Forecast Discussions mentioning any of
"HRRR" "RAP" "RR" "RUC13" "RUC" received at GSD on 12/22/12
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 JACKSONVILLE FL
850 PM EST FRI DEC 21 2012
...FREEZE TONIGHT AND SATURDAY NIGHT...
.UPDATE...WINDS HAVE DECREASED BUT STILL AROUND 10 MPH AS TIGHT
PRESSURE GRADIENT REMAINS OVER THE AREA. CURRENT TEMPERATURES ARE
FALLING INTO THE LOW TO MID 40S. MINIMUM TEMPERATURES TONIGHT EXPECTED
FROM NEAR 27 DEGREES WELL INLAND TO 32 AT THE COAST AND RIVER.
CURRENT FORECAST LOOKS GOOD SO NO CHANGES NEEDED. LIGHTER WINDS
BUT INCREASING HIGH CLOUDINESS SATURDAY NIGHT SHOULD RESULT IN
SIMILAR TEMPERATURES SUNDAY MORNING.
&&
.AVIATION...VFR. SUSTAINED WLY WINDS EXPECTED TO AVERAGE BETWEEN
5-10 KT REST OF TONIGHT AND GIVEN THE STRONG WINDS AT 1000-2000 FT
OF 30-40 KT PER JAX/VAX VWP AND RAP MODEL OUTPUT HAVE PLACED LLWS IN
THE TAFS THROUGH 14Z SAT. SFC WINDS REST OF SATURDAY WILL BE W TO NW
AROUND 10G15KT.
&&
.MARINE...WNW WINDS AROUND 25-30 KT CLOCKED AT THE BUOYS OFFSHORE.
BUOY 41012 REPORTING PEAK GUSTS JUST OVER 35 KT PAST COUPLE OF HRS
SO GALE WARNING CONTINUES LOOK ON TARGET...AND THE SCA LOOKS GOOD
NEARSHORE. SWAN OUTPUT AND BUOY DATA ARE IN LINE WITH SEAS NEAR 3-5
FT NEARSHORE AND 5-8 FT OFFSHORE AND WOULD NOT DISCOUNT SOME 8-10 FT
SEAS RIGHT AT THE OUTER MARK. WILL NOW START A NEW SCA OFFSHORE
AFTER THE GALE WARNING EXPIRES AT 09Z AND CONTINUE IT ALL DAY SAT
SINCE SEAS WILL BE SLOW TO SUBSIDE DUE TO COLD ADVECTION AND NW FLOW
AROUND 15-20 KT.
RIP CURRENTS: LOW RISK THROUGH SAT.
&&
.FIRE WEATHER...RED FLAG VERIFIED WELL FOR NE FL TODAY. FOR
SATURDAY...RH VALUES WILL FALL BELOW 35 PERCENT BY LATE MORNING BUT
WINDS WON`T REACH NEEDED CRITERIA FOR A RED FLAG WARNING.
&&
.PRELIMINARY POINT TEMPS/POPS...
AMG 27 55 27 62 / 0 0 0 0
SSI 32 55 34 60 / 0 0 0 0
JAX 27 58 27 64 / 0 0 0 0
SGJ 31 56 31 61 / 0 0 0 0
GNV 27 57 27 64 / 0 0 0 0
OCF 27 59 27 65 / 0 0 0 0
&&
.JAX WATCHES/WARNINGS/ADVISORIES...
FL...FREEZE WATCH FROM LATE SATURDAY NIGHT THROUGH SUNDAY MORNING FOR
ALACHUA-BAKER-BRADFORD-CLAY-COLUMBIA-DUVAL-GILCHRIST-
HAMILTON-MARION-NASSAU-PUTNAM-ST JOHNS-SUWANNEE-UNION.
FREEZE WARNING FROM 2 AM TO 9 AM EST SATURDAY FOR ALACHUA-BAKER-
BRADFORD-CLAY-COLUMBIA-DUVAL-FLAGLER-GILCHRIST-HAMILTON-
MARION-NASSAU-PUTNAM-ST JOHNS-SUWANNEE-UNION.
GA...FREEZE WATCH FROM LATE SATURDAY NIGHT THROUGH SUNDAY MORNING FOR
APPLING-ATKINSON-BACON-BRANTLEY-CHARLTON-CLINCH-COASTAL
CAMDEN-COASTAL GLYNN-COFFEE-ECHOLS-INLAND CAMDEN-INLAND
GLYNN-JEFF DAVIS-PIERCE-WARE-WAYNE.
FREEZE WARNING FROM 2 AM TO 9 AM EST SATURDAY FOR APPLING-
ATKINSON-BACON-BRANTLEY-CHARLTON-CLINCH-COASTAL CAMDEN-
COASTAL GLYNN-COFFEE-ECHOLS-INLAND CAMDEN-INLAND GLYNN-JEFF
DAVIS-PIERCE-WARE-WAYNE.
AM...SMALL CRAFT ADVISORY FROM 4 AM TO 7 PM EST SATURDAY FOR ALTAMAHA
SOUND GA TO FERNANDINA BEACH FL 20 NM TO 60 NM OFFSHORE-
FERNANDINA BEACH TO ST AUGUSTINE FL 20 NM TO 60 NM OFFSHORE-
ST AUGUSTINE TO FLAGLER BEACH FL 20 NM TO 60 NM OFFSHORE.
GALE WARNING UNTIL 4 AM EST SATURDAY FOR ALTAMAHA SOUND GA TO
FERNANDINA BEACH FL 20 NM TO 60 NM OFFSHORE-FERNANDINA
BEACH TO ST AUGUSTINE FL 20 NM TO 60 NM OFFSHORE-ST
AUGUSTINE TO FLAGLER BEACH FL 20 NM TO 60 NM OFFSHORE.
SMALL CRAFT ADVISORY UNTIL 10 AM EST SATURDAY FOR ALTAMAHA SOUND
GA TO FERNANDINA BEACH FL OUT 20 NM-FERNANDINA BEACH TO ST
AUGUSTINE FL OUT 20 NM-ST AUGUSTINE TO FLAGLER BEACH FL OUT
20 NM.
&&
$$
ZIBURA/SHASHY/WALKER
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 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
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 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 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 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 INDIANAPOLIS IN
1004 PM EST FRI DEC 21 2012
.UPDATE...
THE NEAR TERM SECTION HAS BEEN UPDATED BELOW
&&
.SYNOPSIS...
ISSUED AT 152 PM EST FRI DEC 21 2012
A STRONG STORM SYSTEM WILL CONTINUE TO PULL AWAY FROM THE AREA
TONIGHT. HIGH PRESSURE IS EXPECTED TO BUILD IN FOR THE WEEKEND. A
LOW PRESSURE SYSTEM MAY MOVE THROUGH THE OHIO VALLEY EARLY NEXT
WEEK...AROUND MONDAY. A POTENTIALLY STRONGER SYSTEM MAY AFFECT THE
AREA TOWARDS THE MIDDLE OF NEXT WEEK.
&&
.NEAR TERM /REST OF TONIGHT/...
ISSUED AT 1004 PM EST FRI DEC 21 2012
CLOUDS CONTINUE TO PERSIST ACROSS MUCH OF THE FORECAST AREA.
SATELLITE LOOPS SHOW LITTLE IN THE WAY OF CLEARING WORKING TOWARD
THE AREA AS CYCLONIC FLOW REMAINS DOMINANT.
LATEST HI RES MODEL DATA SHOW THAT CLOUDS LINGERING THROUGH MUCH
OF THE NIGHT ACROSS MUCH OF THE EASTERN HALF OF THE FORECAST AREA.
GIVEN ALL OF THE ABOVE HAVE INCREASED CLOUD COVER OVER MUCH OF THE
AREA THROUGH THE NIGHT.
WITH THE INCREASED CLOUD COVER HAVE BUMPED UP TEMPERATURES A
LITTLE WHERE CLOUDS WILL PERSIST. AM HESITANT TO RAISE TOO MUCH
THOUGH...AS TEMPERATURES WILL DROP QUICKLY WITH ANY BREAKS THAT DO
HAPPEN TO FORM.
&&
.SHORT TERM /SATURDAY THROUGH MONDAY/...
ISSUED AT 152 PM EST FRI DEC 21 2012
MODELS INDICATE UPPER FLOW FLATTENING OUT AS THE DEEP UPPER TROUGH
LIFTS OFF INTO THE CANADIAN MARITIMES BY SUNDAY. CENTRAL INDIANA
WILL ENTER A QUIET FORECAST PERIOD THROUGH THE WEEKEND. TEMPERATURES
WILL MODERATE OVER THIS TIME BACK TO CLIMO...AND EVEN SLIGHT ABOVE
CLIMO BY SUNDAY AFTERNOON.
ONLY ITEM OF INTEREST WILL BE A POTENTIAL SHORT WAVE TROUGH THAT THE
MODELS BRING INTO THE MIDWEST BY LATE SUNDAY NIGHT. SOME OF THE
ENSEMBLE MEMBERS BRING A THREAT FOR SOME LIGHT RAIN OR MIXED
PRECIPITATION ACROSS THE NORTHERN COUNTIES DURING THE DAY MONDAY.
THIS FEATURE LOOKS WEAKER WITH LATEST MODELS RUNS...AND SOME MODELS
(THE GFS) BARELY EVEN DEPICT IT PRODUCING ANY PRECIPITATION FOR
CENTRAL INDIANA. HAVE THEREFORE BACKED OFF ON POP DURING THIS TIME.
&&
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
ISSUED AT 239 PM EST FRI DEC 21 2012
FORECAST FOCUS IS ON SIGNIFICANT STORM SYSTEM MID WEEK...WHICH MAY
OR MAY NOT HIT CENTRAL INDIANA DEPENDING ON THE EXACT TRACK. QUITE A
BIT OF VARIABILITY IN MODEL SOLUTIONS WITH THIS SYSTEM. WITH HIGH
ENSEMBLE SPREAD AND THE GFS ENSEMBLE AVERAGE SOLUTION AND GEM
SOLUTION VARYING SIGNIFICANTLY FROM THE OPERATIONAL GFS AND 12Z
ECMWF THINK BEST COURSE OF ACTION IS TO GO WITH A CONSENSUS AND HOPE
VARIABILITY LESSENS AS SYSTEM APPROACHES.
MONDAY NIGHT A SYSTEM ALONG THE OHIO RIVER SHOULD BE PULLING AWAY
FROM THE AREA. COULD SEE A MIX OF RAIN AND SNOW IN THE SOUTH WITH
SNOW IN THE NORTH BRIEFLY BEFORE THE LOW PULLS FAR ENOUGH AWAY FROM
THE AREA TO BRING PRECIP TO AN END. CHRISTMAS DAY LOOKS LIKE HIGH
PRESSURE WILL BRIEFLY BE OVER THE AREA KEEPING CONDITIONS DRY.
CHRISTMAS NIGHT IS WHEN POPS START TO BE INTRODUCED WITH THE
AFOREMENTIONED SIGNIFICANT SYSTEM. LOW TRACKS VARY FROM UP THE
MISSISSIPPI RIVER THROUGH THE TENNESSEE VALLEY TO ACROSS THE FLORIDA
PANHANDLE AND UP THE EAST COAST. THIS LESSENS CONFIDENCE IN ANY
PARTICULAR SOLUTION. CONSENSUS POPS YIELD CHANCE FOR CHRISTMAS NIGHT
WITH LIKELY IN THE SOUTHEAST ON WEDNESDAY AND CHANCE WEDNESDAY
NIGHT. FOR PRECIP TYPE WILL GO WITH SNOW IN THE NORTH AND A MIX OF
RAIN AND SNOW IN THE SOUTH AS TRACK VARIABILITY IMPACTS THE ARRIVAL
OF THE COLD AIR AS WELL. TEMPERATURES SHOULD BE BELOW NORMAL AFTER
TUESDAY.
&&
.AVIATION /DISCUSSION FOR THE 220300Z IND TAF UPDATE/
SATELLITE TRENDS INDICATE PESKY SC DECK NEAR 2000FT CONTINUING TO
FLOW ACROSS THE LAF...IND AND NOW BMG AREAS...WITH LITTLE
EASTWARD PROGRESS. HRRR INDICATES THIS AREA SHOULD STAY ACROSS
THE TAF SITES TIL AT LEAST 06Z...THUS WILL HOLD OFF ON ANY
CLEARING UNTIL THEN.
/DISCUSSION FOR THE 220000 TAFS/...
ISSUED AT 605 PM EST FRI DEC 21 2012
BRIEF MVFR CONDITIONS AT IND AND LAF WILL END QUICKLY THIS EVENING
GIVING WAY TO VFR CONDITIONS AT ALL TAF SITES.
CLOUD SHIELD ASSOCIATED WITH THE DEPARTING LOW PRESSURE SYSTEM
WILL EXIT TO THE EAST EARLY THIS EVENING AS WEAK AND DRY HIGH
PRESSURE CENTERED OVER THE MISSISSIPPI RIVER VALLEY BUILDS ACROSS
INDIANA. TIME HEIGHTS AND FORECAST SOUNDINGS INDICATE A DRY COLUMN
BY 06Z AND CONVECTIVE TEMPS WILL BE UNATTAINABLE. THUS ONLY A FEW
PASSING HIGH CI CLOUDS POSSIBLE AMID STRONG SUBSIDENCE AND FLOW
ALOFT SLOWLY BECOMING MORE ZONAL.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...SMF
NEAR TERM...50
SHORT TERM...SMF
LONG TERM....CP
AVIATION...JP
AREA FORECAST DISCUSSION
NWS INDIANAPOLIS IN
936 PM EST FRI DEC 21 2012
.UPDATE...
AVIATION SECTION UPDATED
&&
.SYNOPSIS...
ISSUED AT 152 PM EST FRI DEC 21 2012
A STRONG STORM SYSTEM WILL CONTINUE TO PULL AWAY FROM THE AREA
TONIGHT. HIGH PRESSURE IS EXPECTED TO BUILD IN FOR THE WEEKEND. A
LOW PRESSURE SYSTEM MAY MOVE THROUGH THE OHIO VALLEY EARLY NEXT
WEEK...AROUND MONDAY. A POTENTIALLY STRONGER SYSTEM MAY AFFECT THE
AREA TOWARDS THE MIDDLE OF NEXT WEEK.
&&
.NEAR TERM /TONIGHT/...
ISSUED AT 655 PM EST FRI DEC 21 2012
CLOUDS ARE BEING STUBBORN ACROSS THE NORTHERN FORECAST AREA SO HAVE
UPPED SKY COVER FOR THIS EVENING ACROSS THE NORTH. LATEST RAPID
REFRESH MODEL RUN STILL SHOWS EVENTUAL CLEARING LATER TONIGHT. WILL
CONTINUE TO MONITOR.
SNOW LOOKS TO HAVE LEFT RANDOLPH COUNTY PER LATEST RADAR RETURNS.
THUS HAVE REMOVED ANY MENTION OF SNOW THERE.
CHILLY DEPARTURE FROM TEMPERATURES AS OF LATE. WENT CLOSER TO THE
COOL MAV GUIDANCE FOR LOWS 15 TO 20 FOR LOWS.
&&
.SHORT TERM /SATURDAY THROUGH MONDAY/...
ISSUED AT 152 PM EST FRI DEC 21 2012
MODELS INDICATE UPPER FLOW FLATTENING OUT AS THE DEEP UPPER TROUGH
LIFTS OFF INTO THE CANADIAN MARITIMES BY SUNDAY. CENTRAL INDIANA
WILL ENTER A QUIET FORECAST PERIOD THROUGH THE WEEKEND. TEMPERATURES
WILL MODERATE OVER THIS TIME BACK TO CLIMO...AND EVEN SLIGHT ABOVE
CLIMO BY SUNDAY AFTERNOON.
ONLY ITEM OF INTEREST WILL BE A POTENTIAL SHORT WAVE TROUGH THAT THE
MODELS BRING INTO THE MIDWEST BY LATE SUNDAY NIGHT. SOME OF THE
ENSEMBLE MEMBERS BRING A THREAT FOR SOME LIGHT RAIN OR MIXED
PRECIPITATION ACROSS THE NORTHERN COUNTIES DURING THE DAY MONDAY.
THIS FEATURE LOOKS WEAKER WITH LATEST MODELS RUNS...AND SOME MODELS
(THE GFS) BARELY EVEN DEPICT IT PRODUCING ANY PRECIPITATION FOR
CENTRAL INDIANA. HAVE THEREFORE BACKED OFF ON POP DURING THIS TIME.
&&
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
ISSUED AT 239 PM EST FRI DEC 21 2012
FORECAST FOCUS IS ON SIGNIFICANT STORM SYSTEM MID WEEK...WHICH MAY
OR MAY NOT HIT CENTRAL INDIANA DEPENDING ON THE EXACT TRACK. QUITE A
BIT OF VARIABILITY IN MODEL SOLUTIONS WITH THIS SYSTEM. WITH HIGH
ENSEMBLE SPREAD AND THE GFS ENSEMBLE AVERAGE SOLUTION AND GEM
SOLUTION VARYING SIGNIFICANTLY FROM THE OPERATIONAL GFS AND 12Z
ECMWF THINK BEST COURSE OF ACTION IS TO GO WITH A CONSENSUS AND HOPE
VARIABILITY LESSENS AS SYSTEM APPROACHES.
MONDAY NIGHT A SYSTEM ALONG THE OHIO RIVER SHOULD BE PULLING AWAY
FROM THE AREA. COULD SEE A MIX OF RAIN AND SNOW IN THE SOUTH WITH
SNOW IN THE NORTH BRIEFLY BEFORE THE LOW PULLS FAR ENOUGH AWAY FROM
THE AREA TO BRING PRECIP TO AN END. CHRISTMAS DAY LOOKS LIKE HIGH
PRESSURE WILL BRIEFLY BE OVER THE AREA KEEPING CONDITIONS DRY.
CHRISTMAS NIGHT IS WHEN POPS START TO BE INTRODUCED WITH THE
AFOREMENTIONED SIGNIFICANT SYSTEM. LOW TRACKS VARY FROM UP THE
MISSISSIPPI RIVER THROUGH THE TENNESSEE VALLEY TO ACROSS THE FLORIDA
PANHANDLE AND UP THE EAST COAST. THIS LESSENS CONFIDENCE IN ANY
PARTICULAR SOLUTION. CONSENSUS POPS YIELD CHANCE FOR CHRISTMAS NIGHT
WITH LIKELY IN THE SOUTHEAST ON WEDNESDAY AND CHANCE WEDNESDAY
NIGHT. FOR PRECIP TYPE WILL GO WITH SNOW IN THE NORTH AND A MIX OF
RAIN AND SNOW IN THE SOUTH AS TRACK VARIABILITY IMPACTS THE ARRIVAL
OF THE COLD AIR AS WELL. TEMPERATURES SHOULD BE BELOW NORMAL AFTER
TUESDAY.
&&
.AVIATION /DISCUSSION FOR THE 220300Z IND TAF UPDATE/
SATELLITE TRENDS INDICATE PESKY SC DECK NEAR 2000FT CONTINUING TO
FLOW ACROSS THE LAF...IND AND NOW BMG AREAS...WITH LITTLE
EASTWARD PROGRESS. HRRR INDICATES THIS AREA SHOULD STAY ACROSS
THE TAF SITES TIL AT LEAST 06Z...THUS WILL HOLD OFF ON ANY
CLEARING UNTIL THEN.
/DISCUSSION FOR THE 220000 TAFS/...
ISSUED AT 605 PM EST FRI DEC 21 2012
BRIEF MVFR CONDITIONS AT IND AND LAF WILL END QUICKLY THIS EVENING
GIVING WAY TO VFR CONDITIONS AT ALL TAF SITES.
CLOUD SHIELD ASSOCIATED WITH THE DEPARTING LOW PRESSURE SYSTEM
WILL EXIT TO THE EAST EARLY THIS EVENING AS WEAK AND DRY HIGH
PRESSURE CENTERED OVER THE MISSISSIPPI RIVER VALLEY BUILDS ACROSS
INDIANA. TIME HEIGHTS AND FORECAST SOUNDINGS INDICATE A DRY COLUMN
BY 06Z AND CONVECTIVE TEMPS WILL BE UNATTAINABLE. THUS ONLY A FEW
PASSING HIGH CI CLOUDS POSSIBLE AMID STRONG SUBSIDENCE AND FLOW
ALOFT SLOWLY BECOMING MORE ZONAL.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...SMF
NEAR TERM...50/SMF
SHORT TERM...SMF
LONG TERM....CP
AVIATION...JP
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 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 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
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
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
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...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 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 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...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 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 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 WILMINGTON OH
638 PM EST FRI DEC 21 2012
.SYNOPSIS...
A STRONG LOW PRESSURE SYSTEM OVER NEW ENGLAND WILL SLOWLY MOVE
NORTHEAST AWAY FROM THE REGION TONIGHT. A RIDGE OF HIGH PRESSURE
WILL BUILD ACROSS THE REGION ON SATURDAY AND SATURDAY NIGHT. THE
HIGH WILL THEN MOVE EAST ON SUNDAY AS A COLD FRONT APPROACHES THE
AREA FROM THE NORTHWEST.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
STRONG LOW PRESSURE NEAR NRN NEW YORK STATE THIS AFTERNOON WILL
PIVOT SLOWLY NORTHEAST AWAY FROM THE REGION OVERNIGHT.
MOSAIC RADAR CONTINUED TO SHOW CONSIDERABLE SNOW SHOWER ACTIVITY
ACROSS PARTS OF THE NRN AND ERN ZONES. MUCH OF THIS ACTIVITY
APPEARS TO BE LINKED TO A 900-850 MB FRONTOGENETIC AXIS AS
DEPICTED BY THE LATEST RAP MODEL. THE RAP MODEL GRADUALLY SHIFTS
THIS AXIS ESE AND EVENTUALLY WEAKEN IT AS IT DOES SO. THUS...WILL
FORECAST CAT POPS IN THE NRN AND EASTERN SECTIONS INTO THE EVENING
HOURS...AND THEN GRADUALLY TAPER OFF THE POPS TOWARD MIDNIGHT.
HAVE CONTINUED THE WINTER WEATHER ADVISORY UNTIL 10 PM FOR
LOCATIONS THAT WERE ALREADY IN IT AND WHERE LIKELY POPS WERE STILL
FORECAST. WILL ASSESS THE SITUATION BEFORE 6 PM TO SEE IF SOME OF
THE WESTERN COUNTIES IN THE WINTER ADVISORY ADVISORY MAY BE
DROPPED BY THEN. AS FOR THE WINDS...WE COULD SEE AN ISOLATED GUST
NEAR WIND ADVISORY CRITERIA THROUGH THE EARLY EVENING...BUT FOR
THE MOST PART...WIND GUSTS SHOULD STAY BELOW THE CRITERIA
THRESHOLD...SO HAVE ALLOWED THIS TO EXPIRE. WINDS WILL SLOWLY
DIMINISH FROM SW TO NE THROUGH THE OVERNIGHT HOURS AS LOW PRESSURE
CONTINUES TO PULL SLOWLY AWAY.
OTHERWISE...SKIES WILL BE MOSTLY CLOUDY TO CLOUDY THIS EVENING.
CLOUD COVER IS A BIT TRICKY OVERNIGHT. NAM AND GFS CONTINUE TO
DEPICTED MOISTURE AROUND 925 MB PUSHING SE AGAIN INTO THE REGION
OVERNIGHT. AS SUCH HAVE KEPT MOST LOCATIONS MOSTLY CLOUDY EXCEPT
FOR THE SW WHERE IT MAY GO MOSTLY CLEAR. OVERNIGHT LOWS WILL BE
CLOUD DEPENDENT AND WIND DEPENDENT BUT SHOULD RANGE FROM THE UPPER
TEENS SW TO THE MID 20S NORTHEAST.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/...
LOW PRESSURE WILL CONTINUE TO MOVE ENE ON SATURDAY AS A SFC RIDGE
OF HIGH PRESSURE BUILDS INTO THE OHIO VALLEY FROM THE WEST.
AGAIN...MODELS ARE HOLDING ON TO LOW LEVEL MOISTURE ACRS THE NRN
AND ERN SECTIONS THROUGH A GOOD PART OF THE DAY...SO HAVE GONE
PARTLY TO MOSTLY CLOUDY HERE. WE SHOULD GRADUALLY SEE IMPROVEMENT
THROUGH THE DAY SO THAT ALL LOCATIONS SHOULD BE MOSTLY CLEAR BY
SATURDAY EVENING. SKIES SHOULD REMAIN MOSTLY CLEAR SATURDAY NIGHT.
FOR SUNDAY INTO SUNDAY NIGHT...SURFACE HIGH PRESSURE RIDGE WILL
SLIP TO THE EAST. MEANWHILE...A COLD FRONT WILL DROP INTO THE
REGION SUNDAY NIGHT. MOISTURE AND LIFT ARE MEAGER TO START
WITH...SO HAVE ALLOWED FOR CLOUDS TO INCREASE OVERNIGHT...BUT LEFT
CHANCES OF PCPN UNTIL MONDAY MORNING.
AS FOR TEMPS...THEY SHOULD RANGE FROM THE LOWER TO UPPER 30S ON
SATURDAY. A MODIFYING AIRMASS AND RETURN FLOW WILL BRING
TEMPERATURES FROM THE UPPER 30S NORTH TO THE UPPER 40S SOUTH ON
SUNDAY. OVERNIGHT LOWS SATURDAY NIGHT SHOULD BE SOMEWHAT SUBDUED
WITH AN INCREASING SOUTHERLY FLOW. LOWS SUNDAY NIGHT WILL BE CLOUD
DEPENDENT BUT HAVE THEM RANGING FROM THE MID 20S NORTH TO THE
LOWER 30S SOUTH.
&&
.LONG TERM /MONDAY THROUGH FRIDAY/...
AN ACTIVE WEATHER PATTERN WILL EVOLVE DURING THE LONG TERM FORECAST.
WEAK LOW PRESSURE WILL BRING SPREAD PRECIPITATION ACROSS THE OHIO
VALLEY ON MONDAY. THE ONSET TIMING OF SHOWER ACTIVITY IS STILL IN
QUESTION AND WILL HELP TO DETERMINE IF WE SEE A WINTRY MIX MONDAY
MORNING...OR AN ALL RAIN EVENT DURING THE DAY MONDAY. COLDER AIR ON
THE NORTH AND EASTERN SIDE OF THE LOW WILL BRING ABOUT A CHANGEOVER
TO A RAIN/SNOW MIX AND PERHAPS A BRIEF TIME OF LIGHT SNOW MONDAY
EVENING BEFORE PRECIPITATION EXITS THE AREA. BASED ON CURRENT TIMING
OF CHANGEOVER IN THE EVENING AND LIGHT QPF AMOUNTS...DO NOT EXPECT
MUCH IN THE WAY OF ANY SNOW ACCUMULATION FROM THIS SYSTEM.
CHRISTMAS DAY LOOKS TO HAVE FAIR WEATHER WITH SEASONABLE
TEMPERATURES. THE ATTENTION THEN TURNS TO A STORM SYSTEM THAT MAY
AFFECT THE AREA CHRISTMAS NIGHT THROUGH THURSDAY MORNING. FOR THE
PAST FEW DAYS MODELS HAVE BEEN ADJUSTING THEIR FORECAST POSITIONS ON
A DEVELOPING SURFACE LOW IN THE SOUTH CENTRAL PORTIONS OF THE CONUS
AHEAD OF A DEEP TROUGH EXITING THE SOUTHERN ROCKIES ON CHRISTMAS
DAY. THE 12Z ECMWF AND GFS ARE SUGGESTING THAT THIS STORM WILL TRACK
ACROSS THE OHIO VALLEY ON WEDNESDAY. THERE ARE STILL LARGE
DIFFERENCES AMONGST THE FORECAST MODELS FOR THE EXACT LOW TRACK AND
HOW COLD TEMPERATURES WILL BE ALOFT WITH THIS LOW. WENT WITH A ECMWF
WEIGHTED CONSENSUS BLEND FOR POPS AND TEMPERATURES DURING THIS TIME
PERIOD. THE TRACK FORECAST WILL LIKELY CONTINUE TO SHIFT FROM RUN TO
RUN AS WE ARE STILL 5 DAYS OUT. WENT LIKELY FOR POPS DURING THE MOST
CONFIDENT TIME PERIOD THAT THE SYSTEM WOULD AFFECT OUR AREA.
THIS SYSTEM SHOULD EXIT THE REGION THURSDAY WITH HIGH PRESSURE
BUILDING IN FOR FRIDAY.
&&
.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
LOW PRESSURE IS MOVING WELL TO THE EAST. CONDITIONS WILL IMPROVE
AS HIGH PRESSURE STARTS TO BUILD IN FROM THE WEST. SNOW SHOWERS AT
CMH AND LCK WILL DIMINISH TO FLURRIES IN ABOUT AN HOUR. CEILINGS
WILL REMAIN IN THE MVFR RANGE AS LATE AS SATURDAY AFTERNOON WITH
MOISTURE SLOW TO EXIT IN THE CYCLONIC FLOW BEHIND THE LOW. WINDS
WILL SUBSIDE TO AROUND 10 KNOTS OUT OF THE WEST BY 12Z SATURDAY.
OUTLOOK...MVFR CEILINGS AND VSBYS ARE POSSIBLE MONDAY.
&&
.ILN WATCHES/WARNINGS/ADVISORIES...
OH...WINTER WEATHER ADVISORY UNTIL 10 PM EST THIS EVENING FOR
OHZ026-035-043>046-051>056-061>065-072-074.
KY...NONE.
IN...NONE.
&&
$$
SYNOPSIS...HICKMAN
NEAR TERM...HICKMAN
SHORT TERM...HICKMAN
LONG TERM...LATTO
AVIATION...CONIGLIO
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
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
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...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 INDIANAPOLIS IN
336 AM EST SAT DEC 22 2012
.UPDATE...
AVIATION AND LONG TERM SECTIONS HAVE BEEN UPDATED BELOW.
&&
.SYNOPSIS...
ISSUED AT 302 AM EST SAT DEC 22 2012
HIGH PRESSURE IS EXPECTED ACROSS THE AREA OVER THE WEEKEND. A LOW
PRESSURE SYSTEM IS EXPECTED TO MOVE THROUGH THE OHIO VALLEY AROUND
MONDAY. A STRONGER SYSTEM MAY AFFECT THE AREA TOWARDS THE MIDDLE OF
NEXT WEEK. IN THE WAKE OF THIS SYSTEM...HIGH PRESSURE WILL MOVE INTO
THE AREA FOR LATE NEXT WEEK.
&&
.NEAR TERM /TODAY/...
ISSUED AT 302 AM EST SAT DEC 22 2012
SATELLITE LOOP INDICATES BACK EDGE OF LOW CLOUD DECK IS BEGINNING TO
PUSH EAST. EXTRAPOLATION AND SHORT TERM MODEL DATA SUGGEST THE
CLEARING LINE SHOULD REACH THE FAR EASTERN ZONES AROUND SUNRISE.
OTHERWISE...EXPECTING A SUNNY DAY TODAY UNDER HIGH PRESSURE...WITH
ONLY SOME THIN HIGH CLOUD COVER AT TIMES. PROGGED LOW LEVEL
THICKNESSES SUGGEST THE GFS MOS HIGHS FOR TODAY MAY BE A FEW DEGREES
TOO COOL...MAINLY OVER THE NORTH. WILL BUMP UP THE NUMBERS ABOUT 3-4
DEGREES IN THOSE AREAS.
&&
.SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/...
ISSUED AT 302 AM EST SAT DEC 22 2012
MODELS INDICATE UPPER FLOW WILL FLATTEN OUT DURING THIS PERIOD AS
DEEP UPPER TROUGH CURRENTLY OVER THE NORTHEAST LIFTS INTO CANADA.
LOOKS RATHER QUIET THROUGH SUNDAY AS SURFACE AND UPPER RIDGING MOVES
THROUGH. MAIN ITEM OF INTEREST WILL BE A UPPER DISTURBANCE THAT IS
EXPECTED TO MOVE ACROSS THE FORECAST AREA MONDAY INTO MONDAY NIGHT.
SOME OF THE ENSEMBLE MEMBERS BRING A THREAT FOR SOME LIGHT RAIN OR
MIXED PRECIPITATION LATE SUNDAY NIGHT OVER THE FAR SOUTH...WHILE THE
MAJORITY OF THE OPERATIONAL AND ENSEMBLE DATA HOLD OFF THIS THREAT
UNTIL MONDAY. WILL CONTINUE TO KEEP THE FORECAST DRY THROUGH SUNDAY
NIGHT.
LIFT WITH THE SYSTEM COMING IN ON MONDAY LOOKS PRETTY DECENT AT THIS
POINT...ALTHOUGH DEEP MOISTURE IN THE PRECIPITATION BEARING LAYERS
IS QUESTIONABLE. THEREFORE...DOESN/T APPEAR THIS SYSTEM WILL BE A
BIG QPF PRODUCER. WILL GO WITH CHANCE POPS FOR LIGHT RAIN OR SNOW
OVER THE NORTHERN TWO THIRDS OF THE FORECAST AREA ON MONDAY...AND
CHANCE POPS FOR LIGHT RAIN FARTHER SOUTH. APPEARS THIS SYSTEM WILL
MOVE EAST OF THE AREA DURING MONDAY NIGHT...SO WILL KEEP SOME
SMALL CHANCE POPS FOR LIGHT SNOW OR RAIN INTO MONDAY NIGHT.
PROGGED LOW LEVEL THICKNESSES SUGGEST THE GFS MOS TEMPERATURE
GUIDANCE FOR SUNDAY AND MONDAY LOOK TOO COOL...ESPECIALLY THE HIGHS
ON SUNDAY. WILL BUMP UP THE GUIDANCE HIGHS SUNDAY ABOUT 5
DEGREES...AND NUDGE THE SUNDAY NIGHT LOWS AND MONDAY NIGHTS UP
SLIGHTLY.
&&
.LONG TERM /TUESDAY THROUGH FRIDAY/...
ISSUED AT 336 AM EST SAT DEC 22 2012
THE FORECAST FOCUS STILL APPEARS TO BE ON A POSSIBLE WINTER STORM
AROUND MIDWEEK AS ADVERTISED BY THE GFS AND EUROPEAN MODELS.
LIGHT PRECIP FROM MONDAY SYSTEM WILL HAVE ENDED BY TUESDAY AS HIGH
PRESSURE BUILDS ACROSS OUR AREA. BOTH THE GFS AND EURO INDICATE
SIGNIFICANT SNOW ACCUMULATIONS BY WEDNESDAY AS STRONG LOW PRESSURE
TRACKS FROM NORTHERN MISSISSIPPI VALLEY TO THE MID APPALACHIANS. LOW
LEVEL THICKNESS INDICATE PRECIP TO BE ALL SNOW. BUT IT COULD FIRST
START OUT BRIEFLY AS MIXED OVER SOUTHERN SECTIONS TUESDAY NIGHT.
ON THE OTHER HAND...THE DGEX AND CANADIAN TAKE THE SURFACE LOW A
LITTLE FARTHER SOUTH AND EAST AND TRACK THE SIGNIFICANT PRECIP
BARELY SOUTH AND EAST OF OUR REGION. THE GFS ENSEMBLE MEAN SUPPORTS
THE OPERATIONAL GFS SCENARIO WITH POSSIBLE HEAVY SNOW AS FAR
NORTHWEST AS INDY. BUT THERE IS A LARGE SPREAD WITH SURFACE LOW
TRACKS RANGING FROM THE CAROLINA COAST TO THE OHIO VALLEY. FOR NOW
WILL CONTINUE LIKELY POPS OVER THE SOUTHEAST HALF OF OUR REGION
WEDNESDAY. IF THE GFS AND EURO ARE CORRECT THIS MAY WELL END UP AS
OUR NEXT WINTER STORM.
LIGHT SNOW MAY LINGER ACROSS OUR REGION WEDNESDAY NIGHT AND WILL
CONTINUE ISOLATED SNOW SHOWERS NORTHEAST THURSDAY...MAINLY FROM LAKE
EFFECT. THEN DRY WEATHER WILL BE THE RULE THURSDAY AND FRIDAY.
MODELS INDICATE PRECIP MAY OCCUR FRIDAY NIGHT AND SATURDAY AS
ANOTHER SYSTEM MOVES OUR WAY.
ALL BLEND TEMPERATURES SEEM REASONABLE TUESDAY AND WEDNESDAY. WENT
A FEW DEGREES COLDER THAN MOS TEMPERATURES AFTER WEDNESDAY AS THERE
WILL PROBABLY BE SOME SNOW COVER.
&&
.AVIATION /DISCUSSION FOR THE 220900Z KIND TAF UPDATE/...
ISSUED AT 336 AM EST SAT DEC 22 2012
MINOR TWEAKS MADE TO KIND TAF PER OBSERVATIONS. NO OTHER CHANGES
NEEDED AT THIS TIME. PREVIOUS AVIATION DISCUSSION FOLLOWS...
MVFR EXPECTED TO IMPROVE TO VFR DURING THIS TAF PERIOD.
IR IMAGES SHOW BACK EDGE OF THE LARGE CLOUD SHIELD ASSOCIATED WITH
THE STRONG AREA OF LOW PRESSURE TO THE NORTHEAST STILL LINGERING
ACROSS THE TAF SITES AT IND...LAF AND BMG. LATEST RAP INDICATES
THAT THIS FEATURE SHOULD FINALLY DRIFT EAST AFTER 09Z...AND WILL
TREND TAFS THIS WAY.
MODELS SUGGEST MID LEVEL RIDGE BUILDING ACROSS THE AREA ON
SATURDAY...AS THIS SHOULD CERTAINLY PUSH THE CYCLONIC CLOUD SHIELD
EAST. TAF SITES SHOULD GO VFR ON SATURDAY AS FORECAST SOUNDINGS
AND TIME HEIGHT SECTIONS DRY OUT AND CONVECTIVE TEMPERATURES
REMAIN UNATTAINABLE.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...JAS
NEAR TERM...JAS
SHORT TERM...JAS
LONG TERM....JH
AVIATION...JH
AREA FORECAST DISCUSSION
NWS INDIANAPOLIS IN
305 AM EST SAT DEC 22 2012
.UPDATE...
THE SYNOPSIS...NEAR TERM AND SHORT TERM SECTIONS HAVE BEEN UPDATED BELOW.
&&
.SYNOPSIS...
ISSUED AT 302 AM EST SAT DEC 22 2012
HIGH PRESSURE IS EXPECTED ACROSS THE AREA OVER THE WEEKEND. A LOW
PRESSURE SYSTEM IS EXPECTED TO MOVE THROUGH THE OHIO VALLEY AROUND
MONDAY. A STRONGER SYSTEM MAY AFFECT THE AREA TOWARDS THE MIDDLE OF
NEXT WEEK. IN THE WAKE OF THIS SYSTEM...HIGH PRESSURE WILL MOVE INTO
THE AREA FOR LATE NEXT WEEK.
&&
.NEAR TERM /TODAY/...
ISSUED AT 302 AM EST SAT DEC 22 2012
SATELLITE LOOP INDICATES BACK EDGE OF LOW CLOUD DECK IS BEGINNING TO
PUSH EAST. EXTRAPOLATION AND SHORT TERM MODEL DATA SUGGEST THE
CLEARING LINE SHOULD REACH THE FAR EASTERN ZONES AROUND SUNRISE.
OTHERWISE...EXPECTING A SUNNY DAY TODAY UNDER HIGH PRESSURE...WITH
ONLY SOME THIN HIGH CLOUD COVER AT TIMES. PROGGED LOW LEVEL
THICKNESSES SUGGEST THE GFS MOS HIGHS FOR TODAY MAY BE A FEW DEGREES
TOO COOL...MAINLY OVER THE NORTH. WILL BUMP UP THE NUMBERS ABOUT 3-4
DEGREES IN THOSE AREAS.
&&
.SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/...
ISSUED AT 302 AM EST SAT DEC 22 2012
MODELS INDICATE UPPER FLOW WILL FLATTEN OUT DURING THIS PERIOD AS
DEEP UPPER TROUGH CURRENTLY OVER THE NORTHEAST LIFTS INTO CANADA.
LOOKS RATHER QUIET THROUGH SUNDAY AS SURFACE AND UPPER RIDGING MOVES
THROUGH. MAIN ITEM OF INTEREST WILL BE A UPPER DISTURBANCE THAT IS
EXPECTED TO MOVE ACROSS THE FORECAST AREA MONDAY INTO MONDAY NIGHT.
SOME OF THE ENSEMBLE MEMBERS BRING A THREAT FOR SOME LIGHT RAIN OR
MIXED PRECIPITATION LATE SUNDAY NIGHT OVER THE FAR SOUTH...WHILE THE
MAJORITY OF THE OPERATIONAL AND ENSEMBLE DATA HOLD OFF THIS THREAT
UNTIL MONDAY. WILL CONTINUE TO KEEP THE FORECAST DRY THROUGH SUNDAY
NIGHT.
LIFT WITH THE SYSTEM COMING IN ON MONDAY LOOKS PRETTY DECENT AT THIS
POINT...ALTHOUGH DEEP MOISTURE IN THE PRECIPITATION BEARING LAYERS
IS QUESTIONABLE. THEREFORE...DOESN/T APPEAR THIS SYSTEM WILL BE A
BIG QPF PRODUCER. WILL GO WITH CHANCE POPS FOR LIGHT RAIN OR SNOW
OVER THE NORTHERN TWO THIRDS OF THE FORECAST AREA ON MONDAY...AND
CHANCE POPS FOR LIGHT RAIN FARTHER SOUTH. APPEARS THIS SYSTEM WILL
MOVE EAST OF THE AREA DURING MONDAY NIGHT...SO WILL KEEP SOME
SMALL CHANCE POPS FOR LIGHT SNOW OR RAIN INTO MONDAY NIGHT.
PROGGED LOW LEVEL THICKNESSES SUGGEST THE GFS MOS TEMPERATURE
GUIDANCE FOR SUNDAY AND MONDAY LOOK TOO COOL...ESPECIALLY THE HIGHS
ON SUNDAY. WILL BUMP UP THE GUIDANCE HIGHS SUNDAY ABOUT 5
DEGREES...AND NUDGE THE SUNDAY NIGHT LOWS AND MONDAY NIGHTS UP
SLIGHTLY.
&&
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
ISSUED AT 239 PM EST FRI DEC 21 2012
FORECAST FOCUS IS ON SIGNIFICANT STORM SYSTEM MID WEEK...WHICH MAY
OR MAY NOT HIT CENTRAL INDIANA DEPENDING ON THE EXACT TRACK. QUITE A
BIT OF VARIABILITY IN MODEL SOLUTIONS WITH THIS SYSTEM. WITH HIGH
ENSEMBLE SPREAD AND THE GFS ENSEMBLE AVERAGE SOLUTION AND GEM
SOLUTION VARYING SIGNIFICANTLY FROM THE OPERATIONAL GFS AND 12Z
ECMWF THINK BEST COURSE OF ACTION IS TO GO WITH A CONSENSUS AND HOPE
VARIABILITY LESSENS AS SYSTEM APPROACHES.
MONDAY NIGHT A SYSTEM ALONG THE OHIO RIVER SHOULD BE PULLING AWAY
FROM THE AREA. COULD SEE A MIX OF RAIN AND SNOW IN THE SOUTH WITH
SNOW IN THE NORTH BRIEFLY BEFORE THE LOW PULLS FAR ENOUGH AWAY FROM
THE AREA TO BRING PRECIP TO AN END. CHRISTMAS DAY LOOKS LIKE HIGH
PRESSURE WILL BRIEFLY BE OVER THE AREA KEEPING CONDITIONS DRY.
CHRISTMAS NIGHT IS WHEN POPS START TO BE INTRODUCED WITH THE
AFOREMENTIONED SIGNIFICANT SYSTEM. LOW TRACKS VARY FROM UP THE
MISSISSIPPI RIVER THROUGH THE TENNESSEE VALLEY TO ACROSS THE FLORIDA
PANHANDLE AND UP THE EAST COAST. THIS LESSENS CONFIDENCE IN ANY
PARTICULAR SOLUTION. CONSENSUS POPS YIELD CHANCE FOR CHRISTMAS NIGHT
WITH LIKELY IN THE SOUTHEAST ON WEDNESDAY AND CHANCE WEDNESDAY
NIGHT. FOR PRECIP TYPE WILL GO WITH SNOW IN THE NORTH AND A MIX OF
RAIN AND SNOW IN THE SOUTH AS TRACK VARIABILITY IMPACTS THE ARRIVAL
OF THE COLD AIR AS WELL. TEMPERATURES SHOULD BE BELOW NORMAL AFTER
TUESDAY.
&&
.AVIATION /DISCUSSION FOR THE 220600Z IND TAFS/...
ISSUED AT 1118 PM EST FRI DEC 21 2012
MVFR EXPECTED TO IMPROVE TO VFR DURING THIS TAF PERIOD.
IR IMAGES SHOW BACK EDGE OF THE LARGE CLOUD SHIELD ASSOCIATED WITH
THE STRONG AREA OF LOW PRESSURE TO THE NORTHEAST STILL LINGERING
ACROSS THE TAF SITES AT IND...LAF AND BMG. LATEST RAP INDICTATES
THAT THIS FEATURE SHOULD FINALLY DRIFT EAST AFTER 09Z...AND WILL
TREND TAFS THIS WAY.
MODELS SUGGEST MID LEVEL RIDGE BUILDING ACROSS THE AREA ON
SATURDAY...AS THIS SHOULD CERTAINLY PUSH THE CYCLONIC CLOUD SHIELD
EAST. TAF SITES SHOULD GO VFR ON SATURDAY AS FORECAST SOUNDINGS
AND TIME HEIGHT SECTIONS DRY OUT AND CONVECTIVE TEMPERATURES
REMAIN UNATTAINABLE.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...JAS
NEAR TERM...JAS
SHORT TERM...JAS
LONG TERM....CP
AVIATION...JP
AREA FORECAST DISCUSSION
NWS INDIANAPOLIS IN
1126 PM EST FRI DEC 21 2012
.UPDATE...
THE AVIATION SECTION HAS BEEN UPDATED BELOW
&&
.SYNOPSIS...
ISSUED AT 152 PM EST FRI DEC 21 2012
A STRONG STORM SYSTEM WILL CONTINUE TO PULL AWAY FROM THE AREA
TONIGHT. HIGH PRESSURE IS EXPECTED TO BUILD IN FOR THE WEEKEND. A
LOW PRESSURE SYSTEM MAY MOVE THROUGH THE OHIO VALLEY EARLY NEXT
WEEK...AROUND MONDAY. A POTENTIALLY STRONGER SYSTEM MAY AFFECT THE
AREA TOWARDS THE MIDDLE OF NEXT WEEK.
&&
.NEAR TERM /REST OF TONIGHT/...
ISSUED AT 1004 PM EST FRI DEC 21 2012
CLOUDS CONTINUE TO PERSIST ACROSS MUCH OF THE FORECAST AREA.
SATELLITE LOOPS SHOW LITTLE IN THE WAY OF CLEARING WORKING TOWARD
THE AREA AS CYCLONIC FLOW REMAINS DOMINANT.
LATEST HI RES MODEL DATA SHOW THAT CLOUDS LINGERING THROUGH MUCH
OF THE NIGHT ACROSS MUCH OF THE EASTERN HALF OF THE FORECAST AREA.
GIVEN ALL OF THE ABOVE HAVE INCREASED CLOUD COVER OVER MUCH OF THE
AREA THROUGH THE NIGHT.
WITH THE INCREASED CLOUD COVER HAVE BUMPED UP TEMPERATURES A
LITTLE WHERE CLOUDS WILL PERSIST. AM HESITANT TO RAISE TOO MUCH
THOUGH...AS TEMPERATURES WILL DROP QUICKLY WITH ANY BREAKS THAT DO
HAPPEN TO FORM.
&&
.SHORT TERM /SATURDAY THROUGH MONDAY/...
ISSUED AT 152 PM EST FRI DEC 21 2012
MODELS INDICATE UPPER FLOW FLATTENING OUT AS THE DEEP UPPER TROUGH
LIFTS OFF INTO THE CANADIAN MARITIMES BY SUNDAY. CENTRAL INDIANA
WILL ENTER A QUIET FORECAST PERIOD THROUGH THE WEEKEND. TEMPERATURES
WILL MODERATE OVER THIS TIME BACK TO CLIMO...AND EVEN SLIGHT ABOVE
CLIMO BY SUNDAY AFTERNOON.
ONLY ITEM OF INTEREST WILL BE A POTENTIAL SHORT WAVE TROUGH THAT THE
MODELS BRING INTO THE MIDWEST BY LATE SUNDAY NIGHT. SOME OF THE
ENSEMBLE MEMBERS BRING A THREAT FOR SOME LIGHT RAIN OR MIXED
PRECIPITATION ACROSS THE NORTHERN COUNTIES DURING THE DAY MONDAY.
THIS FEATURE LOOKS WEAKER WITH LATEST MODELS RUNS...AND SOME MODELS
(THE GFS) BARELY EVEN DEPICT IT PRODUCING ANY PRECIPITATION FOR
CENTRAL INDIANA. HAVE THEREFORE BACKED OFF ON POP DURING THIS TIME.
&&
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
ISSUED AT 239 PM EST FRI DEC 21 2012
FORECAST FOCUS IS ON SIGNIFICANT STORM SYSTEM MID WEEK...WHICH MAY
OR MAY NOT HIT CENTRAL INDIANA DEPENDING ON THE EXACT TRACK. QUITE A
BIT OF VARIABILITY IN MODEL SOLUTIONS WITH THIS SYSTEM. WITH HIGH
ENSEMBLE SPREAD AND THE GFS ENSEMBLE AVERAGE SOLUTION AND GEM
SOLUTION VARYING SIGNIFICANTLY FROM THE OPERATIONAL GFS AND 12Z
ECMWF THINK BEST COURSE OF ACTION IS TO GO WITH A CONSENSUS AND HOPE
VARIABILITY LESSENS AS SYSTEM APPROACHES.
MONDAY NIGHT A SYSTEM ALONG THE OHIO RIVER SHOULD BE PULLING AWAY
FROM THE AREA. COULD SEE A MIX OF RAIN AND SNOW IN THE SOUTH WITH
SNOW IN THE NORTH BRIEFLY BEFORE THE LOW PULLS FAR ENOUGH AWAY FROM
THE AREA TO BRING PRECIP TO AN END. CHRISTMAS DAY LOOKS LIKE HIGH
PRESSURE WILL BRIEFLY BE OVER THE AREA KEEPING CONDITIONS DRY.
CHRISTMAS NIGHT IS WHEN POPS START TO BE INTRODUCED WITH THE
AFOREMENTIONED SIGNIFICANT SYSTEM. LOW TRACKS VARY FROM UP THE
MISSISSIPPI RIVER THROUGH THE TENNESSEE VALLEY TO ACROSS THE FLORIDA
PANHANDLE AND UP THE EAST COAST. THIS LESSENS CONFIDENCE IN ANY
PARTICULAR SOLUTION. CONSENSUS POPS YIELD CHANCE FOR CHRISTMAS NIGHT
WITH LIKELY IN THE SOUTHEAST ON WEDNESDAY AND CHANCE WEDNESDAY
NIGHT. FOR PRECIP TYPE WILL GO WITH SNOW IN THE NORTH AND A MIX OF
RAIN AND SNOW IN THE SOUTH AS TRACK VARIABILITY IMPACTS THE ARRIVAL
OF THE COLD AIR AS WELL. TEMPERATURES SHOULD BE BELOW NORMAL AFTER
TUESDAY.
&&
.AVIATION /DISCUSSION FOR THE 220600Z IND TAFS/...
ISSUED AT 1118 PM EST FRI DEC 21 2012
MVFR EXPECTED TO IMPROVE TO VFR DURING THIS TAF PERIOD.
IR IMAGES SHOW BACK EDGE OF THE LARGE CLOUD SHIELD ASSOCIATED WITH
THE STRONG AREA OF LOW PRESSURE TO THE NORTHEAST STILL LINGERING
ACROSS THE TAF SITES AT IND...LAF AND BMG. LATEST RAP INDICTATES
THAT THIS FEATURE SHOULD FINALLY DRIFT EAST AFTER 09Z...AND WILL
TREND TAFS THIS WAY.
MODELS SUGGEST MID LEVEL RIDGE BUILDING ACROSS THE AREA ON
SATURDAY...AS THIS SHOULD CERTAINLY PUSH THE CYCLONIC CLOUD SHIELD
EAST. TAF SITES SHOULD GO VFR ON SATURDAY AS FORECAST SOUNDINGS
AND TIME HEIGHT SECTIONS DRY OUT AND CONVECTIVE TEMPERATURES
REMAIN UNATTAINABLE.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...SMF
NEAR TERM...50
SHORT TERM...SMF
LONG TERM....CP
AVIATION...JP
AREA FORECAST DISCUSSION
NWS LOUISVILLE KY
326 AM EST SAT DEC 22 2012
.Short Term (Today - Sunday)...
Issued at 325 AM EST Sat Dec 22 2012
Weather in the short-term period is rather quiet as we wait for our
next set of weather systems to track across the Ohio Valley. A
stratus deck lingers across south-central Indiana and extends
southeastward through eastern Kentucky. The southward push of this
deck has stalled and the back edge is now dissipating with
increasing dry air advection from the west. While most of the
forecast area will start the day clear/sunny, portions of southeast
Indiana, the Bluegrass, and east-central Kentucky will see the
clouds scatter out and head east as the morning progresses.
Otherwise, cold surface high pressure will quickly shift east over
the forecast area today. Being on the northern edge of this high,
northwest surface winds will back and become southwesterly at 5 to
10 mph by later this afternoon. Southwest winds will then remain in
place through the short-term period, allowing temperatures to
moderate a bit.
Temperatures are starting out in the 20s this morning, with wind
chill values in the teens. Temperatures are expected to range from
the mid 30s across southeast Indiana and the Bluegrass region to
lower 40s in the south and southwest CWA by this afternoon, but the
wind chill will make it feel several degrees cooler. For tonight,
guidance continues to indicate south and southwest winds will remain
slightly elevated and clouds should be on the increase from the
southwest late tonight. Low temperatures ranging from the mid 20s to
right around 30 degrees will be common, with normally cooler
locations dropping into the lower 20s. These temps may occur early
in the night, before moderating a bit closer to sunrise.
Clouds will continue to increase from the southwest Sunday, as a
shortwave and low pressure system develop to our west. Southwest
winds will pick up and could become locally breezy, which will help
max temperatures range from the mid 40s to lower 50s. While moisture
return is limited, isentropic lift will be ongoing ahead of this
system, which could spread some light rain across south-central
Kentucky late in the afternoon. With this warm-air advection
pattern, all precip will be in liquid form. Now on to the
interesting portion of the forecast, the long term!
.Long Term (Sunday Night - Friday)...
Issued at 320 AM EST Sat Dec 22 2012
...First Significant Snow Possible the Day after Christmas...
At the start of the period, a warm front will extend northeast of a
low pressure center in the Arklatex, stretching across or just north
of the Ohio Valley. The best isentropic lift indicated in the models
will remain across the southern forecast area, so will keep the
better rain chances down there. By evening, the low is forecast to
be east of the region, taking any light rains along with it. QPF
will be light for this event, as moisture return is limited ahead of
this feature.
After a quiet Christmas Day, the next big system looks to come into
play. Models have been run-to-run consistent and both the GFS and
ECMWF have been in pretty good agreement on this system, both
deterministic and ensembles. The Canadian GEM is farther south with
the system, but its trajectory is more typical of systems this time
of year, so its solution cannot be ruled out. By 00Z Wednesday, the
EC and GFS have the surface low deepening over Mississippi. This low
travels toward eastern Tennessee by daybreak Wednesday, with its
parent upper low over central Tennessee. This track would place a
band of moderate to heavy snow somewhere across our forecast area
Wednesday morning. Trying to get specific for one area and how much
snow it will get is too difficult at this point, but it is appearing
more likely that someone will get heavy snow on the back side of
this low, with the cold air in place. The Canadian GEM solution
brings the heavier snow to our southern forecast, whereas the GFS
has the band over southern Indiana. The ECMWF is in between. As we
have to put some snow in somewhere, have gone with southern Indiana
for now as having the highest snow totals...and that being 5-7
inches of snow. This is well under the foot of snow the GFS has in a
deformation band across southern Indiana. Again look for the peak
values likely to change both in intensity and location!
By Wednesday evening, the surface low will shift quickly to the mid
Atlantic coast, bringing an end to the significant precipitation.
Canadian high pressure will build into the region for Thursday and
Friday. Depending on where the heaviest snow falls, very cold
temperatures are possible Thursday night, as it looks ideal for
radiational cooling combined with a snowpack. Guidance is no help
here either, as it calls for lows around 20. Would not be surprised
to see some single digits in places with the best snow pack, but
these numbers can be refined as the forecast becomes more precise.
Another factor could be some mid/high cloudiness coming in as a
ridge axis aloft crosses our region.
&&
.Aviation (06Z TAF Issuance)...
Issued at 1240 AM EST Sat Dec 22 2012
Strong surface low continues to move into Quebec with high pressure
becoming established across the Mississippi River Valley. The
resultant pressure gradient is starting to gradual weakening this
morning as the low continues to push northeast. Northwest winds will
back to a more west-southwesterly direction between 5 and 10 mph by
about mid morning, as the center of the surface high passes by to
our south.
Lingering cyclonic stratus deck is trying to make southward
progress. Do not think it will push too much further south, with SDF
remaining on the southern edge and LEX overcast until the deck
scatters and shifts northeast later this morning. Models are not
handling this situation well, with the RAP having the best solution.
However, it seems to be currently overdoing the clouds at SDF. Will
continue to monitor. Otherwise, only expect a few upper-level clouds
streaming overhead today.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
KY...NONE.
$$
Short Term.......MJP
Long Term........RJS
Aviation.........MJP
AREA FORECAST DISCUSSION
NWS LOUISVILLE KY
1242 AM EST SAT DEC 22 2012
...Updated Aviation Discussion...
.Forecast Update...
Issued at 949 PM EST Fri Dec 21 2012
Winds have slackened across the region with gustiness subsiding as
well. May still have a few gusts for the next couple of hours. Main
reason for an update this evening is to reintroduce sky cover as
stratus deck has built back into the region with 925mb moisture
advection from the north. This will likely occur as far southwest as
a Salem, IN, to Louisville, to Somerset, KY line. Further southwest,
expect clear skies to persist. Stratus should remainder much of the
night, although surface high over the Mississippi River Valley should
start to push in toward dawn, with drier air working away at the
cloud cover. Overall, stratus should not have a huge impact on
overnight lows as steady cold air advection will win out. That being
said, did raise lows a degree or two underneath the expected cloud
cover. Updated products already out.
&&
.Short Term (Tonight - Saturday Night)...
Issued at 315 PM EST Fri Dec 21 2012
In coordination with other offices and since mesonet sites are still
gusting between 30-40 mph, will continue the SPS until 6 pm EST.
Wind gusts are expected to subside shortly after sunset.
Snow has ended across the region with storm totals generally between
a trace and a half inch over southern Indiana and east central
Kentucky. Elsewhere over central KY, trace amounts to a few tenths
of snow were observed. The highest snow accumulation reported was
0.9 inches reported in Harrison County KY. See our
website...www.weather.gov/lmk...for more details on snow totals and
max wind gusts over the last 36-48 hours.
Skies will continue to clear from SW to NE across the area this
evening with sfc high pressure building in for Saturday. As a
result we`ll see mostly clear skies through Sat night. Tonight low
temperatures will drop pretty low in a very cold post-frontal
airmass. However, they won`t reach their full radiational cooling
potential due to sfc and low level winds staying elevated
overnight. Expect low temps in the upper teens and lower 20s
tonight...potentially colder than that in locations which still have
a light snow coating on the ground.
For Saturday, temperatures will rebound back into the upper 30s and
lower 40s for highs as the cold airmass will already be beginning to
moderate under sunny skies.
Saturday night expect another clear calm night with sfc winds
turning to the south ahead of the next weather system. Lows will be
in the 20s to around 30.
.Long Term (Sunday - Friday)...
Issued at 320 PM EST Fri Dec 21 2012
...First Significant Snow Possible the Day after Christmas...
Sunday will be dry with temperatures a few degrees above normal
across the region. Clouds will be on the increase from the south as
a shortwave and low pressure system develop to the west. Rain will
spread into southern KY Sunday night and continue to overspread the
region Christmas Eve as the low tracks across the forecast area.
With decent warm air moving in with this system, it looks like it
will be an all rain event. Highs on Monday will be in the upper 40s
to lower 50s. The rain will move out Monday night and should be out
of the area by Christmas morning. Lows Christmas morning will be in
the mid to upper 30s. Christmas will be mainly dry, with just a few
showers moving into south central Kentucky during the afternoon as
the next low pressure system begins to move in. Highs will be in the
40s.
The more significant low pressure system will move through on
Wednesday. This low will track across east central Kentucky,
probably just west of the Appalachians through the day on Wednesday
and move up the east coast Wednesday night into Thursday morning.
This system will pull in much colder air on the back side of it. The
models have been fairly consistent in showing some accumulating snow
will be possible across the forecast area with this system. However,
the amount of snow we be will be highly dependent on the low track
and where the deformation band sets up on the back side of this low.
Precipitation will likely start off as all rain on Tuesday night and
then transition to a mix Wednesday morning and then all snow before
ending on Wednesday night. Anyone with travel plans for the day
after Christmas should be sure to check back for updates on this
system as we get closer to the event.
Thursday and Friday will be be much colder with highs in the 30s and
lows in the teens to twenties.
&&
.Aviation (06Z TAF Issuance)...
Issued at 1240 AM EST Sat Dec 22 2012
Strong surface low continues to move into Quebec with high pressure
becoming established across the Mississippi River Valley. The
resultant pressure gradient is starting to gradual weakening this
morning as the low continues to push northeast. Northwest winds will
back to a more west-southwesterly direction between 5 and 10 mph by
about mid morning, as the center of the surface high passes by to
our south.
Lingering cyclonic stratus deck is trying to make southward
progress. Do not think it will push too much further south, with SDF
remaining on the southern edge and LEX overcast until the deck
scatters and shifts northeast later this morning. Models are not
handling this situation well, with the RAP having the best solution.
However, it seems to be currently overdoing the clouds at SDF. Will
continue to monitor. Otherwise, only expect a few upper-level clouds
streaming overhead today.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
KY...NONE.
$$
Update...........BJS
Short Term.......AMS
Long Term........EER
Aviation.........MJP
AREA FORECAST DISCUSSION
NWS MARQUETTE MI
453 AM EST SAT DEC 22 2012
.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 451 AM EST SAT DEC 22 2012
FAIRLY QUIET WEATHER PATTERN IN STORE FOR TODAY AND TONIGHT AS A
WEAK HIGH PRESSURE RIDGE CONTINUES TO SLIDE ACROSS THE CWA TODAY
AND THEN A WEAK COLD FRONT MOVES THROUGH TONIGHT.
THE WEAK HIGH PRESSURE RIDGE IS ASSOCIATED WITH AN UPPER RIDGE THAT
IS CURRENTLY PUSHING INTO WESTERN UPPER MICHIGAN THIS MORNING AND IS
EXPECTED TO QUICKLY SLIDE SOUTHEAST AND DISSIPATE AS A SHORTWAVE
DIVES SOUTHEAST FROM LAKE WINNIPEG TONIGHT. AT THE PRESENT
TIME...PLENTY OF LAKE EFFECT CLOUDS OVER CENTRAL AND EASTERN LAKE
SUPERIOR...AS RAP ANALYZED H925 TEMPS ARE AROUND -10C AND THERE IS
PLENTY OF MOISTURE TRAPPED UNDER THE SUBSIDENCE INVERSION. RADAR
NOT REALLY PICKING UP ON MUCH SNOW...DUE TO THE INVERSION BEING
AT/AROUND 3.5KFT...BUT THERE HAS BEEN LIGHT SNOW/FLURRIES AT THE
OFFICE EARLY THIS MORNING. FARTHER WEST...THE DRIER AIR SEEN ON THE
00Z KINL SOUNDING HAS CONTINUED TO EAT AWAY AT THE LAKE EFFECT OVER
THE WESTERN LAKE AND ALL THAT REMAINS OVER THE THIRD OF WESTERN
UPPER MICHIGAN IS STRATUS TRAPPED BELOW THE INVERSION. RAP/NAM H925
MOISTURE FIELDS SEEM TO HAVE A GOOD HANDLE ON THE BACK EDGE OF THIS
MOISTURE AND WILL FOLLOW THE IDEA OF THE CLOUD EDGE GRADUALLY
PUSHING TO THE NORTHEAST THROUGH THE DAY TODAY AS THE H925 RIDGE
BACKS WINDS TO THE WEST-SOUTHWEST. SINCE UPSTREAM MID/HIGH CLOUDS
WILL LIKELY AFFECT THE AREAS WHERE THE LOW CLOUDS DEPART...WON/T GO
WITH A SUNNY FORECAST AND KEEP IN MOSTLY SUNNY TO PARTLY CLOUDY
AREA.
AS FOR THE LAKE EFFECT CLOUDS AND --SHSN...MODELS NOT REALLY SHOWING
THE H925 RIDGE HAVING TOO MUCH AFFECT ON IT UNTIL THIS
AFTERNOON...EXCEPT OVER NORTH CENTRAL UPPER MICHIGAN. THE DRIER
AIR SHOULD CAUSE THE SUBSIDENCE INVERSION TO LOWER FURTHER AND
TOWARDS 2-2.5KFT OVER EASTERN LAKE SUPERIOR AND UPPER MICHIGAN.
THUS...LIKED THE PREVIOUS SHIFTS HANDLING OF PUSHING THE ISOLATED
SNOW SHOWERS EAST THROUGH THE DAY AND MAINLY FOCUSED EAST OF GRAND
MARAIS THIS AFTERNOON.
TONIGHT...FRONT ARRIVES SHORTLY AFTER SUNSET OVER THE WEST AND H925
MOISTURE SURGES BACK OVER THE AREA AND INCREASES CLOUDS. OVER THE
EAST...THERE COULD BE A BRIEF PERIOD WHERE THE SNOW COMPLETELY
ENDS LATE THIS AFTERNOON OR EARLY EVENING BEFORE THE NEXT WAVE
ARRIVES. THIS FRONT WILL DROP SOUTHEAST ACROSS THE REST OF THE CWA
DURING THE EVENING AND THE FIRST PART OF THE OVERNIGHT HOURS. WITH
WINDS VEERING TO THE NORTHWEST BEHIND THE FRONT AND COLDER AIR
SURGING BACK IN...ENHANCED BY SURFACE LOW DEVELOPING OVER
THE EASTERN LAKE...EXPECT THE LAKE EFFECT CLOUDS AND POTENTIAL SNOW
SHOWERS TO REDEVELOP LATE IN THE EVENING AND CONTINUE OVERNIGHT FOR
THE NORTHWEST TO NORTH-NORTHWEST FAVORED LOCATIONS. BEST LOW LEVEL
LAPSE RATES ARE SEEN OVER EASTERN LAKE SUPERIOR /TO 8.5C/KM /.
MODELS SHOWING SOME DIRECTIONAL SHEAR OVER THE EAST /NORTHWEST H850
WINDS AND NORTH WINDS BELOW H900/...WHICH COMBINED WITH THE FAIRLY
DRY SUB CLOUD LAYER WILL KEEP THE LAKE EFFECT FROM BECOMING
TOO STRONG /LIMITS CLOUD DEPTH TO A FEW KFT EVEN THOUGH INVERSION
HEIGHT IS NEAR 6KFT/ AND COULD ALSO INFLUENCE DEVELOPMENT. THIS IS
ESPECIALLY PREVALENT OVER THE SOUTH CENTRAL LAKE AND NORTH CENTRAL
UPPER MICHIGAN WITH THE LATEST NAM...WHILE THE GFS HAS LESS SHEAR
AND OUR LOCAL REGIONAL WRF HAS BETTER MOISTURE AND UNIDIRECTIONAL
WINDS. WITH THE DIFFERENCES...WILL CONTINUE TO MENTION A
SLIGHT/CHANCE OF SNOW SHOWERS OVER THE NORTH CENTRAL AND EAST
FAVORED LOCATIONS...WITH THE HIGHEST POPS OVER LUCE COUNTY WHERE
INCREASED CONVERGENCE WILL OCCUR WITH THE DEVELOPING SURFACE LOW.
FARTHER WEST...LAKE EFFECT CONDITIONS ARE MORE FAVORABLE IN THE
EVENING WITH BETTER LOW LEVEL MOISTURE AND INVERSION HEIGHTS TO
4.5KFT. WILL CONTINUE CHANCE POPS FOR THAT PERIOD AND THEN START TO
DIMINISH OVERNIGHT AS DRIER AIR WORKS IN. OVERALL...EXPECT MOST
LOCATIONS TO SEE LESS THAN AN INCH OF SNOW.
.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 451 AM EST SAT DEC 22 2012
SUNDAY AND SUNDAY NIGHT...LES CONDITIONS WILL BE LESS FAVORABLE AS
LOW-LVL FLOW BECOMES INCREASINGLY ANTICYCLONIC AND DIVERGENT AS SFC
RIDGE BUILDS INTO THE NRN PLAINS AND UPPER GREAT LAKES AREA.
INCREASING SUBSIDENCE AND INVERSION HEIGHTS LOWERING AOB 3KFT WILL
MAKE IT HARD FOR ACCUMULATING SNOW ESPECIALLY BY SUNDAY NIGHT. KEPT
IN JUST MAINLY 20-30 PCT POPS...HIGHEST EAST WHERE FETCH WILL BE
GREATER ACROSS LAKE SUPERIOR IN NW FLOW.
MON-TUE...MODELS CONTINUE TO TREND SOUTH WITH SHORTWAVE MOVING IN FM
THE NRN PLAINS LATE MONDAY INTO MON NIGHT. SOME WEAK FORCING
ASSOCIATED WITH THIS SHORTWAVE MAY PRODUCE SOME LIGHT SNOW MON INTO
MON EVENING MAINLY OVER SRN PORTIONS OF THE CWA. WITH MODELS SHOWING
850 MB TEMPS DROPPING TO -14C/-15C IN THE WAKE OF THIS
SHORTWAVE...THE ADDED INSTABILITY COULD ALSO PROVIDE A BOOST TO NNW
FLOW LES.
TUE NIGHT-THU...MODELS CONTINUE TO KEEP NEXT SYSTEM EMERGING OUT OF
SRN PLAINS/LWR MS VALLEY WELL SOUTH AND EAST OF THE GREAT LAKES
REGION WITH NO SYNOPTIC SNOW EXPECTED FOR OUR AREA. A MID-LVL TROF
AXIS FROM LOW OVER NRN CANADA IS FCST TO MOVE THROUGH THE UPPER
GREAT LAKES WED NIGHT AND THU...BUT FORCING WITH THIS FEATURE LOOKS
MINIMAL. WITH 850 MB TEMPS OF -10C/-11C CONTRIBUTING TO MARGINAL
INSTABILITY AND A WEAK NRLY FLOW...SOME LIGHT SCT LES IS POSSIBLE
DOWNWIND OF LAKE SUPERIOR OVER NRN COUNTIES. WL MAINTAIN SLIGHT CHC
POPS FOR THESE AREAS.
FRI...MODELS SHOW POTENTIAL FOR ANOTHER SIGNIFICANT MID LEVEL TROUGH
TO MOVE THROUGH THE CNTRL CONUS FOR LATE WEEK. UNCERTAINTY STILL
EXISTS WITH MODELS CONCERNING TRACK OF THIS SYSTEM. THE 00Z ECMWF
CONTINUES TO TREND WITH A MORE AMPLIFIED PATTERN THAN THE GFS...AND
WOULD INDICATE A MORE NRN TRACK WITH LEAD SHORTWAVE EMERGING OUT OF
WRN CONUS TROF. THE ECMWF SCENARIO WOULD RESULT IN A BETTER CHC OF
PCPN FOR LATE FRIDAY INTO FRIDAY NIGHT FOR OUR CWA THAN THE GFS. AT
THIS POINT...GIVEN UNCERTAINTY WILL MAINTAIN JUST SLIGHT CHC POPS
FOR LIGHT SNOW TOWARD FRI EVENING. HOWEVER..WOULD NOT BE SURPRISED
GIVEN RECENT TRENDS...ESPECIALLY WITH THE ECMWF...THAT POPS MAY NEED
TO RAISED FOR LATE WEEK.
&&
.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1231 AM EST SAT DEC 22 2012
CONDITIONS WILL STAY VFR THROUGH SAT FOR IWD UNTIL THE WIND SWITCHES
TO THE NW BY EVENING BRINGING IN AN MVFR LAKE EFFECT CLOUD DECK
AGAIN. FOR CMX...WITH WESTERLY FLOW...MVFR LAKE EFFECT CLOUDS WILL
STAY THROUGH THE WHOLE PERIOD. FOR SAW...UNTIL THE WIND BECOMES
WESTERLY...MVFR LAKE EFFECT CLOUDS WILL STAY. WEST WINDS ON SAT
SHOULD ALLOW THE LOW CLOUDS TO MOVE OUT OF SAW BY AFTERNOON AND VFR
CONDITIONS WILL THEN PREVAIL UNTIL THE END OF THE TAF PERIOD.
&&
.MARINE...(FOR THE 4 AM LAKE SUPERIOR FORECAST ISSUANCE)
ISSUED AT 451 AM EST SAT DEC 22 2012
WINDS HAVE FALLEN BELOW GALES THIS MORNING AS THE PRESSURE GRADIENT
CONTINUES TO RELAX WITH WEAK HIGH PRESSURE RIDGE MOVING THROUGH
TODAY. WINDS ARE EXPECTED TO INCREASE UP TO 25KTS OUT OF THE
NORTHWEST TONIGHT AS A COLD FRONT SWEEPS SOUTHEAST ACROSS LAKE
SUPERIOR. HIGH PRESSURE RIDGE FROM THE CANADIAN PRAIRIES WILL TRY
TO NOSE INTO THE UPPER GREAT LAKES FOR SUNDAY AND THE FIRST HALF OF
NEXT WEEK...KEEPING WINDS BELOW 25KTS.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
UPPER MICHIGAN...
NONE.
LAKE SUPERIOR...
NONE.
LAKE MICHIGAN...
NONE.
&&
$$
SHORT TERM...SRF
LONG TERM...VOSS
AVIATION...07
MARINE...SRF
AREA FORECAST DISCUSSION
NWS LA CROSSE WI
233 AM CST SAT DEC 22 2012
.SHORT TERM...TODAY THROUGH MONDAY NIGHT
233 AM CST SAT DEC 22 2012
MAIN FORECAST CONCERNS ARE ON LOW CLOUD POTENTIAL TONIGHT INTO
SUNDAY AND POTENTIAL FOR SOME LIGHT SNOW SUNDAY NIGHT INTO MONDAY.
CURRENTLY AS OF 08Z...WATER VAPOR LOOP AND RAP 500MB HEIGHT ANALYSIS
SHOWED DEEP TROUGHING APPROACHING THE WESTERN U.S. COAST...RIDGING
ACROSS THE PLAINS AND DEEP TROUGHING ALONG THE U.S. EAST COAST. ON
TOP OF THE RIDGE...A SHORTWAVE WAS PRESENT ACROSS CENTRAL PORTIONS
OF SASKATCHEWAN AND MANITOBA. THE FORECAST AREA LIES CLOSER TO THE
INFLECTION POINT BETWEEN THE RIDGE AND EAST COAST TROUGH...YIELDING
HIGH PRESSURE AT THE SURFACE. OTHER THAN SOME SCATTERED HIGH CLOUDS
ASSOCIATED WITH A COMBINATION OF PACIFIC MOISTURE TOPPING THE RIDGE
AND A 100 KT JET NEAR THE TROPOPAUSE...SKIES WERE MOSTLY CLEAR
ACROSS THE FORECAST AREA. DRY AIR AND SUBSIDENCE SEEN ON THE 00Z
ABR...MPX AND DVN SOUNDINGS ARE HELPING TO PRODUCE THE MOSTLY CLEAR
SKIES. WITH LIGHT WINDS UNDER THE SURFACE RIDGE AND THE FRESH SNOW
COVER...TEMPERATURES HAVE MOSTLY FALLEN INTO THE SINGLE DIGITS ABOVE
ZERO. BLACK RIVER FALLS AND SPARTA HAVE EVEN DROPPED BELOW ZERO. TO
THE NORTHWEST...A COLD FRONT WAS LOCATED OVER MANITOBA AND THE
DAKOTAS ASSOCIATED WITH THE SOUTH CENTRAL CANADA SHORTWAVE. LOW
CLOUDS WERE PRESENT ACROSS SOUTH CENTRAL CANADA AS WELL BEHIND THE
FRONT.
TODAY AND TONIGHT...THE SHORTWAVE SEEN OVER SOUTH CENTRAL CANADA IS
PROGGED TO SLIDE SOUTHEAST ACROSS EASTERN LAKE SUPERIOR THIS
EVENING...DRIVING THE COLD FRONT ACROSS THE DAKOTAS THROUGH THE
FORECAST AREA. NO PRECIPITATION IS EXPECTED WITH OR BEHIND THE FRONT
GIVEN THE DRY AIRMASS PRESENT...AS WELL AS ALL THE FORCING LOCATED
WELL NORTHEAST OF THE AREA. MAIN CONCERNS WITH THE FRONT IS THE
WARMING AHEAD OF IT AND IF ANY LOW CLOUDS COME IN BEHIND IT.
REGARDING THE WARMING...GFS/NAM/ECMWF 925MB TEMPERATURE PROGS SHOW
THEM CLIMBING FROM -3 TO -6C CURRENTLY TO -2 TO -4C. WITH SOME SUN
THROUGH HIGH CLOUDS AND A SOUTHWEST BREEZE...TEMPERATURES SHOULD
EASILY CLIMB INTO THE 20S EVERYWHERE. SOME LOCATIONS IN WISCONSIN...
PARTICULARLY IN VALLEY AREAS...COULD EXCEED 30 THANKS TO LOWER
ALBEDO PRESENT. DECENT COLD ADVECTION LOOKS TO OCCUR TONIGHT BEHIND
THE FRONT AS 925MB TEMPS FALL TO -6 TO -10C BY 12Z SUNDAY ON 15-20
KT NORTHERLY BREEZE. CERTAINLY LOOKS GOOD FOR LAKE EFFECT OFF
SUPERIOR WHICH THE BREEZE WOULD THEN SEND THE CLOUDS SOUTHWARD AT
LEAST INTO THE NORTHERN HALF OF WISCONSIN AFTER MIDNIGHT. IN
ADDITION...SOME OF THE LOW CLOUDS IN GENERAL BEHIND THE FRONT COULD
END UP BEING SENT SOUTH. AS A RESULT...HAVE RAISED CLOUD COVER...
ESPECIALLY ACROSS TAYLOR AND CLARK COUNTIES GIVEN THE BETTER CHANCE
OF BEING IMPACTED BY LAKE EFFECT CLOUDS. GIVEN CLOUDS AND THE WINDS
BEHIND THE FRONT...FOLLOWED A BLEND OF GUIDANCE FOR LOWS.
SUNDAY AND SUNDAY NIGHT...FOCUS SHIFTS TO THE TROUGHING APPROACHING
THE WEST COAST. MODELS TAKE A FAIRLY SIGNIFICANT PORTION OF THE
TROUGH CROSSING THE NORTHERN ROCKIES DURING THE NEXT 24 TO 36 HOURS.
THE QUESTION IS WHAT HAPPENS WITH THE TROUGH FROM THERE. THE 22.00Z
NAM/UKMET ARE A WEAKER SCENARIO WITH THE TROUGH...STRETCHING FROM
NORTHEAST SOUTH DAKOTA INTO CENTRAL IOWA BY 12Z MONDAY.
MEANWHILE...THE 22.00Z GFS/CANADIAN DEPICT A MORE POTENT TROUGH THAT
ENDS UP CROSSING NEBRASKA AND BECOMING SITUATED DOWN IN SOUTHERN
IOWA INTO THE ST LOUIS AREA BY 12Z MONDAY. ALL SCENARIOS YIELD AN
INVERTED TROUGH AT THE SURFACE...JUST THE MORE POTENT GFS/CANADIAN
GROUP WOULD HAVE A BETTER SHOT OF YIELDING PRECIPITATION
DEVELOPMENT. GIVEN THE STRENGTH OF THE TROUGH RIGHT NOW OFF THE WEST
COAST...NOTED TOO BY NUMEROUS LIGHTNING STRIKES...WILL FAVOR THE
MORE POTENT GROUP. THIS MEANS 20 PERCENT CHANCES ARE NEEDED AFTER
MIDNIGHT SUNDAY NIGHT WEST OF THE MISSISSIPPI RIVER TO ACCOUNT FOR
THE DPVA AHEAD OF THE POTENT TROUGH...AS WELL AS ISENTROPIC LIFT.
DID NOT GO HIGHER THAN 20 BECAUSE OF INITIAL DRY AIR TO OVERCOME
SINCE THE SNOW THAT DOES FALL WILL COME OUT OF A MID CLOUD DECK.
OTHERWISE...THE ONLY OTHER CONCERN IS CLOUD COVER. THE LOW CLOUDS
OVER NORTHERN WI AT 12Z SUNDAY COULD END UP EXPANDING SOUTHWESTWARD
THROUGH THE DAY...WHILE MID AND HIGH CLOUDS INCREASE DOWNSTREAM OF
THE POTENT TROUGH. THUS AN INCREASING CLOUD TREND SEEMS APPROPRIATE.
THESE CLOUDS PLUS COLDER 925MB TEMPS IN THE -8 TO -10C RANGE WILL
DEFINITELY YIELD A COLDER DAY. ON THE POSITIVE SIDE...THE CLOUDS
SHOULD HELP HOLD TEMPERATURES UP SUNDAY NIGHT.
MONDAY INTO MONDAY NIGHT...FOLLOWING THE MORE POTENT TROUGH LOOK AS
MENTIONED IN THE SUNDAY/SUNDAY NIGHT DISCUSSION...THE GFS AND
CANADIAN SEND THE TROUGH SOUTHEAST INTO OHIO BY 00Z TUESDAY. CHANCES
OF SNOW STILL LOOK APPROPRIATE FOR MONDAY WITH ISENTROPIC LIFT AND
DPVA PERSISTING...THOUGH THIS SHOULD BE DIMINISHING IN THE AFTERNOON
AS THE TROUGH SHIFTS EAST AND CANADIAN HIGH PRESSURE BUILDS SOUTH
INTO THE DAKOTAS IN ITS WAKE. AS SUCH...MONDAY NIGHT IS LIKELY TO
END UP DRY. REGARDING THE ACTUAL CHANCES...LINGERING LOWER LEVEL DRY
AIR IS A BIG CONCERN...AS WELL AS THE TRACK OF THE TROUGH DROPPING
MORE TO OUR SOUTH. AS A RESULT...KEPT CHANCES IN A 20-30 RANGE.
LOOKS GOOD FOR MOST OF THE AREA TO PICK UP A LITTLE SNOW...BE IT
ACTUAL ACCUMULATING SNOW OR FLURRIES...SO USED OCCASIONAL VERY LIGHT
SNOW VERBIAGE. GIVEN CANADIAN HIGH PRESSURE BUILDING SOUTH...ONE CAN
EXPECT COLDER LOW LEVEL AIR. THIS IS VERY WELL REPRESENTED BY 925MB
TEMPS WHICH FALL TO -10 TO -14C BY 00Z TUESDAY AND -12 TO -14C TO
START OFF CHRISTMAS MORNING. TRENDED BOTH HIGHS AND LOWS COLDER...
CLOSER TO GUIDANCE.
.LONG TERM...CHRISTMAS DAY THROUGH FRIDAY NIGHT
233 AM CST SAT DEC 22 2012
GOOD AGREEMENT CONTINUES FROM YESTERDAY ON THE GENERAL UPPER LEVEL
PATTERN THROUGH THE LONG TERM PERIOD. 22.00Z ECMWF/GFS/CANADIAN AND
UKMET CONTINUE TO SHOW A STRONG TROUGH AND STORM SYSTEM TRACKING
FROM THE SOUTHERN PLAINS ON TUESDAY INTO THE MID-ATLANTIC REGION BY
EARLY THURSDAY. THE FORECAST AREA REMAINS PLENTY FAR AWAY FROM THIS
SYSTEM...KEEPING US IN SUBSIDENCE AND MORE UNDER THE INFLUENCE OF
CANADIAN HIGH PRESSURE. IN FACT...THIS PERIOD FROM CHRISTMAS DAY
THROUGH WEDNESDAY NIGHT LOOKS SEASONABLY COOL...DUE TO 925MB TEMPS
REMAINING BETWEEN -10 AND -14C. WILL REALLY HAVE TO WATCH LOW
TEMPERATURES FOR CLEAR SKIES AND LIGHT WINDS...AS THE SNOW COVER NOW
IN PLACE FAVORS PLUMMETING. HAVE ADJUSTED BOTH HIGH AND LOW
TEMPERATURES DOWNWARD FROM THE PREVIOUS FORECAST ABOUT 5 DEGREES OR
SO...BUT FURTHER LOWERING MAY BE NEEDED...ESPECIALLY WITH LOWS. FOR
THURSDAY ONWARDS...ANOTHER DEEP TROUGH IS PROGGED TO FORM OVER THE
SOUTHWESTERN U.S...BUT THIS ONE GETS EJECTED NORTHEASTWARD TOWARDS
THE FORECAST AREA FOR FRIDAY AND INTO THE WEEKEND. AT THIS POINT
THERE DOES NOT APPEAR TO BE ANY BIG STORM PER SE WITH THIS
TROUGH...BUT SOME WARM ADVECTION SNOW IS SUGGESTED FOR FRIDAY INTO
FRIDAY NIGHT. THUS...30-40 PERCENT CHANCES OF PRECIPITATION ARE IN
THE FORECAST. THE APPROACH OF THE TROUGH SHOULD ALSO HELP TO BRING
WARMER AIR INTO THE FORECAST AREA...AND THIS IS NOTED BY 925MB TEMPS
PROGGED TO CLIMB TO -8 TO -10C AT 00Z FRIDAY AND -6 TO -9C AT 00Z
SATURDAY. FOLLOWED MODEL CONSENSUS FOR HIGHS AND LOWS FROM THURSDAY
ONWARDS...WHICH BRINGS TEMPERATURES BACK UP TO NORMAL FOR FRIDAY.
&&
.AVIATION...
1100 PM CST FRI DEC 21 2012
HIGH PRESSURE WILL CONTINUE TO BUILD ACROSS THE REGION...RESULTING
IN LIGHT WINDS AND MOSTLY CLEAR/PARTLY CLOUDY SKIES THROUGH
SATURDAY. SOME HIGH CLOUDS WILL SPILL ACROSS AN UPPER LEVEL RIDGE...
BUT WON/T HAVE AN AVIATION IMPACT. WINDS WILL BECOME MORE SOUTHERLY
ON SAT AS THE HIGH SLIDES OFF TO THE EAST...GRADUALLY BECOMING
NORTHERLY SATURDAY NIGHT.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
233 AM CST SAT DEC 22 2012
WI...NONE.
MN...NONE.
IA...NONE.
&&
$$
SHORT TERM...AJ
LONG TERM...AJ
AVIATION.....RIECK
AREA FORECAST DISCUSSION
NWS MARQUETTE MI
629 AM EST SAT DEC 22 2012
.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 451 AM EST SAT DEC 22 2012
FAIRLY QUIET WEATHER PATTERN IN STORE FOR TODAY AND TONIGHT AS A
WEAK HIGH PRESSURE RIDGE CONTINUES TO SLIDE ACROSS THE CWA TODAY
AND THEN A WEAK COLD FRONT MOVES THROUGH TONIGHT.
THE WEAK HIGH PRESSURE RIDGE IS ASSOCIATED WITH AN UPPER RIDGE THAT
IS CURRENTLY PUSHING INTO WESTERN UPPER MICHIGAN THIS MORNING AND IS
EXPECTED TO QUICKLY SLIDE SOUTHEAST AND DISSIPATE AS A SHORTWAVE
DIVES SOUTHEAST FROM LAKE WINNIPEG TONIGHT. AT THE PRESENT
TIME...PLENTY OF LAKE EFFECT CLOUDS OVER CENTRAL AND EASTERN LAKE
SUPERIOR...AS RAP ANALYZED H925 TEMPS ARE AROUND -10C AND THERE IS
PLENTY OF MOISTURE TRAPPED UNDER THE SUBSIDENCE INVERSION. RADAR
NOT REALLY PICKING UP ON MUCH SNOW...DUE TO THE INVERSION BEING
AT/AROUND 3.5KFT...BUT THERE HAS BEEN LIGHT SNOW/FLURRIES AT THE
OFFICE EARLY THIS MORNING. FARTHER WEST...THE DRIER AIR SEEN ON THE
00Z KINL SOUNDING HAS CONTINUED TO EAT AWAY AT THE LAKE EFFECT OVER
THE WESTERN LAKE AND ALL THAT REMAINS OVER THE THIRD OF WESTERN
UPPER MICHIGAN IS STRATUS TRAPPED BELOW THE INVERSION. RAP/NAM H925
MOISTURE FIELDS SEEM TO HAVE A GOOD HANDLE ON THE BACK EDGE OF THIS
MOISTURE AND WILL FOLLOW THE IDEA OF THE CLOUD EDGE GRADUALLY
PUSHING TO THE NORTHEAST THROUGH THE DAY TODAY AS THE H925 RIDGE
BACKS WINDS TO THE WEST-SOUTHWEST. SINCE UPSTREAM MID/HIGH CLOUDS
WILL LIKELY AFFECT THE AREAS WHERE THE LOW CLOUDS DEPART...WON/T GO
WITH A SUNNY FORECAST AND KEEP IN MOSTLY SUNNY TO PARTLY CLOUDY
AREA.
AS FOR THE LAKE EFFECT CLOUDS AND --SHSN...MODELS NOT REALLY SHOWING
THE H925 RIDGE HAVING TOO MUCH AFFECT ON IT UNTIL THIS
AFTERNOON...EXCEPT OVER NORTH CENTRAL UPPER MICHIGAN. THE DRIER
AIR SHOULD CAUSE THE SUBSIDENCE INVERSION TO LOWER FURTHER AND
TOWARDS 2-2.5KFT OVER EASTERN LAKE SUPERIOR AND UPPER MICHIGAN.
THUS...LIKED THE PREVIOUS SHIFTS HANDLING OF PUSHING THE ISOLATED
SNOW SHOWERS EAST THROUGH THE DAY AND MAINLY FOCUSED EAST OF GRAND
MARAIS THIS AFTERNOON.
TONIGHT...FRONT ARRIVES SHORTLY AFTER SUNSET OVER THE WEST AND H925
MOISTURE SURGES BACK OVER THE AREA AND INCREASES CLOUDS. OVER THE
EAST...THERE COULD BE A BRIEF PERIOD WHERE THE SNOW COMPLETELY
ENDS LATE THIS AFTERNOON OR EARLY EVENING BEFORE THE NEXT WAVE
ARRIVES. THIS FRONT WILL DROP SOUTHEAST ACROSS THE REST OF THE CWA
DURING THE EVENING AND THE FIRST PART OF THE OVERNIGHT HOURS. WITH
WINDS VEERING TO THE NORTHWEST BEHIND THE FRONT AND COLDER AIR
SURGING BACK IN...ENHANCED BY SURFACE LOW DEVELOPING OVER
THE EASTERN LAKE...EXPECT THE LAKE EFFECT CLOUDS AND POTENTIAL SNOW
SHOWERS TO REDEVELOP LATE IN THE EVENING AND CONTINUE OVERNIGHT FOR
THE NORTHWEST TO NORTH-NORTHWEST FAVORED LOCATIONS. BEST LOW LEVEL
LAPSE RATES ARE SEEN OVER EASTERN LAKE SUPERIOR /TO 8.5C/KM /.
MODELS SHOWING SOME DIRECTIONAL SHEAR OVER THE EAST /NORTHWEST H850
WINDS AND NORTH WINDS BELOW H900/...WHICH COMBINED WITH THE FAIRLY
DRY SUB CLOUD LAYER WILL KEEP THE LAKE EFFECT FROM BECOMING
TOO STRONG /LIMITS CLOUD DEPTH TO A FEW KFT EVEN THOUGH INVERSION
HEIGHT IS NEAR 6KFT/ AND COULD ALSO INFLUENCE DEVELOPMENT. THIS IS
ESPECIALLY PREVALENT OVER THE SOUTH CENTRAL LAKE AND NORTH CENTRAL
UPPER MICHIGAN WITH THE LATEST NAM...WHILE THE GFS HAS LESS SHEAR
AND OUR LOCAL REGIONAL WRF HAS BETTER MOISTURE AND UNIDIRECTIONAL
WINDS. WITH THE DIFFERENCES...WILL CONTINUE TO MENTION A
SLIGHT/CHANCE OF SNOW SHOWERS OVER THE NORTH CENTRAL AND EAST
FAVORED LOCATIONS...WITH THE HIGHEST POPS OVER LUCE COUNTY WHERE
INCREASED CONVERGENCE WILL OCCUR WITH THE DEVELOPING SURFACE LOW.
FARTHER WEST...LAKE EFFECT CONDITIONS ARE MORE FAVORABLE IN THE
EVENING WITH BETTER LOW LEVEL MOISTURE AND INVERSION HEIGHTS TO
4.5KFT. WILL CONTINUE CHANCE POPS FOR THAT PERIOD AND THEN START TO
DIMINISH OVERNIGHT AS DRIER AIR WORKS IN. OVERALL...EXPECT MOST
LOCATIONS TO SEE LESS THAN AN INCH OF SNOW.
.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 451 AM EST SAT DEC 22 2012
SUNDAY AND SUNDAY NIGHT...LES CONDITIONS WILL BE LESS FAVORABLE AS
LOW-LVL FLOW BECOMES INCREASINGLY ANTICYCLONIC AND DIVERGENT AS SFC
RIDGE BUILDS INTO THE NRN PLAINS AND UPPER GREAT LAKES AREA.
INCREASING SUBSIDENCE AND INVERSION HEIGHTS LOWERING AOB 3KFT WILL
MAKE IT HARD FOR ACCUMULATING SNOW ESPECIALLY BY SUNDAY NIGHT. KEPT
IN JUST MAINLY 20-30 PCT POPS...HIGHEST EAST WHERE FETCH WILL BE
GREATER ACROSS LAKE SUPERIOR IN NW FLOW.
MON-TUE...MODELS CONTINUE TO TREND SOUTH WITH SHORTWAVE MOVING IN FM
THE NRN PLAINS LATE MONDAY INTO MON NIGHT. SOME WEAK FORCING
ASSOCIATED WITH THIS SHORTWAVE MAY PRODUCE SOME LIGHT SNOW MON INTO
MON EVENING MAINLY OVER SRN PORTIONS OF THE CWA. WITH MODELS SHOWING
850 MB TEMPS DROPPING TO -14C/-15C IN THE WAKE OF THIS
SHORTWAVE...THE ADDED INSTABILITY COULD ALSO PROVIDE A BOOST TO NNW
FLOW LES.
TUE NIGHT-THU...MODELS CONTINUE TO KEEP NEXT SYSTEM EMERGING OUT OF
SRN PLAINS/LWR MS VALLEY WELL SOUTH AND EAST OF THE GREAT LAKES
REGION WITH NO SYNOPTIC SNOW EXPECTED FOR OUR AREA. A MID-LVL TROF
AXIS FROM LOW OVER NRN CANADA IS FCST TO MOVE THROUGH THE UPPER
GREAT LAKES WED NIGHT AND THU...BUT FORCING WITH THIS FEATURE LOOKS
MINIMAL. WITH 850 MB TEMPS OF -10C/-11C CONTRIBUTING TO MARGINAL
INSTABILITY AND A WEAK NRLY FLOW...SOME LIGHT SCT LES IS POSSIBLE
DOWNWIND OF LAKE SUPERIOR OVER NRN COUNTIES. WL MAINTAIN SLIGHT CHC
POPS FOR THESE AREAS.
FRI...MODELS SHOW POTENTIAL FOR ANOTHER SIGNIFICANT MID LEVEL TROUGH
TO MOVE THROUGH THE CNTRL CONUS FOR LATE WEEK. UNCERTAINTY STILL
EXISTS WITH MODELS CONCERNING TRACK OF THIS SYSTEM. THE 00Z ECMWF
CONTINUES TO TREND WITH A MORE AMPLIFIED PATTERN THAN THE GFS...AND
WOULD INDICATE A MORE NRN TRACK WITH LEAD SHORTWAVE EMERGING OUT OF
WRN CONUS TROF. THE ECMWF SCENARIO WOULD RESULT IN A BETTER CHC OF
PCPN FOR LATE FRIDAY INTO FRIDAY NIGHT FOR OUR CWA THAN THE GFS. AT
THIS POINT...GIVEN UNCERTAINTY WILL MAINTAIN JUST SLIGHT CHC POPS
FOR LIGHT SNOW TOWARD FRI EVENING. HOWEVER..WOULD NOT BE SURPRISED
GIVEN RECENT TRENDS...ESPECIALLY WITH THE ECMWF...THAT POPS MAY NEED
TO RAISED FOR LATE WEEK.
&&
.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 628 AM EST SAT DEC 22 2012
LAKE EFFECT CLOUDS WILL AFFECT KCMX/KSAW THROUGH THE MORNING HOURS
BEFORE WINDS BACK TO THE WEST AND BRING DRIER AIR IN THIS
AFTERNOON. HAVE SHOWN BOTH KSAW/KCMX SCATTERING OUT THIS
AFTERNOON...BUT KSAW SEEMS MOST LIKELY TO SCATTER OUT DUE TO
WINDS ORIGINATING OFF LAND. MEANWHILE...KIWD WILL LIKELY
JUST SEE MID CLOUDS STREAMING THROUGH SINCE THEY CLEARED YESTERDAY
EVENING.
AS A COLD FRONT SWEEPS ACROSS UPPER MICHIGAN THIS EVENING...WINDS
ARE EXPECTED TO TURN TO THE NORTHWEST AND LEAD TO MVFR CEILINGS AND
LAKE EFFECT SNOW AT KCMX/KIWD. NOT OVERLY CONFIDENT ON AMOUNT OF
VISIBILITY RESTRICTIONS AND OPTED TO MENTION HIGH END MVFR AT THIS
POINT. KSAW IS A LITTLE MORE IFFY ON LAKE EFFECT SNOW WITH THE
GENERALLY NORTHWEST WINDS...SO WILL GO WITH BORDERLINE MVFR/VFR
CEILINGS.
&&
.MARINE...(FOR THE 4 AM LAKE SUPERIOR FORECAST ISSUANCE)
ISSUED AT 451 AM EST SAT DEC 22 2012
WINDS HAVE FALLEN BELOW GALES THIS MORNING AS THE PRESSURE GRADIENT
CONTINUES TO RELAX WITH WEAK HIGH PRESSURE RIDGE MOVING THROUGH
TODAY. WINDS ARE EXPECTED TO INCREASE UP TO 25KTS OUT OF THE
NORTHWEST TONIGHT AS A COLD FRONT SWEEPS SOUTHEAST ACROSS LAKE
SUPERIOR. HIGH PRESSURE RIDGE FROM THE CANADIAN PRAIRIES WILL TRY
TO NOSE INTO THE UPPER GREAT LAKES FOR SUNDAY AND THE FIRST HALF OF
NEXT WEEK...KEEPING WINDS BELOW 25KTS.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
UPPER MICHIGAN...
NONE.
LAKE SUPERIOR...
NONE.
LAKE MICHIGAN...
NONE.
&&
$$
SHORT TERM...SRF
LONG TERM...VOSS
AVIATION...SRF
MARINE...SRF
AREA FORECAST DISCUSSION
NWS LA CROSSE WI
555 AM CST SAT DEC 22 2012
.SHORT TERM...TODAY THROUGH MONDAY NIGHT
233 AM CST SAT DEC 22 2012
MAIN FORECAST CONCERNS ARE ON LOW CLOUD POTENTIAL TONIGHT INTO
SUNDAY AND POTENTIAL FOR SOME LIGHT SNOW SUNDAY NIGHT INTO MONDAY.
CURRENTLY AS OF 08Z...WATER VAPOR LOOP AND RAP 500MB HEIGHT ANALYSIS
SHOWED DEEP TROUGHING APPROACHING THE WESTERN U.S. COAST...RIDGING
ACROSS THE PLAINS AND DEEP TROUGHING ALONG THE U.S. EAST COAST. ON
TOP OF THE RIDGE...A SHORTWAVE WAS PRESENT ACROSS CENTRAL PORTIONS
OF SASKATCHEWAN AND MANITOBA. THE FORECAST AREA LIES CLOSER TO THE
INFLECTION POINT BETWEEN THE RIDGE AND EAST COAST TROUGH...YIELDING
HIGH PRESSURE AT THE SURFACE. OTHER THAN SOME SCATTERED HIGH CLOUDS
ASSOCIATED WITH A COMBINATION OF PACIFIC MOISTURE TOPPING THE RIDGE
AND A 100 KT JET NEAR THE TROPOPAUSE...SKIES WERE MOSTLY CLEAR
ACROSS THE FORECAST AREA. DRY AIR AND SUBSIDENCE SEEN ON THE 00Z
ABR...MPX AND DVN SOUNDINGS ARE HELPING TO PRODUCE THE MOSTLY CLEAR
SKIES. WITH LIGHT WINDS UNDER THE SURFACE RIDGE AND THE FRESH SNOW
COVER...TEMPERATURES HAVE MOSTLY FALLEN INTO THE SINGLE DIGITS ABOVE
ZERO. BLACK RIVER FALLS AND SPARTA HAVE EVEN DROPPED BELOW ZERO. TO
THE NORTHWEST...A COLD FRONT WAS LOCATED OVER MANITOBA AND THE
DAKOTAS ASSOCIATED WITH THE SOUTH CENTRAL CANADA SHORTWAVE. LOW
CLOUDS WERE PRESENT ACROSS SOUTH CENTRAL CANADA AS WELL BEHIND THE
FRONT.
TODAY AND TONIGHT...THE SHORTWAVE SEEN OVER SOUTH CENTRAL CANADA IS
PROGGED TO SLIDE SOUTHEAST ACROSS EASTERN LAKE SUPERIOR THIS
EVENING...DRIVING THE COLD FRONT ACROSS THE DAKOTAS THROUGH THE
FORECAST AREA. NO PRECIPITATION IS EXPECTED WITH OR BEHIND THE FRONT
GIVEN THE DRY AIRMASS PRESENT...AS WELL AS ALL THE FORCING LOCATED
WELL NORTHEAST OF THE AREA. MAIN CONCERNS WITH THE FRONT IS THE
WARMING AHEAD OF IT AND IF ANY LOW CLOUDS COME IN BEHIND IT.
REGARDING THE WARMING...GFS/NAM/ECMWF 925MB TEMPERATURE PROGS SHOW
THEM CLIMBING FROM -3 TO -6C CURRENTLY TO -2 TO -4C. WITH SOME SUN
THROUGH HIGH CLOUDS AND A SOUTHWEST BREEZE...TEMPERATURES SHOULD
EASILY CLIMB INTO THE 20S EVERYWHERE. SOME LOCATIONS IN WISCONSIN...
PARTICULARLY IN VALLEY AREAS...COULD EXCEED 30 THANKS TO LOWER
ALBEDO PRESENT. DECENT COLD ADVECTION LOOKS TO OCCUR TONIGHT BEHIND
THE FRONT AS 925MB TEMPS FALL TO -6 TO -10C BY 12Z SUNDAY ON 15-20
KT NORTHERLY BREEZE. CERTAINLY LOOKS GOOD FOR LAKE EFFECT OFF
SUPERIOR WHICH THE BREEZE WOULD THEN SEND THE CLOUDS SOUTHWARD AT
LEAST INTO THE NORTHERN HALF OF WISCONSIN AFTER MIDNIGHT. IN
ADDITION...SOME OF THE LOW CLOUDS IN GENERAL BEHIND THE FRONT COULD
END UP BEING SENT SOUTH. AS A RESULT...HAVE RAISED CLOUD COVER...
ESPECIALLY ACROSS TAYLOR AND CLARK COUNTIES GIVEN THE BETTER CHANCE
OF BEING IMPACTED BY LAKE EFFECT CLOUDS. GIVEN CLOUDS AND THE WINDS
BEHIND THE FRONT...FOLLOWED A BLEND OF GUIDANCE FOR LOWS.
SUNDAY AND SUNDAY NIGHT...FOCUS SHIFTS TO THE TROUGHING APPROACHING
THE WEST COAST. MODELS TAKE A FAIRLY SIGNIFICANT PORTION OF THE
TROUGH CROSSING THE NORTHERN ROCKIES DURING THE NEXT 24 TO 36 HOURS.
THE QUESTION IS WHAT HAPPENS WITH THE TROUGH FROM THERE. THE 22.00Z
NAM/UKMET ARE A WEAKER SCENARIO WITH THE TROUGH...STRETCHING FROM
NORTHEAST SOUTH DAKOTA INTO CENTRAL IOWA BY 12Z MONDAY.
MEANWHILE...THE 22.00Z GFS/CANADIAN DEPICT A MORE POTENT TROUGH THAT
ENDS UP CROSSING NEBRASKA AND BECOMING SITUATED DOWN IN SOUTHERN
IOWA INTO THE ST LOUIS AREA BY 12Z MONDAY. ALL SCENARIOS YIELD AN
INVERTED TROUGH AT THE SURFACE...JUST THE MORE POTENT GFS/CANADIAN
GROUP WOULD HAVE A BETTER SHOT OF YIELDING PRECIPITATION
DEVELOPMENT. GIVEN THE STRENGTH OF THE TROUGH RIGHT NOW OFF THE WEST
COAST...NOTED TOO BY NUMEROUS LIGHTNING STRIKES...WILL FAVOR THE
MORE POTENT GROUP. THIS MEANS 20 PERCENT CHANCES ARE NEEDED AFTER
MIDNIGHT SUNDAY NIGHT WEST OF THE MISSISSIPPI RIVER TO ACCOUNT FOR
THE DPVA AHEAD OF THE POTENT TROUGH...AS WELL AS ISENTROPIC LIFT.
DID NOT GO HIGHER THAN 20 BECAUSE OF INITIAL DRY AIR TO OVERCOME
SINCE THE SNOW THAT DOES FALL WILL COME OUT OF A MID CLOUD DECK.
OTHERWISE...THE ONLY OTHER CONCERN IS CLOUD COVER. THE LOW CLOUDS
OVER NORTHERN WI AT 12Z SUNDAY COULD END UP EXPANDING SOUTHWESTWARD
THROUGH THE DAY...WHILE MID AND HIGH CLOUDS INCREASE DOWNSTREAM OF
THE POTENT TROUGH. THUS AN INCREASING CLOUD TREND SEEMS APPROPRIATE.
THESE CLOUDS PLUS COLDER 925MB TEMPS IN THE -8 TO -10C RANGE WILL
DEFINITELY YIELD A COLDER DAY. ON THE POSITIVE SIDE...THE CLOUDS
SHOULD HELP HOLD TEMPERATURES UP SUNDAY NIGHT.
MONDAY INTO MONDAY NIGHT...FOLLOWING THE MORE POTENT TROUGH LOOK AS
MENTIONED IN THE SUNDAY/SUNDAY NIGHT DISCUSSION...THE GFS AND
CANADIAN SEND THE TROUGH SOUTHEAST INTO OHIO BY 00Z TUESDAY. CHANCES
OF SNOW STILL LOOK APPROPRIATE FOR MONDAY WITH ISENTROPIC LIFT AND
DPVA PERSISTING...THOUGH THIS SHOULD BE DIMINISHING IN THE AFTERNOON
AS THE TROUGH SHIFTS EAST AND CANADIAN HIGH PRESSURE BUILDS SOUTH
INTO THE DAKOTAS IN ITS WAKE. AS SUCH...MONDAY NIGHT IS LIKELY TO
END UP DRY. REGARDING THE ACTUAL CHANCES...LINGERING LOWER LEVEL DRY
AIR IS A BIG CONCERN...AS WELL AS THE TRACK OF THE TROUGH DROPPING
MORE TO OUR SOUTH. AS A RESULT...KEPT CHANCES IN A 20-30 RANGE.
LOOKS GOOD FOR MOST OF THE AREA TO PICK UP A LITTLE SNOW...BE IT
ACTUAL ACCUMULATING SNOW OR FLURRIES...SO USED OCCASIONAL VERY LIGHT
SNOW VERBIAGE. GIVEN CANADIAN HIGH PRESSURE BUILDING SOUTH...ONE CAN
EXPECT COLDER LOW LEVEL AIR. THIS IS VERY WELL REPRESENTED BY 925MB
TEMPS WHICH FALL TO -10 TO -14C BY 00Z TUESDAY AND -12 TO -14C TO
START OFF CHRISTMAS MORNING. TRENDED BOTH HIGHS AND LOWS COLDER...
CLOSER TO GUIDANCE.
.LONG TERM...CHRISTMAS DAY THROUGH FRIDAY NIGHT
233 AM CST SAT DEC 22 2012
GOOD AGREEMENT CONTINUES FROM YESTERDAY ON THE GENERAL UPPER LEVEL
PATTERN THROUGH THE LONG TERM PERIOD. 22.00Z ECMWF/GFS/CANADIAN AND
UKMET CONTINUE TO SHOW A STRONG TROUGH AND STORM SYSTEM TRACKING
FROM THE SOUTHERN PLAINS ON TUESDAY INTO THE MID-ATLANTIC REGION BY
EARLY THURSDAY. THE FORECAST AREA REMAINS PLENTY FAR AWAY FROM THIS
SYSTEM...KEEPING US IN SUBSIDENCE AND MORE UNDER THE INFLUENCE OF
CANADIAN HIGH PRESSURE. IN FACT...THIS PERIOD FROM CHRISTMAS DAY
THROUGH WEDNESDAY NIGHT LOOKS SEASONABLY COOL...DUE TO 925MB TEMPS
REMAINING BETWEEN -10 AND -14C. WILL REALLY HAVE TO WATCH LOW
TEMPERATURES FOR CLEAR SKIES AND LIGHT WINDS...AS THE SNOW COVER NOW
IN PLACE FAVORS PLUMMETING. HAVE ADJUSTED BOTH HIGH AND LOW
TEMPERATURES DOWNWARD FROM THE PREVIOUS FORECAST ABOUT 5 DEGREES OR
SO...BUT FURTHER LOWERING MAY BE NEEDED...ESPECIALLY WITH LOWS. FOR
THURSDAY ONWARDS...ANOTHER DEEP TROUGH IS PROGGED TO FORM OVER THE
SOUTHWESTERN U.S...BUT THIS ONE GETS EJECTED NORTHEASTWARD TOWARDS
THE FORECAST AREA FOR FRIDAY AND INTO THE WEEKEND. AT THIS POINT
THERE DOES NOT APPEAR TO BE ANY BIG STORM PER SE WITH THIS
TROUGH...BUT SOME WARM ADVECTION SNOW IS SUGGESTED FOR FRIDAY INTO
FRIDAY NIGHT. THUS...30-40 PERCENT CHANCES OF PRECIPITATION ARE IN
THE FORECAST. THE APPROACH OF THE TROUGH SHOULD ALSO HELP TO BRING
WARMER AIR INTO THE FORECAST AREA...AND THIS IS NOTED BY 925MB TEMPS
PROGGED TO CLIMB TO -8 TO -10C AT 00Z FRIDAY AND -6 TO -9C AT 00Z
SATURDAY. FOLLOWED MODEL CONSENSUS FOR HIGHS AND LOWS FROM THURSDAY
ONWARDS...WHICH BRINGS TEMPERATURES BACK UP TO NORMAL FOR FRIDAY.
&&
.AVIATION...TODAY AND TONIGHT
555 AM CST SAT DEC 22 2012
FIRST CONCERN WILL BE STRATUS DECK OVER THE MISSISSIPPI RIVER
CHANNEL AND WHETHER IT WILL AFFECT THE KLSE TAF SITE THIS MORNING.
STRATUS DECK FAIRLY EXPANSIVE ON OUR WEBCAM ATOP THE LA CROSSE
RIDGE AND FEEL IT WILL LIKELY IMPACT KLSE THROUGH 15Z THIS
MORNING WITH TEMPO 3SM BR BKN003 CONDITIONS. OTHERWISE...A WEAK
TROUGH OF LOW PRESSURE WILL DRIFT SOUTHEAST ACROSS THE KRST/KLSE
TAF SITES BY THIS EVENING SHIFTING THE WINDS FROM LIGHT SOUTHERLY
TO A LIGHT NORTHERLY DIRECTION. MODELS ARE INDICATING INCREASING
MOISTURE AHEAD OF THE TROUGH WHICH MAY MANIFEST ITSELF IN
SCATTERED STRATOCUMULUS WITH BASES AROUND 1.5KFT AGL AFTER 19Z.
ONCE THE TROUGH IS THROUGH THIS EVENING WILL HAVE TO WATCH A
NORTHERLY FETCH OFF OF LAKE SUPERIOR WHICH MAY ADVECT SOME MORE
STRATOCUMULUS TOWARD THE TAF SITES DURING THE OVERNIGHT HOURS. HAVE
KEPT SCT015 MENTION IN FOR NOW THROUGH THE NIGHT TO ACCOUNT FOR
THIS. WILL PASS ALONG TO THE DAY SHIFT TO ASSESS FURTHER.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
233 AM CST SAT DEC 22 2012
WI...NONE.
MN...NONE.
IA...NONE.
&&
$$
SHORT TERM...AJ
LONG TERM...AJ
AVIATION...DAS
AREA FORECAST DISCUSSION
NWS GOODLAND KS
150 PM MST SAT DEC 22 2012
.SHORT TERM...(TONIGHT THROUGH SUNDAY)
ISSUED AT 150 PM MST SAT DEC 22 2012
EARLY AFTERNOON WV IMAGERY AND RUC H5 ANALYSIS SHOWS BROAD RIDGE
ACROSS THE CENTRAL US EXTENDING NORTH INTO SOUTHERN CANADA...WITH
TROUGHS UP STREAM AND DOWN STREAM ALONG THE COASTS. AT THE SURFACE A
COLD FRONT CURRENTLY EXTENDS ACROSS CENTRAL NEBRASKA...WITH A
PREFRONTAL SURFACE TROUGH ACROSS CENTRAL KANSAS.
TONIGHT THROUGH SUNDAY...PATTERN REMAINS QUIET WITH VERY DRY AIR
MASS IN PLACE...HIGHLIGHTED BY DEWPOINT DEPRESSIONS GREATER THAN 20C
THROUGH ABOUT 400MB THROUGH SUNDAY AFTERNOON. WHILE THERE WILL BE
LARGE SCALE ASCENT ASSOCIATED WITH SHORTWAVE PASSAGE ACROSS NORTHERN
PLAINS AND ASSOCIATED COLD FRONT PASSAGE SUNDAY...I DO NOT THINK WE
WILL SEE MUCH OTHER THAN PASSING HIGH CLOUDS CONSIDERING THE DEEP
DRY AIR MASS. H85 TEMPS COOLING BY ABOUT 4-5C BY SUN MORNING WITH
MOST LOCATIONS 7-10F COOLER AND NEGATIVE VALUES POSSIBLE ACROSS THE
NORTHEAST. I DROPPED HIGH TEMPS A LITTLE SUNDAY ACROSS THE CWA
COMPARED TO THIS AFTERNOON TO ACCOUNT FOR THICKER CLOUD COVER AND
COOLER AIRMASS BEHIND FRONT. SNOWPACK CONTINUES TO MELT ACROSS THE
SW CWA AND WITH WINDS SHIFTING BACK TO THE WEST/SOUTHWEST SNOW PACK
SHOULD START TO HAVE LESS OF AN IMPACT EXCEPT IN THE FAR EAST.
.LONG TERM...(SUNDAY NIGHT THROUGH SATURDAY)
ISSUED AT 150 PM MST SAT DEC 22 2012
FORECAST CONCERNS WILL BE STORM AT THE BEGINNING OF NEXT WEEK...
NEXT STORM TOWARD THE END OF NEXT WEEK...AND HOW COLD TO MAKE IT
NEXT WEEK. SATELLITE SHOWING AN AMPLIFIED/AMPLIFYING FLOW FROM THE
PACIFIC INTO THE ATLANTIC. IN THIS IS A COMPLEX/COLD UPPER TROUGH
ALONG THE WEST COAST OF NORTH AMERICA WHICH HAS CAUSED AN UPPER
RIDGE OVER THE CENTRAL PORTION OF COUNTRY. VERY COLD LOW LEVEL AIR
MASS/COLD FRONT NOT TOO FAR TO OUR NORTH.
MODELS AT MID AND UPPER LEVELS APPEAR TO HAVE INITIALIZED FINE.
HOWEVER BASED ON SATELLITE...WOULD FAVOR THE SLIGHTLY MORE WEST
INITIALIZATION OF THE UPPER TROUGH NEAR THE WEST COAST. THE NAM AND
ECMWF WERE DOING THE BEST ON THE LOW LEVEL SURFACE WIND/PRESSURE
FIELD. OVERALL THE CANADIAN WAS DOING A LITTLE BETTER ON THE LOW
LEVEL THERMAL FIELD.
SUNDAY NIGHT/MONDAY...MAJOR TRANSITION BEGINS ON MONDAY. MID AND
UPPER LEVEL CLOUD COVER WILL INCREASE AT THE SAME TIME A FRONT
BACKDOORS INTO THE AREA. EASTERLY UPSLOPE INCREASES DURING THE DAY.
AS A RESULT HIGH TEMPERATURES WILL END UP BEING WELL BELOW NORMAL
WITH COLDEST TEMPERATURES IN THE NORTHEAST AND THE WARMEST IN THE
SOUTHWEST. GUIDANCE WAS CLUSTERING AROUND COOLER MAXES THAN WHAT
WAS IN THERE FOR PREVIOUS FORECAST. SO REDUCED THE MAXES.
MAIN LIFT AND DEEPER MOISTURE WILL WAIT UNTIL THE NIGHT TO GET HERE.
MORE THAN ONE MODEL SHOWS THE BOUNDARY LAYER SATURATING UP WITH A
DRY MID LAYER. IT WILL BE UNUSUAL BUT IT LOOKS LIKE FOG WILL
DEVELOP IN THE AFTERNOON AND POSSIBLE SOME FREEZING DRIZZLE. SO
INSERTED THAT INTO THE GRIDS.
MONDAY NIGHT/TUESDAY...IN GENERAL MODELS AGREE ON THE EVOLUTION OF
INCOMING SYSTEM WHICH IS TO DEVELOP THE UPPER TROUGH INTO A CLOSED
OFF CIRCULATION...MAINLY AT 700 MB...AS IT DIGS/MOVES TOWARD THE
SOUTHEAST. PREVIOUS EXPERIENCE HAS SHOWN ME THAT THIS USUALLY IS NOT
THE BEST SCENARIO FOR GETTING A SIGNIFICANT AMOUNT OF SNOW. BASED ON
THE PATTERN/SATELLITE IS INDICATING/SHOWING...BELIEVE THIS SYSTEM
WILL BE COMING IN SLOWER AND FURTHER SOUTH AND WEST. THIS FITS THE
BEST WITH THE ECMWF SOLUTION AND TO A LESSER DEGREE THE CANADIAN...
UKMET...AND GFS SOLUTION. THEY DO THE SAME THING BUT FASTER.
AM CONCERNED THAT WITH THE WAY THE PATTERN IS...THAT FUTURE MODEL
RUNS WILL TAKE THE SYSTEM FURTHER SOUTHWEST AND FURTHER DIMINISH THE
AMOUNT OF SNOW. FOR THE NIGHTTIME PERIOD AS IT STANDS NOW...THE
SOUTHWEST HALF OF THE AREA LOOKS TO HAVE THE BEST CHANCE FOR SNOW.
UNTIL THE SNOW STARTS...WILL KEEP THE FOG AND DRIZZLE GOING IN THE
EVENING PER THE REASONING GIVEN ABOVE.
DURING THE DAY TUESDAY...THE BEST CHANCE FOR SNOW WILL TRANSITION
INTO THE SOUTHERN THIRD IN THE MORNING BEFORE DECREASING AND ENDING
IN THE AFTERNOON. AMOUNTS STILL LOOK IN THE 1 TO 3 INCH RANGE WITH
THE SOUTHWEST HALF HAVING THE HIGHEST AMOUNTS. COMBINATION OF
CLOUDS...PRECIPITATION...AND VERY GOOD COLD AIR ADVECTION WILL MAKE
FOR AN EXTREMELY COLD DAY WITH WELL BELOW NORMAL TEMPERATURES.
TENDED TO GO WITH THE CLUSTERING OF GUIDANCE WHICH SUPPORTED
COOLING MAXES FROM PREVIOUS FORECAST. HOWEVER...SOME GUIDANCE IS
SHOWING THAT MAXES COULD BE EVEN COLDER.
TUESDAY NIGHT THROUGH SATURDAY...QUIET WEATHER WILL OCCUR THROUGH
THURSDAY. THE NEXT SYSTEM WILL MOVE THROUGH THE REGION THURSDAY
NIGHT AND FRIDAY. MODELS ARE IN GOOD AGREEMENT WITH THE SPEED OF THE
SYSTEM MOVING THROUGH BUT DIFFER ON THE AMPLITUDE OF THE SYSTEM. THE
ECMWF IS THE OUTLIER WITH A CUTOFF SOLUTION WITH THE REMAINING
DETERMINISTIC SOLUTIONS/ENSEMBLES SUPPORTING THE OPEN WAVE
SOLUTION. LIKE WHAT THE CRH_INIT GAVE ME DUE TO THE MODEL
DIFFERENCES. RIGHT NOW IT IS SLIGHT CHANCE TO CHANCE WHICH IS
REASONABLE BUT THERE IS POTENTIAL TO GO A LITTLE HIGHER. ONE THING
FOR SURE IS THAT HIGH TEMPERATURES WILL BE COLD THROUGH THE ENTIRE
WEAK AND THE INIT TEMPERATURES LOOKED REASONABLE AND MADE LITTLE TO
NO CHANGES.
&&
.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1046 AM MST SAT DEC 22 2012
VFR CONDITIONS ARE EXPECTED AT BOTH KGLD AND KMCK. WEST WINDS WILL
SHIFT TO THE NORTH DURING THE AFTERNOON AS A WEAK PROGRESSIVE COLD
FRONT DROPS SOUTH ACROSS THE AREA BEFORE SHIFTING BACK TO THE WEST
THIS EVENING. WINDS SHOULD GENERALLY REMAIN LESS THAN
12KT...THOUGH SOME HIGHER WINDS COULD BE RULED OUT THIS AFTERNOON
DEPENDING ON AFTERNOON MIXING. CONFIDENCE WAS TOO LOW TO
INCREASE WINDS TOO MUCH...SO WILL MONITOR THIS.
&&
.GLD WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
CO...NONE.
NE...NONE.
&&
$$
SHORT TERM...DR
LONG TERM...BULLER
AVIATION...DR
AREA FORECAST DISCUSSION
NWS MARQUETTE MI
344 PM EST SAT DEC 22 2012
.SHORT TERM...(THIS EVENING THROUGH SUNDAY)
ISSUED AT 341 PM EST SAT DEC 22 2012
WV IMAGERY AND RUC ANALYSIS INDICATED NW MID/UPPER LEVEL FLOW
BETWEEN A TROUGH OVER JAMES BAY INTO QUEBEC AND A RIDGE OVER THE
WESTERN PLAINS. A SHORTWAVE TROUGH WAS LOCATED OVER NW ONTARIO
BETWEEN LAKE WINNIPEG AND THUNDER BAY ONTARIO. THE SHRTWV AND AN
ASSOCIATED COLD FRONT INTO NRN MN SUPPORTED SOME LIGHT SNOW OR
FLURRIES INTO FAR NRN WITH VISIBILITIES GENERALLY AT OR ABOVE 5SM.
VIS SATELLITE LOOP SHOWED MAINLY JUST MID CLOUDS SPREADING ACROSS
UPPER MI ASSOCIATED WITH 285K-295K ISENTROPIC LIFT AHEAD OF THE
TROUGH.
AS THE SHRTWV DIVES TO THE ESE AND PULLS THE COLD FRONT THROUGH
UPPER MI...WINDS WILL VEER FROM W TO NNW. 925-850 MB MOISTURE WILL
ALSO QUICKLY INCREASE ACROSS THE AREA. DESPITE THE RELATIVELY
SHALLOW COLD AIR MASS WITH INVERSION HEIGHTS OF ONLY 4K-5K
FT...EXPECT LES TO INCREASE THIS EVENING AND PEAK LATE TONIGHT AND
EARLY SUNDAY. LAKE INDUCED CAPES BUILD INTO THE 200-300 J/KG RANGE
BUT THE CLOUD LAYER REMAINS MAINLY BELOW THE DGZ. SO...ONLY INCLUDED
SCT/CHANCE POPS WITH ANY ACCUMULATIONS AT OR BELOW A HALF INCH.
LES SHOULD DIMINISH FROM WEST TO EAST BY MIDDAY INTO SUNDAY
AFTERNOON AS HIGH PRES BUILDS INTO THE REGION WITH LOWERING
INVERSION HEIGHTS TO AROUND 3K FT AND INCREASINGLY
ANTICYCLONIC/DIVERGENT LOW LEVEL FLOW.
.LONG TERM...(SUNDAY NIGHT THROUGH SATURDAY)
ISSUED AT 341 PM EST SAT DEC 22 2012
SPLIT FLOW IN PLACE TO START THE LONG TERM. SUBTROPICAL H2 JET IS
ALONG SOUTHERN TIER OF CONUS WHILE NORTHERN STREAM H4-H3 JET RIDES
ACROSS CANADA WITH BROAD UPPER LOW FM HUDSON BAY ACROSS QUEBEC. CORE
OF LOW-LEVEL COLD AIR BENEATH THAT LOW...BUT DEVELOPING NW WINDS IN
WAKE OF FRONT THAT PASSES ACROSS TONIGHT...RESULTS IN ENOUGH OVER
WATER INSTABILITY WITH LAKE-900MB DELTA T/S AOA 15C FOR LK EFFECT SNOW
SHOWERS. AS MENTIONED IN THE SHORT TERM DISCUSSION...INVERSIONS LESS
THAN 5KFT RESULTING FM LARGE SCALE RISING HEIGHTS/SUBSIDENCE AND
ANTICYCLONIC FLOW WILL BE LIMITING FACTORS FOR ANYTHING OTHER THAN
LIGHT SNOW ACCUMS...MAINLY UNDER 1 INCH.
LATER SUNDAY NIGHT AND INTO MONDAY COUPLE OF SHORTWAVES EMERGE
ACROSS MIDDLE CONUS...ONE DIGGING FROM WYOMING TO NORTHERN ILLINOIS
AND THE OTHER SLIDING FROM OK/TX PANHANDLE TO TENNESSEE. OVERALL
MODELS HAVE TRENDED STRONGER WITH NORTHERN WAVE. GFS/NAM/UKMET
STRONGER WITH NORTHERN ONE INITIALLY BUT LAST COUPLE RUNS OF ECMWF
ALSO SHOW SOME IMPACT FOR UPR MICHIGAN ON CHRISTMAS EVE DAY. HAVE
LOW CHANCE POPS EVERYWHERE DUE TO SYSTEM SNOW AND/OR LK EFFECT.
IF TRENDS CONTINUE...POPS MAY NEED INCREASING FOR HIGH POP/LOW QPF
SETUP. MOISTURE IS LIMITED WITH NORTHERN END OF SYSTEM SO ANY SNOW
AMOUNTS WILL BE LESS THAN AN INCH. LK EFFECT AREAS MAY SEE A BIT
MORE SNOW DUE TO WEAK LAKE ENHANCEMENT...THOUGH GFS/NAM SOUNDINGS
REALLY DO NOT SHOW MUCH LAKE RESPONSE FROM THE SYSTEM IN TERMS OF A
HIGHER INVERSION.
LK EFFECT MAY PICK UP SLIGHTLY IN WAKE OF SYSTEM MOVING THROUGH
ON MONDAY AS ECMWF/GFS/NAM INDICATE H85 TEMPS FALLING TO AROUND -15C
MONDAY NIGHT AND TUESDAY. INVERSIONS REMAIN LOWER THAN 5KFT THOUGH
WHICH WILL LIMIT SNOW ACCUMS TO JUST A FEW INCHES. VERY LITTLE
CHANGES IN LARGE SCALE/MESOSCALE PATTERN THROUGH THURSDAY SO EXPECT
PERSISTENT/STEADY STATE LIGHT LK EFFECT ALONG LK SUPERIOR. LATEST
GFS/ECMWF RUNS IN GOOD AGREEMENT WITH TRACK OF SFC LOW LIFTING FM
TENNESSEE RIVER VALLEY ACROSS THE NORTHEAST CONUS WEDNESDAY INTO
THURSDAY. SYNOPTIC SNOW ON NORTHWEST PERIFERY OF SYSTEM STAYS MAINLY
TO THE EAST OF UPR MICHIGAN. 12Z GFS FARTHER NORTHWEST...GRAZING
EASTERN CWA WITH LGT QPF ON WEDNESDAY. GFS IS AN OUTLIER COMPARED TO
ECMWF/GEM-NHEM AND EVEN PREVIOUS RUNS OF GFS. WILL JUST STICK WITH
SCATTERED POPS FOR NORTH-NORTHWEST FLOW LK EFFECT. NUDGED POPS UP
SOME ALONG LK SUPERIOR OVER THE CONSENSUS WITH EXPECTED LK EFFECT.
NEXT CHANCE OF WIDESPREAD SYNOPTIC SNOW COULD BE FRIDAY NIGHT INTO
NEXT SATURDAY IF ECMWF IS CORRECT. ECMWF REMAINS CONSISTENT SHOWING
ACTIVE SOUTHERN STREAM SENDING ANOTHER UPR TROUGH/SFC LOW OUT OF THE
PLAINS ACROSS THE WESTERN GREAT LAKES. NORTHERN STREAM WAVE DIGGING
INTO THE NORTH SIDE SYSTEM AS WELL. GEM-NHEM SIMILAR THROUGH 12Z
FRIDAY BUT GFS IS STUBBORNLY NOT DEVELOPING THE SYSTEM AS IT IS NOT
AS WRAPPED UP WITH SOUTHERN STREAM WAVE COMPARED TO ECMWF AND IT
ALSO HAS MORE SEPARATION BTWN THE NORTHERN AND SOUTHERN BRANCH
STREAMS THROUGH SATURDAY. GIVEN PAST TRACK RECORD IN DAYS 4-7...A
FEW CONSECUTIVE RUNS OF ECMWF SHOWING SOMETHING IS GOOD ENOUGH TO
INCLUDE IT IN EXTENDED. CONSENSUS POPS WERE NOT TOO BAD BUT DID
INCREASE THEM SLIGHTLY ON SATURDAY SO CHANCE FOR SNOW IS IN THERE
FOR ALL CWA. COLDER AIR BEHIND THE SYSTEM MAY RESULT IN PROLONGED LK
EFFECT EVENT JUST BEYOND DAY 7. CERTAINLY NO THAWS IN STORE FOR LAST
WEEK OF 2012 WITH DAYTIME HIGHS IN THE TEENS/20S AND NIGHTIME LOWS
IN SINGLE DIGITS TO TEENS. RECENTLY DEPOSITED SNOW WILL STAY AROUND
UNTIL FURTHER NOTICE.
&&
.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1255 PM EST SAT DEC 22 2012
DRY WESTERLY FLOW WITH A SFC RIDGE MOVING INTO THE AREA HAS
SCOURED OUT MVFR CIGS LEAVING MAINLY MID CLOUDS OVER THE REGION.
AS A COLD FRONT SWEEPS ACROSS UPPER MICHIGAN THIS EVENING...WINDS
ARE EXPECTED TO VEER TO THE NORTHWEST AND LEAD TO MVFR CEILINGS AND
LAKE EFFECT SNOW AT KCMX/KIWD. WITH ONLY LIMITED CONFIDENCE ON
AMOUNT OF VISIBILITY RESTRICTION...FCST ONLY MENTIONS HIGH END MVFR
AT THIS POINT. EVEN THOUGH KSAW IS LESS LIKELY TO SEE LAKE EFFECT
SNOW WITH THE GENERALLY NORTHWEST WINDS...CIGS INTO THE MVFR RANGE
ARE STILL EXPECTED.
&&
.MARINE...(FOR THE 4 PM LAKE SUPERIOR FORECAST ISSUANCE)
ISSUED AT 341 PM EST SAT DEC 22 2012
WINDS ARE EXPECTED TO INCREASE UP TO 30 KNOTS OUT OF THE NORTHWEST
TONIGHT INTO SUNDAY AS A COLD FRONT SWEEPS SOUTHEAST ACROSS LAKE
SUPERIOR. A HIGH PRESSURE RIDGE FROM THE CANADIAN PRAIRIES WILL THEN
BUILD INTO THE UPPER GREAT LAKES FROM SUNDAY NIGHT INTO THE
THE FIRST HALF OF NEXT WEEK...KEEPING WINDS AT OR BELOW 25 KNOTS.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
UPPER MICHIGAN...
NONE.
LAKE SUPERIOR...
NONE.
LAKE MICHIGAN...
NONE.
&&
$$
SHORT TERM...JLB
LONG TERM...JLA
AVIATION...JLB
MARINE...JLB
AREA FORECAST DISCUSSION
NWS MARQUETTE MI
1256 PM EST SAT DEC 22 2012
.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 451 AM EST SAT DEC 22 2012
FAIRLY QUIET WEATHER PATTERN IN STORE FOR TODAY AND TONIGHT AS A
WEAK HIGH PRESSURE RIDGE CONTINUES TO SLIDE ACROSS THE CWA TODAY
AND THEN A WEAK COLD FRONT MOVES THROUGH TONIGHT.
THE WEAK HIGH PRESSURE RIDGE IS ASSOCIATED WITH AN UPPER RIDGE THAT
IS CURRENTLY PUSHING INTO WESTERN UPPER MICHIGAN THIS MORNING AND IS
EXPECTED TO QUICKLY SLIDE SOUTHEAST AND DISSIPATE AS A SHORTWAVE
DIVES SOUTHEAST FROM LAKE WINNIPEG TONIGHT. AT THE PRESENT
TIME...PLENTY OF LAKE EFFECT CLOUDS OVER CENTRAL AND EASTERN LAKE
SUPERIOR...AS RAP ANALYZED H925 TEMPS ARE AROUND -10C AND THERE IS
PLENTY OF MOISTURE TRAPPED UNDER THE SUBSIDENCE INVERSION. RADAR
NOT REALLY PICKING UP ON MUCH SNOW...DUE TO THE INVERSION BEING
AT/AROUND 3.5KFT...BUT THERE HAS BEEN LIGHT SNOW/FLURRIES AT THE
OFFICE EARLY THIS MORNING. FARTHER WEST...THE DRIER AIR SEEN ON THE
00Z KINL SOUNDING HAS CONTINUED TO EAT AWAY AT THE LAKE EFFECT OVER
THE WESTERN LAKE AND ALL THAT REMAINS OVER THE THIRD OF WESTERN
UPPER MICHIGAN IS STRATUS TRAPPED BELOW THE INVERSION. RAP/NAM H925
MOISTURE FIELDS SEEM TO HAVE A GOOD HANDLE ON THE BACK EDGE OF THIS
MOISTURE AND WILL FOLLOW THE IDEA OF THE CLOUD EDGE GRADUALLY
PUSHING TO THE NORTHEAST THROUGH THE DAY TODAY AS THE H925 RIDGE
BACKS WINDS TO THE WEST-SOUTHWEST. SINCE UPSTREAM MID/HIGH CLOUDS
WILL LIKELY AFFECT THE AREAS WHERE THE LOW CLOUDS DEPART...WON/T GO
WITH A SUNNY FORECAST AND KEEP IN MOSTLY SUNNY TO PARTLY CLOUDY
AREA.
AS FOR THE LAKE EFFECT CLOUDS AND --SHSN...MODELS NOT REALLY SHOWING
THE H925 RIDGE HAVING TOO MUCH AFFECT ON IT UNTIL THIS
AFTERNOON...EXCEPT OVER NORTH CENTRAL UPPER MICHIGAN. THE DRIER
AIR SHOULD CAUSE THE SUBSIDENCE INVERSION TO LOWER FURTHER AND
TOWARDS 2-2.5KFT OVER EASTERN LAKE SUPERIOR AND UPPER MICHIGAN.
THUS...LIKED THE PREVIOUS SHIFTS HANDLING OF PUSHING THE ISOLATED
SNOW SHOWERS EAST THROUGH THE DAY AND MAINLY FOCUSED EAST OF GRAND
MARAIS THIS AFTERNOON.
TONIGHT...FRONT ARRIVES SHORTLY AFTER SUNSET OVER THE WEST AND H925
MOISTURE SURGES BACK OVER THE AREA AND INCREASES CLOUDS. OVER THE
EAST...THERE COULD BE A BRIEF PERIOD WHERE THE SNOW COMPLETELY
ENDS LATE THIS AFTERNOON OR EARLY EVENING BEFORE THE NEXT WAVE
ARRIVES. THIS FRONT WILL DROP SOUTHEAST ACROSS THE REST OF THE CWA
DURING THE EVENING AND THE FIRST PART OF THE OVERNIGHT HOURS. WITH
WINDS VEERING TO THE NORTHWEST BEHIND THE FRONT AND COLDER AIR
SURGING BACK IN...ENHANCED BY SURFACE LOW DEVELOPING OVER
THE EASTERN LAKE...EXPECT THE LAKE EFFECT CLOUDS AND POTENTIAL SNOW
SHOWERS TO REDEVELOP LATE IN THE EVENING AND CONTINUE OVERNIGHT FOR
THE NORTHWEST TO NORTH-NORTHWEST FAVORED LOCATIONS. BEST LOW LEVEL
LAPSE RATES ARE SEEN OVER EASTERN LAKE SUPERIOR /TO 8.5C/KM /.
MODELS SHOWING SOME DIRECTIONAL SHEAR OVER THE EAST /NORTHWEST H850
WINDS AND NORTH WINDS BELOW H900/...WHICH COMBINED WITH THE FAIRLY
DRY SUB CLOUD LAYER WILL KEEP THE LAKE EFFECT FROM BECOMING
TOO STRONG /LIMITS CLOUD DEPTH TO A FEW KFT EVEN THOUGH INVERSION
HEIGHT IS NEAR 6KFT/ AND COULD ALSO INFLUENCE DEVELOPMENT. THIS IS
ESPECIALLY PREVALENT OVER THE SOUTH CENTRAL LAKE AND NORTH CENTRAL
UPPER MICHIGAN WITH THE LATEST NAM...WHILE THE GFS HAS LESS SHEAR
AND OUR LOCAL REGIONAL WRF HAS BETTER MOISTURE AND UNIDIRECTIONAL
WINDS. WITH THE DIFFERENCES...WILL CONTINUE TO MENTION A
SLIGHT/CHANCE OF SNOW SHOWERS OVER THE NORTH CENTRAL AND EAST
FAVORED LOCATIONS...WITH THE HIGHEST POPS OVER LUCE COUNTY WHERE
INCREASED CONVERGENCE WILL OCCUR WITH THE DEVELOPING SURFACE LOW.
FARTHER WEST...LAKE EFFECT CONDITIONS ARE MORE FAVORABLE IN THE
EVENING WITH BETTER LOW LEVEL MOISTURE AND INVERSION HEIGHTS TO
4.5KFT. WILL CONTINUE CHANCE POPS FOR THAT PERIOD AND THEN START TO
DIMINISH OVERNIGHT AS DRIER AIR WORKS IN. OVERALL...EXPECT MOST
LOCATIONS TO SEE LESS THAN AN INCH OF SNOW.
.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 451 AM EST SAT DEC 22 2012
SUNDAY AND SUNDAY NIGHT...LES CONDITIONS WILL BE LESS FAVORABLE AS
LOW-LVL FLOW BECOMES INCREASINGLY ANTICYCLONIC AND DIVERGENT AS SFC
RIDGE BUILDS INTO THE NRN PLAINS AND UPPER GREAT LAKES AREA.
INCREASING SUBSIDENCE AND INVERSION HEIGHTS LOWERING AOB 3KFT WILL
MAKE IT HARD FOR ACCUMULATING SNOW ESPECIALLY BY SUNDAY NIGHT. KEPT
IN JUST MAINLY 20-30 PCT POPS...HIGHEST EAST WHERE FETCH WILL BE
GREATER ACROSS LAKE SUPERIOR IN NW FLOW.
MON-TUE...MODELS CONTINUE TO TREND SOUTH WITH SHORTWAVE MOVING IN FM
THE NRN PLAINS LATE MONDAY INTO MON NIGHT. SOME WEAK FORCING
ASSOCIATED WITH THIS SHORTWAVE MAY PRODUCE SOME LIGHT SNOW MON INTO
MON EVENING MAINLY OVER SRN PORTIONS OF THE CWA. WITH MODELS SHOWING
850 MB TEMPS DROPPING TO -14C/-15C IN THE WAKE OF THIS
SHORTWAVE...THE ADDED INSTABILITY COULD ALSO PROVIDE A BOOST TO NNW
FLOW LES.
TUE NIGHT-THU...MODELS CONTINUE TO KEEP NEXT SYSTEM EMERGING OUT OF
SRN PLAINS/LWR MS VALLEY WELL SOUTH AND EAST OF THE GREAT LAKES
REGION WITH NO SYNOPTIC SNOW EXPECTED FOR OUR AREA. A MID-LVL TROF
AXIS FROM LOW OVER NRN CANADA IS FCST TO MOVE THROUGH THE UPPER
GREAT LAKES WED NIGHT AND THU...BUT FORCING WITH THIS FEATURE LOOKS
MINIMAL. WITH 850 MB TEMPS OF -10C/-11C CONTRIBUTING TO MARGINAL
INSTABILITY AND A WEAK NRLY FLOW...SOME LIGHT SCT LES IS POSSIBLE
DOWNWIND OF LAKE SUPERIOR OVER NRN COUNTIES. WL MAINTAIN SLIGHT CHC
POPS FOR THESE AREAS.
FRI...MODELS SHOW POTENTIAL FOR ANOTHER SIGNIFICANT MID LEVEL TROUGH
TO MOVE THROUGH THE CNTRL CONUS FOR LATE WEEK. UNCERTAINTY STILL
EXISTS WITH MODELS CONCERNING TRACK OF THIS SYSTEM. THE 00Z ECMWF
CONTINUES TO TREND WITH A MORE AMPLIFIED PATTERN THAN THE GFS...AND
WOULD INDICATE A MORE NRN TRACK WITH LEAD SHORTWAVE EMERGING OUT OF
WRN CONUS TROF. THE ECMWF SCENARIO WOULD RESULT IN A BETTER CHC OF
PCPN FOR LATE FRIDAY INTO FRIDAY NIGHT FOR OUR CWA THAN THE GFS. AT
THIS POINT...GIVEN UNCERTAINTY WILL MAINTAIN JUST SLIGHT CHC POPS
FOR LIGHT SNOW TOWARD FRI EVENING. HOWEVER..WOULD NOT BE SURPRISED
GIVEN RECENT TRENDS...ESPECIALLY WITH THE ECMWF...THAT POPS MAY NEED
TO RAISED FOR LATE WEEK.
&&
.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1255 PM EST SAT DEC 22 2012
DRY WESTERLY FLOW WITH A SFC RIDGE MOVING INTO THE AREA HAS
SCOURED OUT MVFR CIGS LEAVING MAINLY MID CLOUDS OVER THE REGION.
AS A COLD FRONT SWEEPS ACROSS UPPER MICHIGAN THIS EVENING...WINDS
ARE EXPECTED TO VEER TO THE NORTHWEST AND LEAD TO MVFR CEILINGS AND
LAKE EFFECT SNOW AT KCMX/KIWD. WITH ONLY LIMITED CONFIDENCE ON
AMOUNT OF VISIBILITY RESTRICTION...FCST ONLY MENTIONS HIGH END MVFR
AT THIS POINT. EVEN THOUGH KSAW IS LESS LIKELY TO SEE LAKE EFFECT
SNOW WITH THE GENERALLY NORTHWEST WINDS...CIGS INTO THE MVFR RANGE
ARE STILL EXPECTED.
&&
.MARINE...(FOR THE 4 AM LAKE SUPERIOR FORECAST ISSUANCE)
ISSUED AT 451 AM EST SAT DEC 22 2012
WINDS HAVE FALLEN BELOW GALES THIS MORNING AS THE PRESSURE GRADIENT
CONTINUES TO RELAX WITH WEAK HIGH PRESSURE RIDGE MOVING THROUGH
TODAY. WINDS ARE EXPECTED TO INCREASE UP TO 25KTS OUT OF THE
NORTHWEST TONIGHT AS A COLD FRONT SWEEPS SOUTHEAST ACROSS LAKE
SUPERIOR. HIGH PRESSURE RIDGE FROM THE CANADIAN PRAIRIES WILL TRY
TO NOSE INTO THE UPPER GREAT LAKES FOR SUNDAY AND THE FIRST HALF OF
NEXT WEEK...KEEPING WINDS BELOW 25KTS.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
UPPER MICHIGAN...
NONE.
LAKE SUPERIOR...
NONE.
LAKE MICHIGAN...
NONE.
&&
$$
SHORT TERM...SRF
LONG TERM...VOSS
AVIATION...JLB
MARINE...SRF
AREA FORECAST DISCUSSION
NWS TWIN CITIES/CHANHASSEN MN
200 PM CST SAT DEC 22 2012
.DISCUSSION...
CDFNT NOW JUST W OF MSP AND CONTG TO PUSH EAST WITH NICE AREA OF SFC
PRESSURE RISES ACROSS THE DKTS INTO W MN. NOT MUCH CLOUD COVER IN
WAKE OF FNT WITH MAIN AREA OF CLDS AND --SN PUSHING ESE ACROSS N MN
WITH WEAK UPPER AIR DISTURBANCE NOW PUSHING ACRS NW MN.
EXPANSIVE HIGH PRESSURE WILL CONTINUE TO BUILD INTO THE AREA OUT OF
CANADA KEEPING KEEPING TEMPS COOL THRU THE WEEK. A PIECE OF ENERGY
FROM STRONG NW COAST TROUGH WILL PUSH ACROSS THE NORTHERN ROCKIES
TONIGHT AND THEN ACRS OUR AREA SUNDAY NIGHT/MONDAY. LOOKING PRETTY
GUD FOR A PERIOD OF -SN WITH FAIRLY STRONG UPPER TROF MOVING THRU
AREA...BUT MOISTURE PRETTY LIMITED. UPPED POPS A BIT FOR UP TO AN
INCH OF SNOW. BEST CHC FOR ANY ACCUM SEEMS TO BE ACRS N CWA NEAR
PATH OF MID LEVEL LOW.
ECMWF IN PARTICULAR REMAINS AGGRESSIVE ON POSSIBLE SNOW EVENT FOR
LATE FRIDAY INTO SATURDAY BRINGING MORE OF A SW WAVE INTO AREA AND
ASSOCIATED DEEP SURFACE LOW PRESSURE. MAINTAINED POPS IN THE MID
CHC RANGE AS IN PREVIOUS PACKAGE.
&&
.AVIATION.../18Z TAF ISSUANCE/
RATHER DIFFUSE COLD FRONT IN THE PROCESS OF WORKING THROUGH
STC AND MSP RIGHT NOW. BIGGEST ISSUE ASSOCIATED WITH THIS
BOUNDARY IS WHAT HAPPENS WITH POST FRONTAL STRATUS NOW WORKING
SOUTH ACROSS NRN NODAK/MN. FOLLOWED THE RAP 925-850 RH FOR MOVING
THESE CLOUDS ACROSS THE TERMINALS. FOLLOWING THIS IDEA...EXPECT
THESE CLOUDS TO THIN ALONG THE 925-850 RIDGE AXIS GOING INTO ERN
MN/WRN WI...WITH MOST SIGNIFICANT SWATH OF LOW CLOUDS RIDING SOUTH
THROUGH THE DAKOTAS. CURRENT LAMP GUIDANCE FOLLOWS THIS RAP IDEA
WITH FIRST BATCH OF CIGS COMING IN BETWEEN 00Z AND 06Z. SECOND
ROUND OF MVFR CIGS INDICATED BY THE GFSLAMP SUNDAY MORNING IS A
BIT HARDER TO BELIEVE AT THIS POINT LOOKING AT HOW DRY SOUNDINGS
ARE. THINK THIS SECOND BATCH MAY BE A RESULT OF CLIMATOLOGY
WORKING INTO THE GUIDANCE...AS WIND BECOME NE SUNDAY MORNING.
GIVEN THE SOURCE REGION FOR THOSE NORTHEAST WINDS IS A DRY ARCTIC
HIGH OVER CANADA...ANY CLOUDS ASSOCIATED WITH IT WILL BE
ORIGINATING FROM LAKE SUPERIOR. LOOKING AT NAM RH AROUND 925
MB...ONLY EAU WILL HAVE A SHOT AT SEEING THOSE CLOUDS...WITH
EVERYONE ELSE EXPECTED TO BE SAFELY VFR.
KMSP...BEST SHOT AT SEEING MVFR CIGS WOULD BE 3-8Z WHEN A SCT MVFR
LAYER IS MENTIONED. THE LAST FEW RUNS OF THE GFSLAMP HAVE BEEN
BRINGING SOME MVFR CIGS IN DURING THIS TIMEFRAME. HOWEVER...WITH
ONLY A NARROW STRIP OF HIGHER RH NOTED AT 925 SWINGING THROUGH
DURING THIS TIME ON THE RAP...CONFIDENCE IN THEM OCCURRING STILL TOO
LOW TO BRING IN A CIG. AT THIS TIME...IT LOOKS LIKE A TEMPO MVFR
CIG IN THIS PERIOD WOULD PROBABLY COVER THINGS. AS FOR THE RETURN
TO MVFR CIGS SUNDAY MORNING IN THE GFSLAMP...THIS HAS LITTLE MERIT
WHEN LOOKING AT LOW LEVEL RH FROM THE GFS/NAM OR PROBS FOR MVFR
CIGS OFF THE SREF...SO HAVE THINGS VFR SUNDAY.
/OUTLOOK FOR KMSP/
MON...MVFR CIGS/VSBYS IN -SN POSSIBLE EARLY...THEN VFR.
WINDS N 6 TO 8 KTS.
TUE...VFR. NW 6 TO 8 KTS.
WED...VFR. WINDS NW 5 KTS.
&&
MPX WATCHES/WARNINGS/ADVISORIES...
MN...NONE.
WI...NONE.
$$
BAP/MPG
AREA FORECAST DISCUSSION
NWS TWIN CITIES/CHANHASSEN MN
1134 AM CST SAT DEC 22 2012
.UPDATE...
18Z AVIATION DISCUSSION ADDED BELOW.
&&
.PREV DISCUSSION...
/ISSUED 602 AM CST SAT DEC 22 2012/
MAIN HIGHLIGHTS OF THIS FORECAST PACKAGE INCLUDE A CHANCE OF LIGHT
SNOW MONDAY...BELOW NORMAL TEMPERATURES FOR MOST OF THE NEXT WEEK
/MAINLY NEXT WEEK...MONDAY THROUGH WEDNESDAY ESPECIALLY/...AND A
CHANCE OF SNOW FOR NEXT WEEKEND.
EARLY THIS MORNING TEMPERATURES WERE ACTUALLY BEGINNING TO
INCREASE ACROSS THE WESTERN HALF OF THE CWA. SURFACE RIDGE AXIS
HAS MOVED INTO WESTERN WISCONSIN...SO WINDS WERE INCREASING TO
WEST OF THAT AREA. ONGOING LOW LEVEL WARM AIR ADVECTION /925 AND
850MB/ COUPLED WITH INCREASING SSE WIND SPEEDS HAS HELPED
TEMPERATURES BEGIN TO RISE SEVERAL HOURS BEFORE DAYBREAK. A WEAK
SURFACE LOW WILL DROP SOUTH FROM ONTARIO ACROSS THE UPPER GREAT
LAKES TODAY...AND WILL DRAG A COLD FRONT THROUGH THE CWA BY THIS
EVENING. NO PRECIPITATION IS EXPECTED WITH THIS BOUNDARY DUE TO
VERY DRY AIR AND LACK OF LIFT. AFTER THIS WEAK FRONT MOVES
THROUGH...DAILY HIGH TEMPERATURES WILL GET COLDER FROM DAY TO
DAY...THROUGH THE MIDDLE OF NEXT WEEK...MEANING TODAY WILL QUITE
POSSIBLY BE THE WARMEST OF THE NEXT 7 DAYS. SUNDAY WILL REMAIN DRY
AND SLIGHTLY COOLER THAN TODAY.
THE NEXT SHOT AT MEASURABLE PRECIPITATION IS ON MONDAY...AS AN
UPPER LEVEL SHORTWAVE TROUGH MOVES OVER THE AREA. MODEL
DISAGREEMENT ON TIMING AND PLACEMENT OF ANY PRECIPITATION IS
EVIDENT BETWEEN THE GFS...ECMWF...AND NAM. THE GEM LOOKS MORE IN
LINE WITH THE GFS...AND ULTIMATELY LEANED IN THE DIRECTION OF THE
GFS/GEM AS FAR AS PLACEMENT OF QPF...BUT SLOWED TIMING DOWN A FEW
HOURS AS THE NAM AND ECMWF INDICATED. THERE IS GOOD AGREEMENT
AMONG THE VARIOUS MODELS THAT TEND TO LIMIT QPF AS THE WAVE MOVES
ACROSS THE EASTERN HALF OF THE FA. IT LOOKS LIKE THE REASON FOR
THIS IS DUE TO THE FORCING SIMPLY OUTRUNNING THE SATURATED
AIR...ESPECIALLY MONDAY AFTERNOON. FOR NOW...INDICATED SLIGHT
CHANCE AND CHANCE POPS ACROSS PORTIONS OF THE CWA. WOULD LIKE TO
SEE SATURATION AND AND FORCING LINE UP IN FUTURE MODEL
RUNS...WHICH WOULD GIVE HIGHER CONFIDENCE IN SEEING MEASURABLE
PRECIPITATION. DUE TO THIS...AND THE CURRENT MODEL
DISAGREEMENT...CONFIDENCE IN THE FORECAST FOR MONDAY IS BELOW NORMAL.
CHRISTMAS DAY THROUGH THURSDAY...MID NEXT WEEK LOOKS COLD BEHIND THE
WAVE THAT MOVES THROUGH ON MONDAY. HIGH PRESSURE WILL OOZE
SOUTHWARD FROM CANADA AND PROVIDE THE REGION WITH COLD AND CLEAR
CONDITIONS FOR A FEW DAYS. CHRISTMAS DAY IS FORECAST TO BE THE
COLDEST DAY OF THE FORECAST PERIOD...ESPECIALLY ACROSS THE WEST
WHERE HIGH TEMPERATURES WILL STRUGGLE TO GET ABOVE ZERO. HIGHS IN
THE LOWER TEENS WILL BE SEEN ACROSS THE EAST.
FRIDAY...A POTENT UPPER WAVE WILL MOVE OVER THE INTER MOUNTAIN
WEST...AND SURFACE CYCLOGENESIS WILL ENSUE ON THE LEE OF THE ROCKY
MOUNTAINS. THIS LOW WILL EJECT FROM THE COLORADO/NEW MEXICO REGION
AND CURL ENE WITH THROUGH THE MIDWEST AND PROVIDES THE FA WITH THE
BEST CHANCE OF ACCUMULATING SNOWFALL OVER THE FORECAST PERIOD.
SOUTHERLY SURFACE WINDS AHEAD OF THIS SYSTEM WILL HELP WARM
TEMPERATURES TO NEAR SEASONABLE NORMALS BY THE END OF THE WEEK.
&&
.AVIATION.../18Z TAF ISSUANCE/
RATHER DIFFUSE COLD FRONT IN THE PROCESS OF WORKING THROUGH
STC AND MSP RIGHT NOW. BIGGEST ISSUE ASSOCIATED WITH THIS
BOUNDARY IS WHAT HAPPENS WITH POST FRONTAL STRATUS NOW WORKING
SOUTH ACROSS NRN NODAK/MN. FOLLOWED THE RAP 925-850 RH FOR MOVING
THESE CLOUDS ACROSS THE TERMINALS. FOLLOWING THIS IDEA...EXPECT
THESE CLOUDS TO THIN ALONG THE 925-850 RIDGE AXIS GOING INTO ERN
MN/WRN WI...WITH MOST SIGNIFICANT SWATH OF LOW CLOUDS RIDING SOUTH
THROUGH THE DAKOTAS. CURRENT LAMP GUIDANCE FOLLOWS THIS RAP IDEA
WITH FIRST BATCH OF CIGS COMING IN BETWEEN 00Z AND 06Z. SECOND
ROUND OF MVFR CIGS INDICATED BY THE GFSLAMP SUNDAY MORNING IS A
BIT HARDER TO BELIEVE AT THIS POINT LOOKING AT HOW DRY SOUNDINGS
ARE. THINK THIS SECOND BATCH MAY BE A RESULT OF CLIMATOLOGY
WORKING INTO THE GUIDANCE...AS WIND BECOME NE SUNDAY MORNING.
GIVEN THE SOURCE REGION FOR THOSE NORTHEAST WINDS IS A DRY ARCTIC
HIGH OVER CANADA...ANY CLOUDS ASSOCIATED WITH IT WILL BE
ORIGINATING FROM LAKE SUPERIOR. LOOKING AT NAM RH AROUND 925
MB...ONLY EAU WILL HAVE A SHOT AT SEEING THOSE CLOUDS...WITH
EVERYONE ELSE EXPECTED TO BE SAFELY VFR.
KMSP...BEST SHOT AT SEEING MVFR CIGS WOULD BE 3-8Z WHEN A SCT MVFR
LAYER IS MENTIONED. THE LAST FEW RUNS OF THE GFSLAMP HAVE BEEN
BRINGING SOME MVFR CIGS IN DURING THIS TIMEFRAME. HOWEVER...WITH
ONLY A NARROW STRIP OF HIGHER RH NOTED AT 925 SWINGING THROUGH
DURING THIS TIME ON THE RAP...CONFIDENCE IN THEM OCCURRING STILL TOO
LOW TO BRING IN A CIG. AT THIS TIME...IT LOOKS LIKE A TEMPO MVFR
CIG IN THIS PERIOD WOULD PROBABLY COVER THINGS. AS FOR THE RETURN
TO MVFR CIGS SUNDAY MORNING IN THE GFSLAMP...THIS HAS LITTLE MERIT
WHEN LOOKING AT LOW LEVEL RH FROM THE GFS/NAM OR PROBS FOR MVFR
CIGS OFF THE SREF...SO HAVE THINGS VFR SUNDAY.
/OUTLOOK FOR KMSP/
MON...MVFR CIGS/VSBYS IN -SN POSSIBLE EARLY...THEN VFR.
WINDS N 6 TO 8 KTS.
TUE...VFR. NW 6 TO 8 KTS.
WED...VFR. WINDS NW 5 KTS.
&&
MPX WATCHES/WARNINGS/ADVISORIES...
MN...NONE.
WI...NONE.
$$
SPD/MPG
AREA FORECAST DISCUSSION
NWS OMAHA/VALLEY NE
341 PM CST SAT DEC 22 2012
.SHORT TERM...TONIGHT THROUGH CHRISTMAS DAY.
THE FORECAST CONCERNS IN THE SHORT TERM WILL BE THE CLOUDS...POTENTIAL
FOR FLURRIES OR LIGHT SNOW WITH A NORTHERN STREAM WAVE SUNDAY
NIGHT AND THE SOUTHERN STREAM WAVE CHRISTMAS EVE AND CHRISTMAS
DAY...AND TEMPERATURES.
SUNSHINE AND WARM H85 TEMPERATURES HAVE TRANSLATED INTO READINGS IN
THE 30S AND A FEW 40S FOR MUCH OF THE FORECAST AREA. THE SURFACE
WINDSHIFT TO THE NORTHWEST HAD MADE TO THE VALLEY NWS BY 130PM AND
COOLING IN TEMPERATURES WERE NOTICED FROM YANKTON TO ONEILL.
THE STORM SYSTEM OF INTEREST FOR OUR WEATHER LATER THIS WEEKEND AND
EARLY NEXT WEEK IS JUST STARTING TO BECOME SAMPLED BY THE WEST COAST
STATIONS IN THE 12Z RUNS. AT THIS POINT...THERE IS GOOD AGREEMENT
IN THE SHORT RANGE MODELS THAT LEAD ENERGY FROM THIS SYSTEM WILL
MOVES ACROSS THE NORTHERN ROCKIES...INTO THE PLAINS TONIGHT AND
SUNDAY...FLATTENING THE MID LEVEL RIDGE AND ALLOWING VERY COLD AIR
FROM CANADA TO MOVE SOUTHWARD ACROSS THE DAKOTAS...MINNESOTA...AND
IOWA...WITH SOMEWHAT OF A GLANCING BLOW LOCALLY. AT THIS
TIME...THERE IS AN AREA OF STRATUS AND FLURRIES ACROSS NORTHERN
NORTH DAKOTA. A LOOK AT THE 18Z STLT AND THE 18Z PROJECTIONS FOR
NAM/GFS AND MOST RECENT HRRR SEEM TO BE OVERDOING THE LOW LEVEL RH.
THE 12Z EC SEEMS TO HAVE A BETTER HANDLE ON THE LOW LEVEL RH.
THE WATER VAPOR SATELLITE IMAGERY AND A LOOK AT WINDS ALOFT AND
HEIGHTS SHOW ONE JET SEGMENT WEST OF THE TROF OFF THE WEST COAST AND
ANOTHER JET SEGMENT OVER THE SOUTHWEST U.S. WITH MOISTURE FROM THE
TROPICS STREAMING INTO THE SOUTHERN ROCKIES AND SOUTHERN PLAINS.
HIGH LEVEL CLOUDS WILL BE ON THE INCREASE DURING THE OVERNIGHT HOURS
AND CONTINUE INTO SUNDAY. STRATUS DEVELOPMENT IS LESS CERTAIN...AND
FOR NOW THE BEST CHANCE FOR STRATUS APPEARS TO BE INTO NORTH CENTRAL
NEBRASKA OVERNIGHT WITH SOME STRATUS DEVELOPING OVER PARTS OF THE
FORECAST AREA SUNDAY. THERE IS GOOD MID LEVEL WARM AIR ADVECTION
WELL TO THE NORTH OF THE AREA AND THERE COULD BE SOME FLURRIES IN
THE FAR NORTH/NORTHEAST TOWARD MACY AND MAPLETON WITH THE CLOUDS AND
ALSO AS THE SHORTWAVE IS TRACKING FROM THE DAKOTAS INTO IOWA.
TONIGHT...SURFACE HIGH PRESSURE WILL BUILD IN AND HAVE LOWS IN THE
SINGLE DIGITS AND TEENS. HIGHS SUNDAY SHOULD BE COLDER...ONLY IN
THE TEENS AND 20S. THE SHORTWAVE TROF SUNDAY NIGHT BRINGS A
WINDSHIFT THRU AND MUCH COLDER TEMPERATURES. HIGHS MONDAY SHOULD
MAINLY BE IN THE TEENS.
THE NEXT STRONGER...LARGER STORM SYSTEM JUST MOVING ONTO THE WEST
COAST IS FORECAST TO TRACK ACROSS THE ROCKIES INTO THE PLAINS
CHRISTMAS EVE AND CHRISTMAS DAY. THE SURFACE LOW TRACKS WELL TO THE
SOUTH OVER TEXAS...AND THE BETTER LIFT IS ALSO WELL TO THE SOUTH.
THERE IS SOME BROAD MID AND UPPER LEVEL LIFT AND WITH THE COLD
AIRMASS IS IN PLACE THERE MAY BE SOME FLURRIES OR LIGHT SNOW. FOR
NOW HAVE SOME CHANCE PROB OF PRECIPITATION TOWARD
ALBION...COLUMBUS...AND SEWARD...WITH SLIGHT CHANCE FOR LIGHT SNOW
AND CHANCE OF FLURRIES MENTIONED ACROSS PARTS OF . HIGHS MONDAY
AND TUESDAY LOOK TO HOLD IN THE TEENS.
ZAPOTOCNY
.LONG TERM...TUESDAY NIGHT THROUGH SATURDAY.
NEW MEDIUM RANGE MODELS INDICATING GOING FCST IS IN GOOD
SHAPE...THUS ONLY MINOR ADJUSTMENT MADE. LARGE SCALE FLOW IS
ADVERISED TO BE RATHER PROGRESSIVE THRU THE EXTENDED PDS.
MODELS PROG A LONGWAVE TROF EXITING EWD OF THE REGION TUESDAY NIGHT
WITH ITS AXIS PRETTY MUCH CUTTING DOWN THE MS VLY. MEANWHILE...
UPSTREAM SHORTWAVE TROF OFF THE PAC NW COAST WILL BE THE NEXT SYSTEM
OF INTEREST FOR POSSIBLE ACTIVE WX. THE ECM CONTINUES TO BE THE MOST
ROBUST PUSHING THE SYSTEM ACROSS CA INTO THE INTERMOUNTAIN WEST WED
NIGHT/THURS MORNING WITH 500 MB HGT FALLS AROUND 160M AND INCREASING
DPVA INDUCING SFC CYCLOGENESIS NEAR THE OK PANHANDLE. SYNOPTIC LIFT
INCREASES INTO THURSDAY NIGHT AS NARROW CHANNEL OF VORTICIY ROUNDS
THE BASE OF THE TROF. THIS IN COMBINATION WITH A RELATIVELY WEAK
LOW/MID LYR FRONTOGENETIC CIRCULATION AND MODEST 280K ISENTROPIC
UPGLIDE...THE ECM FOCUSES PCPN INITIATION FROM ABOUT SWRN SD TO NERN
CO THEN PUSHES IT EWD THRU THE DAY ON FRIDAY. AM INCLINED AT THIS
POINT TO FAVOR ECM SOLUTION OVER THE GFS. THEREFORE WILL MAINTAIN
SMALL SNOW POPS THURSDAY NIGHT AND FRIDAY. FRIDAY EVENING...ANY SNOW
ACTIVITY SHOULD BE COMING TO A QUICK END AS CAA/SUBSIDENCE
SUPPRESSES ANY DYNAMIC FORCING. OTHERWISE...BOTH ECM MOS AND MEX
ADVERTISING WELL BELOW NORMAL TEMPS DAYS 4-7.
DEE
&&
.AVIATION...
18Z TAFS FOR KOFK...KOMA AND KLNK. VFR CONDITIONS
VFR CONDITIONS WILL CONTINUE UNTIL THIS EVENING AFTER A COLD FRONT
MOVES ACROSS THE AREA. MVFR TO IFR CEILINGS ARE EXPECTED AFTER
09-10Z ACROSS THE AREA WITH STRATUS AND FOG OCCUR BEHIND THE
FRONT.
SMITH
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
IA...NONE.
&&
$$
AREA FORECAST DISCUSSION
NWS LA CROSSE WI
500 PM CST SAT DEC 22 2012
.SHORT TERM...TONIGHT THROUGH CHRISTMAS DAY
247 PM CST SAT DEC 22 2012
MAIN FORECAST CONCERNS REMAIN ON LOW CLOUD POTENTIAL TONIGHT AND
LIGHT SNOW CHANCES SUNDAY NIGHT THROUGH MONDAY.
LATEST WATER VAPOR IMAGERY SHOWED A BROAD UPPER LEVEL RIDGE OVER THE
CENTRAL CONUS...WITH A DEEP TROUGH OVER THE EASTERN U.S. AND
ANOTHER TROUGH OFF OF THE WEST COAST MOVING INTO THE PACIFIC
NORTHWEST. WEST/NORTHWEST FLOW ALOFT WAS NOTED ACROSS THE UPPER
MISSISSIPPI RIVER VALLEY. AN EMBEDDED SHORTWAVE WAS MOVING
SOUTHEAST ACROSS SOUTHERN MANITOBA...HEADED FOR NORTHERN
MINNESOTA. SURFACE OBSERVATIONS SHOWED A WEAK TROUGH EXTENDING
FROM SOUTHWEST ONTARIO...NEAR THE MN/ONTARIO BORER...SOUTH THROUGH
CENTRAL MINNESOTA INTO FAR SOUTHEAST SOUTH DAKOTA....DRIFTING
SOUTHEAST.
THE SURFACE TROUGH WILL CONTINUE ITS SOUTHEAST PROGRESSION...MOVING
ACROSS THE FORECAST AREA THIS EVENING WITH THE MAIN IMPACT BEING A
WIND SWITCH TO THE NORTH/NORTHWEST AND THE POSSIBILITY OF SEEING
SOME LOW CLOUD DEVELOPMENT. THE NAM CONTINUES TO SHOW 925 MB
RELATIVE HUMIDITY INCREASING INTO THE 90-94 PERCENT RANGE THIS
EVENING. THE RUC IS ALSO HINTING AT THIS INCREASE IN RELATIVE
HUMIDITY BUT ITS A LITTLE LATER THAN THE NAM. THINKING A SCATTERED
TO BROKEN LOW STRATUS DECK WILL DEVELOP. PLAN ON MOSTLY CLEAR SKIES
THIS EVENING...POSSIBLY BECOMING PARTLY CLOUDY LATE THIS EVENING
THROUGH THE LATE NIGHT HOURS IF THE STRATUS DEVELOPS. LOOK FOR LOW
TEMPERATURES TO FALL INTO THE SINGLE DIGITS.
WEAK HIGH PRESSURE WILL ATTEMPTS TO BUILD INTO THE UPPER MISSISSIPPI
RIVER VALLEY ON SUNDAY. NORTHERLY FLOW WILL BRING LAKE EFFECT CLOUDS
TO MUCH OF NORTHERN WISCONSIN OFF OF LAKE SUPERIOR. ALSO...HIGH AND
MID LEVEL CLOUDS WILL BE ON THE INCREASE ON SUNDAY AS A SHORTWAVE
TROUGH MOVES ACROSS THE DAKOTAS AND HEADS EAST TOWARD THE UPPER
MISSISSIPPI RIVER VALLEY. COOLER AIR WILL MOVE OVER THE AREA ON
SUNDAY WITH HIGHS IN THE UPPER TEENS TO LOWER 20S. THE TROUGH IS
EXPECTED TO PUSH INTO WESTERN MINNESOTA/NORTHWEST IOWA LATE SUNDAY
NIGHT THEN INTO CENTRAL IOWA AND SOUTHWEST WISCONSIN DURING THE DAY
ON MONDAY. THE LATEST MODEL GUIDANCE SUGGEST A SLIGHTLY MORE
SOUTHWESTERLY TRACK. THE NAM TAKES THE MAIN PVA...IN THE 300-500 MB
LAYER...ACROSS IOWA JUST BRUSHING SOUTHEAST MINNESOTA AND FAR
SOUTHWEST WISCONSIN. THE GFS IS ALSO LEANING TOWARD A MORE SOUTHERLY
TRACK BUT BRINGS TWO PIECES OF ENERGY THROUGH THE AREA. THE FIRST
PASSES ACROSS SOUTHWESTERN PARTS OF THE FORECAST AREA MAINLY MONDAY
MORNING WITH A SECONDARY WAVE MOVING ACROSS NORTHERN WISCONSIN.
MUCH OF THE FORECAST AREA SHOULD SEE LIGHT SNOW OUT OF THIS SYSTEM
LATE SUNDAY NIGHT INTO MONDAY MORNING. THE HIGHEST CHANCES FOR
MEASURABLE SNOW LOOKS TO BE SOUTH OF INTERSTATE 94. THINKING UP TO
AN INCH IS POSSIBLE ACROSS THESE AREAS SO WILL BE INCREASING
PRECIPITATION CHANCES. WILL MAINTAIN OCCASIONAL VERY LIGHT SNOW
WORDING. HIGH TEMPERATURES ON MONDAY WILL RANGE FROM THE LOWER 20S
ACROSS NORTHERN WISCONSIN TO THE MID TEENS ACROSS WESTERN SECTIONS
OF NORTHEAST IOWA INTO PORTIONS OF SOUTHEAST MINNESOTA. COLDER AIR
WILL SLIDE BACK INTO THE REGION MONDAY NIGHT WITH LOWS FALLING INTO
THE SINGLE DIGITS ABOVE ZERO. FAVORED COLD SPOTS COULD FALL INTO THE
SINGLE DIGITS BELOW ZERO. COOL HIGH PRESSURE WILL REMAIN OVER THE
AREA ON TUESDAY PROVIDING PARTLY SUNNY SKIES AND HIGHS MAINLY IN THE
TEENS. A POTENT UPPER TROUGH IS EXPECTED TO MOVE ACROSS THE SOUTHERN
PLAINS TUESDAY AND HEAD TOWARDS THE LOWER TO MIDDLE MISSISSIPPI
RIVER VALLEY.
.LONG TERM...TUESDAY NIGHT THROUGH SATURDAY
247 PM CST SAT DEC 22 2012
22.12 MEDIUM RANGE MODELS ARE IN REASONABLE AGREEMENT TUESDAY NIGHT
INTO WEDNESDAY SHOWING THE SOUTHERN STREAM TROUGH LIFTING NORTH INTO
THE OHIO RIVER VALLEY AND CLOSING INTO AN UPPER LOW. THIS SYSTEM IS
EXPECTED TO REMAIN WELL TO THE EAST OF THE AREA AS IT LIFTS INTO NEW
ENGLAND WEDNESDAY NIGHT INTO THURSDAY. HIGH PRESSURE WILL MAINTAIN
COOL AND QUIET WEATHER THROUGH THURSDAY WITH HIGHS IN THE TEENS AND
LOWS RANGING FROM THE SINGLE DIGITS BELOW ZERO TO SINGLE DIGITS
ABOVE ZERO. ANOTHER TROUGH WILL CROSS THE ROCKIES ONT THURSDAY AND
MOVE INTO THE PLAINS DURING THE DAY ON FRIDAY. FORECAST MODELS START
TO DIVERGE FRIDAY INTO SATURDAY ON THE EVOLUTION OF THIS TROUGH. THE
ECMWF CONTINUES TO WRAP THIS SYSTEM INTO AN UPPER LOW AS IT LIFTS
INTO THE GREAT LAKES AND MERGES WITH A TROUGH MOVING SOUTHEAST
ACROSS SOUTHERN ALBERTA/SASKATCHEWAN. THE ECMWF SOLUTION WOULD BRING
A PROLONGED PERIOD OF LIGHT SNOW TO THE FORECAST AREA. THE GFS KEEPS
THESE TWO SYSTEMS FROM MERGING AND BRINGS THE NORTHERN STREAM TROUGH
ACROSS THE FORECAST AREA DURING THE DAY ON SATURDAY. GIVEN THE
VARYING MODEL SOLUTIONS DECIDED TO LEAN TOWARD A MODEL CONSENSUS
BLEND APPROACH WITH CHANCES FOR LIGHT SNOW FRIDAY THROUGH
SATURDAY.
&&
.AVIATION...
500 PM CST SAT DEC 22 2012
THE CONCERN TONIGHT IS FOR THE POTENTIAL OF A LOW STRATUS LAYER.
RAP13/NAM12 SHOW AN AREA OF LOW LEVEL SATURATION ACROSS THE
DAKOTAS/NORTHWEST MN...BRINGING THIS SOUTH THROUGH THE NIGHT. THE
RAP13 IS MORE AGGRESSIVE IN ITS EASTWARD EXTENT ON THE STRATUS...AND
WOULD HAVE IT IMPACT KRST OVERNIGHT. SOME SFC OBS OVER WESTERN MN
INDICATE CIGS AROUND 1 KFT...ALTHOUGH NOTHING SEEN ON FOG/STRATUS
SATELLITE IMAGERY. A CLOSER LOOK AT VSBY DURING THE DAYLIGHT HOURS
DOES SHOW SOME VERY SHALLOW CLOUDS STREETS THAT COULD BE RESPONSIBLE
FOR THE OBS. OR...IT COULD ALSO BE SUSPENDED ICE CRYSTALS IN THE
COLDER AIR. BUFKIT SOUNDINGS HAVE A LOW LEVEL INVERSION INTO SUN
MORNING. IF ANY MOISTURE COULD POOL UNDER THAT...STRATUS AND
POSSIBLY SOME BR COULD DEVELOP. CONFIDENCE NOT OVERLY HIGH AT THE
MOMENT THOUGH...AND WILL KEEP ANY CIGS WEST OF THE KRST/KLSE
TONIGHT.
HIGH CLOUDS WILL BE THE INCREASE SUN AFTERNOON...AHEAD OF AN
APPROACHING UPPER LEVEL SHORTWAVE TROUGH. THE CLOUDS WILL GRADUALLY
THICKEN...WITH SOME LOWERING BY MONDAY MORNING. S-- LOOKS LIKE A
GOOD BET LATE SUN NIGHT/MON MORNING...BUT MINIMAL IF ANY
ACCUMULATION. BUFKIT SOUNDINGS SUGGEST MVFR/IFR CIGS WILL RETURN BY
MONDAY MORNING...WHICH COULD HANG AROUND FOR MUCH OF THE DAY.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
247 PM CST SAT DEC 22 2012
WI...NONE.
MN...NONE.
IA...NONE.
&&
$$
SHORT TERM...WETENKAMP
LONG TERM....WETENKAMP
AVIATION.....RIECK
AREA FORECAST DISCUSSION
NWS GREEN BAY WI
307 PM CST SAT DEC 22 2012
.SHORT TERM...TONIGHT AND SUNDAY.
LATEST RUC ANALYSIS AND SATELLITE/RADAR IMAGERY SHOW A COUPLE WEAK
SHORTWAVES...ONE OVER SOUTHEAST SOUTH DAKOTA AND ANOTHER OVER
SOUTHWEST ONTARIO...AND THEY ARE PUSHING AN EQUALLY WEAK COLD FRONT
OVER NORTHWEST WISCONSIN EARLY THIS AFTERNOON. WIDELY SCT FLURRY
ACTIVITY WAS REPORTED IN THE OBS EARLIER TODAY OVER EASTERN NORTH
DAKOTA AND NORTHERN MINNESOTA...BUT NOTHING SO FAR CLOSER TO
WISCONSIN. OTHERWISE...JUST HAVE SOME CIRRUS PASSING OVER CENTRAL
AND SOUTHERN PORTIONS OF THE STATE...AND A BATCH OF MID CLOUDS OVER
NORTHERN WISCONSIN AND THE UPPER PENINSULA. THE MAIN FORECAST
CONCERNS ARE CLOUDS AND LAKE EFFECT SNOW SHOWERS AS WINDS SHIFT TO
THE NORTHWEST FOLLOWING THE PASSAGE OF THE COLD FRONT.
TONIGHT...THE WEAK COLD FRONT WILL PASS ACROSS THE REGION THIS
EVENING WHICH WILL SHIFT WINDS BACK TO THE NORTH-NORTHWEST. THIN
RIBBON OF MID-LEVEL MOISTURE WILL GET STRETCHED OUT ALONG THE FRONT
THIS EVENING WHICH SHOULD LEAVE MOSTLY CLEAR TO PARTLY CLOUDY
CONDITIONS ACROSS THE REGION. BEHIND THE FRONT...A SHALLOW ARCTIC
AIRMASS WILL FILTER SOUTHEAST ACROSS THE NORTHERN WISCONSIN.
STEEPENING LOW LEVEL LAPSE RATES BENEATH A SHARP INVERSION WILL
PROMOTE THE ADVECTION OF LAKE EFFECT CLOUDS OFF LAKE SUPERIOR INTO
NORTHERN WISCONSIN. CAN SEE FLURRIES OR LIGHT SNOW SHOWERS
IMPACTING THE VILAS AND NORTHERN PARTS OF ONEIDA AND FOREST
COUNTY...MAINLY AFTER MIDNIGHT WITH ONLY VERY SMALL ACCUMULATIONS
EXPECTED. THE CLOUDS MAY MAKE A RUN AT WAUSAU/SHAWANO AND CRIVITZ
LATE. LOW LEVEL WINDS OF 15-20 KTS IS MARGINAL FOR DECOUPLING...BUT
CLOUDS ACROSS THE NORTH SHOULD KEEP THEM WARMER THAN LAST NIGHT.
WILL GO WITH LOWS FROM THE MID-SINGLE DIGITS OVER CENTRAL
WISCONSIN...TO THE LOWER 20S NEAR THE LAKE MICHIGAN SHORELINE.
SUNDAY...CANADIAN HIGH PRESSURE WILL GRADUALLY BUILD INTO THE REGION
THROUGH THE DAY. MVFR STRATO-CU WILL LIKELY CREATE A PARTLY TO
MOSTLY CLOUDY START TO THE DAY NORTHWEST OF A AUW TO MNM LINE AS
FLOW WILL REMAIN OUT OF THE NW FOR A GOOD CHUNK OF THE DAY. AM
COUNTING ON WEAK MIXING TO FORCE THE LOW CLOUDS TO RETREAT SOMEWHAT
DURING THE AFTERNOON BUT WILL KEEP PARTLY SUNNY TO MOSTLY CLOUDY
WORDING IN THE GRIDS OVER N-C WISCONSIN. THE RIGHT REAR QUAD OF A JET
STREAK THEN SHIFTS EAST FROM THE NORTHERN PLAINS AND ACROSS THE
STATE DURING THE AFTERNOON. PLENTY OF DRY AIR IN THE MID-LEVELS
WILL KEEP THE AREA PRECIP FREE...BUT SHOULD SEE A DECENT CIRRUS
SHIELD ARRIVE. TEMPS WILL FALL ABOUT 5 DEGREES UP NORTH COMPARED TO
TODAY...PLACING HIGHS IN THE LOW TO MID 20S ACROSS THE REGION.
.LONG TERM...SUNDAY NIGHT THROUGH NEXT SATURDAY.
MODELS SHOWED A MORE ACTIVE WEATHER PATTERN DURING THE PERIOD WITH
LOW AMPLITUDE UPPER LEVEL FLOW THROUGH EARLY NEXT WEEK BEFORE A
WEST COAST TROUGH PUSHES EASTWARD. MODELS WERE IN GOOD AGREEMENT
IN TAKING A 500MB TROUGH THROUGH THE WESTERN GREAT LAKES REGION ON
MONDAY...BUT MOST OF THE ENERGY WITH THAT SHORT WAVE REMAINS SOUTH
OF THE FORECAST AREA. HAVE INCLUDED SOME LOW END CHANCE POPS TO
COVER THAT EVENT. NOT SO MUCH AGREEMENT ON THE PATH OF A STRONGER
SYSTEM THAT WILL BE MOVING NORTHEAST OUT OF THE SOUTHERN PLAINS
MIDWEEK. 12Z ECMWF WOULD HAVE IT MISS THE AREA WHILE THE 12Z GFS
BRINGS QPF TO THE SOUTHEAST 1/3 TO 1/2 OF THE AREA. THERE IS
SLIGHTLY BETTER AGREEMENT IN TAKING A TROUGH ACROSS THE REGION AT
THE END OF THE PERIOD. SO HAVE CHANCE POPS FRIDAY NIGHT AND SATURDAY.
TEMPERATURES SHOULD START THE PERIOD SLIGHTLY BELOW NORMAL BUT
WARM TO NEAR NORMAL BY NEXT WEEKEND.
&&
.AVIATION...A WEAK COLD FRONT WILL PASS ACROSS THE REGION THIS
EVENING. MID AND HIGH CLOUDS WILL PASS OVERHEAD AHEAD OF THE FRONT
LEAVING VFR CONDITIONS THROUGH MUCH OF THE EVENING. WINDS WILL
SHIFT TO THE NNW BEHIND THE FRONT...BRINGING IN A SHALLOW ARCTIC
AIRMASS AS WELL AS LAKE CLOUDS OFF LAKE SUPERIOR. THESE MVFR CLOUDS
WILL PUSH SOUTHEAST THROUGH THE NIGHT...FROM ABOUT AUW TO MNM BY
EARLY SUNDAY MORNING. THESE CLOUDS WILL LIKELY RETREAT A BIT MIDDAY
ONWARD ON SUNDAY.
MPC
&&
.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
MPC/MG
AREA FORECAST DISCUSSION
NWS LA CROSSE WI
247 PM CST SAT DEC 22 2012
.SHORT TERM...TONIGHT THROUGH CHRISTMAS DAY
247 PM CST SAT DEC 22 2012
MAIN FORECAST CONCERNS REMAIN ON LOW CLOUD POTENTIAL TONIGHT AND
LIGHT SNOW CHANCES SUNDAY NIGHT THROUGH MONDAY.
LATEST WATER VAPOR IMAGERY SHOWED A BROAD UPPER LEVEL RIDGE OVER THE
CENTRAL CONUS...WITH A DEEP TROUGH OVER THE EASTERN U.S. AND
ANOTHER TROUGH OFF OF THE WEST COAST MOVING INTO THE PACIFIC
NORTHWEST. WEST/NORTHWEST FLOW ALOFT WAS NOTED ACROSS THE UPPER
MISSISSIPPI RIVER VALLEY. AN EMBEDDED SHORTWAVE WAS MOVING
SOUTHEAST ACROSS SOUTHERN MANITOBA...HEADED FOR NORTHERN
MINNESOTA. SURFACE OBSERVATIONS SHOWED A WEAK TROUGH EXTENDING
FROM SOUTHWEST ONTARIO...NEAR THE MN/ONTARIO BORER...SOUTH THROUGH
CENTRAL MINNESOTA INTO FAR SOUTHEAST SOUTH DAKOTA....DRIFTING
SOUTHEAST.
THE SURFACE TROUGH WILL CONTINUE ITS SOUTHEAST PROGRESSION...MOVING
ACROSS THE FORECAST AREA THIS EVENING WITH THE MAIN IMPACT BEING A
WIND SWITCH TO THE NORTH/NORTHWEST AND THE POSSIBILITY OF SEEING
SOME LOW CLOUD DEVELOPMENT. THE NAM CONTINUES TO SHOW 925 MB
RELATIVE HUMIDITY INCREASING INTO THE 90-94 PERCENT RANGE THIS
EVENING. THE RUC IS ALSO HINTING AT THIS INCREASE IN RELATIVE
HUMIDITY BUT ITS A LITTLE LATER THAN THE NAM. THINKING A SCATTERED
TO BROKEN LOW STRATUS DECK WILL DEVELOP. PLAN ON MOSTLY CLEAR SKIES
THIS EVENING...POSSIBLY BECOMING PARTLY CLOUDY LATE THIS EVENING
THROUGH THE LATE NIGHT HOURS IF THE STRATUS DEVELOPS. LOOK FOR LOW
TEMPERATURES TO FALL INTO THE SINGLE DIGITS.
WEAK HIGH PRESSURE WILL ATTEMPTS TO BUILD INTO THE UPPER MISSISSIPPI
RIVER VALLEY ON SUNDAY. NORTHERLY FLOW WILL BRING LAKE EFFECT CLOUDS
TO MUCH OF NORTHERN WISCONSIN OFF OF LAKE SUPERIOR. ALSO...HIGH AND
MID LEVEL CLOUDS WILL BE ON THE INCREASE ON SUNDAY AS A SHORTWAVE
TROUGH MOVES ACROSS THE DAKOTAS AND HEADS EAST TOWARD THE UPPER
MISSISSIPPI RIVER VALLEY. COOLER AIR WILL MOVE OVER THE AREA ON
SUNDAY WITH HIGHS IN THE UPPER TEENS TO LOWER 20S. THE TROUGH IS
EXPECTED TO PUSH INTO WESTERN MINNESOTA/NORTHWEST IOWA LATE SUNDAY
NIGHT THEN INTO CENTRAL IOWA AND SOUTHWEST WISCONSIN DURING THE DAY
ON MONDAY. THE LATEST MODEL GUIDANCE SUGGEST A SLIGHTLY MORE
SOUTHWESTERLY TRACK. THE NAM TAKES THE MAIN PVA...IN THE 300-500 MB
LAYER...ACROSS IOWA JUST BRUSHING SOUTHEAST MINNESOTA AND FAR
SOUTHWEST WISCONSIN. THE GFS IS ALSO LEANING TOWARD A MORE SOUTHERLY
TRACK BUT BRINGS TWO PIECES OF ENERGY THROUGH THE AREA. THE FIRST
PASSES ACROSS SOUTHWESTERN PARTS OF THE FORECAST AREA MAINLY MONDAY
MORNING WITH A SECONDARY WAVE MOVING ACROSS NORTHERN WISCONSIN.
MUCH OF THE FORECAST AREA SHOULD SEE LIGHT SNOW OUT OF THIS SYSTEM
LATE SUNDAY NIGHT INTO MONDAY MORNING. THE HIGHEST CHANCES FOR
MEASURABLE SNOW LOOKS TO BE SOUTH OF INTERSTATE 94. THINKING UP TO
AN INCH IS POSSIBLE ACROSS THESE AREAS SO WILL BE INCREASING
PRECIPITATION CHANCES. WILL MAINTAIN OCCASIONAL VERY LIGHT SNOW
WORDING. HIGH TEMPERATURES ON MONDAY WILL RANGE FROM THE LOWER 20S
ACROSS NORTHERN WISCONSIN TO THE MID TEENS ACROSS WESTERN SECTIONS
OF NORTHEAST IOWA INTO PORTIONS OF SOUTHEAST MINNESOTA. COLDER AIR
WILL SLIDE BACK INTO THE REGION MONDAY NIGHT WITH LOWS FALLING INTO
THE SINGLE DIGITS ABOVE ZERO. FAVORED COLD SPOTS COULD FALL INTO THE
SINGLE DIGITS BELOW ZERO. COOL HIGH PRESSURE WILL REMAIN OVER THE
AREA ON TUESDAY PROVIDING PARTLY SUNNY SKIES AND HIGHS MAINLY IN THE
TEENS. A POTENT UPPER TROUGH IS EXPECTED TO MOVE ACROSS THE SOUTHERN
PLAINS TUESDAY AND HEAD TOWARDS THE LOWER TO MIDDLE MISSISSIPPI
RIVER VALLEY.
.LONG TERM...TUESDAY NIGHT THROUGH SATURDAY
247 PM CST SAT DEC 22 2012
22.12 MEDIUM RANGE MODELS ARE IN REASONABLE AGREEMENT TUESDAY NIGHT
INTO WEDNESDAY SHOWING THE SOUTHERN STREAM TROUGH LIFTING NORTH INTO
THE OHIO RIVER VALLEY AND CLOSING INTO AN UPPER LOW. THIS SYSTEM IS
EXPECTED TO REMAIN WELL TO THE EAST OF THE AREA AS IT LIFTS INTO NEW
ENGLAND WEDNESDAY NIGHT INTO THURSDAY. HIGH PRESSURE WILL MAINTAIN
COOL AND QUIET WEATHER THROUGH THURSDAY WITH HIGHS IN THE TEENS AND
LOWS RANGING FROM THE SINGLE DIGITS BELOW ZERO TO SINGLE DIGITS
ABOVE ZERO. ANOTHER TROUGH WILL CROSS THE ROCKIES ONT THURSDAY AND
MOVE INTO THE PLAINS DURING THE DAY ON FRIDAY. FORECAST MODELS START
TO DIVERGE FRIDAY INTO SATURDAY ON THE EVOLUTION OF THIS TROUGH. THE
ECMWF CONTINUES TO WRAP THIS SYSTEM INTO AN UPPER LOW AS IT LIFTS
INTO THE GREAT LAKES AND MERGES WITH A TROUGH MOVING SOUTHEAST
ACROSS SOUTHERN ALBERTA/SASKATCHEWAN. THE ECMWF SOLUTION WOULD BRING
A PROLONGED PERIOD OF LIGHT SNOW TO THE FORECAST AREA. THE GFS KEEPS
THESE TWO SYSTEMS FROM MERGING AND BRINGS THE NORTHERN STREAM TROUGH
ACROSS THE FORECAST AREA DURING THE DAY ON SATURDAY. GIVEN THE
VARYING MODEL SOLUTIONS DECIDED TO LEAN TOWARD A MODEL CONSENSUS
BLEND APPROACH WITH CHANCES FOR LIGHT SNOW FRIDAY THROUGH
SATURDAY.
&&
.AVIATION...THIS AFTERNOON THROUGH SUNDAY
1133 AM CST SAT DEC 22 2012
GOOD VFR CONDITIONS WILL CONTINUE THIS AFTERNOON INTO THIS
EVENING...EVEN AS A WEAK TROUGH SLIDES SOUTHEAST ACROSS THE REGION.
MAIN IMPACT WITH THIS FEATURE WILL BE A WIND SHIFT FROM LIGHT SOUTH
TO LIGHT NORTHWEST AND NORTH. MODELS CONTINUE TO SHOW AND INCREASE
OF VERY LOW LEVEL MOISTURE ACROSS THE AREA TONIGHT BEHIND THE
TROUGH...TRAPPED IN/UNDER A STRONG SFC-850MB INVERSION. MODELS PROG
THIS MOISTURE IN THE SFC-950MB LAYER...ON/NEAR SFC. NEAREST LOW
CLOUDS BEHIND THE TROUGH AT MID-DAY ARE IN NORTHERN ND. SUSPECT
MODELS ARE LOADING THE LOWEST LEVELS WITH SUBLIMATION MOISTURE FROM
THE SNOW COVER...WHICH IS THEN TRAPPED UNDER THE STRONG INVERSION.
LIMITED MENTION OF THIS MOISTURE TO SCT010-012 STRATO-CU CLOUDS IN
THE 03Z TO 10-12Z TIME-FRAME WHEN SKIES ABOVE WILL BE SCT200 OR
LESS...AND SOME MVFR VSBYS IN BR AT KRST FOR A FEW HOURS CENTERED ON
12Z SUN.
INCREASING HIGH LEVEL MOISTURE/THICKENING CIRRUS SPREAD EAST ACROSS
THE AREA LATE TONIGHT AND FOR SUN. ONCE THIS BKN-OVC CIRRUS DECK
MOVES IN LATE TONIGHT...ANY LOWER LEVEL STRATO-CU SHOULD DISSIPATE
BUT BR AT KRST WOULD BE A BIT MORE PERSISTENT INTO THE MID MORNING
HOURS. REMAINDER OF SUNDAY LOOKS VFR WITH BKN-OVC150-200 CIGS.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
247 PM CST SAT DEC 22 2012
WI...NONE.
MN...NONE.
IA...NONE.
&&
$$
SHORT TERM...WETENKAMP
LONG TERM...WETENKAMP
AVIATION.....RRS
AREA FORECAST DISCUSSION
NWS LA CROSSE WI
1133 AM CST SAT DEC 22 2012
.SHORT TERM...TODAY THROUGH MONDAY NIGHT
233 AM CST SAT DEC 22 2012
MAIN FORECAST CONCERNS ARE ON LOW CLOUD POTENTIAL TONIGHT INTO
SUNDAY AND POTENTIAL FOR SOME LIGHT SNOW SUNDAY NIGHT INTO MONDAY.
CURRENTLY AS OF 08Z...WATER VAPOR LOOP AND RAP 500MB HEIGHT ANALYSIS
SHOWED DEEP TROUGHING APPROACHING THE WESTERN U.S. COAST...RIDGING
ACROSS THE PLAINS AND DEEP TROUGHING ALONG THE U.S. EAST COAST. ON
TOP OF THE RIDGE...A SHORTWAVE WAS PRESENT ACROSS CENTRAL PORTIONS
OF SASKATCHEWAN AND MANITOBA. THE FORECAST AREA LIES CLOSER TO THE
INFLECTION POINT BETWEEN THE RIDGE AND EAST COAST TROUGH...YIELDING
HIGH PRESSURE AT THE SURFACE. OTHER THAN SOME SCATTERED HIGH CLOUDS
ASSOCIATED WITH A COMBINATION OF PACIFIC MOISTURE TOPPING THE RIDGE
AND A 100 KT JET NEAR THE TROPOPAUSE...SKIES WERE MOSTLY CLEAR
ACROSS THE FORECAST AREA. DRY AIR AND SUBSIDENCE SEEN ON THE 00Z
ABR...MPX AND DVN SOUNDINGS ARE HELPING TO PRODUCE THE MOSTLY CLEAR
SKIES. WITH LIGHT WINDS UNDER THE SURFACE RIDGE AND THE FRESH SNOW
COVER...TEMPERATURES HAVE MOSTLY FALLEN INTO THE SINGLE DIGITS ABOVE
ZERO. BLACK RIVER FALLS AND SPARTA HAVE EVEN DROPPED BELOW ZERO. TO
THE NORTHWEST...A COLD FRONT WAS LOCATED OVER MANITOBA AND THE
DAKOTAS ASSOCIATED WITH THE SOUTH CENTRAL CANADA SHORTWAVE. LOW
CLOUDS WERE PRESENT ACROSS SOUTH CENTRAL CANADA AS WELL BEHIND THE
FRONT.
TODAY AND TONIGHT...THE SHORTWAVE SEEN OVER SOUTH CENTRAL CANADA IS
PROGGED TO SLIDE SOUTHEAST ACROSS EASTERN LAKE SUPERIOR THIS
EVENING...DRIVING THE COLD FRONT ACROSS THE DAKOTAS THROUGH THE
FORECAST AREA. NO PRECIPITATION IS EXPECTED WITH OR BEHIND THE FRONT
GIVEN THE DRY AIRMASS PRESENT...AS WELL AS ALL THE FORCING LOCATED
WELL NORTHEAST OF THE AREA. MAIN CONCERNS WITH THE FRONT IS THE
WARMING AHEAD OF IT AND IF ANY LOW CLOUDS COME IN BEHIND IT.
REGARDING THE WARMING...GFS/NAM/ECMWF 925MB TEMPERATURE PROGS SHOW
THEM CLIMBING FROM -3 TO -6C CURRENTLY TO -2 TO -4C. WITH SOME SUN
THROUGH HIGH CLOUDS AND A SOUTHWEST BREEZE...TEMPERATURES SHOULD
EASILY CLIMB INTO THE 20S EVERYWHERE. SOME LOCATIONS IN WISCONSIN...
PARTICULARLY IN VALLEY AREAS...COULD EXCEED 30 THANKS TO LOWER
ALBEDO PRESENT. DECENT COLD ADVECTION LOOKS TO OCCUR TONIGHT BEHIND
THE FRONT AS 925MB TEMPS FALL TO -6 TO -10C BY 12Z SUNDAY ON 15-20
KT NORTHERLY BREEZE. CERTAINLY LOOKS GOOD FOR LAKE EFFECT OFF
SUPERIOR WHICH THE BREEZE WOULD THEN SEND THE CLOUDS SOUTHWARD AT
LEAST INTO THE NORTHERN HALF OF WISCONSIN AFTER MIDNIGHT. IN
ADDITION...SOME OF THE LOW CLOUDS IN GENERAL BEHIND THE FRONT COULD
END UP BEING SENT SOUTH. AS A RESULT...HAVE RAISED CLOUD COVER...
ESPECIALLY ACROSS TAYLOR AND CLARK COUNTIES GIVEN THE BETTER CHANCE
OF BEING IMPACTED BY LAKE EFFECT CLOUDS. GIVEN CLOUDS AND THE WINDS
BEHIND THE FRONT...FOLLOWED A BLEND OF GUIDANCE FOR LOWS.
SUNDAY AND SUNDAY NIGHT...FOCUS SHIFTS TO THE TROUGHING APPROACHING
THE WEST COAST. MODELS TAKE A FAIRLY SIGNIFICANT PORTION OF THE
TROUGH CROSSING THE NORTHERN ROCKIES DURING THE NEXT 24 TO 36 HOURS.
THE QUESTION IS WHAT HAPPENS WITH THE TROUGH FROM THERE. THE 22.00Z
NAM/UKMET ARE A WEAKER SCENARIO WITH THE TROUGH...STRETCHING FROM
NORTHEAST SOUTH DAKOTA INTO CENTRAL IOWA BY 12Z MONDAY.
MEANWHILE...THE 22.00Z GFS/CANADIAN DEPICT A MORE POTENT TROUGH THAT
ENDS UP CROSSING NEBRASKA AND BECOMING SITUATED DOWN IN SOUTHERN
IOWA INTO THE ST LOUIS AREA BY 12Z MONDAY. ALL SCENARIOS YIELD AN
INVERTED TROUGH AT THE SURFACE...JUST THE MORE POTENT GFS/CANADIAN
GROUP WOULD HAVE A BETTER SHOT OF YIELDING PRECIPITATION
DEVELOPMENT. GIVEN THE STRENGTH OF THE TROUGH RIGHT NOW OFF THE WEST
COAST...NOTED TOO BY NUMEROUS LIGHTNING STRIKES...WILL FAVOR THE
MORE POTENT GROUP. THIS MEANS 20 PERCENT CHANCES ARE NEEDED AFTER
MIDNIGHT SUNDAY NIGHT WEST OF THE MISSISSIPPI RIVER TO ACCOUNT FOR
THE DPVA AHEAD OF THE POTENT TROUGH...AS WELL AS ISENTROPIC LIFT.
DID NOT GO HIGHER THAN 20 BECAUSE OF INITIAL DRY AIR TO OVERCOME
SINCE THE SNOW THAT DOES FALL WILL COME OUT OF A MID CLOUD DECK.
OTHERWISE...THE ONLY OTHER CONCERN IS CLOUD COVER. THE LOW CLOUDS
OVER NORTHERN WI AT 12Z SUNDAY COULD END UP EXPANDING SOUTHWESTWARD
THROUGH THE DAY...WHILE MID AND HIGH CLOUDS INCREASE DOWNSTREAM OF
THE POTENT TROUGH. THUS AN INCREASING CLOUD TREND SEEMS APPROPRIATE.
THESE CLOUDS PLUS COLDER 925MB TEMPS IN THE -8 TO -10C RANGE WILL
DEFINITELY YIELD A COLDER DAY. ON THE POSITIVE SIDE...THE CLOUDS
SHOULD HELP HOLD TEMPERATURES UP SUNDAY NIGHT.
MONDAY INTO MONDAY NIGHT...FOLLOWING THE MORE POTENT TROUGH LOOK AS
MENTIONED IN THE SUNDAY/SUNDAY NIGHT DISCUSSION...THE GFS AND
CANADIAN SEND THE TROUGH SOUTHEAST INTO OHIO BY 00Z TUESDAY. CHANCES
OF SNOW STILL LOOK APPROPRIATE FOR MONDAY WITH ISENTROPIC LIFT AND
DPVA PERSISTING...THOUGH THIS SHOULD BE DIMINISHING IN THE AFTERNOON
AS THE TROUGH SHIFTS EAST AND CANADIAN HIGH PRESSURE BUILDS SOUTH
INTO THE DAKOTAS IN ITS WAKE. AS SUCH...MONDAY NIGHT IS LIKELY TO
END UP DRY. REGARDING THE ACTUAL CHANCES...LINGERING LOWER LEVEL DRY
AIR IS A BIG CONCERN...AS WELL AS THE TRACK OF THE TROUGH DROPPING
MORE TO OUR SOUTH. AS A RESULT...KEPT CHANCES IN A 20-30 RANGE.
LOOKS GOOD FOR MOST OF THE AREA TO PICK UP A LITTLE SNOW...BE IT
ACTUAL ACCUMULATING SNOW OR FLURRIES...SO USED OCCASIONAL VERY LIGHT
SNOW VERBIAGE. GIVEN CANADIAN HIGH PRESSURE BUILDING SOUTH...ONE CAN
EXPECT COLDER LOW LEVEL AIR. THIS IS VERY WELL REPRESENTED BY 925MB
TEMPS WHICH FALL TO -10 TO -14C BY 00Z TUESDAY AND -12 TO -14C TO
START OFF CHRISTMAS MORNING. TRENDED BOTH HIGHS AND LOWS COLDER...
CLOSER TO GUIDANCE.
.LONG TERM...CHRISTMAS DAY THROUGH FRIDAY NIGHT
233 AM CST SAT DEC 22 2012
GOOD AGREEMENT CONTINUES FROM YESTERDAY ON THE GENERAL UPPER LEVEL
PATTERN THROUGH THE LONG TERM PERIOD. 22.00Z ECMWF/GFS/CANADIAN AND
UKMET CONTINUE TO SHOW A STRONG TROUGH AND STORM SYSTEM TRACKING
FROM THE SOUTHERN PLAINS ON TUESDAY INTO THE MID-ATLANTIC REGION BY
EARLY THURSDAY. THE FORECAST AREA REMAINS PLENTY FAR AWAY FROM THIS
SYSTEM...KEEPING US IN SUBSIDENCE AND MORE UNDER THE INFLUENCE OF
CANADIAN HIGH PRESSURE. IN FACT...THIS PERIOD FROM CHRISTMAS DAY
THROUGH WEDNESDAY NIGHT LOOKS SEASONABLY COOL...DUE TO 925MB TEMPS
REMAINING BETWEEN -10 AND -14C. WILL REALLY HAVE TO WATCH LOW
TEMPERATURES FOR CLEAR SKIES AND LIGHT WINDS...AS THE SNOW COVER NOW
IN PLACE FAVORS PLUMMETING. HAVE ADJUSTED BOTH HIGH AND LOW
TEMPERATURES DOWNWARD FROM THE PREVIOUS FORECAST ABOUT 5 DEGREES OR
SO...BUT FURTHER LOWERING MAY BE NEEDED...ESPECIALLY WITH LOWS. FOR
THURSDAY ONWARDS...ANOTHER DEEP TROUGH IS PROGGED TO FORM OVER THE
SOUTHWESTERN U.S...BUT THIS ONE GETS EJECTED NORTHEASTWARD TOWARDS
THE FORECAST AREA FOR FRIDAY AND INTO THE WEEKEND. AT THIS POINT
THERE DOES NOT APPEAR TO BE ANY BIG STORM PER SE WITH THIS
TROUGH...BUT SOME WARM ADVECTION SNOW IS SUGGESTED FOR FRIDAY INTO
FRIDAY NIGHT. THUS...30-40 PERCENT CHANCES OF PRECIPITATION ARE IN
THE FORECAST. THE APPROACH OF THE TROUGH SHOULD ALSO HELP TO BRING
WARMER AIR INTO THE FORECAST AREA...AND THIS IS NOTED BY 925MB TEMPS
PROGGED TO CLIMB TO -8 TO -10C AT 00Z FRIDAY AND -6 TO -9C AT 00Z
SATURDAY. FOLLOWED MODEL CONSENSUS FOR HIGHS AND LOWS FROM THURSDAY
ONWARDS...WHICH BRINGS TEMPERATURES BACK UP TO NORMAL FOR FRIDAY.
&&
.AVIATION...THIS AFTERNOON THROUGH SUNDAY
1133 AM CST SAT DEC 22 2012
GOOD VFR CONDITIONS WILL CONTINUE THIS AFTERNOON INTO THIS
EVENING...EVEN AS A WEAK TROUGH SLIDES SOUTHEAST ACROSS THE REGION.
MAIN IMPACT WITH THIS FEATURE WILL BE A WIND SHIFT FROM LIGHT SOUTH
TO LIGHT NORTHWEST AND NORTH. MODELS CONTINUE TO SHOW AND INCREASE
OF VERY LOW LEVEL MOISTURE ACROSS THE AREA TONIGHT BEHIND THE
TROUGH...TRAPPED IN/UNDER A STRONG SFC-850MB INVERSION. MODELS PROG
THIS MOISTURE IN THE SFC-950MB LAYER...ON/NEAR SFC. NEAREST LOW
CLOUDS BEHIND THE TROUGH AT MID-DAY ARE IN NORTHERN ND. SUSPECT
MODELS ARE LOADING THE LOWEST LEVELS WITH SUBLIMATION MOISTURE FROM
THE SNOW COVER...WHICH IS THEN TRAPPED UNDER THE STRONG INVERSION.
LIMITED MENTION OF THIS MOISTURE TO SCT010-012 STRATO-CU CLOUDS IN
THE 03Z TO 10-12Z TIME-FRAME WHEN SKIES ABOVE WILL BE SCT200 OR
LESS...AND SOME MVFR VSBYS IN BR AT KRST FOR A FEW HOURS CENTERED ON
12Z SUN.
INCREASING HIGH LEVEL MOISTURE/THICKENING CIRRUS SPREAD EAST ACROSS
THE AREA LATE TONIGHT AND FOR SUN. ONCE THIS BKN-OVC CIRRUS DECK
MOVES IN LATE TONIGHT...ANY LOWER LEVEL STRATO-CU SHOULD DISSIPATE
BUT BR AT KRST WOULD BE A BIT MORE PERSISTENT INTO THE MID MORNING
HOURS. REMAINDER OF SUNDAY LOOKS VFR WITH BKN-OVC150-200 CIGS.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
233 AM CST SAT DEC 22 2012
WI...NONE.
MN...NONE.
IA...NONE.
&&
$$
SHORT TERM...AJ
LONG TERM....AJ
AVIATION.....RRS