOULD BE OUT OF THE AREA BY SATURDAY NIGHT AS HIGH PRESSURE
EXTENDS ACROSS THE AREA. WENT BELOW THE MODEL CONSENSUS FOR FORECAST
HIGHS ON SATURDAY ACROSS THE NORTH WHERE CLOUDS AND REMNANT SNOW
COVER WILL KEEP TEMPERATURES DOWN. WENT BELOW THE MODEL CONSENSUS
FOR THE WHOLE AREA SATURDAY NIGHT WITH HIGH PRESSURE AND DECREASING
WINDS HELPING TO PRODUCE FAVORABLE CONDITIONS FOR RADIATIONAL
COOLING.
SUNDAY WILL BE A TRANSITION DAY AS THE HIGH SHIFTS EAST OF THE AREA
AND WEAK LOW PRESSURE APPROACHES FROM THE WEST. ON SUNDAY
NIGHT...CLOUD COVER WILL INCREASE AHEAD OF THIS WEAK LOW AS MOISTURE
GETS DRAWN NORTHWARD INTO THE OHIO VALLEY. MODELS ARE IN FAIR
AGREEMENT ON BRINGING LIGHT PRECIPITATION TO THE FORECAST AREA
SOMETIME BETWEEN EARLY MONDAY MORNING AND EARLY MONDAY
AFTERNOON...DEPENDING ON WHICH MODEL YOU LOOK AT. THIS TIMING WILL
PROBABLY HELP TO DETERMINE PRECIPITATION TYPE. GFS HAS THE COLDEST
AND QUICKEST ARRIVAL OF PRECIPITATION...ALLOWING FOR A PARTIAL MIX
OF RAIN AND SNOW ACROSS MUCH OF THE AREA FOR THIS EVENT. THE
ECMWF/CANADIAN MODELS ARE TOO WARM ALOFT FOR ANY SNOW...HOWEVER
BRING LIGHT RAIN INTO THE AREA WHEN TEMPERATURES ARE NEAR FREEZING
AT THE SURFACE. THEREFORE...THIS PARTICULAR TIME PERIOD WILL NEED
ADJUSTING AS THE TIME DRAWS NEARER. REGARDLESS IT DOES APPEAR THAT
QPF AMOUNTS WILL BE LIGHT FOR THIS LOW WITH NO ACCUMULATION OF ANY
SNOW EXPECTED IF ANY MIX DOES OCCUR.
AFTER A FAIR WEATHER DAY ON CHRISTMAS...THE ATTENTION TURNS TO
CHRISTMAS NIGHT INTO WEDNESDAY AS A VIGOROUS LOW PRESSURE SYSTEM
APPROACHES OUR REGION. MODELS ARE STILL SHIFTING WITH TIMING AND
LOCATION FOR THIS LOW BETWEEN RUNS. HOWEVER...IT DOES APPEAR ONE WAY
OR ANOTHER THAT PRECIPITATION WILL OCCUR. BUMPED UP POPS TO 50
PERCENT. COULD HAVE GONE HIGHER FOR POPS IF THERE WERE NOT STILL
TIMING DIFFERENCES AMONGST THE MODELS.
&&
.AVIATION /06Z THURSDAY THROUGH MONDAY/...
A STRONG COLD FRONT WILL CROSS THE AREA AND HAVE A SUBSTANTIAL
IMPACT ON AVIATION PRIMARILY WITH WINDS. VFR CONDITIONS WILL
PREVAIL INTO THE MORNING WITH EASTERLY WINDS GRADUALLY VEERING.
SHOWERS OUT AHEAD OF THE COLD FRONT WILL PUSH INTO THE AREA AFTER
DAYBREAK AND BRING MVFR CONDITIONS. APPEARS THAT INITIALLY THIS
WILL BE A VISIBILITY RESTRICTION WITH HEAVIER SHOWERS AND THEN
CEILINGS WILL LOWER AS SHOWERS BECOME MORE OFF AND ON. WINDS WILL
CONTINUE TO VEER AND SLOWLY STRENGTHEN WITH SOME GUSTS UP TO 30 KT
POSSIBLE. THE COLD FRONT WILL SWEEP ACROSS THE REGION WITHIN A FEW
HOURS EITHER SIDE OF 00Z. EXPECT ONLY A SLIGHT WIND SHIFT BUT
SPEEDS AND GUSTS SHOULD INCREASE A FAIR AMOUNT. APPEARS THAT THERE
MAY A BRIEF IMPROVEMENT TO VFR AFTER THE FRONTAL PASSAGE. BUT THEN
SNOW SHOWERS WILL SPREAD INTO THE REGION LATE IN THE TAF PERIOD
RESULTING IN A LOWERING OF FLIGHT CATEGORY.
OUTLOOK...MVFR CEILINGS AND MVFR TO IFR VISIBILITIES EXPECTED LATE
THURSDAY NIGHT INTO FRIDAY WITH MVFR CEILINGS POSSIBLY LINGERING
INTO SATURDAY MORNING. WIND GUSTS FROM 25 TO 40 KT EXPECTED TO
CONTINUE INTO FRIDAY. MVFR CEILINGS POSSIBLE MONDAY.
&&
.ILN WATCHES/WARNINGS/ADVISORIES...
OH...WINTER WEATHER ADVISORY FROM 4 PM THIS AFTERNOON TO 4 PM EST
FRIDAY FOR OHZ026-034-035-042>046-051>056-060>062.
WIND ADVISORY FROM 4 PM THIS AFTERNOON TO 4 PM EST FRIDAY FOR
OHZ063>065-070>074-077>082-088.
KY...WIND ADVISORY FROM 4 PM THIS AFTERNOON TO 4 PM EST FRIDAY FOR
KYZ089>100.
IN...WINTER WEATHER ADVISORY FROM 4 PM THIS AFTERNOON TO 4 PM EST
FRIDAY FOR INZ050-058-059.
WIND ADVISORY FROM 4 PM THIS AFTERNOON TO 4 PM EST FRIDAY FOR
INZ066-073>075-080.
&&
$$
SYNOPSIS...BINAU
NEAR TERM...BINAU/CONIGLIO
SHORT TERM...BINAU
LONG TERM...LATTO
AVIATION...
AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NWS SIOUX FALLS SD
1105 PM CST WED DEC 19 2012
.DISCUSSION.../ISSUED AT 930 PM CST/
RADAR IMAGES AND OBS PRESENTLY INDICATE LIGHT SNOW OCCURRING IN
AREAS EAST OF A LINE ROUGHLY FROM JUST EAST OF YANKTON TO LUVERNE TO
JUST WEST OF WINDOM. ONLY VERY LIGHT SNOW HAS FALLEN SO FAR THIS
EVENING PER ONLY A FEW REPORTS...THOUGH AN ENHANCED BAND LOOKS TO BE
DEVELOPING FROM DIXON COUNTY NEBRASKA NORTHEASTWARD THROUGH THE
AKRON/SIOUX CENTER/SHELDON CORRIDOR...AND MEDIA HAD INDICATED THAT
SNOW HAS PICKED UP IN INTENSITY AT SIOUX CITY. THE ABOVE BAND SEEMS
TO BE COLLOCATED WELL WITH RAP 700 MB FRONTOGENESIS...WITH SOME
INSTABILITY ABOVE THE FRONTAL CIRCULATION...AND THIS FRONTOGENESIS
IS STILL PROGGED TO SAG SLOWLY SOUTHEASTWARD THROUGH THE NIGHT. IN
LIGHT OF THAT...LEFT SNOWFALL AMOUNTS CLOSE TO PREVIOUS
FORECAST...THOUGH TRIMMED AMOUNTS BEFORE 00Z AS NO SNOW WAS REPORTED
BEFORE THEN. ALSO TRIMMED BACK THE NORTHWESTERN BACK EDGE OF THE
FORECASTED SNOWFALL AMOUNTS...INCLUDING SIOUX FALLS...WHERE SNOW HAS
PRETTY MUCH ENDED. SO IN SUMMARY...THINK MOST PLACES WILL REACH
HEADLINE CRITERIA...THOUGH OVERALL SNOWFALL AMOUNTS MAY BE A LITTLE
LESS THAN CURRENTLY FORECASTED. LEFT HEADLINES AS IS WITH UPDATES
OUT.
&&
.AVIATION.../FOR 06Z TAF ISSUANCE/
MAIN AVIATION CONCERN IS AN INTENSE LOW PRESSURE SYSTEM MOVING
ACROSS THE CENTRAL PLAINS TONIGHT. MODERATE TO HEAVY SNOW MOVING
THROUGH KSUX AREA AT START OF PERIOD SHOULD MOVE EAST BY 07Z-08Z...
THOUGH MVFR-IFR VISIBILITY EXPECTED TO LINGER THROUGH THE EARLY
MORNING AS NORTH WINDS GUSTING OVER 30KTS CAUSE AREAS OF BLOWING
SNOW. SIMILAR MVFR-IFR CONDITIONS EXPECTED ACROSS MOST OF NORTHWEST
IOWA THROUGH THE PRE-DAWN HOURS...WITH VFR CONDITIONS GRADUALLY
SPREADING EAST THROUGH 18Z AS THE STORM SYSTEM MOVES INTO THE
MISSISSIPPI VALLEY. AREA OF MVFR STRATUS MOVING SOUTH THROUGH THE
MISSOURI AND JAMES RIVER VALLEYS. NOT EXPECTED TO BE WIDESPREAD...
BUT DID ADD PERIOD OF MVFR CEILINGS TO KHON THROUGH 12Z.
&&
.PREV DISCUSSION.../ISSUED AT 300 PM CST/
ALL EYES CONTINUE TO BE ON THE MASSIVE WINTER STORM WELL UNDER WAY
ACROSS THE CENTRAL PLAINS. ELONGATED UPPER LEVEL TROUGH CURRENTLY
CENTERED OVER COLORADO WILL SWING INTO CENTRAL KANSAS BY MIDNIGHT
TONIGHT BEFORE CLOSING OFF AND LIFTING NORTHEAST INTO THE QUAD
CITIES AREA BY THURSDAY AFTERNOON. AHEAD OF THIS TROUGH...A LARGE
SURFACE LOW HAS DEEPENED NEAR THE WESTERN KANSAS AND OKLAHOMA BORDER
AND BEGUN TRACKING NORTHEAST THIS AFTERNOON. ON THE NORTHERN EDGE OF
THE LOW...MODERATE TO HEAVY SNOWFALL WHICH FORMED ALONG A SWATH OF
MID LEVEL FRONTOGENESIS IN WESTERN AND CENTRAL NEBRASKA IS TRACKING
NORTHEASTWARD. MUCH DRIER LOW AND MID LEVELS ACROSS SOUTHEAST SOUTH
DAKOTA AND NORTHWEST IOWA IS PREVENTING PRECIPITATION FROM REACHING
THE SURFACE SO FAR. AS THE LOW TRACKS EASTWARD AND 700 MB
FRONTOGENESIS AND QG FORCING INTENSIFIES OVER NORTHEAST NEBRASKA AND
NORTHWEST IOWA...MOISTURE WILL ADVECT INTO THE COLUMN AND MODERATE
TO HEAVY SNOW WILL BEGIN FALLING LATE THIS AFTERNOON AND EARLY
EVENING.
AROUND AN INCH OR MORE OF SNOW IS EXPECTED TO FALL THIS EVENING AND
OVERNIGHT TO THE SOUTH AND EAST OF A LINE FROM WINDOM TO SIOUX
CENTER TO VERMILLION. THE HEAVIEST SNOW IS EXPECTED IN EASTERN
WOODBURY COUNTY...SOUTHERN DAKOTA...IDA...CHEROKEE AND BUENA VISTA
WHERE 4 TO 6 INCHES IS POSSIBLE WITH AMOUNTS TAPERING OFF QUICKLY AS
YOU MOVE NORTHWEST OF THESE COUNTIES. THE BIGGEST CONCERN WITH THIS
SYSTEM HOWEVER WILL BE THE STRONG NORTHERLY WINDS WHICH ARE
EXPECTED TO INCREASE THIS EVENING AND REMAIN WINDY INTO MUCH OF
THURSDAY. GIVEN THE MODERATE TO HEAVY SNOWFALL AND SUSTAINED WINDS
OF 20 TO 25 KT EXPECTED OVERNIGHT...WILL LIKELY SEE BLIZZARD
CONDITIONS IN THE AFOREMENTIONED COUNTIES. WENT AHEAD AND UPGRADED
THE WINTER WEATHER WATCH AND WINTER STORM WARNING IN THIS AREA TO A
BLIZZARD WARNING. FURTHER NORTH AND WEST...ADVERSE CONDITIONS ARE
EXPECTED...BUT WITH LESSER SNOWFALL AMOUNTS AND SLIGHTLY WEAKER
WINDS WILL GO WITH THE WINTER WEATHER ADVISORY FOR THE REST OF
NORTHWEST IOWA AND ADJACENT COUNTIES IN SD AND MN. THIS ADDS A FEW
COUNTIES TO THE PREVIOUS ADVISORY. IN THE ADVISORY AREA...MANY AREAS
WILL SEE ONLY A FEW INCHES OF NEW SNOW...HOWEVER THE MAIN CONCERN
WOULD BE VISIBILITY ISSUES AND BLOWING/DRIFTING SNOW. FOR THE SIOUX
FALLS METRO AREA...A HALF INCH OR LESS OF SNOW IS FORECAST.
COLD AIR ADVECTION AND BRISK NORTHWEST WINDS WILL MAKE FOR A NOT SO
PLEASANT DAY ON THURSDAY. AFTER LOWS IN THE SINGLE DIGITS AND MID
TEENS TONIGHT...HIGHS ON THURSDAY ARE EXPECTED TO ONLY REACH THE MID
TEENS AND 20S. SKIES ARE EXPECTED TO CLEAR FROM WEST TO EAST THROUGH
THE DAY.
FOR THURSDAY NIGHT THROUGH THE WEEKEND...RATHER QUIET WEATHER
EXPECTED. WITH FRESH SNOW COVER AND CLEARING SKIES...OVERNIGHT LOWS
THURSDAY NIGHT WILL DROP TO A FEW DEGREES EITHER SIDE OF ZERO. THE
EXCEPTION WILL BE THE SOUTHWEST CWA WHERE WARM AIR ADVECTION KICKS
DURING THE NIGHT AND SHOULD PREVENT LOWS FROM DROPPING BELOW 10
ABOVE. WARMER AIR WILL SPREAD ACROSS CWA ON FRIDAY AND
SATURDAY...BUT FRESH SNOW COVER OVER MOST OF CWA AND TO THE SOUTH
WILL INHIBIT THE TRUE POTENTIAL OF WARMING...AND THIS WILL ONLY SEE
HIGHS IN THE 20S AND 30S...WITH THE WARMEST TEMPERATURES ACROSS THE
SOUTHWEST.
A WEAK WAVE WILL DROP SOUTHEAST OUT OF NORTH DAKOTA ON SUNDAY WITH
COLDER TEMPERATURES ACROSS THE CWA. COULD SEE A FEW FLURRIES WITH
THIS WAVE ACROSS NORTHEAST CWA ON SUNDAY...BUT FOR NOW WILL LEAVE
DRY.
MODELS CONTINUE TO DIVERGE ON SOLUTION FOR THE CHRISTMAS
HOLIDAY...ALTHOUGH THE TREND IS FOR A MUCH WEAKER SYSTEM ACROSS THE
PLAINS. IN FACT...BOTH ECMWF AND GFS ONLY SHOW LIGHT SNOW AT BEST.
WILL KEEP SMALL POPS FOR LIGHT SNOW MONDAY INTO TUESDAY DUE TO
INCONSISTENT MODEL RUNS. WILL ALSO SEE A COOL DOWN BEHIND THE WEAK
SYSTEM...WITH HIGH TEMPERATURES ONLY IN THE SINGLE DIGITS AND TEENS
BY WEDNESDAY.
&&
.FSD WATCHES/WARNINGS/ADVISORIES...
IA...WINTER WEATHER ADVISORY UNTIL 6 AM CST THURSDAY FOR IAZ001-012-
020.
WINTER WEATHER ADVISORY UNTIL NOON CST THURSDAY FOR IAZ002-003-
013-014.
BLIZZARD WARNING UNTIL NOON CST THURSDAY FOR IAZ021-022-031-032.
MN...WINTER WEATHER ADVISORY UNTIL NOON CST THURSDAY FOR MNZ081-089-
090.
NE...WINTER WEATHER ADVISORY UNTIL 6 AM CST THURSDAY FOR NEZ013.
BLIZZARD WARNING UNTIL NOON CST THURSDAY FOR NEZ014.
SD...WINTER WEATHER ADVISORY UNTIL 6 AM CST THURSDAY FOR SDZ070-071.
&&
$$
AREA FORECAST DISCUSSION
NWS TAMPA BAY RUSKIN FL
1000 AM EST THU DEC 20 2012
...TURNING MUCH COLDER ON FRIDAY AND INTO THE WEEKEND...
...HAZARDOUS BOATING CONDITIONS DEVELOPING TONIGHT OVER THE
EASTERN GULF OF MEXICO WATERS...
.UPDATE (REST OF TODAY - TONIGHT)...
14Z WATER VAPOR AND H4 RAP ANALYSIS SHOWS AN AMPLIFIED UPPER LEVEL
PATTERN ACROSS THE CONUS THIS MORNING. FROM WEST TO EAST WE FIND
LONGWAVE RIDGING IN PLACE FROM THE 4-CORNERS REGION NORTHWARD
THROUGH THE INTERMOUNTAIN WEST...WITH THE FLOW THEN QUICKLY TURNING
BACK TO THE SOUTH INTO A SHARP AND IMPRESSIVE LONGWAVE TROUGH OVER
THE CENTRAL PORTION OF THE CONTINENT. THIS ENERGY IS SUPPORTING A
SIGNIFICANT AREA OF SURFACE LOW PRESSURE MOVING TROUGH THE UPPER
MIDWEST/GREAT LAKES REGION WITH A TRAILING COLD FRONT BACK DOWN TO
THE NORTH-CENTRAL GULF COAST. THIS SYSTEM IS PROVIDING ALL KINDS OF
WEATHER FROM BLIZZARD CONDITIONS NORTH AND WEST OF THE LOW TRACK TO
SEVERE THUNDERSTORMS AHEAD OF THE COLD FRONT TO THE SOUTH AND EAST.
THE IMPRESSIVE HEIGHT FALLS OVER THE CENTRAL STATES ARE FORCING A
SHORT-TERM DOWNSTREAM AMPLIFICATION TO THE RIDGE OVER THE ATLANTIC
SEABOARD THIS MORNING. THIS RIDGE WILL BE QUICKLY TRANSLATING
EASTWARD INTO THE WESTERN ATLANTIC AS THE UPPER TROUGH TAKES OVER
TONIGHT.
CLOSER TO HOME...STACKED RIDGING THAT HAS BEEN IN PLACE OVER THE FL
PENINSULA IS EXITING TO OUR EAST THIS MORNING AS THE SOUTHERN
PORTION OF THE UPPER TROUGH AXIS MOVES ALONG THE NORTHERN GULF
COAST. LOW LEVEL FLOW HAS SHIFTED TO THE SOUTHEAST BETWEEN THE
SURFACE HIGH TO OUR EAST AND A POTENT COLD FRONT CROSSING
THE LOWER/MS VALLEY.
REST OF TODAY...GENERALLY FAIR AND DRY FORECAST THROUGH THE
AFTERNOON HOURS FOR THE MAJORITY OF THE FORECAST AREA. STILL
EXPECTING A FAIR AMOUNT OF SUNSHINE DESPITE A SLOW INCREASE IN
MID/HIGH LEVEL CLOUDS FROM THE WEST. THE ABUNDANT SOLAR INSOLATION
AND GOOD DIURNAL MIXING WILL TAP INTO WARM 850MB TEMPS OF 14-16C TO
RESULT IN ABOVE NORMAL TEMPERATURES THIS AFTERNOON. MANY LOCATIONS
SHOULD REACH THE UPPER 70S TO LOWER 80S. COOLER SPOTS WILL LIKELY BE
COASTAL LEVY AND PORTIONS OF PINELLAS COUNTY DO TO A SOUTHERLY FLOW
OFF THE COOLER SHELF WATERS. LATE THIS AFTERNOON (GENERALLY AFTER 4
PM)...LARGE SCALE SYNOPTIC SUPPORT/QG FORCING AHEAD OF THE UPPER
TROUGH WILL BEGIN TO OVERSPREAD THE NATURE COAST ZONES. AT THE SAME
TIME LOW LEVEL CONVERGENCE/FOCUS AHEAD OF THE FRONT WILL ALSO BE
INCREASING AND MAY RESULT IN A FEW SHOWERS FOR EARLY EVENING AHEAD
OF THE MAIN CONVECTIVE BAND. SHOWERS (IF ANY) BEFORE SUNSET SHOULD
BE CONFINED TO LEVY/CITRUS COUNTY.
TONIGHT...QUICK MOVING COLD FRONT WILL ENTER THE FORECAST AREA AFTER
SUNSET AND BE WELL OFF TO OUR SOUTH AND EAST BEFORE DAWN. SYNOPTIC
SUPPORT FOR LIFT AHEAD OF THE TROUGH WILL QUICKLY INCREASE AFTER 00Z
WITH A MAXIMUM NORTH OF THE I-4 CORRIDOR. THIS SUPPORT WILL AID
IMPRESSIVE LOW LEVEL FOCUS ALONG THE FRONTAL BOUNDARY TO SUPPORT
WHAT IS EXPECTED TO BE A NARROW BUT SOLID BAND OF SHOWERS/EMBEDDED
STORMS MOVING ACROSS THE NATURE COAST/TAMPA BAY AREA BETWEEN
7PM-2AM. RETURN FLOW PERIOD AHEAD OF THIS FRONT IS SHORT AND
THEREFORE OVERALL INSTABILITY IS REALLY LACKING. THE LACK OF COLUMN
INSTABILITY SHOULD LIMIT THE DEEP CONVECTION...WITH A MORE SHALLOW
CONVECTIVE MODE EXPECTED. LOOKING AT ALL THE HIRES CONVECTION
ALLOWING MODELS AVAILABLE...NONE ARE PRODUCING ANY IMPRESSIVE
UPDRAFT STRENGTHS...WHICH LENDS CONFIDENCE TO ONLY A MARGINAL LOW
END SEVERE THREAT OVER THE NORTHERN HALF OF THE FORECAST AREA.
HOWEVER...LOW LEVEL JET OF 40-50KTS DOES BRIEFLY DIP DOWN INTO THE
NATURE COAST THIS EVENING. IF THERE ARE ANY ISOLATED DAMAGING WIND
GUSTS IT WILL LIKELY BE WITH STORMS TAPPING THIS MOMENTUM. BAND
OF SHALLOW CONVECTION QUICKLY TRANSLATES SOUTH AND EAST FROM THE I-4
CORRIDOR AFTER 2AM AND SHOULD BE OUT OF OUR ZONES BEFORE SUNRISE
FRIDAY. WIND FIELDS AND DYNAMICS FOR OVERALL LIFT ARE MUCH LESS
IMPRESSIVE ACROSS THE SOUTHERN ZONES...AND DO NOT ANTICIPATE ANY
SEVERE THREAT...OR EVEN MUCH THUNDER (IF ANY). THE FRONTAL PASSAGE
TONIGHT LOOKS TO BE FAIRLY NOTICEABLE WITH GUIDANCE SHOWING A QUICK
WINDSHIFT TO THE NW AND SOME GUSTY CONDITIONS DEVELOPING...
ESPECIALLY NEAR THE COAST. BIG TEMPERATURE GRADIENT BY SUNRISE
ACROSS THE FORECAST AREA. THE FRONT WILL JUST BE EXITING AREAS LIKE
FT MYERS WHERE TEMPS WILL STILL BE NEAR 60...HOWEVER UP TOWARD
LEVY/CITRUS/SUMTER COUNTIES WHERE A LONGER DURATION OF CAA WILL BE
ONGOING...TEMPS WILL BE WELL DOWN INTO THE 40S. WINDCHILL VALUES
SHOULD BE IN THE MID/UPPER 30S THIS FAR NORTH FOR THE EARLY MORNING
HOURS.
&&
PREVIOUS DISCUSSION (FRIDAY - SATURDAY)...ON FRIDAY A MUCH COLDER
AND DRIER AIR MASS WILL ADVECT INTO THE REGION IN THE WAKE OF THE
FRONT ON A BRISK NORTHWEST TO NORTHERLY WIND FLOW. STRONG COLD AIR
ADVECTION WILL KEEP TEMPERATURES FROM RISING MUCH DURING THE DAY
WITH HIGHS ONLY EXPECTED TO REACH THE UPPER 50S OVER THE NATURE
COAST...AND LOWER TO MID 60S CENTRAL AND SOUTH WITH THE GUSTY WINDS
MAKING IT FEEL EVEN COLDER.
DURING FRIDAY NIGHT INTO SATURDAY THE COLDER AND DRIER AIRMASS WILL
CONTINUE TO ADVECT INTO THE REGION ON A NORTHERLY WIND FLOW AS
SURFACE HIGH PRESSURE BUILDS IN OVER THE NORTHERN GULF. THE COLD
DRY AIR MASS WILL ALLOW TEMPERATURES TO FALL OFF RAPIDLY AFTER
SUNSET WITH AN ADVECTIVE TYPE FREEZE LIKELY TO OCCUR ACROSS THE
NATURE COAST WHERE TEMPERATURES WILL PLUMMET INTO THE UPPER 20S TO
LOWER 30S BY EARLY SATURDAY MORNING...WITH MID TO UPPER 30 DEGREE
READINGS EXTENDING SOUTH INTO THE CENTRAL INTERIOR ZONES...AND UPPER
30S TO AROUND 40 FAR SOUTH. IN ADDITION TO THE COLD TEMPERATURES
WINDS WILL REMAIN ELEVATED IN THE 8 TO 10 MPH RANGE OVERNIGHT WHICH
WILL LIKELY PRODUCE LOW WIND CHILL READINGS AS WELL. GIVEN THESE
EXPECTED TRENDS WILL HOIST A FREEZE WATCH FOR THE NATURE COAST FOR
LATE FRIDAY NIGHT INTO SATURDAY MORNING IN THE EARLY MORNING
FORECAST PACKAGE. A WIND CHILL ADVISORY MAY ALSO BE REQUIRED IN
LATE FORECASTS. DRY AND VERY COOL WEATHER WITH AMPLE SUNSHINE IS
EXPECTED ON SATURDAY AS HIGH PRESSURE REMAINS IN CONTROL WITH
TEMPERATURES REMAINING WELL BELOW NORMAL WITH HIGHS AGAIN ONLY
REACHING THE 60S IN MOST LOCATIONS.
&&
.AVIATION...
STRONG COLD FRONT WILL BE PRECEDED BY A LINE OF SHOWERS AND
THUNDERSTORMS TONIGHT...THEN FOLLOWED BY GUSTY NORTHWESTERLY WINDS.
A BRIEF PERIOD OF MVFR PERHAPS IFR CONDITIONS SEEM LIKELY WITH THE
FRONT THEN CLEARING NORTH TO SOUTH LATER TONIGHT AND EARLY FRIDAY
MORNING.
&&
.MARINE...
SOUTHERLY FLOW THROUGH THE AFTERNOON AHEAD OF AN APPROACHING COLD
FRONT WILL SHIFT TO THE NORTHWEST FROM NORTH TO SOUTH OVERNIGHT
AFTER THE FRONTAL PASSAGE. STRONG COLD AIR ADVECTION WILL SUPPORT
HAZARDOUS CONDITIONS QUICKLY DEVELOPING. HIGH END SMALL CRAFT
ADVISORY CRITERIA SHOULD BE EASILY MET WITH GALE CONDITIONS POSSIBLE
AT TIMES...ESPECIALLY AFTER MIDNIGHT THROUGH THE MORNING HOURS OF
FRIDAY. ANY GALE FORCE GUSTS SHOULD BE OVER BY LATE FRIDAY
EVENING...HOWEVER ADVISORY CRITERIA WINDS AND SEAS WILL PERSIST
THROUGH AT LEAST FRIDAY NIGHT. HIGH PRESSURE WILL THEN BUILD OVER
THE REGION FOR THE SECOND HALF OF THE WEEKEND ALLOWING WINDS AND
SEAS TO SUBSIDE BELOW HEADLINE CRITERIA. THE NEXT COLD FRONT IS
ANTICIPATED DURING THE EARLY/MIDDLE PORTION OF NEXT WEEK.
THE POTENTIAL FOR HIGH SURF DOES EXIST FOR FRIDAY/FRIDAY NIGHT AS
SWELL GENERATED OVER THE CENTRAL/EASTERN GULF ARRIVES AT OUR
COASTLINE. WILL CONTINUE TO EVALUATE THIS POTENTIAL AND THE
RESULTING ELEVATED RISK OF RIP CURRENTS THAT WILL LIKELY ACCOMPANY
THE SURF.
&&
.FIRE WEATHER...
INCREASING MOISTURE AHEAD OF A COLD FRONT WILL KEEP HUMIDITY VALUES
ABOVE CRITICAL LEVELS TODAY WITH NO FIRE WEATHER ISSUES EXPECTED. A
MUCH COLDER AND DRIER AIR MASS WILL ADVECT INTO THE REGION ON FRIDAY
IN THE WAKE OF A COLD FRONT. THIS DRIER AIR WILL LEAD TO LONG
DURATIONS OF HUMIDITY VALUES BELOW 35 PERCENT ACROSS THE ENTIRE
FORECAST AREA. THESE LOW HUMIDITY VALUES COUPLED WITH 20 FOOT WINDS
IN THE 15 TO 20 MPH RANGE WITH HIGHER GUSTS WILL LIKELY PRODUCE
INSTANTANEOUS RED FLAG CONDITIONS...SO WILL POST A FIRE WEATHER
WATCH FOR THE ENTIRE FORECAST AREA LATER THIS MORNING. ELEVATED FIRE
WEATHER CONDITIONS WILL LIKELY CONTINUE INTO THE BEGINNING OF THE
UPCOMING WEEKEND AS A VERY DRY AIRMASS REMAINS OVER THE AREA.
&&
.PRELIMINARY POINT TEMPS/POPS...
TPA 81 53 64 39 / 10 70 10 0
FMY 82 60 69 41 / 10 50 10 10
GIF 81 53 62 38 / 10 60 10 0
SRQ 80 58 65 42 / 10 70 10 0
BKV 80 47 59 29 / 20 80 10 0
SPG 79 57 61 47 / 10 70 10 0
&&
.TBW WATCHES/WARNINGS/ADVISORIES...
FL...FREEZE WATCH FROM LATE FRIDAY NIGHT THROUGH SATURDAY
MORNING FOR CITRUS-HERNANDO-LEVY-PASCO-SUMTER.
FIRE WEATHER WATCH FRIDAY AFTERNOON FOR CHARLOTTE-CITRUS-
DESOTO-HARDEE-HERNANDO-HIGHLANDS-HILLSBOROUGH-LEE-
LEVY-MANATEE-PASCO-PINELLAS-POLK-SARASOTA-SUMTER.
GULF WATERS...GALE WATCH FROM 7 PM EST THIS EVENING THROUGH FRIDAY
AFTERNOON FOR ENGLEWOOD TO TARPON SPRINGS OUT 20 TO
60 NM-TARPON SPRINGS TO SUWANNEE RIVER OUT 20 TO 60
NM.
SMALL CRAFT ADVISORY FROM 7 PM THIS EVENING TO 10 AM EST
SATURDAY FOR BONITA BEACH TO ENGLEWOOD OUT 20 NM-
BONITA BEACH TO ENGLEWOOD OUT 20 TO 60 NM-ENGLEWOOD
TO TARPON SPRINGS OUT 20 NM-TAMPA BAY WATERS-TARPON
SPRINGS TO SUWANNEE RIVER OUT 20 NM.
&&
$$
UPDATE/MARINE...MROCZKA
PREVIOUS DISCUSSION/FIRE WEATHER...MCMICHAEL
AVIATION...JILLSON
AREA FORECAST DISCUSSION
NWS PEACHTREE CITY GA
1049 AM EST THU DEC 20 2012
.UPDATE...
HAVE MADE SIGNIFICANT UPDATES TO HOURLY GRIDS TO CAPTURE CURRENT
RADAR TRENDS. OVERALL...FRONT HIGH TAILING IT THROUGH THE
REGION...AND PRECIP ACTIVITY HAS ACCELERATED THIS MORNING.
INSTABILITY OVER MUCH OF THE AREA IS VIRTUALLY NON EXISTENT...AND
WHAT IS PRESENT IS NOT ENOUGH TO SUPPORT THUNDERSTORM DEVELOPMENT.
WILL CONTINUE TO WATCH CENTRAL GEORGIA CAREFULLY INTO THE
AFTERNOON HOURS...ESPECIALLY THE FAR SOUTHERN TIER...AS THIS AREA
HAS THE POTENTIAL FOR ISOLATED SEVERE STORMS AS THE MAIN LINE
MOVES THROUGH DUE TO INCREASED INSTABILITY ACROSS THE REGION. AS
OF NOW...HAVE OPTED NOT TO BE INCLUDED WITH THE TORNADO WATCH
ISSUED EARLIER THIS MORNING...BUT WILL CONTINUE TO ANALYZE THE
ENVIRONMENT AS THE BOUNDARY APPROACHES.
WILL CONTINUE TO MAKE ADJUSTMENTS TO THE GRIDS AS NEEDED...ESPECIALLY
POPS AND WX...AS THE PRECIP MOVES THROUGH THE FORECAST AREA. WILL
ALSO BE PAYING CLOSE ATTENTION TO TEMPERATURES AND DEWPOINTS
BEHIND THE LINE AS COOLER AND DRIER AIR MOVES IN QUICKLY.
31
&&
.PREV DISCUSSION... /ISSUED 648 AM EST THU DEC 20 2012/
PREV DISCUSSION... /ISSUED 600 AM EST THU DEC 20 2012/
SHORT TERM /TODAY THROUGH FRIDAY NIGHT/...
PRIMARY CONCERNS ARE TIMING OF PRECIP ONSET AND END TODAY/TONIGHT
.CHC FOR SEVERE CONVECTION THIS AFTERNOON AND EXTENT AND INTENSITY
OF WIND EVENT TONIGHT THROUGH FRI NIGHT. WAA SHRA IN ADVANCE OF
SHORT WAVE ALREADY APPROACHING STATE LINE IN WC GA THIS MORNING.
LATEST RAP ANALYSIS SHOWS ONLY WEAK ELEVATED INSTABILITY EXTENDING
INTO SW 1/3RD OF ALABAMA AND NO LIGHTNING OBSERVED IN THE LAST FEW
HOURS. HAVE DELAYED ONSET OF OF SHRA TO 09-10Z AND SLT CHC TSRA
UNTIL 12Z. 00Z MODEL PROGS IN FAIR AGREEMENT THOUGH AGAIN THE NAM
IS THE MOST AGGRESSIVE WITH LOW LEVEL MOISTURE AND SBCAPE. 06Z NAM
HAS SBCAPE 250-400 J/KG SOUTH OF CSG TO MCN LINE WITH NO SBCAPE TO
THE NORTH. 00Z GFS AND ECMWF KEEP SBCAPE LESS THAN 200 J/KG ACROSS
ALL OF CWA. WILL HAVE TO WATCH MIDDLE GA CLOSE. VERY STRONG LOW
LEVEL VERTICAL WIND SHEAR /0-1KM BULK SHEAR NEAR 50KTS/ ALLOWS 06Z
NAM TO PROG 1.5-2.0 VALUES OF SIG TOR PARAMETER AT 00Z.
EXPERIMENTAL HIGH SHEAR-LOW CAPE SHERB PARAMETER FROM 06Z NAM ONLY
HAS 0.8-1.2 OVER MIDDLE GA. MAIN POINT IS IT WILL NOT TAKE MUCH
INSTABILITY TO PRODUCE BRIEF MESOVORTICES CAPABLE OF WIND DAMAGE
OR A BRIEF TORNADO ...SIMILAR TO WHAT WE SAW MONDAY. TOTAL
RAINFALL WILL NOT BE TOO HIGH WITH AMOUNTS OF 0.5-1.0 INCHES.
SYSTEM WILL MOVE OUT QUICKLY TAKING PRECIP WITH IT. VERY STRONG
PRESSURE GRADIENT AND STRONG VERTICAL CAA AND RESULTING DEEP MIXING
ALLOWS FOR SIGNIFICANT WIND EVENT OVER MUCH OF CWA WITH GUSTS TO
35-40 MPH AND 45+ MPH IN MOUNTAINS. COULD BEGIN LATE THIS AFTERNOON
IN THE WAKE OF PRECIP BUT APPEARS BEST PRESSURE GRADIENT WILL SET UP
AROUND 22Z-00Z. GUIDANCE FOR WIND SPEEDS NOT TOO FAR OFF BUT COULD
GO A LITTLE HIGHER IF SYSTEM INTENSIFIES OR MIXING IS MORE THAN
FCST. IN EXPOSED/HIGHER TERRAIN AREAS OF NE GA...WILL SEE STRONG
WINDS PERSIST. 1-2KM AGL WINDS NOT EXPECTED TO WEAKEN MUCH OVER NE
GA UNTIL AFTER 12Z SAT. HAVE ADJUSTED ADVISORIES APPROPRIATELY AND
BROKE OUT NE GA COUNTIES INTO ITS OWN SEGMENT THROUGHOUT THE EVENT.
SNELSON
LONG TERM /SATURDAY THROUGH WEDNESDAY/...
AN H5 RIDGE BUILDS INTO THE REGION SATURDAY BRINGING DRIER AND MORE
STABLE AIR ALONG WITH A WARMING TREND. THIS RIDGE WILL BE SHORT
LIVED AS THE FLOW FLATTENS TO VERY PROGRESSIVE ZONAL FLOW BY SUNDAY.
THE FIRST SHORT WAVE IN A SERIES OF SHORT WAVES WILL MOVE ACROSS THE
CWA LATE SUNDAY AND INTO MONDAY. FROM THIS POINT TIMING OF THE SHORT
WAVES WILL BE TRICKY AS THE FLOW IS FAST AND THE MODELS APPEAR TO BE
HAVING A DIFFICULT TIME MAINTAINING CONTINUITY WITH IN THEMSELVES.
WILL GO WITH CHANCE POPS BEGINNING SUNDAY NIGHT AND CONTINUE POPS
THROUGH THE LONG TERM...FAVORING HIGHER POPS TOWARD MID WEEK AS BOTH
MODELS SHOWING A SIGNIFICANT SYSTEM MOVING ACROSS THE CWA.
17
FIRE WEATHER...
WINDS WILL BE VERY GUSTY TONIGHT AND FRIDAY WITH 20FT WINDS OF 10-20
MPH WITH GUSTS TO 35 MPH. WILL ALSO SEE A 4 TO 5 HOUR PERIOD OF RH
BELOW 25 PCT ACROSS MUCH OF THE AREA FRIDAY AFTERNOON. FORTUNATELY
10HR FUELS WILL STILL BE WET ON FRIDAY FROM THE RAIN EXPECTED TODAY.
COOLER TEMPS AND LIMITED SUNSHINE WILL MAKE IT DIFFICULT FOR THEM TO
DRY. NOT PLANNING ANY RED FLAG OR FIRE DANGER STATEMENTS.
SNELSON
AVIATION...
12Z UPDATE...
STILL POSSIBLE THAT IFR CIGS/VSBYS COULD OCCUR TODAY BUT SHOULD
JUST STAY ABOVE. CIGS WILL CONTINUE TO DROP AS RAIN PERSISTS
TODAY. CLEARING WILL TAKE PLACE TONIGHT AS THE FRONT MOVES THROUGH
..INITIALLY GOING UP TO BKN040 23Z- 01Z THEN SCT250 05-07Z. STILL
APPEARS THAT INSTABILITY WILL REMAIN SOUTH OF ATL. COULD SEE ONE
OR TWO LIGHTNING STRIKES BUT TOO ISOLD TO WARRANT MENTION IN TAF.
HAVE ADDED TEMPO TSRA TO CSG AND MCN 18-22Z. WINDS MAY END UP THE
BIGGEST IMPACT AS THEY BECOME WEST AND INCREASE WITH FROPA. 20-25KT
GUSTS LIKELY TONIGHT AND 30-35KT POSS FRIDAY MORNING.
//ATL CONFIDENCE...12Z UPDATE...
LOW CONFIDENCE ON WHETHER IFR CIGS WILL DEVELOP TODAY.
HIGH CONFIDENCE ON ALL OTHER ELEMENTS.
SNELSON
&&
.PRELIMINARY POINT TEMPS/POPS...
ATHENS 61 32 48 25 / 100 40 0 0
ATLANTA 60 30 46 28 / 100 30 0 0
BLAIRSVILLE 54 27 41 19 / 100 30 0 0
CARTERSVILLE 58 28 45 24 / 100 20 0 0
COLUMBUS 68 33 52 30 / 100 20 0 0
GAINESVILLE 59 30 45 26 / 100 30 0 0
MACON 69 34 51 26 / 100 50 0 0
ROME 57 27 46 24 / 100 20 0 0
PEACHTREE CITY 63 29 48 25 / 100 20 0 0
VIDALIA 75 40 53 32 / 80 80 0 0
&&
.FFC WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY FROM 6 PM THIS EVENING TO 7 PM EST FRIDAY FOR THE
FOLLOWING ZONES: BALDWIN...BANKS...BARROW...BARTOW...BIBB...
BLECKLEY...BUTTS...CARROLL...CATOOSA...CHATTAHOOCHEE...
CHATTOOGA...CHEROKEE...CLARKE...CLAYTON...COBB...COWETA...
CRAWFORD...CRISP...DADE...DEKALB...DODGE...DOOLY...DOUGLAS...
EMANUEL...FAYETTE...FLOYD...FORSYTH...GLASCOCK...GORDON...
GREENE...GWINNETT...HALL...HANCOCK...HARALSON...HARRIS...HEARD...
HENRY...HOUSTON...JACKSON...JASPER...JEFFERSON...JOHNSON...
JONES...LAMAR...LAURENS...MACON...MADISON...MARION...
MERIWETHER...MONROE...MONTGOMERY...MORGAN...MURRAY...MUSCOGEE...
NEWTON...NORTH FULTON...OCONEE...OGLETHORPE...PAULDING...PEACH...
PIKE...POLK...PULASKI...PUTNAM...ROCKDALE...SCHLEY...SOUTH
FULTON...SPALDING...STEWART...SUMTER...TALBOT...TALIAFERRO...
TAYLOR...TELFAIR...TOOMBS...TREUTLEN...TROUP...TWIGGS...UPSON...
WALKER...WALTON...WARREN...WASHINGTON...WEBSTER...WHEELER...
WHITFIELD...WILCOX...WILKES...WILKINSON.
WIND ADVISORY FROM 6 PM THIS EVENING TO 7 AM EST SATURDAY FOR
THE FOLLOWING ZONES: DAWSON...FANNIN...GILMER...LUMPKIN...
PICKENS...TOWNS...UNION...WHITE.
&&
$$
SHORT TERM...31
LONG TERM....BAKER
AVIATION...31
AREA FORECAST DISCUSSION...UPDATED
NWS PEACHTREE CITY GA
648 AM EST THU DEC 20 2012
.PREV DISCUSSION... /ISSUED 600 AM EST THU DEC 20 2012/
SHORT TERM /TODAY THROUGH FRIDAY NIGHT/...
PRIMARY CONCERNS ARE TIMING OF PRECIP ONSET AND END TODAY/TONIGHT
..CHC FOR SEVERE CONVECTION THIS AFTERNOON AND EXTENT AND INTENSITY
OF WIND EVENT TONIGHT THROUGH FRI NIGHT. WAA SHRA IN ADVANCE OF
SHORT WAVE ALREADY APPROACHING STATE LINE IN WC GA THIS MORNING.
LATEST RAP ANALYSIS SHOWS ONLY WEAK ELEVATED INSTABILITY EXTENDING
INTO SW 1/3RD OF ALABAMA AND NO LIGHTNING OBSERVED IN THE LAST FEW
HOURS. HAVE DELAYED ONSET OF OF SHRA TO 09-10Z AND SLT CHC TSRA
UNTIL 12Z. 00Z MODEL PROGS IN FAIR AGREEMENT THOUGH AGAIN THE NAM
IS THE MOST AGGRESSIVE WITH LOW LEVEL MOISTURE AND SBCAPE. 06Z NAM
HAS SBCAPE 250-400 J/KG SOUTH OF CSG TO MCN LINE WITH NO SBCAPE TO
THE NORTH. 00Z GFS AND ECMWF KEEP SBCAPE LESS THAN 200 J/KG ACROSS
ALL OF CWA. WILL HAVE TO WATCH MIDDLE GA CLOSE. VERY STRONG LOW
LEVEL VERTICAL WIND SHEAR /0-1KM BULK SHEAR NEAR 50KTS/ ALLOWS 06Z
NAM TO PROG 1.5-2.0 VALUES OF SIG TOR PARAMETER AT 00Z.
EXPERIMENTAL HIGH SHEAR-LOW CAPE SHERB PARAMETER FROM 06Z NAM ONLY
HAS 0.8-1.2 OVER MIDDLE GA. MAIN POINT IS IT WILL NOT TAKE MUCH
INSTABILITY TO PRODUCE BRIEF MESOVORTICES CAPABLE OF WIND DAMAGE
OR A BRIEF TORNADO ...SIMILAR TO WHAT WE SAW MONDAY. TOTAL
RAINFALL WILL NOT BE TOO HIGH WITH AMOUNTS OF 0.5-1.0 INCHES.
SYSTEM WILL MOVE OUT QUICKLY TAKING PRECIP WITH IT. VERY STRONG
PRESSURE GRADIENT AND STRONG VERTICAL CAA AND RESULTING DEEP MIXING
ALLOWS FOR SIGNIFICANT WIND EVENT OVER MUCH OF CWA WITH GUSTS TO
35-40 MPH AND 45+ MPH IN MOUNTAINS. COULD BEGIN LATE THIS AFTERNOON
IN THE WAKE OF PRECIP BUT APPEARS BEST PRESSURE GRADIENT WILL SET UP
AROUND 22Z-00Z. GUIDANCE FOR WIND SPEEDS NOT TOO FAR OFF BUT COULD
GO A LITTLE HIGHER IF SYSTEM INTENSIFIES OR MIXING IS MORE THAN
FCST. IN EXPOSED/HIGHER TERRAIN AREAS OF NE GA...WILL SEE STRONG
WINDS PERSIST. 1-2KM AGL WINDS NOT EXPECTED TO WEAKEN MUCH OVER NE
GA UNTIL AFTER 12Z SAT. HAVE ADJUSTED ADVISORIES APPROPRIATELY AND
BROKE OUT NE GA COUNTIES INTO ITS OWN SEGMENT THROUGHOUT THE EVENT.
SNELSON
LONG TERM /SATURDAY THROUGH WEDNESDAY/...
AN H5 RIDGE BUILDS INTO THE REGION SATURDAY BRINGING DRIER AND MORE
STABLE AIR ALONG WITH A WARMING TREND. THIS RIDGE WILL BE SHORT
LIVED AS THE FLOW FLATTENS TO VERY PROGRESSIVE ZONAL FLOW BY SUNDAY.
THE FIRST SHORT WAVE IN A SERIES OF SHORT WAVES WILL MOVE ACROSS THE
CWA LATE SUNDAY AND INTO MONDAY. FROM THIS POINT TIMING OF THE SHORT
WAVES WILL BE TRICKY AS THE FLOW IS FAST AND THE MODELS APPEAR TO BE
HAVING A DIFFICULT TIME MAINTAINING CONTINUITY WITH IN THEMSELVES.
WILL GO WITH CHANCE POPS BEGINNING SUNDAY NIGHT AND CONTINUE POPS
THROUGH THE LONG TERM...FAVORING HIGHER POPS TOWARD MID WEEK AS BOTH
MODELS SHOWING A SIGNIFICANT SYSTEM MOVING ACROSS THE CWA.
17
FIRE WEATHER...
WINDS WILL BE VERY GUSTY TONIGHT AND FRIDAY WITH 20FT WINDS OF 10-20
MPH WITH GUSTS TO 35 MPH. WILL ALSO SEE A 4 TO 5 HOUR PERIOD OF RH
BELOW 25 PCT ACROSS MUCH OF THE AREA FRIDAY AFTERNOON. FORTUNATELY
10HR FUELS WILL STILL BE WET ON FRIDAY FROM THE RAIN EXPECTED TODAY.
COOLER TEMPS AND LIMITED SUNSHINE WILL MAKE IT DIFFICULT FOR THEM TO
DRY. NOT PLANNING ANY RED FLAG OR FIRE DANGER STATEMENTS.
SNELSON
&&
.AVIATION...
12Z UPDATE...
STILL POSSIBLE THAT IFR CIGS/VSBYS COULD OCCUR TODAY BUT SHOULD
JUST STAY ABOVE. CIGS WILL CONTINUE TO DROP AS RAIN PERSISTS
TODAY. CLEARING WILL TAKE PLACE TONIGHT AS THE FRONT MOVES THROUGH
...INITIALLY GOING UP TO BKN040 23Z- 01Z THEN SCT250 05-07Z. STILL
APPEARS THAT INSTABILITY WILL REMAIN SOUTH OF ATL. COULD SEE ONE
OR TWO LIGHTNING STRIKES BUT TOO ISOLD TO WARRANT MENTION IN TAF.
HAVE ADDED TEMPO TSRA TO CSG AND MCN 18-22Z. WINDS MAY END UP THE
BIGGEST IMPACT AS THEY BECOME WEST AND INCREASE WITH FROPA. 20-25KT
GUSTS LIKELY TONIGHT AND 30-35KT POSS FRIDAY MORNING.
//ATL CONFIDENCE...12Z UPDATE...
LOW CONFIDENCE ON WHETHER IFR CIGS WILL DEVELOP TODAY.
HIGH CONFIDENCE ON ALL OTHER ELEMENTS.
SNELSON
&&
.PRELIMINARY POINT TEMPS/POPS...
ATHENS 61 32 48 25 / 100 40 0 0
ATLANTA 60 30 46 28 / 100 20 0 0
BLAIRSVILLE 54 27 41 19 / 100 20 0 0
CARTERSVILLE 58 28 45 24 / 100 20 0 0
COLUMBUS 68 33 52 30 / 100 20 0 0
GAINESVILLE 59 30 45 26 / 100 20 0 0
MACON 69 34 51 26 / 100 40 0 0
ROME 57 27 46 24 / 100 20 0 0
PEACHTREE CITY 63 29 48 25 / 100 20 0 0
VIDALIA 75 40 53 32 / 100 90 0 0
&&
.FFC WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY FROM 6 PM THIS EVENING TO 7 PM EST FRIDAY FOR THE
FOLLOWING ZONES: BALDWIN...BANKS...BARROW...BARTOW...BIBB...
BLECKLEY...BUTTS...CARROLL...CATOOSA...CHATTAHOOCHEE...
CHATTOOGA...CHEROKEE...CLARKE...CLAYTON...COBB...COWETA...
CRAWFORD...CRISP...DADE...DEKALB...DODGE...DOOLY...DOUGLAS...
EMANUEL...FAYETTE...FLOYD...FORSYTH...GLASCOCK...GORDON...
GREENE...GWINNETT...HALL...HANCOCK...HARALSON...HARRIS...HEARD...
HENRY...HOUSTON...JACKSON...JASPER...JEFFERSON...JOHNSON...
JONES...LAMAR...LAURENS...MACON...MADISON...MARION...
MERIWETHER...MONROE...MONTGOMERY...MORGAN...MURRAY...MUSCOGEE...
NEWTON...NORTH FULTON...OCONEE...OGLETHORPE...PAULDING...PEACH...
PIKE...POLK...PULASKI...PUTNAM...ROCKDALE...SCHLEY...SOUTH
FULTON...SPALDING...STEWART...SUMTER...TALBOT...TALIAFERRO...
TAYLOR...TELFAIR...TOOMBS...TREUTLEN...TROUP...TWIGGS...UPSON...
WALKER...WALTON...WARREN...WASHINGTON...WEBSTER...WHEELER...
WHITFIELD...WILCOX...WILKES...WILKINSON.
WIND ADVISORY FROM 6 PM THIS EVENING TO 7 AM EST SATURDAY FOR
THE FOLLOWING ZONES: DAWSON...FANNIN...GILMER...LUMPKIN...
PICKENS...TOWNS...UNION...WHITE.
&&
$$
SHORT TERM...SNELSON
LONG TERM....17
AVIATION...SNELSON
AREA FORECAST DISCUSSION...UPDATED FOR FIRE WEATHER SECTION
NWS PEACHTREE CITY GA
600 AM EST THU DEC 20 2012
.SHORT TERM /TODAY THROUGH FRIDAY NIGHT/...
PRIMARY CONCERNS ARE TIMING OF PRECIP ONSET AND END TODAY/TONIGHT
...CHC FOR SEVERE CONVECTION THIS AFTERNOON AND EXTENT AND INTENSITY
OF WIND EVENT TONIGHT THROUGH FRI NIGHT. WAA SHRA IN ADVANCE OF
SHORT WAVE ALREADY APPROACHING STATE LINE IN WC GA THIS MORNING.
LATEST RAP ANALYSIS SHOWS ONLY WEAK ELEVATED INSTABILITY EXTENDING
INTO SW 1/3RD OF ALABAMA AND NO LIGHTNING OBSERVED IN THE LAST FEW
HOURS. HAVE DELAYED ONSET OF OF SHRA TO 09-10Z AND SLT CHC TSRA
UNTIL 12Z. 00Z MODEL PROGS IN FAIR AGREEMENT THOUGH AGAIN THE NAM
IS THE MOST AGGRESSIVE WITH LOW LEVEL MOISTURE AND SBCAPE. 06Z NAM
HAS SBCAPE 250-400 J/KG SOUTH OF CSG TO MCN LINE WITH NO SBCAPE TO
THE NORTH. 00Z GFS AND ECMWF KEEP SBCAPE LESS THAN 200 J/KG ACROSS
ALL OF CWA. WILL HAVE TO WATCH MIDDLE GA CLOSE. VERY STRONG LOW
LEVEL VERTICAL WIND SHEAR /0-1KM BULK SHEAR NEAR 50KTS/ ALLOWS 06Z
NAM TO PROG 1.5-2.0 VALUES OF SIG TOR PARAMETER AT 00Z.
EXPERIMENTAL HIGH SHEAR-LOW CAPE SHERB PARAMETER FROM 06Z NAM ONLY
HAS 0.8-1.2 OVER MIDDLE GA. MAIN POINT IS IT WILL NOT TAKE MUCH
INSTABILITY TO PRODUCE BRIEF MESOVORTICES CAPABLE OF WIND DAMAGE
OR A BRIEF TORNADO ...SIMILAR TO WHAT WE SAW MONDAY. TOTAL
RAINFALL WILL NOT BE TOO HIGH WITH AMOUNTS OF 0.5-1.0 INCHES.
SYSTEM WILL MOVE OUT QUICKLY TAKING PRECIP WITH IT. VERY STRONG
PRESSURE GRADIENT AND STRONG VERTICAL CAA AND RESULTING DEEP MIXING
ALLOWS FOR SIGNIFICANT WIND EVENT OVER MUCH OF CWA WITH GUSTS TO
35-40 MPH AND 45+ MPH IN MOUNTAINS. COULD BEGIN LATE THIS AFTERNOON
IN THE WAKE OF PRECIP BUT APPEARS BEST PRESSURE GRADIENT WILL SET UP
AROUND 22Z-00Z. GUIDANCE FOR WIND SPEEDS NOT TOO FAR OFF BUT COULD
GO A LITTLE HIGHER IF SYSTEM INTENSIFIES OR MIXING IS MORE THAN
FCST. IN EXPOSED/HIGHER TERRAIN AREAS OF NE GA...WILL SEE STRONG
WINDS PERSIST. 1-2KM AGL WINDS NOT EXPECTED TO WEAKEN MUCH OVER NE
GA UNTIL AFTER 12Z SAT. HAVE ADJUSTED ADVISORIES APPROPRIATELY AND
BROKE OUT NE GA COUNTIES INTO ITS OWN SEGMENT THROUGHOUT THE EVENT.
SNELSON
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
AN H5 RIDGE BUILDS INTO THE REGION SATURDAY BRINGING DRIER AND MORE
STABLE AIR ALONG WITH A WARMING TREND. THIS RIDGE WILL BE SHORT
LIVED AS THE FLOW FLATTENS TO VERY PROGRESSIVE ZONAL FLOW BY SUNDAY.
THE FIRST SHORT WAVE IN A SERIES OF SHORT WAVES WILL MOVE ACROSS THE
CWA LATE SUNDAY AND INTO MONDAY. FROM THIS POINT TIMING OF THE SHORT
WAVES WILL BE TRICKY AS THE FLOW IS FAST AND THE MODELS APPEAR TO BE
HAVING A DIFFICULT TIME MAINTAINING CONTINUITY WITH IN THEMSELVES.
WILL GO WITH CHANCE POPS BEGINNING SUNDAY NIGHT AND CONTINUE POPS
THROUGH THE LONG TERM...FAVORING HIGHER POPS TOWARD MID WEEK AS BOTH
MODELS SHOWING A SIGNIFICANT SYSTEM MOVING ACROSS THE CWA.
17
&&
.FIRE WEATHER...
WINDS WILL BE VERY GUSTY TONIGHT AND FRIDAY WITH 20FT WINDS OF 10-20
MPH WITH GUSTS TO 35 MPH. WILL ALSO SEE A 4 TO 5 HOUR PERIOD OF RH
BELOW 25 PCT ACROSS MUCH OF THE AREA FRIDAY AFTERNOON. FORTUNATELY
10HR FUELS WILL STILL BE WET ON FRIDAY FROM THE RAIN EXPECTED TODAY.
COOLER TEMPS AND LIMITED SUNSHINE WILL MAKE IT DIFFICULT FOR THEM TO
DRY. NOT PLANNING ANY RED FLAG OR FIRE DANGER STATEMENTS.
SNELSON
&&
.AVIATION...06Z UPDATE...
MAIN AVIATION WX CONCERNS ARE ONSET OF IFR CIGS AND PRECIP TODAY
AND LIKELIHOOD OF TSRA THIS AFTERNOON. HIGH CONFIDENCE/QUICK
MOVING RAIN EVENT TODAY. EXPECT RAPID LOWERING OF CLOUDS AFTER 12Z
WITH MVFR CIGS BY 15Z WITH LIGHT RAIN AND NEAR IFR CIGS LIKELY
AROUND 17-19Z AS NEAR SOLID AREA OF MODERATE RAIN BEGINS. TSRA
CANT BE RULED OUT BUT INSTABILITY APPEARS TOO LOW TO MENTION IN
NORTH GA TAFS. HAVE ADDED TEMPO TSRA TO CSG AND MCN TAFS 18-22Z
WHERE INSTABILITY SHOULD BE SUFFICIENT FOR SOME EMBEDDED TS. SE
WINDS WILL BECOME SW AROUND 19-21Z AND THEN WEST 23-01Z AS FRONT
MOVES IN. SPEEDS WILL ALSO INCREASE SIGNIFICANTLY WITH FROPA.
GUSTS OF 23-26KT SHOULD PERSIST THROUGH AT LEAST 06Z FRI.
//ATL CONFIDENCE...06Z UPDATE...
LOW CONFIDENCE ON WHETHER IFR CIGS WILL DEVELOP TODAY.
HIGH CONFIDENCE ON ALL OTHER ELEMENTS.
SNELSON
&&
.PRELIMINARY POINT TEMPS/POPS...
ATHENS 61 32 48 25 / 100 40 0 0
ATLANTA 60 30 46 28 / 100 20 0 0
BLAIRSVILLE 54 27 41 19 / 100 20 0 0
CARTERSVILLE 58 28 45 24 / 100 20 0 0
COLUMBUS 68 33 52 30 / 100 20 0 0
GAINESVILLE 59 30 45 26 / 100 20 0 0
MACON 69 34 51 26 / 100 40 0 0
ROME 57 27 46 24 / 100 20 0 0
PEACHTREE CITY 63 29 48 25 / 100 20 0 0
VIDALIA 75 40 53 32 / 100 90 0 0
&&
.FFC WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY FROM 6 PM THIS EVENING TO 7 PM EST FRIDAY FOR THE
FOLLOWING ZONES: BALDWIN...BANKS...BARROW...BARTOW...BIBB...
BLECKLEY...BUTTS...CARROLL...CATOOSA...CHATTAHOOCHEE...
CHATTOOGA...CHEROKEE...CLARKE...CLAYTON...COBB...COWETA...
CRAWFORD...CRISP...DADE...DEKALB...DODGE...DOOLY...DOUGLAS...
EMANUEL...FAYETTE...FLOYD...FORSYTH...GLASCOCK...GORDON...
GREENE...GWINNETT...HALL...HANCOCK...HARALSON...HARRIS...HEARD...
HENRY...HOUSTON...JACKSON...JASPER...JEFFERSON...JOHNSON...
JONES...LAMAR...LAURENS...MACON...MADISON...MARION...
MERIWETHER...MONROE...MONTGOMERY...MORGAN...MURRAY...MUSCOGEE...
NEWTON...NORTH FULTON...OCONEE...OGLETHORPE...PAULDING...PEACH...
PIKE...POLK...PULASKI...PUTNAM...ROCKDALE...SCHLEY...SOUTH
FULTON...SPALDING...STEWART...SUMTER...TALBOT...TALIAFERRO...
TAYLOR...TELFAIR...TOOMBS...TREUTLEN...TROUP...TWIGGS...UPSON...
WALKER...WALTON...WARREN...WASHINGTON...WEBSTER...WHEELER...
WHITFIELD...WILCOX...WILKES...WILKINSON.
WIND ADVISORY FROM 6 PM THIS EVENING TO 7 AM EST SATURDAY FOR
THE FOLLOWING ZONES: DAWSON...FANNIN...GILMER...LUMPKIN...
PICKENS...TOWNS...UNION...WHITE.
&&
$$
SHORT TERM...SNELSON
LONG TERM....17
AVIATION...SNELSON
AREA FORECAST DISCUSSION
NWS DES MOINES IA
555 AM CST THU DEC 20 2012
...LIFE THREATENING BLIZZARD CONDITIONS TO IMPACT IOWA TODAY...
.UPDATE...
ADDED PART OF SHORT TERM DISCUSSION THAT WAS INADVERTENTLY OMITTED
EARLIER. ALSO ADDED 12Z TAF DISCUSSION.
&&
.SHORT TERM /TODAY/...
CURRENT SITUATION HAS LONG WAVE TROUGH MOVING THROUGH CENTRAL PLAINS
WITH NOTED PV ANOMALY ACROSS ERN OK/KS. VERY STRONG FORCING
STILL EXISTS BACK INTO DEFORMATION ZONE AND IS MAINLY KINEMATIC
BY THIS POINT WITH THETA-E ADVECTION MAX NOW LIFTING OFF TO THE
NORTH AND EAST. HOWEVER JUST TO THE EAST INTO CENTRAL IA
FRONTOGENETICAL FORCING IS STILL EVIDENT AND LIKELY DRIVING ENHANCED
PRECIP WHERE DES MOINES OBS CONTINUE TO FLOAT AROUND 1/4 TO 1/2SM.
LATEST RAP CONTINUES TO DEPICT NEGATIVE H5/H6 THETA-E LAPSE RATES
AND EPV IN DENDRITIC GROWTH ZONE SO SEE NO REASON TO CHANGE CURRENT
AMOUNTS WITH LOW STATIC STABILITY CONTINUING TO REALIZE FORCING AND
PRODUCE MODERATE TO HEAVY SNOW FOR AT LEAST THE NEXT SEVERAL HOURS.
RAIN/SNOW LINE APPEARS TO BE IN FAR SERN IA AND SHOULD CONTINUE
ADVANCING SOUTH AND EAST THROUGH 12Z WHEN ENTIRE FORECAST AREA
SHOULD BE ALL SNOW. STORM TOTALS MAY STILL REACH 14 INCHES IN A FEW
SPOTS OF CENTRAL IA.
ELEVATED MUCAPE/K INDEX VALUES COINCIDENT WITH CURRENT SERN IA
CONVECTION AND LIGHTNING ACTIVITY WILL CONTINUE TO DEPART SUGGESTING
THUNDERSNOW POTENTIAL SHOULD BE DWINDLING BACK INTO DEFORMATION
ZONE. HOWEVER LIGHTNING IN LIQUID PRECIP SE AND CONVECTIVE ELEMENTS
IN TRANSITION ZONE FROM LAMONI TO OSKALOOSA...AND POINTS SE AS
RAIN/SNOW LINE SHIFTS...MAY STILL SEE BRIEF PERIODS OF THUNDERSNOW.
WINDS WILL START TO BECOME A BIGGER CONCERN AND INCREASE INTO THE
MORNING. 08Z OBS SHOW BLIZZARD CRITERIA WINDS ALONG THE HIGHWAY 30
CORRIDOR FROM CARROLL TO MARSHALLTOWN...AND THEN BACK SOUTHWEST FROM
CARROLL INTO SOUTHWEST IA. SOUNDINGS SHOW LOW LEVELS BECOMING
SLIGHTLY MORE MIXED AS COLD ADVECTION INCREASES. EVEN THOUGH IT
WILL ONLY BE TO 950 OR 925 MB...THIS WILL STILL ALLOW GUSTS TO JUMP
INTO THE LOW/MID 40S KTS WORKING EASTWARD WITH TIME. MODELS APPEAR
TO BE UNDERESTIMATING MSLP OF LOW...DOWN TO 992 MB AT 08Z IN CENTRAL
MO...AND WITH PV ANOMALY JUST UPSTREAM OF SURFACE LOW EXPECT IT TO
DEEPEN BEYOND WHAT IS FORECAST BY THE TIME IT REACHES IL. THIS MAY
ALLOW ISOLATED GUSTS TO EXCEED 50 MPH AS THE ISALLOBARIC COUPLET
REACHES CENTRAL IA BY LATE MORNING. POWER OUTAGES MAY BECOME MORE
WIDESPREAD AS WINDS INCREASE WITH TREES CONTINUING TO BE SNOW COATED.
TEMPS WILL BE AT THEIR HIGHS EARLY WITH READINGS FALLING THROUGHOUT
THE DAY. NO CHANGES TO HEADLINES.
.LONG TERM /TONIGHT THROUGH WEDNESDAY/...
FOR TONIGHT...WE WILL STILL BE DEALING WITH BLOWING SNOW AND REDUCED
VISIBILITIES MAINLY OVER THE EASTERN CWA BUT CONDITIONS WILL BE
IMPROVING THROUGH THE EVENING. WITH THE FRESH SNOWPACK...CLEARING
SKIES AND DIMINISHING WIND...TEMPS WILL BE QUITE COLD TONIGHT AND I
EXPECT TEMPS TO BE COLDER THAN WHAT GUIDANCE SUGGESTS THROUGH AT
LEAST FRIDAY.
OTHER THAN COLDER TEMPS THROUGH FRIDAY THE EXTENDED THROUGH MONDAY
LOOKS RATHER QUIET WITH SLOWLY MODERATING TEMPERATURES.
MONDAY NIGHT THROUGH WEDNESDAY THE MODELS ARE STILL IN SUBSTANTIAL
DISAGREEMENT ON THE HANDLING OF A SHORT WAVE MOVING ACROSS THE AREA
THROUGH CHRISTMAS DAY. THE EURO AND CANADIAN ARE ARE MORE SIMILAR
WITH A LITTLE DEEPER AND SLOWER WAVE WITH A SURFACE LOW ACROSS THE
SOUTHERN PLAINS. THE GFS HAS A WEAKER WAVE AND IT IS FASTER AND
FURTHER NORTH WITH IT AND THE SURFACE LOW IS ALSO MUCH WEAKER AND
FURTHER NORTH. FOR NOW THERE WAS LITTLE CHANGE MADE TO THE GOING
FORECAST UNTIL MODEL CONSENSUS BECOMES BETTER ALIGNED.
&&
.AVIATION...20/12Z
WIDESPREAD IFR/LIFR CONDITIONS WILL CONTINUE TO AFFECT MUCH OF AREA
THROUGH THE MORNING WITH LIGHT SNOW AND BLOWING SNOW. ALTHOUGH
ADDITIONAL SNOW ACCUMULATIONS WILL DIMINISH OR END ALTOGETHER BY
MIDDAY...GUSTY NORTH WINDS WILL PERSIST REACHING 35-45KTS AT TIMES
AND CONTINUE TO PRODUCE BLOWING SNOW AND REDUCED VISIBILITIES. MVFR
STRATUS IS EXPECTED TO LINGER INTO THE NIGHT...ESPECIALLY EAST OF
I35...BUT WINDS WILL DIMINISH SOMEWHAT WITH LITTLE IN THE WAY OF
GUSTS.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
BLIZZARD WARNING MUCH OF FORECAST AREA UNTIL NOON
BLIZZARD WARNING ALONG AND EAST OF I35 UNTIL 6PM
WINTER STORM WARNING FAR NW UNTIL NOON
&&
$$
SHORT TERM/AVIATION...BSS
LONG TERM...FAB
AREA FORECAST DISCUSSION
NWS TOPEKA KS
630 AM CST THU DEC 20 2012
...UPDATE TO AVIATION...
.DISCUSSION...
THE STORM SYSTEM SEEMS TO BE PROGRESSING AS FORECASTED WITH A WIDE
BAND OF MODERATE TO HEAVY SNOW AND WINDS GUSTING OVER 45 MPH MOVING
INTO THE EASTERN HALF OF THE AREA. 08Z WATER VAPOR SHOWS THE UPPER
LOW NEARLY OVER EMP CONTINUING TO LIFT NORTHEAST. MEANWHILE SFC OBS
SHOW THE SFC LOW MOVING NORTHEAST THROUGH CENTRAL MO AND DEEPENING.
THE STORM IS ON TRACK TO BE OUT OF THE AREA BY 9 AM. SO MAIN CONCERN
TODAY IS THE WINDS AND WHETHER WE WILL NEED A SEPARATE WIND ADVISORY
ONCE THE SNOW ENDS. LATEST NAM AND RAP PROGS SHOW WINDS SUBSIDING
ONCE THE BAND OF SNOW PASSES TO THE EAST AND CNK IS ALREADY TRENDING
WEAKER...SO THE CURRENT WINTER WEATHER HEADLINES LOOK TO COVER THE
WINDS. THE PLAN IS TO DOWNGRADE THE WARNING TO A WINTER WEATHER
ADVISORY AS THE BACK EDGE OF HEAVIER SNOW MOVES EAST TO ACCOUNT FOR
THE WINDS AND BLOWING SNOW...AND KEEP THE ORIGINAL EXPIRATION TIMES
FOR NOW.
THINGS SHOULD CLEAR OUT QUICKLY TODAY...BUT STRONG WINDS AND TEMPS
REMAINING BELOW FREEZING SHOULD MAKE IT FEEL PRETTY RAW. UPPER LEVEL
RIDGING DEVELOPS AND PERSISTS OVER THE CENTRAL PLAINS INTO THE
WEEKEND WITH DRY WEATHER EXPECTED. PREVIOUS FORECAST TEMPS FOR
FRIDAY AND SATURDAY SEEM TO BE IN THE BALL PARK EXPECTING SOME SNOW
COVER INITIALLY...SO HAVE NOT MADE MANY CHANGES.
THE FORECAST FOR NEXT WEEK CONTINUES TO BE UNCERTAIN AS THE ECMWF
HAS EXHIBITED POOR CONTINUITY FROM RUN TO RUN. THE GFS HAS STARTED
TO SHOW SOME CONSISTENCY...BUT THERE REMAINS SOME VARIATION IN THE
TRACK OF THE STORM SYSTEM FOR CHRISTMAS. THINK THE ECMWF HAS TRENDED
FURTHER SOUTH DUE TO AN ARCTIC INTRUSION FROM THE NORTH WHICH WOULD
BRING SOME VERY COLD AND DRY SOUTH SOUTH INTO THE PLAINS. IT IS
INTERESTING TO NOTE THAT THE GEM SEEMS TO BE IN THE GFS CAMP OF A
DEEPENING SYSTEM AND A CHANCE FOR SNOW. OPTED TO KEEP A 30 PERCENT
CHANCE FOR SNOW MAINLY FOR CHRISTMAS DAY AND TUESDAY NIGHT UNTIL
THERE IS BETTER CONSISTENCY FROM RUN TO RUN. ALSO TRENDED TEMPS
COOLER FOR NEXT WEEK WITH BOTH THE ECMWF AND GFS SHOWING COLD AIR
ADVECTION THROUGH THE PERIOD.
WOLTERS
&&
.AVIATION...
UPPER TROUGH LIFTING QUICKLY TO THE EAST AND SNOW DIMINISHING WEST TO
EAST ACROSS THE TERMINALS AT THIS TIME. DRY AIR ALSO WORKING IN BEHIND
THE SYSTEM...SO CEILINGS SHOULD ALSO IMPROVE RAPIDLY AS THE SNOW ENDS
BY 13Z AT KMHK AND BETWEEN 13 AND 14Z AT KTOP AND KFOE. VFR CEILINGS
WILL RETURN TO ALL TERMINALS BY 17Z. WINDS DIMINISH TONIGHT WITH
CLEAR SKIES.
&&
.TOP WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 9 AM CST THIS MORNING FOR KSZ040-
055-056-058-059.
WINTER STORM WARNING UNTIL 9 AM CST THIS MORNING FOR KSZ011-012-
024-026-038-039.
&&
$$
AREA FORECAST DISCUSSION...UPDATED
NWS TWIN CITIES/CHANHASSEN MN
602 AM CST THU DEC 20 2012
.UPDATE
UPDATED FOR THE 12Z AVIATION DISCUSSION BELOW.
.DISCUSSION...
....BLIZZARD CONDITIONS EXPECTED TODAY ACROSS FAR SOUTHERN
MINNESOTA...
.SHORT TERM...TODAY THROUGH SUNDAY.
THE MAIN FOCUS FOR THIS FORECAST PACKAGE HAS CLEARLY BEEN THE
POWERFUL SYSTEM NOW CENTERED OVER MISSOURI. IT WILL CONTINUE TO
TRACK NORTHEAST INTO NORTHERN ILLINOIS THIS AFTERNOON AND INTO
LOWER MICHIGAN BY THIS EVENING. RADAR CONTINUES TO INDICATE LIGHT
SNOW EAST OF A LINE FROM MANKATO TO MSP AND OSCEOLA. POCKETS OF
MODERATE SNOW CAN BE FOUND FURTHER EAST TOWARD EAU CLAIRE AND
POINTS SOUTH. THIS IS THE BACK EDGE OF THE SYSTEM AND SNOW WILL
CONTINUE TO PIVOT EASTWARD AND EXIT THE CWA LATE THIS MORNING OR
EARLY AFTERNOON. CLEARING SKIES CAN BE FOUND AS CLOSE AS ERN SD
WITH SUBSIDENCE/ISENTROPIC DOWNGLIDE.
AS THE STORM TRACKS NORTHEAST TODAY...THE PRESSURE GRADIENT WILL
INCREASE ACROSS THE AREA WITH STEEPENING LAPSE RATES BELOW 925 MB
IN STRONG CAA REGIME. RAP13 SHOWS 925 MB WINDS STRENGTHENING TO
BETWEEN 40 AND AS HIGH AS 50 KTS ALONG THE IOWA BORDER AFTER 15Z
THIS MORNING. RAP FORECAST SOUNDINGS FROM FAIRMONT AND ROCHESTER
INDICATE MIXING POTENTIAL TO THIS LEVEL...WITH BUFKIT PREDICTED
GUSTS FROM THE 950 MB LEVEL OF AT LEAST 35 KTS. SHOULD SEE
FREQUENT GUSTS EASILY REACH 40 OR 45 MPH...BUT THEY COULD APPROACH
OR EXCEED 50 MPH IN OPEN AREAS OF FAR SOUTHERN
MINNESOTA...INCLUDING ALONG THE I-90 CORRIDOR. GIVEN THE 3 OR 4
INCHES OF POWDERY SNOW THAT FELL TUESDAY MORNING AND THE
ADDITIONAL 2 TO 5 INCHES THAT FELL OVERNIGHT...A GROUND BLIZZARD
IS QUITE LIKELY TODAY SOUTH OF A LINE FROM TRIMONT TO OWATONNA.
WHITEOUT CONDITIONS WILL MAKE FOR NEAR IMPOSSIBLE TRAVEL.
THUS...EXPANDED THE BLIZZARD WARNING WESTWARD TO INCLUDE
WASECA...MARTIN...AND FARIBAULT COUNTIES THROUGH 6 PM. THINK AFTER
THAT TIME...WE WILL LOSE THE STEEP LAPSE RATES AND GUSTS SHOULD
BEGIN RAPIDLY SUBSIDING.
FURTHER NORTH...WINDS SHOULD NOT BE AS STRONG AND TOPOGRAPHY
ISSUES COME INTO PLAY...ESPECIALLY ACROSS WRN WI SO WILL NOT
EXPAND THE BLIZZARD WARNING INTO THOSE AREAS.
CLEAR SKIES AND DIMINISHING WINDS AS THE RIDGE BUILDS EASTWARD
INTO WRN MN WILL BRING TONIGHT/S LOWS DOWN INTO THE SINGLE DIGITS
ABOVE ZERO EAST AND BELOW ZERO WEST.
THE RIDGE WILL WEAKEN OVERHEAD FRIDAY...BUT A STRONGER 1035MB RIDGE
TO ITS NORTHWEST WILL BLEED DOWN INTO THE UPPER MISSISSIPPI VALLEY
SATURDAY KEEPING CONDITIONS DRY THROUGH THE WEEKEND.
.LONG TERM...SUNDAY NIGHT THROUGH WEDNESDAY.
LOTS OF VARIABILITY IN THE MODELS WITH THE EVENTUAL TRACK OF A
STRONG SOUTHERN STREAM SYSTEM AROUND CHRISTMAS DAY. SEEMS AT THIS
POINT THE CONSENSUS WOULD BE TO SHUNT IT EAST OF THE REGION...
/EXCEPT FOR PERHAPS A LITTLE LIGHT SNOW WITH AN INVERTED TROUGH
PER EURO/ WITH COLD AIR DAMMING ALONG THE NORTHERN U.S. ROCKIES AS
A STRONG 1040+ MB HIGH PRESSURE SYSTEM BUILDS SOUTHEAST FROM
WESTERN CANADA. THIS WOULD SPELL A VERY COLD PATTERN WITH HIGHS
POTENTIALLY BELOW ZERO AND LOWS IN THE TEENS BELOW TO POSSIBLY 20S
BELOW. THE CURRENT GRIDS ADVERTISE A MILDER SOLUTION...BUT IF THE
TREND HOLDS...THE LONG TERM WILL NEED TO BE ADJUSTED 10 TO 20
DEGREES COLDER.
&&
.AVIATION.../12Z TAF ISSUANCE/
SNOW IS ON ITS WAY OUT IN EASTERN MN THIS MORNING...SO THE VIS
SHOULD CONTINUE TO SLOWLY IMPROVE AT AIRPORTS IN AND AROUND THE
TWIN CITIES METRO. HOWEVER...THE MOVEMENT IS SLOW ENOUGH THAT KEAU
SHOULD BE STILL SEE IFR RESTRICTIONS THROUGH MOST OF THE MORNING.
THE DRAMATIC INCREASE IN WIND TODAY IS PROBABLY THE BIGGEST
AVIATION CONCERN AT SOME OF THE TAF SITES...THAT COMBINED WITH
IFR/MVFR STRATUS DROPPING DOWN ACROSS THE AREA THIS MORNING. THESE
CLOUDS SHOULD CLEAR MOST OF THE TAF SITES BY LATE THIS AFTERNOON.
THE WINDS SHOULDN`T DEVIATE MUCH IN DIRECTION...STAYING BETWEEN
320 AND 340 MOST OF THE DAY.
KMSP...
THE AIRPORT FINDS ITSELF IN A BRIEF REPRIEVE FROM MVFR/IFR THIS
MORNING. THE SNOW IS ALMOST OUT OF THE PICTURE...BUT 800-1200 FT
STRATUS IS APPROACHING BUT OBSCURED BY 4000-6000 CEILINGS.
HOWEVER...GET A GOOD LOOK AT THE LOW STRATUS IN WESTERN AND THE
DAKOTAS OFF THE SATELLITE. KSTC...JUST PICKED UP A LOW CEILING IN
THE PAST HOUR...SO IT`S OWN IT`S WAY. WINDS BECOMING QUITE STRONG
THIS AFTERNOON. HAVE GUSTS TO 28 KTS IN THE TAF...WHICH MIGHT BE
JUST A HAIR STRONG...BUT THE POTENTIAL IS CERTAINLY THERE. STILL
INCLUDED A CHANCE FOR PERIODIC LIGHT SNOW IN A TEMPO GROUP RIGHT
AT THE START OF THE TAF. IT WILL BE VERY LIGHT.
/OUTLOOK FOR KMSP/
FRI...VFR. WINDS NW AT 10KTS.
SAT...VFR. WINDS SE AT 5 TO 10KTS.
SUN...VFR. WINDS NE AT 5 TO 10KTS.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...WINTER STORM WARNING UNTIL 6 PM CST THIS EVENING FOR GOODHUE-
RICE.
WINTER WEATHER ADVISORY UNTIL 6 PM CST THIS EVENING FOR BLUE
EARTH-DAKOTA-LE SUEUR-WATONWAN.
BLIZZARD WARNING UNTIL 6 PM CST THIS EVENING FOR FARIBAULT-
FREEBORN-MARTIN-STEELE-WASECA.
WI...WINTER STORM WARNING UNTIL 6 PM CST THIS EVENING FOR CHIPPEWA-
DUNN-EAU CLAIRE-PEPIN-PIERCE.
WINTER WEATHER ADVISORY UNTIL 6 PM CST THIS EVENING FOR BARRON-
RUSK-ST. CROIX.
&&
$$
BB/CLF
AREA FORECAST DISCUSSION
NWS TWIN CITIES/CHANHASSEN MN
435 AM CST THU DEC 20 2012
.DISCUSSION...
....BLIZZARD CONDITIONS EXPECTED TODAY ACROSS FAR SOUTHERN
MINNESOTA...
.SHORT TERM...TODAY THROUGH SUNDAY.
THE MAIN FOCUS FOR THIS FORECAST PACKAGE HAS CLEARLY BEEN THE
POWERFUL SYSTEM NOW CENTERED OVER MISSOURI. IT WILL CONTINUE TO
TRACK NORTHEAST INTO NORTHERN ILLINOIS THIS AFTERNOON AND INTO
LOWER MICHIGAN BY THIS EVENING. RADAR CONTINUES TO INDICATE LIGHT
SNOW EAST OF A LINE FROM MANKATO TO MSP AND OSCEOLA. POCKETS OF
MODERATE SNOW CAN BE FOUND FURTHER EAST TOWARD EAU CLAIRE AND
POINTS SOUTH. THIS IS THE BACK EDGE OF THE SYSTEM AND SNOW WILL
CONTINUE TO PIVOT EASTWARD AND EXIT THE CWA LATE THIS MORNING OR
EARLY AFTERNOON. CLEARING SKIES CAN BE FOUND AS CLOSE AS ERN SD
WITH SUBSIDENCE/ISENTROPIC DOWNGLIDE.
AS THE STORM TRACKS NORTHEAST TODAY...THE PRESSURE GRADIENT WILL
INCREASE ACROSS THE AREA WITH STEEPENING LAPSE RATES BELOW 925 MB
IN STRONG CAA REGIME. RAP13 SHOWS 925 MB WINDS STRENGTHENING TO
BETWEEN 40 AND AS HIGH AS 50 KTS ALONG THE IOWA BORDER AFTER 15Z
THIS MORNING. RAP FORECAST SOUNDINGS FROM FAIRMONT AND ROCHESTER
INDICATE MIXING POTENTIAL TO THIS LEVEL...WITH BUFKIT PREDICTED
GUSTS FROM THE 950 MB LEVEL OF AT LEAST 35 KTS. SHOULD SEE
FREQUENT GUSTS EASILY REACH 40 OR 45 MPH...BUT THEY COULD APPROACH
OR EXCEED 50 MPH IN OPEN AREAS OF FAR SOUTHERN
MINNESOTA...INCLUDING ALONG THE I-90 CORRIDOR. GIVEN THE 3 OR 4
INCHES OF POWDERY SNOW THAT FELL TUESDAY MORNING AND THE
ADDITIONAL 2 TO 5 INCHES THAT FELL OVERNIGHT...A GROUND BLIZZARD
IS QUITE LIKELY TODAY SOUTH OF A LINE FROM TRIMONT TO OWATONNA.
WHITEOUT CONDITIONS WILL MAKE FOR NEAR IMPOSSIBLE TRAVEL.
THUS...EXPANDED THE BLIZZARD WARNING WESTWARD TO INCLUDE
WASECA...MARTIN...AND FARIBAULT COUNTIES THROUGH 6 PM. THINK AFTER
THAT TIME...WE WILL LOSE THE STEEP LAPSE RATES AND GUSTS SHOULD
BEGIN RAPIDLY SUBSIDING.
FURTHER NORTH...WINDS SHOULD NOT BE AS STRONG AND TOPOGRAPHY
ISSUES COME INTO PLAY...ESPECIALLY ACROSS WRN WI SO WILL NOT
EXPAND THE BLIZZARD WARNING INTO THOSE AREAS.
CLEAR SKIES AND DIMINISHING WINDS AS THE RIDGE BUILDS EASTWARD
INTO WRN MN WILL BRING TONIGHT/S LOWS DOWN INTO THE SINGLE DIGITS
ABOVE ZERO EAST AND BELOW ZERO WEST.
THE RIDGE WILL WEAKEN OVERHEAD FRIDAY...BUT A STRONGER 1035MB RIDGE
TO ITS NORTHWEST WILL BLEED DOWN INTO THE UPPER MISSISSIPPI VALLEY
SATURDAY KEEPING CONDITIONS DRY THROUGH THE WEEKEND.
.LONG TERM...SUNDAY NIGHT THROUGH WEDNESDAY.
LOTS OF VARIABILITY IN THE MODELS WITH THE EVENTUAL TRACK OF A
STRONG SOUTHERN STREAM SYSTEM AROUND CHRISTMAS DAY. SEEMS AT THIS
POINT THE CONSENSUS WOULD BE TO SHUNT IT EAST OF THE REGION...
/EXCEPT FOR PERHAPS A LITTLE LIGHT SNOW WITH AN INVERTED TROUGH
PER EURO/ WITH COLD AIR DAMMING ALONG THE NORTHERN U.S. ROCKIES AS
A STRONG 1040+ MB HIGH PRESSURE SYSTEM BUILDS SOUTHEAST FROM
WESTERN CANADA. THIS WOULD SPELL A VERY COLD PATTERN WITH HIGHS
POTENTIALLY BELOW ZERO AND LOWS IN THE TEENS BELOW TO POSSIBLY 20S
BELOW. THE CURRENT GRIDS ADVERTISE A MILDER SOLUTION...BUT IF THE
TREND HOLDS...THE LONG TERM WILL NEED TO BE ADJUSTED 10 TO 20
DEGREES COLDER.
&&
.AVIATION... /06Z TAF ISSUANCE/
A MODERATE TO HEAVY BAND OF SNOW IS DEVELOPING LATE THIS EVENING
FROM SOUTH CENTRAL MN INTO WEST CENTRAL WI. THIS WILL BE IMPACTING
KEAU WITH LIFR/VLIFR CONDITIONS DURING THE OVERNIGHT HOURS AND
EARLY THURSDAY. SOME LIGHT SNOW IS ALSO MOVING NORTHEAST ALONG THE
MN RIVER AND SHOULD PASS ACROSS THE TWIN CITIES/MSP OVERNIGHT.
THIS WILL ALSO SLIDE INTO KRNH AS WELL. MVFR/IFR CEILINGS
CONTINUE TO CREEP ESE ACROSS CENTRAL AND WEST CENTRAL MN. KAXN IS
ALREADY DOWN UNDER 010 AND KSTC WILL BE DOWN BY 07Z. SIMILAR
CONDITIONS WILL WORK INTO KRWF BY 09Z ALONG WITH SOME LIGHT SNOW.
THE WIND WILL INCREASE TO 15 TO 20 KNOTS THURSDAY MORNING WITH
GUSTS FROM 25 TO 30 KNOTS FOR THE MN TAF SITES AND 30 TO 35 KNOTS
FOR KRNH AND KEAU. CEILINGS IMPROVING TO VFR FROM WEST TO EAST
DURING THE AFTERNOON/EVENING IN THE WAKE OF THE STORM SYSTEM.
KMSP...ANOTHER ROUND OF LIGHT SNOW EXPECTED OVERNIGHT THEN ENDING
AROUND DAYBREAK. ACCUMULATION WILL BE NEAR 1 INCH. CEILINGS/VSBYS
BECOMING MVFR IN THE SNOW. N TO NW WINDS (330-350) FROM 15 TO 20
KNOTS ON THURSDAY WITH GUSTS NEAR 30 KNOTS FOR THE AFTERNOON AND
EARLY EVENING. CEILINGS BECOMING VFR BY EVENING.
/OUTLOOK FOR KMSP/
FRI...VFR. WINDS NW AT 10KTS.
SAT...VFR. WINDS SE AT 5 TO 10KTS.
SUN...VFR. WINDS NE AT 5 TO 10KTS.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...WINTER STORM WARNING UNTIL 6 PM CST THIS EVENING FOR GOODHUE-
RICE.
WINTER WEATHER ADVISORY UNTIL 6 PM CST THIS EVENING FOR BLUE
EARTH-DAKOTA-LE SUEUR-WATONWAN.
BLIZZARD WARNING UNTIL 6 PM CST THIS EVENING FOR FARIBAULT-
FREEBORN-MARTIN-STEELE-WASECA.
WI...WINTER STORM WARNING UNTIL 6 PM CST THIS EVENING FOR CHIPPEWA-
DUNN-EAU CLAIRE-PEPIN-PIERCE.
WINTER WEATHER ADVISORY UNTIL 6 PM CST THIS EVENING FOR BARRON-
RUSK-ST. CROIX.
&&
$$
BORGHOFF/RAH
AREA FORECAST DISCUSSION
NWS CHARLESTON WV
938 AM EST THU DEC 20 2012
.SYNOPSIS...
WINDY TODAY WITH SHOWERS MOVING IN. STRONG COLD FRONT THIS EVENING.
SNOW SHOWERS BEHIND LOW PRESSURE TONIGHT INTO SATURDAY. LOW PRESSURE
CHRISTMAS EVE.
&&
.NEAR TERM /THROUGH TONIGHT/...
935 AM UPDATE...INCREASED POPS FOR THIS MORNING BASED ON CURRENT
RADAR/OBS SHOWING SHOWERS ALREADY WELL INTO WV. HRRR SEEMED TO
HAVE A FAIRLY GOOD HANDLE ON THE CURRENT...SO STARTED BY BLENDING
THAT IN...AND THEN TRANSITIONED TO A BLEND WITH TOWARDS THE RAP BY
THIS AFTERNOON.
PREVIOUS DISCUSSION...
MODELS IN FAIRLY GOOD AGREEMENT WITH BRINGING A PRE FRONTAL BAND OF
PRECIPITATION ACROSS THE REGION TODAY. BIGGEST QUESTION IS HOW LONG
WILL IT TAKE TO MOISTEN THE LOW LEVELS AND MAKE IT TO THE GROUND.
WILL GO WITH 100 PERCENT POPS...BUT SLIGHTLY SLOWER THAN PREVIOUSLY
INDICATED. EXPECT TO SEE SOME DECENT WINDS/WIND GUSTS TODAY AS
STRONG PRESSURE GRADIENT FROM THE LOW PRESSURE SYSTEM EFFECT THE
AREA.
A STRONG COLD FRONT THEN PUSHES THROUGH THIS EVENING. NAM AND
CANADIAN HAVE NEARLY IDENTICAL TIMING...WITH GFS BEING SLIGHTLY
FASTER. COLDER AIR THEN RUSHES IN BEHIND THE FRONT. CANADIAN AND NAM
ARE CLOSE TO IDENTICAL AND COLDER THAN THE GFS. WILL GO WITH
MAJORITY AND HAVE SNOW SHOWERS DEVELOPING DURING THE NIGHT.
&&
.SHORT TERM /FRIDAY THROUGH SUNDAY/...
BUSY GRAVEYARD SHIFT WITH IMPENDING MULTIPLE WX IMPACTS IN SHORT
TERM. OVERALL...INHERITED GRIDS LOOK GOOD AND ONLY NEEDED TWEAKING.
TRIED TO HOLD TEMPS STEADY FRI...PERHAPS FALLING A COUPLE OF DEGREES
AS CAA CONT. OVERALL SNOW GRIDS LOOKED GOOD. DID LWR AMNTS SOME
OUTSIDE OF THE MTNS. ELECTED TO UPGRADE MOST OF WATCH AREA TO A
WINTER STORM WARNING...SAVE FOR UPSHUR AND RALEIGH WHERE 12HR AND
24HR AMNTS STAYED BLO CRITERIA FOR COUNTY AVG. WILL MENTION NEAR
BLIZZARD CONDITIONS AT TIMES IN THE WORDING. CONFIDENCE JUST NOT
HIGH ON HITTING THE VSBY PART GIVEN WHAT IS EXPECTED TO BE VARYING
INTENSITY/COVERAGE OF SHSN. WENT ADV FOR UPSHUR/RALEIGH ALONG WITH
TIER OF COUNTIES W...TO I79/US 119 CORRIDOR WHERE CONFIDENCE WAS
HIGH ON GETTING 1 TO 4 INCHES...WITH UP TO 7 TOTAL FOR
RALEIGH/UPSHUR. KEPT SE OH...WESTERN LOWLANDS...AND NE KY OUT OF ADV
TO ALLOW NEAR TERM HI RES MDLS TO ENTER THAT TIME FRAME...GIVING A
BETTER DEPICTION OF ACCUMULATIONS WHERE TERRAIN IS LESS OF AN
INFLUENCE COMPARED TO GREAT LAKE/UPR TROF CONTRIBUTIONS. HELD ON TO
WARNING/EASTERN COUNTIES OF ADV ACROSS THE MTNS UNTIL SAT AFTN WITH
LINGERING SHSN STILL EXPECTED EARLY SAT.
CODED UP WIND ADV FOR EVERYONE...ENDING FRI NIGHT LOWLANDS...AND SAT
MORNING MTNS. WITH H85 FLOW TOPPING ARND 50KTS...HARD TO BELIEVE ALL
OF THAT WILL MIX DOWN ACROSS THE MTNS TO WARRANT HIGH WIND WARNING.
CANT RULE IT OUT THOUGH ACROSS THE HIGHEST RIDGES AOA 4KFT. WIND ADV
ACROSS THE LOWLANDS PRIMARILY IMPACT AS NOT SURE ON HITTING 40KTS IN
GUSTS GIVEN MOMENTUM TRANSFER OF MDL SOUNDINGS FOR FRI.
LLVL WAA TO COMMENCE ON SAT AS HEIGHTS BUILD...ALLOWING FOR A
CLEARING TREND FROM ACROSS NE KY/SW VA LATE. HOLD THE CLDS SAT NIGHT
ACROSS SE OH/N WV AS LLVL MOISTURE LINGERS AMID A PINCHING OFF OF
H85 THERMAL TROF. STILL GOING MUCH BLO GUIDANCE FOR HIGHS ON SAT
WITH H925 TEMPS NOT RECOVERING MUCH FROM FRI EVEN THOUGH WAA AT H85
WILL BE OCCURRING.
&&
.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
A COMPLICATED EXTENDED FORECAST WILL DOMINATE THIS PERIOD. A LOW
PRESSURE SYSTEM WILL DEVELOP AND MOVE NORTHEAST FROM THE SOUTHERN
CONUS. WITH H85 AND SURFACE TEMPERATURES REMAINING ABOVE
FREEZING...EXPECT A MAINLY RAIN EVENT. AS THE SYSTEM MOVES AWAY FROM
THE FORECAST AREA...COULD SEEM SOME LIGHT SNOW SHOWERS. PRESENT
TIMING WOULD SUGGEST THE FIRST SYSTEM DEPARTING ON CHRISTMAS EVE.
THE NEXT SYSTEM IS FORECAST TO BE MUCH STRONGER AND CONTAIN MORE
GULF MOISTURE. CHRISTMAS DAY SHOULD BE DRY AS THE SYSTEM IS STILL
SOUTHWEST OF THE REGION. WARMER AIR WILL BE PULLED INTO THE MID
ATLANTIC AHEAD OF THIS STRONG LOW. RAIN IS EXPECTED TO FALL STARTING
LATE CHRISTMAS NIGHT OR EARLY WEDNESDAY. DEPENDING ON THE TIMING OR
EXACT LOCATION...COULD SEE SOME SNOW ON THE BACKSIDE BY LATE NEXT
WEEK.
&&
.AVIATION /15Z THURSDAY THROUGH MONDAY/...
CLOUDS WILL REMAIN VFR EARLY THIS MORNING. AN APPROACHING COLD FRONT
WILL CAUSE LOWERING CLOUDS TODAY AND INCREASING WINDS. RESTRICTIONS
CAN BE EXPECTED IN SHOWERS BY LATE MORNING IN KY AND PORTIONS OF
OHIO...AND OVER THE REMAINDER OF THE AREA THIS AFTERNOON. THE COLD
FRONT WILL COME THROUGH THIS EVENING. MUCH COLDER AIR WILL MOVE IN
BEHIND THE FRONT. THIS WILL CREATE A MVFR STRATUS DECK WITH SNOW
SHOWERS DEVELOPING TONIGHT.
FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 12Z FRIDAY...
FORECAST CONFIDENCE: HIGH THIS MORNING...MODERATE THEREAFTER.
ALTERNATE SCENARIOS: TIMING OF PRECIPITATION AND LOWER CLOUDS COULD
VARY.
EXPERIMENTAL TABLE OF FLIGHT CATEGORY OBJECTIVELY SHOWS CONSISTENCY
OF WFO FORECAST TO AVAILABLE MODEL INFORMATION:
H = HIGH: TAF CONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL.
M = MEDIUM: TAF HAS VARYING LEVEL OF CONSISTENCY WITH MODELS.
L = LOW: TAF INCONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL.
UTC 1HRLY 14 15 16 17 18 19 20 21 22 23 00 01
EST 1HRLY 09 10 11 12 13 14 15 16 17 18 19 20
CRW CONSISTENCY H H H H H H M M M M H H
HTS CONSISTENCY H H H H M M M M H H H H
BKW CONSISTENCY H H H H H H H H H H H H
EKN CONSISTENCY H H H H H H H H H M M M
PKB CONSISTENCY H H H H H M M M M H H H
CKB CONSISTENCY H H H H H H H H M M M M
AFTER 12Z FRIDAY...
IFR POSSIBLE FRIDAY INTO SATURDAY DUE TO SNOW SHOWERS...ESPECIALLY
IN THE MOUNTAINS.
&&
.RLX WATCHES/WARNINGS/ADVISORIES...
WV...WIND ADVISORY FROM 7 PM THIS EVENING TO 10 PM EST FRIDAY FOR
WVZ005>011-013>020-024>034-039-040.
WIND ADVISORY FROM 7 PM THIS EVENING TO 7 AM EST SATURDAY FOR
WVZ035>038-046-047.
WINTER STORM WARNING FROM 1 AM FRIDAY TO 2 PM EST SATURDAY FOR
WVZ036>038-046-047.
WINTER WEATHER ADVISORY FROM 1 AM FRIDAY TO 2 PM EST SATURDAY
FOR WVZ027-028-035-039-040.
WINTER WEATHER ADVISORY FROM 1 AM FRIDAY TO 7 AM EST SATURDAY
FOR WVZ015-016-018-025-026-029>034.
OH...WIND ADVISORY FROM 7 PM THIS EVENING TO 10 PM EST FRIDAY FOR
OHZ066-067-075-076-083>087.
KY...WIND ADVISORY FROM 7 PM THIS EVENING TO 10 PM EST FRIDAY FOR
KYZ101>103-105.
VA...WIND ADVISORY FROM 7 PM THIS EVENING TO 10 PM EST FRIDAY FOR
VAZ003-004.
&&
$$
SYNOPSIS...JB/RPY/30
NEAR TERM...RPY/MZ
SHORT TERM...30
LONG TERM...JB
AVIATION...RPY
AREA FORECAST DISCUSSION...UPDATED
NWS MILWAUKEE/SULLIVAN WI
432 AM CST THU DEC 20 2012
.UPDATE...
TODAY-FORECAST CONFIDENCE HIGH
RAIN/SNOW LINE ROUGHLY JANESVILLE TO WAUKESHA TO PORT
WASHINGTON...WITH 850 MB ZERO LINE PER LATEST RAP FROM JUST SOUTH
OF DBQ TO JVL AND RAC. THIS SHOWS UP WELL IN RADAR PRODUCTS AND
ESPECIALLY DUAL POL CC AND ZDR.
RAP HAS 850 MB ZERO LINE AND BASICALLY THE RAIN/SNOW LINE MOVING
TO ABOUT DARLINGTON TO WATERTOWN TO PORT WASHINGTON IN THE 15Z TO
18Z PERIOD. IT THEN SAGS BACK TO A MKE TO RFD LINE BY 21Z AND
CONTINUES TO COLLAPSE SOUTH THEREAFTER WITH SURFACE LOW HEADING
OVER LAKE MICHIGAN AND 700 MB LOW CONTINUING TO DEEPEN.
THERE WILL BE A LAG IN THE PRECIPITATION FOR A THIS MORNING...AND
MODELS HAVE BEEN CONSISTENT IN BRINGING A STRONG DEFORMATION BAND
THROUGH DURING THE AFTERNOON AND EVENING. THIS LOOKS VERY
CONVECTIVE AND YOU COULD EASILY SEE 2 TO 3 INCH PER HOUR
THUNDERSNOWS AS THE RAP SHOWS HOURLY PRECIP ALONG THE -2 TO -3 850
ISOTHERM IN 0.20 TO 0.30" RANGE.
RAIN SHOULD FALL NEAR LAKE MICHIGAN AND ESPECIALLY
MILWAUKEE...SOUTHEAST WAUKESHA...WALWORTH...RACINE...KENOSHA
COUNTIES MUCH OF THE DAY.
AS STRONG GRADIENT AND COLD ADVECTION PUSHES INTO THE NORTHWEST
HALF THIS AFTERNOON...EXPECT FALLING TEMPERATURES AND A DRIER SNOW
TO PILE UP...ALLOWING FOR BLIZZARD CONDITIONS AS THE WINDS GUST UP
TO 35 OR 40 KNOTS.
TONIGHT-FORECAST CONFIDENCE HIGH
COLD AIR PUSHES INTO THE SOUTHEAST AROUND RUSH HOUR WITH RAIN
TURNING OVER TO HEAVY WET SNOW. ALTHOUGH TOTAL SNOW AMOUNTS MAY
ONLY BE IN THE 3 TO 5 INCH RANGE...IT COULD MAINLY FALL IN A 2 TO
3 HOUR PERIOD WITH THUNDER AND INCREASING WINDS. SO WINTER STORM
WARNING WARRANTED DUE TO POTENTIAL IMPACT.
ELSEWHERE SNOW WILL START TO DIMINISH LATER ON BUT WINDS WILL BE
VERY STRONG AND SIGNIFICANT BLOWING AND DRIFTING EXPECTED OVER THE
WESTERN TWO-THIRDS OF THE AREA.
&&
.AVIATION/12Z TAFS/...
LIFR CONDITIONS EXPECTED FOR KMSN MOST OF THE DAY...WITH WINDS
PICKING UP IN THE AFTERNOON AND EVENING. SIGNIFICANT BLOWING SNOW
AND NEAR ZERO VISIBILITIES LIKELY.
IFR CONDITIONS WITH RAIN MKE AND ENW AND SNOW CHANGING TO RAIN
UES. DURING THE AFTERNOON AND EARLY EVENING EXPECT LIFR CONDITIONS
TO DEVELOP AS RAIN CHANGES OVER TO HEAVY WET SNOW AND VERY STRONG
NORTHWEST WINDS GUSTING TO 35 OR 40 KNOTS DEVELOPS.
&&
.MARINE...
NEAR GALE CONDITIONS TODAY TURNING TO STRONG GALE AND APPROACHING
STORM FORCE THIS EVENING AS LOW CROSSES SOUTHERN LAKE MICHIGAN AND
COLD AIR POURS IN FROM NORTH AND NORTHWEST. 850 MB WINDS INCREASE
TO 70 KNOTS IN THE EVENING AND ABOUT THE ONLY THING THAT WILL KEEP
STORM FORCE WINDS FROM OCCURRING IN NEAR SHORE WATERS IS
FRICTION FROM NORTHWEST WINDS COMING OFF LAND. WILL BE A CLOSE
CALL AND MAY NEED TO BE UPGRADED LATER.
&&
.PREV DISCUSSION... /ISSUED 330 AM CST THU DEC 20 2012/
FRIDAY - CONFIDENCE...MEDIUM
STRONGLY CYCLONIC FLOW PERSISTS IN THE MORNING WITH NVA WORKING IN
DURING THE AFTERNOON. TIGHT GRADIENT LINGERS FOR A TIME WITH 925
WINDS STILL RAMPED UP PRETTY GOOD AT 45-50 KNOTS. WILL PUT IN SOME
BLOWING SNOW TO COINCIDE WITH THE TIGHTER GRADIENT AND SUBSEQUENT
LINGERING STRONGER WIND FIELD. WENT WITH COLDER TEMPS DUE TO THE
FRESH SNOW COVER AND THIS WAS BEST HANDLED BY THE CONSENSUS BLEND
RATHER THAN THE BIAS CORRECTED NUMBERS.
SATURDAY - CONFIDENCE...MEDIUM
SURFACE RIDGE AXIS SLIDES ACROSS WITH A MUCH LIGHTER WIND REGIME.
UPPER FLOW BROADLY ANTICYCLONIC WITH HINTS OF A WEAK SHEARED VORT.
AIRMASS IS BONE DRY PER BUFKIT SOUNDINGS.
SUNDAY - CONFIDENCE...MEDIUM
HIGH PRESSURE CONTINUES TO BUILD IN WITH MID LEVEL RIDGING
DOMINATING. AIRMASS REMAINS DRY. 850 0C ISOTHERM NEAR THE WI/IL
BORDER.
MONDAY AND TUESDAY - CONFIDENCE...MEDIUM
PRETTY DECENT AGREEMENT AMONGST THE MODELS ON THE IDEA OF A
SHORTWAVE PROGRESSING FROM THE PLAINS TOWARDS THE UPPER MIDWEST
THOUGH TIMING AND PLACEMENT DETAILS ARE OFF AT THIS POINT. THE ECMWF
GETS A LITTLE MORE PHASING WITH A SOUTHERN STREAM WAVE AND BRINGS A
MORE DEVELOPED SURFACE LOW NORTHWARD WHILE OTHER MODELS SHOW A MORE
LOOSELY DEFINED INVERTED TROUGH. DESPITE THE TIMING AND STRUCTURE
DIFFERENCES...SOME LIGHT QPF NOTED.
WEDNESDAY - CONFIDENCE...LOW
MORE SIGGY PIECE OF ENERGY MOVES INTO THE CENTRAL PLAINS PER THE GFS
AND ECMWF. SUBSEQUENT CYCLOGENESIS IS HANDLED QUITE DIFFERENTLY
BETWEEN THE MODELS WITH THE ECMWF DEVELOPING A LOW IN THE SE US AND
THE GFS IN THE OH VALLEY. ALLBLEND POPS APPEAR TO BE GIVING A LITTLE
MORE WEIGHTING TO THE GFS POSITION OF LOW...WHICH TENDS TO MAKE MORE
SENSE GIVEN PROGGD LOCATION OF UPPER DYNAMICS.
&&
.MKX WATCHES/WARNINGS/ADVISORIES...
WI...WINTER STORM WARNING UNTIL NOON CST TODAY FOR WIZ046-047-051-
056>059-062>064-067>069.
BLIZZARD WARNING FROM NOON TODAY TO MIDNIGHT CST TONIGHT FOR
WIZ046-047-056-057-062-063-067-068.
BLIZZARD WARNING FROM NOON TODAY TO 3 AM CST FRIDAY FOR WIZ051-
058-059-064-069.
WINTER STORM WARNING FROM 5 PM THIS AFTERNOON TO 3 AM CST FRIDAY
FOR WIZ066-071-072.
WINTER STORM WARNING FROM 2 PM THIS AFTERNOON TO 3 AM CST FRIDAY
FOR WIZ052-060-065-070.
LM...SMALL CRAFT ADVISORY UNTIL NOON CST TODAY FOR LMZ643>646.
GALE WARNING FROM NOON TODAY TO NOON CST FRIDAY FOR LMZ643>646.
&&
$$
UPDATE...CRAVEN
TODAY/TONIGHT AND AVIATION/MARINE...CRAVEN
FRIDAY THROUGH WEDNESDAY...COLLAR
AREA FORECAST DISCUSSION
NWS DENVER/BOULDER CO
951 AM MST THU DEC 20 2012
.UPDATE...
&&
.SHORT TERM...UPPER RIDGE TO BUILD INTO THE AREA THROUGH THE DAY.
AS THE STRONG STORM SYSTEM MOVES ACROSS THE CENTRAL PLAINS. STILL
FAIRLY STRONG NORTHWEST FLOW ALOFT EXPECTED FOR MUCH OF THE DAY
BEFORE SHOWING SOME SIGNS OF DECREASING. WINDS CURRENTLY A BIT
GUSTY ACROSS THE MOUNTAINS AS WELL AS IN AND NEAR THE FOOTHILLS.
LATEST RUC AND HRRR KEEP SOME GUSTY WINDS IN AND NEAR FOOTHILLS
AND HIGHER EAST SLOPES THROUGH THE AFTERNOON...WILL NEED TO ADJUST
THE WIND GRIDS ACCORDINGLY. OTHERWISE...CURRENT FORECASTS LOOK ON
TRACK. MODERATE INVERSIONS WILL LIMIT THE WARMING ACROSS THE FAR
EASTERN PLAINS AS WELL AS THE MOUNTAIN VALLEYS.
.AVIATION...CURRENT TAF TRENDS LOOKING ON TRACK. SOUTHWEST WINDS
TO PREVAIL ACROSS THE AREA AIRPORTS FOR MUCH OF THE DAY. SPEEDS OF
8-12 KTS WILL PREVAIL...THOUGH SOME GUSTS TO 20 KTS COULD OCCUR AT
BJC. LATEST RAP STILL SHOWING THE POTENTIAL FOR WINDS VEERING MORE TO
THE SOUTHEAST AT APA AND DEN AROUND 21Z. THIS TREND SHOWN IN THE
TAFS. VFR TO PREVAIL WITH UNLIMITED CEILINGS.
&&
.PREV DISCUSSION... /ISSUED 348 AM MST THU DEC 20 2012/
SHORT TERM...WEST WINDS GUSTING NEAR 55 MPH DEVELOPED OVERNIGHT
IN THE EAST SLOPES OF THE FRONT RANGE MOUNTAINS SPREADING INTO
THE FOOTHILLS AND WESTERN URBAN CORRIDOR. THIS WAS IN RESPONSE TO
A LOWERING AND STRENGTHENING STABLE LAYER OVER THE MOUNTAINS AS AN
UPPER RIDGE MOVES OVERHEAD. YESTERDAY`S SNOWFALL AND COLD ARCTIC
AIRMASS THAT PUSHED SOUTH COMBINED WITH CLEAR SKIES OVERNIGHT TO
BRING COLD TEMPERATURES EARLY THIS MORNING. TEMPERATURES ARE
BETWEEN -10 AND -25 F DEGREES OVER THE HIGH MOUNTAIN VALLEYS WITH
SOME SINGLE DIGIT READINGS OVER THE PLAINS. THE WEST WINDS OVER
THE FOOTHILLS ARE HELPING TO MODERATE THE MINIMUM TEMPERATURES
THERE...HOWEVER STILL SEEING READINGS IN THE TEENS.
MAX TEMPERATURES TODAY SHOULD WARM UP INTO THE MID 30S TO LOWER
40S FOR THE PLAINS AND INTO THE 20S FOR THE MOUNTAINS AS 700 MB
TEMPERATURES INCREASE BY ABOUT 10 TO 15 DEGREES C FROM YESTERDAY
UNDER THE RIDGE. THE FAR NORTHEASTERN CORNER OF THE PLAINS MAY
STRUGGLE TO GET ABOVE 30 AS A MODERATE LOW LEVEL INVERSION MAY
INHIBIT WARMING. WINDS OVER THE HIGH COUNTRY AND FOOTHILLS WILL BE
DECREASING THROUGH THE DAY...THOUGH WILL STILL SEE GUSTS TO 30
MPH. EXPECT MOSTLY CLEAR SKIES EXCEPT FOR A SMALL WAVE CLOUD MOST
LIKELY OVER BOULDER AND JEFFERSON COUNTIES. TONIGHTS TEMPERATURES
WILL BE WARMER UNDER THE BUILDING RIDGE...HOWEVER WILL STILL SEE
QUITE COLD TEMPERATURES UP IN THE HIGH VALLEYS IN THE MOUNTAINS.
LONG TERM...UPPER LEVEL RIDGE WILL REMAIN OVER THE CENTRAL AND
SOUTHERN ROCKIES THROUGH SATURDAY. THIS WILL BRING MOSTLY CLEAR
SKIES AND WARMER TEMPERATURES TO MOST LOCATIONS. HOWEVER...A VERY
STRONG INVERSION WILL LIKELY HOLD STRONG IN SOME OF THE HIGH
MOUNTAIN VALLEYS...WITH KREMMLING AND THE UPPER COLORADO RIVER
VALLEY MOST PRONE DUE TO EXTENSIVE SNOW COVER THERE. ANOTHER
EXCEPTION COULD BE THE EASTERN PLAINS WHERE MORE SNOW FELL WITH
THIS LAST STORM...ALTHOUGH ENOUGH DOWNSLOPE COMPONENT SHOULD BE
ABLE TO HELP WEAKEN STRENGTH OF INVERSIONS THERE. AS A
RESULT...HAVE COOLED THE ABOVE MENTIONED LOCATIONS FOR THE NEXT
COUPLE DAYS. MEANWHILE...WE SHOULD SEE AT LEAST SOME LOWER 50S
ACROSS THE DENVER METRO AREA WITH SUFFICIENT
SUNSHINE...DOWNSLOPE...AND DWINDLING SNOW COVER.
BY LATE SATURDAY NIGHT INTO SUNDAY...A WEAK DISTURBANCE IS
ADVERTISED TO REACH THE CENTRAL ROCKIES WITH INCREASING FLOW ALOFT
AND A BIT OF MID/UPPER LEVEL MOISTURE. AT THIS TIME...MAIN IMPACT
LOOKS TO BE AN INCREASE IN WINDS IN/NEAR THE FRONT RANGE AND A FEW
SNOW SHOWERS IN THE HIGH COUNTRY.
FOCUS THEN TURNS TOWARD POTENTIAL SNOW FOR CHRISTMAS EVE INTO
CHRISTMAS DAY. LATEST 00Z GFS...ECMWF...CANADIAN...AND MOST GFS
ENSEMBLE MEMBERS SHOW REASONABLE AGREEMENT WITH REGARD TO AN
UPPER LEVEL TROUGH CARVING OUT OVER THE CENTRAL OR SOUTHERN
ROCKIES. AT THE SAME TIME...A COLD ARCTIC HIGH PRESSURE SYSTEM
IS ADVERTISED TO NOSE DOWN ACROSS THE CENTRAL PLAINS. BOTH OF
THESE WOULD BE FAVORABLE IN PRODUCING AT LEAST SOME LIGHT SNOW.
HOWEVER...ITS QUITE INTERESTING THAT 12-24 HOURS AGO THERE WAS A
HUGE AMOUNT OF VARIATION AMONGST MODEL SOLUTIONS. IN ANY CASE...A
CHANCE OF SNOW ALONG WITH COLDER TEMPERATURES IS WARRANTED FOR
CHRISTMAS EVE INTO CHRISTMAS DAY GIVEN THE LATEST TRENDS. THEN DRY
WEATHER SHOULD RETURN BY WEDNESDAY OF NEXT WEEK BUT TEMPERATURES
SHOULD REMAIN BELOW NORMAL.
AVIATION...DRAINAGE WINDS EARLY THIS MORNING WILL LIKELY STAY IN
A SOUTHWEST DIRECTION FOR THE AREA AIRPORTS THROUGH TODAY. THERE
MAY BE A BRIEF PERIOD WHERE THE WINDS VEER BACK A LITTLE MORE TO
THE SOUTHEAST HOWEVER. VFR CONDITIONS EXPECTED THROUGH THURSDAY AS
AN UPPER RIDGE MOVES IN OVERHEAD.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...D-L
LONG TERM....KRIEDERMAN
AVIATION...D-L
AREA FORECAST DISCUSSION
NWS TAMPA BAY RUSKIN FL
215 PM EST THU DEC 20 2012
...MUCH COLDER AIR ARRIVING FOR FRIDAY AND THE WEEKEND...
...HAZARDOUS BOATING CONDITIONS DEVELOPING TONIGHT OVER
THE EASTERN GULF OF MEXICO WATERS...
.SYNOPSIS...
18Z WATER VAPOR AND H4 RAP ANALYSIS SHOWS AN AMPLIFIED UPPER LEVEL
PATTERN ACROSS THE CONUS THIS MORNING. FROM WEST TO EAST WE FIND
LONGWAVE RIDGING IN PLACE FROM THE 4-CORNERS REGION NORTHWARD
THROUGH THE INTERMOUNTAIN WEST...WITH THE FLOW THEN QUICKLY TURNING
BACK TO THE SOUTH INTO A SHARP AND IMPRESSIVE LONGWAVE TROUGH OVER
THE CENTRAL PORTION OF THE CONTINENT. THIS ENERGY IS SUPPORTING A
SIGNIFICANT AREA OF SURFACE LOW PRESSURE MOVING TROUGH THE UPPER
MIDWEST/GREAT LAKES REGION WITH A TRAILING COLD FRONT BACK DOWN TO
THE NORTHEAST GULF COAST. THIS SYSTEM IS PROVIDING ALL KINDS OF
WEATHER FROM BLIZZARD CONDITIONS NORTH AND WEST OF THE LOW TRACK TO
SEVERE THUNDERSTORMS AHEAD OF THE COLD FRONT TO THE SOUTH AND EAST.
THE IMPRESSIVE HEIGHT FALLS OVER THE CENTRAL STATES ARE FORCING A
SHORT-TERM DOWNSTREAM AMPLIFICATION TO THE RIDGE OVER THE ATLANTIC
SEABOARD. THIS RIDGE WILL BE QUICKLY TRANSLATING EASTWARD INTO THE
WESTERN ATLANTIC AS THE UPPER TROUGH TAKES OVER TONIGHT.
CLOSER TO HOME...STACKED RIDGING THAT HAS BEEN IN PLACE OVER THE FL
PENINSULA CONTINUES TO EXIT TO OUR EAST AS THE SOUTHERN PORTION OF
THE UPPER TROUGH AXIS MOVES ALONG THE NORTHERN GULF COAST. LOW LEVEL
FLOW HAS SHIFTED TO THE SOUTHEAST/SOUTH BETWEEN THE SURFACE HIGH TO
OUR EAST AND A POTENT COLD FRONT CROSSING THE FLORIDA
PANHANDLE/EASTERN GULF. LATE THIS AFTERNOON (GENERALLY AFTER 4-5 PM
PM)...LARGE SCALE SYNOPTIC SUPPORT/QG FORCING AHEAD OF THE UPPER
TROUGH WILL BEGIN TO OVERSPREAD THE NATURE COAST ZONES. AT THE SAME
TIME LOW LEVEL CONVERGENCE/FOCUS AHEAD OF THE FRONT WILL ALSO BE
INCREASING AND MAY RESULT IN A FEW SHOWERS FOR EARLY EVENING AHEAD
OF THE MAIN CONVECTIVE BAND. SHOWERS (IF ANY) BEFORE SUNSET SHOULD
BE CONFINED TO LEVY/CITRUS COUNTY.
&&
.SHORT TERM (TONIGHT THROUGH SATURDAY NIGHT)...
TONIGHT...QUICK MOVING COLD FRONT WILL ENTER THE FORECAST AREA AFTER
SUNSET AND BE WELL OFF TO OUR SOUTH AND EAST BEFORE DAWN. SYNOPTIC
SUPPORT FOR LIFT AHEAD OF THE TROUGH WILL QUICKLY INCREASE AFTER 00Z
WITH A MAXIMUM NORTH OF THE I-4 CORRIDOR. THIS SUPPORT WILL AID
IMPRESSIVE LOW LEVEL FOCUS ALONG THE FRONTAL BOUNDARY TO SUPPORT
WHAT IS EXPECTED TO BE A NARROW BUT SOLID BAND OF SHOWERS/EMBEDDED
STORMS MOVING ACROSS THE NATURE COAST/TAMPA BAY AREA BETWEEN
7PM-2AM. RETURN FLOW PERIOD AHEAD OF THIS FRONT IS SHORT AND
THEREFORE OVERALL INSTABILITY IS REALLY LACKING. THE LACK OF COLUMN
INSTABILITY SHOULD LIMIT THE DEEP CONVECTION...WITH A MORE SHALLOW
CONVECTIVE MODE EXPECTED. LOOKING AT ALL THE 00Z/12Z HIRES
CONVECTION ALLOWING MODELS AVAILABLE...NONE ARE PRODUCING ANY
IMPRESSIVE UPDRAFT STRENGTHS...WHICH LENDS CONFIDENCE TO ONLY A
MARGINAL LOW END SEVERE THREAT OVER THE NORTHERN HALF OF THE
FORECAST AREA. HOWEVER...LOW LEVEL JET OF 40-50KTS DOES BRIEFLY DIP
DOWN INTO THE NATURE COAST THIS EVENING. IF THERE ARE ANY ISOLATED
DAMAGING WIND GUSTS IT WILL LIKELY BE WITH STORMS TAPPING THIS
MOMENTUM. BAND OF SHALLOW CONVECTION QUICKLY TRANSLATES SOUTH AND
EAST FROM THE I-4 CORRIDOR AFTER 2AM AND SHOULD BE OUT OF OUR ZONES
BEFORE SUNRISE. WIND FIELDS AND DYNAMICS FOR OVERALL LIFT ARE MUCH
LESS IMPRESSIVE ACROSS THE SOUTHERN ZONES...AND DO NOT ANTICIPATE
ANY SEVERE THREAT...OR EVEN MUCH THUNDER (IF ANY). THE FRONTAL
PASSAGE TONIGHT LOOKS TO BE FAIRLY NOTICEABLE WITH GUIDANCE SHOWING
A QUICK WINDSHIFT TO THE NW AND SOME GUSTY CONDITIONS DEVELOPING...
ESPECIALLY NEAR THE COAST. BIG TEMPERATURE GRADIENT BY SUNRISE
ACROSS THE FORECAST AREA. THE FRONT WILL JUST BE EXITING AREAS LIKE
FT MYERS WHERE TEMPS WILL STILL BE 55-60...HOWEVER UP TOWARD
LEVY/CITRUS/SUMTER COUNTIES WHERE A LONGER DURATION OF CAA WILL BE
ONGOING...TEMPS WILL BE DOWN INTO THE 40S. WINDCHILL VALUES ARE
FORECAST IN THE UPPER 30S TO NEAR 40 THIS FAR NORTH FOR THE EARLY
MORNING HOURS.
FRIDAY/FRIDAY NIGHT...
COLD/DRY AIR ADVECTION CONTINUES TO ARRIVE ON GUSTY NORTHWEST WINDS.
DESPITE GOOD MIXING AND ABUNDANT SUNSHINE...THE CAA WILL HELP KEEP
THE TEMPERATURE RISE IN CHECK. HIGH TEMPERATURES NORTH OF THE I-4
CORRIDOR WILL STRUGGLE TO REACH 60...WHILE FURTHER SOUTH LOWER/MID
60S IS ABOUT IT. SEVERAL POTENTIAL ADVISORY PRODUCTS THAT WILL NEED
TO BE CONSIDERED FOR FRIDAY WITHIN THE NEXT FORECAST PACKAGE INCLUDE
A LAKE WIND ADVISORY...HIGH SURF ADVISORY...AND RIP CURRENT PRODUCT.
FRIDAY NIGHT THINGS REALLY BEGIN TO COOL DOWN. VERY DRY AIR AND
NORTHERLY COLD AIR DRAINAGE DOWN THE PENINSULA WILL ALLOW SOME
LOCATIONS TO FALL BELOW FREEZING...ESPECIALLY FOR NATURE COAST
ZONES. GUIDANCE IS IN AGREEMENT IN BRINGING TEMPS DOWN TO NEAR
FREEZING EVEN FOR OUR INLAND SOUTHERN ZONES. CONFIDENCE IN A LIGHT
FREEZE IS LOWER FOR THESE SOUTHERN ZONES AS MOS IS FAMOUS FOR BEING
TOO COLD WITH THE FIRST ADVECTION NIGHT BEHIND A COLD FRONT. RIDGE
POSITION IS NOT FAVORABLE FOR DE-COUPLING OF THE BOUNDARY LAYER...SO
NO SIGNIFICANT RADIATIONAL COOLING CONTRIBUTION IS EXPECTED. WILL
NOT DEVIATE MUCH FROM A MAV/MET BLEND FOR NOW...BUT WILL HOLD OFF ON
EXPANDING THE CURRENT FREEZE WATCH FURTHER SOUTH UNTIL CONFIDENCE
INCREASES. HOWEVER...WITH SOME WINDS STILL FORECAST...WILL HAVE TO
CONSIDER THE NEED FOR WIND CHILL ADVISORIES AFTER MIDNIGHT FRI NIGHT
INTO EARLY SAT MORNING.
SATURDAY/SATURDAY NIGHT...
HEIGHTS CONTINUE TO RISE IN THE WAKE OF THE DEPARTING TROUGH AND
SHOULD SEE A DECENT DIURNAL SWING BACK INTO THE 60S WITH NEAR 100%
OF THE POSSIBLE SUNSHINE. SURFACE HIGH PRESSURE WILL BE CLOSING IN
DURING THE DAY KEEPING WINDS LIGHTER. THIS FACT ALONE SHOULD HELP
SATURDAY FEEL WARMER. SURFACE HIGH CENTER SETTLES OVER THE REGION
SATURDAY NIGHT. THE LIGHT WINDS AND DRY LOWER LEVELS WILL HELP SETUP
GOOD RADIATIONAL COOLING CONDITIONS. EXPECT A QUICK TEMPERATURE DROP
IN THE EVENING HOURS AND MANY SPOTS AWAY FROM THE COAST MAY AGAIN
APPROACH FREEZING. ONLY CONCERN IS THAT SOME NWP GUIDANCE IS SHOWING
THE POTENTIAL FOR SOME INCREASING HIGH CLOUDS AFTER MIDNIGHT. HAVE
SEEN TIMES WHEN THIS HIGHER LEVEL MOISTURE CAN SLOW THE RADIATIONAL
PROCESS...BUT THE SETUP HAS TO BE JUST RIGHT. AGAIN WILL NOT DEVIATE
FAR FROM THE MOS NUMBERS SINCE THERE IS STILL TIME TO MONITOR.
&&
.LONG TERM (SUNDAY THROUGH NEXT WEDNESDAY)...
THE PERIOD BEGINS WITH AN UPPER RIDGE OVER THE PLAINS STATES AND AN
UPPER TROUGH OFF THE EAST U.S. COAST WHILE A SURFACE HIGH SPRAWLS
ACROSS THE GULF REGION.
THROUGH MON...THE RIDGE FLATTENS AS IT SLIDES EAST WITH A SHORT WAVE
TROUGH OVER THE SE U.S. THE SURFACE HIGH MOVES EAST OUT OVER THE
ATLANTIC BUT RIDGES BACK TO THE GULF AS A SURFACE BOUNDARY SAGS IN
ALONG THE GULF COAST. BOTH THE LATEST ECMWF AND GFS ARE IN FAIRLY
GOOD AGREEMENT ALTHOUGH THE ECMWF IS THE MORE ROBUST. HOWEVER BOTH
KEEP THE BOUNDARY NORTH OF THE AREA.
TUE-WED...THE UPPER RIDGE SLIDES OUT OVER THE ATLANTIC AND BUILDS
NORTHWARD. AN UPPER TROUGH/LOW MOVES OUT OF THE GREAT BASIN AND
ACROSS THE ROCKIES/CENTRAL PLAIN TO THE MISSISSIPPI VALLEY REGION
WITH AN ASSOCIATED COLD FRONT STRETCHING ACROSS THE GULF COAST INTO
THE CENTRAL GULF. THE ATLANTIC HIGH CONTINUES TO RIDGE INTO THE
EASTERN GULF.
THE FORECAST WILL INITIALLY BE CLEAR COLD AND DRY. A FREEZE WATCH OR
WARNING IS LIKELY SUN MORNING AND POSSIBLE MON MORNING...MAINLY
ACROSS THE NORTH. WHEN THE SURFACE HIGH MOVES OUT OVER THE ATLANTIC
MON THE LOW LEVEL FLOW BECOMES MORE NE AND EAST...PROVIDING A WARMER
AND MORE MOIST AIR MASS. THE FLOW CONTINUES TO VEER...SE ON TUE AND
SOUTHERLY BY WED WITH ENOUGH OF AN INCREASE IN MOISTURE...ALONG WITH
THE APPROACHING TROUGH/FRONT...TO SUPPORT A SLIGHT CHANCE OF SHOWERS
WED.
&&
.AVIATION...
STRONG COLD FRONT WILL BE PRECEDED BY A LINE OF SHOWERS AND
THUNDERSTORMS TONIGHT...THEN FOLLOWED BY GUSTY NORTHWESTERLY WINDS.
A BRIEF PERIOD OF MVFR PERHAPS IFR CONDITIONS SEEM LIKELY FOR
TPA...PIE...SRQ AND LAL 03-07Z. ACTIVITY EXPECTED TO BE WEAKENING AS
IT REACHES PGD...FMY AND RSW 06-10Z. WIND GUSTS IN EXCESS OF 25
KNOTS POSSIBLE FRIDAY.
&&
.MARINE...
SOUTHERLY FLOW INTO THE EARLY EVENING AHEAD OF AN APPROACHING COLD
FRONT WILL SHIFT TO THE NORTHWEST FROM NORTH TO SOUTH OVERNIGHT
AFTER THE FRONTAL PASSAGE. STRONG COLD AIR ADVECTION WILL SUPPORT
HAZARDOUS CONDITIONS QUICKLY DEVELOPING. HIGH END SMALL CRAFT
ADVISORY CRITERIA SHOULD BE EASILY MET WITH GALE CONDITIONS POSSIBLE
AT TIMES...ESPECIALLY AFTER MIDNIGHT THROUGH THE MORNING HOURS OF
FRIDAY. ANY GALE FORCE GUSTS SHOULD BE OVER BY LATE FRIDAY
EVENING...HOWEVER ADVISORY CRITERIA WINDS AND SEAS WILL PERSIST
THROUGH AT LEAST FRIDAY NIGHT. HIGH PRESSURE WILL THEN BUILD OVER
THE REGION FOR THE SECOND HALF OF THE WEEKEND ALLOWING WINDS AND
SEAS TO SUBSIDE BELOW HEADLINE CRITERIA. THE NEXT COLD FRONT IS
ANTICIPATED DURING THE EARLY/MIDDLE PORTION OF NEXT WEEK.
THE POTENTIAL FOR HIGH SURF DOES EXIST FOR FRIDAY/FRIDAY NIGHT AS
SWELL GENERATED OVER THE CENTRAL/EASTERN GULF ARRIVES AT OUR
COASTLINE. WILL CONTINUE TO EVALUATE THIS POTENTIAL AND THE
RESULTING ELEVATED RISK OF RIP CURRENTS THAT WILL LIKELY ACCOMPANY
THE SURF.
&&
.FIRE WEATHER...
A STRONG FAST MOVING COLD FRONT WILL MOVE THROUGH THE PENINSULA
TONIGHT WITH SHOWERS AND A FEW THUNDERSTORMS. MUCH COLDER AND DRIER
AIR WILL MOVE IN BEHIND THE FRONT LATE TONIGHT AND FRIDAY
ACCOMPANIED BY WINDS OF 15 TO 20 MPH WITH GUSTS TO 25 MPH. THIS WILL
RESULT IN RED FLAG CONDITIONS FOR MOST LOCATIONS. TEMPERATURES WILL
DROP BELOW FREEZING FOR MUCH OF THE INTERIOR NATURE COAST FRIDAY
NIGHT WHICH WILL KILL TENDER VEGETATION. HUMIDITIES WILL DROP TO
BETWEEN 20 AND 25 PERCENT AGAIN SATURDAY AFTERNOON...BUT WINDS WILL
BE LIGHTER.
&&
.PRELIMINARY POINT TEMPS/POPS...
TPA 52 62 39 62 / 80 0 0 0
FMY 59 67 39 66 / 60 10 0 0
GIF 50 63 32 63 / 60 0 0 0
SRQ 57 64 42 64 / 70 10 0 0
BKV 46 60 31 62 / 80 0 0 0
SPG 54 62 47 63 / 80 0 0 0
&&
.TBW WATCHES/WARNINGS/ADVISORIES...
FL...FREEZE WATCH FROM LATE FRIDAY NIGHT THROUGH SATURDAY
MORNING FOR CITRUS-HERNANDO-LEVY-PASCO-SUMTER.
RED FLAG WARNING FROM NOON TO 6 PM EST FRIDAY FOR
CHARLOTTE-CITRUS-DESOTO-HARDEE-HERNANDO-HIGHLANDS-
HILLSBOROUGH-LEE-LEVY-MANATEE-PASCO-PINELLAS-POLK-
SARASOTA-SUMTER.
GULF WATERS...SMALL CRAFT ADVISORY FROM 4 PM FRIDAY TO 10 AM EST
SATURDAY FOR ENGLEWOOD TO TARPON SPRINGS OUT 20 TO 60
NM-TARPON SPRINGS TO SUWANNEE RIVER OUT 20 TO 60 NM.
GALE WARNING FROM 7 PM THIS EVENING TO 4 PM EST FRIDAY FOR
ENGLEWOOD TO TARPON SPRINGS OUT 20 TO 60 NM-TARPON
SPRINGS TO SUWANNEE RIVER OUT 20 TO 60 NM.
SMALL CRAFT ADVISORY FROM 7 PM THIS EVENING TO 10 AM EST
SATURDAY FOR BONITA BEACH TO ENGLEWOOD OUT 20 NM-
BONITA BEACH TO ENGLEWOOD OUT 20 TO 60 NM-ENGLEWOOD
TO TARPON SPRINGS OUT 20 NM-TAMPA BAY WATERS-TARPON
SPRINGS TO SUWANNEE RIVER OUT 20 NM.
&&
$$
SYNOPSIS/SHORT TERM/MARINE...MROCZKA
LONG TERM...RUDE
AVIATION...JILLSON
FIRE WEATHER...MROCZKA/JILLSON
AREA FORECAST DISCUSSION
NWS PEACHTREE CITY GA
149 PM EST THU DEC 20 2012
.PREV DISCUSSION... /ISSUED 1049 AM EST THU DEC 20 2012/
UPDATE...
HAVE MADE SIGNIFICANT UPDATES TO HOURLY GRIDS TO CAPTURE CURRENT
RADAR TRENDS. OVERALL...FRONT HIGH TAILING IT THROUGH THE
REGION...AND PRECIP ACTIVITY HAS ACCELERATED THIS MORNING.
INSTABILITY OVER MUCH OF THE AREA IS VIRTUALLY NON EXISTENT...AND
WHAT IS PRESENT IS NOT ENOUGH TO SUPPORT THUNDERSTORM DEVELOPMENT.
WILL CONTINUE TO WATCH CENTRAL GEORGIA CAREFULLY INTO THE
AFTERNOON HOURS...ESPECIALLY THE FAR SOUTHERN TIER...AS THIS AREA
HAS THE POTENTIAL FOR ISOLATED SEVERE STORMS AS THE MAIN LINE
MOVES THROUGH DUE TO INCREASED INSTABILITY ACROSS THE REGION. AS
OF NOW...HAVE OPTED NOT TO BE INCLUDED WITH THE TORNADO WATCH
ISSUED EARLIER THIS MORNING...BUT WILL CONTINUE TO ANALYZE THE
ENVIRONMENT AS THE BOUNDARY APPROACHES.
WILL CONTINUE TO MAKE ADJUSTMENTS TO THE GRIDS AS NEEDED...ESPECIALLY
POPS AND WX...AS THE PRECIP MOVES THROUGH THE FORECAST AREA. WILL
ALSO BE PAYING CLOSE ATTENTION TO TEMPERATURES AND DEWPOINTS
BEHIND THE LINE AS COOLER AND DRIER AIR MOVES IN QUICKLY.
31
PREV DISCUSSION... /ISSUED 648 AM EST THU DEC 20 2012/
PREV DISCUSSION... /ISSUED 600 AM EST THU DEC 20 2012/
SHORT TERM /TODAY THROUGH FRIDAY NIGHT/...
PRIMARY CONCERNS ARE TIMING OF PRECIP ONSET AND END TODAY/TONIGHT
CHC FOR SEVERE CONVECTION THIS AFTERNOON AND EXTENT AND INTENSITY
OF WIND EVENT TONIGHT THROUGH FRI NIGHT. WAA SHRA IN ADVANCE OF
SHORT WAVE ALREADY APPROACHING STATE LINE IN WC GA THIS MORNING.
LATEST RAP ANALYSIS SHOWS ONLY WEAK ELEVATED INSTABILITY EXTENDING
INTO SW 1/3RD OF ALABAMA AND NO LIGHTNING OBSERVED IN THE LAST FEW
HOURS. HAVE DELAYED ONSET OF OF SHRA TO 09-10Z AND SLT CHC TSRA
UNTIL 12Z. 00Z MODEL PROGS IN FAIR AGREEMENT THOUGH AGAIN THE NAM
IS THE MOST AGGRESSIVE WITH LOW LEVEL MOISTURE AND SBCAPE. 06Z NAM
HAS SBCAPE 250-400 J/KG SOUTH OF CSG TO MCN LINE WITH NO SBCAPE TO
THE NORTH. 00Z GFS AND ECMWF KEEP SBCAPE LESS THAN 200 J/KG ACROSS
ALL OF CWA. WILL HAVE TO WATCH MIDDLE GA CLOSE. VERY STRONG LOW
LEVEL VERTICAL WIND SHEAR /0-1KM BULK SHEAR NEAR 50KTS/ ALLOWS 06Z
NAM TO PROG 1.5-2.0 VALUES OF SIG TOR PARAMETER AT 00Z.
EXPERIMENTAL HIGH SHEAR-LOW CAPE SHERB PARAMETER FROM 06Z NAM ONLY
HAS 0.8-1.2 OVER MIDDLE GA. MAIN POINT IS IT WILL NOT TAKE MUCH
INSTABILITY TO PRODUCE BRIEF MESOVORTICES CAPABLE OF WIND DAMAGE
OR A BRIEF TORNADO ...SIMILAR TO WHAT WE SAW MONDAY. TOTAL
RAINFALL WILL NOT BE TOO HIGH WITH AMOUNTS OF 0.5-1.0 INCHES.
SYSTEM WILL MOVE OUT QUICKLY TAKING PRECIP WITH IT. VERY STRONG
PRESSURE GRADIENT AND STRONG VERTICAL CAA AND RESULTING DEEP MIXING
ALLOWS FOR SIGNIFICANT WIND EVENT OVER MUCH OF CWA WITH GUSTS TO
35-40 MPH AND 45+ MPH IN MOUNTAINS. COULD BEGIN LATE THIS AFTERNOON
IN THE WAKE OF PRECIP BUT APPEARS BEST PRESSURE GRADIENT WILL SET UP
AROUND 22Z-00Z. GUIDANCE FOR WIND SPEEDS NOT TOO FAR OFF BUT COULD
GO A LITTLE HIGHER IF SYSTEM INTENSIFIES OR MIXING IS MORE THAN
FCST. IN EXPOSED/HIGHER TERRAIN AREAS OF NE GA...WILL SEE STRONG
WINDS PERSIST. 1-2KM AGL WINDS NOT EXPECTED TO WEAKEN MUCH OVER NE
GA UNTIL AFTER 12Z SAT. HAVE ADJUSTED ADVISORIES APPROPRIATELY AND
BROKE OUT NE GA COUNTIES INTO ITS OWN SEGMENT THROUGHOUT THE EVENT.
SNELSON
LONG TERM /SATURDAY THROUGH WEDNESDAY/...
AN H5 RIDGE BUILDS INTO THE REGION SATURDAY BRINGING DRIER AND MORE
STABLE AIR ALONG WITH A WARMING TREND. THIS RIDGE WILL BE SHORT
LIVED AS THE FLOW FLATTENS TO VERY PROGRESSIVE ZONAL FLOW BY SUNDAY.
THE FIRST SHORT WAVE IN A SERIES OF SHORT WAVES WILL MOVE ACROSS THE
CWA LATE SUNDAY AND INTO MONDAY. FROM THIS POINT TIMING OF THE SHORT
WAVES WILL BE TRICKY AS THE FLOW IS FAST AND THE MODELS APPEAR TO BE
HAVING A DIFFICULT TIME MAINTAINING CONTINUITY WITH IN THEMSELVES.
WILL GO WITH CHANCE POPS BEGINNING SUNDAY NIGHT AND CONTINUE POPS
THROUGH THE LONG TERM...FAVORING HIGHER POPS TOWARD MID WEEK AS BOTH
MODELS SHOWING A SIGNIFICANT SYSTEM MOVING ACROSS THE CWA.
17
FIRE WEATHER...
WINDS WILL BE VERY GUSTY TONIGHT AND FRIDAY WITH 20FT WINDS OF 10-20
MPH WITH GUSTS TO 35 MPH. WILL ALSO SEE A 4 TO 5 HOUR PERIOD OF RH
BELOW 25 PCT ACROSS MUCH OF THE AREA FRIDAY AFTERNOON. FORTUNATELY
10HR FUELS WILL STILL BE WET ON FRIDAY FROM THE RAIN EXPECTED TODAY.
COOLER TEMPS AND LIMITED SUNSHINE WILL MAKE IT DIFFICULT FOR THEM TO
DRY. NOT PLANNING ANY RED FLAG OR FIRE DANGER STATEMENTS.
SNELSON
&&
.AVIATION...
18Z UPDATE...
FRONT PUSHING THROUGH THE AREA THIS AFTERNOON WILL CONTINUE TO
PRODUCE SHOWERS AND ISOLATED THUNDERSTORMS. IFR CIGS AND MVFR
VSBYS ASSOCIATED WITH PRECIP. FRONT SHOULD BE THROUGH THE ATL/CSG
AREAS BETWEEN 19-20Z. QUICKLY IMPROVING CONDITIONS BEHIND THE
FRONT...WITH BKN VFR CONDITIONS BY EARLY EVENING...AND FEW-SCT
HIGH CLOUDS INTO THE OVERNIGHT HOURS. WINDS WILL BE THE MAIN
CONCERN...WITH WEST 12-16KT AND GUSTS TO 20-25KT BEHIND THE FRONT INTO
THE OVERNIGHT PERIOD...AND 17-22 KT WITH GUSTS AS HIGH AS 30-32KT
FRIDAY.
//ATL CONFIDENCE...18Z UPDATE...
MEDIUM CONFIDENCE ON CIGS AND VSBY THROUGH 22Z.
HIGH CONFIDENCE ON ALL OTHER ELEMENTS.
31
&&
.PRELIMINARY POINT TEMPS/POPS...
ATHENS 61 32 48 25 / 100 40 0 0
ATLANTA 60 30 46 28 / 100 30 0 0
BLAIRSVILLE 54 27 41 19 / 100 30 0 0
CARTERSVILLE 58 28 45 24 / 100 20 0 0
COLUMBUS 68 33 52 30 / 100 20 0 0
GAINESVILLE 59 30 45 26 / 100 30 0 0
MACON 69 34 51 26 / 100 50 0 0
ROME 57 27 46 24 / 100 20 0 0
PEACHTREE CITY 63 29 48 25 / 100 20 0 0
VIDALIA 75 40 53 32 / 80 80 0 0
&&
.FFC WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY FROM 6 PM THIS EVENING TO 7 PM EST FRIDAY FOR THE
FOLLOWING ZONES: BALDWIN...BANKS...BARROW...BARTOW...BIBB...
BLECKLEY...BUTTS...CARROLL...CATOOSA...CHATTAHOOCHEE...
CHATTOOGA...CHEROKEE...CLARKE...CLAYTON...COBB...COWETA...
CRAWFORD...CRISP...DADE...DEKALB...DODGE...DOOLY...DOUGLAS...
EMANUEL...FAYETTE...FLOYD...FORSYTH...GLASCOCK...GORDON...
GREENE...GWINNETT...HALL...HANCOCK...HARALSON...HARRIS...HEARD...
HENRY...HOUSTON...JACKSON...JASPER...JEFFERSON...JOHNSON...
JONES...LAMAR...LAURENS...MACON...MADISON...MARION...
MERIWETHER...MONROE...MONTGOMERY...MORGAN...MURRAY...MUSCOGEE...
NEWTON...NORTH FULTON...OCONEE...OGLETHORPE...PAULDING...PEACH...
PIKE...POLK...PULASKI...PUTNAM...ROCKDALE...SCHLEY...SOUTH
FULTON...SPALDING...STEWART...SUMTER...TALBOT...TALIAFERRO...
TAYLOR...TELFAIR...TOOMBS...TREUTLEN...TROUP...TWIGGS...UPSON...
WALKER...WALTON...WARREN...WASHINGTON...WEBSTER...WHEELER...
WHITFIELD...WILCOX...WILKES...WILKINSON.
WIND ADVISORY FROM 6 PM THIS EVENING TO 7 AM EST SATURDAY FOR
THE FOLLOWING ZONES: DAWSON...FANNIN...GILMER...LUMPKIN...
PICKENS...TOWNS...UNION...WHITE.
&&
$$
SHORT TERM...31
LONG TERM....BAKER
AVIATION...31
AREA FORECAST DISCUSSION
NWS CHICAGO/ROMEOVILLE IL
356 PM CST THU DEC 20 2012
.MESOSCALE DISCUSSION...
1040 AM CST
THE IMPRESSIVELY STRONG WINTER SYSTEM IS FOR THE MOST PART
UNFOLDING SO FAR AS TO PLAN...WITH NO IMMINENT CHANGES PLANNED TO
HEADLINES...TIMING...OR FORECAST SNOWFALL AMOUNTS.
THE MORNING SATELLITE AND HAND UPPER AIR AND SURFACE ANALYSES
REVEAL A CLASSIC MID-LATITUDE CYCLONE. THE CLOSED UPPER LOW IS
SWINGING NEGATIVELY TITLED LATE THIS MORNING...WITH A DRY SLOT
HAVING ENVELOPED THE SOUTHEAST TWO-THIRDS OF THE FORECAST
AREA...INCLUDING CHICAGO. ARCS OF SHOWERS...WITH A CONVECTIVE-LIKE
APPEARANCE ON RADAR...CONTINUE TO DEVELOP WITHIN THIS DRY SLOT ACROSS
WEST CENTRAL TO CENTRAL IL AND PROPAGATE NORTHWARD INTO THE COOL
SECTOR. THESE HAVE BEEN MOVING INTO A WELL ESTABLISHED HEAVY SNOW
BAND...NOW CENTERED NEAR THE MISSISSIPPI RIVER INTO
SOUTHWEST/SOUTH CENTRAL WI. THIS LINES UP PERFECTLY WITH A
SYNOPTICALLY FAVORED AREA IN THIS STORM SYSTEM FOR THE MOST
INTENSE DYNAMICS...TIGHTEST THERMAL GRADIENT...AND WIND AND
MOISTURE CONVERGENCE. IN ADDITION...THE RAP CONTINUES TO ANALYZE
DEEP LIFT BEING CROSS-HAIRED WITHIN THE DENDRITIC GROWTH
ZONE...OWING TO MORE EFFICIENT SNOW PRODUCTION IN THIS AREA...AND
ESPECIALLY WHEN CONSIDERING PWATS ARE NEAR 0.70 AND INFLOW MIXING
RATIOS ARE 3.5-5.0 G/KG. VISIBILITIES UNDERNEATH THIS SNOW
BAND HAVE REGULARLY BEEN UNDER ONE HALF MILE...AND A ONE INCH PER
HOUR RATE WAS ALREADY OBSERVED IN ROCK ISLAND IL. THE SURFACE LOW
IS CENTERED NEAR LACON AND MOVING NORTHEAST WITH THE PRESSURE
FALL/RISE COUPLET MAGNITUDE AT 7MB/9MB RESPECTIVELY.
SHOWER AND THUNDER POTENTIAL EAST... WHILE THE DRY SLOT HAS
MINIMIZED MUCH OF THE AREAL COVERAGE OF MODERATE TO HEAVY RAIN
SEEN EARLIER THIS MORNING...SCATTERED CONVECTIVE ECHOES ARE
DEVELOPING ALONG AN IMMEDIATE PRE-FRONTAL TROUGH ACROSS EAST
CENTRAL IL. THE PRE-FRONTAL AIR MASS HAS SURFACE DEW POINTS OF 45
TO EVEN THE LOWER 50S AS FAR NORTH AS NORTHWEST/WEST CENTRAL IN.
WHILE NO LOW-LEVEL CAPE IS ANALYZED BY DIAGNOSTIC GUIDANCE AS OF
10 AM...ADAPTED FORECAST SOUNDINGS WITH 54F/50F DO PRODUCE AROUND
50 J/KG OF 0-3 KM CAPE THROUGH 20Z. WITH THE DYNAMIC WIND
FIELD...THERE MAY BE A BRIEF WINDOW OF GUSTY WIND POTENTIAL WITH
THIS ACROSS NORTHWEST IN...THOUGH NO EXPLICIT CONVECTIVE MODELS
THAT WERE LOOKED AT PRODUCE ANYTHING LOOKING OVERLY OMINOUS.
ACROSS CHICAGO...PERIODS OF LIGHT TO MODERATE SHOWERS SHOULD
PREVAIL THROUGH MUCH OF THE DAY WITHIN THE LOW-LEVEL MOISTURE
TRANSPORT UNDER DEEP HEIGHT FALLS/DIFFLUENCE OWING TO ASCENT.
RAIN TO SNOW TIMING...VARIOUS THICKNESS AND WET BULB ANALYSIS
TECHNIQUES ON THE RAP FOR PRECIP TYPE CHANGE LINE UP VERY WELL
WITH THE OBSERVED CHANGE OVER...AND THESE ARE ALL FORECAST TO
CREEP EASTWARD AS THE SURFACE WINDS TURN MORE NNW LOWERING
BOUNDARY LAYER TEMPERATURES. THERE HAS BEEN A REPORT OF SNOW
MIXING IN JUST NORTHWEST OF ROCKFORD AND WITH CONTINUED DYNAMIC
AND ADVECTIVE COOLING IT SHOULD REACH ROCKFORD SOON. THE CHANGE
OVER LINE SHOULD BE NORTH-TO-SOUTH ORIENTED AROUND NOON AND
LIKELY SWING NORTHWEST TO SOUTHEAST ORIENTED BY LATE AFTERNOON AS
IT APPROACHES CHICAGO. THE CHANGE SHOULD ALSO PICK UP IN
PROGRESSION SPEED IN THE WAKE OF THE SURFACE LOW AND UNDERNEATH
THE RAPID COOLING OF THE UPPER LOW.
SNOWFALL AND WIND...WITH CURRENT RADAR AND SATELLITE TRENDS AND
THE PROJECTED PATH OF THE LOW AND ASSOCIATED DEFORMATION...THE
MOST INTENSE SNOWFALL AREA/BANDS WITH RATES OF ONE INCH OR GREATER
PER HOUR SHOULD SLOWLY WORK EASTWARD NORTH OF I-80 THROUGH THE
AFTERNOON. SHORT TERM MODEL FORECASTS OF PRECIP AND VISIBILITY
AGREE WITH THIS EVOLUTION. RATES OF TWO INCHES PER HOUR ARE
POSSIBLE TOWARD ROCKFORD/BELVIDERE/DIXON GIVEN SOME OF THE 40 PLUS
DBZ /NOT ASSOCIATED WITH BRIGHT BANDING/ SEEN ALREADY AND PER THE
FORECAST INSTABILITY...BOTH SLANTWISE AND EVEN UPRIGHT IN FORECAST
SOUNDINGS/CROSS SECTIONS. WINDS HAVE BEEN GUSTING IN EXCESS OF 40
KT ACROSS MUCH OF IA AND MO AND WITH THE DEEPENING OF THE SYSTEM
AND CONTINUED STRENGTHENING COLD AIR ADVECTION...THESE TYPES OF
GUSTS WILL ONLY INCREASE AS THEY ROTATE EAST INTO THE AREA WHICH
MATCHES WELL WITH THE 50-60 MPH WINDS SEEN IN THE BOUNDARY LAYER
OF NAM AND GFS AND SURPRISING EVEN THE RAP. WILL HAVE TO WATCH TO
SEE IF THE BLIZZARD WARNING WILL NEED TO BE EXPANDED SOUTH OR
EAST...TO INCLUDE COUNTIES SUCH AS DEKALB AND LASALLE. ALSO WITH
AS FAR SOUTH AS SNOW HAS BEEN OBSERVED TO THE WEST AND THE EXTENT
OF THE TROWAL...THERE IS NO DOUBT IT WILL SNOW IN THE HIGH WIND
WARNING AREA OF THE SOUTHERN CWA. IT IS JUST UNCERTAIN ON HOW
INTENSE IT WILL BE. WILL CONTINUE TO MENTION BLOWING SNOW AS A
SECONDARY IMPACT IN THE NPW.
MTF
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 22Z...
* VARIABLE CIGS LATE THIS AFTERNOON BECOMING IFR CIGS THROUGH AT
LEAST MIDNIGHT.
* SW WINDS SHIFT TO N EARLY THIS EVENING WITH GUSTS ARND 45 KT
STILL EXPECTED THIS EVENING.
* RAIN QUICKLY CHANGING OVER TO SNOW ARND 23Z. HEAVY SNOW PSBL FOR
A FEW HOURS AFTER INITIAL CHANGE OVER TO ALL SNOW...WITH LOWER
VSBY EXPECTED THROUGH TONIGHT WITH BLOWING SNOW. BMD
//DISCUSSION...UPDATED 18Z...
WITH THE LOW TRACKING RIGHT OVER THE EASTERN TERMINALS...WINDS
HAVE BRIEFLY TURNED SW GUSTING TO ARND 25 KT. STILL EXPECTING
WINDS TO BECOME N AND GUST TO 45 KT THIS EVENING BEHIND THE LOW.
PRECIP HAS FINALLY BEGUN TO CHANGE OVER TO SNOW AT RFD. GIVEN THE
SLOWER TREND...PUSHED THE CHANGE FROM RAIN TO SNOW BACK BY AN HOUR
EVERYWHERE ELSE. HEAVY SNOW INITIALLY IS STILL A CONCERN...AS IS
LOWER VSBY. ALREADY GOT A REPORT OUT OF RFD OF HALF DOLLAR SIZE
SNOWFLAKES WITH SNOW ALREADY BEGINNING TO ACCUMULATE.
LASTLY...REMOVED MAJORITY OF LIFR CIGS AS CIGS ACROSS THE REGION
ARE IFR OR BETTER. WHILE IFR CIGS ARE EXPECTED...THEY COULD BE A
FEW HUNDRED FEET HIGHER THAN CURRENTLY FORECAST. NO CHANGES MADE TO THE
TAFS BEYOND 5Z.
PREVIOUS DISCUSSION...18Z...
THE LOW IS OVER MARSHALL COUNTY IL AND DEEPENING AS IT MOVES
NORTHEAST THROUGH IL. SHOWERS HAVE DEVELOPED ACROSS NORTHERN IL AS
WE ARE WITHIN THE WARM SECTOR OF THE LOW. RADAR REFLECTIVITIES
AND VISIBLE SATELLITE BOTH INDICATE THERE ARE SOME CONVECTIVE
AREAS. A FLASH OR TWO OF LIGHTNING HAS BEEN OBSERVED...AND
THINKING THE BEST AREA OF FORCING AND WEAK INSTABILITY IS OVER
WESTERN AND CENTRAL IL. THEREFORE THE ONLY TAF CARRYING TS IS RFD.
AS THE LOW SHIFTS OVER AND THEN EAST OF THE EASTERN
TERMINALS...EXPECTING WINDS TO SHIFT N AND IMMEDIATELY START
GUSTING. THINKING ARND 20Z...BUT IF LOW CONTINUES TO BE
SLOW...COULD BE LATER. TEMPS WILL FALL ON THE BACK SIDE OF THE LOW
WITH A QUICK TRANSITION TO SN EXPECTED. THINKING AN HOUR OR LESS
OF RASN. ALSO EXPECTING CIGS TO FALL RAPIDLY BEHIND THE LOW. SO
OVERALL HIGH CONFIDENCE IN TAF TRENDS...BUT MEDIUM CONFIDENCE ON
TIMING. GUIDANCE IS STILL INDICATING A FEW HOURS OF MODERATE TO
HEAVY SNOW RIGHT AFTER THE PRECIP TURNS TO ALL SNOW. KEPT 1/2 SM
VSBY FOR THAT PERIOD IN THE EASTERN TERMINALS AND WENT WITH 1/4 SM
AT RFD. COULD SEE 1/4 SM AT THE EASTERN TERMINALS...BUT CONFIDENCE
IS NOT HIGH ENOUGH TO GO WITH 1/4 SM AT THIS TIME. THE INITIAL WET
SNOW WILL BECOME AN AVERAGE SNOW WITHIN AN HOUR OR TWO.
ATTENTION THEN TURNS TO THE WINDS. GUSTY WINDS ARND 45 KT STILL
VERY LIKELY THROUGH MIDNIGHT. SO WHILE SNOWFALL RATES WILL
DIMINISH BY 2-3Z...BLOWING SNOW WILL CONTINUE TO REDUCE VSBYS
THROUGH THE MORNING. EXPECTING SNOW TO TAPER OF TO FLURRIES
SHORTLY AFTER MIDNIGHT.
GUSTY NW WINDS CONTINUE ON FRIDAY...BUT CIGS SHOULD BE RISING TO
VFR FROM W TO E BEGINNING MID FRIDAY MORNING.
JEE
//ORD AND MDW CONFIDENCE...UPDATED 22Z...
* HIGH CONFIDENCE IN TAF TRENDS...CONDITIONS DETERIORATING THROUGH
THIS EVENING.
* MEDIUM CONFIDENCE IN CIG HEIGHTS TONIGHT.
* HIGH CONFIDENCE IN SN...MEDIUM CONFIDENCE IN TIMING AND VSBY.
* HIGH CONFIDENCE IN WIND TRENDS...MEDIUM CONFIDENCE IN TIMING.
* HIGH CONFIDENCE IN CIGS IMPROVING TOMORROW...MEDIUM CONFIDENCE
IN TIMING. BMD
//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...
* FRIDAY NIGHT THROUGH SUNDAY..DRY. VFR.
* MONDAY AND TUESDAY...SLIGHT CHANCE OF SNOW. MVFR POSSIBLE.
* WEDNESDAY...CHANCE OF SNOW. MVFR LIKELY.
&&
.MARINE...
207 PM...MINIMAL ADJUSTMENTS TO CURRENT FORECAST...AND HEADLINES
WILL REMAIN IN PLACE. STORM WARNING WILL REMAIN IN PLACE FOR LATE
THIS AFTERNOON THROUGH FRIDAY AFTERNOON. STORM FORCE CONDITIONS
WILL BEGIN ACROSS THE SOUTHERN HALF OF LAKE MICHIGAN FIRST...THEN
COVER ALL OF LAKE MICHIGAN LATER THIS EVENING.
THE SURFACE LOW PRESSURE THIS AFTERNOON WAS APPROACHING
CHICAGO...AND BASED ON GUIDANCE WILL SLIDE EAST/NORTHEAST ACROSS THE
SOUTHERN TIP OF LAKE MICHIGAN. AS THIS LOW SLIDES EAST THE WINDS
WILL DIMINISH...HOWEVER ALONG THE BACKSIDE OF THE LOW PRESSURE
SYSTEM WINDS WILL RAPIDLY INCREASE TO STORM FORCE GUSTS TO 55 KT BY
TONIGHT FROM THE NORTH/NORTHWEST. AT THIS TIME IT REMAINS POSSIBLE
FOR AN OCCASIONAL GUST TO 60-65 KT...HOWEVER CONFIDENCE REMAINS LOW.
THE TIGHTEST WIND GRADIENT THAT COULD PRODUCE THIS TYPE OF GUST
WOULD BE LATE THIS EVENING THROUGH EARLY FRIDAY MORNING.
THE LOW WILL MOVE EAST AND MERGE WITH ANOTHER LOW MOVING UP THE EAST
COAST SATURDAY. THE COMBINED LOW WILL SLOW AND AND AS HIGH PRESSURE
BUILDS ACROSS THE PLAINS...THE GRADIENT WILL REMAIN STRONG INTO
FRIDAY NIGHT AND FINALLY RELAX SATURDAY. THEN WITH HIGH PRESSURE
SLIDING ACROSS THE OHIO VALLEY FOR THE WEEKEND...WINDS WILL
DIMINISH. THE NEXT SYSTEM APPEARS TO SLIDE ACROSS THE MISSOURI
VALLEY MONDAY ARRIVING ACROSS THE CENTRAL GREAT LAKES MONDAY
NIGHT/CHRISTMAS DAY.
CONFIDENCE IN THE STORM FORCE GUSTS...HIGH.
CONFIDENCE IN THE SYSTEM EARLY NEXT WEEK...MEDIUM.
BEACHLER
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...BLIZZARD WARNING...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019
UNTIL MIDNIGHT FRIDAY.
WINTER STORM WARNING...ILZ006-ILZ012-ILZ013-ILZ014-ILZ020-ILZ021-
ILZ022 UNTIL 3 AM FRIDAY.
WINTER STORM WARNING...ILZ005 UNTIL MIDNIGHT FRIDAY.
HIGH WIND WARNING...ILZ023-ILZ032-ILZ033-ILZ039 UNTIL MIDNIGHT
FRIDAY.
IN...LAKESHORE FLOOD WARNING...INZ001-INZ002...MIDNIGHT FRIDAY TO 3
AM SATURDAY.
WINTER STORM WARNING...INZ001-INZ002 UNTIL 3 AM FRIDAY.
HIGH WIND WARNING...INZ010-INZ011-INZ019 UNTIL MIDNIGHT FRIDAY.
LM...STORM WARNING...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-
LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-
LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 4 PM FRIDAY.
GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565 UNTIL 6
PM THURSDAY.
STORM WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565 UNTIL
4 PM FRIDAY.
&&
$$
AREA FORECAST DISCUSSION
NWS CHICAGO/ROMEOVILLE IL
208 PM CST THU DEC 20 2012
.MESOSCALE DISCUSSION...
1040 AM CST
THE IMPRESSIVELY STRONG WINTER SYSTEM IS FOR THE MOST PART
UNFOLDING SO FAR AS TO PLAN...WITH NO IMMINENT CHANGES PLANNED TO
HEADLINES...TIMING...OR FORECAST SNOWFALL AMOUNTS.
THE MORNING SATELLITE AND HAND UPPER AIR AND SURFACE ANALYSES
REVEAL A CLASSIC MID-LATITUDE CYCLONE. THE CLOSED UPPER LOW IS
SWINGING NEGATIVELY TITLED LATE THIS MORNING...WITH A DRY SLOT
HAVING ENVELOPED THE SOUTHEAST TWO-THIRDS OF THE FORECAST
AREA...INCLUDING CHICAGO. ARCS OF SHOWERS...WITH A CONVECTIVE-LIKE
APPEARANCE ON RADAR...CONTINUE TO DEVELOP WITHIN THIS DRY SLOT ACROSS
WEST CENTRAL TO CENTRAL IL AND PROPAGATE NORTHWARD INTO THE COOL
SECTOR. THESE HAVE BEEN MOVING INTO A WELL ESTABLISHED HEAVY SNOW
BAND...NOW CENTERED NEAR THE MISSISSIPPI RIVER INTO
SOUTHWEST/SOUTH CENTRAL WI. THIS LINES UP PERFECTLY WITH A
SYNOPTICALLY FAVORED AREA IN THIS STORM SYSTEM FOR THE MOST
INTENSE DYNAMICS...TIGHTEST THERMAL GRADIENT...AND WIND AND
MOISTURE CONVERGENCE. IN ADDITION...THE RAP CONTINUES TO ANALYZE
DEEP LIFT BEING CROSS-HAIRED WITHIN THE DENDRITIC GROWTH
ZONE...OWING TO MORE EFFICIENT SNOW PRODUCTION IN THIS AREA...AND
ESPECIALLY WHEN CONSIDERING PWATS ARE NEAR 0.70 AND INFLOW MIXING
RATIOS ARE 3.5-5.0 G/KG. VISIBILITIES UNDERNEATH THIS SNOW
BAND HAVE REGULARLY BEEN UNDER ONE HALF MILE...AND A ONE INCH PER
HOUR RATE WAS ALREADY OBSERVED IN ROCK ISLAND IL. THE SURFACE LOW
IS CENTERED NEAR LACON AND MOVING NORTHEAST WITH THE PRESSURE
FALL/RISE COUPLET MAGNITUDE AT 7MB/9MB RESPECTIVELY.
SHOWER AND THUNDER POTENTIAL EAST... WHILE THE DRY SLOT HAS
MINIMIZED MUCH OF THE AREAL COVERAGE OF MODERATE TO HEAVY RAIN
SEEN EARLIER THIS MORNING...SCATTERED CONVECTIVE ECHOES ARE
DEVELOPING ALONG AN IMMEDIATE PRE-FRONTAL TROUGH ACROSS EAST
CENTRAL IL. THE PRE-FRONTAL AIR MASS HAS SURFACE DEW POINTS OF 45
TO EVEN THE LOWER 50S AS FAR NORTH AS NORTHWEST/WEST CENTRAL IN.
WHILE NO LOW-LEVEL CAPE IS ANALYZED BY DIAGNOSTIC GUIDANCE AS OF
10 AM...ADAPTED FORECAST SOUNDINGS WITH 54F/50F DO PRODUCE AROUND
50 J/KG OF 0-3 KM CAPE THROUGH 20Z. WITH THE DYNAMIC WIND
FIELD...THERE MAY BE A BRIEF WINDOW OF GUSTY WIND POTENTIAL WITH
THIS ACROSS NORTHWEST IN...THOUGH NO EXPLICIT CONVECTIVE MODELS
THAT WERE LOOKED AT PRODUCE ANYTHING LOOKING OVERLY OMINOUS.
ACROSS CHICAGO...PERIODS OF LIGHT TO MODERATE SHOWERS SHOULD
PREVAIL THROUGH MUCH OF THE DAY WITHIN THE LOW-LEVEL MOISTURE
TRANSPORT UNDER DEEP HEIGHT FALLS/DIFFLUENCE OWING TO ASCENT.
RAIN TO SNOW TIMING...VARIOUS THICKNESS AND WET BULB ANALYSIS
TECHNIQUES ON THE RAP FOR PRECIP TYPE CHANGE LINE UP VERY WELL
WITH THE OBSERVED CHANGE OVER...AND THESE ARE ALL FORECAST TO
CREEP EASTWARD AS THE SURFACE WINDS TURN MORE NNW LOWERING
BOUNDARY LAYER TEMPERATURES. THERE HAS BEEN A REPORT OF SNOW
MIXING IN JUST NORTHWEST OF ROCKFORD AND WITH CONTINUED DYNAMIC
AND ADVECTIVE COOLING IT SHOULD REACH ROCKFORD SOON. THE CHANGE
OVER LINE SHOULD BE NORTH-TO-SOUTH ORIENTED AROUND NOON AND
LIKELY SWING NORTHWEST TO SOUTHEAST ORIENTED BY LATE AFTERNOON AS
IT APPROACHES CHICAGO. THE CHANGE SHOULD ALSO PICK UP IN
PROGRESSION SPEED IN THE WAKE OF THE SURFACE LOW AND UNDERNEATH
THE RAPID COOLING OF THE UPPER LOW.
SNOWFALL AND WIND...WITH CURRENT RADAR AND SATELLITE TRENDS AND
THE PROJECTED PATH OF THE LOW AND ASSOCIATED DEFORMATION...THE
MOST INTENSE SNOWFALL AREA/BANDS WITH RATES OF ONE INCH OR GREATER
PER HOUR SHOULD SLOWLY WORK EASTWARD NORTH OF I-80 THROUGH THE
AFTERNOON. SHORT TERM MODEL FORECASTS OF PRECIP AND VISIBILITY
AGREE WITH THIS EVOLUTION. RATES OF TWO INCHES PER HOUR ARE
POSSIBLE TOWARD ROCKFORD/BELVIDERE/DIXON GIVEN SOME OF THE 40 PLUS
DBZ /NOT ASSOCIATED WITH BRIGHT BANDING/ SEEN ALREADY AND PER THE
FORECAST INSTABILITY...BOTH SLANTWISE AND EVEN UPRIGHT IN FORECAST
SOUNDINGS/CROSS SECTIONS. WINDS HAVE BEEN GUSTING IN EXCESS OF 40
KT ACROSS MUCH OF IA AND MO AND WITH THE DEEPENING OF THE SYSTEM
AND CONTINUED STRENGTHENING COLD AIR ADVECTION...THESE TYPES OF
GUSTS WILL ONLY INCREASE AS THEY ROTATE EAST INTO THE AREA WHICH
MATCHES WELL WITH THE 50-60 MPH WINDS SEEN IN THE BOUNDARY LAYER
OF NAM AND GFS AND SURPRISING EVEN THE RAP. WILL HAVE TO WATCH TO
SEE IF THE BLIZZARD WARNING WILL NEED TO BE EXPANDED SOUTH OR
EAST...TO INCLUDE COUNTIES SUCH AS DEKALB AND LASALLE. ALSO WITH
AS FAR SOUTH AS SNOW HAS BEEN OBSERVED TO THE WEST AND THE EXTENT
OF THE TROWAL...THERE IS NO DOUBT IT WILL SNOW IN THE HIGH WIND
WARNING AREA OF THE SOUTHERN CWA. IT IS JUST UNCERTAIN ON HOW
INTENSE IT WILL BE. WILL CONTINUE TO MENTION BLOWING SNOW AS A
SECONDARY IMPACT IN THE NPW.
MTF
&&
.DISCUSSION...
344 AM CST
WINTER STORM TODAY/TONIGHT...
HAVE UPGRADED WATCHES/WARNINGS TO INCLUDE A BLIZZARD WARNING FOR A
PORTION OF NORTH CENTRAL IL...A WINTER STORM WARNING FOR NORTHEAST
IL/NORTHWEST INDIANA NORTH OF ABOUT A STREATOR-KANKAKEE-DE MOTTE
LINE...AND A HIGH WIND WARNING FOR AREAS SOUTH OF THAT SAME LINE.
INTENSE WINTER STORM SYSTEM TAKING AIM AT THE AREA FOR LATER TODAY
AND TONIGHT. AT 08Z...SURFACE ANALYSIS DEPICTED 992 MB LOW OVER
CENTRAL MISSOURI WITH 6 MB/3 HR PRESSURE FALLS SPREADING ACROSS
NORTHERN IL. 00Z GUIDANCE TAKES THE LOW NORTHEAST TO NEAR PONTIAC IL
BY 18Z...AND NEAR THE SOUTH SHORE OF LAKE MICHIGAN AND INTO
SOUTHWEST LOWER MICHIGAN BY 00Z. CURRENT PRECIP SHIELD ACROSS THE
CWA IS NEARLY ALL RAIN...SAVE FOR A LITTLE RAIN/SNOW/SLEET MIX
REPORTED EARLIER OVER ROCKFORD AND AREAS NORTH/WEST OF THERE.
RAIN/SNOW LINE CONTINUES TO WORK SLOWLY NORTHWEST...SO SHOULD BE ALL
RAIN THERE NOW. BAND OF HEAVY SNOW...INCLUDING A CONSIDERABLE AMOUNT
OF LIGHTNING...HAS BEEN OCCURRING FROM SOUTHWESTERN IA INTO
SOUTHWEST/CENTRAL WI.
WFO LOT CWA WILL INITIALLY REMAIN IN WARM SECTOR OF THE STORM
THROUGH THIS MORNING...AS WARM FRONT CURRENTLY LIFTING THROUGH
CENTRAL IL AHEAD OF THE LOW CONTINUES NORTH ACROSS ALL EXCEPT THE
FAR NORTHWEST PART OF THE CWA THIS MORNING. MODELS IN GOOD AGREEMENT
IN SPREADING STEEP MID-LEVEL LAPSE RATES OF 7-7.5 C/KM ACROSS
ESPECIALLY SOUTHEASTERN PARTS OF THE CWA THROUGH THE MORNING/EARLY
AFTERNOON HOURS...WITH SOME SFC/NEAR SFC BASED CAPE NOTED IN
FORECAST SOUNDINGS ACROSS OUR FAR SOUTHEAST AHEAD OF THE SURFACE
LOW/OCCLUDED FRONT WHICH APPROACHES DURING THE LATE MORNING AND
EARLY AFTERNOON HOURS. HAVE INCLUDED A MENTION OF LIKELY THUNDER
ACROSS THE SOUTHEAST TIER OF COUNTIES FOR THIS...AND NOTE THAT WITH
THE INCREASING SOUTHWESTERLY WIND FIELD SPC HAS INCLUDED OUR
SOUTHERN CWA BOUNDARY AREA IN THE 5 PERCENT CONVECTIVE WIND THREAT
IN THE DAY 1 OUTLOOK. PRECIPITATING MAY THEN BECOME MORE SHOWERY IN
NATURE BRIEFLY ACROSS OUR SOUTH/SOUTHEAST THIS AFTERNOON AS NORTHERN
PERIPHERY OF DRY SLOT TRANSLATES EAST-NORTHEAST ACROSS THAT AREA.
PRECIP SHOULD REMAIN ALL RAIN THROUGH MID-DAY...BEFORE PASSAGE OF
STACKED CLOSED UPPER LOW/SURFACE LOW DURING THE MID-DAY/AFTERNOON
HOURS ALLOWS THICKNESS VALUES TO DECREASE RAPIDLY FROM THE WEST AS
COLDER AIR WRAPS AROUND THE WESTERN SIDE OF THE CYCLONE. GUIDANCE
REASONABLY SIMILAR IN DEPICTING A LIKELY CHANGE FROM RAIN TO SNOW
BEGINNING SHORTLY AFTER NOON IN THE WEST...INTO THE FAR WESTERN
REACHES OF THE CHICAGO METRO AROUND 3 PM...WITH MOST OF THE
REMAINING PORTION OF NORTHEAST IL ALL SNOW BY ABOUT 6 PM. NORTHWEST
INDIANA WILL BE LAST TO CHANGE OVER TO ALL SNOW...BUT SHOULD BE
COMPLETE BY 7-8 PM. THE STRONGEST DEFORMATION FORCING SHOULD LARGELY
AFFECT THE NORTHWEST THIRD OR SO OF THE CWA...WHERE THE STRONGEST
PERSISTENT MID-LEVEL FRONTOGENETIC FORCING IS PROGGED. THIS SUGGESTS
THAT THE GREATEST POTENTIAL FOR A PERIOD OF HEAVY SNOW DURING THE
AFTERNOON AND EARLY EVENING HOURS ESPECIALLY NORTHWEST OF A MENDOTA
TO ANTIOCH LINE. SNOWFALL AMOUNTS IN THE 6-9 INCH RANGE APPEAR
REASONABLE ACROSS PARTS OF NORTH CENTRAL IL WITH THE BEST POTENTIAL
FOR LONGER DURATION MODERATE/HEAVY SNOW WITH THE DEFORMATION BAND.
LESSER AMOUNTS ARE EXPECTED FARTHER SOUTHEAST...ROUGHLY 3-7 INCHES
FROM LASALLE INTO LAKE COUNTY IL AND CONTINUING TO TAPER OFF FARTHER
SOUTHEAST. HOWEVER...THE PRESENCE OF STEEP LAPSE RATES ALOFT EVEN
FARTHER SOUTH COULD RESULT IN SMALL SCALE BANDING OF LOCALLY INTENSE
SNOW WHICH MAKES AMOUNT FORECAST DIFFICULT.
THE BIGGEST CONCERN IN ALL OF THIS IS OF COURSE TIED TO THE VERY
STRONG WIND FIELD EXPECTED IN ASSOCIATION WITH THE DEEP LOW
PRESSURE. THE COMBINATION OF A VERY STRONG ISALLOBARIC GRADIENT AND
STEEP LOW LEVEL LAPSE RATES WITH INCREASING COLD ADVECTION THIS
AFTERNOON AND EVENING WILL RESULT IN VERY STRONG WINDS...BECOMING
NORTHWEST AT 30-40 MPH AND LIKELY GUSTING TO 50-60 MPH. EVEN WITH
RELATIVELY LITTLE SNOW ACCUMULATION...THE COMBINATION OF FALLING
SNOW AND SUCH STRONG WINDS WILL LIKELY CAUSE AT LEAST BRIEF PERIODS
OF VERY TREACHEROUS TRAVEL CONDITIONS LATER THIS AFTERNOON AND
EVENING. CONSIDERING ALL OF THESE...FEEL THAT LOCATIONS WHICH HAVE
THE POTENTIAL FOR A PERIOD OF HEAVY SNOW AND SOLID ACCUMULATION THAT
AN UPGRADE TO BLIZZARD WARNING WAS WARRANTED...AND THAT AN UPGRADE
TO WINTER STORM WARNING EVEN FOR AREAS WHICH MAY ONLY SEE 2-5 INCHES
OF SNOW IS PRUDENT. FAR SOUTH...WHERE SNOW ACCUMULATION IS EXPECTED
TO BE SIGNIFICANTLY LOWER...HAVE UPGRADED THE HIGH WIND WATCH TO A
HIGH WIND WARNING...WITH 50+ KT WIND GUSTS EXPECTED. THE POTENTIAL
FOR MINOR WIND DAMAGE DOES EXIST WITH THESE WINDS...IN ADDITION TO
THE POTENTIAL ISSUES WITH BLOWING/DRIFTING SNOW AND VISIBILITY
IMPACTS FOR THE NORTHERN/NORTHWESTERN PARTS OF THE CWA. HAVE ALSO
MAINTAINED THE LAKESHORE FLOOD WARNING FOR LAKE/PORTER COUNTIES FROM
LATE TONIGHT INTO EARLY SATURDAY MORNING FOR LARGE WAVES ALONG THE
LAKE MICHIGAN SHORE.
SNOW SHOULD TAPER FROM WEST TO EAST DURING THE MID/LATE EVENING
HOURS...WITH OVERALL FORCING WEAKENING AS SYSTEM BECOMES MORE
OCCLUDED AND DRIFTS OFF TO THE EAST. PARTS OF NORTHWEST INDIANA
INCLUDING PORTER COUNTY MAY SEE A LITTLE LAKE-ENHANCEMENT OF SNOW
DURING THE EVENING...BEFORE THE CONVERGENT FOCUS SHIFTS TO THE EAST
AS WINDS CONTINUE TO BACK MORE NORTHWEST.
RATZER
REMAINDER OF FORECAST FRIDAY THROUGH SUNDAY...
TAIL END OF WRAP AROUND SNOW AND LAKE EFFECT MAY STILL BE ONGOING
IN PORTER COUNTY EARLY FRIDAY MORNING BUT ALL PRECIP SHOULD BE
DONE BY MID MORNING. SKIES WILL BE CLEARING WEST TO EAST IN THE
MORNING. CORE OF COLDEST AIR WILL BE OVER THE AREA FRIDAY
MORNING...AND MIN TEMPERATURES MAY OCCUR A COUPLE HOURS AFTER
SUNRISE FRIDAY MORNING. WITH FRESH SNOW COVER ON THE
GROUND...LOWEST POSSIBLE SUN ANGLE OF THE YEAR...AND COLD AIR IN
PLACE...WONT SEE MUCH RECOVERY IN TEMPERATURES THROUGH THE DAY.
UNLESS ITS STILL 32 AT MIDNIGHT...FRIDAY MIGHT BE THE FIRST DAY
THIS SEASON WITH THE MAX TEMPERATURE BELOW FREEZING. WINDS WILL
LIKELY STILL BE GUSTING AROUND 40 MPH THROUGH THE MORNING HOURS
BUT WINDS WILL GRADUALLY SUBSIDE THROUGH THE AFTERNOON. DONT WANT
TO COMPLICATE HEADLINE PICTURE ANY MORE THAN NECESSARY AT THIS
TIME...BUT LATER SHIFTS MAY NEED TO CONSIDER A WIND ADVISORY AFTER
THE WINTER HEADLINES DROP INTO FRIDAY MORNING.
FRIDAY NIGHT STRONG UPPER RIDGING OCCURS AND LOW LEVEL WAA BEGINS.
HOWEVER WITH FRESH SNOW COVER...DIMINISHING WINDS...AND SURFACE
RIDGE AXIS MOVING INTO IL BY SATURDAY MORNING...EXPECT ATMOSPHERE TO
DECOUPLE AND VERY STRONG LOW LEVEL INVERSION TO DEVELOP. LOW TEMPS
IN THE SINGLE DIGITS NORTHWEST WHERE DEEPEST SNOW PACK WILL
EXIST...AND TEENS IN DOWNTOWN CHICAGO AND AREAS SOUTH AND EAST OF
CHICAGO.
WAVE COMES ACROSS CENTRAL CANADA OVER THE TOP OF THE RIDGE FRIDAY
NIGHT AND SATURDAY...AND DIVES ACROSS THE GREAT LAKES SATURDAY NIGHT
AND SUNDAY...PUSHING A WEAK BACK DOOR COLD FRONT DOWN THE LAKES.
SURFACE WINDS WILL TURN NORTHEAST SUNDAY BUT NOT MUCH CHANGE IN
TEMPERATURE. CONFIDENCE HIGH
MONDAY THROUGH WEDNESDAY
AFTER MONDAY THERE ARE A LOT OF MODEL INCONSISTENCIES AND LOW
FORECAST CONFIDENCE THIS FAR OUT. 00Z RUN OF THE ECMWF QUITE A BIT
MORE AGGRESSIVE WITH WAVE COMING THROUGH LATE MONDAY INTO CHRISTMAS
MORNING THAN GFS/GEM. ECMWF WOULD SUGGEST AN AREA OF POSSIBLY 1-3
SNOW. WILL JUST MAINTAIN CHANCE POPS FOR NOW. ECMWF THEN TAKES THE
FOLLOWING SYSTEM MUCH FURTHER SOUTH WEDNESDAY. AGAIN WILL NOT MAKE
SIGNIFICANT CHANCES AT THIS TIME AND KEEP CHANCE POPS. BOTH EVENTS
SHOULD BE ALL SNOW...ALTHOUGH SOME MIXED PRECIP POSSIBLE FAR
SOUTHEAST TOWARD WATSEKA-FOWLER MONDAY.
ALLSOPP
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 20Z...
* IFR CIGS THROUGH AT LEAST MIDNIGHT.
* SW WINDS SHIFT TO N EARLY THIS EVENING WITH GUSTS ARND 45 KT
STILL EXPECTED THIS EVENING.
* RAIN QUICKLY CHANGING OVER TO SNOW ARND 23Z. HEAVY SNOW PSBL FOR
A FEW HOURS AFTER INITIAL CHANGE OVER TO ALL SNOW...WITH LOWER
VSBY EXPECTED THROUGH TONIGHT WITH BLOWING SNOW.
JEE
//DISCUSSION...UPDATED 20Z...
WITH THE LOW TRACKING RIGHT OVER THE EASTERN TERMINALS...WINDS
HAVE BRIEFLY TURNED SW GUSTING TO ARND 25 KT. STILL EXPECTING
WINDS TO BECOME N AND GUST TO 45 KT THIS EVENING BEHIND THE LOW.
PRECIP HAS FINALLY BEGUN TO CHANGE OVER TO SNOW AT RFD. GIVEN THE
SLOWER TREND...PUSHED THE CHANGE FROM RAIN TO SNOW BACK BY AN HOUR
EVERYWHERE ELSE. HEAVY SNOW INITIALLY IS STILL A CONCERN...AS IS
LOWER VSBY. ALREADY GOT A REPORT OUT OF RFD OF HALF DOLLAR SIZE
SNOWFLAKES WITH SNOW ALREADY BEGINNING TO ACCUMULATE.
LASTLY...REMOVED MAJORITY OF LIFR CIGS AS CIGS ACROSS THE REGION
ARE IFR OR BETTER. WHILE IFR CIGS ARE EXPECTED...THEY COULD BE A
FEW HUNDRED FEET HIGHER THAN CURRENTLY FORECAST. NO CHANGES MADE TO THE
TAFS BEYOND 5Z.
PREVIOUS DISCUSSION...18Z...
THE LOW IS OVER MARSHALL COUNTY IL AND DEEPENING AS IT MOVES
NORTHEAST THROUGH IL. SHOWERS HAVE DEVELOPED ACROSS NORTHERN IL AS
WE ARE WITHIN THE WARM SECTOR OF THE LOW. RADAR REFLECTIVITIES
AND VISIBLE SATELLITE BOTH INDICATE THERE ARE SOME CONVECTIVE
AREAS. A FLASH OR TWO OF LIGHTNING HAS BEEN OBSERVED...AND
THINKING THE BEST AREA OF FORCING AND WEAK INSTABILITY IS OVER
WESTERN AND CENTRAL IL. THEREFORE THE ONLY TAF CARRYING TS IS RFD.
AS THE LOW SHIFTS OVER AND THEN EAST OF THE EASTERN
TERMINALS...EXPECTING WINDS TO SHIFT N AND IMMEDIATELY START
GUSTING. THINKING ARND 20Z...BUT IF LOW CONTINUES TO BE
SLOW...COULD BE LATER. TEMPS WILL FALL ON THE BACK SIDE OF THE LOW
WITH A QUICK TRANSITION TO SN EXPECTED. THINKING AN HOUR OR LESS
OF RASN. ALSO EXPECTING CIGS TO FALL RAPIDLY BEHIND THE LOW. SO
OVERALL HIGH CONFIDENCE IN TAF TRENDS...BUT MEDIUM CONFIDENCE ON
TIMING. GUIDANCE IS STILL INDICATING A FEW HOURS OF MODERATE TO
HEAVY SNOW RIGHT AFTER THE PRECIP TURNS TO ALL SNOW. KEPT 1/2 SM
VSBY FOR THAT PERIOD IN THE EASTERN TERMINALS AND WENT WITH 1/4 SM
AT RFD. COULD SEE 1/4 SM AT THE EASTERN TERMINALS...BUT CONFIDENCE
IS NOT HIGH ENOUGH TO GO WITH 1/4 SM AT THIS TIME. THE INITIAL WET
SNOW WILL BECOME AN AVERAGE SNOW WITHIN AN HOUR OR TWO.
ATTENTION THEN TURNS TO THE WINDS. GUSTY WINDS ARND 45 KT STILL
VERY LIKELY THROUGH MIDNIGHT. SO WHILE SNOWFALL RATES WILL
DIMINISH BY 2-3Z...BLOWING SNOW WILL CONTINUE TO REDUCE VSBYS
THROUGH THE MORNING. EXPECTING SNOW TO TAPER OF TO FLURRIES
SHORTLY AFTER MIDNIGHT.
GUSTY NW WINDS CONTINUE ON FRIDAY...BUT CIGS SHOULD BE RISING TO
VFR FROM W TO E BEGINNING MID FRIDAY MORNING.
JEE
//ORD AND MDW CONFIDENCE...UPDATED 20Z...
* HIGH CONFIDENCE IN TAF TRENDS...CONDITIONS DETERIORATING THROUGH
THIS EVENING.
* MEDIUM CONFIDENCE IN CIG HEIGHTS TONIGHT.
* HIGH CONFIDENCE IN SN...MEDIUM CONFIDENCE IN TIMING AND VSBY.
* HIGH CONFIDENCE IN WIND TRENDS...MEDIUM CONFIDENCE IN TIMING.
* HIGH CONFIDENCE IN CIGS IMPROVING TOMORROW...MEDIUM CONFIDENCE
IN TIMING.
JEE
//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...
* FRIDAY NIGHT THROUGH SUNDAY..DRY. VFR.
* MONDAY AND TUESDAY...SLIGHT CHANCE OF SNOW. MVFR POSSIBLE.
* WEDNESDAY...CHANCE OF SNOW. MVFR LIKELY.
&&
.MARINE...
207 PM...MINIMAL ADJUSTMENTS TO CURRENT FORECAST...AND HEADLINES
WILL REMAIN IN PLACE. STORM WARNING WILL REMAIN IN PLACE FOR LATE
THIS AFTERNOON THROUGH FRIDAY AFTERNOON. STORM FORCE CONDITIONS
WILL BEGIN ACROSS THE SOUTHERN HALF OF LAKE MICHIGAN FIRST...THEN
COVER ALL OF LAKE MICHIGAN LATER THIS EVENING.
THE SURFACE LOW PRESSURE THIS AFTERNOON WAS APPROACHING
CHICAGO...AND BASED ON GUIDANCE WILL SLIDE EAST/NORTHEAST ACROSS THE
SOUTHERN TIP OF LAKE MICHIGAN. AS THIS LOW SLIDES EAST THE WINDS
WILL DIMINISH...HOWEVER ALONG THE BACKSIDE OF THE LOW PRESSURE
SYSTEM WINDS WILL RAPIDLY INCREASE TO STORM FORCE GUSTS TO 55 KT BY
TONIGHT FROM THE NORTH/NORTHWEST. AT THIS TIME IT REMAINS POSSIBLE
FOR AN OCCASIONAL GUST TO 60-65 KT...HOWEVER CONFIDENCE REMAINS LOW.
THE TIGHTEST WIND GRADIENT THAT COULD PRODUCE THIS TYPE OF GUST
WOULD BE LATE THIS EVENING THROUGH EARLY FRIDAY MORNING.
THE LOW WILL MOVE EAST AND MERGE WITH ANOTHER LOW MOVING UP THE EAST
COAST SATURDAY. THE COMBINED LOW WILL SLOW AND AND AS HIGH PRESSURE
BUILDS ACROSS THE PLAINS...THE GRADIENT WILL REMAIN STRONG INTO
FRIDAY NIGHT AND FINALLY RELAX SATURDAY. THEN WITH HIGH PRESSURE
SLIDING ACROSS THE OHIO VALLEY FOR THE WEEKEND...WINDS WILL
DIMINISH. THE NEXT SYSTEM APPEARS TO SLIDE ACROSS THE MISSOURI
VALLEY MONDAY ARRIVING ACROSS THE CENTRAL GREAT LAKES MONDAY
NIGHT/CHRISTMAS DAY.
CONFIDENCE IN THE STORM FORCE GUSTS...HIGH.
CONFIDENCE IN THE SYSTEM EARLY NEXT WEEK...MEDIUM.
BEACHLER
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...BLIZZARD WARNING...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019
UNTIL MIDNIGHT FRIDAY.
WINTER STORM WARNING...ILZ006-ILZ012-ILZ013-ILZ014-ILZ020-ILZ021-
ILZ022 UNTIL 3 AM FRIDAY.
WINTER STORM WARNING...ILZ005 UNTIL MIDNIGHT FRIDAY.
HIGH WIND WARNING...ILZ023-ILZ032-ILZ033-ILZ039 UNTIL MIDNIGHT
FRIDAY.
IN...LAKESHORE FLOOD WARNING...INZ001-INZ002...MIDNIGHT FRIDAY TO 3
AM SATURDAY.
WINTER STORM WARNING...INZ001-INZ002 UNTIL 3 AM FRIDAY.
HIGH WIND WARNING...INZ010-INZ011-INZ019 UNTIL MIDNIGHT FRIDAY.
LM...GALE WARNING...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-
LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-
LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 4 PM THURSDAY.
STORM WARNING...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-
LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-
LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 4 PM FRIDAY.
GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565 UNTIL 6
PM THURSDAY.
STORM WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565...6 PM
THURSDAY TO 4 PM FRIDAY.
&&
$$
AREA FORECAST DISCUSSION
NWS CHICAGO/ROMEOVILLE IL
1204 PM CST THU DEC 20 2012
.MESOSCALE DISCUSSION...
1040 AM CST
THE IMPRESSIVELY STRONG WINTER SYSTEM IS FOR THE MOST PART
UNFOLDING SO FAR AS TO PLAN...WITH NO IMMINENT CHANGES PLANNED TO
HEADLINES...TIMING...OR FORECAST SNOWFALL AMOUNTS.
THE MORNING SATELLITE AND HAND UPPER AIR AND SURFACE ANALYSES
REVEAL A CLASSIC MID-LATITUDE CYCLONE. THE CLOSED UPPER LOW IS
SWINGING NEGATIVELY TITLED LATE THIS MORNING...WITH A DRY SLOT
HAVING ENVELOPED THE SOUTHEAST TWO-THIRDS OF THE FORECAST
AREA...INCLUDING CHICAGO. ARCS OF SHOWERS...WITH A CONVECTIVE-LIKE
APPEARANCE ON RADAR...CONTINUE TO DEVELOP WITHIN THIS DRY SLOT ACROSS
WEST CENTRAL TO CENTRAL IL AND PROPAGATE NORTHWARD INTO THE COOL
SECTOR. THESE HAVE BEEN MOVING INTO A WELL ESTABLISHED HEAVY SNOW
BAND...NOW CENTERED NEAR THE MISSISSIPPI RIVER INTO
SOUTHWEST/SOUTH CENTRAL WI. THIS LINES UP PERFECTLY WITH A
SYNOPTICALLY FAVORED AREA IN THIS STORM SYSTEM FOR THE MOST
INTENSE DYNAMICS...TIGHTEST THERMAL GRADIENT...AND WIND AND
MOISTURE CONVERGENCE. IN ADDITION...THE RAP CONTINUES TO ANALYZE
DEEP LIFT BEING CROSS-HAIRED WITHIN THE DENDRITIC GROWTH
ZONE...OWING TO MORE EFFICIENT SNOW PRODUCTION IN THIS AREA...AND
ESPECIALLY WHEN CONSIDERING PWATS ARE NEAR 0.70 AND INFLOW MIXING
RATIOS ARE 3.5-5.0 G/KG. VISIBILITIES UNDERNEATH THIS SNOW
BAND HAVE REGULARLY BEEN UNDER ONE HALF MILE...AND A ONE INCH PER
HOUR RATE WAS ALREADY OBSERVED IN ROCK ISLAND IL. THE SURFACE LOW
IS CENTERED NEAR LACON AND MOVING NORTHEAST WITH THE PRESSURE
FALL/RISE COUPLET MAGNITUDE AT 7MB/9MB RESPECTIVELY.
SHOWER AND THUNDER POTENTIAL EAST... WHILE THE DRY SLOT HAS
MINIMIZED MUCH OF THE AREAL COVERAGE OF MODERATE TO HEAVY RAIN
SEEN EARLIER THIS MORNING...SCATTERED CONVECTIVE ECHOES ARE
DEVELOPING ALONG AN IMMEDIATE PRE-FRONTAL TROUGH ACROSS EAST
CENTRAL IL. THE PRE-FRONTAL AIR MASS HAS SURFACE DEW POINTS OF 45
TO EVEN THE LOWER 50S AS FAR NORTH AS NORTHWEST/WEST CENTRAL IN.
WHILE NO LOW-LEVEL CAPE IS ANALYZED BY DIAGNOSTIC GUIDANCE AS OF
10 AM...ADAPTED FORECAST SOUNDINGS WITH 54F/50F DO PRODUCE AROUND
50 J/KG OF 0-3 KM CAPE THROUGH 20Z. WITH THE DYNAMIC WIND
FIELD...THERE MAY BE A BRIEF WINDOW OF GUSTY WIND POTENTIAL WITH
THIS ACROSS NORTHWEST IN...THOUGH NO EXPLICIT CONVECTIVE MODELS
THAT WERE LOOKED AT PRODUCE ANYTHING LOOKING OVERLY OMINOUS.
ACROSS CHICAGO...PERIODS OF LIGHT TO MODERATE SHOWERS SHOULD
PREVAIL THROUGH MUCH OF THE DAY WITHIN THE LOW-LEVEL MOISTURE
TRANSPORT UNDER DEEP HEIGHT FALLS/DIFFLUENCE OWING TO ASCENT.
RAIN TO SNOW TIMING...VARIOUS THICKNESS AND WET BULB ANALYSIS
TECHNIQUES ON THE RAP FOR PRECIP TYPE CHANGE LINE UP VERY WELL
WITH THE OBSERVED CHANGE OVER...AND THESE ARE ALL FORECAST TO
CREEP EASTWARD AS THE SURFACE WINDS TURN MORE NNW LOWERING
BOUNDARY LAYER TEMPERATURES. THERE HAS BEEN A REPORT OF SNOW
MIXING IN JUST NORTHWEST OF ROCKFORD AND WITH CONTINUED DYNAMIC
AND ADVECTIVE COOLING IT SHOULD REACH ROCKFORD SOON. THE CHANGE
OVER LINE SHOULD BE NORTH-TO-SOUTH ORIENTED AROUND NOON AND
LIKELY SWING NORTHWEST TO SOUTHEAST ORIENTED BY LATE AFTERNOON AS
IT APPROACHES CHICAGO. THE CHANGE SHOULD ALSO PICK UP IN
PROGRESSION SPEED IN THE WAKE OF THE SURFACE LOW AND UNDERNEATH
THE RAPID COOLING OF THE UPPER LOW.
SNOWFALL AND WIND...WITH CURRENT RADAR AND SATELLITE TRENDS AND
THE PROJECTED PATH OF THE LOW AND ASSOCIATED DEFORMATION...THE
MOST INTENSE SNOWFALL AREA/BANDS WITH RATES OF ONE INCH OR GREATER
PER HOUR SHOULD SLOWLY WORK EASTWARD NORTH OF I-80 THROUGH THE
AFTERNOON. SHORT TERM MODEL FORECASTS OF PRECIP AND VISIBILITY
AGREE WITH THIS EVOLUTION. RATES OF TWO INCHES PER HOUR ARE
POSSIBLE TOWARD ROCKFORD/BELVIDERE/DIXON GIVEN SOME OF THE 40 PLUS
DBZ /NOT ASSOCIATED WITH BRIGHT BANDING/ SEEN ALREADY AND PER THE
FORECAST INSTABILITY...BOTH SLANTWISE AND EVEN UPRIGHT IN FORECAST
SOUNDINGS/CROSS SECTIONS. WINDS HAVE BEEN GUSTING IN EXCESS OF 40
KT ACROSS MUCH OF IA AND MO AND WITH THE DEEPENING OF THE SYSTEM
AND CONTINUED STRENGTHENING COLD AIR ADVECTION...THESE TYPES OF
GUSTS WILL ONLY INCREASE AS THEY ROTATE EAST INTO THE AREA WHICH
MATCHES WELL WITH THE 50-60 MPH WINDS SEEN IN THE BOUNDARY LAYER
OF NAM AND GFS AND SURPRISING EVEN THE RAP. WILL HAVE TO WATCH TO
SEE IF THE BLIZZARD WARNING WILL NEED TO BE EXPANDED SOUTH OR
EAST...TO INCLUDE COUNTIES SUCH AS DEKALB AND LASALLE. ALSO WITH
AS FAR SOUTH AS SNOW HAS BEEN OBSERVED TO THE WEST AND THE EXTENT
OF THE TROWAL...THERE IS NO DOUBT IT WILL SNOW IN THE HIGH WIND
WARNING AREA OF THE SOUTHERN CWA. IT IS JUST UNCERTAIN ON HOW
INTENSE IT WILL BE. WILL CONTINUE TO MENTION BLOWING SNOW AS A
SECONDARY IMPACT IN THE NPW.
MTF
&&
.DISCUSSION...
344 AM CST
WINTER STORM TODAY/TONIGHT...
HAVE UPGRADED WATCHES/WARNINGS TO INCLUDE A BLIZZARD WARNING FOR A
PORTION OF NORTH CENTRAL IL...A WINTER STORM WARNING FOR NORTHEAST
IL/NORTHWEST INDIANA NORTH OF ABOUT A STREATOR-KANKAKEE-DE MOTTE
LINE...AND A HIGH WIND WARNING FOR AREAS SOUTH OF THAT SAME LINE.
INTENSE WINTER STORM SYSTEM TAKING AIM AT THE AREA FOR LATER TODAY
AND TONIGHT. AT 08Z...SURFACE ANALYSIS DEPICTED 992 MB LOW OVER
CENTRAL MISSOURI WITH 6 MB/3 HR PRESSURE FALLS SPREADING ACROSS
NORTHERN IL. 00Z GUIDANCE TAKES THE LOW NORTHEAST TO NEAR PONTIAC IL
BY 18Z...AND NEAR THE SOUTH SHORE OF LAKE MICHIGAN AND INTO
SOUTHWEST LOWER MICHIGAN BY 00Z. CURRENT PRECIP SHIELD ACROSS THE
CWA IS NEARLY ALL RAIN...SAVE FOR A LITTLE RAIN/SNOW/SLEET MIX
REPORTED EARLIER OVER ROCKFORD AND AREAS NORTH/WEST OF THERE.
RAIN/SNOW LINE CONTINUES TO WORK SLOWLY NORTHWEST...SO SHOULD BE ALL
RAIN THERE NOW. BAND OF HEAVY SNOW...INCLUDING A CONSIDERABLE AMOUNT
OF LIGHTNING...HAS BEEN OCCURRING FROM SOUTHWESTERN IA INTO
SOUTHWEST/CENTRAL WI.
WFO LOT CWA WILL INITIALLY REMAIN IN WARM SECTOR OF THE STORM
THROUGH THIS MORNING...AS WARM FRONT CURRENTLY LIFTING THROUGH
CENTRAL IL AHEAD OF THE LOW CONTINUES NORTH ACROSS ALL EXCEPT THE
FAR NORTHWEST PART OF THE CWA THIS MORNING. MODELS IN GOOD AGREEMENT
IN SPREADING STEEP MID-LEVEL LAPSE RATES OF 7-7.5 C/KM ACROSS
ESPECIALLY SOUTHEASTERN PARTS OF THE CWA THROUGH THE MORNING/EARLY
AFTERNOON HOURS...WITH SOME SFC/NEAR SFC BASED CAPE NOTED IN
FORECAST SOUNDINGS ACROSS OUR FAR SOUTHEAST AHEAD OF THE SURFACE
LOW/OCCLUDED FRONT WHICH APPROACHES DURING THE LATE MORNING AND
EARLY AFTERNOON HOURS. HAVE INCLUDED A MENTION OF LIKELY THUNDER
ACROSS THE SOUTHEAST TIER OF COUNTIES FOR THIS...AND NOTE THAT WITH
THE INCREASING SOUTHWESTERLY WIND FIELD SPC HAS INCLUDED OUR
SOUTHERN CWA BOUNDARY AREA IN THE 5 PERCENT CONVECTIVE WIND THREAT
IN THE DAY 1 OUTLOOK. PRECIPITATING MAY THEN BECOME MORE SHOWERY IN
NATURE BRIEFLY ACROSS OUR SOUTH/SOUTHEAST THIS AFTERNOON AS NORTHERN
PERIPHERY OF DRY SLOT TRANSLATES EAST-NORTHEAST ACROSS THAT AREA.
PRECIP SHOULD REMAIN ALL RAIN THROUGH MID-DAY...BEFORE PASSAGE OF
STACKED CLOSED UPPER LOW/SURFACE LOW DURING THE MID-DAY/AFTERNOON
HOURS ALLOWS THICKNESS VALUES TO DECREASE RAPIDLY FROM THE WEST AS
COLDER AIR WRAPS AROUND THE WESTERN SIDE OF THE CYCLONE. GUIDANCE
REASONABLY SIMILAR IN DEPICTING A LIKELY CHANGE FROM RAIN TO SNOW
BEGINNING SHORTLY AFTER NOON IN THE WEST...INTO THE FAR WESTERN
REACHES OF THE CHICAGO METRO AROUND 3 PM...WITH MOST OF THE
REMAINING PORTION OF NORTHEAST IL ALL SNOW BY ABOUT 6 PM. NORTHWEST
INDIANA WILL BE LAST TO CHANGE OVER TO ALL SNOW...BUT SHOULD BE
COMPLETE BY 7-8 PM. THE STRONGEST DEFORMATION FORCING SHOULD LARGELY
AFFECT THE NORTHWEST THIRD OR SO OF THE CWA...WHERE THE STRONGEST
PERSISTENT MID-LEVEL FRONTOGENETIC FORCING IS PROGGED. THIS SUGGESTS
THAT THE GREATEST POTENTIAL FOR A PERIOD OF HEAVY SNOW DURING THE
AFTERNOON AND EARLY EVENING HOURS ESPECIALLY NORTHWEST OF A MENDOTA
TO ANTIOCH LINE. SNOWFALL AMOUNTS IN THE 6-9 INCH RANGE APPEAR
REASONABLE ACROSS PARTS OF NORTH CENTRAL IL WITH THE BEST POTENTIAL
FOR LONGER DURATION MODERATE/HEAVY SNOW WITH THE DEFORMATION BAND.
LESSER AMOUNTS ARE EXPECTED FARTHER SOUTHEAST...ROUGHLY 3-7 INCHES
FROM LASALLE INTO LAKE COUNTY IL AND CONTINUING TO TAPER OFF FARTHER
SOUTHEAST. HOWEVER...THE PRESENCE OF STEEP LAPSE RATES ALOFT EVEN
FARTHER SOUTH COULD RESULT IN SMALL SCALE BANDING OF LOCALLY INTENSE
SNOW WHICH MAKES AMOUNT FORECAST DIFFICULT.
THE BIGGEST CONCERN IN ALL OF THIS IS OF COURSE TIED TO THE VERY
STRONG WIND FIELD EXPECTED IN ASSOCIATION WITH THE DEEP LOW
PRESSURE. THE COMBINATION OF A VERY STRONG ISALLOBARIC GRADIENT AND
STEEP LOW LEVEL LAPSE RATES WITH INCREASING COLD ADVECTION THIS
AFTERNOON AND EVENING WILL RESULT IN VERY STRONG WINDS...BECOMING
NORTHWEST AT 30-40 MPH AND LIKELY GUSTING TO 50-60 MPH. EVEN WITH
RELATIVELY LITTLE SNOW ACCUMULATION...THE COMBINATION OF FALLING
SNOW AND SUCH STRONG WINDS WILL LIKELY CAUSE AT LEAST BRIEF PERIODS
OF VERY TREACHEROUS TRAVEL CONDITIONS LATER THIS AFTERNOON AND
EVENING. CONSIDERING ALL OF THESE...FEEL THAT LOCATIONS WHICH HAVE
THE POTENTIAL FOR A PERIOD OF HEAVY SNOW AND SOLID ACCUMULATION THAT
AN UPGRADE TO BLIZZARD WARNING WAS WARRANTED...AND THAT AN UPGRADE
TO WINTER STORM WARNING EVEN FOR AREAS WHICH MAY ONLY SEE 2-5 INCHES
OF SNOW IS PRUDENT. FAR SOUTH...WHERE SNOW ACCUMULATION IS EXPECTED
TO BE SIGNIFICANTLY LOWER...HAVE UPGRADED THE HIGH WIND WATCH TO A
HIGH WIND WARNING...WITH 50+ KT WIND GUSTS EXPECTED. THE POTENTIAL
FOR MINOR WIND DAMAGE DOES EXIST WITH THESE WINDS...IN ADDITION TO
THE POTENTIAL ISSUES WITH BLOWING/DRIFTING SNOW AND VISIBILITY
IMPACTS FOR THE NORTHERN/NORTHWESTERN PARTS OF THE CWA. HAVE ALSO
MAINTAINED THE LAKESHORE FLOOD WARNING FOR LAKE/PORTER COUNTIES FROM
LATE TONIGHT INTO EARLY SATURDAY MORNING FOR LARGE WAVES ALONG THE
LAKE MICHIGAN SHORE.
SNOW SHOULD TAPER FROM WEST TO EAST DURING THE MID/LATE EVENING
HOURS...WITH OVERALL FORCING WEAKENING AS SYSTEM BECOMES MORE
OCCLUDED AND DRIFTS OFF TO THE EAST. PARTS OF NORTHWEST INDIANA
INCLUDING PORTER COUNTY MAY SEE A LITTLE LAKE-ENHANCEMENT OF SNOW
DURING THE EVENING...BEFORE THE CONVERGENT FOCUS SHIFTS TO THE EAST
AS WINDS CONTINUE TO BACK MORE NORTHWEST.
RATZER
REMAINDER OF FORECAST FRIDAY THROUGH SUNDAY...
TAIL END OF WRAP AROUND SNOW AND LAKE EFFECT MAY STILL BE ONGOING
IN PORTER COUNTY EARLY FRIDAY MORNING BUT ALL PRECIP SHOULD BE
DONE BY MID MORNING. SKIES WILL BE CLEARING WEST TO EAST IN THE
MORNING. CORE OF COLDEST AIR WILL BE OVER THE AREA FRIDAY
MORNING...AND MIN TEMPERATURES MAY OCCUR A COUPLE HOURS AFTER
SUNRISE FRIDAY MORNING. WITH FRESH SNOW COVER ON THE
GROUND...LOWEST POSSIBLE SUN ANGLE OF THE YEAR...AND COLD AIR IN
PLACE...WONT SEE MUCH RECOVERY IN TEMPERATURES THROUGH THE DAY.
UNLESS ITS STILL 32 AT MIDNIGHT...FRIDAY MIGHT BE THE FIRST DAY
THIS SEASON WITH THE MAX TEMPERATURE BELOW FREEZING. WINDS WILL
LIKELY STILL BE GUSTING AROUND 40 MPH THROUGH THE MORNING HOURS
BUT WINDS WILL GRADUALLY SUBSIDE THROUGH THE AFTERNOON. DONT WANT
TO COMPLICATE HEADLINE PICTURE ANY MORE THAN NECESSARY AT THIS
TIME...BUT LATER SHIFTS MAY NEED TO CONSIDER A WIND ADVISORY AFTER
THE WINTER HEADLINES DROP INTO FRIDAY MORNING.
FRIDAY NIGHT STRONG UPPER RIDGING OCCURS AND LOW LEVEL WAA BEGINS.
HOWEVER WITH FRESH SNOW COVER...DIMINISHING WINDS...AND SURFACE
RIDGE AXIS MOVING INTO IL BY SATURDAY MORNING...EXPECT ATMOSPHERE TO
DECOUPLE AND VERY STRONG LOW LEVEL INVERSION TO DEVELOP. LOW TEMPS
IN THE SINGLE DIGITS NORTHWEST WHERE DEEPEST SNOW PACK WILL
EXIST...AND TEENS IN DOWNTOWN CHICAGO AND AREAS SOUTH AND EAST OF
CHICAGO.
WAVE COMES ACROSS CENTRAL CANADA OVER THE TOP OF THE RIDGE FRIDAY
NIGHT AND SATURDAY...AND DIVES ACROSS THE GREAT LAKES SATURDAY NIGHT
AND SUNDAY...PUSHING A WEAK BACK DOOR COLD FRONT DOWN THE LAKES.
SURFACE WINDS WILL TURN NORTHEAST SUNDAY BUT NOT MUCH CHANGE IN
TEMPERATURE. CONFIDENCE HIGH
MONDAY THROUGH WEDNESDAY
AFTER MONDAY THERE ARE A LOT OF MODEL INCONSISTENCIES AND LOW
FORECAST CONFIDENCE THIS FAR OUT. 00Z RUN OF THE ECMWF QUITE A BIT
MORE AGGRESSIVE WITH WAVE COMING THROUGH LATE MONDAY INTO CHRISTMAS
MORNING THAN GFS/GEM. ECMWF WOULD SUGGEST AN AREA OF POSSIBLY 1-3
SNOW. WILL JUST MAINTAIN CHANCE POPS FOR NOW. ECMWF THEN TAKES THE
FOLLOWING SYSTEM MUCH FURTHER SOUTH WEDNESDAY. AGAIN WILL NOT MAKE
SIGNIFICANT CHANCES AT THIS TIME AND KEEP CHANCE POPS. BOTH EVENTS
SHOULD BE ALL SNOW...ALTHOUGH SOME MIXED PRECIP POSSIBLE FAR
SOUTHEAST TOWARD WATSEKA-FOWLER MONDAY.
ALLSOPP
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 18Z...
* IFR CIGS LOWERING TO LIFR BY MID AFTN.
* WINDS SHIFT TO N THEN NW WITH GUSTS ARND 45 KT EXPECTED EARLY
THIS EVENING.
* RAIN QUICKLY CHANGING OVER TO SNOW ARND 22Z. HEAVY SNOW PSBL FOR
A FEW HOURS AFTER INITIAL CHANGE OVER TO ALL SNOW...WITH LOWER
VSBY EXPECTED THROUGH TONIGHT WITH BLOWING SNOW.
JEE
//DISCUSSION...UPDATED 18Z...
THE LOW IS OVER MARSHALL COUNTY IL AND DEEPENING AS IT MOVES
NORTHEAST THROUGH IL. SHOWERS HAVE DEVELOPED ACROSS NORTHERN IL AS
WE ARE WITHIN THE WARM SECTOR OF THE LOW. RADAR REFLECTIVITIES
AND VISIBLE SATELLITE BOTH INDICATE THERE ARE SOME CONVECTIVE
AREAS. A FLASH OR TWO OF LIGHTNING HAS BEEN OBSERVED...AND
THINKING THE BEST AREA OF FORCING AND WEAK INSTABILITY IS OVER
WESTERN AND CENTRAL IL. THEREFORE THE ONLY TAF CARRYING TS IS RFD.
AS THE LOW SHIFTS OVER AND THEN EAST OF THE EASTERN
TERMINALS...EXPECTING WINDS TO SHIFT N AND IMMEDIATELY START
GUSTING. THINKING ARND 20Z...BUT IF LOW CONTINUES TO BE
SLOW...COULD BE LATER. TEMPS WILL FALL ON THE BACK SIDE OF THE LOW
WITH A QUICK TRANSITION TO SN EXPECTED. THINKING AN HOUR OR LESS
OF RASN. ALSO EXPECTING CIGS TO FALL RAPIDLY BEHIND THE LOW. SO
OVERALL HIGH CONFIDENCE IN TAF TRENDS...BUT MEDIUM CONFIDENCE ON
TIMING. GUIDANCE IS STILL INDICATING A FEW HOURS OF MODERATE TO
HEAVY SNOW RIGHT AFTER THE PRECIP TURNS TO ALL SNOW. KEPT 1/2 SM
VSBY FOR THAT PERIOD IN THE EASTERN TERMINALS AND WENT WITH 1/4 SM
AT RFD. COULD SEE 1/4 SM AT THE EASTERN TERMINALS...BUT CONFIDENCE
IS NOT HIGH ENOUGH TO GO WITH 1/4 SM AT THIS TIME. THE INITIAL WET
SNOW WILL BECOME AN AVERAGE SNOW WITHIN AN HOUR OR TWO.
ATTENTION THEN TURNS TO THE WINDS. GUSTY WINDS ARND 45 KT STILL
VERY LIKELY THROUGH MIDNIGHT. SO WHILE SNOWFALL RATES WILL
DIMINISH BY 2-3Z...BLOWING SNOW WILL CONTINUE TO REDUCE VSBYS
THROUGH THE MORNING. EXPECTING SNOW TO TAPER OF TO FLURRIES
SHORTLY AFTER MIDNIGHT.
GUSTY NW WINDS CONTINUE ON FRIDAY...BUT CIGS SHOULD BE RISING TO
VFR FROM W TO E BEGINNING MID FRIDAY MORNING.
JEE
//ORD AND MDW CONFIDENCE...UPDATED 18Z...
* HIGH CONFIDENCE IN TAF TRENDS...CONDITIONS DETERIORATING THROUGH
THIS EVENING.
* HIGH CONFIDENCE IN SN...MEDIUM CONFIDENCE IN TIMING AND VSBY.
* HIGH CONFIDENCE IN WIND FCST...MEDIUM CONFIDENCE SHIFT TO N
WIND TIMING.
* HIGH CONFIDENCE IN CIGS IMPROVING TOMORROW...MEDIUM CONFIDENCE
IN TIMING.
* MEDIUM-LOW CONFIDENCE IN TIMING OF LIFR CIGS THIS AFTN.
JEE
//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...
* FRIDAY NIGHT THROUGH SUNDAY..DRY. VFR.
* MONDAY AND TUESDAY...SLIGHT CHANCE OF SNOW. MVFR POSSIBLE.
* WEDNESDAY...CHANCE OF SNOW. MVFR LIKELY.
&&
.MARINE...
407 AM...OVERALL NO MAJOR CHANGES THIS MORNING...OTHER THAN TO
DELAY STORM WARNING START TIME FOR A FEW HRS THIS AFTERNOON. LOW
PRESSURE NOW OVER MISSOURI WILL LIFT NORTHEAST TO NEAR THE
SOUTHERN TIP OF LAKE MICHIGAN BY LATE THIS AFTERNOON AS IT DEEPENS
AND THEN IT SHIFTS EAST INTO SOUTHERN LOWER MICHIGAN. GRADIENT
CONTINUES TO TIGHTEN NORTH OF THE LOW THIS MORNING WITH EASTERLY
GALES SPREADING NORTH. WIND DIRECTION AND SPEEDS BECOME A BIT
PROBLEMATIC OVER THE SOUTHERN THIRD OR QUARTER OF THE LAKE THIS
AFTERNOON DEPENDING ON THE EXACT TRACK OF THE LOW. WINDS WILL
LIKELY TURN NORTHEAST AND REMAIN FAIRLY STRONG ALONG THE WISCONSIN
SHORE AND EITHER TURN SOUTHERLY OR PERHAPS BECOME LIGHT/VARIABLE
ALONG THE SOUTHWEST MICHIGAN SHORE. THE LOW ALSO SLOWS JUST A BIT
AND THE LATEST GUIDANCE HAS THE LOW MOVING JUST A TAD FURTHER
WEST...PERHAPS RIGHT OVER CHICAGO. SO WHILE STORM FORCE WINDS ARE
STILL EXPECTED... THEY MIGHT NOT DEVELOP OVER THE NORTHERN TWO
THIRDS OF THE LAKE UNTIL JUST AFTER SUNSET...THEN QUICKLY SPREAD
ACROSS THE REST OF THE SOUTH END OF THE LAKE THIS EVENING...THUS
THE DELAY TO THE START TIME OF THE STORM WARNING BY A FEW HRS.
MAINTAINED THE HURRICANE GUST POTENTIAL AS THERE COULD BE SOME
GUSTS IN THE 60-65 KT RANGE BUT CONFIDENCE IS FAIRLY LOW. APPEARS
BEST TIMING FOR THE STRONGEST WINDS WOULD BE FROM LATE EVENING
THROUGH THE OVERNIGHT HRS. THE LOW WILL MOVE EAST AND MERGE WITH
ANOTHER LOW MOVING UP THE EAST COAST. THE COMBINED LOW WILL SLOW
AND AND AS HIGH PRESSURE BUILDS ACROSS THE PLAINS...THE GRADIENT
WILL REMAIN STRONG INTO FRIDAY NIGHT AND FINALLY RELAX SATURDAY.
CMS
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...BLIZZARD WARNING...ILZ003-ILZ004-ILZ008-ILZ010 UNTIL MIDNIGHT
FRIDAY.
WINTER STORM WARNING...ILZ006-ILZ012-ILZ013-ILZ014-ILZ020-ILZ021-
ILZ022...3 PM THURSDAY TO 3 AM FRIDAY.
WINTER STORM WARNING...ILZ005-ILZ011-ILZ019...3 PM THURSDAY TO
MIDNIGHT FRIDAY.
HIGH WIND WARNING...ILZ023-ILZ032-ILZ033-ILZ039...3 PM THURSDAY
TO MIDNIGHT FRIDAY.
IN...LAKESHORE FLOOD WARNING...INZ001-INZ002...MIDNIGHT FRIDAY TO 3
AM SATURDAY.
WINTER STORM WARNING...INZ001-INZ002...3 PM THURSDAY TO 3 AM
FRIDAY.
HIGH WIND WARNING...INZ010-INZ011-INZ019...3 PM THURSDAY TO
MIDNIGHT FRIDAY.
LM...GALE WARNING...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-
LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-
LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 4 PM THURSDAY.
STORM WARNING...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-
LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-
LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...4 PM THURSDAY TO 4 PM
FRIDAY.
GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565 UNTIL 6
PM THURSDAY.
STORM WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565...6 PM
THURSDAY TO 4 PM FRIDAY.
&&
$$
AREA FORECAST DISCUSSION...UPDATED
NWS CHICAGO/ROMEOVILLE IL
1047 AM CST THU DEC 20 2012
.MESOSCALE DISCUSSION...
1040 AM CST
THE IMPRESSIVELY STRONG WINTER SYSTEM IS FOR THE MOST PART
UNFOLDING SO FAR AS TO PLAN...WITH NO IMMINENT CHANGES PLANNED TO
HEADLINES...TIMING...OR FORECAST SNOWFALL AMOUNTS.
THE MORNING SATELLITE AND HAND UPPER AIR AND SURFACE ANALYSES
REVEAL A CLASSIC MID-LATITUDE CYCLONE. THE CLOSED UPPER LOW IS
SWINGING NEGATIVELY TITLED LATE THIS MORNING...WITH A DRY SLOT
HAVING ENVELOPED THE SOUTHEAST TWO-THIRDS OF THE FORECAST
AREA...INCLUDING CHICAGO. ARCS OF SHOWERS...WITH A CONVECTIVE-LIKE
APPEARANCE ON RADAR...CONTINUE TO DEVELOP WITHIN THIS DRY SLOT ACROSS
WEST CENTRAL TO CENTRAL IL AND PROPAGATE NORTHWARD INTO THE COOL
SECTOR. THESE HAVE BEEN MOVING INTO A WELL ESTABLISHED HEAVY SNOW
BAND...NOW CENTERED NEAR THE MISSISSIPPI RIVER INTO
SOUTHWEST/SOUTH CENTRAL WI. THIS LINES UP PERFECTLY WITH A
SYNOPTICALLY FAVORED AREA IN THIS STORM SYSTEM FOR THE MOST
INTENSE DYNAMICS...TIGHTEST THERMAL GRADIENT...AND WIND AND
MOISTURE CONVERGENCE. IN ADDITION...THE RAP CONTINUES TO ANALYZE
DEEP LIFT BEING CROSS-HAIRED WITHIN THE DENDRITIC GROWTH
ZONE...OWING TO MORE EFFICIENT SNOW PRODUCTION IN THIS AREA...AND
ESPECIALLY WHEN CONSIDERING PWATS ARE NEAR 0.70 AND INFLOW MIXING
RATIOS ARE 3.5-5.0 G/KG. VISIBILITIES UNDERNEATH THIS SNOW
BAND HAVE REGULARLY BEEN UNDER ONE HALF MILE...AND A ONE INCH PER
HOUR RATE WAS ALREADY OBSERVED IN ROCK ISLAND IL. THE SURFACE LOW
IS CENTERED NEAR LACON AND MOVING NORTHEAST WITH THE PRESSURE
FALL/RISE COUPLET MAGNITUDE AT 7MB/9MB RESPECTIVELY.
SHOWER AND THUNDER POTENTIAL EAST... WHILE THE DRY SLOT HAS
MINIMIZED MUCH OF THE AREAL COVERAGE OF MODERATE TO HEAVY RAIN
SEEN EARLIER THIS MORNING...SCATTERED CONVECTIVE ECHOES ARE
DEVELOPING ALONG AN IMMEDIATE PRE-FRONTAL TROUGH ACROSS EAST
CENTRAL IL. THE PRE-FRONTAL AIR MASS HAS SURFACE DEW POINTS OF 45
TO EVEN THE LOWER 50S AS FAR NORTH AS NORTHWEST/WEST CENTRAL IN.
WHILE NO LOW-LEVEL CAPE IS ANALYZED BY DIAGNOSTIC GUIDANCE AS OF
10 AM...ADAPTED FORECAST SOUNDINGS WITH 54F/50F DO PRODUCE AROUND
50 J/KG OF 0-3 KM CAPE THROUGH 20Z. WITH THE DYNAMIC WIND
FIELD...THERE MAY BE A BRIEF WINDOW OF GUSTY WIND POTENTIAL WITH
THIS ACROSS NORTHWEST IN...THOUGH NO EXPLICIT CONVECTIVE MODELS
THAT WERE LOOKED AT PRODUCE ANYTHING LOOKING OVERLY OMINOUS.
ACROSS CHICAGO...PERIODS OF LIGHT TO MODERATE SHOWERS SHOULD
PREVAIL THROUGH MUCH OF THE DAY WITHIN THE LOW-LEVEL MOISTURE
TRANSPORT UNDER DEEP HEIGHT FALLS/DIFFLUENCE OWING TO ASCENT.
RAIN TO SNOW TIMING...VARIOUS THICKNESS AND WET BULB ANALYSIS
TECHNIQUES ON THE RAP FOR PRECIP TYPE CHANGE LINE UP VERY WELL
WITH THE OBSERVED CHANGE OVER...AND THESE ARE ALL FORECAST TO
CREEP EASTWARD AS THE SURFACE WINDS TURN MORE NNW LOWERING
BOUNDARY LAYER TEMPERATURES. THERE HAS BEEN A REPORT OF SNOW
MIXING IN JUST NORTHWEST OF ROCKFORD AND WITH CONTINUED DYNAMIC
AND ADVECTIVE COOLING IT SHOULD REACH ROCKFORD SOON. THE CHANGE
OVER LINE SHOULD BE NORTH-TO-SOUTH ORIENTED AROUND NOON AND
LIKELY SWING NORTHWEST TO SOUTHEAST ORIENTED BY LATE AFTERNOON AS
IT APPROACHES CHICAGO. THE CHANGE SHOULD ALSO PICK UP IN
PROGRESSION SPEED IN THE WAKE OF THE SURFACE LOW AND UNDERNEATH
THE RAPID COOLING OF THE UPPER LOW.
SNOWFALL AND WIND...WITH CURRENT RADAR AND SATELLITE TRENDS AND
THE PROJECTED PATH OF THE LOW AND ASSOCIATED DEFORMATION...THE
MOST INTENSE SNOWFALL AREA/BANDS WITH RATES OF ONE INCH OR GREATER
PER HOUR SHOULD SLOWLY WORK EASTWARD NORTH OF I-80 THROUGH THE
AFTERNOON. SHORT TERM MODEL FORECASTS OF PRECIP AND VISIBILITY
AGREE WITH THIS EVOLUTION. RATES OF TWO INCHES PER HOUR ARE
POSSIBLE TOWARD ROCKFORD/BELVIDERE/DIXON GIVEN SOME OF THE 40 PLUS
DBZ /NOT ASSOCIATED WITH BRIGHT BANDING/ SEEN ALREADY AND PER THE
FORECAST INSTABILITY...BOTH SLANTWISE AND EVEN UPRIGHT IN FORECAST
SOUNDINGS/CROSS SECTIONS. WINDS HAVE BEEN GUSTING IN EXCESS OF 40
KT ACROSS MUCH OF IA AND MO AND WITH THE DEEPENING OF THE SYSTEM
AND CONTINUED STRENGTHENING COLD AIR ADVECTION...THESE TYPES OF
GUSTS WILL ONLY INCREASE AS THEY ROTATE EAST INTO THE AREA WHICH
MATCHES WELL WITH THE 50-60 MPH WINDS SEEN IN THE BOUNDARY LAYER
OF NAM AND GFS AND SURPRISING EVEN THE RAP. WILL HAVE TO WATCH TO
SEE IF THE BLIZZARD WARNING WILL NEED TO BE EXPANDED SOUTH OR
EAST...TO INCLUDE COUNTIES SUCH AS DEKALB AND LASALLE. ALSO WITH
AS FAR SOUTH AS SNOW HAS BEEN OBSERVED TO THE WEST AND THE EXTENT
OF THE TROWAL...THERE IS NO DOUBT IT WILL SNOW IN THE HIGH WIND
WARNING AREA OF THE SOUTHERN CWA. IT IS JUST UNCERTAIN ON HOW
INTENSE IT WILL BE. WILL CONTINUE TO MENTION BLOWING SNOW AS A
SECONDARY IMPACT IN THE NPW.
MTF
&&
.DISCUSSION...
344 AM CST
WINTER STORM TODAY/TONIGHT...
HAVE UPGRADED WATCHES/WARNINGS TO INCLUDE A BLIZZARD WARNING FOR A
PORTION OF NORTH CENTRAL IL...A WINTER STORM WARNING FOR NORTHEAST
IL/NORTHWEST INDIANA NORTH OF ABOUT A STREATOR-KANKAKEE-DE MOTTE
LINE...AND A HIGH WIND WARNING FOR AREAS SOUTH OF THAT SAME LINE.
INTENSE WINTER STORM SYSTEM TAKING AIM AT THE AREA FOR LATER TODAY
AND TONIGHT. AT 08Z...SURFACE ANALYSIS DEPICTED 992 MB LOW OVER
CENTRAL MISSOURI WITH 6 MB/3 HR PRESSURE FALLS SPREADING ACROSS
NORTHERN IL. 00Z GUIDANCE TAKES THE LOW NORTHEAST TO NEAR PONTIAC IL
BY 18Z...AND NEAR THE SOUTH SHORE OF LAKE MICHIGAN AND INTO
SOUTHWEST LOWER MICHIGAN BY 00Z. CURRENT PRECIP SHIELD ACROSS THE
CWA IS NEARLY ALL RAIN...SAVE FOR A LITTLE RAIN/SNOW/SLEET MIX
REPORTED EARLIER OVER ROCKFORD AND AREAS NORTH/WEST OF THERE.
RAIN/SNOW LINE CONTINUES TO WORK SLOWLY NORTHWEST...SO SHOULD BE ALL
RAIN THERE NOW. BAND OF HEAVY SNOW...INCLUDING A CONSIDERABLE AMOUNT
OF LIGHTNING...HAS BEEN OCCURRING FROM SOUTHWESTERN IA INTO
SOUTHWEST/CENTRAL WI.
WFO LOT CWA WILL INITIALLY REMAIN IN WARM SECTOR OF THE STORM
THROUGH THIS MORNING...AS WARM FRONT CURRENTLY LIFTING THROUGH
CENTRAL IL AHEAD OF THE LOW CONTINUES NORTH ACROSS ALL EXCEPT THE
FAR NORTHWEST PART OF THE CWA THIS MORNING. MODELS IN GOOD AGREEMENT
IN SPREADING STEEP MID-LEVEL LAPSE RATES OF 7-7.5 C/KM ACROSS
ESPECIALLY SOUTHEASTERN PARTS OF THE CWA THROUGH THE MORNING/EARLY
AFTERNOON HOURS...WITH SOME SFC/NEAR SFC BASED CAPE NOTED IN
FORECAST SOUNDINGS ACROSS OUR FAR SOUTHEAST AHEAD OF THE SURFACE
LOW/OCCLUDED FRONT WHICH APPROACHES DURING THE LATE MORNING AND
EARLY AFTERNOON HOURS. HAVE INCLUDED A MENTION OF LIKELY THUNDER
ACROSS THE SOUTHEAST TIER OF COUNTIES FOR THIS...AND NOTE THAT WITH
THE INCREASING SOUTHWESTERLY WIND FIELD SPC HAS INCLUDED OUR
SOUTHERN CWA BOUNDARY AREA IN THE 5 PERCENT CONVECTIVE WIND THREAT
IN THE DAY 1 OUTLOOK. PRECIPITATING MAY THEN BECOME MORE SHOWERY IN
NATURE BRIEFLY ACROSS OUR SOUTH/SOUTHEAST THIS AFTERNOON AS NORTHERN
PERIPHERY OF DRY SLOT TRANSLATES EAST-NORTHEAST ACROSS THAT AREA.
PRECIP SHOULD REMAIN ALL RAIN THROUGH MID-DAY...BEFORE PASSAGE OF
STACKED CLOSED UPPER LOW/SURFACE LOW DURING THE MID-DAY/AFTERNOON
HOURS ALLOWS THICKNESS VALUES TO DECREASE RAPIDLY FROM THE WEST AS
COLDER AIR WRAPS AROUND THE WESTERN SIDE OF THE CYCLONE. GUIDANCE
REASONABLY SIMILAR IN DEPICTING A LIKELY CHANGE FROM RAIN TO SNOW
BEGINNING SHORTLY AFTER NOON IN THE WEST...INTO THE FAR WESTERN
REACHES OF THE CHICAGO METRO AROUND 3 PM...WITH MOST OF THE
REMAINING PORTION OF NORTHEAST IL ALL SNOW BY ABOUT 6 PM. NORTHWEST
INDIANA WILL BE LAST TO CHANGE OVER TO ALL SNOW...BUT SHOULD BE
COMPLETE BY 7-8 PM. THE STRONGEST DEFORMATION FORCING SHOULD LARGELY
AFFECT THE NORTHWEST THIRD OR SO OF THE CWA...WHERE THE STRONGEST
PERSISTENT MID-LEVEL FRONTOGENETIC FORCING IS PROGGED. THIS SUGGESTS
THAT THE GREATEST POTENTIAL FOR A PERIOD OF HEAVY SNOW DURING THE
AFTERNOON AND EARLY EVENING HOURS ESPECIALLY NORTHWEST OF A MENDOTA
TO ANTIOCH LINE. SNOWFALL AMOUNTS IN THE 6-9 INCH RANGE APPEAR
REASONABLE ACROSS PARTS OF NORTH CENTRAL IL WITH THE BEST POTENTIAL
FOR LONGER DURATION MODERATE/HEAVY SNOW WITH THE DEFORMATION BAND.
LESSER AMOUNTS ARE EXPECTED FARTHER SOUTHEAST...ROUGHLY 3-7 INCHES
FROM LASALLE INTO LAKE COUNTY IL AND CONTINUING TO TAPER OFF FARTHER
SOUTHEAST. HOWEVER...THE PRESENCE OF STEEP LAPSE RATES ALOFT EVEN
FARTHER SOUTH COULD RESULT IN SMALL SCALE BANDING OF LOCALLY INTENSE
SNOW WHICH MAKES AMOUNT FORECAST DIFFICULT.
THE BIGGEST CONCERN IN ALL OF THIS IS OF COURSE TIED TO THE VERY
STRONG WIND FIELD EXPECTED IN ASSOCIATION WITH THE DEEP LOW
PRESSURE. THE COMBINATION OF A VERY STRONG ISALLOBARIC GRADIENT AND
STEEP LOW LEVEL LAPSE RATES WITH INCREASING COLD ADVECTION THIS
AFTERNOON AND EVENING WILL RESULT IN VERY STRONG WINDS...BECOMING
NORTHWEST AT 30-40 MPH AND LIKELY GUSTING TO 50-60 MPH. EVEN WITH
RELATIVELY LITTLE SNOW ACCUMULATION...THE COMBINATION OF FALLING
SNOW AND SUCH STRONG WINDS WILL LIKELY CAUSE AT LEAST BRIEF PERIODS
OF VERY TREACHEROUS TRAVEL CONDITIONS LATER THIS AFTERNOON AND
EVENING. CONSIDERING ALL OF THESE...FEEL THAT LOCATIONS WHICH HAVE
THE POTENTIAL FOR A PERIOD OF HEAVY SNOW AND SOLID ACCUMULATION THAT
AN UPGRADE TO BLIZZARD WARNING WAS WARRANTED...AND THAT AN UPGRADE
TO WINTER STORM WARNING EVEN FOR AREAS WHICH MAY ONLY SEE 2-5 INCHES
OF SNOW IS PRUDENT. FAR SOUTH...WHERE SNOW ACCUMULATION IS EXPECTED
TO BE SIGNIFICANTLY LOWER...HAVE UPGRADED THE HIGH WIND WATCH TO A
HIGH WIND WARNING...WITH 50+ KT WIND GUSTS EXPECTED. THE POTENTIAL
FOR MINOR WIND DAMAGE DOES EXIST WITH THESE WINDS...IN ADDITION TO
THE POTENTIAL ISSUES WITH BLOWING/DRIFTING SNOW AND VISIBILITY
IMPACTS FOR THE NORTHERN/NORTHWESTERN PARTS OF THE CWA. HAVE ALSO
MAINTAINED THE LAKESHORE FLOOD WARNING FOR LAKE/PORTER COUNTIES FROM
LATE TONIGHT INTO EARLY SATURDAY MORNING FOR LARGE WAVES ALONG THE
LAKE MICHIGAN SHORE.
SNOW SHOULD TAPER FROM WEST TO EAST DURING THE MID/LATE EVENING
HOURS...WITH OVERALL FORCING WEAKENING AS SYSTEM BECOMES MORE
OCCLUDED AND DRIFTS OFF TO THE EAST. PARTS OF NORTHWEST INDIANA
INCLUDING PORTER COUNTY MAY SEE A LITTLE LAKE-ENHANCEMENT OF SNOW
DURING THE EVENING...BEFORE THE CONVERGENT FOCUS SHIFTS TO THE EAST
AS WINDS CONTINUE TO BACK MORE NORTHWEST.
RATZER
REMAINDER OF FORECAST FRIDAY THROUGH SUNDAY...
TAIL END OF WRAP AROUND SNOW AND LAKE EFFECT MAY STILL BE ONGOING
IN PORTER COUNTY EARLY FRIDAY MORNING BUT ALL PRECIP SHOULD BE
DONE BY MID MORNING. SKIES WILL BE CLEARING WEST TO EAST IN THE
MORNING. CORE OF COLDEST AIR WILL BE OVER THE AREA FRIDAY
MORNING...AND MIN TEMPERATURES MAY OCCUR A COUPLE HOURS AFTER
SUNRISE FRIDAY MORNING. WITH FRESH SNOW COVER ON THE
GROUND...LOWEST POSSIBLE SUN ANGLE OF THE YEAR...AND COLD AIR IN
PLACE...WONT SEE MUCH RECOVERY IN TEMPERATURES THROUGH THE DAY.
UNLESS ITS STILL 32 AT MIDNIGHT...FRIDAY MIGHT BE THE FIRST DAY
THIS SEASON WITH THE MAX TEMPERATURE BELOW FREEZING. WINDS WILL
LIKELY STILL BE GUSTING AROUND 40 MPH THROUGH THE MORNING HOURS
BUT WINDS WILL GRADUALLY SUBSIDE THROUGH THE AFTERNOON. DONT WANT
TO COMPLICATE HEADLINE PICTURE ANY MORE THAN NECESSARY AT THIS
TIME...BUT LATER SHIFTS MAY NEED TO CONSIDER A WIND ADVISORY AFTER
THE WINTER HEADLINES DROP INTO FRIDAY MORNING.
FRIDAY NIGHT STRONG UPPER RIDGING OCCURS AND LOW LEVEL WAA BEGINS.
HOWEVER WITH FRESH SNOW COVER...DIMINISHING WINDS...AND SURFACE
RIDGE AXIS MOVING INTO IL BY SATURDAY MORNING...EXPECT ATMOSPHERE TO
DECOUPLE AND VERY STRONG LOW LEVEL INVERSION TO DEVELOP. LOW TEMPS
IN THE SINGLE DIGITS NORTHWEST WHERE DEEPEST SNOW PACK WILL
EXIST...AND TEENS IN DOWNTOWN CHICAGO AND AREAS SOUTH AND EAST OF
CHICAGO.
WAVE COMES ACROSS CENTRAL CANADA OVER THE TOP OF THE RIDGE FRIDAY
NIGHT AND SATURDAY...AND DIVES ACROSS THE GREAT LAKES SATURDAY NIGHT
AND SUNDAY...PUSHING A WEAK BACK DOOR COLD FRONT DOWN THE LAKES.
SURFACE WINDS WILL TURN NORTHEAST SUNDAY BUT NOT MUCH CHANGE IN
TEMPERATURE. CONFIDENCE HIGH
MONDAY THROUGH WEDNESDAY
AFTER MONDAY THERE ARE A LOT OF MODEL INCONSISTENCIES AND LOW
FORECAST CONFIDENCE THIS FAR OUT. 00Z RUN OF THE ECMWF QUITE A BIT
MORE AGGRESSIVE WITH WAVE COMING THROUGH LATE MONDAY INTO CHRISTMAS
MORNING THAN GFS/GEM. ECMWF WOULD SUGGEST AN AREA OF POSSIBLY 1-3
SNOW. WILL JUST MAINTAIN CHANCE POPS FOR NOW. ECMWF THEN TAKES THE
FOLLOWING SYSTEM MUCH FURTHER SOUTH WEDNESDAY. AGAIN WILL NOT MAKE
SIGNIFICANT CHANCES AT THIS TIME AND KEEP CHANCE POPS. BOTH EVENTS
SHOULD BE ALL SNOW...ALTHOUGH SOME MIXED PRECIP POSSIBLE FAR
SOUTHEAST TOWARD WATSEKA-FOWLER MONDAY.
ALLSOPP
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 16Z...
* IFR CIGS LOWERING TO LIFR BY EARLY AFTN.
* SHRA SPREADING EASTWARD INTO TERMINALS...WITH TSRA PSBL THROUGH
EARLY AFTN.
* WINDS SHIFT TO N THEN NW WITH GUSTS ARND 45 KT EXPECTED EARLY
THIS EVENING.
* RAIN QUICKLY CHANGING OVER TO SNOW ARND 22Z. HEAVY SNOW PSBL FOR
A FEW HOURS AFTER INITIAL CHANGE OVER TO ALL SNOW...WITH LOWER
VSBY EXPECTED THROUGH TONIGHT WITH BLOWING SNOW.
JEE
//DISCUSSION...UPDATED 16Z...
SHOWERS HAVE FILLED IN THE DRY SLOT AND ARE SPREADING EASTWARD.
TAFS IN GENERAL LOOK VERY GOOD. ADJUSTED CIGS SO LIFR CIGS MOVE
IN SHORTLY AFTER WINDS TURN NORTH. OBS TO THE NORTH AND WEST
SUPPORT THIS TREND. KEPT TS IN TAFS DESPITE LOW CONFIDENCE IN
OCCURRENCE AND LOCATION. BUT RADAR RETURNS LOOK CONVECTIVE IN
NATURE...SO DID NOT FEEL COMFORTABLE TAKING TS OUT. TIMING FOR
RAIN/SNOW CHANGEOVER STILL LOOK VERY ACCURATE GIVEN LATEST TRENDS
AND GUIDANCE. GUIDANCE ALSO SUPPORTS THAT MOD TO HEAVY SNOW IS
PROBABLE FOR THE FIRST FEW HOURS AFTER PRECIP TURNS OVER TO ALL
SNOW. REDUCED VSBY TO 1/2 SEEM REASONABLE GIVEN UPSTREAM
SITES.
PREVIOUS DISCUSSION...12Z...
LOW PRESSURE NOW OVER NORTHEAST MISSOURI WILL CONTINUE LIFTING
NORTHEAST TO NEAR CHICAGO/SOUTHERN LAKE MICHIGAN BY LATE THIS
AFTERNOON. CURRENT AREA OF RAIN WILL LIFT NORTH THROUGH THE
TERMINALS IN THE NEXT FEW HRS WITH A DRY SLOT EXPECTED LATER THIS
MORNING. BY EARLY AFTERNOON...COULD BE A FAST MOVING LINE OF
SHOWERS WITH SOME EMBEDDED TSRA ACROSS NORTHERN IL. CONFIDENCE IS
LOW BUT NOT LOW ENOUGH TO REMOVE FROM THIS FORECAST THOUGH
DURATION IF ANY TSRA DO OCCUR SHOULD BE RATHER SHORT...ONE HR OR
LESS.
MEDIUM TO HIGH CONFIDENCE THAT IFR CIGS TO START WILL LOWER TO
LIFR THIS MORNING BUT CONFIDENCE LOW REGARDING TIMING. WITH THE
SURFACE LOW DEEPENING AS IT APPROACHES...EXPECT LIFR CIGS TO
CONTINUE INTO THIS AFTERNOON AND WHEN THE LOW REACHES NORTHEAST
IL...COULD BE A PERIOD OF LOWER VISIBILITY...PERHAPS 1SM OR LESS.
AS THE LOW CONTINUES NORTHEAST THIS EVENING...COLDER AIR WILL
SHIFT EAST WITH A BAND OF MODERATE PERHAPS HEAVY SNOW SHIFTING
EAST ACROSS THE TERMINALS. HAVE INCLUDED A MIX OF RAIN/SNOW FOR
AN HOUR OR SO BEFORE THE CHANGEOVER TO SNOW BUT HAVE MOSTLY
MAINTAINED TRENDS FROM PREVIOUS FORECAST. PREVAILING VIS UNDER
1SM WITH POSSIBLY 1/2SM OR 1/4SM SHOULD ANY CONVECTIVE ELEMENTS
DEVELOP WITH THE SNOW. AS NOTED EARLIER...FINER DETAILS WILL
LIKELY NEED TO BE ADDED/ADJUSTED ONCE THE BAND IS ON ITS WAY.
AS THE LOW PASSES EAST OF TERMINALS...WIND SPEEDS/GUSTS WILL
RAPIDLY INCREASE FIRST AT RFD EARLY IN THE AFTERNOON THEN ACROSS
THE REST OF THE TERMINALS DURING THE LATE AFTERNOON AND EARLY
EVENING. WIND GUSTS 40-45KTS LOOK ON TRACK WITH SOME LOCALLY
HIGHER GUSTS ALSO POSSIBLE. MORE PREVAILING GUSTS TO 50 KTS MOST
LIKELY WILL OCCUR SOUTH OF THE TERMINALS BUT STILL POSSIBLE. CMS
//ORD AND MDW CONFIDENCE...UPDATED 16Z...
* HIGH CONFIDENCE IN TAF TRENDS...CONDITIONS DETERIORATING THROUGH
THIS EVENING.
* LOW CONFIDENCE IN TSRA...TIMING...LOCATION...AND OCCURRENCE.
* HIGH CONFIDENCE IN SN...MEDIUM-HIGH CONFIDENCE IN TIMING AND VSBY.
* HIGH CONFIDENCE IN WIND FCST.
JEE
//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...
* FRIDAY NIGHT THROUGH SUNDAY..DRY. VFR.
* MONDAY AND TUESDAY...SLIGHT CHANCE OF SNOW. MVFR POSSIBLE.
* WEDNESDAY...CHANCE OF SNOW. MVFR LIKELY.
&&
.MARINE...
407 AM...OVERALL NO MAJOR CHANGES THIS MORNING...OTHER THAN TO
DELAY STORM WARNING START TIME FOR A FEW HRS THIS AFTERNOON. LOW
PRESSURE NOW OVER MISSOURI WILL LIFT NORTHEAST TO NEAR THE
SOUTHERN TIP OF LAKE MICHIGAN BY LATE THIS AFTERNOON AS IT DEEPENS
AND THEN IT SHIFTS EAST INTO SOUTHERN LOWER MICHIGAN. GRADIENT
CONTINUES TO TIGHTEN NORTH OF THE LOW THIS MORNING WITH EASTERLY
GALES SPREADING NORTH. WIND DIRECTION AND SPEEDS BECOME A BIT
PROBLEMATIC OVER THE SOUTHERN THIRD OR QUARTER OF THE LAKE THIS
AFTERNOON DEPENDING ON THE EXACT TRACK OF THE LOW. WINDS WILL
LIKELY TURN NORTHEAST AND REMAIN FAIRLY STRONG ALONG THE WISCONSIN
SHORE AND EITHER TURN SOUTHERLY OR PERHAPS BECOME LIGHT/VARIABLE
ALONG THE SOUTHWEST MICHIGAN SHORE. THE LOW ALSO SLOWS JUST A BIT
AND THE LATEST GUIDANCE HAS THE LOW MOVING JUST A TAD FURTHER
WEST...PERHAPS RIGHT OVER CHICAGO. SO WHILE STORM FORCE WINDS ARE
STILL EXPECTED... THEY MIGHT NOT DEVELOP OVER THE NORTHERN TWO
THIRDS OF THE LAKE UNTIL JUST AFTER SUNSET...THEN QUICKLY SPREAD
ACROSS THE REST OF THE SOUTH END OF THE LAKE THIS EVENING...THUS
THE DELAY TO THE START TIME OF THE STORM WARNING BY A FEW HRS.
MAINTAINED THE HURRICANE GUST POTENTIAL AS THERE COULD BE SOME
GUSTS IN THE 60-65 KT RANGE BUT CONFIDENCE IS FAIRLY LOW. APPEARS
BEST TIMING FOR THE STRONGEST WINDS WOULD BE FROM LATE EVENING
THROUGH THE OVERNIGHT HRS. THE LOW WILL MOVE EAST AND MERGE WITH
ANOTHER LOW MOVING UP THE EAST COAST. THE COMBINED LOW WILL SLOW
AND AND AS HIGH PRESSURE BUILDS ACROSS THE PLAINS...THE GRADIENT
WILL REMAIN STRONG INTO FRIDAY NIGHT AND FINALLY RELAX SATURDAY.
CMS
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...BLIZZARD WARNING...ILZ003-ILZ004-ILZ008-ILZ010 UNTIL MIDNIGHT
FRIDAY.
WINTER STORM WARNING...ILZ006-ILZ012-ILZ013-ILZ014-ILZ020-ILZ021-
ILZ022...3 PM THURSDAY TO 3 AM FRIDAY.
WINTER STORM WARNING...ILZ005-ILZ011-ILZ019...3 PM THURSDAY TO
MIDNIGHT FRIDAY.
HIGH WIND WARNING...ILZ023-ILZ032-ILZ033-ILZ039...3 PM THURSDAY
TO MIDNIGHT FRIDAY.
IN...LAKESHORE FLOOD WARNING...INZ001-INZ002...MIDNIGHT FRIDAY TO 3
AM SATURDAY.
WINTER STORM WARNING...INZ001-INZ002...3 PM THURSDAY TO 3 AM
FRIDAY.
HIGH WIND WARNING...INZ010-INZ011-INZ019...3 PM THURSDAY TO
MIDNIGHT FRIDAY.
LM...GALE WARNING...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-
LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-
LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 4 PM THURSDAY.
STORM WARNING...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-
LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-
LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...4 PM THURSDAY TO 4 PM
FRIDAY.
GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565 UNTIL 6
PM THURSDAY.
STORM WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565...6 PM
THURSDAY TO 4 PM FRIDAY.
&&
$$
AREA FORECAST DISCUSSION
NWS DES MOINES IA
1210 PM CST THU DEC 20 2012
...LIFE THREATENING BLIZZARD CONDITIONS TO IMPACT IOWA TODAY...
.UPDATE...
HAVE ALLOWED BLIZZARD WARNING TO EXPIRE FOR WESTERN PORTION OF CWA
WITH PRECIPITATION ENDING AND VISIBILITIES IMPROVING. HOWEVER...AS
WINDS REMAIN STRONG AND GUSTY FROM THE NORTHWEST...WITH FRESH
SNOWFALL...SNOW WILL CONTINUE TO BLOW AND DRIFT...REDUCING
VISIBILITIES. A WINTER WEATHER ADVISORY HAS REPLACED THE BLIZZARD
WARNING FOR STRONG WINDS AND REDUCED VISIBILITIES DUE TO BLOWING
SNOW.
&&
.SHORT TERM /TODAY/...
CURRENT SITUATION HAS LONG WAVE TROUGH MOVING THROUGH CENTRAL PLAINS
WITH NOTED PV ANOMALY ACROSS ERN OK/KS. VERY STRONG FORCING
STILL EXISTS BACK INTO DEFORMATION ZONE AND IS MAINLY KINEMATIC
BY THIS POINT WITH THETA-E ADVECTION MAX NOW LIFTING OFF TO THE
NORTH AND EAST. HOWEVER JUST TO THE EAST INTO CENTRAL IA
FRONTOGENETICAL FORCING IS STILL EVIDENT AND LIKELY DRIVING ENHANCED
PRECIP WHERE DES MOINES OBS CONTINUE TO FLOAT AROUND 1/4 TO 1/2SM.
LATEST RAP CONTINUES TO DEPICT NEGATIVE H5/H6 THETA-E LAPSE RATES
AND EPV IN DENDRITIC GROWTH ZONE SO SEE NO REASON TO CHANGE CURRENT
AMOUNTS WITH LOW STATIC STABILITY CONTINUING TO REALIZE FORCING AND
PRODUCE MODERATE TO HEAVY SNOW FOR AT LEAST THE NEXT SEVERAL HOURS.
RAIN/SNOW LINE APPEARS TO BE IN FAR SERN IA AND SHOULD CONTINUE
ADVANCING SOUTH AND EAST THROUGH 12Z WHEN ENTIRE FORECAST AREA
SHOULD BE ALL SNOW. STORM TOTALS MAY STILL REACH 14 INCHES IN A FEW
SPOTS OF CENTRAL IA.
ELEVATED MUCAPE/K INDEX VALUES COINCIDENT WITH CURRENT SERN IA
CONVECTION AND LIGHTNING ACTIVITY WILL CONTINUE TO DEPART SUGGESTING
THUNDERSNOW POTENTIAL SHOULD BE DWINDLING BACK INTO DEFORMATION
ZONE. HOWEVER LIGHTNING IN LIQUID PRECIP SE AND CONVECTIVE ELEMENTS
IN TRANSITION ZONE FROM LAMONI TO OSKALOOSA...AND POINTS SE AS
RAIN/SNOW LINE SHIFTS...MAY STILL SEE BRIEF PERIODS OF THUNDERSNOW.
WINDS WILL START TO BECOME A BIGGER CONCERN AND INCREASE INTO THE
MORNING. 08Z OBS SHOW BLIZZARD CRITERIA WINDS ALONG THE HIGHWAY 30
CORRIDOR FROM CARROLL TO MARSHALLTOWN...AND THEN BACK SOUTHWEST FROM
CARROLL INTO SOUTHWEST IA. SOUNDINGS SHOW LOW LEVELS BECOMING
SLIGHTLY MORE MIXED AS COLD ADVECTION INCREASES. EVEN THOUGH IT
WILL ONLY BE TO 950 OR 925 MB...THIS WILL STILL ALLOW GUSTS TO JUMP
INTO THE LOW/MID 40S KTS WORKING EASTWARD WITH TIME. MODELS APPEAR
TO BE UNDERESTIMATING MSLP OF LOW...DOWN TO 992 MB AT 08Z IN CENTRAL
MO...AND WITH PV ANOMALY JUST UPSTREAM OF SURFACE LOW EXPECT IT TO
DEEPEN BEYOND WHAT IS FORECAST BY THE TIME IT REACHES IL. THIS MAY
ALLOW ISOLATED GUSTS TO EXCEED 50 MPH AS THE ISALLOBARIC COUPLET
REACHES CENTRAL IA BY LATE MORNING. POWER OUTAGES MAY BECOME MORE
WIDESPREAD AS WINDS INCREASE WITH TREES CONTINUING TO BE SNOW COATED.
TEMPS WILL BE AT THEIR HIGHS EARLY WITH READINGS FALLING THROUGHOUT
THE DAY. NO CHANGES TO HEADLINES.
.LONG TERM /TONIGHT THROUGH WEDNESDAY/...
FOR TONIGHT...WE WILL STILL BE DEALING WITH BLOWING SNOW AND REDUCED
VISIBILITIES MAINLY OVER THE EASTERN CWA BUT CONDITIONS WILL BE
IMPROVING THROUGH THE EVENING. WITH THE FRESH SNOWPACK...CLEARING
SKIES AND DIMINISHING WIND...TEMPS WILL BE QUITE COLD TONIGHT AND I
EXPECT TEMPS TO BE COLDER THAN WHAT GUIDANCE SUGGESTS THROUGH AT
LEAST FRIDAY.
OTHER THAN COLDER TEMPS THROUGH FRIDAY THE EXTENDED THROUGH MONDAY
LOOKS RATHER QUIET WITH SLOWLY MODERATING TEMPERATURES.
MONDAY NIGHT THROUGH WEDNESDAY THE MODELS ARE STILL IN SUBSTANTIAL
DISAGREEMENT ON THE HANDLING OF A SHORT WAVE MOVING ACROSS THE AREA
THROUGH CHRISTMAS DAY. THE EURO AND CANADIAN ARE ARE MORE SIMILAR
WITH A LITTLE DEEPER AND SLOWER WAVE WITH A SURFACE LOW ACROSS THE
SOUTHERN PLAINS. THE GFS HAS A WEAKER WAVE AND IT IS FASTER AND
FURTHER NORTH WITH IT AND THE SURFACE LOW IS ALSO MUCH WEAKER AND
FURTHER NORTH. FOR NOW THERE WAS LITTLE CHANGE MADE TO THE GOING
FORECAST UNTIL MODEL CONSENSUS BECOMES BETTER ALIGNED.
&&
.AVIATION...20/18Z
SNOW WILL CONTINUE TO PULL EAST OF AREA AS LOW DEPARTS.
HOWEVER...WINDS WILL BE STRONG AND NORTHWESTERLY WITH BLOWING SNOW
REDUCING VISIBILITIES TO IFR AND LIFR. LOW MVFR CEILINGS WILL ALSO
PREVAIL WITH STRATUS DECK BEHIND LOW. WINDS WILL DIMINISH OVERNIGHT
WITH HIGH PRESSURE PUSHING IN HELPING TO BRING VISIBILITIES UP TO
VFR AND CEILINGS WILL ALSO LIFT.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
BLIZZARD WARNING ALONG AND EAST OF I35 UNTIL 6PM
WINTER WEATHER ADVISORY FOR AREAS WEST OF I35 UNTIL 4PM
&&
$$
SHORT TERM...BSS
LONG TERM...FAB
AVIATION...AWB
AREA FORECAST DISCUSSION
NWS DES MOINES IA
1145 AM CST THU DEC 20 2012
...LIFE THREATENING BLIZZARD CONDITIONS TO IMPACT IOWA TODAY...
.UPDATE...
ADDED PART OF SHORT TERM DISCUSSION THAT WAS INADVERTENTLY OMITTED
EARLIER. ALSO ADDED 12Z TAF DISCUSSION.
&&
.SHORT TERM /TODAY/...
CURRENT SITUATION HAS LONG WAVE TROUGH MOVING THROUGH CENTRAL PLAINS
WITH NOTED PV ANOMALY ACROSS ERN OK/KS. VERY STRONG FORCING
STILL EXISTS BACK INTO DEFORMATION ZONE AND IS MAINLY KINEMATIC
BY THIS POINT WITH THETA-E ADVECTION MAX NOW LIFTING OFF TO THE
NORTH AND EAST. HOWEVER JUST TO THE EAST INTO CENTRAL IA
FRONTOGENETICAL FORCING IS STILL EVIDENT AND LIKELY DRIVING ENHANCED
PRECIP WHERE DES MOINES OBS CONTINUE TO FLOAT AROUND 1/4 TO 1/2SM.
LATEST RAP CONTINUES TO DEPICT NEGATIVE H5/H6 THETA-E LAPSE RATES
AND EPV IN DENDRITIC GROWTH ZONE SO SEE NO REASON TO CHANGE CURRENT
AMOUNTS WITH LOW STATIC STABILITY CONTINUING TO REALIZE FORCING AND
PRODUCE MODERATE TO HEAVY SNOW FOR AT LEAST THE NEXT SEVERAL HOURS.
RAIN/SNOW LINE APPEARS TO BE IN FAR SERN IA AND SHOULD CONTINUE
ADVANCING SOUTH AND EAST THROUGH 12Z WHEN ENTIRE FORECAST AREA
SHOULD BE ALL SNOW. STORM TOTALS MAY STILL REACH 14 INCHES IN A FEW
SPOTS OF CENTRAL IA.
ELEVATED MUCAPE/K INDEX VALUES COINCIDENT WITH CURRENT SERN IA
CONVECTION AND LIGHTNING ACTIVITY WILL CONTINUE TO DEPART SUGGESTING
THUNDERSNOW POTENTIAL SHOULD BE DWINDLING BACK INTO DEFORMATION
ZONE. HOWEVER LIGHTNING IN LIQUID PRECIP SE AND CONVECTIVE ELEMENTS
IN TRANSITION ZONE FROM LAMONI TO OSKALOOSA...AND POINTS SE AS
RAIN/SNOW LINE SHIFTS...MAY STILL SEE BRIEF PERIODS OF THUNDERSNOW.
WINDS WILL START TO BECOME A BIGGER CONCERN AND INCREASE INTO THE
MORNING. 08Z OBS SHOW BLIZZARD CRITERIA WINDS ALONG THE HIGHWAY 30
CORRIDOR FROM CARROLL TO MARSHALLTOWN...AND THEN BACK SOUTHWEST FROM
CARROLL INTO SOUTHWEST IA. SOUNDINGS SHOW LOW LEVELS BECOMING
SLIGHTLY MORE MIXED AS COLD ADVECTION INCREASES. EVEN THOUGH IT
WILL ONLY BE TO 950 OR 925 MB...THIS WILL STILL ALLOW GUSTS TO JUMP
INTO THE LOW/MID 40S KTS WORKING EASTWARD WITH TIME. MODELS APPEAR
TO BE UNDERESTIMATING MSLP OF LOW...DOWN TO 992 MB AT 08Z IN CENTRAL
MO...AND WITH PV ANOMALY JUST UPSTREAM OF SURFACE LOW EXPECT IT TO
DEEPEN BEYOND WHAT IS FORECAST BY THE TIME IT REACHES IL. THIS MAY
ALLOW ISOLATED GUSTS TO EXCEED 50 MPH AS THE ISALLOBARIC COUPLET
REACHES CENTRAL IA BY LATE MORNING. POWER OUTAGES MAY BECOME MORE
WIDESPREAD AS WINDS INCREASE WITH TREES CONTINUING TO BE SNOW COATED.
TEMPS WILL BE AT THEIR HIGHS EARLY WITH READINGS FALLING THROUGHOUT
THE DAY. NO CHANGES TO HEADLINES.
.LONG TERM /TONIGHT THROUGH WEDNESDAY/...
FOR TONIGHT...WE WILL STILL BE DEALING WITH BLOWING SNOW AND REDUCED
VISIBILITIES MAINLY OVER THE EASTERN CWA BUT CONDITIONS WILL BE
IMPROVING THROUGH THE EVENING. WITH THE FRESH SNOWPACK...CLEARING
SKIES AND DIMINISHING WIND...TEMPS WILL BE QUITE COLD TONIGHT AND I
EXPECT TEMPS TO BE COLDER THAN WHAT GUIDANCE SUGGESTS THROUGH AT
LEAST FRIDAY.
OTHER THAN COLDER TEMPS THROUGH FRIDAY THE EXTENDED THROUGH MONDAY
LOOKS RATHER QUIET WITH SLOWLY MODERATING TEMPERATURES.
MONDAY NIGHT THROUGH WEDNESDAY THE MODELS ARE STILL IN SUBSTANTIAL
DISAGREEMENT ON THE HANDLING OF A SHORT WAVE MOVING ACROSS THE AREA
THROUGH CHRISTMAS DAY. THE EURO AND CANADIAN ARE ARE MORE SIMILAR
WITH A LITTLE DEEPER AND SLOWER WAVE WITH A SURFACE LOW ACROSS THE
SOUTHERN PLAINS. THE GFS HAS A WEAKER WAVE AND IT IS FASTER AND
FURTHER NORTH WITH IT AND THE SURFACE LOW IS ALSO MUCH WEAKER AND
FURTHER NORTH. FOR NOW THERE WAS LITTLE CHANGE MADE TO THE GOING
FORECAST UNTIL MODEL CONSENSUS BECOMES BETTER ALIGNED.
&&
.AVIATION...20/18Z
SNOW WILL CONTINUE TO PULL EAST OF AREA AS LOW DEPARTS.
HOWEVER...WINDS WILL BE STRONG AND NORTHWESTERLY WITH BLOWING SNOW
REDUCING VISIBILITIES TO IFR AND LIFR. LOW MVFR CEILINGS WILL ALSO
PREVAIL WITH STRATUS DECK BEHIND LOW. WINDS WILL DIMINISH OVERNIGHT
WITH HIGH PRESSURE PUSHING IN HELPING TO BRING VISIBILITIES UP TO
VFR AND CEILINGS WILL ALSO LIFT.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
BLIZZARD WARNING MUCH OF FORECAST AREA UNTIL NOON
BLIZZARD WARNING ALONG AND EAST OF I35 UNTIL 6PM
WINTER STORM WARNING FAR NW UNTIL NOON
&&
$$
SHORT TERM...BSS
LONG TERM...FAB
AVIATION...AWB
AREA FORECAST DISCUSSION
NWS TOPEKA KS
1127 AM CST THU DEC 20 2012
...UPDATE TO AVIATION...
.DISCUSSION...
THE STORM SYSTEM SEEMS TO BE PROGRESSING AS FORECASTED WITH A WIDE
BAND OF MODERATE TO HEAVY SNOW AND WINDS GUSTING OVER 45 MPH MOVING
INTO THE EASTERN HALF OF THE AREA. 08Z WATER VAPOR SHOWS THE UPPER
LOW NEARLY OVER EMP CONTINUING TO LIFT NORTHEAST. MEANWHILE SFC OBS
SHOW THE SFC LOW MOVING NORTHEAST THROUGH CENTRAL MO AND DEEPENING.
THE STORM IS ON TRACK TO BE OUT OF THE AREA BY 9 AM. SO MAIN CONCERN
TODAY IS THE WINDS AND WHETHER WE WILL NEED A SEPARATE WIND ADVISORY
ONCE THE SNOW ENDS. LATEST NAM AND RAP PROGS SHOW WINDS SUBSIDING
ONCE THE BAND OF SNOW PASSES TO THE EAST AND CNK IS ALREADY TRENDING
WEAKER...SO THE CURRENT WINTER WEATHER HEADLINES LOOK TO COVER THE
WINDS. THE PLAN IS TO DOWNGRADE THE WARNING TO A WINTER WEATHER
ADVISORY AS THE BACK EDGE OF HEAVIER SNOW MOVES EAST TO ACCOUNT FOR
THE WINDS AND BLOWING SNOW...AND KEEP THE ORIGINAL EXPIRATION TIMES
FOR NOW.
THINGS SHOULD CLEAR OUT QUICKLY TODAY...BUT STRONG WINDS AND TEMPS
REMAINING BELOW FREEZING SHOULD MAKE IT FEEL PRETTY RAW. UPPER LEVEL
RIDGING DEVELOPS AND PERSISTS OVER THE CENTRAL PLAINS INTO THE
WEEKEND WITH DRY WEATHER EXPECTED. PREVIOUS FORECAST TEMPS FOR
FRIDAY AND SATURDAY SEEM TO BE IN THE BALL PARK EXPECTING SOME SNOW
COVER INITIALLY...SO HAVE NOT MADE MANY CHANGES.
THE FORECAST FOR NEXT WEEK CONTINUES TO BE UNCERTAIN AS THE ECMWF
HAS EXHIBITED POOR CONTINUITY FROM RUN TO RUN. THE GFS HAS STARTED
TO SHOW SOME CONSISTENCY...BUT THERE REMAINS SOME VARIATION IN THE
TRACK OF THE STORM SYSTEM FOR CHRISTMAS. THINK THE ECMWF HAS TRENDED
FURTHER SOUTH DUE TO AN ARCTIC INTRUSION FROM THE NORTH WHICH WOULD
BRING SOME VERY COLD AND DRY SOUTH SOUTH INTO THE PLAINS. IT IS
INTERESTING TO NOTE THAT THE GEM SEEMS TO BE IN THE GFS CAMP OF A
DEEPENING SYSTEM AND A CHANCE FOR SNOW. OPTED TO KEEP A 30 PERCENT
CHANCE FOR SNOW MAINLY FOR CHRISTMAS DAY AND TUESDAY NIGHT UNTIL
THERE IS BETTER CONSISTENCY FROM RUN TO RUN. ALSO TRENDED TEMPS
COOLER FOR NEXT WEEK WITH BOTH THE ECMWF AND GFS SHOWING COLD AIR
ADVECTION THROUGH THE PERIOD.
WOLTERS
&&
.AVIATION...
TERMINALS MAY SEE SOME LOW GROUND BLOWING SNOW BUT NOT ENOUGH TO
RESTRICT VISBY TODAY. WINDS SUBSIDE THROUGH THE LATE AFTERNOON.
WITH SOME MELTING...CLEAR SKIES AND LIGHT WINDS...COULD SEE SOME
BR TOWARD MORNING BUT HAVE ONLY A TEMPO GROUP AT TOP/MHK AT THIS
TIME WITH CONSIDERABLE DRY AIR JUST ABOVE THE SURFACE. 67
&&
.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
AREA FORECAST DISCUSSION...UPDATED
NWS GAYLORD MI
603 PM EST THU DEC 20 2012
.SYNOPSIS...
ISSUED AT 414 PM EST THU DEC 20 2012
STRONG LOW PRESSURE OVER THE SOUTHERN GREAT LAKES...WILL CONTINUE TO
LIFT INTO SOUTHERN MICHIGAN...GENERATING CONTINUED WINTRY WEATHER
ACROSS NORTHERN MICHIGAN THROUGH FRIDAY. PERIODS OF HEAVY SNOW IS
EXPECTED FOR AREAS OF NORTHERN MICHIGAN THROUGH FRIDAY AFTERNOON.
ANY PRECIPITATION FALLING AS RAIN OR A RAIN....SNOW MIX WILL CHANGE
OVER TO SNOW THIS EVENING. WINDS WILL INCREASE TONIGHT AND CONTINUE
THROUGH FRIDAY.
&&
.UPDATE...
ISSUED AT 556 PM EST THU DEC 20 2012
LOW PRESSURE CROSSING SOUTHERN LAKE MICHIGAN AT THIS HOUR...NEAR
983 MB /STILL A LITTLE BELOW NEAR TERM RUC GUIDANCE/. RAIN-SNOW
LINE HAS BEEN FLIRTING WITH THE TVC-GOV-APN CORRIDOR AND THIS IS
IN GOOD AGREEMENT WITH H8 WETBULB ZERO LINE. EXPECT THAT THIS WILL
SHIFT A LITTLE FURTHER NORTH AND EAST THIS EVENING UNTIL THE LOW
REACHES OUR LONGITUDE AROUND 9-10PM...IN LINE WITH RAP
EXPECTATIONS.
PRIMARY CHANGES INCLUDE REMOVING BLOWING SNOW MENTION THROUGH THE
EVENING UNTIL WE CAN GET THE NNW WINDS TO STRENGTHEN IN
COMBINATION WITH SLOWLY COOLING BL TEMPS. HAVE ALSO ADJUSTED
WEATHER GRIDS TO ACCOUNT FOR EXPECTED MOVEMENT OF THE RAIN/SNOW
LINE. FINALLY...HAVE ADJUSTED OVERNIGHT PRECIPITATION TOTALS PER
LATEST HRRR/RAP...BUT THIS ONLY RESULTS IN A MINOR CHANGE TO
PREVIOUS GRIDDED FORECAST. STILL EXPECT SOME SPOTS OVER INTERIOR
NORTHERN LOWER AND EASTERN UPPER TO SEE UPWARDS OF 6 ADDITIONAL
INCHES OVERNIGHT. WHILE A LITTLE LESS WILL FALL AT THE COASTS...IT
WILL BE FAR MORE THAN HAS BEEN SEEN THUS FAR...THEREFORE CAUSING
TRAVEL CONDITIONS IN THESE REGIONS TO DETERIORATE RAPIDLY.
HAVE ISSUED AN SPS TO HIGHLIGHT THE CHANGING EVENING CONDITIONS.
OTHERWISE...HEADLINES LOOK GOOD. WILL REASSESS OUR FAR SOUTHEAST
FOR POTENTIAL WINTER WEATHER ADVISORY NEEDED WELL AFTER MIDNIGHT.
&&
.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 414 PM EST THU DEC 20 2012
ON THE LATEST SURFACE WEATHER MAP OF INTEREST...984 MB LOW PRESSURE
WAS CENTERED NEAR CHICAGO ILLINOIS. APX AND SURROUNDING RADARS
SHOWED MODERATE TO HEAVY PRECIPITATION ACROSS MUCH OF NORTHERN
MICHIGAN. THE FORM OF WHICH IS ALL OVER THE MAP...SOME SPOTS ACROSS
THE HIGHER TERRAIN HAS HAD 6 INCHES OR MORE...WHILE THE LOWER
ELEVATIONS HAVE HAD 2 INCHES OR LESS (IN SOME CASES NEARLY NONE AT
ALL). FORECAST CHALLENGES ARE NUMEROUS WITH CHANGEOVER TO ALL SNOW
AND ADDITIONAL ACCUMULATIONS THE MAIN ONES.
TONIGHT...STORM SYSTEM WILL CONTINUE TO TRACK NORTHEAST ACROSS LOWER
MICHIGAN TONIGHT THEN INTO WESTERN NEW YORK FRIDAY. SNOWFALL RATES
ARE EXPECTED TO PICK UP ONCE AGAIN AND AS COLDER AIR GETS PULLED
INTO THE REGION FROM THE NORTH...SNOWFALL RATES ARE EXPECTED TO
INCREASE. WATER VAPOR LOOPS DEPICT A WELL-DEFINED BAROCLINIC LEAF
STRUCTURE. ACCOMPANYING STRONG DIVERGENCE WITHIN A COUPLED UPPER JET
STRUCTURE ATOP LOW/MID-LEVEL FRONTOGENESIS WILL SUPPORT AN INCREASE
IN SNOW RATES DURING THE NEXT FEW HOURS. DEEP ASCENT THROUGH
DENDRITIC GROWTH ZONES WITHIN THE 700-500-MB LAYER WILL SUPPORT
EFFICIENT SNOW GROWTH...WITH ISOTHERMAL PROFILES IN THE 850-700-MB
LAYER YIELDING EFFICIENT SNOW AGGREGATION. SNOWFALL RATES OF 1-1.5
INCHES WILL LIKELY BECOME COMMON LATER THIS EVENING...AS ONE OR MORE
NE/SW-ORIENTED SNOW BANDS DEVELOP WHILE THE SFC LOW APPROACHES. THE
ENHANCED SFC PRESSURE GRADIENT WILL SUPPORT NNE TO ENE WINDS OF
20-25 MPH WITH GUSTS REACHING 30 TO OCCASIONALLY 35 MPH. THIS WILL
SUPPORT REDUCED VISIBILITIES TO ONE-HALF MILE IN BLOWING SNOW...AND
LOCALIZED BLIZZARD CONDITIONS MAY OCCUR. ADDITIONAL ACCUMULATIONS
WILL VARY WIDELY FROM AN INCH OR LESS NEAR THE LAKE HURON LAKE
SHORES TO BETWEEN 4 AND 8 INCHES ACROSS EASTERN UPPER AND THE HIGHER
TERRAIN OF NORTHERN LOWER. LOWS RANGING FROM THE MIDDLE 20S NORTH TO
THE LOWER 30S SOUTHEAST.
FRIDAY...WRAP AROUND SNOW SHOWERS IN THE MORNING THEN DRIER
AIR/SUBSIDENCE/RIDGING BY LATE IN THE DAY WHICH SHOULD DIMINISH
ACTIVITY. THERE IS ALSO A BIT OF OVER LAKE INSTABILITY (DELTA TS OF
ABOUT 14) WITH STRONG NORTHERLY FLOW. THIS WILL LEAD TO WIDESPREAD
BLOWING AND DRIFTING SNOW...WITH ONLY ABOUT 2 INCHES OR LESS OF
ADDITIONAL ACTUAL ACCUMULATION. HIGHS IN THE UPPER 20S NORTH TO THE
MIDDLE 30S SOUTHEAST.
.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)
ISSUED AT 414 PM EST THU DEC 20 2012
FOUR WAVE NRN HEMISPHERIC PATTERN IN PLACE TODAY WITH MAJOR TROUGH
AXES OVER FAR EASTERN ASIA AND ALONG THE NOAM WEST COAST. SW
FLOW/RIDGING AND RELATIVELY MILD TEMPERATURES EXISTS DOWNSTREAM
THROUGH THE PLAINS AND THE EASTERN CONUS...WITH MUCH OF NRN MICHIGAN
JUST COLD ENOUGH TO GET IN ON THE HEAVY SNOW WITH OUR ONGOING WINTER
STORM (ACTUALLY PARTS OF THE CWA IS WITHIN THE SWEET SPOT...THE
TRANSITION ZONE FROM RAIN TO SNOW WHERE YOU GET MAXIMUM MOISTURE
INFLOW). FLOW PATTERN REMAINS SOMEWHAT PROGRESSIVE ACROSS THE CONUS
THROUGH THE UPCOMING SEVEN DAY STRETCH BUT STILL ON THE OVERALL MILD
SIDE OF THE THINGS AS THE REALLY COLD AIR REMAINS STUCK ACROSS THE
POLE INTO EASTERN ASIA...A PATTERN THAT HAS DOMINATED THIS
FALL/EARLY WINTER SEASON SO FAR. BUT FIRST...HAVE TO GET THROUGH THE
ONGOING STORM.
FRIDAY NIGHT AND SATURDAY...ONGOING STRONG SYSTEM WILL BE EXITING
EAST OF THE STATE BY FRIDAY EVENING WITH MID LEVEL RIDING/SFC HIGH
PRESSURE AND DRIER AIR NOSING INTO THE WESTERN GREAT LAKES THROUGH
THE NIGHT. NNW FLOW LAKE SNOW SHOWERS AND GUSTY WINDS WILL PERSIST
THROUGH FRIDAY EVENING BEFORE DIMINISHING SUBSTANTIALLY OVERNIGHT
INTO THE DAY SATURDAY. ACCORDINGLY...WILL START OUT WITH CATEGORICAL
NNW FLOW LAKE SNOW SHOWERS FRIDAY EVENING BEFORE DIMINISHING/ENDING
BY SATURDAY MORNING. CURR
SATURDAY NIGHT THROUGH CHRISTMAS EVE...A RELATIVE LULL IN THE
WEATHER ACTION FOR THE LATTER HALF OF THE WEEKEND THROUGH CHRISTMAS
EVE WITH BROAD HIGH PRESSURE AND WEDGE OF DRIER AIR IN THE REGION.
THAT SAID...GUIDANCE DOES DEPICT A COUPLE WAVES WITHIN THE FAST NW
FLOW ALOFT SKITING THROUGH THE NRN PART OF THE STATE...ONE SATURDAY
NIGHT AND A STRONGER ONE ON SUNDAY. SOME COLDER AIR SAGGING BACK
INTO THE REGION BEHIND THE WAVE ENOUGH TO MAINTAIN AND/OR GENERATE
SOME LAKE SNOWS OFF THE GREAT LAKES...ESPECIALLY SUNDAY AS THE
STRONGER WAVE PASSES THROUGH. BUT OVERALL NOT A BIG DEAL WITH FAIRLY
DRY AIR IN CONTROL. SUNDAY NIGHT THROUGH CHRISTMAS EVE LOOKING QUIET
AT THIS POINT WITH BROAD HIGH PRESSURE THROUGH THE REGION.
CHRISTMAS DAY THROUGH THURSDAY (EXTENDED PERIODS)...SOLUTION
DIFFERENCES AMONG THE MEDIUM RANGE GUIDANCE...AS USUAL. GEM/GFS
SOLUTIONS ARE IN ONE CAMP KEEPING THINGS ON THE QUIET SIDE FOR
CHRISTMAS DAY (ALTHOUGH THE GFS DOES HAVE A WEAK FAST MOVING WAVE
MOVING THROUGH THE REGION). ECMWF HINTING AT ANOTHER STRONGER STORM
FOR TWO RUNS NOW PUSHING UP THROUGH THE OHIO VALLEY/GREAT LAKES ON
CHRISTMAS DAY. DIFFERENCES AMONG THE GUIDANCE ARE THE RESULT OF THE
DEGREE OF PHASING BETWEEN THE NRN AND SOUTHERN STREAMS WITH OBVIOUS
BIG IMPLICATIONS. NO WAY OF KNOWING THE CORRECT SOLUTION AT THIS
JUNCTURE...BUT WILL HAVE LOWER END SNOW CHANCES ON TUESDAY FOR NOW.
ANOTHER SHOT FOR A STORM SYSTEM MAY COME WEDNESDAY NIGHT THROUGH
THURSDAY WITH THE POTENTIAL FOR YET ANOTHER STORM TO SPIN UP OFF THE
GULF AND LIFT NORTHWARD THROUGH THE EASTERN CONUS. AGAIN...BIG
DIFFERENCES ON THE TIME/TRACK OF THAT STORM (IF IT OCCURS AT ALL).
BUT WILL CARRY CHANCE POPS FOR SNOW DURING THAT TIME.
&&
.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1239 PM EST THU DEC 20 2012
TOUGH AVIATION FORECAST FOR SURE. SNOW WILL LEAD TO WIDESPREAD IFR
AND TEMPORARY VLIFR CONDITIONS THROUGH MUCH OF THE EVENING AS
STRONG LOW PRESSURE MOVES INTO THE AREA. RAIN WILL MIX WITH THE
SNOW AT ALPENA AND MANISTEE THROUGH THE EVENING HOURS. SNOWS WILL
TAPER OFF LATE TONIGHT...BUT WRAP AROUND MOISTURE IN COMBINATION
WITH LAKE EFFECT WILL KICK IN FOR PRIMARILY TVC/MBL FRIDAY. STILL
LOOKING FOR BRISK EASTERLY WINDS TO TURN OUT OF THE NNW/NW LATER
TONIGHT AND START TO BECOME VERY GUSTY OVER ALL BUT APN...WHERE
THIS COULD TAKE UNTIL FRIDAY BEFORE THE REAL STRONG WINDS ARE
REALIZED. GUSTS TO 40-45 MPH TOWARD THE END OF THE TAF PERIOD.
&&
.MARINE...
ISSUED AT 414 PM EST THU DEC 20 2012
MAJOR WINTER STORM LIFTING NE INTO THE GREAT LAKES THROUGH
TONIGHT...BEFORE DEPARTING FRIDAY. OVERLAKE INSTABILITY WITH
EASTERLY WINDS AT 20-35KTS TO DEVELOP AS MODERATE TO HEAVY SNOWS
(MIXED WITH OR ALL RAIN ACROSS LAKE HURON). THE SNOWS WILL BE
INCREASINGLY INTENSE THIS EVENING. WINDS WILL DECREASE SOME ACROSS A
GOOD CHUNK OF THE NEARSHORES THIS EVENING...BUT THEN RAMP BACK UP
AGAIN LATE TONIGHT AND FRIDAY WITH COLD ADVECTION FOLLOWING THE
DEPARTING SFC LOW PRESSURE. WINDS WILL GUST AS HIGH AS
50KTS...RESULTING IN STORM FORCE WINDS FOR THE NW LOWER NEARSHORES.
SOLID GALES ALL OTHER MARINE AREAS. GRADIENT GRADUALLY LOOSENS UP
OVER THE WEEKEND...BUT GALES AND OBVIOUSLY CHOPPY WAVES WILL PERSIST
THROUGH FRIDAY NIGHT.
&&
.APX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER STORM WARNING UNTIL 7 PM EST FRIDAY FOR MIZ008-015>029-
031>034.
WINTER WEATHER ADVISORY UNTIL 7 PM EST FRIDAY FOR MIZ030-035-041.
LH...GALE WARNING UNTIL 7 AM EST SATURDAY FOR LHZ345>349.
LM...GALE WARNING UNTIL 7 AM EST SATURDAY FOR LMZ341.
STORM WARNING FROM 10 PM THIS EVENING TO 7 PM EST FRIDAY FOR
LMZ323-342-344>346.
GALE WARNING UNTIL 10 PM EST THIS EVENING FOR LMZ323-342-344>346.
GALE WARNING FROM 7 PM FRIDAY TO 7 AM EST SATURDAY FOR LMZ323-
342-344>346.
LS...GALE WARNING UNTIL 7 AM EST SATURDAY FOR LSZ321-322.
&&
$$
UPDATE...ARNOTT
SYNOPSIS...TL
SHORT TERM...AS
LONG TERM...BA
AVIATION...AS
MARINE...AS
AREA FORECAST DISCUSSION
NWS TWIN CITIES/CHANHASSEN MN
1217 PM CST THU DEC 20 2012
.UPDATE...
18Z AVIATION DISCUSSION ADDED BELOW.
/UPDATE ISSUED AT 1049 AM CST THU DEC 20 2012/
JUST A QUICK UPDATE ON WHERE THINGS STAND THIS MORNING. SFC LOW
HAS DEEPENED TO 987 MB AND IS NEAR PEORIA IL AT 1030 AM AND
RAPIDLY ON ITS WAY TO CHICAGO VIA I-55. MAIN DEFORMATION SNOW BAND
NOW EAST OF THE MPX CWA...WITH MAINLY LIGHT SNOW LEFT ACROSS FAR
ERN MN AND WRN WI WITH SNOW RATES NOW A HALF INCH PER HOUR AT
BEST. MAIN ACCUMULATIONS ARE DONE...WITH AN ADDITIONAL 1-2 INCHES
OF SNOW POSSIBLE THE REST OF THE DAY FROM PEPIN UP TO LADYSMITH
AND POINTS SOUTHEAST. THIS WILL LIKELY PUSH OUR HIGHEST SNOWFALL
REPORT THUS FAR FROM AUGUSTA IN FAR SE EAU CLAIRE COUNTY UP OVER
THE 10 INCH MARK WHEN ALL IS SAID AND DONE.
AS FOR HEADLINES...PLAN TO LEAVE THOSE AS IS FOR NOW...LEAVING ANY
MAJOR CHANGES TO THE HEADLINES FOR THE AFTERNOON PACKAGE UPDATE AT
4 PM. VISIBILITIES /AT AIRPORT SENSORS/ IN BLSN ACROSS SRN MN HAVE BEEN
HANGING UP AROUND 1-2 SM...BUT WITH DRIFTING EXPECTED IN THE STRONG
WINDS...WILL KEEP THE BLIZZARD WARNING AS IS FOR NOW TO AVOID
CONFUSION IF WE DECIDED TO FALL BACK TO AN ADVISORY FOR JUST THE
BLOWING SNOW...AS TRAVEL CONDITIONS IN THE SOUTH...ESPECIALLY
TOWARD I-35 REMAIN DIFFICULT.
&&
.PREV DISCUSSION...
/ISSUED 602 AM CST THU DEC 20 2012/
...BLIZZARD CONDITIONS EXPECTED TODAY ACROSS FAR SOUTHERN
MINNESOTA...
SHORT TERM...TODAY THROUGH SUNDAY.
THE MAIN FOCUS FOR THIS FORECAST PACKAGE HAS CLEARLY BEEN THE
POWERFUL SYSTEM NOW CENTERED OVER MISSOURI. IT WILL CONTINUE TO
TRACK NORTHEAST INTO NORTHERN ILLINOIS THIS AFTERNOON AND INTO
LOWER MICHIGAN BY THIS EVENING. RADAR CONTINUES TO INDICATE LIGHT
SNOW EAST OF A LINE FROM MANKATO TO MSP AND OSCEOLA. POCKETS OF
MODERATE SNOW CAN BE FOUND FURTHER EAST TOWARD EAU CLAIRE AND
POINTS SOUTH. THIS IS THE BACK EDGE OF THE SYSTEM AND SNOW WILL
CONTINUE TO PIVOT EASTWARD AND EXIT THE CWA LATE THIS MORNING OR
EARLY AFTERNOON. CLEARING SKIES CAN BE FOUND AS CLOSE AS ERN SD
WITH SUBSIDENCE/ISENTROPIC DOWNGLIDE.
AS THE STORM TRACKS NORTHEAST TODAY...THE PRESSURE GRADIENT WILL
INCREASE ACROSS THE AREA WITH STEEPENING LAPSE RATES BELOW 925 MB
IN STRONG CAA REGIME. RAP13 SHOWS 925 MB WINDS STRENGTHENING TO
BETWEEN 40 AND AS HIGH AS 50 KTS ALONG THE IOWA BORDER AFTER 15Z
THIS MORNING. RAP FORECAST SOUNDINGS FROM FAIRMONT AND ROCHESTER
INDICATE MIXING POTENTIAL TO THIS LEVEL...WITH BUFKIT PREDICTED
GUSTS FROM THE 950 MB LEVEL OF AT LEAST 35 KTS. SHOULD SEE
FREQUENT GUSTS EASILY REACH 40 OR 45 MPH...BUT THEY COULD APPROACH
OR EXCEED 50 MPH IN OPEN AREAS OF FAR SOUTHERN
MINNESOTA...INCLUDING ALONG THE I-90 CORRIDOR. GIVEN THE 3 OR 4
INCHES OF POWDERY SNOW THAT FELL TUESDAY MORNING AND THE
ADDITIONAL 2 TO 5 INCHES THAT FELL OVERNIGHT...A GROUND BLIZZARD
IS QUITE LIKELY TODAY SOUTH OF A LINE FROM TRIMONT TO OWATONNA.
WHITEOUT CONDITIONS WILL MAKE FOR NEAR IMPOSSIBLE TRAVEL.
THUS...EXPANDED THE BLIZZARD WARNING WESTWARD TO INCLUDE
WASECA...MARTIN...AND FARIBAULT COUNTIES THROUGH 6 PM. THINK AFTER
THAT TIME...WE WILL LOSE THE STEEP LAPSE RATES AND GUSTS SHOULD
BEGIN RAPIDLY SUBSIDING.
FURTHER NORTH...WINDS SHOULD NOT BE AS STRONG AND TOPOGRAPHY
ISSUES COME INTO PLAY...ESPECIALLY ACROSS WRN WI SO WILL NOT
EXPAND THE BLIZZARD WARNING INTO THOSE AREAS.
CLEAR SKIES AND DIMINISHING WINDS AS THE RIDGE BUILDS EASTWARD
INTO WRN MN WILL BRING TONIGHT/S LOWS DOWN INTO THE SINGLE DIGITS
ABOVE ZERO EAST AND BELOW ZERO WEST.
THE RIDGE WILL WEAKEN OVERHEAD FRIDAY...BUT A STRONGER 1035MB RIDGE
TO ITS NORTHWEST WILL BLEED DOWN INTO THE UPPER MISSISSIPPI VALLEY
SATURDAY KEEPING CONDITIONS DRY THROUGH THE WEEKEND.
LONG TERM...SUNDAY NIGHT THROUGH WEDNESDAY.
LOTS OF VARIABILITY IN THE MODELS WITH THE EVENTUAL TRACK OF A
STRONG SOUTHERN STREAM SYSTEM AROUND CHRISTMAS DAY. SEEMS AT THIS
POINT THE CONSENSUS WOULD BE TO SHUNT IT EAST OF THE REGION...
/EXCEPT FOR PERHAPS A LITTLE LIGHT SNOW WITH AN INVERTED TROUGH
PER EURO/ WITH COLD AIR DAMMING ALONG THE NORTHERN U.S. ROCKIES AS
A STRONG 1040+ MB HIGH PRESSURE SYSTEM BUILDS SOUTHEAST FROM
WESTERN CANADA. THIS WOULD SPELL A VERY COLD PATTERN WITH HIGHS
POTENTIALLY BELOW ZERO AND LOWS IN THE TEENS BELOW TO POSSIBLY 20S
BELOW. THE CURRENT GRIDS ADVERTISE A MILDER SOLUTION...BUT IF THE
TREND HOLDS...THE LONG TERM WILL NEED TO BE ADJUSTED 10 TO 20
DEGREES COLDER.
&&
.AVIATION.../18Z TAF ISSUANCE/
DEEP SFC LOW JUST NOW MOVING INTO CHICAGO...WITH -SN SHIELD SLOWLY
PULLING EAST THROUGH WRN WI. FOLLOWED THE RAP/HRRR TO TIME ENDING OF
FALLING SN AT RNH/EAU. GOING TAFS HAD A GOOD HANDEL ON WIND
SPEEDS/DIRECTIONS AND DID NOT CHANGE THEM MUCH...EXPECT ALL 30+ KT
GUSTS TO REMAIN SE OF FIELDS...THOUGH SHOULD MAINTAIN AT LEAST
OCCASIONAL GUSTS THROUGH 06Z. CLOUD FORECAST IS A BIT TRICKY THOUGH
FOR TODAY. MN NOW ON THE SUBSIDENCE/DRYING SIDE OF THE SYSTEM TO
THE SE. HOWEVER...THIS DRYING OF THE ATMO IS BEING OFFSET BY CAA.
THIS HAS RESULTED IN MAINLY BKN MVFR CIGS ALL THE WAY WEST TO I-29
IN ERN SODAK. AS A RESULT DELAYED CLEARING IN TAFS...CLOSER TO
WHAT FORECAST SOUNDINGS FROM THE 12Z NAM WOULD INDICATE. AFTER
THAT...FRIDAY IS LOOKING QUIET...WITH LIGHT WINDS AND MAINLY SKC SKIES.
KMSP...DELAYED ONSET OF VFR CONDITIONS...THOUGH SAT TRENDS WOULD
INDICATE A FEW SCT PERIODS COULD BE POSSIBLE PRIOR TO 4Z. BASED
ON CIG HEIGHTS ACROSS THE STATE ALL 015 OR LOWER...KEPT CIGS AT
MSP BELOW 017...THOUGH WILL HAVE TO WATCH TRENDS THIS AFTERNOON TO
SEE IF THE CIGS GO ABOVE THAT. OTHER THAN THE CIG HEIGHT
TRENDS...CONFIDENCE IS HIGH IN REST OF TAF.
/OUTLOOK FOR KMSP/
SAT...VFR. WINDS S AT 5KTS.
SUN...VFR. WINDS NE AT 5 TO 10KTS.
MON...MVFR OR LOWER CIG/VIS POSSIBLE WITH CHC OF -SN. WINDS NE AT
5 KTS.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...WINTER STORM WARNING UNTIL 6 PM CST THIS EVENING FOR GOODHUE-
RICE.
WINTER WEATHER ADVISORY UNTIL 6 PM CST THIS EVENING FOR BLUE
EARTH-DAKOTA-LE SUEUR-WATONWAN.
BLIZZARD WARNING UNTIL 6 PM CST THIS EVENING FOR FARIBAULT-
FREEBORN-MARTIN-STEELE-WASECA.
WI...WINTER STORM WARNING UNTIL 6 PM CST THIS EVENING FOR CHIPPEWA-
DUNN-EAU CLAIRE-PEPIN-PIERCE.
WINTER WEATHER ADVISORY UNTIL 6 PM CST THIS EVENING FOR BARRON-
RUSK-ST. CROIX.
&&
$$
BORGHOFF/MPG
AREA FORECAST DISCUSSION
NWS TWIN CITIES/CHANHASSEN MN
1049 AM CST THU DEC 20 2012
.UPDATE...
JUST A QUICK UPDATE ON WHERE THINGS STAND THIS MORNING. SFC LOW
HAS DEEPENED TO 987 MB AND IS NEAR PEORIA IL AT 1030 AM AND
RAPIDLY ON ITS WAY TO CHICAGO VIA I-55. MAIN DEFORMATION SNOW BAND
NOW EAST OF THE MPX CWA...WITH MAINLY LIGHT SNOW LEFT ACROSS FAR
ERN MN AND WRN WI WITH SNOW RATES NOW A HALF INCH PER HOUR AT
BEST. MAIN ACCUMULATIONS ARE DONE...WITH AN ADDITIONAL 1-2 INCHES
OF SNOW POSSIBLE THE REST OF THE DAY FROM PEPIN UP TO LADYSMITH
AND POINTS SOUTHEAST. THIS WILL LIKELY PUSH OUR HIGHEST SNOWFALL
REPORT THUS FAR FROM AUGUSTA IN FAR SE EAU CLAIRE COUNTY UP OVER
THE 10 INCH MARK WHEN ALL IS SAID AND DONE.
AS FOR HEADLINES...PLAN TO LEAVE THOSE AS IS FOR NOW...LEAVING ANY
MAJOR CHANGES TO THE HEADLINES FOR THE AFTERNOON PACKAGE UPDATE AT
4 PM. VISIBILITIES /AT AIRPORT SENSORS/ IN BLSN ACROSS SRN MN HAVE BEEN
HANGING UP AROUND 1-2 SM...BUT WITH DRIFTING EXPECTED IN THE STRONG
WINDS...WILL KEEP THE BLIZZARD WARNING AS IS FOR NOW TO AVOID
CONFUSION IF WE DECIDED TO FALL BACK TO AN ADVISORY FOR JUST THE
BLOWING SNOW...AS TRAVEL CONDITIONS IN THE SOUTH...ESPECIALLY
TOWARD I-35 REMAIN DIFFICULT.
&&
.AVIATION.../12Z TAF ISSUANCE/
SNOW IS ON ITS WAY OUT IN EASTERN MN THIS MORNING...SO THE VIS
SHOULD CONTINUE TO SLOWLY IMPROVE AT AIRPORTS IN AND AROUND THE
TWIN CITIES METRO. HOWEVER...THE MOVEMENT IS SLOW ENOUGH THAT KEAU
SHOULD BE STILL SEE IFR RESTRICTIONS THROUGH MOST OF THE MORNING.
THE DRAMATIC INCREASE IN WIND TODAY IS PROBABLY THE BIGGEST
AVIATION CONCERN AT SOME OF THE TAF SITES...THAT COMBINED WITH
IFR/MVFR STRATUS DROPPING DOWN ACROSS THE AREA THIS MORNING. THESE
CLOUDS SHOULD CLEAR MOST OF THE TAF SITES BY LATE THIS AFTERNOON.
THE WINDS SHOULDN`T DEVIATE MUCH IN DIRECTION...STAYING BETWEEN
320 AND 340 MOST OF THE DAY.
KMSP...
THE AIRPORT FINDS ITSELF IN A BRIEF REPRIEVE FROM MVFR/IFR THIS
MORNING. THE SNOW IS ALMOST OUT OF THE PICTURE...BUT 800-1200 FT
STRATUS IS APPROACHING BUT OBSCURED BY 4000-6000 CEILINGS.
HOWEVER...GET A GOOD LOOK AT THE LOW STRATUS IN WESTERN AND THE
DAKOTAS OFF THE SATELLITE. KSTC...JUST PICKED UP A LOW CEILING IN
THE PAST HOUR...SO IT`S OWN IT`S WAY. WINDS BECOMING QUITE STRONG
THIS AFTERNOON. HAVE GUSTS TO 28 KTS IN THE TAF...WHICH MIGHT BE
JUST A HAIR STRONG...BUT THE POTENTIAL IS CERTAINLY THERE. STILL
INCLUDED A CHANCE FOR PERIODIC LIGHT SNOW IN A TEMPO GROUP RIGHT
AT THE START OF THE TAF. IT WILL BE VERY LIGHT.
/OUTLOOK FOR KMSP/
FRI...VFR. WINDS NW AT 10KTS.
SAT...VFR. WINDS SE AT 5 TO 10KTS.
SUN...VFR. WINDS NE AT 5 TO 10KTS.
&&
.PREV DISCUSSION...
/ISSUED 602 AM CST THU DEC 20 2012/
...BLIZZARD CONDITIONS EXPECTED TODAY ACROSS FAR SOUTHERN
MINNESOTA...
SHORT TERM...TODAY THROUGH SUNDAY.
THE MAIN FOCUS FOR THIS FORECAST PACKAGE HAS CLEARLY BEEN THE
POWERFUL SYSTEM NOW CENTERED OVER MISSOURI. IT WILL CONTINUE TO
TRACK NORTHEAST INTO NORTHERN ILLINOIS THIS AFTERNOON AND INTO
LOWER MICHIGAN BY THIS EVENING. RADAR CONTINUES TO INDICATE LIGHT
SNOW EAST OF A LINE FROM MANKATO TO MSP AND OSCEOLA. POCKETS OF
MODERATE SNOW CAN BE FOUND FURTHER EAST TOWARD EAU CLAIRE AND
POINTS SOUTH. THIS IS THE BACK EDGE OF THE SYSTEM AND SNOW WILL
CONTINUE TO PIVOT EASTWARD AND EXIT THE CWA LATE THIS MORNING OR
EARLY AFTERNOON. CLEARING SKIES CAN BE FOUND AS CLOSE AS ERN SD
WITH SUBSIDENCE/ISENTROPIC DOWNGLIDE.
AS THE STORM TRACKS NORTHEAST TODAY...THE PRESSURE GRADIENT WILL
INCREASE ACROSS THE AREA WITH STEEPENING LAPSE RATES BELOW 925 MB
IN STRONG CAA REGIME. RAP13 SHOWS 925 MB WINDS STRENGTHENING TO
BETWEEN 40 AND AS HIGH AS 50 KTS ALONG THE IOWA BORDER AFTER 15Z
THIS MORNING. RAP FORECAST SOUNDINGS FROM FAIRMONT AND ROCHESTER
INDICATE MIXING POTENTIAL TO THIS LEVEL...WITH BUFKIT PREDICTED
GUSTS FROM THE 950 MB LEVEL OF AT LEAST 35 KTS. SHOULD SEE
FREQUENT GUSTS EASILY REACH 40 OR 45 MPH...BUT THEY COULD APPROACH
OR EXCEED 50 MPH IN OPEN AREAS OF FAR SOUTHERN
MINNESOTA...INCLUDING ALONG THE I-90 CORRIDOR. GIVEN THE 3 OR 4
INCHES OF POWDERY SNOW THAT FELL TUESDAY MORNING AND THE
ADDITIONAL 2 TO 5 INCHES THAT FELL OVERNIGHT...A GROUND BLIZZARD
IS QUITE LIKELY TODAY SOUTH OF A LINE FROM TRIMONT TO OWATONNA.
WHITEOUT CONDITIONS WILL MAKE FOR NEAR IMPOSSIBLE TRAVEL.
THUS...EXPANDED THE BLIZZARD WARNING WESTWARD TO INCLUDE
WASECA...MARTIN...AND FARIBAULT COUNTIES THROUGH 6 PM. THINK AFTER
THAT TIME...WE WILL LOSE THE STEEP LAPSE RATES AND GUSTS SHOULD
BEGIN RAPIDLY SUBSIDING.
FURTHER NORTH...WINDS SHOULD NOT BE AS STRONG AND TOPOGRAPHY
ISSUES COME INTO PLAY...ESPECIALLY ACROSS WRN WI SO WILL NOT
EXPAND THE BLIZZARD WARNING INTO THOSE AREAS.
CLEAR SKIES AND DIMINISHING WINDS AS THE RIDGE BUILDS EASTWARD
INTO WRN MN WILL BRING TONIGHT/S LOWS DOWN INTO THE SINGLE DIGITS
ABOVE ZERO EAST AND BELOW ZERO WEST.
THE RIDGE WILL WEAKEN OVERHEAD FRIDAY...BUT A STRONGER 1035MB RIDGE
TO ITS NORTHWEST WILL BLEED DOWN INTO THE UPPER MISSISSIPPI VALLEY
SATURDAY KEEPING CONDITIONS DRY THROUGH THE WEEKEND.
LONG TERM...SUNDAY NIGHT THROUGH WEDNESDAY.
LOTS OF VARIABILITY IN THE MODELS WITH THE EVENTUAL TRACK OF A
STRONG SOUTHERN STREAM SYSTEM AROUND CHRISTMAS DAY. SEEMS AT THIS
POINT THE CONSENSUS WOULD BE TO SHUNT IT EAST OF THE REGION...
/EXCEPT FOR PERHAPS A LITTLE LIGHT SNOW WITH AN INVERTED TROUGH
PER EURO/ WITH COLD AIR DAMMING ALONG THE NORTHERN U.S. ROCKIES AS
A STRONG 1040+ MB HIGH PRESSURE SYSTEM BUILDS SOUTHEAST FROM
WESTERN CANADA. THIS WOULD SPELL A VERY COLD PATTERN WITH HIGHS
POTENTIALLY BELOW ZERO AND LOWS IN THE TEENS BELOW TO POSSIBLY 20S
BELOW. THE CURRENT GRIDS ADVERTISE A MILDER SOLUTION...BUT IF THE
TREND HOLDS...THE LONG TERM WILL NEED TO BE ADJUSTED 10 TO 20
DEGREES COLDER.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...WINTER STORM WARNING UNTIL 6 PM CST THIS EVENING FOR GOODHUE-
RICE.
WINTER WEATHER ADVISORY UNTIL 6 PM CST THIS EVENING FOR BLUE
EARTH-DAKOTA-LE SUEUR-WATONWAN.
BLIZZARD WARNING UNTIL 6 PM CST THIS EVENING FOR FARIBAULT-
FREEBORN-MARTIN-STEELE-WASECA.
WI...WINTER STORM WARNING UNTIL 6 PM CST THIS EVENING FOR CHIPPEWA-
DUNN-EAU CLAIRE-PEPIN-PIERCE.
WINTER WEATHER ADVISORY UNTIL 6 PM CST THIS EVENING FOR BARRON-
RUSK-ST. CROIX.
&&
$$
BORGHOFF/MPG
AREA FORECAST DISCUSSION
NWS RALEIGH NC
410 PM EST THU DEC 20 2012
.SYNOPSIS...
SURFACE HIGH PRESSURE OVER THE REGION WILL GRADUALLY SHIFT
OFFSHORE...AHEAD OF A STRONG COLD FRONT. THIS COLD FRONT WILL MOVE
ACROSS THE REGION TONIGHT...WITH BLUSTERY AND MUCH COOLER CONDITIONS
EXPECTED BEHIND THE FRONT. COOL AND DRY WEATHER WILL THEN DOMINATE
FOR THE WEEKEND AS HIGH PRESSURE BUILDS IN.
&&
.NEAR TERM /THROUGH FRIDAY NIGHT/...
AS OF 235 PM THURSDAY...
STRONG LOW PRESSURE MOVING INTO THE UPPER GREAT LAKES WITH VERY GOOD
TEMPERATURE AND MOISTURE ADVECTION STARTING TO TAKE PLACE ACROSS
SOUTH CAROLINA...TOWARD THE NORTH CAROLINA BORDER WHERE WINDS ARE
FINALLY STARTING TO SHOW A GUSTY CHARACTER. WEAK BOUNDARY EVIDENT
WITH BACKING WINDS NEAR AND JUST NORTHWEST OF THE TRIAD...IN
VICINITY OF KINT...AND AS THE RAIN MOVES IN THIS COULD BECOME A
WEDGE FRONT ALONG WHICH THE TRIPLE POINT MOVES NEAR THIS EVENING.
OVERALL EXPECTATIONS HAVE NOT CHANGED MUCH WITH THIS FORECAST
PACKAGE...WITH WIDESPREAD SHOWERS EXPECTED TO PUSH ACROSS CENTRAL
NORTH CAROLINA THIS EVENING. STILL HAVE THE MENTION OF THUNDER IN
AREA-WIDE...ALTHOUGH THE GREATEST POTENTIAL COULD BE...AGAIN...
ALONG AND NEAR A LINE FROM ABOUT WADESBORO AND ALBEMARLE NORTHEAST
THROUGH THE TRIANGLE TO NEAR KIXA AND KRWI. IT IS IN THIS AREA WHERE
THE DEEPER MOISTURE SHOULD END UP...AND LOOKING AT SOME LOW-LEVEL
MOISTURE PARAMETERS FOR THE LATE AFTERNOON AND EVENING REALLY LIKE
THE LATEST RUC DEPICTION OF THE POTENTIAL OF SOME LOWER 60S DEW
POINTS ADVECTING INTO THAT AREA VERY LATE THIS AFTERNOON AND INTO
THIS EVENING IN ADVANCE OF THE FRONT. IF THIS HOLDS...QUITE POSSIBLE
THAT HIGH TEMPERATURES COULD BE REALIZED AS LATE AS AROUND OR JUST
AFTER SUNSET...AND WILL ATTEMPT TO ACCOUNT FOR SOME OF THIS FINE
DETAIL IN THE GRIDDED FORECAST.
GFS AND NAM SOUNDINGS REMAIN MARGINAL WHEN IT COMES TO INSTABILITY...
BUT THE LATEST RUC SOUNDINGS...PARTICULARLY TOWARD KFAY...PAINT A
MARGINALLY OMINOUS PICTURE. LAPSE RATES THERE...IF THE RUC VERIFIES
EXACTLY...ARE NEAR MOIST ADIABATIC...AND GIVEN THE LIFT AND SHEAR...
RELATIVE TO THE REST OF CENTRAL NORTH CAROLINA THE BETTER POTENTIAL
FOR NEAR-SURFACE BASED ROTATING LOW-TOPPED STORMS WOULD BE AROUND
THERE. THIS COINCIDES WITH THE LATEST SPC DAY ONE OUTLOOK...AND
NEARER THE LOCAL WRF MODEL DEPICTION THE MAXIMUM UPDRAFT HELICITY.
WHAT STILL APPEARS MOST LIKELY IS NUMEROUS CELLS WITH MID-LEVEL
ROTATION...STRONG WINDS WHICH MAY APPROACH ADVISORY CRITERIA IN THE
STRONG THICKNESS PACKING AS THE DRY SLOT MOVES IN IMMEDIATELY BEHIND
THE SHOWERS AND THE FRONT...A MODEST POTENTIAL FOR SEVERE
STRAIGHT-LINE WINDS IN THE RICHER DEW POINT AIR...AND SOME POTENTIAL
FOR AN ISOLATED TORNADO KEYING ON THE AREA MAINLY EAST OF THE LINE
FROM KAFP TO KRWI. FOR NOW...THINK THAT THE LONGEVITY OF ADVISORY
CRITERIA WINDS MAY BE BRIEF AND NOTED CLOSE TO DEEP CONVECTION...
WITH BUFR SOUNDINGS AND GUIDANCE ACTUALLY SHOWING SOME MODEST
DECREASE TO WIND GUST POTENTIAL LATE. AS A RESULT...FOR NOW OPTED
NOT TO ISSUE A WIND ADVISORY OVERNIGHT...THOUGH BRIEF CONDITIONS MAY
WARRANT A SHORT-FUSED STATEMENT AT LEAST.
THOUGHTS THEN SHIFT TO THE POTENTIAL FOR VERY WINDY CONDITIONS IN
THE TIGHT GRADIENT FRIDAY. BUFR SOUNDINGS FROM BOTH THE NAM AND THE
GFS SUGGEST A HIGH PROBABILITY OF LOW-LEVEL WIND ADVISORY CRITERIA
FRIDAY...WITH POTENTIAL MIXING TO 40KT. HOWEVER...AS THE MID-LEVEL
TROUGH MOVES OVERHEAD...THE GFS IN PARTICULAR FORECASTS ENOUGH
MOISTURE TO PROVIDE FOR AREAS OF HIGH-LEVEL SC OR LOW-LEVEL AC
DURING THE LATE MORNING INTO THE AFTERNOON. IF CLOUDS ARE REALIZED A
LITTLE MORE THAN FORECAST...THIS COULD LIMIT MIXING POTENTIAL. FOR
THIS FORECAST WILL OPT TO ISSUE A WIND ADVISORY FOR FRIDAY...WITH A
FOCUS ON THE LATE MORNING THROUGH THE AFTERNOON...AS EVEN IF
CONDITIONS ARE ON THE MARGINS THERE COULD BE IMPACT AS IT SEEMS LIKE
IT HAS BEEN A WHILE SINCE CENTRAL NORTH CAROLINA HAS EXPERIENCED
WINDS EVEN CLOSE TO ADVISORY CRITERIA.
FRIDAY NIGHT...UNDER POSSIBLE LINGERING CLOUDS...ANTICIPATE THE
WINDS RELAXING RELATIVELY QUICKLY BUT STILL WITH A GUSTY CHARACTER
AS THE TROUGH AXIS DEPARTS AND THE GRADIENT REMAINS TIGHTER THAN
USUAL. AFTER OVERNIGHT LOWS TONIGHT FALLING TO THE LOWER TO MID 30S
NEAR THE YADKIN RIVER AND TO NEAR 40 TOWARD INTERSTATE 95...HIGHS ON
FRIDAY SHOULD RANGE FROM THE MID 40S TO AROUND 50...ACTUALLY FAIRLY
CLOSE TO OR JUST A CATEGORY BELOW NORMAL. LOWS FRIDAY NIGHT 25 TO
30...ANTICIPATING ENOUGH MIXING AND A FEW CLOUDS TO KEEP
TEMPERATURES FROM FALLING TOO FAR.
&&
.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
AS OF 255 PM THURSDAY...
SAT AND SAT NIGHT: IT WILL REMAIN RATHER BRISK IN CONTINUED
CAA...WITH BUFR MIXED LAYER WINDS SUGGESTIVE OF NORTHWESTERLY WINDS
GUSTING TO BETWEEN 25-30 KTS...HIGHEST NORTHEAST. THESE WINDS...IN
CONJUNCTION WITH DEWPOINTS IN THE TEENS AND CONSEQUENT RH AOB 25
PERCENT MAY RESULT IN FIRE WEATHER CONCERNS. WHILE SKIES SHOULD
REMAIN CLEAR OVERALL...THERE REMAINS A STRONG SIGNAL FOR OROGRAPHIC
CIRRUS OVER THE MIDDLE ATLANTIC FOOTHILLS/WESTERN PIEDMONT SAT
NIGHT. PREVIOUSLY FORECAST UPPER 40S TO LOWER-MIDDLE 50S REMAIN ON
TARGET. WINDS SHOULD DIMINISH OVERNIGHT OVER ALL BUT PERHAPS THE
NORTHEAST PIEDMONT AND NORTHERN COASTAL PLAIN...AS HIGH PRESSURE
OVER THE GULF COAST STATES RIDGES NORTHWARD. LOWS IN THE MIDDLE TO
UPPER 20S...TO AROUND 30 DEGREES OVER THE NW PIEDMONT IF OPAQUE
CIRRUS MATERIALIZES THERE.
A NORTHERN STREAM COLD FRONT WILL SETTLE SLOWLY SOUTHWARD TOWARD THE
VA STATE LINE BY SUNDAY NIGHT...WHERE IT WILL LIKELY STALL THERE IN
ADVANCE OF A LEAD S/W TROUGH AND SURFACE FRONTAL WAVE APPROACHING
FROM THE PLAINS. TRANQUIL AND GENERALLY MOSTLY CLEAR CONDITIONS...
ASIDE FROM CIRRUS...SHOULD ACCORDINGLY CONTINUE. MINIMALLY MILDER
HIGHS AND LESS CHILLY LOWS...IN THE LOWER TO MIDDLE 50S AND
30S...RESPECTIVELY.
&&
.LONG TERM /MONDAY THROUGH THURSDAY/...
AS OF 317 PM THURSDAY...
BECOMING WET COURTESY OF A POWERFUL EASTERN US STORM BY MID-WEEK.
WHILE MEDIUM RANGE GUIDANCE REMAINS IN GENERAL AGREEMENT WITH THE
HEMISPHERIC FLOW...INDIVIDUAL MODEL SOLUTIONS REGARDING THE TRACK OF
THE EASTERN US CYCLONE STILL VARY...AND ARE HIGHLY SENSITIVE TO
SUBTLETIES OF LOCATION OF BOTH HIGH LATITUDE BLOCKING FORECAST TO
DEVELOP INVOF BAFFIN ISLAND...AND AN ELONGATED VORTEX ACROSS
SOUTHERN CANADA. THESE SUBTLETIES...AND THE AMPLITUDE AND DEGREE
OF PHASING OF THE S/W TROUGHS EMBEDDED WITHIN A STRONG PACIFIC JET
ALL CAST FORECAST UNCERTAINTY...BUT THE PROBABILITY OF A SOAKING
RAIN MID-WEEK REMAINS HIGH...WITH THE THREAT OF WINTRY WEATHER STILL
LIKELY TO HOLD TO THE NORTH AND WEST OF EVEN THE FAVORED NC PIEDMONT
DAMMING REGION.
A LEAD S/W TROUGH WILL PIVOT FROM THE CENTRAL PLAINS TO THE GREAT
LAKES AND BE ACCOMPANIED BY A RELATIVELY WEAK SURFACE FRONTAL WAVE
THAT WILL MIGRATE THROUGH THE MIDDLE ATLANTIC STATES MON-MON NIGHT.
A PRECEDING WARM CONVEYOR/ISENTROPICALLY-DRIVEN CLOUD BAND AND
EMBEDDED SCATTERED SHOWERS WILL SPREAD EASTWARD ACROSS CENTRAL NC
MON AFTERNOON AND OVERNIGHT...BUT THE DEPTH OF THE ASSOCIATED
SATURATION IS FORECAST TO BE SHALLOWER/WARMER THAN WHAT IT APPEARED
24 HOURS AGO...SO PRECIPITATION AMOUNTS SHOULD BE GENERALLY A TENTH
OF AN INCH OR LESS...AND ONLY SCATTERED ABOUT.
THE TRAILING FRONT WILL THEN STALL OVER NC...IN ADVANCE OF THE MUCH
STRONGER WAVE FORECAST TO LIFT NORTHEASTWARD FROM THE GOM. THIS
BOUNDARY WILL FOCUS PRECIPITATION TUE-TUE NIGHT...CULMINATING IN
WIDESPREAD RAIN AS THE LOW TRACKS NORTH ON WED. IT STILL APPEARS
THAT ENOUGH DAMMING WILL HOLD EAST OF THE APPALACHIANS TO INDUCE
MILLER TYPE-B REDEVELOPMENT EAST OF THE INITIAL WAVE LIFTING OUT OF
THE GOM...BUT THE DEGREE OF THIS SEPARATION...AND DAMMING IN
BETWEEN...WILL BE A FUNCTION OF HOW THE AFOREMENTIONED HIGH-LATITUDE
BLOCKING AND CAD-SUPPORTING CONFLUENCE ALOFT EVOLVE. FAVOR AT THIS
TIME A MORE DOMINANT CONFLUENT REGIME ALOFT AND STRONGER CAD...WHICH
SUGGESTS THE NORTHWEST PIEDMONT SHOULD HOLD IN THE 40S ON WED...
RANGING TO LOWER-MIDDLE 60S OVER THE COASTAL PLAIN. MUCH COOLER AND
DRIER CONDITIONS WILL PREVAIL IN THE WAKE OF THE STORM BY WED NIGHT
AND ESPECIALLY THU.
&&
.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
AS OF 1240 PM THURSDAY...
VFR CONDITIONS WILL DETERIORATE AT LEAST INTO MVFR...AND LIKELY
BRIEFLY TO IFR...AS A STRONG COLD FRONT SWEEPS ACROSS CENTRAL NORTH
CAROLINA THIS EVENING INTO THE EARLY OVERNIGHT HOURS. CURRENT TIMING
WOULD SUGGEST THE FRONT MOVING THROUGH THE TRIAD AROUND 01Z...AROUND
03Z TOWARD KRDU AND KFAY...AND BY 05Z AT KRWI. AVIATION INTERESTS
SHOULD ANTICIPATE STRONG WIND GUSTS IMMEDIATELY FOLLOWING THE FRONT
WITH A QUICK SHIFT IN WIND DIRECTION FROM SOUTHERLY...TO SOUTHWEST
OR WEST-SOUTHWEST. WHILE SURFACE WINDS SHOULD DECREASE SOME WITHIN
AN HOUR FOLLOWING THE FRONT...AS CEILINGS ALSO RISE...WINDS OFF OF
THE SURFACE NEAR 2000FT SHOULD STILL BE AS HIGH AS 40KT.
WITH MIXING...GUSTY WINDS FRIDAY COULD RESULT IN GUSTS TO AROUND
35KT. IN THE COLD AIR WITH THE MID-LEVEL TROUGH OF LOW PRESSURE...
SOME VFR LEVEL CLOUDS ARE LIKELY WITH A HIGHER CONCENTRATION FOR
PERIODS OF THESE NORTH OF KFAY. THESE CLOUDS COULD LIMIT THE
POTENTIAL GUSTS SOMEWHAT AT THE SURFACE...BUT EVEN SO...WINDS WITHIN
2500FT OF THE SURFACE SHOULD EASILY APPROACH 40KT.
A GRADUAL DECREASE IN WINDS OCCURS FRIDAY NIGHT INTO SATURDAY. AHEAD
OF A WEAKER LOW PRESSURE SYSTEM...MOISTURE SHOULD START TO INCREASE
ONCE AGAIN BY EARLY NEXT WEEK. AS A RESULT...ADVERSE AVIATION
CONDITIONS MAINLY IN LOW CLOUDS COULD RETURN AS EARLY AS LATE IN THE
DAY MONDAY AND CONTINUING INTO TUESDAY...WITH CURRENTLY THE HIGHER
PROBABILITY TOWARD THE TRIAD ESPECIALLY LATE MONDAY INTO MONDAY
NIGHT.
&&
.FIRE WEATHER...
AS OF 410 PM THURSDAY...
BEHIND A POWERFUL CYCLONE FORECAST TO MIGRATE FROM THE UPPER MIDWEST
TO THE NORTHEAST...NORTHWEST WINDS WILL REMAIN STRONG -- IN THE
15-20 MPH RANGE WITH GUSTS IN THE UPPER 20S TO LOWER 30S MPH -- ON
SATURDAY. IN ADDITION...MUCH DRIER AIR CHARACTERIZED BY SURFACE
DEWPOINTS IN THE TEENS...WILL SUPPORT AFTERNOON HUMIDITY VALUES OF
20-25 PERCENT. THESE CONDITIONS MAY RESULT IN INCREASED FIRE
DANGER...AND FURTHER COORDINATION WITH THE NCFS REGARDING THIS
SCENARIO WILL TAKE PLACE ON FRI.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY FROM 9 AM TO 7 PM EST FRIDAY FOR NCZ007>011-
021>028-038>043-073>078-083>086-088-089.
&&
$$
SYNOPSIS...DJF
NEAR TERM...DJF
SHORT TERM...MWS
LONG TERM....MWS
AVIATION...DJF
FIRE WEATHER...MWS
AREA FORECAST DISCUSSION
NWS RALEIGH NC
317 PM EST THU DEC 20 2012
.SYNOPSIS...
SURFACE HIGH PRESSURE OVER THE REGION WILL GRADUALLY SHIFT
OFFSHORE...AHEAD OF A STRONG COLD FRONT. THIS COLD FRONT WILL MOVE
ACROSS THE REGION TONIGHT...WITH BLUSTERY AND MUCH COOLER CONDITIONS
EXPECTED BEHIND THE FRONT. COOL AND DRY WEATHER WILL THEN DOMINATE
FOR THE WEEKEND AS HIGH PRESSURE BUILDS IN.
&&
.NEAR TERM /THROUGH FRIDAY NIGHT/...
AS OF 235 PM THURSDAY...
STRONG LOW PRESSURE MOVING INTO THE UPPER GREAT LAKES WITH VERY GOOD
TEMPERATURE AND MOISTURE ADVECTION STARTING TO TAKE PLACE ACROSS
SOUTH CAROLINA...TOWARD THE NORTH CAROLINA BORDER WHERE WINDS ARE
FINALLY STARTING TO SHOW A GUSTY CHARACTER. WEAK BOUNDARY EVIDENT
WITH BACKING WINDS NEAR AND JUST NORTHWEST OF THE TRIAD...IN
VICINITY OF KINT...AND AS THE RAIN MOVES IN THIS COULD BECOME A
WEDGE FRONT ALONG WHICH THE TRIPLE POINT MOVES NEAR THIS EVENING.
OVERALL EXPECTATIONS HAVE NOT CHANGED MUCH WITH THIS FORECAST
PACKAGE...WITH WIDESPREAD SHOWERS EXPECTED TO PUSH ACROSS CENTRAL
NORTH CAROLINA THIS EVENING. STILL HAVE THE MENTION OF THUNDER IN
AREA-WIDE...ALTHOUGH THE GREATEST POTENTIAL COULD BE...AGAIN...
ALONG AND NEAR A LINE FROM ABOUT WADESBORO AND ALBEMARLE NORTHEAST
THROUGH THE TRIANGLE TO NEAR KIXA AND KRWI. IT IS IN THIS AREA WHERE
THE DEEPER MOISTURE SHOULD END UP...AND LOOKING AT SOME LOW-LEVEL
MOISTURE PARAMETERS FOR THE LATE AFTERNOON AND EVENING REALLY LIKE
THE LATEST RUC DEPICTION OF THE POTENTIAL OF SOME LOWER 60S DEW
POINTS ADVECTING INTO THAT AREA VERY LATE THIS AFTERNOON AND INTO
THIS EVENING IN ADVANCE OF THE FRONT. IF THIS HOLDS...QUITE POSSIBLE
THAT HIGH TEMPERATURES COULD BE REALIZED AS LATE AS AROUND OR JUST
AFTER SUNSET...AND WILL ATTEMPT TO ACCOUNT FOR SOME OF THIS FINE
DETAIL IN THE GRIDDED FORECAST.
GFS AND NAM SOUNDINGS REMAIN MARGINAL WHEN IT COMES TO INSTABILITY...
BUT THE LATEST RUC SOUNDINGS...PARTICULARLY TOWARD KFAY...PAINT A
MARGINALLY OMINOUS PICTURE. LAPSE RATES THERE...IF THE RUC VERIFIES
EXACTLY...ARE NEAR MOIST ADIABATIC...AND GIVEN THE LIFT AND SHEAR...
RELATIVE TO THE REST OF CENTRAL NORTH CAROLINA THE BETTER POTENTIAL
FOR NEAR-SURFACE BASED ROTATING LOW-TOPPED STORMS WOULD BE AROUND
THERE. THIS COINCIDES WITH THE LATEST SPC DAY ONE OUTLOOK...AND
NEARER THE LOCAL WRF MODEL DEPICTION THE MAXIMUM UPDRAFT HELICITY.
WHAT STILL APPEARS MOST LIKELY IS NUMEROUS CELLS WITH MID-LEVEL
ROTATION...STRONG WINDS WHICH MAY APPROACH ADVISORY CRITERIA IN THE
STRONG THICKNESS PACKING AS THE DRY SLOT MOVES IN IMMEDIATELY BEHIND
THE SHOWERS AND THE FRONT...A MODEST POTENTIAL FOR SEVERE
STRAIGHT-LINE WINDS IN THE RICHER DEW POINT AIR...AND SOME POTENTIAL
FOR AN ISOLATED TORNADO KEYING ON THE AREA MAINLY EAST OF THE LINE
FROM KAFP TO KRWI. FOR NOW...THINK THAT THE LONGEVITY OF ADVISORY
CRITERIA WINDS MAY BE BRIEF AND NOTED CLOSE TO DEEP CONVECTION...
WITH BUFR SOUNDINGS AND GUIDANCE ACTUALLY SHOWING SOME MODEST
DECREASE TO WIND GUST POTENTIAL LATE. AS A RESULT...FOR NOW OPTED
NOT TO ISSUE A WIND ADVISORY OVERNIGHT...THOUGH BRIEF CONDITIONS MAY
WARRANT A SHORT-FUSED STATEMENT AT LEAST.
THOUGHTS THEN SHIFT TO THE POTENTIAL FOR VERY WINDY CONDITIONS IN
THE TIGHT GRADIENT FRIDAY. BUFR SOUNDINGS FROM BOTH THE NAM AND THE
GFS SUGGEST A HIGH PROBABILITY OF LOW-LEVEL WIND ADVISORY CRITERIA
FRIDAY...WITH POTENTIAL MIXING TO 40KT. HOWEVER...AS THE MID-LEVEL
TROUGH MOVES OVERHEAD...THE GFS IN PARTICULAR FORECASTS ENOUGH
MOISTURE TO PROVIDE FOR AREAS OF HIGH-LEVEL SC OR LOW-LEVEL AC
DURING THE LATE MORNING INTO THE AFTERNOON. IF CLOUDS ARE REALIZED A
LITTLE MORE THAN FORECAST...THIS COULD LIMIT MIXING POTENTIAL. FOR
THIS FORECAST WILL OPT TO ISSUE A WIND ADVISORY FOR FRIDAY...WITH A
FOCUS ON THE LATE MORNING THROUGH THE AFTERNOON...AS EVEN IF
CONDITIONS ARE ON THE MARGINS THERE COULD BE IMPACT AS IT SEEMS LIKE
IT HAS BEEN A WHILE SINCE CENTRAL NORTH CAROLINA HAS EXPERIENCED
WINDS EVEN CLOSE TO ADVISORY CRITERIA.
FRIDAY NIGHT...UNDER POSSIBLE LINGERING CLOUDS...ANTICIPATE THE
WINDS RELAXING RELATIVELY QUICKLY BUT STILL WITH A GUSTY CHARACTER
AS THE TROUGH AXIS DEPARTS AND THE GRADIENT REMAINS TIGHTER THAN
USUAL. AFTER OVERNIGHT LOWS TONIGHT FALLING TO THE LOWER TO MID 30S
NEAR THE YADKIN RIVER AND TO NEAR 40 TOWARD INTERSTATE 95...HIGHS ON
FRIDAY SHOULD RANGE FROM THE MID 40S TO AROUND 50...ACTUALLY FAIRLY
CLOSE TO OR JUST A CATEGORY BELOW NORMAL. LOWS FRIDAY NIGHT 25 TO
30...ANTICIPATING ENOUGH MIXING AND A FEW CLOUDS TO KEEP
TEMPERATURES FROM FALLING TOO FAR.
&&
.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
AS OF 255 PM THURSDAY...
SAT AND SAT NIGHT: IT WILL REMAIN RATHER BRISK IN CONTINUED
CAA...WITH BUFR MIXED LAYER WINDS SUGGESTIVE OF NORTHWESTERLY WINDS
GUSTING TO BETWEEN 25-30 KTS...HIGHEST NORTHEAST. THESE WINDS...IN
CONJUNCTION WITH DEWPOINTS IN THE TEENS AND CONSEQUENT RH AOB 25
PERCENT MAY RESULT IN FIRE WEATHER CONCERNS. WHILE SKIES SHOULD
REMAIN CLEAR OVERALL...THERE REMAINS A STRONG SIGNAL FOR OROGRAPHIC
CIRRUS OVER THE MIDDLE ATLANTIC FOOTHILLS/WESTERN PIEDMONT SAT
NIGHT. PREVIOUSLY FORECAST UPPER 40S TO LOWER-MIDDLE 50S REMAIN ON
TARGET. WINDS SHOULD DIMINISH OVERNIGHT OVER ALL BUT PERHAPS THE
NORTHEAST PIEDMONT AND NORTHERN COASTAL PLAIN...AS HIGH PRESSURE
OVER THE GULF COAST STATES RIDGES NORTHWARD. LOWS IN THE MIDDLE TO
UPPER 20S...TO AROUND 30 DEGREES OVER THE NW PIEDMONT IF OPAQUE
CIRRUS MATERIALIZES THERE.
A NORTHERN STREAM COLD FRONT WILL SETTLE SLOWLY SOUTHWARD TOWARD THE
VA STATE LINE BY SUNDAY NIGHT...WHERE IT WILL LIKELY STALL THERE IN
ADVANCE OF A LEAD S/W TROUGH AND SURFACE FRONTAL WAVE APPROACHING
FROM THE PLAINS. TRANQUIL AND GENERALLY MOSTLY CLEAR CONDITIONS...
ASIDE FROM CIRRUS...SHOULD ACCORDINGLY CONTINUE. MINIMALLY MILDER
HIGHS AND LESS CHILLY LOWS...IN THE LOWER TO MIDDLE 50S AND
30S...RESPECTIVELY.
&&
.LONG TERM /MONDAY THROUGH THURSDAY/...
AS OF 317 PM THURSDAY...
BECOMING WET COURTESY OF A POWERFUL EASTERN US STORM BY MID-WEEK.
WHILE MEDIUM RANGE GUIDANCE REMAINS IN GENERAL AGREEMENT WITH THE
HEMISPHERIC FLOW...INDIVIDUAL MODEL SOLUTIONS REGARDING THE TRACK OF
THE EASTERN US CYCLONE STILL VARY...AND ARE HIGHLY SENSITIVE TO
SUBTLETIES OF LOCATION OF BOTH HIGH LATITUDE BLOCKING FORECAST TO
DEVELOP INVOF BAFFIN ISLAND...AND AN ELONGATED VORTEX ACROSS
SOUTHERN CANADA. THESE SUBTLETIES...AND THE AMPLITUDE AND DEGREE
OF PHASING OF THE S/W TROUGHS EMBEDDED WITHIN A STRONG PACIFIC JET
ALL CAST FORECAST UNCERTAINTY...BUT THE PROBABILITY OF A SOAKING
RAIN MID-WEEK REMAINS HIGH...WITH THE THREAT OF WINTRY WEATHER STILL
LIKELY TO HOLD TO THE NORTH AND WEST OF EVEN THE FAVORED NC PIEDMONT
DAMMING REGION.
A LEAD S/W TROUGH WILL PIVOT FROM THE CENTRAL PLAINS TO THE GREAT
LAKES AND BE ACCOMPANIED BY A RELATIVELY WEAK SURFACE FRONTAL WAVE
THAT WILL MIGRATE THROUGH THE MIDDLE ATLANTIC STATES MON-MON NIGHT.
A PRECEDING WARM CONVEYOR/ISENTROPICALLY-DRIVEN CLOUD BAND AND
EMBEDDED SCATTERED SHOWERS WILL SPREAD EASTWARD ACROSS CENTRAL NC
MON AFTERNOON AND OVERNIGHT...BUT THE DEPTH OF THE ASSOCIATED
SATURATION IS FORECAST TO BE SHALLOWER/WARMER THAN WHAT IT APPEARED
24 HOURS AGO...SO PRECIPITATION AMOUNTS SHOULD BE GENERALLY A TENTH
OF AN INCH OR LESS...AND ONLY SCATTERED ABOUT.
THE TRAILING FRONT WILL THEN STALL OVER NC...IN ADVANCE OF THE MUCH
STRONGER WAVE FORECAST TO LIFT NORTHEASTWARD FROM THE GOM. THIS
BOUNDARY WILL FOCUS PRECIPITATION TUE-TUE NIGHT...CULMINATING IN
WIDESPREAD RAIN AS THE LOW TRACKS NORTH ON WED. IT STILL APPEARS
THAT ENOUGH DAMMING WILL HOLD EAST OF THE APPALACHIANS TO INDUCE
MILLER TYPE-B REDEVELOPMENT EAST OF THE INITIAL WAVE LIFTING OUT OF
THE GOM...BUT THE DEGREE OF THIS SEPARATION...AND DAMMING IN
BETWEEN...WILL BE A FUNCTION OF HOW THE AFOREMENTIONED HIGH-LATITUDE
BLOCKING AND CAD-SUPPORTING CONFLUENCE ALOFT EVOLVE. FAVOR AT THIS
TIME A MORE DOMINANT CONFLUENT REGIME ALOFT AND STRONGER CAD...WHICH
SUGGESTS THE NORTHWEST PIEDMONT SHOULD HOLD IN THE 40S ON WED...
RANGING TO LOWER-MIDDLE 60S OVER THE COASTAL PLAIN. MUCH COOLER AND
DRIER CONDITIONS WILL PREVAIL IN THE WAKE OF THE STORM BY WED NIGHT
AND ESPECIALLY THU.
&&
.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
AS OF 1240 PM THURSDAY...
VFR CONDITIONS WILL DETERIORATE AT LEAST INTO MVFR...AND LIKELY
BRIEFLY TO IFR...AS A STRONG COLD FRONT SWEEPS ACROSS CENTRAL NORTH
CAROLINA THIS EVENING INTO THE EARLY OVERNIGHT HOURS. CURRENT TIMING
WOULD SUGGEST THE FRONT MOVING THROUGH THE TRIAD AROUND 01Z...AROUND
03Z TOWARD KRDU AND KFAY...AND BY 05Z AT KRWI. AVIATION INTERESTS
SHOULD ANTICIPATE STRONG WIND GUSTS IMMEDIATELY FOLLOWING THE FRONT
WITH A QUICK SHIFT IN WIND DIRECTION FROM SOUTHERLY...TO SOUTHWEST
OR WEST-SOUTHWEST. WHILE SURFACE WINDS SHOULD DECREASE SOME WITHIN
AN HOUR FOLLOWING THE FRONT...AS CEILINGS ALSO RISE...WINDS OFF OF
THE SURFACE NEAR 2000FT SHOULD STILL BE AS HIGH AS 40KT.
WITH MIXING...GUSTY WINDS FRIDAY COULD RESULT IN GUSTS TO AROUND
35KT. IN THE COLD AIR WITH THE MID-LEVEL TROUGH OF LOW PRESSURE...
SOME VFR LEVEL CLOUDS ARE LIKELY WITH A HIGHER CONCENTRATION FOR
PERIODS OF THESE NORTH OF KFAY. THESE CLOUDS COULD LIMIT THE
POTENTIAL GUSTS SOMEWHAT AT THE SURFACE...BUT EVEN SO...WINDS WITHIN
2500FT OF THE SURFACE SHOULD EASILY APPROACH 40KT.
A GRADUAL DECREASE IN WINDS OCCURS FRIDAY NIGHT INTO SATURDAY. AHEAD
OF A WEAKER LOW PRESSURE SYSTEM...MOISTURE SHOULD START TO INCREASE
ONCE AGAIN BY EARLY NEXT WEEK. AS A RESULT...ADVERSE AVIATION
CONDITIONS MAINLY IN LOW CLOUDS COULD RETURN AS EARLY AS LATE IN THE
DAY MONDAY AND CONTINUING INTO TUESDAY...WITH CURRENTLY THE HIGHER
PROBABILITY TOWARD THE TRIAD ESPECIALLY LATE MONDAY INTO MONDAY
NIGHT.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY FROM 9 AM TO 7 PM EST FRIDAY FOR NCZ007>011-
021>028-038>043-073>078-083>086-088-089.
&&
$$
SYNOPSIS...DJF
NEAR TERM...DJF
SHORT TERM...MWS
LONG TERM....MWS
AVIATION...DJF
AREA FORECAST DISCUSSION
NWS RALEIGH NC
258 PM EST THU DEC 20 2012
.SYNOPSIS...
SURFACE HIGH PRESSURE OVER THE REGION WILL GRADUALLY SHIFT
OFFSHORE...AHEAD OF A STRONG COLD FRONT. THIS COLD FRONT WILL MOVE
ACROSS THE REGION TONIGHT...WITH BLUSTERY AND MUCH COOLER CONDITIONS
EXPECTED BEHIND THE FRONT. COOL AND DRY WEATHER WILL THEN DOMINATE
FOR THE WEEKEND AS HIGH PRESSURE BUILDS IN.
&&
.NEAR TERM /THROUGH FRIDAY NIGHT/...
AS OF 235 PM THURSDAY...
STRONG LOW PRESSURE MOVING INTO THE UPPER GREAT LAKES WITH VERY GOOD
TEMPERATURE AND MOISTURE ADVECTION STARTING TO TAKE PLACE ACROSS
SOUTH CAROLINA...TOWARD THE NORTH CAROLINA BORDER WHERE WINDS ARE
FINALLY STARTING TO SHOW A GUSTY CHARACTER. WEAK BOUNDARY EVIDENT
WITH BACKING WINDS NEAR AND JUST NORTHWEST OF THE TRIAD...IN
VICINITY OF KINT...AND AS THE RAIN MOVES IN THIS COULD BECOME A
WEDGE FRONT ALONG WHICH THE TRIPLE POINT MOVES NEAR THIS EVENING.
OVERALL EXPECTATIONS HAVE NOT CHANGED MUCH WITH THIS FORECAST
PACKAGE...WITH WIDESPREAD SHOWERS EXPECTED TO PUSH ACROSS CENTRAL
NORTH CAROLINA THIS EVENING. STILL HAVE THE MENTION OF THUNDER IN
AREA-WIDE...ALTHOUGH THE GREATEST POTENTIAL COULD BE...AGAIN...
ALONG AND NEAR A LINE FROM ABOUT WADESBORO AND ALBEMARLE NORTHEAST
THROUGH THE TRIANGLE TO NEAR KIXA AND KRWI. IT IS IN THIS AREA WHERE
THE DEEPER MOISTURE SHOULD END UP...AND LOOKING AT SOME LOW-LEVEL
MOISTURE PARAMETERS FOR THE LATE AFTERNOON AND EVENING REALLY LIKE
THE LATEST RUC DEPICTION OF THE POTENTIAL OF SOME LOWER 60S DEW
POINTS ADVECTING INTO THAT AREA VERY LATE THIS AFTERNOON AND INTO
THIS EVENING IN ADVANCE OF THE FRONT. IF THIS HOLDS...QUITE POSSIBLE
THAT HIGH TEMPERATURES COULD BE REALIZED AS LATE AS AROUND OR JUST
AFTER SUNSET...AND WILL ATTEMPT TO ACCOUNT FOR SOME OF THIS FINE
DETAIL IN THE GRIDDED FORECAST.
GFS AND NAM SOUNDINGS REMAIN MARGINAL WHEN IT COMES TO INSTABILITY...
BUT THE LATEST RUC SOUNDINGS...PARTICULARLY TOWARD KFAY...PAINT A
MARGINALLY OMINOUS PICTURE. LAPSE RATES THERE...IF THE RUC VERIFIES
EXACTLY...ARE NEAR MOIST ADIABATIC...AND GIVEN THE LIFT AND SHEAR...
RELATIVE TO THE REST OF CENTRAL NORTH CAROLINA THE BETTER POTENTIAL
FOR NEAR-SURFACE BASED ROTATING LOW-TOPPED STORMS WOULD BE AROUND
THERE. THIS COINCIDES WITH THE LATEST SPC DAY ONE OUTLOOK...AND
NEARER THE LOCAL WRF MODEL DEPICTION THE MAXIMUM UPDRAFT HELICITY.
WHAT STILL APPEARS MOST LIKELY IS NUMEROUS CELLS WITH MID-LEVEL
ROTATION...STRONG WINDS WHICH MAY APPROACH ADVISORY CRITERIA IN THE
STRONG THICKNESS PACKING AS THE DRY SLOT MOVES IN IMMEDIATELY BEHIND
THE SHOWERS AND THE FRONT...A MODEST POTENTIAL FOR SEVERE
STRAIGHT-LINE WINDS IN THE RICHER DEW POINT AIR...AND SOME POTENTIAL
FOR AN ISOLATED TORNADO KEYING ON THE AREA MAINLY EAST OF THE LINE
FROM KAFP TO KRWI. FOR NOW...THINK THAT THE LONGEVITY OF ADVISORY
CRITERIA WINDS MAY BE BRIEF AND NOTED CLOSE TO DEEP CONVECTION...
WITH BUFR SOUNDINGS AND GUIDANCE ACTUALLY SHOWING SOME MODEST
DECREASE TO WIND GUST POTENTIAL LATE. AS A RESULT...FOR NOW OPTED
NOT TO ISSUE A WIND ADVISORY OVERNIGHT...THOUGH BRIEF CONDITIONS MAY
WARRANT A SHORT-FUSED STATEMENT AT LEAST.
THOUGHTS THEN SHIFT TO THE POTENTIAL FOR VERY WINDY CONDITIONS IN
THE TIGHT GRADIENT FRIDAY. BUFR SOUNDINGS FROM BOTH THE NAM AND THE
GFS SUGGEST A HIGH PROBABILITY OF LOW-LEVEL WIND ADVISORY CRITERIA
FRIDAY...WITH POTENTIAL MIXING TO 40KT. HOWEVER...AS THE MID-LEVEL
TROUGH MOVES OVERHEAD...THE GFS IN PARTICULAR FORECASTS ENOUGH
MOISTURE TO PROVIDE FOR AREAS OF HIGH-LEVEL SC OR LOW-LEVEL AC
DURING THE LATE MORNING INTO THE AFTERNOON. IF CLOUDS ARE REALIZED A
LITTLE MORE THAN FORECAST...THIS COULD LIMIT MIXING POTENTIAL. FOR
THIS FORECAST WILL OPT TO ISSUE A WIND ADVISORY FOR FRIDAY...WITH A
FOCUS ON THE LATE MORNING THROUGH THE AFTERNOON...AS EVEN IF
CONDITIONS ARE ON THE MARGINS THERE COULD BE IMPACT AS IT SEEMS LIKE
IT HAS BEEN A WHILE SINCE CENTRAL NORTH CAROLINA HAS EXPERIENCED
WINDS EVEN CLOSE TO ADVISORY CRITERIA.
FRIDAY NIGHT...UNDER POSSIBLE LINGERING CLOUDS...ANTICIPATE THE
WINDS RELAXING RELATIVELY QUICKLY BUT STILL WITH A GUSTY CHARACTER
AS THE TROUGH AXIS DEPARTS AND THE GRADIENT REMAINS TIGHTER THAN
USUAL. AFTER OVERNIGHT LOWS TONIGHT FALLING TO THE LOWER TO MID 30S
NEAR THE YADKIN RIVER AND TO NEAR 40 TOWARD INTERSTATE 95...HIGHS ON
FRIDAY SHOULD RANGE FROM THE MID 40S TO AROUND 50...ACTUALLY FAIRLY
CLOSE TO OR JUST A CATEGORY BELOW NORMAL. LOWS FRIDAY NIGHT 25 TO
30...ANTICIPATING ENOUGH MIXING AND A FEW CLOUDS TO KEEP
TEMPERATURES FROM FALLING TOO FAR.
&&
.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
AS OF 255 PM THURSDAY...
SAT AND SAT NIGHT: IT WILL REMAIN RATHER BRISK IN CONTINUED
CAA...WITH BUFR MIXED LAYER WINDS SUGGESTIVE OF NORTHWESTERLY WINDS
GUSTING TO BETWEEN 25-30 KTS...HIGHEST NORTHEAST. THESE WINDS...IN
CONJUNCTION WITH DEWPOINTS IN THE TEENS AND CONSEQUENT RH AOB 25
PERCENT MAY RESULT IN FIRE WEATHER CONCERNS. WHILE SKIES SHOULD
REMAIN CLEAR OVERALL...THERE REMAINS A STRONG SIGNAL FOR OROGRAPHIC
CIRRUS OVER THE MIDDLE ATLANTIC FOOTHILLS/WESTERN PIEDMONT SAT
NIGHT. PREVIOUSLY FORECAST UPPER 40S TO LOWER-MIDDLE 50S REMAIN ON
TARGET. WINDS SHOULD DIMINISH OVERNIGHT OVER ALL BUT PERHAPS THE
NORTHEAST PIEDMONT AND NORTHERN COASTAL PLAIN...AS HIGH PRESSURE
OVER THE GULF COAST STATES RIDGES NORTHWARD. LOWS IN THE MIDDLE TO
UPPER 20S...TO AROUND 30 DEGREES OVER THE NW PIEDMONT IF OPAQUE
CIRRUS MATERIALIZES THERE.
A NORTHERN STREAM COLD FRONT WILL SETTLE SLOWLY SOUTHWARD TOWARD THE
VA STATE LINE BY SUNDAY NIGHT...WHERE IT WILL LIKELY STALL THERE IN
ADVANCE OF A LEAD S/W TROUGH AND SURFACE FRONTAL WAVE APPROACHING
FROM THE PLAINS. TRANQUIL AND GENERALLY MOSTLY CLEAR CONDITIONS...
ASIDE FROM CIRRUS...SHOULD ACCORDINGLY CONTINUE. MINIMALLY MILDER
HIGHS AND LESS CHILLY LOWS...IN THE LOWER TO MIDDLE 50S AND
30S...RESPECTIVELY.
&&
.LONG TERM /MONDAY THROUGH WEDNESDAY/...
AS OF 300 AM THURSDAY...
DRY CONDITIONS WILL CONTINUE INTO THE FIRST HALF OF CHRISTMAS EVE
DAY BEFORE A WEAK QUICK HITTING SOUTHERN STREAM WAVE BRINGS SOME
LIGHT PRECIP/RAIN TO THE FORECAST AREA CHRISTMAS EVE EVENING/NIGHT.
IT APPEARS THERE WILL BE A BRIEF LULL ON CHRISTMAS DAY IN THE WAKE
OF THE AFOREMENTIONED SYSTEM AS A 1030 MB CONTINENTAL POLAR HIGH
PRESSURE BUILDS SOUTH INTO THE MID-ATLANTIC REGION.
CHRISTMAS NIGHT ON...MODEL SPREAD INCREASES SIGNIFICANTLY
WITH HOW MUCH INTERACTION/PHASING WILL RESULT IN UPSTREAM
AMPLIFICATION OF NEXT SOUTHERN STREAM SYSTEM. DESPITE THESE
DIFFERENCES...MODELS ARE SIMILAR WITH THE TIMING OF PRECIP SPREADING
INTO THE AREA LATE CHRISTMAS NIGHT AND INTO WEDNESDAY AS WARMER AIR
ALOFT OVERSPREADS OVER THE REGION...WITH SOME DEGREE OF COLD AIR
DAMMING OVER THE CAROLINAS. AT THIS TIME...IT APPEARS TOO WARM TO
SUPPORT ANYTHING BUT RAIN...WITH THE POTENTIAL FOR A WIDESPREAD
SOAKING OF A HALF TO ONE INCH POSSIBLE ACROSS THE AREA.
&&
.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
AS OF 1240 PM THURSDAY...
VFR CONDITIONS WILL DETERIORATE AT LEAST INTO MVFR...AND LIKELY
BRIEFLY TO IFR...AS A STRONG COLD FRONT SWEEPS ACROSS CENTRAL NORTH
CAROLINA THIS EVENING INTO THE EARLY OVERNIGHT HOURS. CURRENT TIMING
WOULD SUGGEST THE FRONT MOVING THROUGH THE TRIAD AROUND 01Z...AROUND
03Z TOWARD KRDU AND KFAY...AND BY 05Z AT KRWI. AVIATION INTERESTS
SHOULD ANTICIPATE STRONG WIND GUSTS IMMEDIATELY FOLLOWING THE FRONT
WITH A QUICK SHIFT IN WIND DIRECTION FROM SOUTHERLY...TO SOUTHWEST
OR WEST-SOUTHWEST. WHILE SURFACE WINDS SHOULD DECREASE SOME WITHIN
AN HOUR FOLLOWING THE FRONT...AS CEILINGS ALSO RISE...WINDS OFF OF
THE SURFACE NEAR 2000FT SHOULD STILL BE AS HIGH AS 40KT.
WITH MIXING...GUSTY WINDS FRIDAY COULD RESULT IN GUSTS TO AROUND
35KT. IN THE COLD AIR WITH THE MID-LEVEL TROUGH OF LOW PRESSURE...
SOME VFR LEVEL CLOUDS ARE LIKELY WITH A HIGHER CONCENTRATION FOR
PERIODS OF THESE NORTH OF KFAY. THESE CLOUDS COULD LIMIT THE
POTENTIAL GUSTS SOMEWHAT AT THE SURFACE...BUT EVEN SO...WINDS WITHIN
2500FT OF THE SURFACE SHOULD EASILY APPROACH 40KT.
A GRADUAL DECREASE IN WINDS OCCURS FRIDAY NIGHT INTO SATURDAY. AHEAD
OF A WEAKER LOW PRESSURE SYSTEM...MOISTURE SHOULD START TO INCREASE
ONCE AGAIN BY EARLY NEXT WEEK. AS A RESULT...ADVERSE AVIATION
CONDITIONS MAINLY IN LOW CLOUDS COULD RETURN AS EARLY AS LATE IN THE
DAY MONDAY AND CONTINUING INTO TUESDAY...WITH CURRENTLY THE HIGHER
PROBABILITY TOWARD THE TRIAD ESPECIALLY LATE MONDAY INTO MONDAY
NIGHT.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY FROM 9 AM TO 7 PM EST FRIDAY FOR NCZ007>011-
021>028-038>043-073>078-083>086-088-089.
&&
$$
SYNOPSIS...DJF
NEAR TERM...DJF
SHORT TERM...MWS
LONG TERM....CBL
AVIATION...DJF
AREA FORECAST DISCUSSION
NWS RALEIGH NC
235 PM EST THU DEC 20 2012
.SYNOPSIS...
SURFACE HIGH PRESSURE OVER THE REGION WILL GRADUALLY SHIFT
OFFSHORE...AHEAD OF A STRONG COLD FRONT. THIS COLD FRONT WILL MOVE
ACROSS THE REGION TONIGHT...WITH BLUSTERY AND MUCH COOLER CONDITIONS
EXPECTED BEHIND THE FRONT. COOL AND DRY WEATHER WILL THEN DOMINATE
FOR THE WEEKEND AS HIGH PRESSURE BUILDS IN.
&&
.NEAR TERM /THROUGH FRIDAY NIGHT/...
AS OF 235 PM THURSDAY...
STRONG LOW PRESSURE MOVING INTO THE UPPER GREAT LAKES WITH VERY GOOD
TEMPERATURE AND MOISTURE ADVECTION STARTING TO TAKE PLACE ACROSS
SOUTH CAROLINA...TOWARD THE NORTH CAROLINA BORDER WHERE WINDS ARE
FINALLY STARTING TO SHOW A GUSTY CHARACTER. WEAK BOUNDARY EVIDENT
WITH BACKING WINDS NEAR AND JUST NORTHWEST OF THE TRIAD...IN
VICINITY OF KINT...AND AS THE RAIN MOVES IN THIS COULD BECOME A
WEDGE FRONT ALONG WHICH THE TRIPLE POINT MOVES NEAR THIS EVENING.
OVERALL EXPECTATIONS HAVE NOT CHANGED MUCH WITH THIS FORECAST
PACKAGE...WITH WIDESPREAD SHOWERS EXPECTED TO PUSH ACROSS CENTRAL
NORTH CAROLINA THIS EVENING. STILL HAVE THE MENTION OF THUNDER IN
AREA-WIDE...ALTHOUGH THE GREATEST POTENTIAL COULD BE...AGAIN...
ALONG AND NEAR A LINE FROM ABOUT WADESBORO AND ALBEMARLE NORTHEAST
THROUGH THE TRIANGLE TO NEAR KIXA AND KRWI. IT IS IN THIS AREA WHERE
THE DEEPER MOISTURE SHOULD END UP...AND LOOKING AT SOME LOW-LEVEL
MOISTURE PARAMETERS FOR THE LATE AFTERNOON AND EVENING REALLY LIKE
THE LATEST RUC DEPICTION OF THE POTENTIAL OF SOME LOWER 60S DEW
POINTS ADVECTING INTO THAT AREA VERY LATE THIS AFTERNOON AND INTO
THIS EVENING IN ADVANCE OF THE FRONT. IF THIS HOLDS...QUITE POSSIBLE
THAT HIGH TEMPERATURES COULD BE REALIZED AS LATE AS AROUND OR JUST
AFTER SUNSET...AND WILL ATTEMPT TO ACCOUNT FOR SOME OF THIS FINE
DETAIL IN THE GRIDDED FORECAST.
GFS AND NAM SOUNDINGS REMAIN MARGINAL WHEN IT COMES TO INSTABILITY...
BUT THE LATEST RUC SOUNDINGS...PARTICULARLY TOWARD KFAY...PAINT A
MARGINALLY OMINOUS PICTURE. LAPSE RATES THERE...IF THE RUC VERIFIES
EXACTLY...ARE NEAR MOIST ADIABATIC...AND GIVEN THE LIFT AND SHEAR...
RELATIVE TO THE REST OF CENTRAL NORTH CAROLINA THE BETTER POTENTIAL
FOR NEAR-SURFACE BASED ROTATING LOW-TOPPED STORMS WOULD BE AROUND
THERE. THIS COINCIDES WITH THE LATEST SPC DAY ONE OUTLOOK...AND
NEARER THE LOCAL WRF MODEL DEPICTION THE MAXIMUM UPDRAFT HELICITY.
WHAT STILL APPEARS MOST LIKELY IS NUMEROUS CELLS WITH MID-LEVEL
ROTATION...STRONG WINDS WHICH MAY APPROACH ADVISORY CRITERIA IN THE
STRONG THICKNESS PACKING AS THE DRY SLOT MOVES IN IMMEDIATELY BEHIND
THE SHOWERS AND THE FRONT...A MODEST POTENTIAL FOR SEVERE
STRAIGHT-LINE WINDS IN THE RICHER DEW POINT AIR...AND SOME POTENTIAL
FOR AN ISOLATED TORNADO KEYING ON THE AREA MAINLY EAST OF THE LINE
FROM KAFP TO KRWI. FOR NOW...THINK THAT THE LONGEVITY OF ADVISORY
CRITERIA WINDS MAY BE BRIEF AND NOTED CLOSE TO DEEP CONVECTION...
WITH BUFR SOUNDINGS AND GUIDANCE ACTUALLY SHOWING SOME MODEST
DECREASE TO WIND GUST POTENTIAL LATE. AS A RESULT...FOR NOW OPTED
NOT TO ISSUE A WIND ADVISORY OVERNIGHT...THOUGH BRIEF CONDITIONS MAY
WARRANT A SHORT-FUSED STATEMENT AT LEAST.
THOUGHTS THEN SHIFT TO THE POTENTIAL FOR VERY WINDY CONDITIONS IN
THE TIGHT GRADIENT FRIDAY. BUFR SOUNDINGS FROM BOTH THE NAM AND THE
GFS SUGGEST A HIGH PROBABILITY OF LOW-LEVEL WIND ADVISORY CRITERIA
FRIDAY...WITH POTENTIAL MIXING TO 40KT. HOWEVER...AS THE MID-LEVEL
TROUGH MOVES OVERHEAD...THE GFS IN PARTICULAR FORECASTS ENOUGH
MOISTURE TO PROVIDE FOR AREAS OF HIGH-LEVEL SC OR LOW-LEVEL AC
DURING THE LATE MORNING INTO THE AFTERNOON. IF CLOUDS ARE REALIZED A
LITTLE MORE THAN FORECAST...THIS COULD LIMIT MIXING POTENTIAL. FOR
THIS FORECAST WILL OPT TO ISSUE A WIND ADVISORY FOR FRIDAY...WITH A
FOCUS ON THE LATE MORNING THROUGH THE AFTERNOON...AS EVEN IF
CONDITIONS ARE ON THE MARGINS THERE COULD BE IMPACT AS IT SEEMS LIKE
IT HAS BEEN A WHILE SINCE CENTRAL NORTH CAROLINA HAS EXPERIENCED
WINDS EVEN CLOSE TO ADVISORY CRITERIA.
FRIDAY NIGHT...UNDER POSSIBLE LINGERING CLOUDS...ANTICIPATE THE
WINDS RELAXING RELATIVELY QUICKLY BUT STILL WITH A GUSTY CHARACTER
AS THE TROUGH AXIS DEPARTS AND THE GRADIENT REMAINS TIGHTER THAN
USUAL. AFTER OVERNIGHT LOWS TONIGHT FALLING TO THE LOWER TO MID 30S
NEAR THE YADKIN RIVER AND TO NEAR 40 TOWARD INTERSTATE 95...HIGHS ON
FRIDAY SHOULD RANGE FROM THE MID 40S TO AROUND 50...ACTUALLY FAIRLY
CLOSE TO OR JUST A CATEGORY BELOW NORMAL. LOWS FRIDAY NIGHT 25 TO
30...ANTICIPATING ENOUGH MIXING AND A FEW CLOUDS TO KEEP
TEMPERATURES FROM FALLING TOO FAR.
&&
.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
AS OF 235 AM THURSDAY...
WHILE MODELS INDICATE SLIGHTLY SHALLOWER MIXING ON SATURDAY...FCST
SOUNDINGS CONTINUE TO SHOW 30 TO 33 KTS WITHIN THE MIXED LAYER
AND CONTINUED TIGHT PACKING OF ISOBARS ACROSS THE CAROLINAS
THROUGH AT LEAST MIDDAY...BEFORE WEAKENING LATE IN THE DAY AS SURFACE
HIGH OVER THE NORTHERN GULF BUILDS EASTWARD. WHILE NOT AS STRONG AS
FRIDAY...CENTRAL NC WILL STILL SEE BRISK WEST-NORTHWESTERLY WINDS OF
15 TO 20KTS WITH GUSTS OF 25 TO 28KTS. TEMPERATURES/THICKNESSES
BEGIN TO REBOUND AS THERMAL TROUGH AXIS LIFTS OUT OF THE AREA. HIGHS
IN THE UPPER 40S/NEAR 50 NORTH TO LOWER/MID 50S SOUTH. WINDS FINALLY
DECOUPLE SATURDAY NIGHT...WHICH WITH CLEAR SKIES WILL LEAD TO A
LARGER SPREAD IN MIN TEMPS. LOWS RANGING FROM LOWER 20S IN
RURAL/OUTLYING AREAS TO MID AND UPPER 20S ELSEWHERE.
&&
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
AS OF 300 AM THURSDAY...
DRY CONDITIONS WILL CONTINUE SUNDAY AND INTO THE FIRST HALF OF
CHRISTMAS EVE DAY BEFORE A WEAK QUICK HITTING SOUTHERN STREAM WAVE
BRINGS SOME LIGHT PRECIP/RAIN TO THE FORECAST AREA CHRISTMAS EVE
EVENING/NIGHT. IT APPEARS THERE WILL BE A BRIEF LULL ON CHRISTMAS
DAY IN THE WAKE OF THE AFOREMENTIONED SYSTEM AS A 1030 MB
CONTINENTAL POLAR HIGH PRESSURE BUILDS SOUTH INTO THE MID-ATLANTIC
REGION.
CHRISTMAS NIGHT ON...MODEL SPREAD INCREASES SIGNIFICANTLY
WITH HOW MUCH INTERACTION/PHASING WILL RESULT IN UPSTREAM
AMPLIFICATION OF NEXT SOUTHERN STREAM SYSTEM. DESPITE THESE
DIFFERENCES...MODELS ARE SIMILAR WITH THE TIMING OF PRECIP SPREADING
INTO THE AREA LATE CHRISTMAS NIGHT AND INTO WEDNESDAY AS WARMER AIR
ALOFT OVERSPREADS OVER THE REGION...WITH SOME DEGREE OF COLD AIR
DAMMING OVER THE CAROLINAS. AT THIS TIME...IT APPEARS TOO WARM TO
SUPPORT ANYTHING BUT RAIN...WITH THE POTENTIAL FOR A WIDESPREAD
SOAKING OF A HALF TO ONE INCH POSSIBLE ACROSS THE AREA.
&&
.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
AS OF 1240 PM THURSDAY...
VFR CONDITIONS WILL DETERIORATE AT LEAST INTO MVFR...AND LIKELY
BRIEFLY TO IFR...AS A STRONG COLD FRONT SWEEPS ACROSS CENTRAL NORTH
CAROLINA THIS EVENING INTO THE EARLY OVERNIGHT HOURS. CURRENT TIMING
WOULD SUGGEST THE FRONT MOVING THROUGH THE TRIAD AROUND 01Z...AROUND
03Z TOWARD KRDU AND KFAY...AND BY 05Z AT KRWI. AVIATION INTERESTS
SHOULD ANTICIPATE STRONG WIND GUSTS IMMEDIATELY FOLLOWING THE FRONT
WITH A QUICK SHIFT IN WIND DIRECTION FROM SOUTHERLY...TO SOUTHWEST
OR WEST-SOUTHWEST. WHILE SURFACE WINDS SHOULD DECREASE SOME WITHIN
AN HOUR FOLLOWING THE FRONT...AS CEILINGS ALSO RISE...WINDS OFF OF
THE SURFACE NEAR 2000FT SHOULD STILL BE AS HIGH AS 40KT.
WITH MIXING...GUSTY WINDS FRIDAY COULD RESULT IN GUSTS TO AROUND
35KT. IN THE COLD AIR WITH THE MID-LEVEL TROUGH OF LOW PRESSURE...
SOME VFR LEVEL CLOUDS ARE LIKELY WITH A HIGHER CONCENTRATION FOR
PERIODS OF THESE NORTH OF KFAY. THESE CLOUDS COULD LIMIT THE
POTENTIAL GUSTS SOMEWHAT AT THE SURFACE...BUT EVEN SO...WINDS WITHIN
2500FT OF THE SURFACE SHOULD EASILY APPROACH 40KT.
A GRADUAL DECREASE IN WINDS OCCURS FRIDAY NIGHT INTO SATURDAY. AHEAD
OF A WEAKER LOW PRESSURE SYSTEM...MOISTURE SHOULD START TO INCREASE
ONCE AGAIN BY EARLY NEXT WEEK. AS A RESULT...ADVERSE AVIATION
CONDITIONS MAINLY IN LOW CLOUDS COULD RETURN AS EARLY AS LATE IN THE
DAY MONDAY AND CONTINUING INTO TUESDAY...WITH CURRENTLY THE HIGHER
PROBABILITY TOWARD THE TRIAD ESPECIALLY LATE MONDAY INTO MONDAY
NIGHT.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY FROM 9 AM TO 7 PM EST FRIDAY FOR NCZ007>011-
021>028-038>043-073>078-083>086-088-089.
&&
$$
SYNOPSIS...DJF
NEAR TERM...DJF
SHORT TERM...CBL
LONG TERM....CBL
AVIATION...DJF
AREA FORECAST DISCUSSION
NWS CHARLESTON WV
436 PM EST THU DEC 20 2012
.SYNOPSIS...
STRONG COLD FRONT PLOWS THROUGH THIS EVENING. SNOW SHOWERS BEHIND
LOW PRESSURE TONIGHT INTO SATURDAY. HIGH PRESSURE PASSES SUNDAY. LOW
PRESSURE CHRISTMAS EVE AND AGAIN MIDWEEK.
&&
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
INITIAL PRECIP FROM THIS MORNING HAS MOSTLY LIFTED TO THE
NORTH...WITH THE NEXT BATCH ALREADY WELL INTO WESTERN CWA. HAVE
GOTTEN SOME REPORTS OF LIGHT SNOW FALLING ACROSS HIGHER TERRAIN IN
NORTHERN WV MOUNTAINS. THIS IS TIED TO A SMALL COLD POOL STILL IN
PLACE...BUT AS WINDS SHIFT AROUND TO MORE S THEN SW...THIS COLD POOL
SHOULD BE CLEARED OUT WITH A RETURN TO RAIN UNTIL TONIGHT. ALL THIS
CURRENT PRECIP IS STILL WELL PRE-FRONTAL...WITH THE COLD FRONT
CURRENTLY RUNNING FROM THE LOW IN NORTHEASTERN IL...THROUGH SW
IN...AND CENTRAL KY/TN. AT 19Z...FRONT SHOWING UP WELL ON RADAR IN
KY...RUNNING FROM ROUGHLY KGLW TO KSDF. PRE-FRONTAL PRECIP SHOULD
WRAP UP BEFORE THE FRONT...WITH A THIN LINE OF SHOWERS RIGHT ALONG
THE FRONT. IN GENERAL PRE-FRONTAL WIND GUSTS HAVE BEEN 20-35
KTS...WITH THE STRONGER GUSTS BEHIND THE FRONT. CONSIDERED STARTING
WIND ADVISORY EARLIER...BUT NOT SEEING ANY OBS WITH CRITERIA OPTED
TO LEAVE AS IS...WAITING FOR THOSE STRONGER GUSTS BEHIND THE FRONT.
MODELS STILL SHOWING A PRETTY GOOD DRY SLOT BEHIND THE FRONT...SO
TRANSITION AN AREA OF LOW SLIGHT CHANCE POPS ACROSS THE CWA FROM
ABOUT 03Z TO 06Z...THEN HAVE WRAP AROUND MOISTURE SURGING BACK IN.
INITIALLY...COLD AIR WILL STILL BE LAGGING BEHIND THE FRONT OF THE
PRECIP SHIELD...SO WRAP AROUND SHOULD START AS RAIN SHOWERS. THEN AS
COLD AIR SURGES IN WILL SEE A TRANSITION FROM RAIN TO SNOW IN THE
MOUNTAINS AND ALSO MOVING ACROSS THE LOWLANDS FROM WEST TO EAST.
WITH THE WRAP AROUND...COORDINATED WITH SHORT TERM FORECASTER ON A
WINTER WEATHER ADVISORY STARTING AT 06Z FROM PERRY COUNTY OHIO EAST
TO THE ALREADY IN PLACE ADVISORY IN WV.
&&
.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
SIGNIFICANT UPSLOPE SNOW EVENT IMPACTS THE AREA THIS PERIOD.
WRAP AROUND ARRIVES FROM THE W RIGHT AT THE START OF THE PERIOD.
MODELS INCLUDING NEAR TERM HIRES SUGGESTS THIS IMPACTS MID SE OHIO
BEFORE LIFTING THROUGH FAR NORTHERN WV AND ON INTO PA FRI. GENERAL
UPSLOPE FLOW ALSO SETS UP RIGHT AT THE START OF THE PERIOD AND
PERSISTS INTO SAT BEFORE WINDING DOWN SAT AFTERNOON AND EVENING.
AS COMMA / WRAP AROUND TAIL LIFTS OUT FRI...SECOND PLUME OFF LAKE
MICHIGAN MAY SET UP FOR A TIME...PERHAPS A LITTLE S OF WHERE THE
INITIAL WRAP AROUND OCCURS. IT THEN WILL EITHER DRIFT INTO THE SAME
AREA AFFECTED BY THE INITIAL RAP AROUND OR SIMPLY FADE IN PLACE LATE
FRI.
THE WESTERN SLOPES OF THE MOUNTAINS EXPERIENCE STRONG UPSLOPE
WINDS AS THE HIGH SPEEDS SOMEWHAT MAKE UP THE THE LESS THAN
PERPENDICULAR ANGLE PER W FLOW. AIR MASS IS COLD ENOUGH AND
MOISTURE DEPTH GREAT ENOUGH TO EASILY SUPPORT FAVORED DENDRITIC
GROWTH MOST OF THE TIME AND THUS SIGNIFICANT SNOW ACCUMULATIONS.
LEFT WARNINGS AND ADVISORIES AS IS EXCEPT TO EXPAND THE ADVISORY W
ACROSS OUR FAR NORTHERN WV COUNTIES AND ON BACK THROUGH MID SE OHIO
WHERE INITIAL WRAP AROUND SETS UP. SNOW AMOUNTS FARTHER S AND W ARE
ONLY A LITTLE LOWER THOUGH AND REMAINING COUNTIES NOT WARNED OR
ADVISED WILL STILL HAVE WINTRY IMPACTS.
ENTERTAINED BLIZZARD WARNINGS NORTHERN MOUNTAINS BUT RECKONED 3 HRS
OF 1/4SM SN BLSN WOULD BE HARD TO REALIZE SAVE MAYBE FOR THE HIGHEST
WINDWARD SLOPES. SIMILAR DEAL ON HIGH WIND WARNING AS ONLY A FEW
LOCATIONS WILL EXPERIENCE BRIEF GUSTS PAST 50 KTS. 60-65 KTS FLOW
SHOWN AT H85 FRI NT PER NOCTURNAL JET BUT THIS WILL NOT BE REALIZED
AT SURFACE...CLOSE ONLY ACROSS THE HIGHEST EXPOSED RIDGES.
MAINTAINED AREA WIDE WIND ADVISORY.
SNOWS AND WINDS WIND DOWN AND CLEARING COMMENCES SW TO NE SAT MIDDAY
THROUGH SAT NT AS HEIGHTS RISE AND WEAK LOW-MID LEVEL WARM ADVECTION
COMMENCES.
USED A HIRES/NAM/MOS COMBINATION ON TEMPERATURES THROUGH FRI NT
WHICH REFLECTS CORE OF THE COLD AIR CROSSING FRI MIDDAY AND
AFTERNOON. HAVE SUBFREEZING TEMPERATURES EVERYWHERE DURING THAT
TIME WHICH...TOGETHER WITH THE WINTER SOLSTICE...WILL FAVOR DAYTIME
ACCUMULATIONS. TEMPERATURES SAT AND SAT NT NEEDED NOTHING MORE THAN
MINOR EDITS IN LIGHT OF LATEST OF GUIDANCE / ON LOW SIDE / ...AS
SYSTEM SLOWLY PULLS OUT.
&&
.LONG TERM /SUNDAY THROUGH THURSDAY/...
THIS WILL BE A VERY UNSETTLED WEATHER PATTERN WITH CHANGEABLE
TEMPERATURES...IN WHICH TWO LOW PRESSURE SYSTEMS WILL AFFECT THE
AREA. THE MODELS ARE NOT IN GOOD AGREEMENT WITH THE STRENGTH AND
TIMING OF THESE SYSTEMS. RELYING MORE ON THE ENSEMBLES TO MITIGATE
THE DIFFERENCES WILL BE THE WAY TO GO...SO HPC GUIDANCE WITH THE
BLEND OF MODEL DATA WAS FOLLOWED CLOSELY.
EXPECT A DRY AND CHILLY DAY SUNDAY UNDER HIGH PRESSURE.
THE FIRST SYSTEM MONDAY AND MONDAY NIGHT WILL BE ON THE FLAT SIDE
WITH A WEAK LOW PRESSURE SYSTEM TRACKING ACROSS ALONG THE OHIO
RIVER. THIS WILL PUT US ON THE MILD SIDE WITH MAINLY RAIN
MONDAY...EXCEPT POSSIBLY SNOW IN THE NORTHERN
MOUNTAINS...TRANSITIONING TO SOME LIGHT SNOW ON THE BACK SIDE ACROSS
THE NORTH MONDAY NIGHT.
KEPT LOW LIQUID POPS SOUTH TUESDAY WITH FRONTAL SYSTEM TO OUR
SOUTH...BUT MOST OF THE AREA WILL BE DRY AND CHILLY WITH WEAK HIGH
PRESSURE.
SECOND SYSTEM LOOKS TO BE MUCH STRONGER AS IT TRACKS NORTHEASTWARD
TO THE WEST OF OUR AREA...BRINGING A GOOD SHOT OF MILD AIR AND
SIGNIFICANT RAIN WEDNESDAY. AS THE LOW PASSES WEDNESDAY
NIGHT...EXPECT A GENERAL TRANSITION TO SNOW WEDNESDAY NIGHT INTO
THURSDAY MORNING.
&&
.AVIATION /21Z THURSDAY THROUGH TUESDAY/...
HAVE AN AREA OF VFR TO MVFR SHOWERS CURRENTLY MOVING NORTH ACROSS
NORTHERN THIRD OF CWA...WITH NEXT BATCH OF SHOWERS NOW MOVING INTO
WESTERN CWA FROM THE SW. IN GENERAL WILL SEE MVFR ACROSS THE
NORTH...TRANSITION BACK TO VFR. AND MVFR WILL BE MOVING BACK IN
FROM THE SW. AS A COLD FRONT APPROACHES LATE THIS AFTERNOON...WILL
SEE LOWER CEILINGS MOVE IN ALONG WITH HEAVIER SHOWERS. FOLLOWING
COLD FRONT...WILL SEE A BRIEF DRY SLOT WITH LITTLE TO NO PRECIP
BEFORE WRAP-AROUND MOISTURE SURGES IN. WITH COLDER AIR MOVING IN
BEHIND THE FRONT...PRECIP WILL CHANGE TO SNOW OVERNIGHT.
VERY STRONG WINDS WILL TURN FROM THE S/SE TO MORE WESTERLY WITH
THE COLD FRONT PASSAGE. GUSTS INTO TONIGHT WILL GENERALLY BE
20-30 KTS INCREASING TO 30-40 KTS ON FRIDAY.
FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 18Z FRIDAY...
FORECAST CONFIDENCE: MEDIUM.
ALTERNATE SCENARIOS: TIMING OF PRECIPITATION AND LOWER CLOUDS COULD
VARY.
EXPERIMENTAL TABLE OF FLIGHT CATEGORY OBJECTIVELY SHOWS CONSISTENCY
OF WFO FORECAST TO AVAILABLE MODEL INFORMATION:
H = HIGH: TAF CONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL.
M = MEDIUM: TAF HAS VARYING LEVEL OF CONSISTENCY WITH MODELS.
L = LOW: TAF INCONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL.
UTC 1HRLY 20 21 22 23 00 01 02 03 04 05 06 07
EST 1HRLY 15 16 17 18 19 20 21 22 23 00 01 02
CRW CONSISTENCY M M M M M H H H H M L L
HTS CONSISTENCY M M M H H H H M M L L L
BKW CONSISTENCY M M M H H H H H M M L L
EKN CONSISTENCY H M M H M M M M H L L M
PKB CONSISTENCY H M M H H H H H H M L L
CKB CONSISTENCY M M M M M M M M H H L L
AFTER 18Z FRIDAY...
IFR POSSIBLE LATE TONIGHT INTO SATURDAY DUE TO SNOW
SHOWERS...ESPECIALLY IN THE MOUNTAINS.
&&
.RLX WATCHES/WARNINGS/ADVISORIES...
WV...WIND ADVISORY FROM 7 PM THIS EVENING TO 10 PM EST FRIDAY FOR
WVZ005>011-013>020-024>034-039-040.
WIND ADVISORY FROM 7 PM THIS EVENING TO 7 AM EST SATURDAY FOR
WVZ035>038-046-047.
WINTER STORM WARNING FROM 1 AM FRIDAY TO 2 PM EST SATURDAY FOR
WVZ036>038-046-047.
WINTER WEATHER ADVISORY FROM 1 AM FRIDAY TO 2 PM EST SATURDAY
FOR WVZ027-028-035-039-040.
WINTER WEATHER ADVISORY FROM 1 AM FRIDAY TO 7 AM EST SATURDAY
FOR WVZ009>011-015>020-025-026-029>034.
OH...WIND ADVISORY FROM 7 PM THIS EVENING TO 10 PM EST FRIDAY FOR
OHZ066-067-075-076-083>087.
WINTER WEATHER ADVISORY FROM 1 AM FRIDAY TO 7 AM EST SATURDAY
FOR OHZ066-067-076.
KY...WIND ADVISORY FROM 7 PM THIS EVENING TO 10 PM EST FRIDAY FOR
KYZ101>103-105.
VA...WIND ADVISORY FROM 7 PM THIS EVENING TO 10 PM EST FRIDAY FOR
VAZ003-004.
&&
$$
SYNOPSIS...TRM/JMV/MZ
NEAR TERM...MZ
SHORT TERM...TRM
LONG TERM...JMV
AVIATION...MZ