Forecast Discussions mentioning any of "HRRR" "RAP" "RR" "RUC13" "RUC" received at GSD on 09/04/12


AREA FORECAST DISCUSSION...UPDATED
NWS PHOENIX AZ
515 PM MST MON SEP 3 2012 .UPDATE... UPDATED AVIATION SECTION. && .SYNOPSIS... HIGH PRESSURE ALOFT WILL REMAIN CENTERED OVER OR NEAR NEW MEXICO THROUGH MUCH OF THE UPCOMING WEEK. VERY MOIST AND MODERATELY UNSTABLE AIR WILL OVERSPREAD THE AREA...WHILE WEAK WEATHER DISTURBANCES PERIODICALLY MOVE WEST ACROSS NORTHERN MEXICO. AS A RESULT...EXPECT A RATHER ACTIVE PERIOD OF WEATHER THIS WEEK...WITH AN ABOVE NORMAL CHANCE FOR MAINLY LATE AFTERNOON AND EVENING THUNDERSTORMS. LOCALLY HEAVY RAINFALL AND STRONG WINDS ARE LIKELY WITH THE MORE INTENSE STORMS. && .DISCUSSION ISSUED 300 PM... LATEST RAP ANALYZED A DIFFUSE TROUGH EXTENDING FROM SOUTHERN NM TO HERMOSILLO MEXICO...THOUGH THIS IS DIFFICULT TO IDENTIFY ON WV IMAGERY. STRONG STORMS HAVE DEVELOPED IN THE DIFLUENT REGION BETWEEN THIS TROUGH AND AN ANTICYCLONE CENTERED NEAR THE WHITE MOUNTAINS. FURTHER NORTH ACROSS THE MOGOLLON RIM...OROGRAPHICALLY-INDUCED SHOWERS AND THUNDERSTORMS HAVE ALSO FORMED BUT CONTINUE TO DRIFT NORTHEASTWARD TOWARDS THE CO PLATEAU WITHIN A 10 KT MEAN LAYER FLOW. EARLIER MOISTURE SURGE ALONG THE GOC AND ACROSS YUMA AND THE IMPERIAL VALLEY YIELDED HEAT INDICES BETWEEN 110 AND 115 DEGREES...BUT HAVE SINCE LOWERED AS THE ATMOSPHERE MIXES OUT. LATEST MESOANALYSIS SHOWS MODERATELY STRONG CONVECTIVE INHIBITION ACROSS MUCH OF THE FORECAST AREA...LARGELY DUE TO A RIDGE AND THE ASSOCIATED WARM/DRY AIR IN THE 800-700 MB LAYER. MODEL SOUNDINGS INDICATE THAT THIS LAYER WILL MOISTEN ACROSS WESTERN AZ THIS AFTERNOON...WHICH WILL HELP TO ERODE THE CIN AND INITIATE ISOLATED CONVECTION. NMM-B BASED WRF FROM UNIV OF AZ APPEARS TO HAVE THE BEST HANDLE ON THE SHORT-TERM EVOLUTION AND SUGGESTS STORMS WILL FIRE ACROSS YUMA AND LA PAZ COUNTIES THIS AFTERNOON. ISOLATED ACTIVITY IN THE IMPERIAL VALLEY ALSO CANNOT BE RULED OUT...GIVEN THE SOUTHWESTERLY STEERING FLOW AND PRESENCE OF CB/TCU ON VISIBLE SATELLITE ALONG THE BAJA SPINE. ACROSS THE PHOENIX METRO AREA...THE MAIN IMPACT APPEARS TO BE THE POTENTIAL BLOWING DUST FROM THUNDERSTORMS TO THE SOUTH...THOUGH POPS REMAIN 5 TO 10 PERCENT ABOVE THE CLIMATOLOGICAL AVERAGE. && .PREVIOUS DISCUSSION ISSUED 425 AM... IN THE SHORT TERM (MONDAY-WEDNESDAY)...EXPECT A DAY TO DAY INCREASE IN STORM ACTIVITY...ESPECIALLY OVER AZ PORTION OF THE CWA. VERY MOIST AIR MASS CURRENTLY EXISTS OVER NORTHWEST MEXICO. SYNOPTIC PATTERN...WITH RATHER STRONG TROUGH OF LOW PRESSURE MOVING EAST ACROSS SOUTH-CENTRAL CANADA WHILE A TROPICAL DISTURBANCE (NOW TS JOHN) MOVES WEST JUST OFF THE SOUTHERN END OF BAJA CALIFORNIA...CERTAINLY SUPPORTS A MOISTURE INCREASE OVER OUR AREA...AND THE GFS/ECMWF/NAM CERTAINLY AGREE THE ATMOSPHERE WILL MOISTEN SIGNIFICANTLY DURING THE NEXT 36 HRS. WITH ATMOSPHERIC MOISTENING CONTINUING ON TUESDAY (ANOMALOUSLY HIGH PRECIPITABLE WATER NEAR 2" BY THEN) AND MORE DIFLUENT UPPER LEVEL FLOW OVER SOUTHEAST AZ BY TUESDAY AFTN...PRECIP CHANCE WILL BE A BIT GREATER TUESDAY EVENING...ESPECIALLY OVER SOUTH-CENTRAL AZ. VERY MOIST AND MODERATELY UNSTABLE ATMOSPHERE REMAINS IN PLACE ON WEDNESDAY...AND PRECIP CHANCES WILL BE ENHANCED AS A WEAK WEATHER DISTURBANCE MOVES WEST ACROSS SONORA. WITH SUCH HIGH ATMOSPHERIC MOISTURE CONTENT...DECENT CAPE...AND WEAK STEERING FLOW...LOCALLY HEAVY RAINFALL CAN BE EXPECTED...THOUGH STRONG/DAMAGING WINDS WILL ALSO BE POSSIBLE. IN THE EXTENDED PERIOD(THURSDAY-SUNDAY)...NUMERICAL MODELS INDICATE ATMOSPHERE WILL REMAIN ANOMALOUSLY MOIST AND MODERATELY UNSTABLE WHILE WEAK WEATHER DISTURBANCE CONTINUE TO AFFECT THE DESERT SOUTHWEST. WENT WITH SLIGHT CHANCE POPS DURING THE LATE AFTN/EVENING HOURS FOR SOUTH-CENTRAL AZ EACH DAY...BUT WOULD NOT BE SURPRISED IF PRECIP CHANCES WILL ACTUALLY BE SOMEWHAT HIGHER THAN CURRENTLY PORTRAYED. && .AVIATION... SOUTH-CENTRAL ARIZONA...INCLUDING KPHX...KIWA...AND KSDL... LACK OF STORM ACTIVITY OVER THE CENTRAL DESERTS SUGGESTS A CAP IS HINDERING DEVELOPMENT AND THUS IT WILL BE DIFFICULT FOR OUTFLOWS TO AFFECT THE PHOENIX AREA THIS EVENING LET ALONE HAVE TSTMS DIRECTLY HIT THE TAF SITES...THOUGH NOT IMPOSSIBLE. THERE IS AN OUTSIDE POSSIBILITY OF STORMS FROM LA PAZ GENERATING NEW STORMS OVER MARICOPA COUNTY BUT TOO LOW TO REFLECT IN THE TAFS. OTHERWISE EXPECT WEST WINDS THROUGH THE EVENING BEFORE SLOWLY BECOMING DOWNVALLEY LATE TONIGHT. SOUTHEAST CA AND SOUTHWEST AZ...INCLUDING KIPL AND KBLH... STORMS OVER LA PAZ COUNTY WILL HAVE A GOOD CHANCE OF PRODUCING OUTFLOW THAT REACHES KBLH BY 01Z AND PRODUCES NEW STORMS WITHIN THE VICINITY OF THE AIRFIELD. HAVE HELD OFF INSERTING TEMPO TSRA FOR NOW BUT THIS WILL NEED TO BE WATCHED CLOSELY. KIPL WILL BE LESS LIKELY TO BE AFFECTED BY STORMS AS INDICATED BY DISSIPATION OF STORMS OVER NORTHERN BAJA. OTHERWISE...EXPECT SOUTH AND SOUTHEAST WINDS TO CONTINUE. AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS. && .FIRE WEATHER... THURSDAY THROUGH MONDAY... SIGNIFICANT MONSOON MOISTURE WILL COVER THE REGION. A SLIGHT CHANCE OF AFTERNOON AND EVENING THUNDERSTORMS WILL CONTINUE MAINLY OVER SOUTH CENTRAL ARIZONA...PARTICULARLY MOUNTAINS. MINIMUM RELATIVE HUMIDITIES WILL RANGE FROM 20 TO 25 PERCENT...EXCEPT 15 TO 20 PERCENT IN IN SOUTHEAST CALIFORNIA. RELATIVELY LIGHT WINDS ARE EXPECTED. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...NONE. CA...NONE. && $$ VISIT US ON FACEBOOK...TWITTER...AND AT WEATHER.GOV/PHOENIX DISCUSSION...HIRSCH PREVIOUS DISCUSSION...DG AVIATION...AJ FIRE WEATHER...VASQUEZ
AREA FORECAST DISCUSSION
NWS DENVER CO
259 PM MDT SUN SEP 2 2012 .SHORT TERM...DURING THE NEXT FEW HOURS SHOULD SEE A STEADY INCREASE IN SHOWER/T-STORM FORMATION OVER THE MTNS AND HIGH VALLEYS. THIS INCREASE IN CONVECTION IS IN RESPONSE TO A REGION OF MID/UPPER LEVEL LIFT/INSTABILITY GENERATED ON THE NOSE OF 40-50KT 300-500MB JET MAXIMA DARTING NORTHEASTWARD ACROSS SOUTHEAST UTAH AT THE MOMENT. AT ITS PRESENT SPEED SHOULD SEE THIS WEATHER MAKER REACHING THE FRONT RANGE URBAN CORRIDOR/DENVER METRO AREA AROUND 00Z THIS EVENING. MODELS INDICATE GENERALLY LIGHT QPF ON THE NORTHEAST PLAINS DURING THE EVENING HOURS AS THIS JET MAX AND WEAK QG ASCENT PASS OVERHEAD. WRF SYNTHETIC IR CLOUD MODEL SHOWS A FAIRLY THICK SOUTHWEST-NORTHEAST SWATH OF CLOUD COVER ACROSS THE FORECAST AREA PRETTY MUCH ALL EVENING....AND OVER THE FAR NORTHEAST COUNTIES THROUGH THE EARLY MORNING HOURS. THIS MATCHES UP WELL WITH 700-500MB RH FIELDS OF THE NAM...GFS...EC AND HI RES MODELS. CURRENT FORECAST GRIDS INDICATE SCATTERED POPS IN THE HIGH COUNTRY...WITH THE HIGHER PRECIP CHANCES ROUGHLY SOUTH OF I-70. ON THE PLAINS 10-20 PERCENT POPS PREVAIL...ALTHOUGH THE HRRR AND HI RES MODEL REFLECTIVITY FIELDS INDICATE A LINE OF STORMS FORMING IN MORGAN...EASTERN ADAMS...EASTERN ARAPAHOE AND EASTERN ELBERT COUNTIES BETWEEN 00-03Z...THEN MOVING EAST INTO WASHINGTON AND LINCOLN COUNTIES AS THE EVENING GOES ON. STORMS APPEAR TO FORM ALONG A WIND SHEER AXIS IN THE AREA. SHOULD THIS HAPPEN...NO DOUBT PRECIP CHANCES WOULD NEED TO BE REVISED UPWARD IN THIS AREA. BY LATE TONIGHT....THE WAVE MOVES EAST OF THE STATE AS THE SOUTHWESTERLY FLOW ALOFT TRANSITIONS MORE TO A WESTERLY COMPONENT. THE SHIFT IN WINDS ALOFT APPEAR TO MIX DOWN MONDAY MORNING CAUSING DRYING ALONG THE EAST FACE OF THE FRONT RANGE...PARTICULARLY UP NEAR THE WYOMING BORDER. DURING THE DAY...COULD SEE ISOLATED STORMS FORMING ALONG THE PALMER RIDGE AND HIGHER AREAS ACROSS SOUTHERN PORTIONS OF THE CWFA DURING THE AFTERNOON HOURS WITH WEAK UPSLOPE FLOW WITH NORTHERLY BOUNDARY LAYER FLOW. OTHERWISE A DRIER DAY WITH TEMPERATURE SIMILAR OR SLIGHTLY COOLER THAN TODAY. .LONG TERM...ON MONDAY NIGHT NIGHT...UPPER LEVEL HIGH PRESSURE IS CENTERED OVER WEST TEXAS...WITH AN UPPER LEVEL TROUGH OF LOW PRESSURE OVER THE NORTHERN ROCKIES. COLORADO LIES BETWEEN TWO SYSTEMS UNDER THE INFLUENCE OF A WESTERLY FLOW ALOFT. BOTH THE NAM AND THE GFS SHOW A 60 KT JET OVER NORTHEASTERN COLORADO...HOWEVER ACCORDING TO THE MODELS...VERY LITTLE QG IS ASSOCIATED WITH THE JET. AS FOR MOISTURE...MODELS SHOW THAT THE MOUNTAINS ARE VERY DRY WITH PW`S LESS THAN ONE HALF INCH...WITH PW`S FROM THREE QUARTERS OF AN INCH TO AN INCH EAST OF THE MOUNTAINS. NAM AND GFS SOUNDINGS SHOW CAPE VALUES UNDER 300 J/KG...WITH DEWPOINTS IN THE 40S....AND SOME MID LEVEL MOISTURE BETWEEN 500 AND 600 MILLIBARS. BOTH THE NAM AND GFS ARE ALSO SHOWING LIGHT PRECIPITATION MOVING ACROSS NORTHEASTERN COLORADO MAINLY SOUTH OF INTERSTATE 76 DURING THE LATE EVENING AND OVERNIGHT. LOOKS LIKE THE BEST CHANCE FOR ANY PRECIPITATION WOULD BE OVER THE PALMER DIVIDE...THEREFORE I HAVE INCREASED POPS SLIGHTLY THERE. DUE TO THE INVERTED V SOUNDINGS...I WOULD SUSPECT ANY STORMS WOULD BE PRODUCE MAINLY LIGHT RAIN AND GUSTY WINDS. ON TUESDAY INTO WEDNESDAY...DRIER AIR SPREADS ACROSS ALL OF NORTHEASTERN COLORADO...ENDING ANY CHANCES OF PRECIPITATION ACROSS THE CWA...WITH THE EXCEPTION OF PORTIONS OF THE CENTRAL MOUNTAINS MAINLY SOUTH OF INTERSTATE 70. WEDNESDAY NIGHT AND INTO THURSDAY...AN UPPER LEVEL TROUGH DROPPING INTO THE NORTHERN ROCKIES WILL INDUCE A WEAK RIDGE OVER COLORADO. THIS WILL PUSH TEMPERATURES ABOVE NORMAL AGAIN WITH A JUST A SLIGHT CHANCE FOR SHOWERS AND THUNDERSTORMS DURING THE AFTERNOON AND EVENING HOURS. AS THE UPPER LEVEL TROUGH MOVES EAST OVER THE NORTHERN PLAINS IT WILL PUSH A COLD FRONT THROUGH COLORADO THURSDAY NIGHT. THIS WILL USHER IN COOLER AIR FOR FRIDAY AND SATURDAY. NOT MUCH MOISTURE BEHIND THE FRONT...SO WILL KEEP POPS LOW FOR NOW. IF ANY PRECIPITATION DEVELOPS...IT IS EXPECTED TO BE LIGHT AND OCCUR FRIDAY. SURFACE HIGH BEHIND THE FRONT WILL DRIFT SOUTH OVER COLORADO FRIDAY. THE CLEAR SKIES COMBINED WITH THE COOL AND DRY AIRMASS WILL LEAD TO COOL OVERNIGHT LOWS FRIDAY NIGHT. ON SUNDAY...UPPER LEVEL RIDGE WILL BE OVER THE FOUR CORNERS. THIS WILL SEND WARMER AIR BACK INTO COLORADO WITH HIGHS CLIMBING BACK INTO THE 80S. && .AVIATION...VFR CONDITIONS IN THE DENVER AREA THROUGH 00Z TODAY. AFTER 00Z THIS EVENING...ISOLATED SHOWERS AND THUNDERSTORMS MOVING OFF THE FRONT RANGE AND FORMING IN THE DENVER AREA COULD LOWER CEILINGS TO AROUND 6000 FT AGL FOR SHORT PERIODS OF TIME. THERE IS ALSO A SLIGHT CHANCE THAT MODERATE RAINFALL FROM PASSING STORMS COULD BRIEFLY REDUCE VISIBILITIES TO 5 MILES. IMPROVEMENT SHOULD OCCUR AFTER 04Z THIS EVENING WITH DRIER AIR MOVING DOWN OFF THE FOOTHILLS. ON MONDAY...VFR CONDITIONS ARE ANTICIPATED ALL DAY...HOWEVER THERE IS A SLIGHT CHANCE OF A LIGHT SHOWERS OR WEAK T-STORM IN THE DENVER AREA AFTER 2 PM MDT. && .HYDROLOGY...THERE IS A CHANCE THAT THE FRONT RANGE BURN SCARS COULD SEE A FEW SHOWERS AND THUNDERSTORMS THIS EVENING WITH PASSAGE OF A WEAK UPPER LEVEL WEATHER DISTURBANCE. THE STRONGER STORMS MAY PRODUCE UP TO 0.30 INCH OF RAIN IN UNDER 35 MINUTES. WHILE FLASH FLOODING IS NOT ANTICIPATED...THE BRIEF HEAVY RAINFALL COULD CAUSE MINOR RISES IN CREEKS AND SMALL STREAMS AS WELL AS SOME MUDDY RUNOFF. THIS SHOWERY PRECIPITATION SHOULD COME TO AN END BY MIDNIGHT. ON MONDAY THERE ISA A SLIGHT CHANCE OF THUNDERSTORMS AFTER 3 PM. ANY RAINFALL SHOULD BE LIGHT...GENERALLY UNDER A TENTH OF AN INCH. && .BOU WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...BAKER LONG TERM....KALINA/MEIER AVIATION...BAKER
AREA FORECAST DISCUSSION
NWS DENVER CO
1105 AM MDT SUN SEP 2 2012 .UPDATE AND CORRECTION...FOR MINOR CHANGES TO FIRST AND SECOND PERIODS AND TO CORRECT TIMES IN AVIATION DISCUSSION - 2ND PARAGRAPH && .SHORT TERM...PLAN TO MAKE FEW CHANGES TO ONGOING FORECAST AT THIS TIME. PROBABLY THE BIGGEST CHANGE WAS TO ADJUST SKY COVERAGE TO BETTER REFLECT THE PASSING BAND OF MID/HIGH LEVEL CLOUDS. STILL EXPECT TO SEE THE BATCH OF CLOUDS AND PRECIP PRESENTLY NEAR THE 4-CORNERS TO RACE NORTHEAST OVER SOUTHERN AND EASTERN PORTIONS OF THE FORECAST AREA LATER THIS AFTERNOON AND EVENING. LOW POPS STILL ON TRACK WITH THE BETTER ODDS FOR MEASURABLE PRECIP IN MTN AREAS ROUGHLY SOUTH OF INTERSTATE 70. CURRENT TEMPERATURE FCST LOOKS OKAY...BUT MAY NEED TO LOWER A DEG OR TWO SHOULD CLOUDS INCREASE EARLIER THAN EXPECTED. .AVIATION...VFR CONDITIONS AT DENVER AREA AIRPORT THROUGH 21Z TODAY. AFTER 21Z...ISOLATED SHOWERS AND T-STORMS FORMING OVER THE FRONT RANGE ARE EXPECTED TO DRIFT NORTHEAST OVER PORTIONS OF THE DENVER METRO AREA. ADDITIONAL STORM FORMATION WILL BE POSSIBLE ALONG OUTFLOW BOUNDARIES MOVING EAST OF THE DENVER AREA AFTER 22Z. PRECIP AMOUNTS IN THE DENVER AREA SHOULD BE ON THE LOW SIDE...GENERALLY UNDER A TENTH OF AN INCH. SHOWERY PRECIP IN MOST INSTANCES NOT EXPECTED TO LOWER VISIBILITIES BELOW 6 MILES. MOST OF THIS STORM ACTIVITY IS EXPECTED TO SHIFT EAST OF THE METRO AREA AFTER 02Z WITH GRADUAL CLEARING OVERNIGHT. LIGHT AND VARIABLE SURFACE WINDS ARE FORECAST TO BECOME EAST-SOUTHEAST 6-12KT AFTER 19Z TODAY...THEN GRADUALLY GOING TO A DRAINAGE PATTERN AT SPEEDS OF 5-12 KTS BY 05Z THIS EVENING. && .HYDROLOGY...ISOLATED SHOWERS AND T-STORMS MOVING NORTHEAST AT 20-25KTS AND MAINLY OVER CENTRAL AND SOUTHERN PORTIONS OF THE FRONT RANGE AFTER 21Z TODAY WILL THE POTENTIAL TO RAIN AMOUNTS RANGING FROM 0.10 TO 0.30 INCH IN UNDER 40 MINUTES. DO NOT ANTICIPATE AS MUCH WIND WITH STORMS IN THE HIGH COUNTRY TODAY. BELIEVE THE CHANCE FOR FLASH FLOODING AT THE BURN SCARS WILL BE LOW TODAY. && .PREV DISCUSSION... /ISSUED 310 AM MDT SUN SEP 2 2012/ SHORT TERM...THE UPPER LEVEL RIDGE WILL WEAKEN TODAY WITH INCREASING SWLY FLOW ALOFT. WATER VAPOR IMAGERY SHOWS A DISTURBANCE OVER NWRN CO WHICH WAS TRIGGERING A FEW SHOWERS IN THE NRN MTNS EARLY THIS MORNING. MEANWHILE A WK FNT WAS MOVING ACROSS NERN CO THIS MORNING AND WILL BRING SLIGHTLY COOLER TEMPS WITH READINGS ON AVERAGE 5 DEGREES COOLER THAN SAT OVER THE PLAINS. FOR THIS AFTN SOUNDINGS HAVE BETTER INSTABILITY ACROSS NERN CO THAN THE LAST FEW DAYS SO THERE SHOULD BE AT LEAST A SLIGHTLY BETTER CHC FOR TSTMS ACROSS THE PLAINS INTO THE EVENING HOURS. IN THE MTNS WILL KEEP SCT TSTMS IN THE FCST FOR THIS AFTN WITH WDLY SCT ACTIVITY OVER THE HIGHER VALLEYS. LONG TERM...A FLAT UPPER RIDGE WILL REMAIN SOUTH OF COLORADO MONDAY THROUGH TUESDAY NIGHT. THE FLOW ALOFT WILL BE WEST-SOUTHWESTERLY ON MONDAY...THEN ZONAL MONDAY NIGHT THROUGH TUESDAY NIGHT. THE SYNOPTIC SCALE ENERGY REMAINS BENIGN THROUGH THE PERIODS. THE LOW LEVEL PRESSURE GRADIENT IS WEAK THROUGH TUESDAY EVENING SO NORMAL DIURNAL WIND PATTERNS WILL DOMINATE. A WEAK COLD FRONT AND UPSLOPE IS PROGGED TO MOVE INTO THE PLAINS LATE TUESDAY NIGHT OR EARLY WEDNESDAY. FOR MOISTURE...THERE IS SOME IN THE MID AND UPPER LEVELS MONDAY AND MONDAY EVENING. TUESDAY AND TUESDAY NIGHT LOOK PRETTY DRY. THE BOUNDARY LAYER DEW POINTS ARE PROGGED IN THE 30 TO MID 40S F RANGE FOR ALL AREAS BY LATE DAY MONDAY. THEY ARE A BIT LOWER FOR LATE DAY TUESDAY. PRECIPITABLE WATER VALUES ARE PROGGED IN THE 0.60 TO 0.90 INCH RANGE LATE DAY MONDAY...THEN IN THE 0.55 TO 0.70 INCH RANGE LATE DAY TUESDAY. THERE IS A TAD OF CAPE OVER THE CWA LATE DAY MONDAY...THEN ANOTHER SMALL AMOUNT IS PROGGED OVER THE SOUTHERN CWA LATE DAY TUESDAY. THE QPF FIELDS SHOW A TAD OF MEASURABLE RAINFALL OVER THE CWA LATE MONDAY...AND A BIT LESS LATE DAY TUESDAY. THERE IS NOT MUCH A MID LEVEL CAP IN PLACE ON THE LAPSE RATE FIELDS FOR LATE DAY MONDAY. THERE IS A BIT OF ONE PROGGED FOR LATE DAY TUESDAY. FOR POPS WILL GO WITH 10-20%S BOTH LATE DAY MONDAY AND LATE DAY TUESDAY. FOR TEMPERATURES...MONDAY`S HIGHS ARE 0-1 C COOLER THAN TODAY`S. TUESDAY`S ARE 0-1 C WARMER THAN MONDAY`S. FOR THE LATER DAYS...WEDNESDAY THROUGH SATURDAY...THE UPPER RIDGE STAYS SOUTH OF COLORADO WITH ZONAL FLOW ALOFT THROUGH THURSDAY. MODELS STILL HAVE AN UPPER TROUGH TO PUSH ACROSS THE CWA THURSDAY NIGHT INTO FRIDAY. THE FLOW IS MORE NORTHWESTERLY FRIDAY AND SATURDAY. MOISTURE IS POOR ALL FOUR DAYS FOR ALL THE CWA. A WEAK COLD FRONT IS EXPECTED EARLY ON WEDNESDAY...THEN A SLIGHTLY STRONGER ONE COMES IN LATE THURSDAY NIGHT/FRIDAY MORNING. AVIATION...A WK FNT HAS ALREADY MOVED ACROSS THE AREA AS WINDS HAVE BEEN LIGHT NNE EARLY THIS MORNING. LATEST RAP AND HRRR SHOW WINDS BECOMING MORE SELY BY MID MORNING AND KEEP THEM THAT WAY THRU MUCH OF THE AFTN. INSTABILITY WILL BE BETTER THIS AFTN SO COULD SEE A TSTM AFFECT THE AIRPORT MAINLY AFTER 21Z. FOR NOW WILL JUST MENTION VCTS IN THE TAF. FOR THIS EVENING TSTM THREAT SHOULD END BY 01Z OR SO WITH BEST CHC TO THE N AND E OF THE AIRPORT. WINDS SHOULD BECOME MORE SSW THIS EVENING. HYDROLOGY...THERE WILL BE A SLIGHT BETTER CHC OF THUNDERSTORMS THIS AFTERNOON WITH RAINFALL AMOUNTS AROUND A QUARTER INCH POSSIBLE. AN ISOLATED STRONGER STORM COULD PRODUCE UP TO ONE HALF INCH IN LESS THAN 30 MINUTES. THE FLOW ALOFT IS STRONGER TODAY SO STORMS WILL BE MOVING FAIRLY QUICKLY. && .BOU WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...BAKER/RPK LONG TERM....RJK AVIATION...BAKER/RPK
AREA FORECAST DISCUSSION
NWS DENVER CO
310 AM MDT SUN SEP 2 2012 .SHORT TERM...THE UPPER LEVEL RIDGE WILL WEAKEN TODAY WITH INCREASING SWLY FLOW ALOFT. WATOR VAPOR IMAGERY SHOWS A DISTURBANCE OVER NWRN CO WHICH WAS TRIGGERING A FEW SHOWERS IN THE NRN MTNS EARLY THIS MORNING. MEANWHILE A WK FNT WAS MOVING ACROSS NERN CO THIS MORNING AND WILL BRING SLIGHTLY COOLER TEMPS WITH READINGS ON AVERAGE 5 DEGREES COOLER THAN SAT OVER THE PLAINS. FOR THIS AFTN SOUNDINGS HAVE BETTER INSTABILITY ACROSS NERN CO THAN THE LAST FEW DAYS SO THERE SHOULD BE AT LEAST A SLIGHTLY BETTER CHC FOR TSTMS ACROSS THE PLAINS INTO THE EVENING HOURS. IN THE MTNS WILL KEEP SCT TSTMS IN THE FCST FOR THIS AFTN WITH WDLY SCT ACTIVITY OVER THE HIGHER VALLEYS. .LONG TERM...A FLAT UPPER RIDGE WILL REMAIN SOUTH OF COLORADO MONDAY THROUGH TUESDAY NIGHT. THE FLOW ALOFT WILL BE WEST-SOUTHWESTERLY ON MONDAY...THEN ZONAL MONDAY NIGHT THROUGH TUESDAY NIGHT. THE SYNOPTIC SCALE ENERGY REMAINS BENIGN THROUGH THE PERIODS. THE LOW LEVEL PRESSURE GRADIENT IS WEAK THROUGH TUESDAY EVENING SO NORMAL DIURNAL WIND PATTERNS WILL DOMINATE. A WEAK COLD FRONT AND UPSLOPE IS PROGGED TO MOVE INTO THE PLAINS LATE TUESDAY NIGHT OR EARLY WEDNESDAY. FOR MOISTURE...THERE IS SOME IN THE MID AND UPPER LEVELS MONDAY AND MONDAY EVENING. TUESDAY AND TUESDAY NIGHT LOOK PRETTY DRY. THE BOUNDARY LAYER DEW POINTS ARE PROGGED IN THE 30 TO MID 40S F RANGE FOR ALL AREAS BY LATE DAY MONDAY. THEY ARE A BIT LOWER FOR LATE DAY TUESDAY. PRECIPITABLE WATER VALUES ARE PROGGED IN THE 0.60 TO 0.90 INCH RANGE LATE DAY MONDAY...THEN IN THE 0.55 TO 0.70 INCH RANGE LATE DAY TUESDAY. THERE IS A TAD OF CAPE OVER THE CWA LATE DAY MONDAY...THEN ANOTHER SMALL AMOUNT IS PROGGED OVER THE SOUTHERN CWA LATE DAY TUESDAY. THE QPF FIELDS SHOW A TAD OF MEASURABLE RAINFALL OVER THE CWA LATE MONDAY...AND A BIT LESS LATE DAY TUESDAY. THERE IS NOT MUCH A MID LEVEL CAP IN PLACE ON THE LAPSE RATE FIELDS FOR LATE DAY MONDAY. THERE IS A BIT OF ONE PROGGED FOR LATE DAY TUESDAY. FOR POPS WILL GO WITH 10-20%S BOTH LATE DAY MONDAY AND LATE DAY TUESDAY. FOR TEMPERATURES...MONDAY`S HIGHS ARE 0-1 C COOLER THAN TODAY`S. TUESDAY`S ARE 0-1 C WARMER THAN MONDAY`S. FOR THE LATER DAYS...WEDNESDAY THROUGH SATURDAY...THE UPPER RIDGE STAYS SOUTH OF COLORADO WITH ZONAL FLOW ALOFT THROUGH THURSDAY. MODELS STILL HAVE AN UPPER TROUGH TO PUSH ACROSS THE CWA THURSDAY NIGHT INTO FRIDAY. THE FLOW IS MORE NORTHWESTERLY FRIDAY AND SATURDAY. MOISTURE IS POOR ALL FOUR DAYS FOR ALL THE CWA. A WEAK COLD FRONT IS EXPECTED EARLY ON WEDNESDAY...THEN A SLIGHTLY STRONGER ONE COMES IN LATE THURSDAY NIGHT/FRIDAY MORNING. && AVIATION...A WK FNT HAS ALREADY MOVED ACROSS THE AREA AS WINDS HAVE BEEN LIGHT NNE EARLY THIS MORNING. LATEST RAP AND HRRR SHOW WINDS BECOMING MORE SELY BY MID MORNING AND KEEP THEM THAT WAY THRU MUCH OF THE AFTN. INSTABILITY WILL BE BETTER THIS AFTN SO COULD SEE A TSTM AFFECT THE AIRPORT MAINLY AFTER 21Z. FOR NOW WILL JUST MENTION VCTS IN THE TAF. FOR THIS EVENING TSTM THREAT SHOULD END BY 01Z OR SO WITH BEST CHC TO THE N AND E OF THE AIRPORT. WINDS SHOULD BECOME MORE SSW THIS EVENING. && HYDROLOGY...THERE WILL BE A SLIGHT BETTER CHC OF THUNDERSTORMS THIS AFTERNOON WITH RAINFALL AMOUNTS AROUND A QUARTER INCH POSSIBLE. AN ISOLATED STRONGER STORM COULD PRODUCE UP TO ONE HALF INCH IN LESS THAN 30 MINUTES. THE FLOW ALOFT IS STRONGER TOAY SO STORMS WILL BE MOVING FAIRLY QUICKLY. && .BOU WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...RPK LONG TERM....RJK AVIATION...RPK
AREA FORECAST DISCUSSION
NWS TAMPA BAY RUSKIN FL
310 AM EDT SUN SEP 2 2012 .SYNOPSIS... 07Z WATER VAPOR AND H4 RAP ANALYSIS SHOW AN AREA OF UPPER LEVEL RIDGING REMAINS IN CONTROL FROM THE SOUTHERN PLAINS EASTWARD ALONG THE NORTHERN GULF COAST TO THE FL PENINSULA. THE EASTERN PORTION OF THIS RIDGE (INCLUDING OUR REGION) IS WEAKENING WITH TIME AS A STRONG SHORTWAVE APPROACHES THE SOUTHEAST CONUS FROM THE TN VALLEY...AND A CUT-OFF LOW RETROGRADES WESTWARD TOWARD THE EASTERN FLORIDA PENINSULA. 02/00Z KTBW SOUNDING PROFILE SHOWS THAT THE COLUMN DID DRY OUT SOMEWHAT DURING THE DAY ON SATURDAY...ESPECIALLY ABOVE 500MB...HOWEVER THE LACK OF CONVECTIVE COVERAGE ON SATURDAY WAS LIKELY MORE TIED TO OUR WARM/CAPPED MID-LEVEL THERMODYNAMIC PROFILE ASSOCIATED WITH THE UPPER RIDGE. TEMPS AROUND 500MB RANGED FROM -2 TO -5C WHICH ARE FAIRLY WARM...AND WHEN COMBINED WITH THE DRY AIR ADVECTION WAS ENOUGH TO SUPPRESS CONVECTION. 00Z NWP GUIDANCE SUITE SHOWS THAT THE DEEPEST LAYER DRY AIR WAS "ON OUR DOORSTEP" AT 00Z AND WAS LIKELY NOT COMPLETELY SAMPLED BY THE RAOB. WOULD EXPECT TO SEE OUR PW VALUES COME DOWN FURTHER WITH THE 12Z SOUNDING AS THE DEEP LAYER DRY AIR SHOULD BE FIRMLY IN PLACE. AT THE SURFACE...SUBTROPICAL RIDGE AXIS IS ALIGNED OVER THE NORTHERN FL PENINSULA AND INTO THE NE GULF OF MEXICO. DEWPOINTS ARE LOW FOR EARLY SEPTEMBER WITH READINGS THIS PAST EVENING IN THE UPPER 60S TO LOWER 70S. HAVE SEEN MOST OF THE UPPER 60S REBOUND A FEW DEGREES...BUT STILL A RATHER COMFORTABLE MORNING COMPARED TO THE PAST COUPLE MONTHS. && .SHORT TERM (TODAY THROUGH TUESDAY)... TODAY/TONIGHT...ANOTHER DAY WITH WELL BELOW NORMAL RAIN CHANCES ACROSS MUCH OF THE FORECAST AREA. SOUTH-NORTH CROSS-SECTIONS THROUGH THE DAY SHOW A DEEP LAYER OF VERY DRY AIR (RH < 20%) IN PLACE. THIS LAYER IS DEEP ENOUGH TO BE QUITE HOSTILE TO CONVECTION AND WOULD THINK EVEN ISOLATED CELLS ARE UNLIKELY FOR MOST LOCATIONS. LATE IN THE DAY...SOME MOISTURE ADVECTION BEGINS TO IMPINGE ON THIS DRY LAYER OVER THE FAR NORTHERN ZONES (LEVY/CITRUS/HERNANDO/SUMTER) IN ADVANCE OF A SHORTWAVE TROUGH DROPPING INTO AL/GA. COLUMN IS STILL NOT FAVORABLE FOR DEEP CONVECTION...BUT CAN`T RULE OUT A FEW ISOLATED STORMS FOR THE NORTHERN NATURE COAST...ESPECIALLY WITH THE SUBTROPICAL RIDGE AXIS POSITION ALLOWING FOR A WELL-DEFINED SEA-BREEZE FRONT. LOCAL HI-RES WRFARW SEEMS TO HAVE A GOOD HANDLE ON THIS SITUATION AND DOES SUPPORT A FEW NON-ROBUST SHOWERS NORTH OF TAMPA BAY AFTER 20Z. OTHERWISE THE LACK OF CONVECTION WILL AGAIN ALLOW FOR TEMPERATURES AWAY FROM THE BEACHES TO REACH THE 92-95 RANGE. NOT ANTICIPATING ANY HEAT INDEX PROBLEMS AS THE DRIER AIRMASS HOLDS THESE VALUES GENERALLY BELOW 100. ANY ISOLATED LAND-BASED SHOWERS UP NORTH SHOULD DISSIPATE WITH SUNSET ALLOWING FOR A DRY AND QUIET OVERNIGHT PERIOD. MAY SEE A FEW LATE NIGHT SHOWERS OVER THE NORTHERN COASTAL WATERS IN CLOSER PROXIMITY TO SOME DEEPER MOISTURE ONCE THE LAND BREEZE BECOMES ESTABLISHED. MONDAY...UPPER RIDGE CONTINUES TO WEAKEN AS IT IS SQUEEZED BETWEEN THE SHORTWAVE OVER AL/GA/FL PANHANDLE AND A CUT-OFF LOW APPROACHING THE SOUTHEAST FL COAST. GUIDANCE SHOWING THAT WE WILL STILL HAVE A "TONGUE" OF DRIER AIR ABOVE THE SURFACE EXTENDING ACROSS THE CENTRAL FORECAST PENINSULA IN BETWEEN THESE 2 FEATURES. HOWEVER THE EXTENT/DEPTH OF THE DRY AIR IS LESS AND WILL RE-INTRODUCE AT LEAST A SLIGHT CHANCE 20% POP FOR ALL ZONES. BEST CHANCES FOR THE AFTERNOON SHOWERS ~30% WILL BE DOWN TOWARD FORT MYERS ASSOCIATED WITH THE SYNOPTIC SUPPORT/COOLER MID-LEVELS AROUND THE UPPER LOW...AND ALSO UP TOWARD LEVY COUNTY ASSOCIATED WITH THE PROXIMITY TO THE SE CONUS SHORTWAVE. GFS/ECMWF BOTH SHOW SOME ENHANCED DEEP LAYER (700-300MB) QG FORCING OVER SOUTH FLORIDA TO THE WEST OF THE UPPER LOW CENTER MONDAY AFTERNOON...AND COMBINED WITH THE ENHANCED INSTABILITY... WOULD NOT BE SURPRISED TO SEE A FEW OF THE STORMS OVER THE SOUTHERN PENINSULA BECOME STRONG. BEST CHANCE FOR THESE ENHANCED UPDRAFTS WOULD LIKELY BE EAST OF LEE/CHARLOTTE COUNTIES UNDERNEATH THE COLDEST MID-LEVELS...BUT WORTH WATCHING. TUESDAY...UPPER LOW BEGIN TO VERY SLOWLY MIGRATE NORTHWARD UP THE EAST COAST OF THE PENINSULA. OVERALL THE SYNOPTIC PATTERN WILL NOT HAVE CHANGED MUCH FROM LATE MONDAY. KEEPING RAIN CHANCES SIMILAR WITH AN EXPANSION OF THE CHANCE 30-40% POPS NORTHWARD INTO HARDEE/DESOTO/HIGHLANDS/POLK COUNTIES FOLLOWING THE CORE OF THE UPPER LOW. && .LONG TERM (TUESDAY NIGHT THROUGH SATURDAY)... UPPER-LEVEL LOW WILL BE TURNING NORTHWARD AND MOVING BY TO OUR EAST TUESDAY NIGHT AND WEDNESDAY WHICH WILL KEEP THE DEEPER MOISTURE AND BEST INSTABILITY TO OUR EAST. THE GFS AND ECMWF DIG AN UPPER-LEVEL TROUGH OVER THE EASTERN STATES ON THURSDAY AND THURSDAY NIGHT WHICH IN TURN PUSHES AN EARLY SEASON COLD FRONT INTO THE DEEP SOUTH. THE ECMWF IS THE STRONGEST AND FARTHEST SOUTH WITH THE FRONT...REACHING OUR NORTHERN ZONES ON FRIDAY. THE GFS HOLDS THE FRONT NORTH OF THE REGION BUT DOES DISPLACE THE RIDGE AXIS WELL TO OUR SOUTH RESULTING IN ENHANCED WESTERLY FLOW BETWEEN THE FRONT AND THE RIDGE. THE DIFFERENCES BETWEEN THE TWO MODELS REALLY SHOWS UP BY SATURDAY WHEN THE ECMWF SHOWS LOW PRESSURE OFF THE COAST ALONG 30 DEGREES NORTH LATITUDE WHILE THE GFS SHOWS MAINLY TROUGHING AND SIGNIFICANTLY FARTHER NORTH. IT IS LIKELY TOO EARLY IN THE SEASON TO GET THE FRONTAL BOUNDARY AS FAR SOUTH AS SUGGESTED BY THE ECMWF SO WILL USE THE GFS AS THE BASIS FOR THE EXTENDED FORECAST. WILL GENERALLY FOLLOW MEX GUIDANCE SHOWING SCATTERED STORMS EACH DAY. WE MAY HAVE A DAY OR TWO WHERE LOW-LEVEL CONVERGENCE SETS UP IN PERSISTENT LINES BRINGING SOME LOCALLY HEAVY RAINFALL TO SOME LOCATIONS...BUT ITS TOO EARLY TO PINPOINT WHERE THIS WILL OCCUR IF AT ALL. && .AVIATION... VFR NEXT 24 HOURS. SOME RISK OF BRIEF MVFR VISIBILITIES NEAR SUNRISE AT PGD AND RSW. NOT EXPECTING ENOUGH AFTERNOON SHRA COVERAGE TO INCLUDE IN TAFS AT THIS TIME. && .MARINE... THE SUBTROPICAL RIDGE AXIS ALIGNED OVER THE NORTHEAST GULF OF MEXICO TODAY WILL SLOWLY SETTLE SOUTHWARD TOWARD THE SOUTHERN PENINSULA AND SOUTHEAST GULF BY THE MIDDLE PORTION OF THE WEEK. THE CLOSE PROXIMITY OF THE RIDGE AXIS THROUGH THE FORECAST PERIOD WILL KEEP WINDS AND SEAS GENERALLY LIGHT ACROSS THE EASTERN GULF WITH EASTERLY FLOW TODAY TRENDING MORE SOUTH AND SOUTHWEST THROUGH THE UPCOMING WEEK. && .FIRE WEATHER... A DRIER LOW LEVEL AIRMASS IN PLACE WILL ALLOW INLAND RELATIVE HUMIDITY LEVELS TO DROP INTO THE UPPER 30S TO LOWER 40S FOR A BRIEF TIME THIS AFTERNOON. LDSI VALUES WILL BE UNDER 75 AND WINDS GENERALLY LIGHT...SO NOT SIGNIFICANT FIRE WEATHER CONCERNS ARE ANTICIPATED. A SLOW LOW LEVEL MOISTURE RETURN WILL BEGIN DURING THE EARLY PORTION OF THE WEEK. && .PRELIMINARY POINT TEMPS/POPS... TPA 92 75 90 76 / 10 10 20 10 FMY 93 73 90 74 / 10 10 30 10 GIF 93 72 92 72 / 10 10 20 10 SRQ 90 73 89 74 / 10 10 20 10 BKV 92 69 92 69 / 20 10 20 10 SPG 93 78 89 78 / 10 10 20 10 && .TBW WATCHES/WARNINGS/ADVISORIES... FL...NONE. GULF WATERS...NONE. && $$ SYNOPSIS/SHORT TERM/MARINE/FIRE WX...MROCZKA LONG TERM/AVIATION...JILLSON
AREA FORECAST DISCUSSION...UPDATED
NWS PEACHTREE CITY GA
952 PM EDT MON SEP 3 2012 .UPDATE... HAVE MADE SEVERAL UPDATES TO THE GRIDS THROUGH THE EVENING... MAINLY TO ADJUST POPS TO ACCOUNT FOR CONVECTIVE TRENDS. REDUCED POPS NORTHWEST AND INCREASED IN A LINE ROUGHLY FROM AHN TO CSG WHERE CONVECTION LINGERED THROUGH THE EVENING...WITH A SLOW INCREASING TREND NORTHWEST OVER NIGH. HRRR AND OTHER HIRES GUIDANCE STILL INDICATING THAT CONVECTION FROM ALABAMA WILL WORK ITS WAY INTO GEORGIA...ESPECIALLY WHAT HAS BEEN DEVELOPING IN NORTHEAST ALABAMA. DID REDUCE THUNDER WORDING FOR THE OVERNIGHT PERIOD. TEMPS THROUGH THE EVENING DUE TO THE RAIN...AND OVERNIGHT LOWS MAY BE A LITTLE TOO HIGH. HAVE MADE SOME MINOR ADJUSTMENTS BUT WITH DEWPOINTS SO HIGH DO NOT FEEL COMFORTABLE LOWERING MINS ANY MORE. TDP && .PREV DISCUSSION... /ISSUED 759 PM EDT MON SEP 3 2012/ PREV DISCUSSION... /ISSUED 334 PM EDT MON SEP 3 2012/ SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/... REMNANTS OF ISAAC STILL SPINNING NEAR THE IN/KY BORDER THIS AFTERNOON. TWO RAIN BANDS MOVING THROUGH GA AT THE MOMENT. THE FIRST ONE IS DOWN ALONG THE GA COAST WITH THE SECOND NOW MOVING THROUGH THE ATL/AHN AREAS. MAINLY SHOWERS WITH THIS BAND BUT THERE ARE SOME ISOLATED THUNDERSTORMS . THESE STORMS ARE NOT SEVERE BUT THEY ARE INCREASING IN INTENSITY AS THEY MOVE INTO MORE UNSTABLE AIR ACROSS CENTRAL GA. INSTABILITIES HAVE INCREASED INTO THE 1500-2500 J/KG RANGE ACROSS CENTRAL GA AND WILL SUPPORT SOME STRONG STORMS. MODELS INDICATING POSSIBLE MCS DEVELOPMENT OVERNIGHT JUST WEST OF THE CWA. HAVE KEPT POPS HIGH THROUGH TUESDAY...WITH GENERALLY LIKELY ACROSS MUCH OF THE CWA. ALTHOUGH BEST DESTABILIZATION IS OCCURRING RIGHT NOW...THERE SHOULD BE ENOUGH INSTABILITY TO SUPPORT ISOLATED TO SCATTERED THUNDERSTORMS THROUGH THE OVERNIGHT HOURS. MOST PLACES WILL SEE PRECIPITATION AMOUNTS OF 1-2 INCHES THROUGH THE SHORT TERM. FLASH FLOOD GUIDANCE WELL ABOVE THIS SO DO NOT ANTICIPATE ANY ISSUES. AS FOR TEMPERATURES...MAV GUIDANCE HA BEEN RUNNING A BIT COLD ON MIN TEMPS AND A BIT WARM ON MAX TEMPS. HAVE MADE SLIGHT ADJUSTMENTS TO COMPENSATE FOR THIS. 01 LONG TERM /WEDNESDAY THROUGH MONDAY/... LATEST EXTENDED GUIDANCE SHOWS BEST MOISTURE HANGING AROUND A LITTLE LONGER INTO WEDNESDAY AND THURSDAY AND ONLY CHANGE WAS TO BUMP UP INTO LOW LIKELY/HIGH CHANCE RANGE. REMAINDER OF THE EXTENDED REMAINS UNCHANGED. DEESE TROPICAL MOISTURE BECOMES STRETCHED OUT ACROSS THE CWA THROUGH WEDNESDAY WITH SOME HINT AT DRYING THURSDAY INTO FRIDAY AS THE UPPER RIDGE NOSES EASTWARD. HAVE NOT REMOVED POPS FOR THE BRIEF DRIER PERIOD...JUST REDUCED THEM OVER MUCH OF THE CWA. BY THE WEEKEND BOTH MODELS SHOW A SIGNIFICANT CLOSED LOW DEVELOPING VICINITY OF THE OHIO VALLEY. THIS KEEPS THE UNSETTLED WEATHER OVER THE CWA AND HAVE CONTINUED WITH CHANCE OR SLIGHT CHANCE POPS. MODEL MAX TEMPERATURES LOOKED A BIT HIGH GIVEN THE UPPER PATTERN SO HAVE TWEAKED THEM DOWN A BIT MOST AREAS. 41 AVIATION... 00Z UPDATE... TSRA HAS MOVED SOUTH AND EAST...AFFECTING STILL MCN AND CSG BUT OUT OF THE NORTHERN TAFS. SEEING SHRA DEVELOP ACROSS N AL SO HAVE CONTINUED SHRA IN THE OVERNIGHT PERIOD FOR THE NORTHERN TAFS BUT REMOVED TSRA...AND REMOVED MENTION OF PRECIP IN CSG AND MCN AFTER 03Z. EXPECT IFR CIGS BY 08-09Z...LIFR AT AHN...WITH MVFR TO POSSIBLY IFR FOG. HAVE KEPT TSRA IN TAFS FOR TUESDAY AFTERNOON EXCEPT AT CSG AND MCN. SW WINDS THROUGH THE PERIOD...THOUGH SOME GUIDANCE INDICATING BRIEF SE WINDS POSSIBLE. //ATL CONFIDENCE...00Z UPDATE... LOW ON CONVECTION IMPACTING ATL TONIGHT. HIGH ON IFR CIGS DEVELOPING OVERNIGHT...MEDIUM ON TIMING AND POSSIBILITY OF LIFR CIGS. MEDIUM ON WINDS. TDP && .PRELIMINARY POINT TEMPS/POPS... ATHENS 71 86 71 87 / 60 60 50 50 ATLANTA 73 84 72 86 / 60 60 40 40 BLAIRSVILLE 68 79 65 82 / 70 70 50 40 CARTERSVILLE 71 85 71 86 / 70 70 50 40 COLUMBUS 73 88 73 89 / 90 70 40 50 GAINESVILLE 71 82 71 85 / 60 70 50 50 MACON 73 89 72 89 / 70 60 40 50 ROME 72 86 71 87 / 70 70 40 30 PEACHTREE CITY 71 85 71 86 / 60 60 40 40 VIDALIA 74 91 73 90 / 80 60 40 40 && .FFC WATCHES/WARNINGS/ADVISORIES... NONE. && $$
AREA FORECAST DISCUSSION
NWS LINCOLN IL
250 PM CDT SUN SEP 2 2012 .DISCUSSION... ISSUED 250 PM CDT SUN SEP 2 2012 THE IMPACT OF THE REMNANTS OF HURRICANE ISAAC WILL CONTINUE TO WANE OVER THE NEXT 24 HOUR ACROSS CENTRAL AND SOUTHEAST ILLINOIS. THEN...ATTENTION TURNS TO PERIODIC DISTURBANCES/FRONTAL PASSAGES THAT WILL AFFECT THE REGION FROM TIME TO TIME THIS WEEK. MAIN FORECAST PROBLEMS TODAY REVOLVE AROUND PRECIPITATION CHANCES UNTIL ISAAC/S REMNANTS DEPART AND WITH EACH DISTURBANCE/FROPA. 12Z MODELS IN REASONABLE AGREEMENT OVER THE NEXT FEW DAYS. HOWEVER...AGREEMENT IN THE DETAILS...ESPECIALLY WITH RESPECT TO TIMING...WITH THE DISTURBANCES/FROPAS IS INCREASINGLY POOR TOWARD THE END OF THE WEEK. THIS HAS BEEN A PERSISTENT PROBLEM THE PAST FEW DAYS AND WILL CONTINUE TO FAVOR AN ENSEMBLE MEAN SOLUTION TO KNOCK OUT SOME OF THE NOISE. AN UNFORTUNATE RESULT OF THIS METHOD IS AN EXTENDED PERIOD OF LOW POPS. SHORT TERM...TONIGHT THROUGH WEDNESDAY...THE UPPER CIRCULATION CENTER OF ISAAC/S REMNANTS HAS PUSHED EAST INTO INDIANA...WITH THE SURFACE REFLECTION LINGERING A LITTLE FURTHER TO THE WEST. THIS HAS RESULTED IN THE BETTER RAIN/THUNDER CHANCES SHIFTING TO OUR EAST...WITH THE SHOWERS OCCURRING LOCALLY ALMOST ENTIRELY DIURNALLY DRIVEN. THIS SHOULD CONTINUE TO BE THE CASE THROUGH MONDAY AS THE PRECIPITATION CHANCES GRADUALLY END FROM WEST TO EAST. ATTENTION THEN TURNS TO A COUPLE DISTURBANCES THAT WILL PUSH A FRONT TOWARD AND/OR THROUGH THE FORECAST AREA. THE FIRST DISTURBANCES IS MOVING EAST ACROSS SASKATCHEWAN AND WILL PUSH A VERY WEAK FRONT TOWARD THE REGION AND WASHES IT OUT. DO NOT REALLY EXPECT MUCH...IF ANY...PRECIPITATION WITH THIS FEATURE BUT HAVE MAINTAINED SLIGHT CHANCE POPS IN MOST AREAS FOR MONDAY NIGHT INTO TUESDAY. A STRONGER FRONT WILL PUSH THROUGH WEDNESDAY...DRIVEN BY A WAVE CURRENTLY DIGGING THROUGH BRITISH COLUMBIA. THIS FRONT HAS A BETTER CHANCE OF PRODUCING SHOWERS/STORMS...AND IT WILL USHER IN BELOW NORMAL TEMPERATURES FOR THE REST OF THE WEEK. CONSIDERING HOW MUCH RAIN HAS FALLEN THE PAST COUPLE OF DAYS...FOG WILL DEFINITELY BE A CONCERN FOR AT LEAST THE NEXT COUPLE OF NIGHTS WHILE THE AIRMASS REMAINS VERY HUMID. HAVE LIMITED FOG MENTION TO WESTERN SECTIONS OF THE FORECAST AREA TONIGHT DUE TO THE LINGERING CLOUD COVER IN PLACE. FOG WILL LIKELY BE A BIGGER THREAT MONDAY NIGHT AS THE CLOUD COVER SHOULD BE MUCH MORE MINIMAL. LONG TERM...THURSDAY THROUGH SUNDAY...ANOTHER STRONG WAVE/FRONT WILL PUSH THROUGH THE AREA FRIDAY OR SATURDAY AS THE MEAN UPPER TROF FROM CENTRAL NORTH AMERICA DEEPENS AND SHIFTS EAST WITH TIME. SPECIFIC PRECIPITATION TIMING FOR THE END OF THE WEEK IS PRETTY UNCERTAIN. IN FACT...THE 12Z ECMWF CAME IN WITH ENOUGH COLD AIR AND CYCLONIC FLOW BEHIND THE FRONT TO KEEP AT LEAST DIURNAL SHOWERS A RISK THROUGH THE WEEKEND. FOR NOW...HAVE LIMITED MENTIONABLE SHOWER/STORM CHANCES TO FRIDAY AND SATURDAY...BUT THIS WILL CERTAINLY NEED TO BE TWEAKED AT THE ULTIMATE SOLUTION BECOMES MORE CLEAR. BAK && .AVIATION... ISSUED 1245 PM CDT SUN SEP 2 2012 LOW PRESSURE CONTINUES TO SPIN OVER KMTO...WITH IFR CEILINGS ON THE NORTH/WEST SIDE OF THE SYSTEM. DUE TO ONLY VERY SLOW EASTWARD MOVEMENT...WILL KEEP IFR CEILINGS IN PLACE THROUGH THE AFTERNOON AT KCMI...KDEC...AND KBMI. FURTHER WEST...A DRY SLOT HAS WORKED IN FROM THE NORTH...RESULTING IN MVFR CEILINGS AT THE REMAINING TERMINALS. SHOWERS WILL CONTINUE TO BLOSSOM ACROSS THE AREA THIS AFTERNOON...PARTICULARLY ALONG/EAST OF I-55. PRECIP WILL BE LARGELY DIURNAL...WITH 12Z HRRR INDICATING SHOWERS DIMINISHING AND COMING TO AN END BY SUNSET. QUESTION AFTER THAT BECOMES WHETHER OR NOT ANY CLEARING CAN OCCUR AND IF FOG WILL BECOME A PROBLEM. NAM FORECAST SOUNDINGS KEEP LOW CLOUDS IN PLACE ACROSS CENTRAL ILLINOIS THROUGH THE NIGHT. DUE TO THE POTENTIAL FOR PARTIAL CLEARING OVERNIGHT...WILL CONTINUE TO FORECAST PATCHY FOG WITH VSBYS BETWEEN 2 AND 4SM. ANY FOG THAT DEVELOPS WILL GRADUALLY LIFT INTO AN MVFR OVERCAST AFTER 14Z. SKIES WILL THEN CLEAR OUT BY MONDAY AFTERNOON...AS LOW PRESSURE SLOWLY EXITS THE REGION. BARNES && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$
AREA FORECAST DISCUSSION
NWS LINCOLN IL
1245 PM CDT SUN SEP 2 2012 .DISCUSSION... ISSUED 1040 AM CDT SUN SEP 2 2012 15Z/10AM SURFACE ANALYSIS SHOWS CENTER OF HURRICANE ISSAC REMNANTS OVER MATTOON. DEEPEST TROPICAL MOISTURE AND STRONGEST LIFT WILL BE LOCATED TO THE EAST/SOUTHEAST OF THE LOW ACROSS THE OHIO RIVER VALLEY TODAY. FURTHER WEST ACROSS CENTRAL ILLINOIS...THE PRECIP WILL BE LIGHTER AND MUCH MORE SCATTERED IN NATURE. A FEW BREAKS IN THE OVERCAST WILL OCCUR FROM TIME TO TIME...WHICH WILL ALLOW POCKETS OF MODERATE INSTABILITY TO DEVELOP THIS AFTERNOON. AS A RESULT...MAY SEE ISOLATED THUNDER AS WELL. HAVE UPDATED THE FORECAST TO LOWER POPS...OPTING TO GO WITH SCATTERED SHOWERS/ISOLATED THUNDER ACROSS THE BOARD. DUE TO THE CLOUD COVER AND PRECIP...HIGHS WILL ONLY REACH THE UPPER 70S AND LOWERS 80S. && .AVIATION... ISSUED 1245 PM CDT SUN SEP 2 2012 LOW PRESSURE CONTINUES TO SPIN OVER KMTO...WITH IFR CEILINGS ON THE NORTH/WEST SIDE OF THE SYSTEM. DUE TO ONLY VERY SLOW EASTWARD MOVEMENT...WILL KEEP IFR CEILINGS IN PLACE THROUGH THE AFTERNOON AT KCMI...KDEC...AND KBMI. FURTHER WEST...A DRY SLOT HAS WORKED IN FROM THE NORTH...RESULTING IN MVFR CEILINGS AT THE REMAINING TERMINALS. SHOWERS WILL CONTINUE TO BLOSSOM ACROSS THE AREA THIS AFTERNOON...PARTICULARLY ALONG/EAST OF I-55. PRECIP WILL BE LARGELY DIURNAL...WITH 12Z HRRR INDICATING SHOWERS DIMINISHING AND COMING TO AN END BY SUNSET. QUESTION AFTER THAT BECOMES WHETHER OR NOT ANY CLEARING CAN OCCUR AND IF FOG WILL BECOME A PROBLEM. NAM FORECAST SOUNDINGS KEEP LOW CLOUDS IN PLACE ACROSS CENTRAL ILLINOIS THROUGH THE NIGHT. DUE TO THE POTENTIAL FOR PARTIAL CLEARING OVERNIGHT...WILL CONTINUE TO FORECAST PATCHY FOG WITH VISBYS BETWEEN 2 AND 4SM. ANY FOG THAT DEVELOPS WILL GRADUALLY LIFT INTO AN MVFR OVERCAST AFTER 14Z. SKIES WILL THEN CLEAR OUT BY MONDAY AFTERNOON...AS LOW PRESSURE SLOWLY EXITS THE REGION. BARNES && .PREV DISCUSSION... ISSUED 330 AM CDT SUN SEP 2 2012 SHORT TERM...TODAY THROUGH TUESDAY NIGHT 1007 MB LOW PRESSURE (REMNANTS OF ISAAC) WAS EAST OF ST LOUIS EARLY THIS MORNING WITH A FEW SPIRAL BANDS OF SHOWERS OVER EASTERN AND NORTHERN COUNTIES WHILE HEAVIER SHOWERS AND ISOLATED THUNDERSTORMS WERE INTO NE IL AND NORTHERN INDIANA. TROPICAL AIRMASS STILL IN PLACE WITH DEWPOINTS IN THE LOWER 70S (EXCEPT 69F AT GALESBURG). MODELS HAVE TRENDED A SLOW SE MOVEMENT OF LOW PRESSURE FROM EAST OF ST LOUIS INTO SE IL BY EARLY EVENING AND INTO WESTERN KY ON LABOR DAY. HAVE HIGHEST CHANCES OF SHOWERS AND ISOLATED THUNDERSTORMS OVER EASTERN/SE IL TODAY WITH ADDITIONAL RAINFALL AMOUNTS OF A HALF TO 1 INCH. THE RISK OF BRIEF/WEAK TORNADOES AND HEAVIEST RAINS SHOULD SHIFT EAST OF IL OVER IN/KY WHERE AIRMASS WILL BE MORE UNSTABLE. HIGHS GENERALLY IN THE LOWER 80S TODAY WITH A FEW UPPER 70S IN EAST CENTRAL IL WITH A FAIR AMOUNT OF LOW CLOUD COVER...THOUGH SOME PEEKS OF SUNSHINE AS HAS BEE THE CASE THE PAST FEW DAYS. CHANCES OF SHOWERS DIMINISH FROM WEST TO EAST TONIGHT AND MONDAY AND COULD SEE PATCHY FOG DEVELOP OVERNIGHT WEST/NW OF I-55 ESPECIALLY IF WE CAN CLEAR OUT DUE TO VERY MOIST AIRMASS AND LIGHT WINDS. A BIT WARMER MONDAY WITH MORE SUNSHINE AND HIGHS GENERALLY IN THE MID 80S. A WEAK SHORT WAVE RACES EASTWARD INTO IL FROM THE CENTRAL PLAINS TUE AND COULD BRING ISOLATED SHOWERS AND THUNDERSTORMS ESPECIALLY TUE AFTERNOON WITH HUMID AIR MASS LINGERING. RISK OF SEVERE STORMS IS WEST OF IL TUE OVER NEBRASKA WITH 5% RISK OVER SCHUYLER COUNTY IN WEST CENTRAL IL. HIGHS IN THE MID TO UPPER 80S TUE. LONG TERM...WEDNESDAY THROUGH SATURDAY ENSEMBLE MODELS CONTINUE TO SHOW UPPER LEVEL TROUGHING INTO THE MIDWEST AND GREAT LAKES REGION DURING THE 2ND HALF OF THIS WEEK WITH A PROGRESSIVE STEERING FLOW OVER IL. A FEW DISTURBANCES TRACK EAST SOUTHEAST INTO THE REGION BRINGING PERIODIC CHANCES OF CONVECTION. THE BEST THREAT FOR PRECIPITATION DURING THIS PERIOD WILL BE ON WEDNESDAY AS AN UPPER DISTURBANCE PASSES EAST ACROSS THE UPPER GREAT LAKES AND AGAIN LATER IN THE WEEK...AS MORE ENSEMBLE MEMBERS DROP ANOTHER DISTURBANCE INTO THE MIDWEST. COOLER AND LESS HUMID AIR TO FILTER INTO IL AFTER WED WITH A COLD FRONT SLIDING SE THROUGH IL WED AFTERNOON/EVENING. KH && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$
AREA FORECAST DISCUSSION
NWS GOODLAND KS
859 PM MDT MON SEP 3 2012 .UPDATE... ISSUED AT 841 PM MDT MON SEP 3 2012 JUST COMPLETED AN UPDATE. PRECIPITATION FORECAST APPEARS TO BE ON TRACK. EARLIER PRECIPITATION HAS DECREASED OR ENDED. HOWEVER...ENTRANCE REGION OF UPPER JET REMAINS IN THE AREA THROUGH THE NIGHT AS ANOTHER SHORTWAVE TROUGH MOVES THROUGH. ALSO SOME SURFACE CONVERGENCE AROUND MAINLY IN THE NORTHWEST. CURRENT ANALYSIS HAS INCREASING ELEVATED CINH AND DECREASING ELEVATED CAPE. NAM SHOWS NO INSTABILITY DURING THE NIGHT WITH GFS MAINTAINING A DECENT AMOUNT OF ELEVATED CAPE WITH NOT A LOT OF CINH. MODELS INSISTING ON KEEPING OR REDEVELOPING PRECIPITATION OVER THE SOUTHERN PORTION OF THE AREA THROUGH THE NIGHT. AFTER SAYING ALL THAT CURRENT GRIDS DO HAVE THIS DEPICTION AND FEEL COMFORTABLE IN KEEPING THIS FORECAST AT THIS TIME. WEST WINDS AND LOWER DEWPOINTS LOOK TO SPREAD FROM WEST TO EAST ACROSS THE AREA THROUGH THE NIGHT WITH THE THICKEST CLOUD COVER OVER THE SOUTH. AS A RESULT LOWERED DEWPOINTS OVER THE ENTIRE AREA AND LOWERED MINS OVER THE NORTHERN HALF TO TWO THIRDS. && .SHORT TERM...(THIS EVENING THROUGH TUESDAY) ISSUED AT 200 PM MDT MON SEP 3 2012 LATEST WV IMAGERY SHOWS A NARROW BAND OF SUBSIDENCE OVER EASTERN COLORADO MOVING INTO THE TRI-STATE AREA BEHIND THE UPPER LEVEL TROUGH THAT BROUGHT LIGHT RAINFALL TODAY. RUC ANALYSIS HAS A SECOND SHORT WAVE TROUGH FOLLOWING THE SUBSIDENCE BEHIND THE INITIAL SHORT WAVE. AT THE SURFACE THE COLD FRONT FROM YESTERDAY EXTENDS FROM SOUTHWEST KANSAS NORTHEAST TO IOWA. ANY STORM ACTIVITY THAT DEVELOPS ALONG THE FRONT SHOULD BE WELL SOUTH OF THE AREA. OTHERWISE A SUBTLE SURFACE TROUGH WAS LOCATED BETWEEN WRAY AND SAINT FRANCIS...WHICH MAY SERVE TO HELP FOCUS CONVECTION OVER THE NORTHWEST LATE THIS AFTERNOON AND THIS EVENING. EARLY THIS EVENING SURFACE CONVERGENCE WILL DEVELOP OVER THE NORTHWEST PART OF THE AREA BELOW A 700-500MB SHORT WAVE TROUGH. THE DEEP LIFTING WILL GIVE THE BEST SHOT FOR RAINFALL TO REACH THE GROUND. MEANWHILE THERE MAY BE SOME LINGERING STORMS IN THE HILL CITY TO MCCOOK AREA...AS THE 700-500MB SHORT WAVE TROUGH THAT BROUGHT RAIN EARLIER TODAY DEPARTS THE AREA. AS THE NIGHT PROGRESSES PRECIP. CHANCES SHIFT FROM THE NORTHWEST TO THE SOUTH AS A ANOTHER SHORT WAVE TROUGH MOVES ACROSS THE AREA. WITH A DEEP DRY LAYER IN PLACE...AM NOT TOO CONFIDENT ANYTHING WILL REACH THE GROUND. TUESDAY ANOTHER SHORT WAVE TROUGH WILL MOVE THROUGH THE AREA. DURING THE LATE MORNING THROUGH THE AFTERNOON A PRE-FRONTAL TROUGH WILL DEVELOP AT THE SURFACE BELOW THE SHORT WAVE TROUGH. LIFT ALONG THE SURFACE AND MID LEVEL TROUGH INCREASE THROUGH THE DAY. WITH STRONGER LIFT OCCURRING DURING THE AFTERNOON HAVE INCREASED PRECIP. CHANCES ALONG AND EAST OF THE SURFACE TROUGH. THESE AREAS WILL BE MORE LIKELY TO HAVE STRONG TO SEVERE THUNDERSTORMS DUE TO THE BETTER INSTABILITY. THE 0-6KM SHEAR WILL BE AROUND 30 TO 35 KTS FOR THE PERIOD...WHICH WILL SUPPORT ORGANIZED STORM STRUCTURE WITH PROLONGED UPDRAFTS. AM THINKING THE MAIN THREAT WITH THESE STORMS WILL BE STRONG TO SEVERE WIND GUSTS DUE TO THE HIGH CLOUD BASES. TEMPERATURES WILL BE SIMILAR TO LAST NIGHT AND TODAY...WITH LOWS IN UPPER 50S TO LOW 60S AND HIGHS IN THE 90S. .LONG TERM...(TUESDAY NIGHT THROUGH MONDAY) ISSUED AT 131 PM MDT MON SEP 3 2012 TUESDAY NIGHT-THURSDAY...WILL KEEP A SMALL CHANCE OF PRECIPITATION IN THE FORECAST EARLY TUESDAY NIGHT BEFORE DRIER AIR WORKS INTO THE AREA UNDER NORTHWEST FLOW ALOFT THROUGH EARLY THURSDAY MORNING. NOT TERRIBLY EXCITED ABOUT PRECIPITATION CHANCES THURSDAY AFTERNOON DESPITE MOISTURE AVAILABILITY AS DYNAMICS RATHER WEAK. TRIMMED POPS DOWN JUST A BIT. HIGH TEMPERATURES WEDNESDAY IN THE LOW TO MID 80S...WARMING INTO THE UPPER 80S TO LOW 90S THURSDAY. LOWS IN THE 50S TO LOW 60S. THURSDAY NIGHT-FRIDAY NIGHT...PRECIPITATION CHANCES WILL SLOWLY INCREASE THROUGH FRIDAY AS AN UPPER TROUGH AND COLD FRONT APPROACH THEN MOVE THROUGH THE AREA. PRECIP CHANCES DECREASE FROM NORTH TO SOUTH FRIDAY NIGHT AS THE SYSTEM MOVES OUT OF THE AREA AND STABLE HIGH PRESSURE MOVES IN. HIGH TEMPERATURES FRIDAY 75-80. LOWS THURSDAY NIGHT IN THE LOW 60S COOLING INTO THE LOW TO MID 50S FRIDAY NIGHT BEHIND THE FRONT. SATURDAY-MONDAY...DRY. HIGH TEMPERATURES SATURDAY IN THE MID TO UPPER 70S...WARMING INTO THE MID 80S TO AROUND 90 BY MONDAY. OVERNIGHT LOWS NEAR TO SLIGHTLY ABOVE NORMAL. && .AVIATION...(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING) ISSUED AT 513 PM MDT MON SEP 3 2012 VFR CONDITIONS WILL PERSIST THROUGH THE TAF PERIOD AT BOTH GLD AND MCK. SKIES HAVE CLEARED THIS EVENING FOLLOWING AN AREA OF SHOWERS AND SKIES ARE EXPECTED TO REMAIN MOSTLY CLEAR THROUGH THE NIGHT. LATE TOMORROW MORNING AN UPPER LEVEL SHORTWAVE WILL MOVE THROUGH BRINGING SOME CLOUDS AND ISOLATED THUNDERSTORMS...BUT AT THIS POINT BEST AXIS FOR PRECIPITATION LOOKS TO STAY EAST OF BOTH TERMINALS. && .FIRE WEATHER... ISSUED AT 200 PM MDT MON SEP 3 2012 TUESDAY AFTERNOON AREAS NORTH OF A KIT CARSON TO MCCOOK LINE WILL HAVE RELATIVE HUMIDITIES DROP TO AROUND 15 PERCENT DURING THE AFTERNOON. IN ADDITION WIND GUSTS AROUND 20 MPH CAN BE EXPECTED. WHILE THIS IS BELOW ISSUANCE CRITERIA...CARE SHOULD BE TAKEN FOR ANY OUTDOOR BURNING. && .GLD WATCHES/WARNINGS/ADVISORIES... KS...NONE. CO...NONE. NE...NONE. && $$ UPDATE...BULLER SHORT TERM...JTL LONG TERM...99 AVIATION...JJM/BULLER FIRE WEATHER...JTL
AREA FORECAST DISCUSSION
NWS GOODLAND KS
515 PM MDT MON SEP 3 2012 .SHORT TERM...(THIS EVENING THROUGH TUESDAY) ISSUED AT 200 PM MDT MON SEP 3 2012 LATEST WV IMAGERY SHOWS A NARROW BAND OF SUBSIDENCE OVER EASTERN COLORADO MOVING INTO THE TRI-STATE AREA BEHIND THE UPPER LEVEL TROUGH THAT BROUGHT LIGHT RAINFALL TODAY. RUC ANALYSIS HAS A SECOND SHORT WAVE TROUGH FOLLOWING THE SUBSIDENCE BEHIND THE INITIAL SHORT WAVE. AT THE SURFACE THE COLD FRONT FROM YESTERDAY EXTENDS FROM SOUTHWEST KANSAS NORTHEAST TO IOWA. ANY STORM ACTIVITY THAT DEVELOPS ALONG THE FRONT SHOULD BE WELL SOUTH OF THE AREA. OTHERWISE A SUBTLE SURFACE TROUGH WAS LOCATED BETWEEN WRAY AND SAINT FRANCIS...WHICH MAY SERVE TO HELP FOCUS CONVECTION OVER THE NORTHWEST LATE THIS AFTERNOON AND THIS EVENING. EARLY THIS EVENING SURFACE CONVERGENCE WILL DEVELOP OVER THE NORTHWEST PART OF THE AREA BELOW A 700-500MB SHORT WAVE TROUGH. THE DEEP LIFTING WILL GIVE THE BEST SHOT FOR RAINFALL TO REACH THE GROUND. MEANWHILE THERE MAY BE SOME LINGERING STORMS IN THE HILL CITY TO MCCOOK AREA...AS THE 700-500MB SHORT WAVE TROUGH THAT BROUGHT RAIN EARLIER TODAY DEPARTS THE AREA. AS THE NIGHT PROGRESSES PRECIP. CHANCES SHIFT FROM THE NORTHWEST TO THE SOUTH AS A ANOTHER SHORT WAVE TROUGH MOVES ACROSS THE AREA. WITH A DEEP DRY LAYER IN PLACE...AM NOT TOO CONFIDENT ANYTHING WILL REACH THE GROUND. TUESDAY ANOTHER SHORT WAVE TROUGH WILL MOVE THROUGH THE AREA. DURING THE LATE MORNING THROUGH THE AFTERNOON A PRE-FRONTAL TROUGH WILL DEVELOP AT THE SURFACE BELOW THE SHORT WAVE TROUGH. LIFT ALONG THE SURFACE AND MID LEVEL TROUGH INCREASE THROUGH THE DAY. WITH STRONGER LIFT OCCURRING DURING THE AFTERNOON HAVE INCREASED PRECIP. CHANCES ALONG AND EAST OF THE SURFACE TROUGH. THESE AREAS WILL BE MORE LIKELY TO HAVE STRONG TO SEVERE THUNDERSTORMS DUE TO THE BETTER INSTABILITY. THE 0-6KM SHEAR WILL BE AROUND 30 TO 35 KTS FOR THE PERIOD...WHICH WILL SUPPORT ORGANIZED STORM STRUCTURE WITH PROLONGED UPDRAFTS. AM THINKING THE MAIN THREAT WITH THESE STORMS WILL BE STRONG TO SEVERE WIND GUSTS DUE TO THE HIGH CLOUD BASES. TEMPERATURES WILL BE SIMILAR TO LAST NIGHT AND TODAY...WITH LOWS IN UPPER 50S TO LOW 60S AND HIGHS IN THE 90S. .LONG TERM...(TUESDAY NIGHT THROUGH MONDAY) ISSUED AT 131 PM MDT MON SEP 3 2012 TUESDAY NIGHT-THURSDAY...WILL KEEP A SMALL CHANCE OF PRECIPITATION IN THE FORECAST EARLY TUESDAY NIGHT BEFORE DRIER AIR WORKS INTO THE AREA UNDER NORTHWEST FLOW ALOFT THROUGH EARLY THURSDAY MORNING. NOT TERRIBLY EXCITED ABOUT PRECIPITATION CHANCES THURSDAY AFTERNOON DESPITE MOISTURE AVAILABILITY AS DYNAMICS RATHER WEAK. TRIMMED POPS DOWN JUST A BIT. HIGH TEMPERATURES WEDNESDAY IN THE LOW TO MID 80S...WARMING INTO THE UPPER 80S TO LOW 90S THURSDAY. LOWS IN THE 50S TO LOW 60S. THURSDAY NIGHT-FRIDAY NIGHT...PRECIPITATION CHANCES WILL SLOWLY INCREASE THROUGH FRIDAY AS AN UPPER TROUGH AND COLD FRONT APPROACH THEN MOVE THROUGH THE AREA. PRECIP CHANCES DECREASE FROM NORTH TO SOUTH FRIDAY NIGHT AS THE SYSTEM MOVES OUT OF THE AREA AND STABLE HIGH PRESSURE MOVES IN. HIGH TEMPERATURES FRIDAY 75-80. LOWS THURSDAY NIGHT IN THE LOW 60S COOLING INTO THE LOW TO MID 50S FRIDAY NIGHT BEHIND THE FRONT. SATURDAY-MONDAY...DRY. HIGH TEMPERATURES SATURDAY IN THE MID TO UPPER 70S...WARMING INTO THE MID 80S TO AROUND 90 BY MONDAY. OVERNIGHT LOWS NEAR TO SLIGHTLY ABOVE NORMAL. && .AVIATION...(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING) ISSUED AT 513 PM MDT MON SEP 3 2012 VFR CONDITIONS WILL PERSIST THROUGH THE TAF PERIOD AT BOTH GLD AND MCK. SKIES HAVE CLEARED THIS EVENING FOLLOWING AN AREA OF SHOWERS AND SKIES ARE EXPECTED TO REMAIN MOSTLY CLEAR THROUGH THE NIGHT. LATE TOMORROW MORNING AN UPPER LEVEL SHORTWAVE WILL MOVE THROUGH BRINGING SOME CLOUDS AND ISOLATED THUNDERSTORMS...BUT AT THIS POINT BEST AXIS FOR PRECIPITATION LOOKS TO STAY EAST OF BOTH TERMINALS. && .FIRE WEATHER... ISSUED AT 200 PM MDT MON SEP 3 2012 TUESDAY AFTERNOON AREAS NORTH OF A KIT CARSON TO MCCOOK LINE WILL HAVE RELATIVE HUMIDITIES DROP TO AROUND 15 PERCENT DURING THE AFTERNOON. IN ADDITION WIND GUSTS AROUND 20 MPH CAN BE EXPECTED. WHILE THIS IS BELOW ISSUANCE CRITERIA...CARE SHOULD BE TAKEN FOR ANY OUTDOOR BURNING. && .GLD WATCHES/WARNINGS/ADVISORIES... KS...NONE. CO...NONE. NE...NONE. && $$ SHORT TERM...JTL LONG TERM...99 AVIATION...JJM/BULLER FIRE WEATHER...JTL
AREA FORECAST DISCUSSION
NWS MARQUETTE MI
826 PM EDT MON SEP 3 2012 .SHORT TERM...(THIS EVENING THROUGH TUESDAY) ISSUED AT 517 PM EDT MON SEP 3 2012 WATER VAPOR IMAGERY AND RUC ANALYSIS SHOW WSW FLOW OVER THE UPPER GREAT LAKES BTWN UPPER RIDGE EXTENDING FROM THE PLAINS TO THE LWR LAKES AND A DEEP...OCCLUDED LOW OVER NRN MANITOBA. NARROW MOISTURE RIBBON HAS SHIFTED INTO THE UPPER LAKES IN ASSOCIATION WITH DISSIPATING SFC TROF ORIGINALLY ASSOCIATED WITH DEEP SYSTEM IN NRN MANITOBA. LEFT EXIT OF UPPER JET STREAK AIDED EARLY MORNING CONVECTION OVER NW UPPER MI/LAKE SUPERIOR. BASED ON LATEST RUC ANALYSIS...IT APPEARS CONVECTION THAT HAS BEEN DEVELOPING MAY BE GETTING SOME SUPPORT FROM THE RIGHT ENTRANCE OF JET STREAK NOW. ONGOING CONVECTION OVER ROUGHLY THE SE HALF OF THE FCST AREA WILL CONTINUE SETTLE SE INTO THE EVENING HRS. WITH MUCAPE ON THE ORDER OF 1000-2000J/KG AND DEEP LAYER SHEAR AROUND 40KT...ORGANIZED STORMS WILL CONTINUE ALONG WITH THE POTENTIAL OF SVR FOR THE NEXT SEVERAL HRS. SHRA/TSRA SHOULD BE OUT OF THE SE/SCNTRL FCST AREA MID TO LATE EVENING. HEALTHY DRYING ALOFT (NOTE UPSTREAM 12Z KINL SOUNDING) WILL THEN OCCUR THRU THE NIGHT...ENDING ANY THREAT OF ADDITIONAL PCPN. CONSIDERING DRYNESS OF INCOMING AIR MASS AND LIGHT/CALM WIND UNDER BUBBLE SFC HI PRES BUILDING INTO THE AREA...FAVORED THE LOWER SIDE OF AVBL GUIDANCE FOR MIN TEMPS. VIGOROUS DRYING ALOFT/LIGHT WINDS FAVOR FOG DEVELOPMENT...ESPECIALLY SINCE THERE HAS BEEN RAINFALL TODAY. THUS...MAINTAINED MENTION OF AREAS OF FOG OVER MUCH OF THE INTERIOR. ON TUE...ATTENTION TURNS TO A COUPLE OF SHORTWAVES EXTENDING FROM ND INTO MT. ONE OR BOTH OF THESE WAVES WILL REACH THE UPPER LAKES TUE AND WILL LIKELY PROVIDE SUFFICIENT FORCING FOR ISOLD/SCT CONVECTION. GIVEN THAT CONVECTION IS CURRENTLY BEING OBSERVED OVER THE ERN DAKOTAS AHEAD OF THE FIRST WAVE...BUMPED POPS UP INTO THE CHC CATEGORY OVER ROUGHLY THE W HALF OF THE FCST AREA TUE. ALTHOUGH NAM/GFS MLCAPES ARE IN THE 1500-2500J/KG RANGE...DEEP LAYER SHEAR IS UNDER 30KT WHICH WILL WORK TO LIMIT MORE WIDESPREAD SVR POTENTIAL. NONETHELESS...IF STORMS DO DEVELOP...MAY SEE SOME ISOLD/PULSE TYPE SVR STORMS TUE AFTN. .LONG TERM...(TUESDAY NIGHT THROUGH MONDAY) ISSUED AT 517 PM EDT MON SEP 3 2012 BASIC OUTLOOK OF THE LONG TERM NOT TOO DIFFERENT FROM YESTERDAY. WV LOOP AND 12Z RAOBS INDICATE PAIR OF UPPER LOWS IN CANADA FROM NORTHERN MANITOBA INTO NORTHERN BRITISH COLUMBIA. MANITOBA LOW STAYS FAIRLY STATIONARY THROUGH WEDNESDAY WHILE THE BRITISH COLUMBIA LOW DIGS TO ITS SOUTH AND EVENTUALLY SOUTHEAST INTO NORTHERN ONTARIO. AS THIS OCCURS...STRONG SFC-H85 COLD FRONT MARCHES ACROSS UPPER GREAT LAKES WEDNESDAY AFTERNOON AND EVENING. DYNAMICS PROVIDED BY 12-HR H5 HEIGHT FALLS TO 60M AND A COUPLED JET STRUCTURE COMBINE WITH SFC-H85 FRONT AND SURGE OF H85 MOISTURE TRANSPORT TO GENERATE SHRA ALONG AND AHEAD OF THE FRONT. DEPENDING ON TIMING OF FRONT AND HEATING AHEAD OF FRONT...TSRA COULD BE STRONG GIVEN 0-6KM CAPES UP TO 1500 J/KG AND AS H85 JET INCREASES OVER CWA AND BECOMES PARALLEL TO THE H5 FLOW. SETUP IS FAVORABLE FOR DYNAMICALLY DRIVEN BOW-ECHO SOMEWHERE OVER THE AREA AS THERE IS A DRY H7-H5 LAYER PUNCHING INTO THE AREA FROM THE WEST WITH DWPNT DEPRESSIONS OVR 20C BY LATER AFTN. BEST CHANCE FOR SEVERE PROBABLY ENDS UP SOUTH AND EAST OF CWA WHERE GREATEST MLCAPES ARE FORECAST IN THE AFTN. AT THE LEAST...LIKELY POPS ARE CERTAINLY WARRANTED AS THE SFC-H85 FRONT WORKS ACROSS THE CWA. ONCE FRONT PLOWS THROUGH MAY SEE HIGHER WIND GUSTS WEDNESDAY NIGHT INTO THURSDAY AS SFC LOW WRAPS UP BTWN LAKE SUPERIOR AND HUDSON BAY. GFS/ECMWF H85 WINDS NOT THAT STRONG...MAYBE UP TO 30 KTS...SO DOES NOT APPEAR THAT WINDS WILL BECOME TOO STRONG. IF THE SFC LOW ENDS UP DEEPENING CLOSER TO LK SUPERIOR...COULD SEE NORTHWESTERLY WIND GUSTS ALONG LK SUPERIOR 40-45 MPH. AT THIS POINT...WX ON THURSDAY SHOULD END UP QUIET AS UPR MICHIGAN IS BTWN THE STRONG SHORTWAVE TROUGH THAT MOVES THROUGH MID WEEK AND RE-INFORCING TROUGH THAT IS FORECAST TO ROTATE THROUGH ON FRIDAY. FORECAST SOUNDINGS FROM GFS AND OUTPUT FROM GEM-NHEM INDICATE SOME POTENTIAL FOR LIGHT SHRA OVER THE EASTERN CWA IN WEAK AREA OF LOW-LEVEL CONVERGENCE. SEEMS GREATER CHANCE OF SHRA ARRIVES ON FRIDAY WITH THE INCOMING TROUGH AND INDICATION OF SHORTWAVE RIDING THROUGH IN WEST/NORTHWEST FLOW ALOFT. THIS FORCING ALONG WITH INCREASING OVER-WATER INSTABILITY WITH LAKE EFFECT CAPES PUSHING AOA 500J/KG SUGGESTS HYBRID LATE SUMMER AND EARLY FALL TYPE SHRA AND MAYBE EVEN MENTION OF TSRA GIVEN LAKE INDUCED EQL OVER 20KFT WHICH PUSHES CONVECTIVE DEPTH BLO 0C. GIVEN LAKE-H85 DELTA T AOA 15C...DEEP LAKE INDUCED CLOUD DEPTH...AND WINDS WITHIN THE MIXED LAYER STAYING BLO 25 KTS...PARAMETERS STILL LINE UP FOR WATERSPOUT POTENTIAL ON FRIDAY...ESPECIALLY IF SUBTLE LOW-LEVEL TROUGH THAT IS SHOWING UP IN MODELS OVER EASTERN LK SUPERIOR/EASTERN CWA DOES INDEED VERIFY. TOUGH TO INCLUDE MENTION OF WATERSPOUTS THIS FAR OUT IN THE FORECAST BUT WILL BE INTERESTING TO SEE OUTPUT IN THE NEXT COUPLE DAYS FROM THE NEW EXPERIMENTAL GREAT LAKES WATERSPOUT FORECAST BASED ON THE SZILAGYI WATERSPOUT INDEX /SWI/ THAT COMES OUT OF THE INTERNATIONAL CENTRE FOR WATERSPOUT RESEARCH /ICWR/. IN ADDITION TO WATERSPOUTS...WILL ALSO LIKELY HAVE INCREASED RISK OF RIP CURRENTS ALONG LK SUPERIOR BEACHES...MAINLY IN ALGER COUNTY WITH THE EXPECTED NORTHWEST WINDS. UPPER TROUGH SLOWLY MOVES EAST THROUGH NEXT WEEKEND. THIS PLACES UPPER LAKES WITHIN ZONE OF SHARP CONFLUENCE AND ASSOCIATED SFC RIDGING. ECMWF HAS DEFINITELY TRENDED FARTHER EAST WITH TROUGH AND KEEPS QPF OUT OF UPR MICHIGAN FOR THE WEEKEND. GFS IS SLIGHTLY FARTHER WEST WITH THE TROUGH AND WOULD KEEP THREAT OF SHRA OVER EASTERN CWA ON SATURDAY. BASED ON AMPLIFIED PATTERN CANNOT RULE THIS IDEA OUT AND WILL AT THE LEAST KEEP CONSENSUS SLIGHT CHANCE POPS AND BUMP UP SKY COVER. SUNDAY INTO MONDAY IS TOUGH TO FIGURE OUT AS ECMWF CONTINUES TO INDICATE STRONGER SHORTWAVE WITHIN BASE OF TROUGH LIFTING NORTH AND AFFECTING THE EASTERN PORTIONS OF CWA WITH SOME SHRA WHILE THE GFS KEEPS ALL THIS TOO FAR TO THE EAST TO AFFECT THE AREA. NO REAL CONSISTENT SIGNAL FOR EITHER SOLUTION SO HAVE TO KEEP CONSENSUS POPS AT THIS TIME. && .AVIATION...(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING) ISSUED AT 825 PM EDT MON SEP 3 2012 THE WEAK SFC TROF RESPONSIBLE FOR THE SHRA ACTIVITY TODAY HAS MOVED SOUTHEAST OF TAF SITES. WITH MOISTURE FROM RECENT RAINFALL AND SFC WINDS DIMINISHING TO LIGHT/CALM UNDER THE UPPER LEVEL DRYING...FOG/STRATUS IS LIKELY TO FORM TONIGHT WITH IFR POSSIBLE LIFR CONDITIONS. FOG WILL DISSIPATE WITHIN A COUPLE OF HRS AFTER SUNRISE WED. NEXT DISTURBANCE APPROACHING THE AREA MAY TRIGGER ISOLD/SCT CONVECTION WED AFTERNOON...ESPECIALLY IN VCNTY OF KIWD. && .MARINE...(FOR THE 4 AM LAKE SUPERIOR FORECAST ISSUANCE) ISSUED AT 429 AM EDT MON SEP 3 2012 EXPECT S WINDS UP TO 20 KTS IN ADVANCE OF AN APPROACHING COLD FRONT TO DIMINISH THIS EVENING AS THE FRONT TENDS TO WEAKEN. LIGHT WINDS WILL THEN PREVAIL THRU TONIGHT AS A WEAK HI PRES SYSTEM MOVES INTO THE UPPER GREAT LAKES. A SERIES OF LOW PRESSURE SYSTEMS AND COLD FRONTS WILL MOVE NEAR LAKE SUPERIOR TUESDAY THROUGH SUNDAY...LEADING TO PERIODS OF INCREASED WINDS. HOWEVER...AT THIS TIME WINDS ARE EXPECTED TO REMAIN BELOW 25KTS. && .MQT WATCHES/WARNINGS/ADVISORIES... UPPER MICHIGAN... NONE. LAKE SUPERIOR... NONE. LAKE MICHIGAN... NONE. && $$ SHORT TERM...ROLFSON LONG TERM...JLA AVIATION...VOSS MARINE...KC/TITUS
AREA FORECAST DISCUSSION
NWS MARQUETTE MI
656 PM EDT SUN SEP 2 2012 .SHORT TERM...(THIS EVENING THROUGH MONDAY) ISSUED AT 347 PM EDT SUN SEP 2 2012 WATER VAPOR IMAGERY AND RUC ANALYSIS SHOW A STRONG SHORTWAVE/MID LEVEL LOW MOVING NE THRU CNTRL SASKATCHEWAN. DOWNSTREAM RIDGE EXTENDS FROM THE SW PLAINS THRU THE UPPER LAKES WHILE REMNANT OF ISAAC DRIFTS THRU THE LWR OHIO VALLEY. DUE TO ISAAC...MOISTURE RETURN THRU THE PLAINS HAS BEEN VERY LIMITED AS 12Z RAOBS SHOW 850MB DWPT DEPRESSIONS BTWN 15-25C. NONETHELESS...SCT HIGH BASED -SHRA/TSRA HAVE BEEN OCCURRING ACROSS THE DAKOTAS INTO NW MN TODAY IN THE VCNTY OF COLD FRONT ASSOCIATED WITH THE PARENT SHORTWAVE OVER SASKATCHEWAN. A COUPLE OF MINOR SHORTWAVES APPEAR TO BE AIDING THE CONVECTION. IN THE SHORT TERM...MAIN FOCUS WILL BE ON PCPN CHANCES LATE TONIGHT THRU MON AS WEAKENING COLD FRONT ARRIVES. WITH ONLY A NARROW RIBBON OF MOISTURE SUPPORTING PCPN TO THE W...THE EVENING HRS TONIGHT WILL REMAIN DRY WHILE AWAITING COLD FRONT/MOISTURE RIBBON TO MOVE CLOSER. IN CONJUNCTION WITH THE COLD FRONT...A SHORTWAVE NOW OVER THE DAKOTAS WILL LIFT NE TONIGHT. ALONG TAIL OF WAVE AND LEFT EXIT OF SUPPORTING JET STREAK...SHOULD SEE A BAND OF SCT CONVECTION TONIGHT. THAT CONVECTION MAY SHIFT OUT OVER LAKE SUPERIOR AND NW UPPER MI LATE TONIGHT. AS FOR TEMPS...THE HIGHEST MIN TEMPS TONIGHT WILL BE IN THE DOWNSLOPE AREAS NEAR LAKE SUPERIOR...PARTICULARLY THE W WHERE MOISTENING WILL BE MORE PRONOUNCED. TEMPS SHOULDN`T FALL LWR THAN THE MID/UPPER 60S IN THOSE AREAS. 50S WILL BE THE RULE OVER THE SCNTRL/E. SHORTWAVE/MID LEVEL LOW CURRENTLY OVER SASKATCHEWAN DRIFTS INTO NRN MANITOBA MON. WITH MAIN SYSTEM WELL TO THE NW OF HERE...SFC COLD FRONT WILL BE WEAKENING AS IT REACHES UPPER MI. LACK OF DYNAMICS AND DIMINISHING LOW-LEVEL CONVERGENCE ALONG FRONT WILL WORK TO LIMIT COVERAGE OF CONVECTION MON...ESPECIALLY SINCE THERE WILL BE SOME DRY AIR TO OVERCOME. HOWEVER...NARROW RIBBON OF BOUNDARY LAYER MOISTURE SHOULD BE SUFFICIENT FOR ISOLD/SCT CONVECTION. AS AFORMENTIONED JET STREAK AIDING PCPN LATE TONIGHT SHIFTS NE...THE RIGHT ENTRANCE OF THE JET WILL PROBABLY PROVIDE BEST SUPPORT FOR NEW CONVECTION IN THE AFTN HRS OVER SCNTRL UPPER MI INTO NE WI. PROVIDED MLCAPE INCREASES TO UPWARDS OF 1500-2000J/KG PER GFS AND ESPECIALLY NAM...DEEP LAYER SHEAR OF 30-40KT WILL SUPPORT ORGANIZED STORMS AND SVR POTENTIAL IF ANY STORMS DO DEVELOP. COVERAGE OF SVR STORMS WOULD LIKELY BE ISOLD. .LONG TERM...(MONDAY NIGHT THROUGH SUNDAY) ISSUED AT 347 PM EDT SUN SEP 2 2012 LONG TERM PERIOD STARTS OUT WITH UPPER LOW OVER MANITOBA WHILE ADDITIONAL SHORTWAVE TROUGH CURRENTLY DIGGING INTO FAR NORTHERN BRITISH COLUMBIA MERGES WITH THE LOW ON WEDNESDAY. INITIAL FRONT THAT MOVES THROUGH UPR MICHIGAN ON LABOR DAY LIKELY STALLS OUT MONDAY NIGHT INTO TUESDAY AS IT PARALLELS UPPER FLOW. MAJORITY OF SHRA/TSRA...ALBEIT ONLY ISOLD/SCT COVERAGE...SHOULD BE DIMINISHING BY LATER MONDAY NIGHT. KEPT SMALL POPS IN ONLY FOR THE SOUTH AND EAST CWA AS THOSE AREAS STAY IN AT LEAST A WEAK AREA OF RIGHT ENTRANCE JET FORCING. LINGERED SLIGHT CHANCES FOR THE SAME AREAS THROUGH MOST OF THE NIGHT AS THE SURFACE FRONT REMAINS IN THE VICINITY AND LOW-LEVEL MOISTURE POOLS ALONG THE BOUNDARY. VERY SMALL CHANCES BUT CAN NOT COMPLETELY PULL THE POPS JUST YET. FRONT COULD SERVE AS FOCUS FOR MORE SHRA/TSRA ON TUESDAY AS NAM/00Z ECMWF INDICATE H85 TROUGH AND THETA-E ADVECTION ARRIVES DURING PEAK HEATING OF THE AFTERNOON. H85 DWPNTS ON THE LOW SIDE TO START THE DAY...SO SHOULD SEE BETTER CHANCES OF SHRA/TSRA AFTERNOON AND EVENING...SPREADING FROM WEST TO EAST AS H85 TROUGH CROSSES AREA. THOUGH 0-6KM SHEAR 20-25 KTS NOT TOO IMPRESSIVE FOR ORGANIZED SEVERE STORMS...MLCAPES AOA 1000 J/KG AND HIGH DEWPOINT DEPRESSIONS AT H7-H5 WITH MOIST LOW-LEVELS POINT TO POSSIBLE GUSTY WINDS WITH ANY TSRA. ANY SHRA/TSRA WOULD WANE BY LATER EVENING WITH LOSS OF HEATING/WEAKENING SFC-H85 CONVERGENCE. GFS AND LATEST GEM-NHEM AND 12Z ECMWF FOCUS H85 TROUGH MORE LATER TUESDAY NIGHT AND MORE SO ON WEDNESDAY WITH ARRIVAL OF PRIMARY COLD FRONT. BASED ON TREND FROM LATEST ECMWF...DECIDED TO NOT GO TOO HIGH FOR POPS ON TUESDAY. AS LARGER FORMED UPPER LOW COMPLEX OVER MANITOBA RUMBLES EAST INTO ONTARIO...EXPECT SHARP COLD FRONT TO SWEEP ACROSS GREAT LAKES REGION WEDNESDAY AND THURSDAY. WOULD THINK THERE WOULD BE DECENT CHANCE FOR RAIN WITH THE FROPA. BY TIME FRONT ARRIVES GFS AND GEM-NHEM SHOWS SHARP H85 WIND SHIFT AND MOISTURE ADVECTION INTO THE AREA. OTHER MODELS ALREADY SHOVE THE H85 TROUGH THROUGH SHUNTING MORE ABUNDANT MOISTURE SOUTHEAST OF CWA...BUT AS MENTIONED BEFORE LATEST ECMWF HAS TRENDED THIS WAY AS WELL. CONSISTENCY ON THESE SOLUTIONS NOT THE GREATEST. THERE ARE ALSO HINTS THAT YET ANOTHER WEAKER WAVE/H7 MOISTURE MAY BE SLIDING THROUGH AREA WHILE FRONT SLIDES THROUGH. DETAILS CERTAINLY STILL NEED TO BE SORTED OUT AS TO LOCATION AND COVERAGE OF BEST RAIN CHANCES ON WEDNESDAY. CHANCE POPS FOR SCT SHRA/TSRA COVER IT FINE FOR NOW. PRESSURE GRADIENT TIGHTENS WEDNESDAY NIGHT AND THURSDAY IN WAKE OF THE COLD FRONT BUT OTHER THAN FOR A BRIEF PERIOD WEDNESDAY EVENING WHERE GFS SHOWS 950-925MB WINDS 30-35 KTS...H925-H85 WINDS INTO THURSDAY ARE ONLY AROUND 20 KTS. SO EVEN THOUGH STEADY COOLING ALOFT OCCURS INTO THURSDAY...THIS SYSTEM DOES NOT LOOK TO PRODUCE VERY STRONG WINDS AS EARLY FALL SYSTEMS SOMETIMES CAN DO. TWO ISSUES THAT WILL NEED TO BE MONITORED THOUGH IN WAKE OF THE COLD FROPA WILL BE AN INCREASED RISK OF RIP CURRENTS AND POSSIBLE UPPER LOW TYPE WATERSPOUTS LATER THURSDAY INTO FRIDAY. ALTHOUGH HIGH PRESSURE TRIES TO BUILD IN LATE THIS WEEK IT REMAINS PRETTY WEAK AND DIFFUSE AS UPPER FLOW IS NOT CONFLUENT. BY FAR THE STRONGER SURFACE FEATURE WILL BE WRAPPED UP SURFACE LOW VICINITY OF HUDSON BAY AND JAMES BAY. BY LATER THURSDAY INTO FRIDAY CANNOT RULE OUT AT LEAST LIGHT LK EFFECT SHRA SINCE H85 TEMPS DROP TO 4-6C /WATER TEMPS STILL RUNNING 18-20C/ AND SINCE THERE COULD BE ANOTHER WEAKER SHORTWAVE/ADDITIONAL MOISTURE PUSHING INTO WESTERN GREAT LAKES PER GFS/ECMWF. NOT A BIG CHANCE AS LOW-LEVEL FLOW IS NOT THAT FAVORABLE GIVEN NEUTRAL TO ANTICYCLONIC LOOK...BUT SOME LIGHT PRECIP SEEMS POSSIBLE. MODEL DIFFERENCES EMERGE BY NEXT WEEKEND WITH THE MAIN ISSUE ON HOW QUICK THE 00Z GFS BRINGS ANOTHER LARGER SCALE TROUGH EAST ACROSS THE NORTHERN PLAINS. 00Z ECMWF INDICATES RIDGING BUILDS IN ALOFT WITH A SHARPER SURFACE RIDGE FROM THE PLAINS INTO FAR NORTHERN PORTION OF UPPER GREAT LAKES. 06Z-12Z RUNS OF GFS HAVE TRENDED ECMWF WAY. LATEST COUPLE RUNS OF ECMWF POINT TO UPPER LAKES BEING ON THE DRY FRINGE OF SET OF DISTURBANCES WHICH WOULD BRING RAIN TO PORTIONS OF GREAT LAKES TO START NEXT WEEKEND. HPC PREFERS TO SIDE WITH ECMWF IDEA AND THIS FORECAST WILL TILT THAT WAY AS WELL WITH A GENERAL DRY FCST NEXT WEEKEND. AFTER SLIGHTLY THAN NORMAL HIGH TEMPERATURES FRIDAY AND SATURDAY...EXPECT SOME MODERATION IN TEMPERATURES BY NEXT SUNDAY. && .AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING) ISSUED AT 655 PM EDT SUN SEP 2 2012 ALTHOUGH A FEW -SHRA MAY ARRIVE AT KIWD/KCMX LATE TONIGHT AND AT KSAW LATE MON MORNING AHEAD OF AN APPROACHING COLD FRONT...EXPECT VFR CONDITIONS THRU THIS FCST PERIOD AS LOW-LEVEL DRY AIR HOLDS. THERE IS A VERY SMALL POTENTIAL FOR STRATUS TO DEVELOP AT KSAW TONIGHT AS SE WINDS COULD ADVECT MARINE MODIFIED HIGHER DWPTS OFF LAKE MI INLAND AND UPSLOPE INTO COOLER BOUNDARY LAYER AIR. WILL BE SOMETHING TO MONITOR. MODEST LOW-LEVEL JET AHEAD OF COLD FRONT MAY RESULT IN LLWS AT KIWD/KCMX TONIGHT. && .MARINE...(FOR THE 4 PM LAKE SUPERIOR FORECAST ISSUANCE) ISSUED AT 347 PM EDT SUN SEP 2 2012 TIGHTENING PRES GRADIENT BTWN HIGH PRES TO THE E AND AN APPROACHING COLD FRONT TO THE W WILL RESULT IN SE TO S WINDS INCREASING TO AROUND 20KT TONIGHT. SOUTHERLY WINDS MAY GUST TO AROUND 25KT AT HIGHER OBS PLATFORMS...ESPECIALLY OVER CNTRL AND ERN PORTIONS OF THE LAKE. PRES GRADIENT THEN SLACKENS WITH PASSING/WEAKENING COLD FRONT MON...RESULTING IN WINDS DIMINISHING BACK TO UNDER 15KT MON INTO TUE. NEXT COLD FRONT PASSING TUE NIGHT/WED WILL BRING AN INCREASE IN W TO NW WINDS TO AROUND 20KT...MAYBE HIGHER...LATER WED INTO THU. WINDS WILL DIMINISH SLIGHTLY FRI AS NEXT TROF PASSES EARLY IN THE DAY. && .MQT WATCHES/WARNINGS/ADVISORIES... UPPER MICHIGAN... NONE. LAKE SUPERIOR... NONE. LAKE MICHIGAN... NONE. && $$ SHORT TERM...ROLFSON LONG TERM...JLA AVIATION...VOSS MARINE...ROLFSON
AREA FORECAST DISCUSSION
NWS MARQUETTE MI
356 PM EDT SUN SEP 2 2012 .SHORT TERM...(THIS EVENING THROUGH MONDAY) ISSUED AT 347 PM EDT SUN SEP 2 2012 WATER VAPOR IMAGERY AND RUC ANALYSIS SHOW A STRONG SHORTWAVE/MID LEVEL LOW MOVING NE THRU CNTRL SASKATCHEWAN. DOWNSTREAM RIDGE EXTENDS FROM THE SW PLAINS THRU THE UPPER LAKES WHILE REMNANT OF ISAAC DRIFTS THRU THE LWR OHIO VALLEY. DUE TO ISAAC...MOISTURE RETURN THRU THE PLAINS HAS BEEN VERY LIMITED AS 12Z RAOBS SHOW 850MB DWPT DEPRESSIONS BTWN 15-25C. NONETHELESS...SCT HIGH BASED -SHRA/TSRA HAVE BEEN OCCURRING ACROSS THE DAKOTAS INTO NW MN TODAY IN THE VCNTY OF COLD FRONT ASSOCIATED WITH THE PARENT SHORTWAVE OVER SASKATCHEWAN. A COUPLE OF MINOR SHORTWAVES APPEAR TO BE AIDING THE CONVECTION. IN THE SHORT TERM...MAIN FOCUS WILL BE ON PCPN CHANCES LATE TONIGHT THRU MON AS WEAKENING COLD FRONT ARRIVES. WITH ONLY A NARROW RIBBON OF MOISTURE SUPPORTING PCPN TO THE W...THE EVENING HRS TONIGHT WILL REMAIN DRY WHILE AWAITING COLD FRONT/MOISTURE RIBBON TO MOVE CLOSER. IN CONJUNCTION WITH THE COLD FRONT...A SHORTWAVE NOW OVER THE DAKOTAS WILL LIFT NE TONIGHT. ALONG TAIL OF WAVE AND LEFT EXIT OF SUPPORTING JET STREAK...SHOULD SEE A BAND OF SCT CONVECTION TONIGHT. THAT CONVECTION MAY SHIFT OUT OVER LAKE SUPERIOR AND NW UPPER MI LATE TONIGHT. AS FOR TEMPS...THE HIGHEST MIN TEMPS TONIGHT WILL BE IN THE DOWNSLOPE AREAS NEAR LAKE SUPERIOR...PARTICULARLY THE W WHERE MOISTENING WILL BE MORE PRONOUNCED. TEMPS SHOULDN`T FALL LWR THAN THE MID/UPPER 60S IN THOSE AREAS. 50S WILL BE THE RULE OVER THE SCNTRL/E. SHORTWAVE/MID LEVEL LOW CURRENTLY OVER SASKATCHEWAN DRIFTS INTO NRN MANITOBA MON. WITH MAIN SYSTEM WELL TO THE NW OF HERE...SFC COLD FRONT WILL BE WEAKENING AS IT REACHES UPPER MI. LACK OF DYNAMICS AND DIMINISHING LOW-LEVEL CONVERGENCE ALONG FRONT WILL WORK TO LIMIT COVERAGE OF CONVECTION MON...ESPECIALLY SINCE THERE WILL BE SOME DRY AIR TO OVERCOME. HOWEVER...NARROW RIBBON OF BOUNDARY LAYER MOISTURE SHOULD BE SUFFICIENT FOR ISOLD/SCT CONVECTION. AS AFORMENTIONED JET STREAK AIDING PCPN LATE TONIGHT SHIFTS NE...THE RIGHT ENTRANCE OF THE JET WILL PROBABLY PROVIDE BEST SUPPORT FOR NEW CONVECTION IN THE AFTN HRS OVER SCNTRL UPPER MI INTO NE WI. PROVIDED MLCAPE INCREASES TO UPWARDS OF 1500-2000J/KG PER GFS AND ESPECIALLY NAM...DEEP LAYER SHEAR OF 30-40KT WILL SUPPORT ORGANIZED STORMS AND SVR POTENTIAL IF ANY STORMS DO DEVELOP. COVERAGE OF SVR STORMS WOULD LIKELY BE ISOLD. .LONG TERM...(MONDAY NIGHT THROUGH SUNDAY) ISSUED AT 347 PM EDT SUN SEP 2 2012 LONG TERM PERIOD STARTS OUT WITH UPPER LOW OVER MANITOBA WHILE ADDITIONAL SHORTWAVE TROUGH CURRENTLY DIGGING INTO FAR NORTHERN BRITISH COLUMBIA MERGES WITH THE LOW ON WEDNESDAY. INITIAL FRONT THAT MOVES THROUGH UPR MICHIGAN ON LABOR DAY LIKELY STALLS OUT MONDAY NIGHT INTO TUESDAY AS IT PARALLELS UPPER FLOW. MAJORITY OF SHRA/TSRA...ALBEIT ONLY ISOLD/SCT COVERAGE...SHOULD BE DIMINISHING BY LATER MONDAY NIGHT. KEPT SMALL POPS IN ONLY FOR THE SOUTH AND EAST CWA AS THOSE AREAS STAY IN AT LEAST A WEAK AREA OF RIGHT ENTRANCE JET FORCING. LINGERED SLIGHT CHANCES FOR THE SAME AREAS THROUGH MOST OF THE NIGHT AS THE SURFACE FRONT REMAINS IN THE VICINITY AND LOW-LEVEL MOISTURE POOLS ALONG THE BOUNDARY. VERY SMALL CHANCES BUT CAN NOT COMPLETELY PULL THE POPS JUST YET. FRONT COULD SERVE AS FOCUS FOR MORE SHRA/TSRA ON TUESDAY AS NAM/00Z ECMWF INDICATE H85 TROUGH AND THETA-E ADVECTION ARRIVES DURING PEAK HEATING OF THE AFTERNOON. H85 DWPNTS ON THE LOW SIDE TO START THE DAY...SO SHOULD SEE BETTER CHANCES OF SHRA/TSRA AFTERNOON AND EVENING...SPREADING FROM WEST TO EAST AS H85 TROUGH CROSSES AREA. THOUGH 0-6KM SHEAR 20-25 KTS NOT TOO IMPRESSIVE FOR ORGANIZED SEVERE STORMS...MLCAPES AOA 1000 J/KG AND HIGH DEWPOINT DEPRESSIONS AT H7-H5 WITH MOIST LOW-LEVELS POINT TO POSSIBLE GUSTY WINDS WITH ANY TSRA. ANY SHRA/TSRA WOULD WANE BY LATER EVENING WITH LOSS OF HEATING/WEAKENING SFC-H85 CONVERGENCE. GFS AND LATEST GEM-NHEM AND 12Z ECMWF FOCUS H85 TROUGH MORE LATER TUESDAY NIGHT AND MORE SO ON WEDNESDAY WITH ARRIVAL OF PRIMARY COLD FRONT. BASED ON TREND FROM LATEST ECMWF...DECIDED TO NOT GO TOO HIGH FOR POPS ON TUESDAY. AS LARGER FORMED UPPER LOW COMPLEX OVER MANITOBA RUMBLES EAST INTO ONTARIO...EXPECT SHARP COLD FRONT TO SWEEP ACROSS GREAT LAKES REGION WEDNESDAY AND THURSDAY. WOULD THINK THERE WOULD BE DECENT CHANCE FOR RAIN WITH THE FROPA. BY TIME FRONT ARRIVES GFS AND GEM-NHEM SHOWS SHARP H85 WIND SHIFT AND MOISTURE ADVECTION INTO THE AREA. OTHER MODELS ALREADY SHOVE THE H85 TROUGH THROUGH SHUNTING MORE ABUNDANT MOISTURE SOUTHEAST OF CWA...BUT AS MENTIONED BEFORE LATEST ECMWF HAS TRENDED THIS WAY AS WELL. CONSISTENCY ON THESE SOLUTIONS NOT THE GREATEST. THERE ARE ALSO HINTS THAT YET ANOTHER WEAKER WAVE/H7 MOISTURE MAY BE SLIDING THROUGH AREA WHILE FRONT SLIDES THROUGH. DETAILS CERTAINLY STILL NEED TO BE SORTED OUT AS TO LOCATION AND COVERAGE OF BEST RAIN CHANCES ON WEDNESDAY. CHANCE POPS FOR SCT SHRA/TSRA COVER IT FINE FOR NOW. PRESSURE GRADIENT TIGHTENS WEDNESDAY NIGHT AND THURSDAY IN WAKE OF THE COLD FRONT BUT OTHER THAN FOR A BRIEF PERIOD WEDNESDAY EVENING WHERE GFS SHOWS 950-925MB WINDS 30-35 KTS...H925-H85 WINDS INTO THURSDAY ARE ONLY AROUND 20 KTS. SO EVEN THOUGH STEADY COOLING ALOFT OCCURS INTO THURSDAY...THIS SYSTEM DOES NOT LOOK TO PRODUCE VERY STRONG WINDS AS EARLY FALL SYSTEMS SOMETIMES CAN DO. TWO ISSUES THAT WILL NEED TO BE MONITORED THOUGH IN WAKE OF THE COLD FROPA WILL BE AN INCREASED RISK OF RIP CURRENTS AND POSSIBLE UPPER LOW TYPE WATERSPOUTS LATER THURSDAY INTO FRIDAY. ALTHOUGH HIGH PRESSURE TRIES TO BUILD IN LATE THIS WEEK IT REMAINS PRETTY WEAK AND DIFFUSE AS UPPER FLOW IS NOT CONFLUENT. BY FAR THE STRONGER SURFACE FEATURE WILL BE WRAPPED UP SURFACE LOW VICINITY OF HUDSON BAY AND JAMES BAY. BY LATER THURSDAY INTO FRIDAY CANNOT RULE OUT AT LEAST LIGHT LK EFFECT SHRA SINCE H85 TEMPS DROP TO 4-6C /WATER TEMPS STILL RUNNING 18-20C/ AND SINCE THERE COULD BE ANOTHER WEAKER SHORTWAVE/ADDITIONAL MOISTURE PUSHING INTO WESTERN GREAT LAKES PER GFS/ECMWF. NOT A BIG CHANCE AS LOW-LEVEL FLOW IS NOT THAT FAVORABLE GIVEN NEUTRAL TO ANTICYCLONIC LOOK...BUT SOME LIGHT PRECIP SEEMS POSSIBLE. MODEL DIFFERENCES EMERGE BY NEXT WEEKEND WITH THE MAIN ISSUE ON HOW QUICK THE 00Z GFS BRINGS ANOTHER LARGER SCALE TROUGH EAST ACROSS THE NORTHERN PLAINS. 00Z ECMWF INDICATES RIDGING BUILDS IN ALOFT WITH A SHARPER SURFACE RIDGE FROM THE PLAINS INTO FAR NORTHERN PORTION OF UPPER GREAT LAKES. 06Z-12Z RUNS OF GFS HAVE TRENDED ECMWF WAY. LATEST COUPLE RUNS OF ECMWF POINT TO UPPER LAKES BEING ON THE DRY FRINGE OF SET OF DISTURBANCES WHICH WOULD BRING RAIN TO PORTIONS OF GREAT LAKES TO START NEXT WEEKEND. HPC PREFERS TO SIDE WITH ECMWF IDEA AND THIS FORECAST WILL TILT THAT WAY AS WELL WITH A GENERAL DRY FCST NEXT WEEKEND. AFTER SLIGHTLY THAN NORMAL HIGH TEMPERATURES FRIDAY AND SATURDAY...EXPECT SOME MODERATION IN TEMPERATURES BY NEXT SUNDAY. && .AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON) ISSUED AT 132 PM EDT SUN SEP 2 2012 ALTHOUGH A FEW -SHRA MAY ARRIVE AT KIWD/KCMX LATE TONIGHT AHEAD OF AN APPROACHING COLD FRONT...EXPECT VFR CONDITIONS THRU THIS FCST PERIOD AS LOW-LEVEL DRY AIR HOLDS. THERE IS A VERY SMALL POTENTIAL FOR STRATUS TO DEVELOP AT KSAW TONIGHT AS SE WINDS VERY SRLY ACROSS LAKE MI...RESULTING IN ADVECTION OF MARINE MODIFIED HIGHER DWPTS INLAND/UPSLOPE INTO COOLER BOUNDARY LAYER AIR. WILL BE SOMETHING TO MONITOR. MODEST LOW-LEVEL JET AHEAD OF COLD FRONT MAY RESULT IN LLWS AT KIWD/KCMX TONIGHT. WITH MUCH UNCERTAINTY ON POSSIBLE CONVECTIVE DEVELOPMENT MON IN VCNTY OF COLD FRONT...NO MENTION OF PCPN WAS INCLUDED AT KSAW WITH THIS FCST ISSUANCE. && .MARINE...(FOR THE 4 PM LAKE SUPERIOR FORECAST ISSUANCE) ISSUED AT 347 PM EDT SUN SEP 2 2012 TIGHTENING PRES GRADIENT BTWN HIGH PRES TO THE E AND AN APPROACHING COLD FRONT TO THE W WILL RESULT IN SE TO S WINDS INCREASING TO AROUND 20KT TONIGHT. SOUTHERLY WINDS MAY GUST TO AROUND 25KT AT HIGHER OBS PLATFORMS...ESPECIALLY OVER CNTRL AND ERN PORTIONS OF THE LAKE. PRES GRADIENT THEN SLACKENS WITH PASSING/WEAKENING COLD FRONT MON...RESULTING IN WINDS DIMINISHING BACK TO UNDER 15KT MON INTO TUE. NEXT COLD FRONT PASSING TUE NIGHT/WED WILL BRING AN INCREASE IN W TO NW WINDS TO AROUND 20KT...MAYBE HIGHER...LATER WED INTO THU. WINDS WILL DIMINISH SLIGHTLY FRI AS NEXT TROF PASSES EARLY IN THE DAY. && .MQT WATCHES/WARNINGS/ADVISORIES... UPPER MICHIGAN... NONE. LAKE SUPERIOR... NONE. LAKE MICHIGAN... NONE. && $$ SHORT TERM...ROLFSON LONG TERM...JLA AVIATION...ROLFSON MARINE...ROLFSON
AREA FORECAST DISCUSSION
NWS MARQUETTE MI
134 PM EDT SUN SEP 2 2012 .SHORT TERM...(TODAY AND TONIGHT) ISSUED AT 429 AM EDT SUN SEP 2 2012 00Z RAOBS/LATEST WV IMAGERY AND RUC ANALYSIS SHOW UPR RDG AXIS CENTERED FM FAR NW ONTARIO SWD THRU THE UPR MS RIVER VALLEY BTWN TROFFING OVER SW CAN/NRN ROCKIES AND ANOTHER UPR TROF IN QUEBEC. SFC HI PRES CENTERED JUST E OF LK SUP AND DRY AIRMASS SHOWN ON THE 00Z GRB ARE BRINGING A TRANQUIL EARLY MRNG TO UPR MI. TO THE S...THE REMNANTS OF HURRICANE ISAAC/DEEP MSTR ARE IN THE OHIO RIVER VALLEY. TO THE W...THERE ARE CLUSTERS OF SHRA/TS IN THE NRN PLAINS ALONG A COLD FNT ASSOCIATED WITH UPR TROF/STRONG SHRTWV OVER ALBERTA THAT IS DRIFTING SLOWLY ENEWD. COVERAGE OF SHRA IN THE NRN PLAINS IS LIMITED BY VERY DRY AIR SHOWN ON 00Z AREA RAOBS/LIMITED MSTR RETURN INTO THE PLAINS DISRUPTED BY THE CIRCULATION ARND ISAAC. TODAY...ALTHOUGH THE SFC HI PRES CENTER IS FCST TO RETREAT INTO FAR WRN QUEBEC BY 00Z MON...LINGERING SFC-H85 RDG AXIS EXTENDING WWD FM THE HI CENTER INTO THE UPR LKS TO THE N OF ISAAC WL BRING ANOTHER DRY DAY TO UPR MI. MIXING TO H85 ON NAM FCST SDNGS YIELDS HI TEMPS 80 TO 85 AWAY FM MODERATION MAINLY DOWNSTREAM OF LK MI IN LLVL SSE FLOW. WITH THIS MIXING DEPTH...SFC DEWPTS SHOULD DIP AS LO AS THE UPR 40S OVER THE INTERIOR W AND FAR E AWAY FM LK MI MODERATION... SETTING UP MIN RH ARND 30 PCT. FORTUNATELY FOR FIRE WX CONCERNS... THE PRES GRADIENT IS NOT FCST TO TIGHTEN SGNFTLY UNTIL LATER IN THE DAY AND MAINLY OVER THE W CLOSER TO APRCHG COLD FNT MOVING INTO WRN MN LATE IN THE DAY. BUT WITH WIND GUSTS UP TO 15 TO 20 MPH AND EXPECTED CONDITIONS/RECENT DRYNESS... WL CONTINUE TO MENTION ELEVATED RISK OF WILDFIRES IN HWO. TNGT...CLOSED/OCCLUDED LO PRES IS PROGGED TO DRIFT TO JUST NW OF LK WINNIPEG BY 12Z MON. ATTENDANT COLD FNT PRECEDED BY RELATIVELY NARROW RIBBON OF WARM CONVEYOR BELT MSTR LIMITED BY DRYNESS OF AIRMASS IN THE PLAINS AS INDICATED ON 00Z RAOBS IS FCST TO APRCH WRN LK SUP TOWARD 12Z MON. ONE POSITIVE FOR POPS IS RIBBON OF STRONGER H3 WINDS THAT IS FCST TO DVLP OVER THE PLAINS INTO THE UPR LKS WELL TO THE S OF MAIN CLOSED LO TO THE N. VARIOUS MODELS...INCLUDING THE 00Z GFS/NAM...SHOW AN 80KT H3 JET MAX WITHIN THIS FLOW/SHRTWV/SOME H4-2 DVGC APRCHG THE WRN ZNS LATE. BUT GIVEN THE LIMITED MSTR RETURN THAT MAINTAINS CIN ON FCST SDNGS DESPITE FAIRLY STEEP H7-5 LAPSE RATES...PASSAGE OF MOST SGNFT DEEP LYR QVECTOR CNVGC TO THE N CLOSER TO MAIN CLOSED LO...TREND FOR SLOWER EWD MOTION OF COLD FNT TO THE E...AND ARRIVAL OF SHRA AT MIN HEATING TIME...TENDED TO FOLLOW THE DRIER 00Z GFS/CNDN MODELS TO RESTRICT POPS TO THE FAR WRN COUNTIES MAINLY AFT 09Z. THE GFS IS ON THE DRIER SIDE EVEN WITH APRCHG JET MAX...SO SUSPECT THESE NEGATIVES WL OUTWEIGH IMPACT OF ANY DISTURBANCE THAT MIGHT APRCH FM THE WSW. EXPECT THE WARMEST MIN TEMPS OVER THE W NEAR LK SUP UNDER SHARPER PRES GRADIENT AND WHERE MOISTENING WL BE MOST PRONOUNCED/S WIND WL DOWNSLOPE. .LONG TERM...(MONDAY THROUGH SATURDAY) ISSUED AT 429 AM EDT SUN SEP 2 2012 THROUGH MUCH OF THE LONG TERM...WEATHER WILL BE IMPACTED BY A CLOSED 500MB LOW CURRENTLY OVER ALBERTA. THE LOW WILL MOVE TO MANITOBA BY 12Z MON...WHERE IT WILL SIT UNTIL TUE NIGHT WHEN ADDITIONAL ENERGY MERGES WITH THE SYSTEM. THE LOW WILL THEN SPIN ACROSS FAR NRN ONTARIO FROM LAKE WED INTO FRI...AND MODELS AGREE WELL ON THIS...WITH MUCH REDUCED MODEL AGREEMENT /AND THEREFOR FORECAST CONFIDENCE/ THROUGH SAT AS MODELS DIFFER CONSIDERABLE WITH HOW FAST TO MOVE HAVE THE LOW EXIT THE REGION. MONDAY...MODELS SHOW A WEAKENING COLD FRONT MOVING THROUGH BETWEEN ROUGHLY 18Z MON AND 06Z TUE...DURING PEAK HEATING. WITH 850MB TEMPS AROUND 18C...HIGH TEMPS ARE FORECAST TO BEE IN THE UPPER 70S AND 80S. THESE WARM SFC TEMPS...COMBINED WITH COOLING MID/UPPER LEVELS AND STEEPENING LAPSE RATES...WILL LEAD TO INCREASED INSTABILITY WITH LITTLE TO NO CIN. MODEL GUIDANCE AND FORECAST SOUNDINGS INDICATED POTENTIAL FOR 1500-2000J/KG OF CAPE OVER MAINLY CENTRAL AND WRN UPPER MI DURING THE AFTERNOON AND EARLY EVENING. UNIDIRECTIONAL WINDS INCREASE STEADILY WITH HEIGHT...LEADING TO 35-40KTS OF 0-6KM SHEAR /0-1 KM SHEAR OF 15KTS OR LESS/. MID LEVELS AROUND 500MB LOOK FAIRLY DRY...WITH AMPLE LOW LEVEL MOSTURE. ALL THIS LOOKS TO ADD UP TO A MODERATE POTENTIAL FOR STRONG TO SEVERE STORMS WITH WINDS BEING THE PRIMARY THREAT...AND HAIL BEING A SOMEWHAT LOWER SECONDARY THREAT. WOULD EXPECT STORM COVERAGE/INTENSITY TO DIMINISH AFTER LOSS OF SFC HEATING. TUESDAY...MODELS SHOW ANOTHER COLD FRONT MOVING THROUGH THE CWA. INSTABILITY LOOKS LOWER THAN MONDAY WITH WEAKER UNIDIRECTIONAL FLOW. THUS...IF THUNDERSTORMS DEVELOP THEY WILL BE WEAKER...WITH MAYBE SOME STRONGER STORMS POSSIBLE IN THE AFTERNOON. WILL CONTINUE SHOWING CHANCE POPS FOR TUE AFTERNOON/EVENING. WEDNESDAY...A STRONGER PUSH OF 500MB HEIGHT FALLS MOVES OVER THE AREA WED AS AN ADDITIONAL PIECE OF UPPER ENERGY WRAPS AROUND THE UPPER LOW. THIS BRINGS ANOTHER...ALBEIT MORE DEFINED...COLD FRONT THROUGH THE CWA. ALHOUGH SHEAR LOOKS A BIT STRONGER THAN TUE...INSTABILITY SHOULD AGAIN BE LOWER. SO MAYBE A STRONGER THUNDERSTORMS OR TWO COULD OCCUR WHERE PRECIP DEVELOPS. THURSDAY AND FRIDAY...WE WILL TRANSITION TO BEING MORE ON THE BACK SIDE OF THE UPPER LOW THURSDAY AFTERNOON AFTER THE MAIN UPPER TROUGH PASSES THROUGH. SFC HIGH PRESSURE WILL BE PUSHING IN FROM THE W THROUGH FRI...LEADING TO NW FLOW AND MUCH COOLER AIR MOVING INTO THE REGION. 850MB TEMPS THU AFTERNOON SHOULD BE AROUND 7C...THEN DOWN TO AROUND 5C BY FRIDAY AFTERNOON. RESULTING HIGH TEMPS LOOK TO BE IN THE 60S TO LOW 70S. SATURDAY...AS PREVIOUSLY MENTIONED...MODEL AGREEMENT AND FORECAST CONFIDENCE DECREASE SHARPLY LATE FRI INTO SAT AS MODELS DIFFER WITH HOW FAST TO USHER AWAY THE UPPER LOW. JUST WENT WITH A CONSENSUS OF GUIDANCE FOR NOW. && .AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON) ISSUED AT 132 PM EDT SUN SEP 2 2012 ALTHOUGH A FEW -SHRA MAY ARRIVE AT KIWD/KCMX LATE TONIGHT AHEAD OF AN APPROACHING COLD FRONT...EXPECT VFR CONDITIONS THRU THIS FCST PERIOD AS LOW-LEVEL DRY AIR HOLDS. THERE IS A VERY SMALL POTENTIAL FOR STRATUS TO DEVELOP AT KSAW TONIGHT AS SE WINDS VERY SRLY ACROSS LAKE MI...RESULTING IN ADVECTION OF MARINE MODIFIED HIGHER DWPTS INLAND/UPSLOPE INTO COOLER BOUNDARY LAYER AIR. WILL BE SOMETHING TO MONITOR. MODEST LOW-LEVEL JET AHEAD OF COLD FRONT MAY RESULT IN LLWS AT KIWD/KCMX TONIGHT. WITH MUCH UNCERTAINTY ON POSSIBLE CONVECTIVE DEVELOPMENT MON IN VCNTY OF COLD FRONT...NO MENTION OF PCPN WAS INCLUDED AT KSAW WITH THIS FCST ISSUANCE. && .MARINE...(FOR THE 4 AM LAKE SUPERIOR FORECAST ISSUANCE) ISSUED AT 429 AM EDT SUN SEP 2 2012 EXPECT LIGHT SSE WINDS THIS MORNING UNDER HI PRES RIDGE AXIS TO INCREASE LATER TODAY INTO MON UNDER SHARPENING PRES GRADIENT AS THE HI MOVES TO THE E AND A COLD FRONT APPROACHES FROM THE W. ARRIVAL OF WEAKER PRES GRADIENT LATER ON MON INTO WED WILL BRING A RETURN OF WINDS UNDER 15 KTS. THE PASSAGE OF A STRONGER COLD FRONT ON WED SHOULD BRING A RETURN OF STRONGER W-NW WINDS TO 20 OR PERHAPS 25 KTS FOR LATER WED THRU THU. && .MQT WATCHES/WARNINGS/ADVISORIES... UPPER MICHIGAN... NONE. LAKE SUPERIOR... NONE. LAKE MICHIGAN... NONE. && $$ SHORT TERM...KC LONG TERM...TITUS AVIATION...ROLFSON MARINE...KC
AREA FORECAST DISCUSSION
NWS MARQUETTE MI
722 AM EDT SUN SEP 2 2012 .SHORT TERM...(TODAY AND TONIGHT) ISSUED AT 429 AM EDT SUN SEP 2 2012 00Z RAOBS/LATEST WV IMAGERY AND RUC ANALYSIS SHOW UPR RDG AXIS CENTERED FM FAR NW ONTARIO SWD THRU THE UPR MS RIVER VALLEY BTWN TROFFING OVER SW CAN/NRN ROCKIES AND ANOTHER UPR TROF IN QUEBEC. SFC HI PRES CENTERED JUST E OF LK SUP AND DRY AIRMASS SHOWN ON THE 00Z GRB ARE BRINGING A TRANQUIL EARLY MRNG TO UPR MI. TO THE S...THE REMNANTS OF HURRICANE ISAAC/DEEP MSTR ARE IN THE OHIO RIVER VALLEY. TO THE W...THERE ARE CLUSTERS OF SHRA/TS IN THE NRN PLAINS ALONG A COLD FNT ASSOCIATED WITH UPR TROF/STRONG SHRTWV OVER ALBERTA THAT IS DRIFTING SLOWLY ENEWD. COVERAGE OF SHRA IN THE NRN PLAINS IS LIMITED BY VERY DRY AIR SHOWN ON 00Z AREA RAOBS/LIMITED MSTR RETURN INTO THE PLAINS DISRUPTED BY THE CIRCULATION ARND ISAAC. TODAY...ALTHOUGH THE SFC HI PRES CENTER IS FCST TO RETREAT INTO FAR WRN QUEBEC BY 00Z MON...LINGERING SFC-H85 RDG AXIS EXTENDING WWD FM THE HI CENTER INTO THE UPR LKS TO THE N OF ISAAC WL BRING ANOTHER DRY DAY TO UPR MI. MIXING TO H85 ON NAM FCST SDNGS YIELDS HI TEMPS 80 TO 85 AWAY FM MODERATION MAINLY DOWNSTREAM OF LK MI IN LLVL SSE FLOW. WITH THIS MIXING DEPTH...SFC DEWPTS SHOULD DIP AS LO AS THE UPR 40S OVER THE INTERIOR W AND FAR E AWAY FM LK MI MODERATION... SETTING UP MIN RH ARND 30 PCT. FORTUNATELY FOR FIRE WX CONCERNS... THE PRES GRADIENT IS NOT FCST TO TIGHTEN SGNFTLY UNTIL LATER IN THE DAY AND MAINLY OVER THE W CLOSER TO APRCHG COLD FNT MOVING INTO WRN MN LATE IN THE DAY. BUT WITH WIND GUSTS UP TO 15 TO 20 MPH AND EXPECTED CONDITIONS/RECENT DRYNESS... WL CONTINUE TO MENTION ELEVATED RISK OF WILDFIRES IN HWO. TNGT...CLOSED/OCCLUDED LO PRES IS PROGGED TO DRIFT TO JUST NW OF LK WINNIPEG BY 12Z MON. ATTENDANT COLD FNT PRECEDED BY RELATIVELY NARROW RIBBON OF WARM CONVEYOR BELT MSTR LIMITED BY DRYNESS OF AIRMASS IN THE PLAINS AS INDICATED ON 00Z RAOBS IS FCST TO APRCH WRN LK SUP TOWARD 12Z MON. ONE POSITIVE FOR POPS IS RIBBON OF STRONGER H3 WINDS THAT IS FCST TO DVLP OVER THE PLAINS INTO THE UPR LKS WELL TO THE S OF MAIN CLOSED LO TO THE N. VARIOUS MODELS...INCLUDING THE 00Z GFS/NAM...SHOW AN 80KT H3 JET MAX WITHIN THIS FLOW/SHRTWV/SOME H4-2 DVGC APRCHG THE WRN ZNS LATE. BUT GIVEN THE LIMITED MSTR RETURN THAT MAINTAINS CIN ON FCST SDNGS DESPITE FAIRLY STEEP H7-5 LAPSE RATES...PASSAGE OF MOST SGNFT DEEP LYR QVECTOR CNVGC TO THE N CLOSER TO MAIN CLOSED LO...TREND FOR SLOWER EWD MOTION OF COLD FNT TO THE E...AND ARRIVAL OF SHRA AT MIN HEATING TIME...TENDED TO FOLLOW THE DRIER 00Z GFS/CNDN MODELS TO RESTRICT POPS TO THE FAR WRN COUNTIES MAINLY AFT 09Z. THE GFS IS ON THE DRIER SIDE EVEN WITH APRCHG JET MAX...SO SUSPECT THESE NEGATIVES WL OUTWEIGH IMPACT OF ANY DISTURBANCE THAT MIGHT APRCH FM THE WSW. EXPECT THE WARMEST MIN TEMPS OVER THE W NEAR LK SUP UNDER SHARPER PRES GRADIENT AND WHERE MOISTENING WL BE MOST PRONOUNCED/S WIND WL DOWNSLOPE. .LONG TERM...(MONDAY THROUGH SATURDAY) ISSUED AT 429 AM EDT SUN SEP 2 2012 THROUGH MUCH OF THE LONG TERM...WEATHER WILL BE IMPACTED BY A CLOSED 500MB LOW CURRENTLY OVER ALBERTA. THE LOW WILL MOVE TO MANITOBA BY 12Z MON...WHERE IT WILL SIT UNTIL TUE NIGHT WHEN ADDITIONAL ENERGY MERGES WITH THE SYSTEM. THE LOW WILL THEN SPIN ACROSS FAR NRN ONTARIO FROM LAKE WED INTO FRI...AND MODELS AGREE WELL ON THIS...WITH MUCH REDUCED MODEL AGREEMENT /AND THEREFOR FORECAST CONFIDENCE/ THROUGH SAT AS MODELS DIFFER CONSIDERABLE WITH HOW FAST TO MOVE HAVE THE LOW EXIT THE REGION. MONDAY...MODELS SHOW A WEAKENING COLD FRONT MOVING THROUGH BETWEEN ROUGHLY 18Z MON AND 06Z TUE...DURING PEAK HEATING. WITH 850MB TEMPS AROUND 18C...HIGH TEMPS ARE FORECAST TO BEE IN THE UPPER 70S AND 80S. THESE WARM SFC TEMPS...COMBINED WITH COOLING MID/UPPER LEVELS AND STEEPENING LAPSE RATES...WILL LEAD TO INCREASED INSTABILITY WITH LITTLE TO NO CIN. MODEL GUIDANCE AND FORECAST SOUNDINGS INDICATED POTENTIAL FOR 1500-2000J/KG OF CAPE OVER MAINLY CENTRAL AND WRN UPPER MI DURING THE AFTERNOON AND EARLY EVENING. UNIDIRECTIONAL WINDS INCREASE STEADILY WITH HEIGHT...LEADING TO 35-40KTS OF 0-6KM SHEAR /0-1 KM SHEAR OF 15KTS OR LESS/. MID LEVELS AROUND 500MB LOOK FAIRLY DRY...WITH AMPLE LOW LEVEL MOSTURE. ALL THIS LOOKS TO ADD UP TO A MODERATE POTENTIAL FOR STRONG TO SEVERE STORMS WITH WINDS BEING THE PRIMARY THREAT...AND HAIL BEING A SOMEWHAT LOWER SECONDARY THREAT. WOULD EXPECT STORM COVERAGE/INTENSITY TO DIMINISH AFTER LOSS OF SFC HEATING. TUESDAY...MODELS SHOW ANOTHER COLD FRONT MOVING THROUGH THE CWA. INSTABILITY LOOKS LOWER THAN MONDAY WITH WEAKER UNIDIRECTIONAL FLOW. THUS...IF THUNDERSTORMS DEVELOP THEY WILL BE WEAKER...WITH MAYBE SOME STRONGER STORMS POSSIBLE IN THE AFTERNOON. WILL CONTINUE SHOWING CHANCE POPS FOR TUE AFTERNOON/EVENING. WEDNESDAY...A STRONGER PUSH OF 500MB HEIGHT FALLS MOVES OVER THE AREA WED AS AN ADDITIONAL PIECE OF UPPER ENERGY WRAPS AROUND THE UPPER LOW. THIS BRINGS ANOTHER...ALBEIT MORE DEFINED...COLD FRONT THROUGH THE CWA. ALHOUGH SHEAR LOOKS A BIT STRONGER THAN TUE...INSTABILITY SHOULD AGAIN BE LOWER. SO MAYBE A STRONGER THUNDERSTORMS OR TWO COULD OCCUR WHERE PRECIP DEVELOPS. THURSDAY AND FRIDAY...WE WILL TRANSITION TO BEING MORE ON THE BACK SIDE OF THE UPPER LOW THURSDAY AFTERNOON AFTER THE MAIN UPPER TROUGH PASSES THROUGH. SFC HIGH PRESSURE WILL BE PUSHING IN FROM THE W THROUGH FRI...LEADING TO NW FLOW AND MUCH COOLER AIR MOVING INTO THE REGION. 850MB TEMPS THU AFTERNOON SHOULD BE AROUND 7C...THEN DOWN TO AROUND 5C BY FRIDAY AFTERNOON. RESULTING HIGH TEMPS LOOK TO BE IN THE 60S TO LOW 70S. SATURDAY...AS PREVIOUSLY MENTIONED...MODEL AGREEMENT AND FORECAST CONFIDENCE DECREASE SHARPLY LATE FRI INTO SAT AS MODELS DIFFER WITH HOW FAST TO USHER AWAY THE UPPER LOW. JUST WENT WITH A CONSENSUS OF GUIDANCE FOR NOW. && .AVIATION...(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING) ISSUED AT 721 AM EDT SUN SEP 2 2012 ALTHOUGH A FEW -SHRA MAY ARRIVE AT IWD/CMX LATE TNGT AHEAD OF AN APRCHG COLD FNT...EXPECT VFR CONDITIONS THRU THIS FCST PERIOD WITH A PERSISTENCE OF PLENTY OF LLVL DRY AIR ASSOCIATED WITH HI PRES RDG STRETCHING FM QUEBEC INTO THE UPR GRT LKS. SOME LLWS MAY IMPACT IWD TNGT AS A LLJ DEVELOPS UNDER THE SHARPENING PRES GRADIENT BTWN THE DEPARTING HI AND THE APRCHG FNT. && .MARINE...(FOR THE 4 AM LAKE SUPERIOR FORECAST ISSUANCE) ISSUED AT 429 AM EDT SUN SEP 2 2012 EXPECT LIGHT SSE WINDS THIS MORNING UNDER HI PRES RIDGE AXIS TO INCREASE LATER TODAY INTO MON UNDER SHARPENING PRES GRADIENT AS THE HI MOVES TO THE E AND A COLD FRONT APPROACHES FROM THE W. ARRIVAL OF WEAKER PRES GRADIENT LATER ON MON INTO WED WILL BRING A RETURN OF WINDS UNDER 15 KTS. THE PASSAGE OF A STRONGER COLD FRONT ON WED SHOULD BRING A RETURN OF STRONGER W-NW WINDS TO 20 OR PERHAPS 25 KTS FOR LATER WED THRU THU. && .MQT WATCHES/WARNINGS/ADVISORIES... UPPER MICHIGAN... NONE. LAKE SUPERIOR... NONE. LAKE MICHIGAN... NONE. && $$ SHORT TERM...KC LONG TERM...TITUS AVIATION...KC MARINE...KC
AREA FORECAST DISCUSSION
NWS MARQUETTE MI
433 AM EDT SUN SEP 2 2012 .SHORT TERM...(TODAY AND TONIGHT) ISSUED AT 429 AM EDT SUN SEP 2 2012 00Z RAOBS/LATEST WV IMAGERY AND RUC ANALYSIS SHOW UPR RDG AXIS CENTERED FM FAR NW ONTARIO SWD THRU THE UPR MS RIVER VALLEY BTWN TROFFING OVER SW CAN/NRN ROCKIES AND ANOTHER UPR TROF IN QUEBEC. SFC HI PRES CENTERED JUST E OF LK SUP AND DRY AIRMASS SHOWN ON THE 00Z GRB ARE BRINGING A TRANQUIL EARLY MRNG TO UPR MI. TO THE S...THE REMNANTS OF HURRICANE ISAAC/DEEP MSTR ARE IN THE OHIO RIVER VALLEY. TO THE W...THERE ARE CLUSTERS OF SHRA/TS IN THE NRN PLAINS ALONG A COLD FNT ASSOCIATED WITH UPR TROF/STRONG SHRTWV OVER ALBERTA THAT IS DRIFTING SLOWLY ENEWD. COVERAGE OF SHRA IN THE NRN PLAINS IS LIMITED BY VERY DRY AIR SHOWN ON 00Z AREA RAOBS/LIMITED MSTR RETURN INTO THE PLAINS DISRUPTED BY THE CIRCULATION ARND ISAAC. TODAY...ALTHOUGH THE SFC HI PRES CENTER IS FCST TO RETREAT INTO FAR WRN QUEBEC BY 00Z MON...LINGERING SFC-H85 RDG AXIS EXTENDING WWD FM THE HI CENTER INTO THE UPR LKS TO THE N OF ISAAC WL BRING ANOTHER DRY DAY TO UPR MI. MIXING TO H85 ON NAM FCST SDNGS YIELDS HI TEMPS 80 TO 85 AWAY FM MODERATION MAINLY DOWNSTREAM OF LK MI IN LLVL SSE FLOW. WITH THIS MIXING DEPTH...SFC DEWPTS SHOULD DIP AS LO AS THE UPR 40S OVER THE INTERIOR W AND FAR E AWAY FM LK MI MODERATION... SETTING UP MIN RH ARND 30 PCT. FORTUNATELY FOR FIRE WX CONCERNS... THE PRES GRADIENT IS NOT FCST TO TIGHTEN SGNFTLY UNTIL LATER IN THE DAY AND MAINLY OVER THE W CLOSER TO APRCHG COLD FNT MOVING INTO WRN MN LATE IN THE DAY. BUT WITH WIND GUSTS UP TO 15 TO 20 MPH AND EXPECTED CONDITIONS/RECENT DRYNESS... WL CONTINUE TO MENTION ELEVATED RISK OF WILDFIRES IN HWO. TNGT...CLOSED/OCCLUDED LO PRES IS PROGGED TO DRIFT TO JUST NW OF LK WINNIPEG BY 12Z MON. ATTENDANT COLD FNT PRECEDED BY RELATIVELY NARROW RIBBON OF WARM CONVEYOR BELT MSTR LIMITED BY DRYNESS OF AIRMASS IN THE PLAINS AS INDICATED ON 00Z RAOBS IS FCST TO APRCH WRN LK SUP TOWARD 12Z MON. ONE POSITIVE FOR POPS IS RIBBON OF STRONGER H3 WINDS THAT IS FCST TO DVLP OVER THE PLAINS INTO THE UPR LKS WELL TO THE S OF MAIN CLOSED LO TO THE N. VARIOUS MODELS...INCLUDING THE 00Z GFS/NAM...SHOW AN 80KT H3 JET MAX WITHIN THIS FLOW/SHRTWV/SOME H4-2 DVGC APRCHG THE WRN ZNS LATE. BUT GIVEN THE LIMITED MSTR RETURN THAT MAINTAINS CIN ON FCST SDNGS DESPITE FAIRLY STEEP H7-5 LAPSE RATES...PASSAGE OF MOST SGNFT DEEP LYR QVECTOR CNVGC TO THE N CLOSER TO MAIN CLOSED LO...TREND FOR SLOWER EWD MOTION OF COLD FNT TO THE E...AND ARRIVAL OF SHRA AT MIN HEATING TIME...TENDED TO FOLLOW THE DRIER 00Z GFS/CNDN MODELS TO RESTRICT POPS TO THE FAR WRN COUNTIES MAINLY AFT 09Z. THE GFS IS ON THE DRIER SIDE EVEN WITH APRCHG JET MAX...SO SUSPECT THESE NEGATIVES WL OUTWEIGH IMPACT OF ANY DISTURBANCE THAT MIGHT APRCH FM THE WSW. EXPECT THE WARMEST MIN TEMPS OVER THE W NEAR LK SUP UNDER SHARPER PRES GRADIENT AND WHERE MOISTENING WL BE MOST PRONOUNCED/S WIND WL DOWNSLOPE. .LONG TERM...(MONDAY THROUGH SATURDAY) ISSUED AT 429 AM EDT SUN SEP 2 2012 THROUGH MUCH OF THE LONG TERM...WEATHER WILL BE IMPACTED BY A CLOSED 500MB LOW CURRENTLY OVER ALBERTA. THE LOW WILL MOVE TO MANITOBA BY 12Z MON...WHERE IT WILL SIT UNTIL TUE NIGHT WHEN ADDITIONAL ENERGY MERGES WITH THE SYSTEM. THE LOW WILL THEN SPIN ACROSS FAR NRN ONTARIO FROM LAKE WED INTO FRI...AND MODELS AGREE WELL ON THIS...WITH MUCH REDUCED MODEL AGREEMENT /AND THEREFOR FORECAST CONFIDENCE/ THROUGH SAT AS MODELS DIFFER CONSIDERABLE WITH HOW FAST TO MOVE HAVE THE LOW EXIT THE REGION. MONDAY...MODELS SHOW A WEAKENING COLD FRONT MOVING THROUGH BETWEEN ROUGHLY 18Z MON AND 06Z TUE...DURING PEAK HEATING. WITH 850MB TEMPS AROUND 18C...HIGH TEMPS ARE FORECAST TO BEE IN THE UPPER 70S AND 80S. THESE WARM SFC TEMPS...COMBINED WITH COOLING MID/UPPER LEVELS AND STEEPENING LAPSE RATES...WILL LEAD TO INCREASED INSTABILITY WITH LITTLE TO NO CIN. MODEL GUIDANCE AND FORECAST SOUNDINGS INDICATED POTENTIAL FOR 1500-2000J/KG OF CAPE OVER MAINLY CENTRAL AND WRN UPPER MI DURING THE AFTERNOON AND EARLY EVENING. UNIDIRECTIONAL WINDS INCREASE STEADILY WITH HEIGHT...LEADING TO 35-40KTS OF 0-6KM SHEAR /0-1 KM SHEAR OF 15KTS OR LESS/. MID LEVELS AROUND 500MB LOOK FAIRLY DRY...WITH AMPLE LOW LEVEL MOSTURE. ALL THIS LOOKS TO ADD UP TO A MODERATE POTENTIAL FOR STRONG TO SEVERE STORMS WITH WINDS BEING THE PRIMARY THREAT...AND HAIL BEING A SOMEWHAT LOWER SECONDARY THREAT. WOULD EXPECT STORM COVERAGE/INTENSITY TO DIMINISH AFTER LOSS OF SFC HEATING. TUESDAY...MODELS SHOW ANOTHER COLD FRONT MOVING THROUGH THE CWA. INSTABILITY LOOKS LOWER THAN MONDAY WITH WEAKER UNIDIRECTIONAL FLOW. THUS...IF THUNDERSTORMS DEVELOP THEY WILL BE WEAKER...WITH MAYBE SOME STRONGER STORMS POSSIBLE IN THE AFTERNOON. WILL CONTINUE SHOWING CHANCE POPS FOR TUE AFTERNOON/EVENING. WEDNESDAY...A STRONGER PUSH OF 500MB HEIGHT FALLS MOVES OVER THE AREA WED AS AN ADDITIONAL PIECE OF UPPER ENERGY WRAPS AROUND THE UPPER LOW. THIS BRINGS ANOTHER...ALBEIT MORE DEFINED...COLD FRONT THROUGH THE CWA. ALHOUGH SHEAR LOOKS A BIT STRONGER THAN TUE...INSTABILITY SHOULD AGAIN BE LOWER. SO MAYBE A STRONGER THUNDERSTORMS OR TWO COULD OCCUR WHERE PRECIP DEVELOPS. THURSDAY AND FRIDAY...WE WILL TRANSITION TO BEING MORE ON THE BACK SIDE OF THE UPPER LOW THURSDAY AFTERNOON AFTER THE MAIN UPPER TROUGH PASSES THROUGH. SFC HIGH PRESSURE WILL BE PUSHING IN FROM THE W THROUGH FRI...LEADING TO NW FLOW AND MUCH COOLER AIR MOVING INTO THE REGION. 850MB TEMPS THU AFTERNOON SHOULD BE AROUND 7C...THEN DOWN TO AROUND 5C BY FRIDAY AFTERNOON. RESULTING HIGH TEMPS LOOK TO BE IN THE 60S TO LOW 70S. SATURDAY...AS PREVIOUSLY MENTIONED...MODEL AGREEMENT AND FORECAST CONFIDENCE DECREASE SHARPLY LATE FRI INTO SAT AS MODELS DIFFER WITH HOW FAST TO USHER AWAY THE UPPER LOW. JUST WENT WITH A CONSENSUS OF GUIDANCE FOR NOW. && .AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT) ISSUED AT 123 AM EDT SUN SEP 2 2012 EXPECT VFR CONDITIONS THIS FCST PERIOD AS DRY HIGH PRESSURE REMAINS OVER/NEAR THE UPPER GREAT LAKES. && .MARINE...(FOR THE 4 AM LAKE SUPERIOR FORECAST ISSUANCE) ISSUED AT 429 AM EDT SUN SEP 2 2012 EXPECT LIGHT SSE WINDS THIS MORNING UNDER HI PRES RIDGE AXIS TO INCREASE LATER TODAY INTO MON UNDER SHARPENING PRES GRADIENT AS THE HI MOVES TO THE E AND A COLD FRONT APPROACHES FROM THE W. ARRIVAL OF WEAKER PRES GRADIENT LATER ON MON INTO WED WILL BRING A RETURN OF WINDS UNDER 15 KTS. THE PASSAGE OF A STRONGER COLD FRONT ON WED SHOULD BRING A RETURN OF STRONGER W-NW WINDS TO 20 OR PERHAPS 25 KTS FOR LATER WED THRU THU. && .MQT WATCHES/WARNINGS/ADVISORIES... UPPER MICHIGAN... NONE. LAKE SUPERIOR... NONE. LAKE MICHIGAN... NONE. && $$ SHORT TERM...KC LONG TERM...TITUS AVIATION...VOSS MARINE...KC
AREA FORECAST DISCUSSION
NWS MARQUETTE MI
124 AM EDT SUN SEP 2 2012 .SHORT TERM...(THIS EVENING THROUGH SUNDAY) ISSUED AT 407 PM EDT SAT SEP 1 2012 WATER VAPOR IMAGERY AND RUC ANALYSIS SHOW A TROF OVER THE PACIFIC NW WITH DOWNSTREAM RIDGE EXTENDING N INTO SCNTRL CANADA. REMNANT OF ISAAC IS OVER THE MID MISSISSIPPI VALLEY. DOWNSTREAM OF THE RIDGE AXIS AND WELL N OF ISAAC REMNANT...TRANQUIL WEATHER DOMINATES UPPER MI THIS AFTN UNDER ABUNDANT SUNSHINE. THE TRANQUIL WEATHER WILL PERSIST THRU THE SHORT TERM AS THE UPSTREAM RIDGE SHIFTS E... REACHING THE GREAT LAKES SUN. AS SFC HIGH OVER LAKE SUPERIOR DRIFTS E TONIGHT...LIGHT RETURN FLOW WILL GET UNDERWAY...ESPECIALLY W. SHOULD STILL BE A GOOD RADIATIONAL COOLING NIGHT UNDER MAINLY CLEAR SKIES...THOUGH NOT AS GOOD AS LAST NIGHT DUE TO DEVELOPING LIGHT RETURN FLOW AND INCREASING COLUMN MOISTURE. FAVORED THE LOW SIDE OF AVBL GUIDANCE WHICH HAS TRADITIONAL COLD SPOTS DROPPING TO THE LWR 40S. THERE IS SOME CONCERN THAT DEVELOPING LOW-LEVEL E TO SE FLOW ACROSS NRN LAKE MI COULD LEAD TO STRATUS/FOG DEVELOPMENT OVER THE SCNTRL FCST AREA AS MARINE MODIFIED HIGHER DWPTS ADVECT INLAND/UPSLOPE INTO THE RADIATIONALLY COOLED BOUNDARY LAYER INLAND. AT THIS TIME...IT APPEARS SFC WINDS WILL BE BACKED ENOUGH OVER SCNTRL UPPER MI TO PREVENT MUCH INLAND ADVECTION OF MOISTURE. WILL BE SOMETHING TO MONITOR OVERNIGHT. DRY AIR MASS WILL LINGER THRU SUN AFTN...PROVIDING ONE MORE DRY/WARM EARLY SEPT DAY. PER FCST SOUNDINGS...STRENGTHENING CAP SUN WILL LIMIT MIXING DEPTH COMPARED TO RECENT DAYS. MIXING TO 850MB YIELDS MAX TEMPS MOSTLY IN THE LWR 80S AWAY FROM LAKE MODERATION. ALTHOUGH VERY DRY AIR LINGERS ALOFT (CENTERED AROUND 800MB)...SFC DWPTS SHOULDN`T FALL AS MUCH AS IN RECENT AFTNS SINCE MIXING WON`T TAP AS SIGNIFICANTLY INTO THE DRIER ALOFT. STILL...WITH DWPTS FALLING TOWARD 50F IN THE AFTN...RH WILL BOTTOM OUT AS LOW AS 30-35PCT. ALTHOUGH PRES GRADIENT WILL BEGIN TO TIGHTEN BTWN DEPARTING SFC HIGH AND APPROACHING COLD FRONT OVER THE PLAINS...SFC RIDGING EXTENDING BACK TO UPPER MI WILL HELP TO SLOW THE INCREASE IN WINDS...AND THIS WILL HELP TO EASE FIRE WX CONCERNS SUN. .LONG TERM...(SUNDAY NIGHT THROUGH SATURDAY) ISSUED AT 407 PM EDT SAT SEP 1 2012 MUCH OF OUR WEATHER FOR THIS LONG TERM PERIOD WILL BE HEAVILY INFLUENCED BY THE 500MB LOW CURRENTLY SPINNING ALONG THE BRITISH COLUMBIA/ALBERTA BORDER...WHICH WILL SET UP HOUSE OVER ONTARIO/HUDSON BAY/QUEBEC FROM WEDNESDAY THROUGH AT LEAST NEXT SATURDAY. SUNDAY NIGHT... WILL BEGIN SUNDAY NIGHT WITH THE WRAPPED UP SFC LOW SET UP ACROSS N SASKATCHEWAN...WITH THE COLD FRONT/OCCLUDED FRONT PUSHING SSE THROUGH C MANITOBA AND DOWN THROUGH THE RED RIVER VALLEY OF THE N. LIGHT S WINDS WILL BE COMMON...KEEPING TEMPS FROM FALLING INTO THE LOW 50S...WITH THE WARMEST TEMPS IN THE 60S NEAR THE GREAT LAKES. MONDAY... TIMING OF THE COLD FRONT HAS SLOWED DOWN A BIT...NO LONGER OVER W LAKE SUPERIOR BY 12Z MONDAY...BUT JUST W. THE LOW ITSELF WILL ONLY BE ABLE TO PUSH TO W CENTRAL MANITOBA WHERE IT WILL BECOME NEARLY STATIONARY...SLOWLY EDGING TO NE MANITOBA BY 00Z WEDNESDAY. MEANWHILE ACROSS UPPER MICHIGAN...UNIDIRECTIONAL WINDS AND AFTERNOON HEATING COMBINED WITH THE WEAKENING COLD FRONT WILL ALLOW FOR SHOWER AND THUNDERSTORM DEVELOPMENT. THE MAIN THREAT WILL BE STRONG GUSTY WINDS DURING THE AFTERNOON...AND EARLY EVENING HOURS FAR E. MUCH OF THE AREA IS IN A SPC SLIGHT RISK AREA FOR DAY 3/MONDAY. ADDED THE POTENTIAL TO THE HWO...BUT IT LOOKS MODERATE AT THIS TIME...GIVEN 0-6KM BULK SHEAR VALUES AOB 35KTS...WITH HIGHER VALUES REMAINING W AND S OF THE CWA. WHILE THE OUTPUT FROM THE 12Z GFS IS NOT AS EXCITED ABOUT THE POTENTIAL...THE NAM DOES HAVE 0-3KM SHR VALUES OF 150-200M2/S2 OVER FAR W UPPER MI BY 18Z...AND OVER MUCH OF W UPPER MI BY 21Z. THE BRUNT OF THE STORMS/PRECIP SHOULD BE TRACKING E 15-20KTS. TUESDAY THROUGH WEDNESDAY... WARMED UP HIGH TEMPS FOR TUESDAY ROUGHLY 5 DEGREES...WITH THE HIGHEST VALUES S CENTRAL AND E. THIS AREA SHOULD HAVE THE LEAST CHANCE OF SEEING PRECIP AND LIGHT SSW WINDS. ANOTHER SURGE OF COOLER AIR WILL BE TO OUR W...WITH THE SECONDARY COLD FRONT SET UP OVER MN TUESDAY AFTERNOON. IT SHOULD MOVE ACROSS W UPPER MI TUESDAY EVENING. SPED UP THE EXIT OF TS IN THE GRIDS FOR WEDNESDAY. THURSDAY THROUGH SATURDAY... COOL NW FLOW WITH 850MB TEMPS FALLING TO 6-9C...ASSISTED ADDITIONAL WEAK SHORTWAVES ALOFT...WILL LIKELY RESULT IN SPRINKLES/DRIZZLE ACROSS THE FAVORED UPSLOPE LOCATIONS NEAR LAKE SUPERIOR AND E. THESE LOW POP/LOW QFP SHOWERS WILL CONTINUE OFF AND OFF THROUGH FRIDAY AS 850MB TEMPS COOL A COUPLE MORE DEGREES...AND THE MAIN 500MB TROUGH SINKS ACROSS THE CWA. MODEL GUIDANCE IS IN FAIRLY GOOD SHAPE...WRT THE 12Z ISSUANCES...THROUGH FRIDAY MORNING. AFTER THAT TIME THE 12Z GFS EJECTS THE MAIN 500MB LOW THAT HAD BEEN SITTING NEAR JAMES BAY AT 12Z FRIDAY QUICKLY NORTHEASTWARD. THE ECMWF ON THE OTHER HAND JUST HAS THE LOW SLOWLY SINK SE TO QUEBEC. EVEN SO...HIGH PRESSURE SHOULD STILL BE ABLE TO PUSH ACROSS THE UPPER GREAT LAKES SATURDAY...THE GFS IS JUST A BIT QUICKER. LAKE BREEZES DOMINATING AT LEAST LAKE MI BY THE EARLY AFTERNOON HOURS. W FLOW MAY BE MORE STEADY N ACROSS LAKE SUPERIOR. && .AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT) ISSUED AT 123 AM EDT SUN SEP 2 2012 EXPECT VFR CONDITIONS THIS FCST PERIOD AS DRY HIGH PRESSURE REMAINS OVER/NEAR THE UPPER GREAT LAKES. && .MARINE...(FOR THE 4 PM LAKE SUPERIOR FORECAST ISSUANCE) ISSUED AT 407 PM EDT SAT SEP 1 2012 UNDER SFC HIGH PRES...WINDS ACROSS LAKE SUPERIOR WILL REMAIN LIGHT TONIGHT...MOSTLY UNDER 15KT. AS THE HIGH SHIFTS TO THE E SUN...E TO SE WINDS WILL BEGIN TO INCREASE...REACHING UP TO 20KT OVER FAR WRN LAKE SUPERIOR AND PORTIONS OF CNTRL LAKE SUPERIOR IN THE AFTN. AS A COLD FRONT APPROACHES SUN NIGHT...SOUTHERLY WINDS MAY GUST AS HIGH AS 25KT AT HIGHER OBS PLATFORMS...ESPECIALLY OVER THE E HALF OF THE LAKE. PRES GRADIENT THEN SLACKENS WITH PASSING COLD FRONT MON... RESULTING IN WINDS DIMINISHING BACK TO UNDER 15KT MON INTO TUE. NEXT COLD FRONT PASSING WED WILL BRING AN INCREASE IN W TO NW WINDS TO AROUND 20KT...MAYBE HIGHER...LATER WED INTO THU. && .MQT WATCHES/WARNINGS/ADVISORIES... UPPER MICHIGAN... NONE. LAKE SUPERIOR... NONE. LAKE MICHIGAN... NONE. && $$ SHORT TERM...ROLFSON LONG TERM...KF AVIATION...VOSS MARINE...ROLFSON
AREA FORECAST DISCUSSION
NWS KANSAS CITY/PLEASANT HILL MO
745 PM CDT MON SEP 3 2012 .UPDATE... Recent satellite imagery suggests the embedded mid level impulse crossing through Nebraska/Kansas may be a bit more robust than earlier anticipated. 00Z KTOP sounding shows that substantial moistening in the 850-800mb layer has taken place over the past 12 hours with an appreciable increase in W/SW mid level flow in the 800-600mb layer averaging 25 knots. Despite the lack of robust diurnally driven convection, elevated forcing for ascent looks more than ample to drive an increase axis of convection from extreme SE Nebraska southwest across northeast/east central Kansas early this evening with MUCAPEs approaching 1000 J/kg. Precipitable water values approaching 2" could yield some heavier rainfall rates, but do not anticipate any concerns given the pulse/multi-cell nature to the convection and an expected swift motion off to the northeast at 35-40 mph. Have increased POPs over NE KS/NW MO this evening and further south into MO after midnight assuming this activity gains some traction. No strong/severe weather is expected. Aviation wise, will wait and see if any lightning activity picks up before amending the TAFs, as these elevated cells would otherwise provide VFR conditions with a brief couple minute visibility reduction if a core crossed the terminals. Bookbinder .DISCUSSION... A rather hot and humid day across the region as temperatures have climbed into the 90s in most locations. The warmest airmass has been confined across south central Kansas and Oklahoma where a surface warm has formed just west of the CWA. Convergence along the warm front has allowed a few isolated storms to develop. Given building MLCAPE values approaching 1500-2000 J/KG in areas along and west of the state line, couldn`t rule out an isolated strong to severe storm. Concerns turn towards convective chances later tonight and through Tuesday morning as shortwave energy crossing Colorado begins to influence the airmass. Moisture convergence on the nose of a slightly increasing low level jet will begin to focus itself in northeast Kansas and northern Missouri. Some uncertainty does present itself with setup given meager moisture values and dry airmass advecting in from the southwest. However its possible that activity that develops late this aftn and evening in convergence zone under surface low near Salina to Topeka could sustain itself and begin to propagate eastward into the overnight hours. Models remain all over the place, and will continue to hold lower precipitation chances. Tuesday-Wednesday: Models have trended towards a dry forecast through the daytime hours with temperatures warming significantly over previous forecast. Despite a fairly messy mid-level flow pattern, low level moisture transport remains focused towards the Western Plains, with soundings in the local area remaining capped for much of the day. 850 mb temperatures in the mid-20s should result in another day of middle 90s with a few upper 90s in southern zones. Another uncertain precipitation forecast. With EML firmly in place over the CWA best forcing for convection should remain across western KS and central NE Tuesday afternoon along a cold front pressing southeast. Convection developing along this boundary should remain just west of the CWA as prevailing storm motion pushes convection into Iowa. However will watch for the development of the nocturnal LLJ which should provide enough support to develop scattered convection over eastern KS and Missouri into Wednesday night. Given the veered nature of the LLJ, current precipitation chances are focused over the NW corner and then the southern zones. The front will move through the area on Friday, albeit slower than earlier projections. This will result in a slight upwards tick in temperatures over the southern zones. The best chance for convective redevelopment appear to be focused over the Ozarks. 31 Medium Range (Thursday through Monday)... Surface front will stall across the Ozarks on Thursday while elevated boundary hangs back near and north of I-70. These boundaries will begin to lift to the north Thursday and Thursday evening ahead of a broad upper trough dropping into the Northern Plains. Increasing southerly flow interacting with this baroclinic zone across the CWA will result in broad isentropic ascent and a likely set up for rain and elevated thunder, particularly Thursday night. Could see rain and a few storms linger into Friday as the upper wave deepens into the Central Plains sending the boundary back southward across the forecast area. Amplified northerly flow behind the front will bring dry weather and cooler temps for the weekend. Hawblitzel && .AVIATION... For the 00Z TAFs, clear skies and southeast winds of 8-10 knots should continue this evening with a gradual increase in mid cloud. Thus far, little more than widely scattered showers have developed along a diffuse frontal zone to the northwest. The NAM seems overly aggressive with respect to convection developing this evening/overnight and prefer the HRRR representation which has more closely followed reality to this point. Thus, while thunderstorms could impact the terminals later tonight, the coverage and intensity at this point would not warrant inclusion in the TAFs. So will maintain VFR conditions and southeast winds through the period, although a trend toward light east winds is expected on Tuesday. At STJ, some MVFR light fog could develop late tonight, but radiational cooling could be restricted by cloud cover to some degree. Bookbinder && .EAX WATCHES/WARNINGS/ADVISORIES... MO...NONE. KS...NONE. && $$ WFO EAX
AREA FORECAST DISCUSSION
NWS KANSAS CITY/PLEASANT HILL MO
635 PM CDT MON SEP 3 2012 ...UPDATED AVIATION DISCUSSION... .DISCUSSION... A rather hot and humid day across the region as temperatures have climbed into the 90s in most locations. The warmest airmass has been confined across south central Kansas and Oklahoma where a surface warm has formed just west of the CWA. Convergence along the warm front has allowed a few isolated storms to develop. Given building MLCAPE values approaching 1500-2000 J/KG in areas along and west of the state line, couldn`t rule out an isolated strong to severe storm. Concerns turn towards convective chances later tonight and through Tuesday morning as shortwave energy crossing Colorado begins to influence the airmass. Moisture convergence on the nose of a slightly increasing low level jet will begin to focus itself in northeast Kansas and northern Missouri. Some uncertainty does present itself with setup given meager moisture values and dry airmass advecting in from the southwest. However its possible that activity that develops late this aftn and evening in convergence zone under surface low near Salina to Topeka could sustain itself and begin to propagate eastward into the overnight hours. Models remain all over the place, and will continue to hold lower precipitation chances. Tuesday-Wednesday: Models have trended towards a dry forecast through the daytime hours with temperatures warming significantly over previous forecast. Despite a fairly messy mid-level flow pattern, low level moisture transport remains focused towards the Western Plains, with soundings in the local area remaining capped for much of the day. 850 mb temperatures in the mid-20s should result in another day of middle 90s with a few upper 90s in southern zones. Another uncertain precipitation forecast. With EML firmly in place over the CWA best forcing for convection should remain across western KS and central NE Tuesday afternoon along a cold front pressing southeast. Convection developing along this boundary should remain just west of the CWA as prevailing storm motion pushes convection into Iowa. However will watch for the development of the nocturnal LLJ which should provide enough support to develop scattered convection over eastern KS and Missouri into Wednesday night. Given the veered nature of the LLJ, current precipitation chances are focused over the NW corner and then the southern zones. The front will move through the area on Friday, albeit slower than earlier projections. This will result in a slight upwards tick in temperatures over the southern zones. The best chance for convective redevelopment appear to be focused over the Ozarks. 31 Medium Range (Thursday through Monday)... Surface front will stall across the Ozarks on Thursday while elevated boundary hangs back near and north of I-70. These boundaries will begin to lift to the north Thursday and Thursday evening ahead of a broad upper trough dropping into the Northern Plains. Increasing southerly flow interacting with this baroclinic zone across the CWA will result in broad isentropic ascent and a likely set up for rain and elevated thunder, particularly Thursday night. Could see rain and a few storms linger into Friday as the upper wave deepens into the Central Plains sending the boundary back southward across the forecast area. Amplified northerly flow behind the front will bring dry weather and cooler temps for the weekend. Hawblitzel && .AVIATION... For the 00Z TAFs, clear skies and southeast winds of 8-10 knots should continue this evening with a gradual increase in mid cloud. Thus far, little more than widely scattered showers have developed along a diffuse frontal zone to the northwest. The NAM seems overly aggressive with respect to convection developing this evening/overnight and prefer the HRRR representation which has more closely followed reality to this point. Thus, while thunderstorms could impact the terminals later tonight, the coverage and intensity at this point would not warrant inclusion in the TAFs. So will maintain VFR conditions and southeast winds through the period, although a trend toward light east winds is expected on Tuesday. At STJ, some MVFR light fog could develop late tonight, but radiational cooling could be restricted by cloud cover to some degree. Bookbinder && .EAX WATCHES/WARNINGS/ADVISORIES... MO...NONE. KS...NONE. && $$ WFO EAX
AREA FORECAST DISCUSSION...UPDATED AVIATION
NWS ST LOUIS MO
1207 AM CDT SUN SEP 2 2012 .UPDATE... ISSUED AT 853 PM CDT SAT SEP 1 2012 POST TROPICAL REMNANT SFC LOW OF ISAAC HAS MOVED NEWD TO JUST W OF STL THIS EVNG. MOST OF THE CONVECTION AND THE HEAVIER SHOWERS/SEVERE STORMS HAVE SHIFTED E OR SE OF OUR FORECAST AREA WITH MAINLY JUST SCATTERED SHOWERS AND AREAS OF RAIN CONTINUING TO ROTATE AROUND SFC/UPPER LEVEL LOW OVER OUR AREA. THIS TREND SHOULD CONTINUE AS THE SFC/UPPER LEVEL LOW CONTINUES TO MOVE SLOWLY EWD WITH THE BEST COVERAGE OF RAIN OVER THE ERN PORTION OF THE AREA...EAST OF THE MISSISSIPPI RIVER. MAY STILL GET BRIEF HEAVY DOWNPOURS WITH PRECIPITABLE WATER VALUES OVER 2 INCHES AND DEEP WARM CLOUD LAYER DEPTHS WITH HIGH FREEZING LEVELS. GKS && .SHORT TERM... ISSUED AT 347 PM CDT SAT SEP 1 2012 (TONIGHT AND SUNDAY) MAIN CONCERN CONTINUES TO BE SEVERE POTENTIAL AND LOCALLY HEAVY RAINFALL. THIN LINE OF STORMS EXTENDING FROM CENTRAL ILLINOIS SOUTHWESTWARD INTO SOUTHEAST MISSOURI WILL CONTINUE TO MOVE NORTH NORTHEAST THE NEXT FEW HOURS. THE RAP IS SHOWING PERSISTENT LOW LEVEL MOISTURE CONVERGENCE AS A VORT MAX MOVES AROUND THE SOUTH SIDE OF THE UPPER LOW NOW MEANDERING OVER MISSOURI. OBJECTIVE ANALYSIS OVER THIS SAME AREA DEPICTS SBCAPES 1000-1500 J/KG WHICH SHOULD DIMINISH THROUGH THE EVENING. LIKE YESTERDAY...THERE IS LITTLE DEEP LAYER SHEAR WITH THIS SYSTEM...SO ANY SEVERE WEATHER WILL BE SHORT LIVED. MAIN CONCERN IS WHERE THE TORNADO WATCH IS IN EFFECT FOR SHORT LIVED TORNADOES WHERE 0-1KM SRH VALUES ARE CURRENTLY IN THE 200-250 J/KG RANGE. SEVERE THREAT WILL WANE THROUGH THE EVENING AS THE INSTABILITY WEAKENS. WILL CONTINUE TO SEE AREAS OF RAIN THIS EVENING INTO THE OVERNIGHT. WILL BEGIN TO SLOWLY LOWER POPS FROM WEST TO EAST TONIGHT AS THE UPPER LOW MOVES EAST. THERE MAY BE SOME LOCALLY HEAVY RAINFALL WITH THE THUNDERSTORMS INTO EARLY EVENING THAT COULD CAUSE SOME LOCALIZED FLOODING ALONG AREA CREEKS AND LOW LYING AREAS. ADDITIONAL RAINFALL TOTALS WILL RANGE FROM A COUPLE OF TENTHS OVER CENTRAL MISSOURI TO OVER AN INCH OVER SOUTH CENTRAL ILLINOIS. BRITT && .LONG TERM... ISSUED AT 347 PM CDT SAT SEP 1 2012 (SUNDAY NIGHT THROUGH NEXT SATURDAY) FOLLOWED THE GFS WHICH HAS THE UPPER LOW CONTINUING TO MOVE EAST ON SUNDAY AND SUNDAY NIGHT. STILL HAVE CHANCE OR LIKELY POPS GOING SUNDAY WITH CHANCE POPS OVER THE SOUTHEAST HALF THE CWA ON SUNDAY EVENING. THEREAFTER...STILL LOOKS FAIRLY ACTIVE FOR EARLY SEPTEMBER. GLOBAL MODELS ARE SHOWING ZONAL FLOW OVER THE NORTHERN HALF OF THE NATION WHICH WILL BRING A SHORTWAVE ACROSS THE AREA TUESDAY INTO WEDNESDAY. THERE IS SOME DIFFERENCES BETWEEN THE GFS/ECMWF LATER IN THE WEEK WITH HOW QUICKLY A TROUGH WILL DIG INTO THE CENTRAL U.S.. FOR NOW WILL HAVE A CHANCE OF SHOWERS/ THUNDERSTORMS GOING LATE WEEK INTO EARLY NEXT WEEKEND. BRITT && .AVIATION... ISSUED AT 1145 PM CDT SAT SEP 1 2012 REMAINS OF ISSAC IS CENTERED APPROXIMATELY 30 MILES SOUTHEAST KLSX AND CONTINUES TO MOVE EASTWARD. LIGHT RAIN CONTINUES TO ROTATION AROUND THE LOW CENTER WITH THE LARGER BAND ROTATING OVER PARTS OF EASTERN ILLINOIS THORUGH SOUTHEAST MISSOURI. THE LOW CENTER IS FORECAST TO MOVE INTO SOUTHEAST ILLINOIS BY 1200 UTC SUNDAY MORNING. WILL CONTINUE WITH LOW CEILINGS AND OCCASIONAL VSBYS OF 3 TO 5 MILES IN LIGHT RAIN AND LIGHT FOG THROUGH SUNDAY MORNING. SPECIFICS FOR KSTL...CEILINGS WILL CONTINUE TO LOWER OVER MUCH OF EASTERN MISSOURI BETWEEN 0600 AND 0800 UTC. EXPECT CEILING TO DROP BELOW 010 KFT AND VISIBILITIES WILL OCCASIONALLY DROP 3 TO 5 MILES IN LIGHT RAIN AND LIGHT FOG. WINDS WILL BECOME NORTH NORTHEAST 10 TO 12 KTS AFTER 0600 UTC. LOW CEILINGS WILL BEGIN TO LIFT AFTER 1500-1600 UTC TIME PERIOD WITH VISIBILITIES ABOVE 6 MILES. ISOLATED TO WIDELY SCATTERED SHOWERS POSSIBLE DURING DAY ON SUNDAY OVER STL. RP && .LSX WATCHES/WARNINGS/ADVISORIES... MO...NONE. IL...NONE. && $$ WFO LSX
AREA FORECAST DISCUSSION
NWS RALEIGH NC
1009 PM EDT MON SEP 3 2012 .SYNOPSIS... UNSETTLED WEATHER WILL PERSIST THROUGH WEDNESDAY AS THE REMNANTS OF TROPICAL CYCLONE ISAAC TRACK SLOWLY EAST AND GRADUALLY WEAKEN ALONG THE CENTRAL AND SOUTHERN APPALACHIANS. && .NEAR TERM /THROUGH TUESDAY NIGHT/... AS OF 1005 PM MONDAY... TONIGHT: FORECAST RATIONALE RELATIVELY UNCHANGED FROM EARLIER THINKING. ONE WEAKENING BAND OF CONVECTION AND EMBEDDED MCV/S NEAR KFVX AND KLHZ WILL CONTINUE TO CROSS THE FAR NORTHEAST PIEDMONT AND NORTHERN COASTAL PLAIN THROUGH MIDNIGHT. HEAVY RAIN WILL BE THE PRIMARY HAZARD WITH THIS CONVECTION. THE MAIN FOCUS FOR SCATTERED CONVECTION OVERNIGHT WILL THEN OCCUR OVER THE WESTERN HALF OF THE RAH CWFA....PARTICULARLY OVER THE WESTERN PIEDMONT...WHERE DEEP LAYER MOISTURE TRANSPORT AND GLANCING FORCING FOR ASCENT ASSOCIATED WITH WEAK PERTURBATIONS IN SOUTHWESTERLY FLOW ALOFT -- EVIDENT ON 02Z WV IMAGERY AND RAP ANALYZED VORTICITY FIELDS FROM EASTERN AL TO THE SC UPSTATE -- ARE FORECAST TO BE MAXIMIZED. PERSISTENCE LOWS GENERALLY IN THE LOWER 70S...WITH AREAS OF STRATUS AND/OR FOG LATE. THESE SHOWERS AND ISOLATED STORMS TOO WILL POSE A RISK OF HEAVY RAIN...BUT THE SCATTERED NATURE AND DIMINISHED INSTABILITY SUGGEST A MINIMAL THREAT OF FLOODING. AS OF 340 PM MONDAY... OVERVIEW: THE REMNANTS OF TROPICAL CYCLONE ISAAC WILL GET STRETCHED AND SHEARED APART DURING THE DAY ON TUESDAY...LEAVING BEHIND A WEAK MID/UPPER LEVEL TROUGHINESS ACROSS THE CAROLINAS. TUESDAY AND TUESDAY NIGHT: THE MOIST AIRMASS FEATURING PWATS AT OR ABOVE 2.0" WILL REMAIN IN PLACE ACROSS THE CAROLINAS ON TUESDAY. THERE REMAINS SOME QUESTIONS/UNCERTAINTY REGARDING PENDING DEVELOPMENT AND EVOLUTION OF A SOUTHWARD PROPAGATING MCS TOWARDS THE GULF COAST STATES THAT COULD AUGMENT/DISTURB MOISTURE CONVERGENCE OVER THE AREA...BUT OVERALL THINKING IS THAT WE WILL SEE DIURNAL ENHANCEMENT IN CONVECTIVE COVERAGE TUESDAY AFTERNOON...ESPECIALLY OVER THE WESTERN PIEDMONT INVOF OF THE BROAD TROUGHINESS AND CONTINUED UPSLOPE REGIME ALONG THE EASTERN SLOPES. ELSEWHERE...MUCH LIKE TODAY...FORCING WILL BE MOSTLY CONFINED TO VIA MESOSCALE BOUNDARIES SUCH AS DIFFERENTIAL HEATING...OUTFLOW OR SEABREEZE. POPS RANGING FROM LIKELY WEST TO CHANCE POPS EAST. HIGHS TUESDAY SHOULD BE VERY SIMILAR TO TODAY...DEPENDENT ON HOW EARLY CONVECTION/RAIN MOVES INTO WESTERN PORTIONS OF THE FORECAST AREA. HIGHS IN THE LOWER TO MID 80S WEST TO NEAR 90 CENTRAL AND EASTERN AREAS. LOWS 69 TO 73. SEVERE THREAT...ORGANIZED SEVERE WEATHER APPEARS UNLIKELY THIS AFTERNOON AND AGAIN TOMORROW WITH INSTABILITY TEMPERED BY CLOUD COVER AND WEAK MID-LEVEL LAPSE RATES. HOWEVER...AN ISOLATED SEVERE THREAT CANNOT BE RULED OUT WHERE MESOSCALE PROCESSES LOCALLY ENHANCE LOW/MID LEVEL SHEAR AND ASCENT. THE MAIN CONCERN WILL BE FROM HEAVY RAINFALL AND FLASH FLOODING...PRIMARILY IN THE WESTERN PIEDMONT WHERE A SLOW MOVING NORTH-SOUTH ORIENTED LINE OF CONVECTION COULD PERSIST FOR SEVERAL HOURS. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... AS OF 300 PM MONDAY... UNSETTLED WEATHER WILL LIKELY PERSIST ACROSS CENTRAL NC THROUGH THE SHORT TERM PERIOD AS WEAK TROUGHING ALOFT REMAINS OVER THE AREA. AT THE SURFACE...A WEAK BOUNDARY WILL APPROACH THE AREA LATE WEDNESDAY INTO THURSDAY. ALL OF THIS COMBINED WITH AMPLE MOISTURE (PWAT VALUES EXCEEDING 2 INCHES) AND A MODERATELY UNSTABLE AIR MASS WILL RESULT IN SCATTERED SHOWERS AND THUNDERSTORMS...MAINLY DURING THE AFTERNOON AND EVENING HOURS. AT THIS TIME...AM EXPECTING THE BEST COVERAGE TO BE ACROSS THE WEST ON WEDNESDAY AS THERE WILL BE SLIGHTLY DRIER AIR ACROSS THE EAST AND THEN THE BEST FOCUS SHOULD SHIFT TO THE EAST FOR THURSDAY AS SLIGHTLY DRIER AIR MOVES IN BEHIND THE AFOREMENTIONED SURFACE BOUNDARY. THE MAIN THREAT IS EXPECTED TO BE HEAVY RAIN THAT COULD LEAD TO SOME FLOODING...ESPECIALLY IN URBAN AREAS. HIGH TEMPS WILL BE NEAR NORMAL...GENERALLY IN THE MID/UPPER 80S...WITH OVERNIGHT LOWS RUNNING SLIGHTLY ABOVE NORMAL...GENERALLY IN THE UPPER 60S TO LOWER 70S. && .LONG TERM /FRIDAY THROUGH MONDAY/... AS OF 300 PM MONDAY... AN UNSETTLED WEATHER PATTERN IS EXPECTED TO CONTINUE THROUGH MUCH OF THE LONG TERM PERIOD. FOR FRIDAY...THE BROAD TROUGH ALOFT WILL STILL BE OVER THE AREA...WHILE AT THE SURFACE A WEAK SURFACE BOUNDARY (SEE ABOVE SHORT TERM DISCUSSION) WILL LIKELY BE WASHING OUT OVER THE AREA. NEVERTHELESS...WITH MOISTURE CONTENT STILL EXPECTED TO BE HIGH ACROSS THE REGION...AM EXPECTING ANOTHER GOOD CHANCE OF SHOWERS AND THUNDERSTORMS. BY THE WEEKEND...A SHORT WAVE COMING OUT OF CENTRAL CANADA WILL RESULT IN A TROUGH AMPLIFYING AS IT MOVES ACROSS THE MIDWEST ON SATURDAY AND TOWARDS THE EAST COAST BY SUNDAY. AS THIS RATHER DEEP TROUGH AND ITS ASSOCIATED SURFACE FRONT APPROACHES THE REGION...THIS SHOULD RESULT IN A PROLONGED PERIOD OF GOOD PRECIP CHANCES THROUGH AT LEAST THE END OF THE WEEKEND. AS CAN BE EXPECTED THIS FAR OUT...THERE ARE TIMING AND STRENGTH DIFFERENCES....BUT WILL BEGIN TO TAPER POPS DOWNWARD LATE SUNDAY AND INTO EARLY NEXT WEEK. THERE ARE STILL FAIRLY STRONG INDICATIONS THAT COOLER AND DRIER AIR SHOULD ARRIVE SOMETIME EARLY NEXT WEEK AS A RATHER DEEP TROUGH/CUT OFF LOW DEVELOPS. OVERALL...TEMPS WILL BE NEAR NORMAL EARLY ON IN THE PERIOD BEFORE TRENDING BELOW NORMAL AS INCREASED PRECIP CHANCES AND THE DEEP TROUGH/ASSOCIATED SURFACE FRONT APPROACH AND MOVE THROUGH THE REGION. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... AS OF 750 PM MONDAY... 24 HOUR TAF PERIOD: TOUGH FORECAST TONIGHT AS TWO PRIMARY LINES OF CONVECTION CONTINUE TO INFLUENCE THE AREA. THE FIRST IS IN A LINE RUNNING FROM KHNZ TO KMEB WHICH SPLITS THE CWA IN TWO. HEAVIEST ACTIVITY AT THIS TIME IS OCCURRING JUST EAST OF KRDU. THIS LINE IS EXPECTED TO CONTINUE TO THE EAST BUT COULD WEAKEN OVER THE NEXT SEVERAL HOURS. TOUGH TO TELL AT THIS TIME WHETHER OR NOT KRWI WILL BE AFFECTED BY THIS LINE BUT SHOULD AT LEAST HAVE SHOWERS IN THE VICINITY OVER THE NEXT SEVERAL HOURS. BEHIND THIS FIRST LINE...A WEAKER LINE OF MODERATE SHOWERS AND THUNDERSTORMS RUNS FROM KINT TO KCLT AND THIS TOO WILL GRADUALLY WORK EASTWARD BRINGING SHOWERS INTO KGSO IN THE NEXT TWO TO THREE HOURS. WINDS IN BOTH LINES COULD GUST TO 20 KNOTS. OTHERWISE LIGHT AND VARIABLE CONDITIONS WILL PREVAIL DURING THE OVERNIGHT HOURS. WITH MOISTURE IN THE LOW LEVELS VERY HIGH...EXPECT MOST IF NOT ALL SITES TO ENCOUNTER LOW STRATUS IN THE 500-1000 FOOT RANGE. WILL KEEP PREVAILING LOW STRATUS AFTER 9Z THROUGH SUNRISE AT ALL SITES WITH A TEMPO GROUP FOR 1/2 MILE VISIBILITY AND FOG. AFTER SUNRISE FOG AND STRATUS SHOULD LIFT AFTER 15Z WITH SOUTH SOUTHWESTERLY WINDS AT 5-10 KNOTS WITH BROKEN CEILINGS AROUND 5 KFT. AFTERNOON CONVECTION WILL AGAIN BE PRESENT BUT WITH FORECAST CONFIDENCE VERY LOW IN REGARDS TO TIMING AND LOCATION WILL LEAVE OUT OF TAFS FOR NOW. THE BEST CHANCE FOR CONVECTION WILL BE AT KINT AND KGSO TOMORROW WITH SLIGHTLY LESS CONVECTION FURTHER TO THE EAST. LONG TERM: THE PATTERN REMAINS VERY UNSETTLED FOR THE LONG TERM WITH SUB-VFR CONDITIONS EACH DAY DUE TO AFTERNOON/EARLY EVENING SHOWERS AND THUNDERSTORMS. ADDITIONAL ADVERSE CONDITIONS COULD BE POSSIBLE DURING THE OVERNIGHT HOURS IN THE FORM OF FOG AND LOW STRATUS. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...CBL NEAR TERM....MWS/CBL SHORT TERM...KRR LONG TERM...KRR AVIATION...ELLIS
AREA FORECAST DISCUSSION
NWS RALEIGH NC
621 PM EDT SUN SEP 2 2012 .SYNOPSIS... WARM AND UNSETTLED WEATHER WILL CONTINUE THROUGH MID-WEEK AS THE REMNANTS OF ISAAC APPROACH THE AREA FROM THE WEST. && .NEAR TERM /THROUGH MONDAY NIGHT/... AS OF 145 PM SUNDAY... OVERVIEW: THE FOLLOWING SYNOPTIC FEATURES HAVE BEEN NOTED THIS AFTERNOON... -CIRCULATION ASSOC WITH ISAAC REMNANTS SLOWLY DRIFTING EAST ACROSS THE MIDWEST. -DIFFUSE SFC BOUNDARY DRAPED ACROSS NORTHCENTRAL AND NORTHEAST NC EXTENDING TO THE EAST AND WELL OFFSHORE -MIDLEVEL S/W RIDGE AXIS OVER THE CENTRAL CAROLINAS EXTENDING NORTH INTO VA...WITH A VORTICITY SHEAR AXIS JUST UPSTREAM AND CROSSING THE MOUNTAINS. FOR THE REST OF TODAY...SCATTERED SHOWERS/TSTMS HAVE DEVELOPED ACROSS OUR CENTRAL ZONES IN AN AREA OF LOW-LEVEL CONVERGENCE AND MODERATE INSTABILITY. EXPECT THIS ACTIVITY TO CONTINUE THIS AFTERNOON...AND ADDITIONAL ACTIVITY TO DEVELOP ACROSS THE THE WESTERN PIEDMONT WITH THE APPROACHING MID-LEVEL SHEAR AXIS. OUTFLOW BOUNDARIES FROM INITIAL ACTIVITY SHOULD TRIGGER ADDITIONAL CELLS WHICH WILL SLOWLY MOVE TOWARD THE EAST GIVEN A 240-270 DEG STORM MOTION <6 KTS AS SEEN IN FORECAST SOUNDINGS. LATEST MESOANALYSIS SHOWS THE BEST INSTABILITY ACROSS THE SOUTHERN HALF OF OUR FORECAST AREA. NOTED THAT BULK SHEAR REMAINS <20KT ACROSS OUR ENTIRE CWA. AS FOR DCAPE...WHILE BEST VALUES FOR WIND GUSTS ARE WELL TO OUR SOUTH...3 TO 6 HOUR RAP PROGS SUGGEST INCREASING DCAPE EXTENDING UP ACROSS THE COASTAL PLAIN AND THE SANDHILLS AREAS. FINALLY PWAT VALUES REMAIN RATHER HIGH (2+ INCHES) ACROSS MOST OF OUR CWA. SO IN SUMMARY...TSTMS SHOULD BE MORE PULSE IN NATURE...AND GIVEN ANTICIPATED SLOW MOVEMENT AND HIGH PWAT VALUES...HEAVY DOWNPOURS AND LOCAL POOR DRAINAGE FLOODING WILL BE THE PRIMARY CONCERN TODAY. A SECONDARY CONCERN WILL BE THE POTENTIAL FOR ISOLATED AND BRIEF DAMAGING WIND GUSTS...PARTICULARLY ACROSS THE S/SE HALF OF OUR CWA WHERE CAPE AND DCAPE ARE ENHANCED. TONIGHT...SHOWER/TSTM ACTIVITY SHOULD WIND DOWN BY 10 PM LEAVING THE OVERNIGHT PERIOD PARTLY TO MOSTLY CLOUDY. NO CHANGE IN AIRMASS FROM RECENT DAYS...SO EXPECT LOWS IN THE LOW-MID 70S. MONDAY AND MONDAY NIGHT...MID LEVEL CIRCULATION FROM ISAAC REMNANTS IS FORECAST TO SLOW FORWARD MOVEMENT AND SPLIT OVER THE OH/TN VALLEY AS IT ENCOUNTERS THE MID-LEVEL RIDGE ALONG THE MID ATLANTIC AND CAROLINA COAST. ONE PORTION OF THE AFOREMENTIONED CIRCULATION IS PROGGED TO MOVE TO THE NE AND ANOTHER TO THE S. SIMILAR TO TODAY... ANOTHER VORTICITY AXIS ROTATING AROUND THE LARGE-SCALE SYSTEM IS PROGGED TO CROSS THE MOUNTAINS DURING THE DAYTIME...AND SHOULD HELP SERVE AS A FOCUS FOR SHOWER/TSTM DEVELOPMENT PARTICULARLY ACROSS THE WESTERN HALF OF OUR CWA. SIMILAR TO TODAY...EXPECT A HIGH PWAT AND LOW SHEAR ENVIRONMENT TO SUPPORT PULSE TYPE ACTIVITY AND WITH STORM MOTION PROGGED AOB 7 KTS...ONCE AGAIN LOCALIZED POOR DRAINAGE FLOODING LIKELY TO BE THE PRIMARY CONCERN. AS FOR POPS...WILL CONTINUE TO CARRY STRONG-CHANCE POPS TAPERED SLIGHTLY HIGHER ACROSS OUR WESTERN HALF. LITTLE CHANGE IN AIRMASS SO WILL CONTINUE TO SEE ABOVE NORMAL TEMPS WITH HIGHS AROUND 90. GIVEN PROXIMITY OF ISAAC REMNANTS AND SUBSEQUENT MID LEVEL IMPULSES AROUND IT AND ENHANCED SOUTHERLY LOW-LEVEL FLOW... SHOWER/TSTM ACTIVITY MAY LINGER ON A BIT LONGER INTO THE EVENING HOURS...ESP ACROSS OUR WESTERN ZONES. LOWS MONDAY NIGHT ONCE AGAIN IN THE LOW-MID 70S. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... AS OF 210 PM SUNDAY... FOR TUESDAY/TUESDAY NIGHT: THE QUICKLY-DAMPENING MID LEVEL SHORTWAVE TROUGH -- THE REMAINS OF ISAAC -- WILL APPROACH WRN/CENTRAL NC FROM THE WEST ON TUESDAY... ALTHOUGH THE BULK OF THE DPVA WILL SLIDE TO OUR SW ACROSS GA WITH JUST A WEAK SHEAR AXIS SETTLING EASTWARD INTO THE NC MOUNTAINS BY TUESDAY NIGHT... WHILE ANOTHER WEAK PERTURBATION AND ATTENDANT SURFACE LOW TRACK JUST NORTH OF HIGHWAY 80 FROM LAKE ERIE TO NEW ENGLAND. DESPITE THE WEAKENING WAVE`S APPROACH FROM THE WEST... DYNAMIC FORCING FOR LIFT WILL BE QUITE LOW WITH WEAK MID LEVEL RIDGING OVER CENTRAL/ERN NC... WEAK MID LEVEL WINDS... AND LOW DEEP LAYER SHEAR (5-10 KTS AT BEST). MOISTURE WILL REMAIN DECENT IN THE WESTERN CWA WITH PW VALUES NEAR 2.0 INCHES... BUT WILL SEE LOWER VALUES (NEAR 1.5 INCHES--CLOSE TO NORMAL) IN THE EAST WHERE SOME DRIER MID LEVEL AIR WILL BE PULLED ONSHORE FROM THE ESE. ALSO... MODELS INDICATE SOMEWHAT POOR CONVECTIVE PARAMETERS WITH 1000-1500 J/KG MLCAPE CONFINED TO THE SOUTHWESTERN SECTIONS... AND THE MODELS ARE GENERATING VERY LITTLE QPF... WITH SREF PROBABILITIES OF ANY PRECIP HOLDING UNDER 30 PERCENT OVER ALL BUT THE FAR WEST. WILL HOLD ONTO CHANCE POPS IN THE FAR WEST TUESDAY... BUT WILL DROP TO JUST SLIGHT CHANCE OVER THE REST OF THE CWA. HIGHS 85-89 WITH THICKNESSES HOLDING ABOVE NORMAL. LOWS 69-73 WITH AREAS OF FOG DEVELOPING. FOR WEDNESDAY/WEDNESDAY NIGHT: THE WEAK MID LEVEL SHEAR AXIS CONTINUES TO DRIFT EASTWARD... MOVING INTO CENTRAL NC WEDNESDAY. ACCORDINGLY... THE HIGHER PW VALUES SPREAD EASTWARD AS WELL INTO THIS AREA... CLIMBING TO 2.0-2.2 INCHES IN A RIBBON THROUGH CENTRAL NC. INSTABILITY MAY BE A BIT BETTER AS WELL WITH MODELS SHOWING 1200-1800 J/KG OF MLCAPE AREAWIDE... HOWEVER DEEP LAYER SHEAR REMAINS POOR AT JUST 5-10 KTS. BUT THE HIGHER SREF PROBABILITIES OF MEASURABLE PRECIP KICK EASTWARD WEDNESDAY WITH 50-70 PERCENT CHANCES COVERING CENTRAL NC... AND WITH THE MINOR HEIGHT FALLS AND SLIGHT UPTICK IN DYNAMICALLY-INDUCED LIFT... WILL STAY WITH FORECAST OF SCATTERED STORMS AREAWIDE DEVELOPING IN THE AFTERNOON... CONTINUING THROUGH THE EVENING. THESE WILL LIKELY BE SLOW-MOVERS... WITH A HEIGHTENED THREAT OF STREET FLOODING. HIGHS AGAIN 85-89. LOWS 68-73 WITH ANOTHER ROUND OF FOG POSSIBLE LATE. -GIH && .LONG TERM /THURSDAY THROUGH SUNDAY/... AS OF 1140 AM SUNDAY... EXPECT WET WEATHER EARLY BUT WITH DRIER CONDITIONS HEADING INTO NEXT WEEKEND. THIS PERIOD BEGINS WITH FAST MID LEVEL FLOW AND A VERY BROAD TROUGH COVERING THE NORTHERN THIRD OF THE CONUS INTO CANADA (AROUND A STRONG VORTEX OVER FAR NRN ONTARIO)... WHILE AN E-W ELONGATED RIDGE COVERS THE FAR SOUTHWEST INTO NRN MEXICO... AND A WEAK LIKELY SUBTROPICAL LOW SITS JUST OFF THE NE COAST OF FL. A WEAK MID LEVEL SHEAR AXIS PERSISTS THROUGH THE CENTRAL CAROLINAS... ALONG A SURFACE LEE TROUGH... WELL AHEAD OF AN INCOMING SYNOPTIC COLD FRONT. FOR THURSDAY/THURSDAY NIGHT: ONE LARGE BUT LOW-AMPLITUDE SHORTWAVE TROUGH SWINGS THROUGH THE EASTERN GREAT LAKES/ST LAWRENCE VALLEY AND THE NORTHEAST STATES ON THURSDAY... AND THE ENSUING HEIGHT FALLS ALOFT COMBINED WITH DEEP MOISTURE IN PLACE AND PREFRONTAL INSTABILITY SHOULD INSTIGATE GOOD COVERAGE OF SHOWERS AND STORMS OVER CENTRAL NC... PARTICULARLY THURSDAY AFTERNOON AND EVENING... WITH GREATER COVERAGE ALONG/EAST OF HIGHWAY 1 GIVEN THE DRIER MID LEVEL AIR FILTERING INTO THE WEST. LOW LEVEL THICKNESSES REMAIN 5-10 METERS ABOVE NORMAL... ALTHOUGH THIS WARMTH WILL BE SOMEWHAT TEMPERED BY CONSIDERABLE MID AND HIGH CLOUDS. HIGHS MAINLY IN THE MID-UPPER 80S. THE LONGWAVE TROUGH BEGINS TO DIG PROMINENTLY OVER THE MIDWEST/PLAINS LATE THURSDAY THROUGH THURSDAY NIGHT DUE TO ENERGY DROPPING FROM MT/WY/DAKOTAS INTO THE BROAD TROUGH BASE. IN RESPONSE... THE DOWNSTREAM BROAD MID LEVEL TROUGHING THROUGH THE CAROLINAS WILL WEAKEN QUICKLY AS IT HEADS TO OUR NE. (THE WEAK LOW OFF FL APPEARS LIKELY TO STAY ENOUGH TO OUR SSE TO NOT BE A FACTOR IN OUR WEATHER.) THE GFS/ECMWF BRING THE SURFACE COLD FRONT TO THE WESTERN APPALACHIAN SLOPES BY LATE THURSDAY NIGHT... HOWEVER THE PUSH OF COOL AIR IMMEDIATELY BEHIND IT WILL BE MUTED WITH THE AIR MASS QUICKLY MODIFYING IN RESPONSE TO THE STRONG FRONTOGENESIS OVER THE UPPER MIDWEST. SO WHILE THE MID LEVELS WILL CONTINUE TO DRY OUT WEST TO EAST ACROSS CENTRAL NC THURSDAY NIGHT... THE REDUCTION IN SURFACE-BASED MOISTURE WILL BE MUCH MORE SUBTLE. AS SUCH... EXPECT A MINIMAL DIP IN TEMPS. LOWS THURSDAY NIGHT 66-71. FOR FRIDAY/FRIDAY NIGHT: THE FRONT APPROACHING FROM THE NW EARLY FRIDAY WILL HAVE LOST MOST OF ITS STEAM AS THE AIR MASS BEHIND IT MODIFIES. THE LOWEST 1-2 KM WILL REMAIN MOIST ENOUGH FOR BROKEN DIURNAL CLOUDS MUCH OF THE DAY... BUT THE MID-UPPER LEVEL DRYING AND SUBSEQUENT LOWERING OF PW SHOULD GREATLY LIMIT COVERAGE AND STRENGTH OF ANY CONVECTION. WITH THE ABSENCE OF MOISTURE IN THE MIXED PHASE REGION ALOFT... LIGHTNING PRODUCTION SHOULD BE MINIMAL AND EXPECT NO MORE THAN A FEW SHOWERS AT BEST FRIDAY WITH A LACK OF BOTH MOISTURE AND FORCING FOR ASCENT. THICKNESSES CHANGE VERY LITTLE AND STAY ABOVE NORMAL... SO EXPECT HIGHS OF 86-90. LOWS 65-70 WITH FAIR SKIES. FOR SATURDAY/SUNDAY: THE CANADIAN VORTEX WOBBLES SLOWLY ACROSS JAMES BAY WHILE THE TROUGH DIGS THROUGH THE CENTRAL US AND GREAT LAKES. MODEL SOLUTIONS BEGIN TO DIVERGE WITH THE ECMWF SHOWING THIS NORTHERN STREAM SEPARATING... WITH THE CANADIAN VORTEX CROSSING NRN QUEBEC... WHILE THE TROUGH STRONGLY AMPLIFIES AND CLOSES OFF ANOTHER LOW OVER THE OHIO VALLEY BY THE END OF THE WEEKEND. THE 06Z GFS ON THE OTHER HAND REMAINS PHASED AND PUSHES A POSITIVELY-TILTED TROUGH THROUGH THE NORTHEAST/APPALACHIANS/MID SOUTH... WITH A LARGE COOL FALL HIGH PRESSURE AREA CENTERED OVER THE GREAT LAKES BUILDING SOUTHEASTWARD INTO THE FORECAST AREA OVER THE WEEKEND. WHILE THE ECMWF ENSEMBLE MEAN IS MUCH MORE SUBDUED WITH THE GREAT LAKES/OHIO VALLEY TROUGHING THAN ITS OPERATIONAL COUNTERPART... THE TWO AGREE WELL ON TIMING AND PLACEMENT... AND THIS SOLUTION HAS SUPPORT FROM THE GEFS MEAN AND FROM THE NEW 12Z GFS. WILL LEAN TOWARD THE ECMWF SOLUTION. EXPECT DRY WEATHER WITH TEMPS HOLDING JUST ABOVE SEASONAL NORMALS WELL EAST OF THE TROUGH. AS THIS TROUGH MOVES EASTWARD INTO THE MID SOUTH REGION AND APPROACHES NC... WILL BRING IN A SMALL CHANCE OF STORMS LATE SUNDAY... ALONG WITH WARM TEMPS. -GIH && .AVIATION /00Z MONDAY THROUGH FRIDAY/... AS OF 620 PM SUNDAY... 24 HOUR TAF PERIOD: SHOWER AND THUNDERSTORM ACTIVITY HAS MOVED OUT OF EASTERN STATIONS BUT KINT AND KGSO ARE CURRENTLY BEING AFFECTED BY SHOWER AND THUNDERSTORM ACTIVITY EXPECTED TO CONTINUE FOR THE NEXT HOUR OR TWO. OVERNIGHT TONIGHT EXPECT PROBLEMS WITH FOG AND LOW STRATUS AT ALL SITES. LOW CEILINGS 500-1000 IS THE MAIN CONCERN OVERNIGHT WITH VISIBILITIES IN THE 3 TO 5 MILE RANGE SECONDARY. TIMING WOULD BE AFTER 9Z UNTIL SUNRISE WITH EASTERN SITES HAVING THE POTENTIAL TO REMAIN SUB-VFR LONGER THROUGH MID MORNING. AFTERNOON SHOWERS AND THUNDERSTORMS WILL BE PREVALENT TOMORROW AFTERNOON WITH THE BETTER CHANCES IN THE NORTHWEST BUT POSSIBLE AT ALL SITES. WILL LEAVE OUT OF TAFS FOR NOW SINCE TIMING AND EXACT LOCATION IS VERY UNCERTAIN AT THIS TIME BUT CONFIDENCE IS FAIRLY HIGH THAT THERE WILL BE CONVECTION TOMORROW AFTERNOON INTO THE EVENING. WINDS WILL STAY LIGHT AND VARIABLE THOUGHT THE TAF PERIOD. LONG TERM: AS THE REMNANTS OF ISAAC APPROACH THE AREA FROM THE WEST...SCATTERED AFTERNOON/EARLY EVENING SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE THROUGH TUESDAY. THE BIGGEST THREAT WITH THESE STORMS WILL BE HEAVY RAIN WITH LOCALIZED POTENTIAL FOR SEVERE WIND GUSTS. OTHERWISE CONDITIONS ARE EXPECTED TO BE LARGELY VFR THROUGH THE LONG TERM. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...ELLIS NEAR TERM....NP SHORT TERM...HARTFIELD LONG TERM...HARTFIELD AVIATION...ELLIS
AREA FORECAST DISCUSSION
NWS RALEIGH NC
210 PM EDT SUN SEP 2 2012 .SYNOPSIS... A WARM AND HUMID AIR MASS COUPLED WITH THE SLOW APPROACH OF AN UPPER LEVEL TROUGH WILL KEEP THE WEATHER UNSETTLED ACROSS CENTRAL NC THROUGH MID WEEK. && .NEAR TERM /THROUGH MONDAY NIGHT/... AS OF 145 PM SUNDAY... OVERVIEW: THE FOLLOWING SYNOPTIC FEATURES HAVE BEEN NOTED THIS AFTERNOON... -CIRCULATION ASSOC WITH ISAAC REMNANTS SLOWLY DRIFTING EAST ACROSS THE MIDWEST. -DIFFUSE SFC BOUNDARY DRAPED ACROSS NORTHCENTRAL AND NORTHEAST NC EXTENDING TO THE EAST AND WELL OFFSHORE -MIDLEVEL S/W RIDGE AXIS OVER THE CENTRAL CAROLINAS EXTENDING NORTH INTO VA...WITH A VORTICITY SHEAR AXIS JUST UPSTREAM AND CROSSING THE MOUNTAINS. FOR THE REST OF TODAY...SCATTERED SHOWERS/TSTMS HAVE DEVELOPED ACROSS OUR CENTRAL ZONES IN AN AREA OF LOW-LEVEL CONVERGENCE AND MODERATE INSTABILITY. EXPECT THIS ACTIVITY TO CONTINUE THIS AFTERNOON...AND ADDITIONAL ACTIVITY TO DEVELOP ACROSS THE THE WESTERN PIEDMONT WITH THE APPROACHING MID-LEVEL SHEAR AXIS. OUTFLOW BOUNDARIES FROM INITIAL ACTIVITY SHOULD TRIGGER ADDITIONAL CELLS WHICH WILL SLOWLY MOVE TOWARD THE EAST GIVEN A 240-270 DEG STORM MOTION <6 KTS AS SEEN IN FORECAST SOUNDINGS. LATEST MESOANALYSIS SHOWS THE BEST INSTABILITY ACROSS THE SOUTHERN HALF OF OUR FORECAST AREA. NOTED THAT BULK SHEAR REMAINS <20KT ACROSS OUR ENTIRE CWA. AS FOR DCAPE...WHILE BEST VALUES FOR WIND GUSTS ARE WELL TO OUR SOUTH...3 TO 6 HOUR RAP PROGS SUGGEST INCREASING DCAPE EXTENDING UP ACROSS THE COASTAL PLAIN AND THE SANDHILLS AREAS. FINALLY PWAT VALUES REMAIN RATHER HIGH (2+ INCHES) ACROSS MOST OF OUR CWA. SO IN SUMMARY...TSTMS SHOULD BE MORE PULSE IN NATURE...AND GIVEN ANTICIPATED SLOW MOVEMENT AND HIGH PWAT VALUES...HEAVY DOWNPOURS AND LOCAL POOR DRAINAGE FLOODING WILL BE THE PRIMARY CONCERN TODAY. A SECONDARY CONCERN WILL BE THE POTENTIAL FOR ISOLATED AND BRIEF DAMAGING WIND GUSTS...PARTICULARLY ACROSS THE S/SE HALF OF OUR CWA WHERE CAPE AND DCAPE ARE ENHANCED. TONIGHT...SHOWER/TSTM ACTIVITY SHOULD WIND DOWN BY 10 PM LEAVING THE OVERNIGHT PERIOD PARTLY TO MOSTLY CLOUDY. NO CHANGE IN AIRMASS FROM RECENT DAYS...SO EXPECT LOWS IN THE LOW-MID 70S. MONDAY AND MONDAY NIGHT...MID LEVEL CIRCULATION FROM ISAAC REMNANTS IS FORECAST TO SLOW FORWARD MOVEMENT AND SPLIT OVER THE OH/TN VALLEY AS IT ENCOUNTERS THE MID-LEVEL RIDGE ALONG THE MID ATLANTIC AND CAROLINA COAST. ONE PORTION OF THE AFOREMENTIONED CIRCULATION IS PROGGED TO MOVE TO THE NE AND ANOTHER TO THE S. SIMILAR TO TODAY... ANOTHER VORTICITY AXIS ROTATING AROUND THE LARGE-SCALE SYSTEM IS PROGGED TO CROSS THE MOUNTAINS DURING THE DAYTIME...AND SHOULD HELP SERVE AS A FOCUS FOR SHOWER/TSTM DEVELOPMENT PARTICULARLY ACROSS THE WESTERN HALF OF OUR CWA. SIMILAR TO TODAY...EXPECT A HIGH PWAT AND LOW SHEAR ENVIRONMENT TO SUPPORT PULSE TYPE ACTIVITY AND WITH STORM MOTION PROGGED AOB 7 KTS...ONCE AGAIN LOCALIZED POOR DRAINAGE FLOODING LIKELY TO BE THE PRIMARY CONCERN. AS FOR POPS...WILL CONTINUE TO CARRY STRONG-CHANCE POPS TAPERED SLIGHTLY HIGHER ACROSS OUR WESTERN HALF. LITTLE CHANGE IN AIRMASS SO WILL CONTINUE TO SEE ABOVE NORMAL TEMPS WITH HIGHS AROUND 90. GIVEN PROXIMITY OF ISAAC REMNANTS AND SUBSEQUENT MID LEVEL IMPULSES AROUND IT AND ENHANCED SOUTHERLY LOW-LEVEL FLOW... SHOWER/TSTM ACTIVITY MAY LINGER ON A BIT LONGER INTO THE EVENING HOURS...ESP ACROSS OUR WESTERN ZONES. LOWS MONDAY NIGHT ONCE AGAIN IN THE LOW-MID 70S. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... AS OF 210 PM SUNDAY... FOR TUESDAY/TUESDAY NIGHT: THE QUICKLY-DAMPENING MID LEVEL SHORTWAVE TROUGH -- THE REMAINS OF ISAAC -- WILL APPROACH WRN/CENTRAL NC FROM THE WEST ON TUESDAY... ALTHOUGH THE BULK OF THE DPVA WILL SLIDE TO OUR SW ACROSS GA WITH JUST A WEAK SHEAR AXIS SETTLING EASTWARD INTO THE NC MOUNTAINS BY TUESDAY NIGHT... WHILE ANOTHER WEAK PERTURBATION AND ATTENDANT SURFACE LOW TRACK JUST NORTH OF HIGHWAY 80 FROM LAKE ERIE TO NEW ENGLAND. DESPITE THE WEAKENING WAVE`S APPROACH FROM THE WEST... DYNAMIC FORCING FOR LIFT WILL BE QUITE LOW WITH WEAK MID LEVEL RIDGING OVER CENTRAL/ERN NC... WEAK MID LEVEL WINDS... AND LOW DEEP LAYER SHEAR (5-10 KTS AT BEST). MOISTURE WILL REMAIN DECENT IN THE WESTERN CWA WITH PW VALUES NEAR 2.0 INCHES... BUT WILL SEE LOWER VALUES (NEAR 1.5 INCHES--CLOSE TO NORMAL) IN THE EAST WHERE SOME DRIER MID LEVEL AIR WILL BE PULLED ONSHORE FROM THE ESE. ALSO... MODELS INDICATE SOMEWHAT POOR CONVECTIVE PARAMETERS WITH 1000-1500 J/KG MLCAPE CONFINED TO THE SOUTHWESTERN SECTIONS... AND THE MODELS ARE GENERATING VERY LITTLE QPF... WITH SREF PROBABILITIES OF ANY PRECIP HOLDING UNDER 30 PERCENT OVER ALL BUT THE FAR WEST. WILL HOLD ONTO CHANCE POPS IN THE FAR WEST TUESDAY... BUT WILL DROP TO JUST SLIGHT CHANCE OVER THE REST OF THE CWA. HIGHS 85-89 WITH THICKNESSES HOLDING ABOVE NORMAL. LOWS 69-73 WITH AREAS OF FOG DEVELOPING. FOR WEDNESDAY/WEDNESDAY NIGHT: THE WEAK MID LEVEL SHEAR AXIS CONTINUES TO DRIFT EASTWARD... MOVING INTO CENTRAL NC WEDNESDAY. ACCORDINGLY... THE HIGHER PW VALUES SPREAD EASTWARD AS WELL INTO THIS AREA... CLIMBING TO 2.0-2.2 INCHES IN A RIBBON THROUGH CENTRAL NC. INSTABILITY MAY BE A BIT BETTER AS WELL WITH MODELS SHOWING 1200-1800 J/KG OF MLCAPE AREAWIDE... HOWEVER DEEP LAYER SHEAR REMAINS POOR AT JUST 5-10 KTS. BUT THE HIGHER SREF PROBABILITIES OF MEASURABLE PRECIP KICK EASTWARD WEDNESDAY WITH 50-70 PERCENT CHANCES COVERING CENTRAL NC... AND WITH THE MINOR HEIGHT FALLS AND SLIGHT UPTICK IN DYNAMICALLY-INDUCED LIFT... WILL STAY WITH FORECAST OF SCATTERED STORMS AREAWIDE DEVELOPING IN THE AFTERNOON... CONTINUING THROUGH THE EVENING. THESE WILL LIKELY BE SLOW-MOVERS... WITH A HEIGHTENED THREAT OF STREET FLOODING. HIGHS AGAIN 85-89. LOWS 68-73 WITH ANOTHER ROUND OF FOG POSSIBLE LATE. -GIH && .LONG TERM /THURSDAY THROUGH SUNDAY/... AS OF 1140 AM SUNDAY... EXPECT WET WEATHER EARLY BUT WITH DRIER CONDITIONS HEADING INTO NEXT WEEKEND. THIS PERIOD BEGINS WITH FAST MID LEVEL FLOW AND A VERY BROAD TROUGH COVERING THE NORTHERN THIRD OF THE CONUS INTO CANADA (AROUND A STRONG VORTEX OVER FAR NRN ONTARIO)... WHILE AN E-W ELONGATED RIDGE COVERS THE FAR SOUTHWEST INTO NRN MEXICO... AND A WEAK LIKELY SUBTROPICAL LOW SITS JUST OFF THE NE COAST OF FL. A WEAK MID LEVEL SHEAR AXIS PERSISTS THROUGH THE CENTRAL CAROLINAS... ALONG A SURFACE LEE TROUGH... WELL AHEAD OF AN INCOMING SYNOPTIC COLD FRONT. FOR THURSDAY/THURSDAY NIGHT: ONE LARGE BUT LOW-AMPLITUDE SHORTWAVE TROUGH SWINGS THROUGH THE EASTERN GREAT LAKES/ST LAWRENCE VALLEY AND THE NORTHEAST STATES ON THURSDAY... AND THE ENSUING HEIGHT FALLS ALOFT COMBINED WITH DEEP MOISTURE IN PLACE AND PREFRONTAL INSTABILITY SHOULD INSTIGATE GOOD COVERAGE OF SHOWERS AND STORMS OVER CENTRAL NC... PARTICULARLY THURSDAY AFTERNOON AND EVENING... WITH GREATER COVERAGE ALONG/EAST OF HIGHWAY 1 GIVEN THE DRIER MID LEVEL AIR FILTERING INTO THE WEST. LOW LEVEL THICKNESSES REMAIN 5-10 METERS ABOVE NORMAL... ALTHOUGH THIS WARMTH WILL BE SOMEWHAT TEMPERED BY CONSIDERABLE MID AND HIGH CLOUDS. HIGHS MAINLY IN THE MID-UPPER 80S. THE LONGWAVE TROUGH BEGINS TO DIG PROMINENTLY OVER THE MIDWEST/PLAINS LATE THURSDAY THROUGH THURSDAY NIGHT DUE TO ENERGY DROPPING FROM MT/WY/DAKOTAS INTO THE BROAD TROUGH BASE. IN RESPONSE... THE DOWNSTREAM BROAD MID LEVEL TROUGHING THROUGH THE CAROLINAS WILL WEAKEN QUICKLY AS IT HEADS TO OUR NE. (THE WEAK LOW OFF FL APPEARS LIKELY TO STAY ENOUGH TO OUR SSE TO NOT BE A FACTOR IN OUR WEATHER.) THE GFS/ECMWF BRING THE SURFACE COLD FRONT TO THE WESTERN APPALACHIAN SLOPES BY LATE THURSDAY NIGHT... HOWEVER THE PUSH OF COOL AIR IMMEDIATELY BEHIND IT WILL BE MUTED WITH THE AIR MASS QUICKLY MODIFYING IN RESPONSE TO THE STRONG FRONTOGENESIS OVER THE UPPER MIDWEST. SO WHILE THE MID LEVELS WILL CONTINUE TO DRY OUT WEST TO EAST ACROSS CENTRAL NC THURSDAY NIGHT... THE REDUCTION IN SURFACE-BASED MOISTURE WILL BE MUCH MORE SUBTLE. AS SUCH... EXPECT A MINIMAL DIP IN TEMPS. LOWS THURSDAY NIGHT 66-71. FOR FRIDAY/FRIDAY NIGHT: THE FRONT APPROACHING FROM THE NW EARLY FRIDAY WILL HAVE LOST MOST OF ITS STEAM AS THE AIR MASS BEHIND IT MODIFIES. THE LOWEST 1-2 KM WILL REMAIN MOIST ENOUGH FOR BROKEN DIURNAL CLOUDS MUCH OF THE DAY... BUT THE MID-UPPER LEVEL DRYING AND SUBSEQUENT LOWERING OF PW SHOULD GREATLY LIMIT COVERAGE AND STRENGTH OF ANY CONVECTION. WITH THE ABSENCE OF MOISTURE IN THE MIXED PHASE REGION ALOFT... LIGHTNING PRODUCTION SHOULD BE MINIMAL AND EXPECT NO MORE THAN A FEW SHOWERS AT BEST FRIDAY WITH A LACK OF BOTH MOISTURE AND FORCING FOR ASCENT. THICKNESSES CHANGE VERY LITTLE AND STAY ABOVE NORMAL... SO EXPECT HIGHS OF 86-90. LOWS 65-70 WITH FAIR SKIES. FOR SATURDAY/SUNDAY: THE CANADIAN VORTEX WOBBLES SLOWLY ACROSS JAMES BAY WHILE THE TROUGH DIGS THROUGH THE CENTRAL US AND GREAT LAKES. MODEL SOLUTIONS BEGIN TO DIVERGE WITH THE ECMWF SHOWING THIS NORTHERN STREAM SEPARATING... WITH THE CANADIAN VORTEX CROSSING NRN QUEBEC... WHILE THE TROUGH STRONGLY AMPLIFIES AND CLOSES OFF ANOTHER LOW OVER THE OHIO VALLEY BY THE END OF THE WEEKEND. THE 06Z GFS ON THE OTHER HAND REMAINS PHASED AND PUSHES A POSITIVELY-TILTED TROUGH THROUGH THE NORTHEAST/APPALACHIANS/MID SOUTH... WITH A LARGE COOL FALL HIGH PRESSURE AREA CENTERED OVER THE GREAT LAKES BUILDING SOUTHEASTWARD INTO THE FORECAST AREA OVER THE WEEKEND. WHILE THE ECMWF ENSEMBLE MEAN IS MUCH MORE SUBDUED WITH THE GREAT LAKES/OHIO VALLEY TROUGHING THAN ITS OPERATIONAL COUNTERPART... THE TWO AGREE WELL ON TIMING AND PLACEMENT... AND THIS SOLUTION HAS SUPPORT FROM THE GEFS MEAN AND FROM THE NEW 12Z GFS. WILL LEAN TOWARD THE ECMWF SOLUTION. EXPECT DRY WEATHER WITH TEMPS HOLDING JUST ABOVE SEASONAL NORMALS WELL EAST OF THE TROUGH. AS THIS TROUGH MOVES EASTWARD INTO THE MID SOUTH REGION AND APPROACHES NC... WILL BRING IN A SMALL CHANCE OF STORMS LATE SUNDAY... ALONG WITH WARM TEMPS. -GIH && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... AS OF 145 AM SUNDAY... 24 HOUR TAF PERIOD: SCATTERED SHOWERS AND TSTMS ACROSS THE CENTRAL PORTION OF THE STATE ATTM WILL RESULT IN LOCALLY REDUCED CIGS AND VSBY ALONG WITH BRIEF GUSTY SFC WINDS. THE TAF SITES MOSTLY LIKELY TO BE AFFECTED WITH IFR CONDITIONS THROUGH 20Z INCLUDE KRDU AND KFAY. KINT/KGSO/KRWI MAY BE IMPACTED LATER THIS AFTERNOON AS THIS ACTIVITY CONTINUES TO EVOLVE. OUTSIDE OF THESE STORMS...EXPECT VFR CONDITIONS. LATER TONIGHT... ENHANCED LOW LEVEL MOISTURE MAY SET THE STAGE FOR A BRIEF PERIOD OF REDUCED VSBY AND CIGS WITH FOG AND LOW CLOUDS POSSIBLE TOWARD SUNRISE MONDAY. OUTLOOK: SCATTERED AFTERNOON AND EARLY EVENING SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE EACH DAY AS ENHANCED MOISTURE AND A SLOW MOVING FRONT GRADUALLY MOVE ACROSS THE REGION. ALTHOUGH FLT CONDITIONS ARE EXPECTED TO BE VFR MOST OF THIS TIME...ANY SHOWER/TSTM ACTIVITY AND/OR EARLY MORNING FOG AND STRATUS WILL BE CAPABLE OF PRODUCING PERIODS OF REDUCED CIGS AND VSBY. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...WSS NEAR TERM....NP SHORT TERM...HARTFIELD LONG TERM...HARTFIELD AVIATION...NP
AREA FORECAST DISCUSSION
NWS RALEIGH NC
145 PM EDT SUN SEP 2 2012 .SYNOPSIS... A WARM AND HUMID AIR MASS COUPLED WITH THE SLOW APPROACH OF AN UPPER LEVEL TROUGH WILL KEEP THE WEATHER UNSETTLED ACROSS CENTRAL NC THROUGH MID WEEK. && .NEAR TERM /THROUGH MONDAY NIGHT/... AS OF 145 PM SUNDAY... OVERVIEW: THE FOLLOWING SYNOPTIC FEATURES HAVE BEEN NOTED THIS AFTERNOON... -CIRCULATION ASSOC WITH ISAAC REMNANTS SLOWLY DRIFTING EAST ACROSS THE MIDWEST. -DIFFUSE SFC BOUNDARY DRAPED ACROSS NORTHCENTRAL AND NORTHEAST NC EXTENDING TO THE EAST AND WELL OFFSHORE -MIDLEVEL S/W RIDGE AXIS OVER THE CENTRAL CAROLINAS EXTENDING NORTH INTO VA...WITH A VORTICITY SHEAR AXIS JUST UPSTREAM AND CROSSING THE MOUNTAINS. FOR THE REST OF TODAY...SCATTERED SHOWERS/TSTMS HAVE DEVELOPED ACROSS OUR CENTRAL ZONES IN AN AREA OF LOW-LEVEL CONVERGENCE AND MODERATE INSTABILITY. EXPECT THIS ACTIVITY TO CONTINUE THIS AFTERNOON...AND ADDITIONAL ACTIVITY TO DEVELOP ACROSS THE THE WESTERN PIEDMONT WITH THE APPROACHING MID-LEVEL SHEAR AXIS. OUTFLOW BOUNDARIES FROM INITIAL ACTIVITY SHOULD TRIGGER ADDITIONAL CELLS WHICH WILL SLOWLY MOVE TOWARD THE EAST GIVEN A 240-270 DEG STORM MOTION <6 KTS AS SEEN IN FORECAST SOUNDINGS. LATEST MESOANALYSIS SHOWS THE BEST INSTABILITY ACROSS THE SOUTHERN HALF OF OUR FORECAST AREA. NOTED THAT BULK SHEAR REMAINS <20KT ACROSS OUR ENTIRE CWA. AS FOR DCAPE...WHILE BEST VALUES FOR WIND GUSTS ARE WELL TO OUR SOUTH...3 TO 6 HOUR RAP PROGS SUGGEST INCREASING DCAPE EXTENDING UP ACROSS THE COASTAL PLAIN AND THE SANDHILLS AREAS. FINALLY PWAT VALUES REMAIN RATHER HIGH (2+ INCHES) ACROSS MOST OF OUR CWA. SO IN SUMMARY...TSTMS SHOULD BE MORE PULSE IN NATURE...AND GIVEN ANTICIPATED SLOW MOVEMENT AND HIGH PWAT VALUES...HEAVY DOWNPOURS AND LOCAL POOR DRAINAGE FLOODING WILL BE THE PRIMARY CONCERN TODAY. A SECONDARY CONCERN WILL BE THE POTENTIAL FOR ISOLATED AND BRIEF DAMAGING WIND GUSTS...PARTICULARLY ACROSS THE S/SE HALF OF OUR CWA WHERE CAPE AND DCAPE ARE ENHANCED. TONIGHT...SHOWER/TSTM ACTIVITY SHOULD WIND DOWN BY 10 PM LEAVING THE OVERNIGHT PERIOD PARTLY TO MOSTLY CLOUDY. NO CHANGE IN AIRMASS FROM RECENT DAYS...SO EXPECT LOWS IN THE LOW-MID 70S. MONDAY AND MONDAY NIGHT...MID LEVEL CIRCULATION FROM ISAAC REMNANTS IS FORECAST TO SLOW FORWARD MOVEMENT AND SPLIT OVER THE OH/TN VALLEY AS IT ENCOUNTERS THE MID-LEVEL RIDGE ALONG THE MID ATLANTIC AND CAROLINA COAST. ONE PORTION OF THE AFOREMENTIONED CIRCULATION IS PROGGED TO MOVE TO THE NE AND ANOTHER TO THE S. SIMILAR TO TODAY... ANOTHER VORTICITY AXIS ROTATING AROUND THE LARGE-SCALE SYSTEM IS PROGGED TO CROSS THE MOUNTAINS DURING THE DAYTIME...AND SHOULD HELP SERVE AS A FOCUS FOR SHOWER/TSTM DEVELOPMENT PARTICULARLY ACROSS THE WESTERN HALF OF OUR CWA. SIMILAR TO TODAY...EXPECT A HIGH PWAT AND LOW SHEAR ENVIRONMENT TO SUPPORT PULSE TYPE ACTIVITY AND WITH STORM MOTION PROGGED AOB 7 KTS...ONCE AGAIN LOCALIZED POOR DRAINAGE FLOODING LIKELY TO BE THE PRIMARY CONCERN. AS FOR POPS...WILL CONTINUE TO CARRY STRONG-CHANCE POPS TAPERED SLIGHTLY HIGHER ACROSS OUR WESTERN HALF. LITTLE CHANGE IN AIRMASS SO WILL CONTINUE TO SEE ABOVE NORMAL TEMPS WITH HIGHS AROUND 90. GIVEN PROXIMITY OF ISAAC REMNANTS AND SUBSEQUENT MID LEVEL IMPULSES AROUND IT AND ENHANCED SOUTHERLY LOW-LEVEL FLOW... SHOWER/TSTM ACTIVITY MAY LINGER ON A BIT LONGER INTO THE EVENING HOURS...ESP ACROSS OUR WESTERN ZONES. LOWS MONDAY NIGHT ONCE AGAIN IN THE LOW-MID 70S. && .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/... AS OF 3 AM SUNDAY... AN AREA OF HIGH PRESSURE CENTERED OFF THE NEW ENGLAND COAST IN CONJUNCTION WITH AN AREA OF LOW PRESSURE OVER THE LOWER OH VALLEY WILL MAINTAIN A SLY LOW LEVEL FLOW OVER CENTRAL NC...KEEPING THE AIR MASS QUITE MOIST. THIS MOISTURE-RICH AIR MASS COUPLED WITH A SLOW MOVING MID-UPPER TROUGH TO OUR WEST OVER THE TN VALLEY WILL CAUSE SCATTERED SHOWERS AND THUNDERSTORMS THROUGH THIS PERIOD. CONVECTION WILL BE MOST PROMINENT DURING THE HEAT OF THE DAY AND LINGER INTO THE FIRST HALF OF THE EVENING. DUE TO ITS PROXIMITY TO BETTER DYNAMICS/SUPPORT ALOFT...EXPECT CONVECTIVE COVERAGE TO BE GREATEST IN THE WESTERN PIEDMONT VERSUS THE COASTAL PLAIN. DUE TO LACK OF A DISCERNIBLE SURFACE FEATURE/BOUNDARY TO FOCUS CONVECTION...WILL KEEP POPS IN THE SOLID CHANCE CATEGORY FOR NOW. HOWEVER...RESIDUAL OUTFLOW BOUNDARIES FROM THE PREVIOUS DAY`S CONVECTION WILL LIKELY BE LOCATED SOME PLACE ACROSS CENTRAL NC. THUS...ONCE ITS DETERMINED WHERE THESE FEATURES EXISTS...POPS CAN THEN BE ACCORDINGLY INCREASED. WHILE THERE WILL BE PLENTY OF FUEL FOR SHOWERS AND STORMS...MOST STORMS SHOULD REMAIN BELOW SEVERE CRITERIA DUE TO LACK OF SUFFICIENT WIND FIELD ALOFT. HOWEVER STORMS THAT ARE ABLE TO ATTAIN A DECENT UPDRAFT FOR 20-30 MINUTES MAY PRODUCE STRONG GUSTY WINDS DUE TO PRECIP LOADING. MAX TEMPS TUESDAY AND WEDNESDAY WILL BE DETERMINED BY EXTENT OF CLOUD COVERAGE IN THE MORNING AND CONVECTION IN THE AFTERNOON. EXPECT LITTLE IF ANY CHANGES TO TEMPS THIS PERIOD FROM THE PREVIOUS FORECAST. HIGH TEMPS IN THE MID-UPPER 80S AND MIN TEMPS NEAR 70-LOWER 70S. && .LONG TERM /THURSDAY THROUGH SUNDAY/... AS OF 1140 AM SUNDAY... EXPECT WET WEATHER EARLY BUT WITH DRIER CONDITIONS HEADING INTO NEXT WEEKEND. THIS PERIOD BEGINS WITH FAST MID LEVEL FLOW AND A VERY BROAD TROUGH COVERING THE NORTHERN THIRD OF THE CONUS INTO CANADA (AROUND A STRONG VORTEX OVER FAR NRN ONTARIO)... WHILE AN E-W ELONGATED RIDGE COVERS THE FAR SOUTHWEST INTO NRN MEXICO... AND A WEAK LIKELY SUBTROPICAL LOW SITS JUST OFF THE NE COAST OF FL. A WEAK MID LEVEL SHEAR AXIS PERSISTS THROUGH THE CENTRAL CAROLINAS... ALONG A SURFACE LEE TROUGH... WELL AHEAD OF AN INCOMING SYNOPTIC COLD FRONT. FOR THURSDAY/THURSDAY NIGHT: ONE LARGE BUT LOW-AMPLITUDE SHORTWAVE TROUGH SWINGS THROUGH THE EASTERN GREAT LAKES/ST LAWRENCE VALLEY AND THE NORTHEAST STATES ON THURSDAY... AND THE ENSUING HEIGHT FALLS ALOFT COMBINED WITH DEEP MOISTURE IN PLACE AND PREFRONTAL INSTABILITY SHOULD INSTIGATE GOOD COVERAGE OF SHOWERS AND STORMS OVER CENTRAL NC... PARTICULARLY THURSDAY AFTERNOON AND EVENING... WITH GREATER COVERAGE ALONG/EAST OF HIGHWAY 1 GIVEN THE DRIER MID LEVEL AIR FILTERING INTO THE WEST. LOW LEVEL THICKNESSES REMAIN 5-10 METERS ABOVE NORMAL... ALTHOUGH THIS WARMTH WILL BE SOMEWHAT TEMPERED BY CONSIDERABLE MID AND HIGH CLOUDS. HIGHS MAINLY IN THE MID-UPPER 80S. THE LONGWAVE TROUGH BEGINS TO DIG PROMINENTLY OVER THE MIDWEST/PLAINS LATE THURSDAY THROUGH THURSDAY NIGHT DUE TO ENERGY DROPPING FROM MT/WY/DAKOTAS INTO THE BROAD TROUGH BASE. IN RESPONSE... THE DOWNSTREAM BROAD MID LEVEL TROUGHING THROUGH THE CAROLINAS WILL WEAKEN QUICKLY AS IT HEADS TO OUR NE. (THE WEAK LOW OFF FL APPEARS LIKELY TO STAY ENOUGH TO OUR SSE TO NOT BE A FACTOR IN OUR WEATHER.) THE GFS/ECMWF BRING THE SURFACE COLD FRONT TO THE WESTERN APPALACHIAN SLOPES BY LATE THURSDAY NIGHT... HOWEVER THE PUSH OF COOL AIR IMMEDIATELY BEHIND IT WILL BE MUTED WITH THE AIR MASS QUICKLY MODIFYING IN RESPONSE TO THE STRONG FRONTOGENESIS OVER THE UPPER MIDWEST. SO WHILE THE MID LEVELS WILL CONTINUE TO DRY OUT WEST TO EAST ACROSS CENTRAL NC THURSDAY NIGHT... THE REDUCTION IN SURFACE-BASED MOISTURE WILL BE MUCH MORE SUBTLE. AS SUCH... EXPECT A MINIMAL DIP IN TEMPS. LOWS THURSDAY NIGHT 66-71. FOR FRIDAY/FRIDAY NIGHT: THE FRONT APPROACHING FROM THE NW EARLY FRIDAY WILL HAVE LOST MOST OF ITS STEAM AS THE AIR MASS BEHIND IT MODIFIES. THE LOWEST 1-2 KM WILL REMAIN MOIST ENOUGH FOR BROKEN DIURNAL CLOUDS MUCH OF THE DAY... BUT THE MID-UPPER LEVEL DRYING AND SUBSEQUENT LOWERING OF PW SHOULD GREATLY LIMIT COVERAGE AND STRENGTH OF ANY CONVECTION. WITH THE ABSENCE OF MOISTURE IN THE MIXED PHASE REGION ALOFT... LIGHTNING PRODUCTION SHOULD BE MINIMAL AND EXPECT NO MORE THAN A FEW SHOWERS AT BEST FRIDAY WITH A LACK OF BOTH MOISTURE AND FORCING FOR ASCENT. THICKNESSES CHANGE VERY LITTLE AND STAY ABOVE NORMAL... SO EXPECT HIGHS OF 86-90. LOWS 65-70 WITH FAIR SKIES. FOR SATURDAY/SUNDAY: THE CANADIAN VORTEX WOBBLES SLOWLY ACROSS JAMES BAY WHILE THE TROUGH DIGS THROUGH THE CENTRAL US AND GREAT LAKES. MODEL SOLUTIONS BEGIN TO DIVERGE WITH THE ECMWF SHOWING THIS NORTHERN STREAM SEPARATING... WITH THE CANADIAN VORTEX CROSSING NRN QUEBEC... WHILE THE TROUGH STRONGLY AMPLIFIES AND CLOSES OFF ANOTHER LOW OVER THE OHIO VALLEY BY THE END OF THE WEEKEND. THE GFS ON THE OTHER HAND REMAINS PHASED AND PUSHES A POSITIVELY-TILTED TROUGH THROUGH THE NORTHEAST/APPALACHIANS/MID SOUTH... WITH A LARGE COOL FALL HIGH PRESSURE AREA CENTERED OVER THE GREAT LAKES BUILDING SOUTHEASTWARD INTO THE FORECAST AREA OVER THE WEEKEND. WHILE THE ECMWF ENSEMBLE MEAN IS MUCH MORE SUBDUED WITH THE GREAT LAKES/OHIO VALLEY TROUGHING THAN ITS OPERATIONAL COUNTERPART... THE TWO AGREE WELL ON TIMING AND PLACEMENT... AND THIS SOLUTION HAS SUPPORT FROM THE GEFS MEAN. WILL LEAN TOWARD THE ECMWF SOLUTION. EXPECT DRY WEATHER WITH TEMPS HOLDING JUST ABOVE SEASONAL NORMALS WELL EAST OF THE TROUGH. AS THIS TROUGH MOVES EASTWARD INTO THE MID SOUTH REGION AND APPROACHES NC... WILL BRING IN A SMALL CHANCE OF STORMS LATE SUNDAY... ALONG WITH WARM TEMPS. -GIH && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... AS OF 145 AM SUNDAY... 24 HOUR TAF PERIOD: SCATTERED SHOWERS AND TSTMS ACROSS THE CENTRAL PORTION OF THE STATE ATTM WILL RESULT IN LOCALLY REDUCED CIGS AND VSBY ALONG WITH BRIEF GUSTY SFC WINDS. THE TAF SITES MOSTLY LIKELY TO BE AFFECTED WITH IFR CONDITIONS THROUGH 20Z INCLUDE KRDU AND KFAY. KINT/KGSO/KRWI MAY BE IMPACTED LATER THIS AFTERNOON AS THIS ACTIVITY CONTINUES TO EVOLVE. OUTSIDE OF THESE STORMS...EXPECT VFR CONDITIONS. LATER TONIGHT... ENHANCED LOW LEVEL MOISTURE MAY SET THE STAGE FOR A BRIEF PERIOD OF REDUCED VSBY AND CIGS WITH FOG AND LOW CLOUDS POSSIBLE TOWARD SUNRISE MONDAY. OUTLOOK: SCATTERED AFTERNOON AND EARLY EVENING SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE EACH DAY AS ENHANCED MOISTURE AND A SLOW MOVING FRONT GRADUALLY MOVE ACROSS THE REGION. ALTHOUGH FLT CONDITIONS ARE EXPECTED TO BE VFR MOST OF THIS TIME...ANY SHOWER/TSTM ACTIVITY AND/OR EARLY MORNING FOG AND STRATUS WILL BE CAPABLE OF PRODUCING PERIODS OF REDUCED CIGS AND VSBY. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...WSS NEAR TERM....NP SHORT TERM...WSS LONG TERM...HARTFIELD AVIATION...NP
AREA FORECAST DISCUSSION
NWS GRAND FORKS ND
958 AM CDT SUN SEP 2 2012 .DISCUSSION... MORNING UPDATE FOCUSED ON PRECIP AND TODAYS HIGHS. CURRENT RADAR SHOWERS OVER NORTHWEST MINNESOTA ALONG WITH SOME HIGH BASED TSTMS. TO THE WEST...RADAR ECHOES APPEAR TO BE MID CLOUDS. MOST ACTUAL RAIN REPORTS HAVE BEEN BETWEEN GRAND FORKS AND ROSEAU. COLD FRONT WORKING ITS WAY INTO DVL REGION HOWEVER COOLER AIR STILL BACK IN SASKATCHEWAN. CLOUD COVER IS INHIBITING MUCH RISE IN TEMPERATURES AND A BLEND OF PREV BLEND WITH MOST RECENT RUC GUIDANCE DROPPED TEMPS A GOOD 7 DEG IN GFK...AND DID A DECENT JOB REFLECTING CLOUD COVER ELSE WHERE. THUS SOME SIGNIFICANT CHANGES TO DAYTIME HIGHS WHERE THICKEST CLOUDS AND/OR RAIN IS OCCURRING. MADE MINOR ADJUSTMENTS TO POPS (INCREASED TO 40 PER CENT AREAL COVERAGE FOR AFOREMENTIONED AREAS OF RAIN) THROUGH 09Z. CAN EXPECT SCATTERED SHOWERS AND ISOLATED STORMS TO CONTINUE THROUGH MORNING...WITH SCATTERED STORMS IN AFTN. STILL TO EARLY TO TELL IF WE WILL SEE SEVERE STORMS LATE THIS AFTN...BUT THE CLOUD COVER AND UPPER CAP WILL CERTAINLY TRY TO PUT THE DAMPER ON ANY SEVERE DEVELOPMENT. CONFIDENCE IS LOW. && .AVIATION... COLD FRONT WILL SLOWLY MOVE THROUGH FA TODAY. WILL STILL SEE SOME GUSTY S WINDS THIS AM AHEAD OF FRONT. SPOTTY SHRA/TSRA WILL SPREAD FROM NW-SE ACROSS FA WITH FROPA HOWEVER CIGS SHOULD REMAIN VFR. COULD SEE SOME STRONGER STORMS THIS EVENING MAINLY ACROSS WEST CENTRAL MN. && .PREV DISCUSSION... /ISSUED 235 AM CDT SUN SEP 2 2012/ DISCUSSION... FORECAST CHALLENGE CONCERNS PCPN CHANCES AND TEMPERATURES. TOSSED GFS LOW LEVEL MOISTURE FIELDS WHICH ARE WAY TOO MOIST OTHERWISE MODELS IN FAIRLY GOOD AGREEMENT AND WILL USE BLEND FOR FORECAST. COLD FRONT MOVING INTO CENTRAL DAKOTAS AND WILL PROPAGATE SLOWLY EAST TODAY BEING FAIRLY PARALLEL TO UPPER FLOW. WITH STRONG CAP UPSTREAM BAND OF SHRA/TSRA LOOKS TO BE ALONG AND BEHIND BOUNDARY. WITH SLIGHTLY SLOWER FROPA INDICATED BY MODELS AND CURRENT PCPN TRENDS WILL PUSH POPS BACK TO THE WEST TODAY. MOIST AXIS FAIRLY NARROW AND UPSTREAM COVERAGE SUPPORTS CURRENT CHANCE POPS. FAIRLY RESPECTABLE CAP HOLDS IN MOST OF DAY HOWEVER IF ANY CONVECTION CAN BREAK CAP BASED ON CONVECTIVE PARAMETERS COULD SEE A FEW STRONG STORMS FROM SOUTHERN VALLEY INTO WEST CENTRAL/NORTH CENTRAL MN. TEMPERATURES MAY BE TRICKY TODAY DEPENDENT ON CLOUD COVER. COLUMN REMAINS QUITE WARM AND AHEAD OF PCPN BAND LOOKS TO BE MOSTLY CI SO WITH WARM START WILL NOT TAKE MUCH TO GET INTO THE 80S. BEGINNING OF NEXT WEEK WILL FEATURE BROAD MID LEVEL TROUGHING...ALMOST ZONAL ACROSS NORTHERN TIER OF STATES. SECONDARY COLD FRONT DROPS THROUGH FA MONDAY. TIME SECTIONS REVEAL THAT COLUMN LOOKS QUITE DRY AND NOT MUCH UPPER SUPPORT SO VERY LOW CONFIDENCE ON ANY PCPN OCCURRING WITH FROPA. DID INSERT SOME SLIGHT CHANCE POPS ACROSS SW FA MAINLY FOR COORDINATION PURPOSES. COLUMN COOLS SOMEWHAT BUT STILL LIKELY TO SEE ABOVE AVERAGE TEMPERATURES. TUESDAY LOOKS QUIET WITH ANOTHER COOLING FRONT DROPPING THROUGH TUESDAY NIGHT. ALTHOUGH MOISTURE STILL MARGINAL THIS BOUNDARY HAS MORE SUPPORT FROM THE MID LEVELS SO HAVE EXPANDED POPS. LONG TERM...WEDNESDAY THROUGH SUNDAY CONSISTENT MODEL TO MODEL RUN LEADS TO A DECENT HANDLE ON THE EXTENDED FORECAST. AT THE START OF THE PERIOD WE SEE A WELL ADVERTISED SHORT WAVE MOVING ACROSS SOUTHERN CANADA IN BROAD NORTHWEST FLOW. SHORTWAVE TROUGH CROSSES THE AREA LATE WEDNESDAY INTO THURSDAY WITH VERY LOW THREAT OF SHRA. THICKNESS FALL WITH 850 TEMPS FALLING INTO THE 7 TO 10C RANGE OVER THE NORTHEAST CWFA AND 10 TO 15C SOUTHWEST MAY MAKE FOR A DECENT EARLY FALL TEMPERATURE GRADIENT. MODEL CONTINUITY CONTINUES IN FAIR AGREEMENT AS 00Z ECMWF COMING MORE IN LINE WITH 00Z GFS/DGEX/GEM AS THEY MOVE THE WAVE THROUGH LATE THURSDAY INTO FRIDAY. WITH A WEAK SURFACE REFLECTION SOME SHRA/TSRA LIKELY ALONG AND BEHIND BOUNDARY. ECMWF SLOWER THAN OTHER OPERATIONAL MODELS FOR END OF THIS EXTENDED PERIOD. AS THE COLUMN DRIES OUT AND WARMS UP UNDER BUILDING UPPER HEIGHTS TEMPERATURES BEGIN TO WARM BACK ABOVE EARLY SEPTEMBER MEANS. ALLBELNDS SEEMS TO CAPTURE THE CONSENSUS OF THE MODELS MOST IN AGREEMENT AND HAVE FOLLOWED CLOSELY. && .FGF WATCHES/WARNINGS/ADVISORIES... ND...NONE. MN...NONE. && $$ SPEICHER/VOELKER
AREA FORECAST DISCUSSION
NWS CLEVELAND OH
832 PM EDT MON SEP 3 2012 .SYNOPSIS... THE REMNANTS OF ISAAC WILL BE WITH US FOR ONE MORE DAY AS ITS REMNANT LOW WILL MOVE UP THE UPPER OHIO RIVER VALLEY TUESDAY. THE HUMID AIRMASS WILL CONTINUE TO MAKE HEAVY RAINFALL A THREAT. HIGH PRESSURE WILL MOVE OVERHEAD WEDNESDAY AND A STRONGER COLD FRONT WILL MOVE ACROSS THE AREA EARLY THURSDAY. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... MUCH OF THE DIURNAL CONVECTION HAS DIMINISHED EXCEPT FOR THE CLEVELAND METRO AREA. SHORT RANGE MODELS AND THE GFS TRY AND CONTINUE TO REDEVELOP CONVECTION EAST FROM THE CLE AREA INTO NW PA FOR THE NEXT 6 HOURS OR SO. NOT OVERLY CONFIDENT IN THIS GIVEN THE CURRENT PROBLEMS THE HRRR IS HAVING IN PRECIP PLACEMENT. WILL TAPER BACK POPS FOR REST OF THE NIGHT SINCE MOST CONVECTION HAS DIED OFF BUT WILL AT LEAST KEEP A SLIGHT CHANCE GOING ALMOST EVERYWHERE. HUMID AIRMASS AIDED IN SPOTS FROM RAINFALL PAST 6 HOURS SHOULD SET THE STAGE FOR AT LEAST PATCHY FOG AND STRATUS TO DEVELOP TONIGHT AS WINDS REMAIN LIGHT. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY NIGHT/... WILL HAVE LIKELY TO CATEGORICAL PRECIP CHANCES FOR A BIG PORTION OF TUESDAY. WEAK LOW TO MOVE UP THE UPPER OHIO RIVER VALLEY AND WILL HAVE JET SUPPORT TO ALLOW FOR WHAT SHOULD BE FAIRLY WIDESPREAD SHOWERS. QUESTION WILL BE HOW QUICKLY THE SHOWERS/TS BREAK OUT. GRADIENT IN HIGH TEMPS EXPECTED WITH THE COOLEST...AROUND 80 TEMPS ACROSS THE EAST AND LOWER/MID 80S FAR WEST. PULL PRECIP AWAY FAIRLY QUICKLY TUESDAY EVENING AS UPPER SHORTWAVE EXITS. WEAK HIGH PRESSURE FOR WEDNESDAY. IF WE HAVE ENOUGH SUN WE COULD WARM NICELY INTO THE UPPER 80S...BUT WE WILL STILL BE HUMID. NEXT COLD FRONT...AN AIRMASS CHANGING FRONT...WILL WORK ACROSS THE AREA EARLY THURSDAY. HAVE MAINTAINED THE PRECIP CHANCES AS THEY WERE. TEMPS WILL BE CLOSER TO NORMAL THURSDAY WITH THE HUMIDITY LEVELS SLOWLY FALLING. && .LONG TERM /FRIDAY THROUGH MONDAY/... HIGH PRESSURE WILL BRIEFLY MOVE INTO THE REGION ON FRIDAY. AN UPPER LEVEL TROUGH WILL THEN MOVE INTO THE WESTERN GREAT LAKES BY SATURDAY. HOWEVER THERE IS UNCERTAINTY ON THE STRENGTH AND TIMING OF ENERGY ROTATING THROUGH THIS TROUGH. ECMWF IS THE STRONGEST WITH A CUTOFF LOW DEVELOPING OVER OHIO. FOR NOW HAVE GONE WITH CHANCES IN THE FORECAST AND WE WILL MODIFY POPS AS MODELS COME TO A BETTER CONSENSUS. TEMPERATURES WILL BE IN THE MIDDLE TO UPPER 70S ON FRIDAY BUT WILL DECREASE BELOW SEASONAL AVERAGES FOR THE WEEKEND. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... MOIST TROPICAL AIR REMAINS OVER NRN OHIO AND NWRN PA THIS EVENING WITH SCATTERED SHOWERS AND A FEW THUNDERSTORMS STILL OCCURRING ACROSS THE AREA. CONDITIONS ACROSS THE AREA ARE GENERALLY VFR ALTHOUGH WITHIN SHOWERS CONDITIONS LIKELY DROP TO IFR. THIS CONVECTION WILL LIKELY DISSIPATE THROUGH THE EVENING AND LIKE LAST NIGHT...WOULD EXPECT MOSTLY DRY CONDITIONS OVERNIGHT WITH MVFR FOG TOWARDS MORNING. FOR TUESDAY AIRMASS WILL REMAIN MOIST AND MODELS SHOW UPPER DIVERGENCE ASSOCIATED WITH A RT ENTRANCE REGION OF AN UPPER JET MOVING ACROSS THE AREA. GUIDANCE POPS HAVE PICKED UP ON THIS AND ARE ANTICIPATING PLENTY OF UPWARD MOTION ACROSS THE AREA. WOULD ANTICIPATE NUMEROUS TO WIDESPREAD SHOWERS WITH A FEW THUNDERSTORMS AS WELL THROUGH THE DAY. FOR NOW WILL GO WITH PREDOMINANT VFR CONDITIONS IN SHOWERS AND THUNDERSTORMS THROUGH THE PERIOD HOWEVER WOULD ANTICIPATE MVFR OF IFR CONDITIONS POSSIBLE WITHIN SHOWERS AND STORMS. .OUTLOOK...NON VFR POSSIBLE THURSDAY. EARLY MORNING FOG WILL BE POSSIBLE WEDNESDAY AND THURSDAY. && .MARINE... LAKE BREEZE PUSHED INLAND THIS MORNING AND SHOULD HOLD THROUGH THE EVENING HOURS AND THEN BECOME LIGHT SOUTHERLY AGAIN OVERNIGHT. GENERALLY LIGHT WINDS WILL PREVAIL THROUGH WEDNESDAY. FLOW EVENTUALLY SHIFTS AROUND TO A WESTERLY DIRECTION AND INCREASES IN SPEED THURSDAY. THINKING IS THAT SMALL CRAFT ADVISORIES MAY BE NEEDED BY THURSDAY AND COULD EXTEND INTO THE EARLY PART OF THE WEEKEND. && .CLE WATCHES/WARNINGS/ADVISORIES... OH...NONE. PA...NONE. MARINE...NONE. && $$ SYNOPSIS...OUDEMAN NEAR TERM...OUDEMAN/ADAMS SHORT TERM...OUDEMAN LONG TERM...MULLEN AVIATION...TK MARINE...LOMBARDY
AREA FORECAST DISCUSSION
NWS CLEVELAND OH
653 PM EDT SUN SEP 2 2012 .SYNOPSIS... THE REMNANTS OF ISAAC WILL MOVE EAST ACROSS THE OHIO VALLEY THROUGH TUESDAY WITH A HUMID AIRMASS AND PERIODS OF HEAVY RAIN. A WEAK FRONT WILL HELP TO DRY US OUT ON TUESDAY NIGHT WITH A STRONGER COLD FRONT WITH AN AIRMASS CHANGE PUSHING SOUTH ACROSS THE AREA ON THURSDAY. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... FEW CHANGES FOR 630 UPDATE...LEFT CHANCE POPS GOING EVERYWHERE EXCEPT SW PORTION OF AREA. ORIGINAL DISCUSSION... STILL MAY GET SOME SHOWERS/THUNDERSTORMS TO DEVELOP THIS EVENING. WHILE INSTABILITY IS NOT AS GOOD AS YESTERDAY IT SEEMS THAT CAPE OF 2K IS ENOUGH TO GET SOME STORMS TO POP IN NORTHERN INDIANA. WILL KEEP THE LIKELY POPS FROM FDY TO MNN TO MT VERNON FOR THIS EVENING...WITH LESS OF A CHANCE ACROSS THE REST OF OH AND STILL DRY ACROSS NW PA. FLASH FLOOD GUIDANCE IS LOW /AROUND ONE INCH IN THREE HOURS/ FROM THE RAIN LAST NIGHT ACROSS THE FAR SOUTHWEST. ANY THUNDERSTORMS THAT DO DEVELOP THIS EVENING WILL HAVE THE POTENTIAL FOR HEAVY RAIN BUT WE HAVE HAD ALL DAY RAIN FREE THERE TO ALLOW THE WATER TO RECEDE. WIDESPREAD FLOODING TO PROMPT A FLASH FLOOD/FLOOD WARNING IS NOT EXPECTED. ISOLATED MINOR FLOODING COULD OCCUR. THE REMAINDER OF THE NIGHT LOOKS DRIER THAN NOT AND JUST LINGER LOW PRECIP CHANCES THROUGH THE NIGHT. DID NOT MENTION THUNDER OVERNIGHT EITHER BASED MORE ON SREF PROB. MORE HUMID AIR IS STARTING TO CREEP INTO NW PA WITH MID 60S DEWPOINTS AT GKJ/MEADVILLE. SO WHILE ERI MAY STILL HAVE A RELATIVELY COMFORTABLE NIGHT...THE REST OF NRN OH WILL BE WARM AND HUMID TONIGHT. LOWS WILL BE SIMILAR TO LAST NIGHT. WE WILL KEEP THE OVERCAST SKIES. && .SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY NIGHT/... LOW SPINNING ACROSS ILLINOIS WILL CONTINUE TO FILL AND DRIFT EAST- SOUTHEAST OVER THE NEXT TWO DAYS. COVERAGE OF SHOWERS/TS COULD BE ON THE UPTICK FOR MONDAY. HAVE MAINTAINED SOME OF THE LIKELY POPS ESPECIALLY ACROSS THE SOUTH AND SOUTHEAST. STUCK WITH SIMILAR HIGHS FOR TOMORROW. UPPER TROUGH BEGINS TO OPEN UP AND WITH SOME DIURNAL HEATING TS SHOULD POP UP. WILL HAVE TO CONTINUE THE PRECIP CHANCES INTO MONDAY NIGHT. AT THIS POINT WE WILL BE GETTING SOME EXTRA UPPER SUPPORT IN THE FORM OF A SHORTWAVE/JET COMING ACROSS THE GREAT LAKES. THE COLD FRONT WILL MOVE ACROSS TUESDAY. WE WILL STILL HAVE TO BE ON THE LOOKOUT FOR HEAVIER RAINFALL ESPECIALLY LATER MONDAY NIGHT AND TUESDAY WITH BETTER FOCUSING MECHANISMS LOCALLY. LOCALIZED FLOODING WILL STILL BE A CONCERN THROUGH TUESDAY. WEDNESDAY LOOKS LIKE THE FIRST GOOD DRY/IN BETWEEN SYSTEMS DAY. WEAK HIGH PRESSURE OVER THE AREA AND SOME SUN SHOULD BE ABLE TO BRING TEMPS UP INTO THE MID 80S...OR MAYBE EVEN SOME UPPER 80S. WE WILL NOT GET A GOOD AIRMASS CHANGE UNTIL AFTER WEDNESDAY NIGHT WITH THE NEXT SYSTEM IN THE EXTENDED. && .LONG TERM /THURSDAY THROUGH SUNDAY/... A COLD FRONT WILL MOVE ACROSS THE REGION THURSDAY WITH SOME SCATTERED SHOWERS AND THUNDERSTORMS ANTICIPATED. THE FRONT SHOULD CLEAR THE ENTIRE REGION BY THURSDAY EVENING. THIS WILL ALLOW HIGH PRESSURE TO RETURN FOR FRIDAY. THIS LOOKS TO BE SHORT LIVED AS THE NEXT TROUGH MOVES INTO THE WESTERN GREAT LAKES ON FRIDAY. TEMPERATURES WILL BE NEAR TO SLIGHTLY ABOVE SEASONAL AVERAGES ON THURSDAY. COOLER IN THE WAKE OF THE FRONT FOR FRIDAY INTO SATURDAY WITH HIGHS GENERALLY IN THE MIDDLE TO UPPER 70S. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... SATELLITE LOOP SHOWS THE CENTER OF THE REMNANTS OF ISAAC OVER SERN IL AT 23Z WITH RADAR SHOWING CONVECTION FROM CENTRAL INDIANA THROUGH THE KDAY VICINITY INTO SERN OHIO. MORE CONVECTION IS MOVING NORTH OUT OF KY. ACROSS NWRN OHIO AND NWRN PA CONDITIONS RANGE FROM MOSTLY VFR FAR EAST TO VFR/MVFR WEST AND SOUTH. DEWPOINTS 65 TO 70 ACROSS MUCH OF THE AREA WITH LOWER 70S IN KFDY AND UPPER 50S KERI. FOLLOWING THE HRRR HIGH RESOLUTION MODEL HAVE KEPT PRECIP OUT OF THE AREA OVERNIGHT. BEST CHANCES HOWEVER WOULD BE FROM KFDY TO KMFD IF THE BAND DID MANAGE TO REACH THE AREA. MAIN CONCERN OF THE OVERNIGHT WOULD BE LOWERING CIGS AND VISIBILITIES IN FOG AND STRATUS WITH DEEP MOISTURE ACROSS THE AREA. DID BRING TAFS DOWN THROUGH MVFR AFTER MIDNIGHT TO MVFR/IFR AROUND SUNRISE. AT KERI...WINDS EXPECTED TO TURN SE OVERNIGHT WHICH WOULD BRING MORE MOISTURE INTO THE AREA SO DID BRING MVFR CONDITIONS THERE OVERNIGHT AS WELL. ON MONDAY MODELS SHOW CIRCULATION MOVING SE IN KY. BEST CHANCE FOR CONVECTION GETTING INTO THE AREA WOULD BE THE SOUTH CENTRAL COUNTIES OF THE CWA. FOR NOW BROUGHT VCTS TO THE AREA AT KMFD AND KCAK FOR THE AFTERNOON. .OUTLOOK...NON VFR POSSIBLE MONDAY NIGHT AND TUESDAY WITH OVERNIGHT AND EARLY MORNING FOG AS WELL AS SCATTERED TO NUMEROUS SHOWERS/THUNDERSTORMS. && .MARINE... WINDS HAVE INCREASED TO AROUND 15 KNOTS FOR THE OPEN WATERS AND A PORTION OF THE NEARSHORE WATERS FROM CONNEAUT TO RIPLEY. THIS HAS CAUSED SOME LOCALLY HIGHER WAVES FOR THE ERIE AREA WITH 2 TO 4 FOOT WAVES A DECENT BET INTO THE EVENING. WINDS SHOULD DECREASE THIS EVENING WITH WAVES DECREASING. OTHERWISE WE CONTINUE TO WATCH LOW PRESSURE THAT WILL TRACK ALONG THE OHIO RIVER VALLEY INTO MONDAY NIGHT. THIS WILL KEEP AN EASTERLY FLOW ON THE LAKE UNTIL A WEAKENING COLD FRONT PASSES ON TUESDAY. WINDS WILL SHIFT AROUND TO THE NW AND NORTH WITH THE FRONTAL PASSAGE. WINDS AT THIS POINT DO NOT LOOK STRONG ENOUGH TO NEED A SMALL CRAFT ADVISORY. HIGH PRESSURE WILL TAKE CONTROL OF LAKE ERIE TUESDAY NIGHT INTO WEDNESDAY. A STRONGER COLD FRONT LOOKS TO ARRIVE ON THURSDAY WITH SOME GUSTY NW WINDS POSSIBLE. THE STRONGER WINDS MAY NOT ARRIVE UNTIL THURSDAY NIGHT AS HIGH PRESSURE BUILDS ONTO THE WESTERN END OF THE LAKE. && .CLE WATCHES/WARNINGS/ADVISORIES... OH...NONE. PA...NONE. MARINE...NONE. && $$ SYNOPSIS...DJB/OUDEMAN NEAR TERM...OUDEMAN SHORT TERM...OUDEMAN LONG TERM...MULLEN AVIATION...TK MARINE...MULLEN
AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NWS SIOUX FALLS SD
932 PM CDT MON SEP 3 2012 .DISCUSSION... WILL VERY LIKELY BE ABLE TO LET THE REMAINDER OF THE SEVERE THUNDERSTORM WATCH EXPIRE AT 03Z. TOWARD SUNSET...THE STORMS BECAME INCREASINGLY LOW CENTROID...AND ELIMINATED THE WESTERN ZONES FROM THE WATCH. OTHERWISE HAVE ADJUSTED THE GRIDS BASED ON CURRENT TRENDS...INCREASING LATE EVENING POPS ALONG THE I 90 CORRIDOR... EAST CENTRAL SD AND EVEN INTO PARTS OF SW MN. CONVERSELY... BASICALLY ELIMINATED POPS IN OUR SOUTHERN ZONES AS AT LEAST AT THE MOMENT...THEY ARE GENERALLY CAPPED OFF WITH THE SHORT WAVE DYNAMICS ALONG AND NORTH OF I 90. THE INDIVIDUAL CELLS CONTINUE TO BUILD SLIGHTLY TO THE SOUTH...SO IT IS POSSIBLE THAT SIOUX FALLS ITSELF MAY BE GET HIT AROUND 04Z...AND THUS INCREASED POPS TO A STRONG SCATTERED. IT IS A BIT SURPRISING THAT THE STORMS HAVE HELD THIS INTENSITY FOR THIS LONG...KNOWING THAT THEY WERE LIKELY TIED TO THE SURFACE BOUNDARY EARLIER THIS EVENING. BUT THE SHORT WAVE MAY BE STRONGER THAN THE EARLIER MODELS WERE INDICATING. FOR OTHER ELEMENTS...LOW TEMPERATURES STILL LOOK GOOD. GRID UPDATE IS OUT AND WILL UPDATE THE ZFP VERY SHORTLY. /MJF && .AVIATION.../FOR THE 00Z TAF ISSUANCE/ ISOLATED THUNDERSTORMS WEST OF JAMES RIVER AT START OF THE PERIOD COULD BRUSH KHON TAF SITE...BRINGING POSSIBILITY OF ERRATIC WINDS THROUGH 01Z. OTHERWISE THESE STORMS ARE EXPECTED TO WEAKEN AS THE MOVE EAST TOWARD I-29 CORRIDOR THROUGH THE EVENING...SO WILL LEAVE MENTION OF THUNDER OUT OF KFSD/KSUX TAFS. WITH LOW LEVEL MOISTURE AND LIGHT WINDS WITHIN SURFACE RIDGE AXIS OVER NORTHWEST IOWA... COULD SEE SOME POCKETS OF MVFR FOG TONIGHT AND WILL KEEP SOME LIGHT FOG FOR KSUX TOWARD DAYBREAK. CONVECTIVE CHANCES INCREASE INTO THE MISSOURI RIVER VALLEY LATE TUESDAY AFTERNOON...BUT CONFIDENCE IS LOW IN TIMING/COVERAGE BEFORE 05/00Z...SO WILL LEAVE OUT OF KSUX TAF AT THIS TIME. && .PREV DISCUSSION.../ISSUED AT 315 PM CDT/ LIGHT SHOWERS MAINLY CONFINED TO NORTHWEST IOWA SO FAR THIS AFTERNOON. MID LEVEL CLOUDS ALSO DISSIPATING IN OUR WEST ALLOWING FOR DECENT HEATING. DEWPOINTS HAVE FALLEN RAPIDLY ONCE MIXING COMMENCED...WITH DRY AIR ALOFT. THIS WAS SHOWN WELL BY THE HRRR AND NAM. BOTH OF THESE MODELS SHOW SOME DEWPOINT RECOVERY BY LATER THIS AFTERNOON RIGHT AHEAD OF THE APPROACHING FRONTAL BOUNDARY. THE QUESTION IS WHETHER THEY RECOVER ENOUGH TO HELP BREAK THE CAP. HRRR HAS BACKED OFF SOME OF ITS EARLIER IDEA OF SCATTERED TO NUMEROUS STORMS FORMING AS THE BOUNDARY ENTERED OUR CWA. STILL THINKING WE POSSIBLY GET SOME ISOLATED DEVELOPMENT AFTER 4 OR 5 PM WEST OF THE JAMES RIVER. FULL SUN COMBINED WITH CONVERGENCE ALONG THE FRONT AND AN APPROACHING SHORTWAVE...MAY BE ENOUGH TO AT LEAST GET ISOLATED DEVELOPMENT. CAPE COULD BE AROUND 1500 J/KG NEAR THE BOUNDARY...AND A VEERING WIND PROFILE WITH DECENT WINDS ALOFT SHOULD RESULT IN AROUND 40 KTS EFFECTIVE SHEAR. SO ANY STORM THAT IS ABLE TO FORM COULD BE SEVERE...WITH STRONG WINDS AND LARGE HAIL. STORMS WOULD MOVE EAST OR EAST SOUTHEAST...BUT THINKING MOST ACTIVITY WILL BE DIURNALLY DRIVEN AND THUS DIE AS THE EVENING PROGRESSES. KEPT CHANCE POPS MAINLY ALONG AND WEST OF THE JAMES RIVER....WITH SLIGHT CHANCE THROUGH THE REST OF THE CWA...JUST IN CASE STORMS PERSIST ALONG THERE OUTFLOW LONGER THAN EXPECTED. SKIES SHOULD CLEAR LATER TONIGHT...WITH LOWS IN THE 50S AND 60S. COULD SEE SOME FOG DEVELOPMENT IN THE SOUTH...ESPECIALLY WHERE RAIN HAS FALLEN TODAY IN NORTHWEST IOWA. TUESDAY SHOULD START MOSTLY SUNNY WITH HIGHS IN THE 80S AND 90S. TRICKY PART OF TUESDAYS FORECAST WILL BE HOW FAR SOUTH THE BOUNDARY MAKES IT LATE TONIGHT...AND HOW QUICKLY IT PUSHES BACK NORTH AS A WARM FRONT TOMORROW BEFORE THE COLD FRONT PUSHES THROUGH. WITH STABLE DRIER AIR NORTH OF THIS BOUNDARY...CONVECTION CHANCES WILL BE CONFINED TO ALONG AND SOUTH OF IT DURING THE DAY...AS ANOTHER SHORTWAVE PUSHES ACROSS. NAM IS THE FURTHEST SOUTH WITH THE BOUNDARY...ONLY PUSHING AS FAR NORTH AS SPENCER TO YANKTON BY AFTERNOON. THE GFS IS FURTHEST NORTH...WITH THE ECMWF IN BETWEEN. NAM HAS BEEN A LITTLE TOO AGGRESSIVE WITH FRONTS...BUT GENERALLY HAS BEEN THE BEST. THUS TEND TO THINK A SOLUTION SOMEWHERE BETWEEN THE ECMWF AND NAM WILL BE CLOSEST. THIS WOULD GENERALLY KEEP THE THUNDERSTORM THREAT SOUTH OF INTERSTATE 90 THROUGH 7 PM TUESDAY. STORMS THAT DO FORM IN THE AFTERNOON WILL HAVE THE POTENTIAL OF BEING SEVERE...WITH AROUND 2000 J/KG OF CAPE AND DEEP LAYER SHEAR OF 40 KTS. LARGE HAIL AND STRONG WINDS WILL BE POSSIBLE IN ANY STORM THAT DOES FORM. CAP SHOULD HOLD STRONG FOR MUCH OF THE AFTERNOON...HOWEVER CONTINUED HEATING AND THE APPROACHING WAVE SHOULD BREAK IT AT SOME POINT EITHER LATE AFTERNOON OR EVENING. /CHENARD THAT APPROACHING WAVE AND FRONT SHOULD BRING MORE NUMEROUS SHOWERS AND THUNDERSTORMS TUESDAY EVENING...MAINLY TO THE EASTERN PART OF THE AREA WHERE MOISTURE POOLING AND INFLOW WILL BE GOOD. SYSTEM MOVING FAST ENOUGH AND MID TO UPPER FLOW IS STRONG ENOUGH SO THAT RAINFALL AMOUNTS SHOULD NOT BE TOO HIGH. FRONT WILL BE MOVING ACROSS AREA WITH COOLER AIR SPREADING IN BEHIND IT...AND PRECIPITATION DECREASING STEADILY AFTER MIDNIGHT. GUIDANCE SEEMS OK AT THIS POINT ON COOLING FOR LOW TEMPERATURES. MOVEMENT LOOKS FAST ENOUGH TO KEEP OUT ANY MENTION OF LINGERING SHOWERS FOR WEDNESDAY AND DRYING CERTAINLY LOOKS STRONG...SO WE SHOULD BE HEADING TO A SUNNY/MOSTLY SUNNY DAY WEDNESDAY AFTER MORNING CLOUDS SOUTHEAST DECREASE. LATE THURSDAY INTO FRIDAY LOOKS LIKE ANOTHER THREAT OF SHOWERS AND STORMS AS NEXT WAVE AND COLD FRONT IS PRECEDED BY FAVORABLY THERMAL ADVECTION PATTERN. WILL GO WITH LOW POPS AS PER GUIDANCE FOR NOW BUT OVERALL THREAT SEEMS A LITTLE HIGHER AND WHEN WE CAN NARROW DOWN THE TIMING BETTER...THE POPS FOR AT LEAST PART OF THAT TIME...PERHAPS THURSDAY NIGHT...MAY GO UP. THIS SYSTEM WILL BRING IN EVEN COOLER AIR FOR FRIDAY AND SATURDAY. SOLIDLY DRY PATTERN WILL ALSO DEVELOP BEHIND THIS SYSTEM...AND THE DRY PATTERN WILL REMAIN IN PLACE AS SLOW BUT STEADY WARMING SETS IN SUNDAY AFTERNOON THROUGH MONDAY. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...NONE. MN...NONE. IA...NONE. NE...NONE. $$
AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NWS SIOUX FALLS SD
637 PM CDT MON SEP 3 2012 .DISCUSSION.../ISSUED AT 315 PM CDT/ LIGHT SHOWERS MAINLY CONFINED TO NORTHWEST IOWA SO FAR THIS AFTERNOON. MID LEVEL CLOUDS ALSO DISSIPATING IN OUR WEST ALLOWING FOR DECENT HEATING. DEWPOINTS HAVE FALLEN RAPIDLY ONCE MIXING COMMENCED...WITH DRY AIR ALOFT. THIS WAS SHOWN WELL BY THE HRRR AND NAM. BOTH OF THESE MODELS SHOW SOME DEWPOINT RECOVERY BY LATER THIS AFTERNOON RIGHT AHEAD OF THE APPROACHING FRONTAL BOUNDARY. THE QUESTION IS WHETHER THEY RECOVER ENOUGH TO HELP BREAK THE CAP. HRRR HAS BACKED OFF SOME OF ITS EARLIER IDEA OF SCATTERED TO NUMEROUS STORMS FORMING AS THE BOUNDARY ENTERED OUR CWA. STILL THINKING WE POSSIBLY GET SOME ISOLATED DEVELOPMENT AFTER 4 OR 5 PM WEST OF THE JAMES RIVER. FULL SUN COMBINED WITH CONVERGENCE ALONG THE FRONT AND AN APPROACHING SHORTWAVE...MAY BE ENOUGH TO AT LEAST GET ISOLATED DEVELOPMENT. CAPE COULD BE AROUND 1500 J/KG NEAR THE BOUNDARY...AND A VEERING WIND PROFILE WITH DECENT WINDS ALOFT SHOULD RESULT IN AROUND 40 KTS EFFECTIVE SHEAR. SO ANY STORM THAT IS ABLE TO FORM COULD BE SEVERE...WITH STRONG WINDS AND LARGE HAIL. STORMS WOULD MOVE EAST OR EAST SOUTHEAST...BUT THINKING MOST ACTIVITY WILL BE DIURNALLY DRIVEN AND THUS DIE AS THE EVENING PROGRESSES. KEPT CHANCE POPS MAINLY ALONG AND WEST OF THE JAMES RIVER....WITH SLIGHT CHANCE THROUGH THE REST OF THE CWA...JUST IN CASE STORMS PERSIST ALONG THERE OUTFLOW LONGER THAN EXPECTED. SKIES SHOULD CLEAR LATER TONIGHT...WITH LOWS IN THE 50S AND 60S. COULD SEE SOME FOG DEVELOPMENT IN THE SOUTH...ESPECIALLY WHERE RAIN HAS FALLEN TODAY IN NORTHWEST IOWA. TUESDAY SHOULD START MOSTLY SUNNY WITH HIGHS IN THE 80S AND 90S. TRICKY PART OF TUESDAYS FORECAST WILL BE HOW FAR SOUTH THE BOUNDARY MAKES IT LATE TONIGHT...AND HOW QUICKLY IT PUSHES BACK NORTH AS A WARM FRONT TOMORROW BEFORE THE COLD FRONT PUSHES THROUGH. WITH STABLE DRIER AIR NORTH OF THIS BOUNDARY...CONVECTION CHANCES WILL BE CONFINED TO ALONG AND SOUTH OF IT DURING THE DAY...AS ANOTHER SHORTWAVE PUSHES ACROSS. NAM IS THE FURTHEST SOUTH WITH THE BOUNDARY...ONLY PUSHING AS FAR NORTH AS SPENCER TO YANKTON BY AFTERNOON. THE GFS IS FURTHEST NORTH...WITH THE ECMWF IN BETWEEN. NAM HAS BEEN A LITTLE TOO AGGRESSIVE WITH FRONTS...BUT GENERALLY HAS BEEN THE BEST. THUS TEND TO THINK A SOLUTION SOMEWHERE BETWEEN THE ECMWF AND NAM WILL BE CLOSEST. THIS WOULD GENERALLY KEEP THE THUNDERSTORM THREAT SOUTH OF INTERSTATE 90 THROUGH 7 PM TUESDAY. STORMS THAT DO FORM IN THE AFTERNOON WILL HAVE THE POTENTIAL OF BEING SEVERE...WITH AROUND 2000 J/KG OF CAPE AND DEEP LAYER SHEAR OF 40 KTS. LARGE HAIL AND STRONG WINDS WILL BE POSSIBLE IN ANY STORM THAT DOES FORM. CAP SHOULD HOLD STRONG FOR MUCH OF THE AFTERNOON...HOWEVER CONTINUED HEATING AND THE APPROACHING WAVE SHOULD BREAK IT AT SOME POINT EITHER LATE AFTERNOON OR EVENING. /CHENARD THAT APPROACHING WAVE AND FRONT SHOULD BRING MORE NUMEROUS SHOWERS AND THUNDERSTORMS TUESDAY EVENING...MAINLY TO THE EASTERN PART OF THE AREA WHERE MOISTURE POOLING AND INFLOW WILL BE GOOD. SYSTEM MOVING FAST ENOUGH AND MID TO UPPER FLOW IS STRONG ENOUGH SO THAT RAINFALL AMOUNTS SHOULD NOT BE TOO HIGH. FRONT WILL BE MOVING ACROSS AREA WITH COOLER AIR SPREADING IN BEHIND IT...AND PRECIPITATION DECREASING STEADILY AFTER MIDNIGHT. GUIDANCE SEEMS OK AT THIS POINT ON COOLING FOR LOW TEMPERATURES. MOVEMENT LOOKS FAST ENOUGH TO KEEP OUT ANY MENTION OF LINGERING SHOWERS FOR WEDNESDAY AND DRYING CERTAINLY LOOKS STRONG...SO WE SHOULD BE HEADING TO A SUNNY/MOSTLY SUNNY DAY WEDNESDAY AFTER MORNING CLOUDS SOUTHEAST DECREASE. LATE THURSDAY INTO FRIDAY LOOKS LIKE ANOTHER THREAT OF SHOWERS AND STORMS AS NEXT WAVE AND COLD FRONT IS PRECEDED BY FAVORABLY THERMAL ADVECTION PATTERN. WILL GO WITH LOW POPS AS PER GUIDANCE FOR NOW BUT OVERALL THREAT SEEMS A LITTLE HIGHER AND WHEN WE CAN NARROW DOWN THE TIMING BETTER...THE POPS FOR AT LEAST PART OF THAT TIME...PERHAPS THURSDAY NIGHT...MAY GO UP. THIS SYSTEM WILL BRING IN EVEN COOLER AIR FOR FRIDAY AND SATURDAY. SOLIDLY DRY PATTERN WILL ALSO DEVELOP BEHIND THIS SYSTEM...AND THE DRY PATTERN WILL REMAIN IN PLACE AS SLOW BUT STEADY WARMING SETS IN SUNDAY AFTERNOON THROUGH MONDAY. && .AVIATION.../FOR THE 00Z TAF ISSUANCE/ ISOLATED THUNDERSTORMS WEST OF JAMES RIVER AT START OF THE PERIOD COULD BRUSH KHON TAF SITE...BRINGING POSSIBILITY OF ERRATIC WINDS THROUGH 01Z. OTHERWISE THESE STORMS ARE EXPECTED TO WEAKEN AS THE MOVE EAST TOWARD I-29 CORRIDOR THROUGH THE EVENING...SO WILL LEAVE MENTION OF THUNDER OUT OF KFSD/KSUX TAFS. WITH LOW LEVEL MOISTURE AND LIGHT WINDS WITHIN SURFACE RIDGE AXIS OVER NORTHWEST IOWA... COULD SEE SOME POCKETS OF MVFR FOG TONIGHT AND WILL KEEP SOME LIGHT FOG FOR KSUX TOWARD DAYBREAK. CONVECTIVE CHANCES INCREASE INTO THE MISSOURI RIVER VALLEY LATE TUESDAY AFTERNOON...BUT CONFIDENCE IS LOW IN TIMING/COVERAGE BEFORE 05/00Z...SO WILL LEAVE OUT OF KSUX TAF AT THIS TIME. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...NONE. MN...NONE. IA...NONE. NE...NONE. $$
AREA FORECAST DISCUSSION
NWS MORRISTOWN TN
239 PM EDT SUN SEP 2 2012 .SHORT TERM (TONIGHT AND MONDAY)... THE SLOW EASTWARD MOVEMENT OF THE REMNANT LOW FROM ISSAC AND A VERY MOIST AIRMASS IN PLACE WITH PW VALUES ABOVE 2 INCHES WILL MAKE FOR A WET SHORT TERM PERIOD. AFTER A ROUND OF SHOWERS AND THUNDERSTORMS PASSES THROUGH THE AREA THIS AFTERNOON...ANOTHER ROUND IS SHOWN BY THE NAM AND THE RUC ARRIVING TOWARD MIDNIGHT. STRONG TO SEVERE STORMS ARE EXPECTED TO DEVELOP ACROSS NORTHERN MS/AL IN A LOW LEVEL CONVERGENCE ZONE AND THETA-E MAX...AND MOVE NORTHEAST INTO OUR AREA. WHILE THE STORMS SHOULD LOSE SOME INTENSITY DUE TO DIMINISHING SURFACE-BASED INSTABILITY...SOME ELEVATED INSTABILITY AND A 30-40 KT LLJ WILL HELP KEEP A CHANCE OF STRONG STORMS IN THE SOUTHERN CUMBERLAND PLATEAU AND SOUTHERN TN VALLEY TONIGHT. GUSTY WINDS AND HEAVY RAIN WILL BE THE MAIN THREATS. CATEGORICAL POPS WILL CONTINUE FROM TONIGHT THROUGH THE DAY MONDAY AS THE CLOSED CYCLONIC CIRCULATION MOVES DIRECTLY OVER THE AREA. WHILE THE BEST DYNAMICS FOR LIFT WILL BE TO OUR EAST...COOLING MIDLEVEL TEMPS UNDER THE LOW AND A TROPICAL AIR MASS WILL KEEP PERIODS OF SHOWERS AND THUNDERSTORMS GOING THROUGH THE DAY. .LONG TERM (MONDAY NIGHT THROUGH SUNDAY)... WEAKENING LOW PRESSURE SYSTEM SLIDES SOUTHEAST AND LOSES IDENTITY OVER THE EAST TN VALLEY EARLY IN THE PERIOD. LAYER MOISTURE REMAINS HIGH WITH ABOVE NORMAL PRECIPITATION CHANCES AND TEMPERATURES THROUGH WEDNESDAY. DEEPER MOISTURE SHIFTS EAST FOR THE LATER HALF OF THE WEAK WITH DIURNAL CONVECTION FAVORING THE HIGHER ELEVATIONS. MODELS CONTINUE TREND OF DEVELOPING STRONG TROUGH OVER THE EASTERN U.S. BY LATE IN THE PERIOD. SIGNIFICANT COLD FRONT PROGGED TO MOVE INTO THE SOUTHERN APPALACHIANS LATE SAT OR EARLY SUN. STRONG CONVECTION A POSSIBILITY SAT AHEAD OF FRONT. TROUGH AXIS REMAINS WEST OF AREA SUNDAY WITH LINGERING PRECIPITATION CHANCES. DRY CONDITIONS AND COOL NIGHTS SETTING UP FOR EARLY NEXT WEEK. && .PRELIMINARY POINT TEMPS/POPS... CHATTANOOGA AIRPORT, TN 72 85 72 86 71 / 90 90 50 60 30 KNOXVILLE MCGHEE TYSON AIRPORT, TN 72 83 70 85 70 / 90 90 50 60 30 OAK RIDGE, TN 71 82 71 85 69 / 90 90 50 60 30 TRI CITIES AIRPORT, TN 70 83 70 84 68 / 70 90 50 60 40 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ DGS/SON
AREA FORECAST DISCUSSION...UPDATED
NWS MEMPHIS TN
1140 PM CDT SAT SEP 1 2012 .UPDATE... UPDATED FOR AVIATION. && .PREV DISCUSSION... /ISSUED 1120 PM CDT SAT SEP 1 2012/ DISCUSSION... SEVERE WEATHER EVENT WINDING DOWN ACROSS THE FORECAST AREA BUT NOT COMPLETELY DISAPPEARING. ENERGY FROM ISAAC WILL CONTINUE THE THREAT OF THUNDERSTORMS THROUGH THE NIGHT WITH AN ISOLATED SEVERE STORM POSSIBLE. THE REMNANT LOW FROM ISAAC NEAR THE MO/IL BORDER WILL TRACK INTO THE OH VALLEY SUNDAY. AN ASSOCIATED UPPER TROUGH WILL DRAG THROUGH THE AREA SUNDAY CONTINUING THE HIGH CHANCES OF SHOWERS AND THUNDERSTORMS. EXPECT STRONG STORMS ON SUNDAY. SWC PREV DISCUSSION... /ISSUED 331 PM CDT SAT SEP 1 2012/ DISCUSSION...19Z SURFACE ANALYSIS CENTERS THE REMNANTS OF ISAAC JUST NORTH OF COLUMBIA MISSOURI. THERE HAS BEEN A BREAK IN THE SHOWER AND THUNDERSTORM ACTIVITY ACROSS THE MID SOUTH FROM LATE THIS MORNING THROUGH MID AFTERNOON AS A DRY SLOT /INDICATED BY WATER VAPOR SATELLITE TRENDS/ HAS BUILT IN TO ARKANSAS AND MUCH OF THE MID SOUTH. THUNDERSTORMS ARE ONLY BEGINNING TO DEVELOP ONCE AGAIN UP ACROSS EXTREME NORTHWEST ARKANSAS IN ASSOCIATION WITH AN APPROACHING SHORTWAVE ASSOCIATED WITH THE REMNANTS OF ISAAC. TEMPERATURES AS OF 3 PM CDT ARE IN THE MIDDLE 80S TO LOWER 90S ACROSS THE FORECAST AREA. STRONG TO SEVERE THUNDERSTORM POTENTIAL TONIGHT AND CONVECTIVE CHANCES INTO NEXT WEEK ARE THE MAIN FORECAST CHALLENGES FOR THIS AFTERNOON/S FORECAST ISSUANCE. SHORT TERM...(TONIGHT THROUGH TUESDAY)...LATEST SHORT TERM MODELS...ESPECIALLY THE HRRR AND THE 12Z WRF SUGGEST THE RELATIVELY RAIN FREE CONDITIONS CURRENTLY OCCURRING ACROSS THE MID SOUTH WILL COME TO AN END THIS EVENING AS ANOTHER SHORTWAVE ROTATING AROUND THE REMNANTS OF ISAAC MOVES ACROSS THE LOWER MISSISSIPPI VALLEY TONIGHT. DAYTIME INSTABILITY /SURFACE BASED CAPE VALUES AVERAGING BETWEEN 2000-3500 J/KG...LI/S BETWEEN -5 TO -6/ AND STEEP LOW LEVEL LAPSE RATES HAVE RESULTED IN THE DEVELOPMENT OF SCATTERED SHOWERS AND THUNDERSTORMS ACROSS ARKANSAS...FROM NEAR WALNUT RIDGE BACK THROUGH CENTRAL AND WEST CENTRAL ARKANSAS. AT THIS TIME BELIEVE THIS ACTIVITY WILL GRADUALLY INCREASE IN COVERAGE AS IT MOVES ACROSS THE MID SOUTH TONIGHT...ESPECIALLY ALONG AND NORTH OF I-40. THUS...INCREASED POPS ACROSS THE ABOVE MENTIONED AREAS. A FEW STRONG TO PERHAPS ISOLATED SEVERE THUNDERSTORMS ARE POSSIBLE TONIGHT AS THIS SHORTWAVE MOVES THROUGH THE MID SOUTH. DAMAGING WINDS WILL BE THE MAIN THREAT FOR ANY THUNDERSTORM THAT REACHES SEVERE LIMITS. A TROPICAL AIR MASS COMBINED WITH PRECIPITABLE WATER VALUES ABOVE 2 INCHES SUGGESTS THE POTENTIAL FOR LOCALIZED FLASH FLOODING FROM HEAVY RAINFALL WITHIN THUNDERSTORMS. SHORT TERM MODELS INDICATE THE REMNANTS OF ISAAC WILL GRADUALLY MOVE EAST SOUTHEAST TO THE OHIO AND TENNESSEE VALLEYS FOR SUNDAY THROUGH TUESDAY. AS A RESULT...A CONTINUED CHANCE FOR SHOWERS AND THUNDERSTORMS WILL PERSIST BUT GRADUALLY DECREASE THROUGH THE REMAINDER OF THE PERIOD. A STRONG THUNDERSTORM OR TWO CONTAINING HEAVY RAINFALL AND GUSTY WINDS WILL ALSO BE POSSIBLE ON SUNDAY AFTERNOON. LONG TERM...(WEDNESDAY THROUGH SATURDAY)...12Z GFS/ECMWF LONG RANGE MODELS INDICATE CHANCES FOR SHOWERS AND THUNDERSTORMS WILL PERSIST ACROSS THE AREA THROUGHOUT THE PERIOD AS ANOTHER COLD FRONT DROPS INTO THE AREA WEDNESDAY NIGHT INTO THURSDAY NIGHT AND THEN STALLS OUT ACROSS THE AREA INTO NEXT WEEKEND. KEPT PRECIPITATION CHANCES ON THE LOW END FOR THE TIME BEING AS THERE ARE SOME TIMING/COVERAGE DIFFERENCES BETWEEN THE LONG TERM MODEL SOLUTIONS. CJC && .AVIATION... 06Z TAFS PRIMARY FORECAST CONCERN IS OVERNIGHT SHRA/TSRA IN THE MOIST AND MODERATELY UNSTABLE NIGHTTIME TROPICAL AIRMASS. ALL BUT JBR APPEAR TO BE SUFFICIENTLY UNSTABLE FOR TSRA REDEVELOPMENT. BEST TS CHANCE APPEARS TO BE AT MKL...IN CLOSER TO PROXIMITY TO ONE OF THE NUMEROUS BAROCLINIC BANDS ROTATING AROUND THE SOUTHERN PERIPHERY OF ISAAC/S REMNANT LOW. BEST TSRA CHANCE FOR SUNDAY APPEARS TO BE MKL AND TUP. MEM AND JBR SHOULD SEE MORE MARGINAL...NONZERO TS CHANCES. PWB && .PRELIMINARY POINT TEMPS/POPS... MEM 74 93 76 94 / 60 40 40 20 MKL 72 89 72 89 / 70 60 50 30 JBR 75 90 72 93 / 70 50 30 20 TUP 74 90 73 92 / 50 40 50 30 && .MEG WATCHES/WARNINGS/ADVISORIES... AR...NONE. MO...NONE. MS...NONE. TN...NONE. && $$
AREA FORECAST DISCUSSION
NWS MEMPHIS TN
1120 PM CDT SAT SEP 1 2012 .DISCUSSION... SEVERE WEATHER EVENT WINDING DOWN ACROSS THE FORECAST AREA BUT NOT COMPLETELY DISAPPEARING. ENERGY FROM ISAAC WILL CONTINUE THE THREAT OF THUNDERSTORMS THROUGH THE NIGHT WITH AN ISOLATED SEVERE STORM POSSIBLE. THE REMNANT LOW FROM ISAAC NEAR THE MO/IL BORDER WILL TRACK INTO THE OH VALLEY SUNDAY. AN ASSOCIATED UPPER TROUGH WILL DRAG THROUGH THE AREA SUNDAY CONTINUING THE HIGH CHANCES OF SHOWERS AND THUNDERSTORMS. EXPECT STRONG STORMS ON SUNDAY. SWC && .PREV DISCUSSION... /ISSUED 331 PM CDT SAT SEP 1 2012/ DISCUSSION...19Z SURFACE ANALYSIS CENTERS THE REMNANTS OF ISAAC JUST NORTH OF COLUMBIA MISSOURI. THERE HAS BEEN A BREAK IN THE SHOWER AND THUNDERSTORM ACTIVITY ACROSS THE MID SOUTH FROM LATE THIS MORNING THROUGH MID AFTERNOON AS A DRY SLOT /INDICATED BY WATER VAPOR SATELLITE TRENDS/ HAS BUILT IN TO ARKANSAS AND MUCH OF THE MID SOUTH. THUNDERSTORMS ARE ONLY BEGINNING TO DEVELOP ONCE AGAIN UP ACROSS EXTREME NORTHWEST ARKANSAS IN ASSOCIATION WITH AN APPROACHING SHORTWAVE ASSOCIATED WITH THE REMNANTS OF ISAAC. TEMPERATURES AS OF 3 PM CDT ARE IN THE MIDDLE 80S TO LOWER 90S ACROSS THE FORECAST AREA. STRONG TO SEVERE THUNDERSTORM POTENTIAL TONIGHT AND CONVECTIVE CHANCES INTO NEXT WEEK ARE THE MAIN FORECAST CHALLENGES FOR THIS AFTERNOON/S FORECAST ISSUANCE. SHORT TERM...(TONIGHT THROUGH TUESDAY)...LATEST SHORT TERM MODELS...ESPECIALLY THE HRRR AND THE 12Z WRF SUGGEST THE RELATIVELY RAIN FREE CONDITIONS CURRENTLY OCCURRING ACROSS THE MID SOUTH WILL COME TO AN END THIS EVENING AS ANOTHER SHORTWAVE ROTATING AROUND THE REMNANTS OF ISAAC MOVES ACROSS THE LOWER MISSISSIPPI VALLEY TONIGHT. DAYTIME INSTABILITY /SURFACE BASED CAPE VALUES AVERAGING BETWEEN 2000-3500 J/KG...LI/S BETWEEN -5 TO -6/ AND STEEP LOW LEVEL LAPSE RATES HAVE RESULTED IN THE DEVELOPMENT OF SCATTERED SHOWERS AND THUNDERSTORMS ACROSS ARKANSAS...FROM NEAR WALNUT RIDGE BACK THROUGH CENTRAL AND WEST CENTRAL ARKANSAS. AT THIS TIME BELIEVE THIS ACTIVITY WILL GRADUALLY INCREASE IN COVERAGE AS IT MOVES ACROSS THE MID SOUTH TONIGHT...ESPECIALLY ALONG AND NORTH OF I-40. THUS...INCREASED POPS ACROSS THE ABOVE MENTIONED AREAS. A FEW STRONG TO PERHAPS ISOLATED SEVERE THUNDERSTORMS ARE POSSIBLE TONIGHT AS THIS SHORTWAVE MOVES THROUGH THE MID SOUTH. DAMAGING WINDS WILL BE THE MAIN THREAT FOR ANY THUNDERSTORM THAT REACHES SEVERE LIMITS. A TROPICAL AIR MASS COMBINED WITH PRECIPITABLE WATER VALUES ABOVE 2 INCHES SUGGESTS THE POTENTIAL FOR LOCALIZED FLASH FLOODING FROM HEAVY RAINFALL WITHIN THUNDERSTORMS. SHORT TERM MODELS INDICATE THE REMNANTS OF ISAAC WILL GRADUALLY MOVE EAST SOUTHEAST TO THE OHIO AND TENNESSEE VALLEYS FOR SUNDAY THROUGH TUESDAY. AS A RESULT...A CONTINUED CHANCE FOR SHOWERS AND THUNDERSTORMS WILL PERSIST BUT GRADUALLY DECREASE THROUGH THE REMAINDER OF THE PERIOD. A STRONG THUNDERSTORM OR TWO CONTAINING HEAVY RAINFALL AND GUSTY WINDS WILL ALSO BE POSSIBLE ON SUNDAY AFTERNOON. LONG TERM...(WEDNESDAY THROUGH SATURDAY)...12Z GFS/ECMWF LONG RANGE MODELS INDICATE CHANCES FOR SHOWERS AND THUNDERSTORMS WILL PERSIST ACROSS THE AREA THROUGHOUT THE PERIOD AS ANOTHER COLD FRONT DROPS INTO THE AREA WEDNESDAY NIGHT INTO THURSDAY NIGHT AND THEN STALLS OUT ACROSS THE AREA INTO NEXT WEEKEND. KEPT PRECIPITATION CHANCES ON THE LOW END FOR THE TIME BEING AS THERE ARE SOME TIMING/COVERAGE DIFFERENCES BETWEEN THE LONG TERM MODEL SOLUTIONS. CJC && .AVIATION... 18Z TAFS STARTING TO SEE ANOTHER ROUND OF SHOWERS/STORMS BEGIN TO DEVELOP ACROSS THE MIDSOUTH AS TEMPERATURES CLIMB INTO THE UPPER 80S. SHOWERS WILL BE HIT AND MISS THROUGH MOST OF THE AFTERNOON...MUCH LIKE YESTERDAY. AROUND 00-04Z A BAND OF POSSIBLY STRONGER SHOWERS AND THUNDERSTORMS IS EXPECTED TO DEVELOP NEAR JBR TO LITTLE ROCK AND MOVE TO THE EAST. TRIED TO TIME THIS UN- DEVELOPED LINE BY ADDING VCTS TO JBR...THEN MEM AND MKL. HOWEVER TIMING OF THIS FEATURE WILL BECOME MUCH MORE CERTAIN AFTER...OR EVEN IF IT DEVELOPS. WILL AMEND WHEN THERE IS SOMETHING MORE CONCRETE TO TRACK. STRONG WIND AND BRIEF IFR VISIBILITY DUE TO HEAVY RAIN CAN BE EXPECTED. OTHERWISE...EXPECT PRECIPITATION INTENSITY AND COVERAGE TO DIMINISH BY 06Z...WITH MVFR TO IFR LOW CLOUDS DURING TH EARLY MORNING HOURS. && .PRELIMINARY POINT TEMPS/POPS... MEM 75 93 76 94 / 60 40 40 20 MKL 72 89 72 89 / 70 60 50 30 JBR 75 90 72 93 / 70 50 30 20 TUP 74 90 73 92 / 50 40 50 30 && .MEG WATCHES/WARNINGS/ADVISORIES... AR...NONE. MO...NONE. MS...NONE. TN...NONE. && $$
AREA FORECAST DISCUSSION
NWS LA CROSSE WI
636 PM CDT MON SEP 3 2012 .SHORT TERM...TONIGHT THROUGH THURSDAY 256 PM CDT MON SEP 3 2012 MAIN FORECAST CONCERNS ARE ON PRECIPITATION CHANCES THROUGH WEDNESDAY. CURRENTLY AS OF 20Z...WATER VAPOR LOOP AND RAP 500MB HEIGHT ANALYSIS SHOWED BROAD TROUGHING OVER SOUTHWEST AND SOUTH CENTRAL CANADA... WITH NEARLY ZONAL FLOW ON ITS SOUTH SIDE ACROSS MUCH OF THE NORTHERN U.S.. WITHIN THE BROAD UPPER TROUGHING...A PORTENT SHORTWAVE IS EVIDENT OVER CENTRAL ALBERTA. IN THE ZONAL FLOW...THERE ARE NUMEROUS WEAK SHORTWAVES...WHICH DURING THIS MORNING PRETTY MUCH ALL HAD AT LEAST ACCAS OR CONVECTION WITH THEM: ONE IN NORTH DAKOTA...ANOTHER IN WESTERN MINNESOTA...ONE IN WESTERN NEBRASKA AND LASTLY ONE IN CENTRAL IOWA. DPVA AHEAD OF THE SHORTWAVE IN CENTRAL IOWA COMBINED WITH A WEAKENING SURFACE COLD FRONT EXTENDING FROM CENTRAL UPPER MICHIGAN TO NEAR DES MOINES...AS WELL AS MLCAPE VALUES THAT HAVE CLIMBED TO 1500-2000 J/KG WITH LITTLE CIN PER RAP ANALYSIS...HAS ALLOWED FOR SHOWER AND THUNDERSTORM DEVELOPMENT. MOST OF THE ACTIVITY HAS BEEN DISORGANIZED...DUE TO 0-6KM SHEAR BELOW 30 KT WHERE STORMS ARE IN THE FORECAST AREA. ALSO...A SURGE OF MONSOONAL MID-CLOUDS THROUGH THE UPPER FLOW IS HELPING TO PUT A LID ON THE AMOUNT OF INSTABILITY. THERE ARE EVEN SOME SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS COMING OUT OF THESE MID CLOUDS. WITH THE VARYING CLOUD COVER AND PRECIPITATION...TEMPERATURES TODAY ARE ALL OVER THE PLACE IN THE FORECAST AREA. MOST LOCATIONS REACHED 80...WHILE BOSCOBEL GOT CLOSE TO 90. ABNORMALLY HIGH DEWPOINTS PERSIST TOO...WITH MOST OF THE AREA SEEING READINGS AROUND 70F. TONIGHT AND TUESDAY...VERY TRICKY FORECAST TO SAY THE LEAST. THE NEAR ZONAL FLOW WILL PERSIST THROUGH THIS PERIOD AS THE POTENT ALBERT SHORTWAVE DIGS DOWN INTO THE NORTHERN PLAINS. MODELS CONTINUE TO INDICATE WEAK SHORTWAVES MOVING THROUGH THIS FLOW...LIKE THOSE AROUND THE DAKOTAS TODAY. WITH MUCAPE VALUES PROGGED TO NOT DROP MUCH BELOW 1000 J/KG...HIGHLY CONCERNED THERE COULD BE OFF AND ON SHOWERS AND THUNDERSTORMS THROUGHOUT THIS PERIOD. THIS HAS BEEN SUGGESTED THE PAST FEW DAYS...ESPECIALLY BY THE ECMWF...THOUGH THE LATEST 03.12Z ECMWF IS NOT AS ACTIVE. NOW SOME HI RESOLUTION MODEL RUNS HAVE SUGGESTED THAT THE CURRENT AFTERNOON CONVECTION DROPS SOUTHEAST THIS EVENING...WHILE OTHER CONVECTION DEVELOPS IN IOWA AND DROPS SOUTHEAST. THIS ALLOWS THE FORECAST AREA TO END UP DRY AFTER MIDNIGHT. FOR NOW HOLDING ON TO SOME LOW CHANCES OF PRECIPITATION BECAUSE OF TOO MUCH UNCERTAINTY TO GO DRY BASED ON THE ENVIRONMENT. IF SKIES CLEAR OUT TONIGHT...THE HIGH AMOUNT OF SURFACE MOISTURE AROUND AND WEAK WIND FIELD WOULD LIKELY RESULT IN WIDESPREAD RADIATION FOG. NOT ENTIRELY CONFIDENT WE WILL HAVE A LONG PERIOD OF CLEAR SKIES...THOUGH. SO IN SUMMARY...THERE APPEARS TO BE TWO SCENARIOS FOR TONIGHT: 1. SKIES CLEAR AND WE END UP WITH DENSE FOG 2. PERIODS OF ACCAS AND ISOLATED SHOWERS/STORMS RIGHT NOW...BANKING ON NUMBER 2 AND ACKNOWLEDGING THE FOG BY ADDING AT LEAST A PATCHY MENTION AFTER MIDNIGHT INTO TUESDAY MORNING. WITH THE HIGH AMOUNT OF SURFACE MOISTURE...ANTICIPATING TEMPERATURES OUTSIDE OF THE TYPICAL COLD SPOTS TO NOT DROP BELOW THE MID 60S. DEPENDING ON AMOUNT OF SUN ON TUESDAY...WITH 850MB TEMPS BETWEEN 18-20C...HIGHS COULD GET CLOSE TO 90. TUESDAY NIGHT AND WEDNESDAY...THE POTENT SHORTWAVE TROUGH COMING INTO THE NORTHERN PLAINS AT 00Z WEDNESDAY IS FORECAST TO DIG INTO MINNESOTA BY 12Z...THEN RAPIDLY SHOOT EAST OVER MUCH OF MICHIGAN BY 00Z THURSDAY. THIS RAPID MOVEMENT MEANS AN OVERALL SHORT TIME WINDOW FOR PRECIPITATION FORCED BY THE TROUGH. NOTE THAT THE BEST 500-300MB PV ADVECTION IS STILL SUGGESTED TO STAY TO THE NORTH OF THE FORECAST AREA. HOWEVER...THE COMBINATION OF WEAK 500MB HEIGHT FALLS...A SURGE OF LOW TO MID LEVEL MOISTURE TRANSPORT...AS WELL AS AT LEAST 1000-1500 J/KG OF MUCAPE ACCOMPANYING THE MOISTURE TRANSPORT SHOULD PRODUCE SHOWERS AND THUNDERSTORMS ACROSS MUCH OF THE AREA. SOME OF THESE COULD GET GOING AS EARLY AS THE EVENING...BUT BETTER CHANCES ARE EXPECTED AFTER MIDNIGHT THROUGH ABOUT 15Z WEDNESDAY...WHEN THE TROUGH IS HAVING ITS BIGGEST FORCING INFLUENCE. 1-6KM SHEAR IS GENERALLY 15-25KT...WHICH SHOULD KEEP CONVECTION SUB-SEVERE. AFTER 15Z...STRONG SUBSIDENCE WILL WORK IN WEST TO EAST...CLEARING SKIES OUT. WINDS SHOULD PICK UP TOO AS THE PRESSURE GRADIENT TIGHTENS... COLD ADVECTION AND DEEP MIXING OCCUR. NOTING ABOUT THE COLD ADVECTION...850MB TEMPS WHICH LOOK TO HOVER BETWEEN 16-20C TUESDAY NIGHT END UP FALLING TO 12-14C OR SLIGHTLY COOLER BY 00Z WEDNESDAY. THUS...EXPECT COOLER HIGHS FOR WEDNESDAY ON THE ORDER OF MID 70S TO LOWER 80S. TUESDAY NIGHT WILL STILL BE WARM WITH LOWS IN THE 60S...THANKS TO SOUTH FLOW AHEAD OF THE SHORTWAVE/ASSOCIATED COLD FRONT AND HIGHER DEWPOINTS. WEDNESDAY NIGHT AND THURSDAY...IN THE WAKE OF WEDNESDAYS POTENT SHORTWAVE...UPPER FLOW TURNS ZONAL OVER THE AREA. BUT THIS IS BRIEF...WITH ATTENTION TURNING BACK TO ALBERTA WHERE YET ANOTHER POTENT SHORTWAVE IS PROGGED TO DROP SOUTH INTO MONTANA BY 00Z FRIDAY. WEDNESDAY NIGHT STILL LOOKS DRY THANKS TO LINGERING DRY AIR AND SUBSIDENCE IN THE WAKE OF WEDNESDAYS TROUGH. THURSDAY IS A LITTLE MORE PROBLEMATIC. TO THE NORTH...MODELS ARE INDICATING A COUPLE OF SHORTWAVES CROSSING NORTHERN MINNESOTA AND WISCONSIN... WHICH BRING DOWN A COLD FRONT INTO NORTHWEST WI BY 00Z. BOTH THE 03.12Z NAM AND 03.06Z GFS DEPICT SOME LIGHT QPF ACROSS TAYLOR COUNTY WITH THIS FEATURE IN THE AFTERNOON. SOUNDINGS SUGGEST VERY LITTLE MUCAPE WITH THIS FRONT AND A FAIRLY DRY BOUNDARY LAYER BELOW 750MB. NEW 03.12Z GFS HAS CAME IN DRY. THEREFORE...HAVE HELD OFF ON MENTION ANY PRECIPITATION CHANCES UP AROUND TAYLOR COUNTY. FOR THE REST OF THE AREA...300-305K ISENTROPIC LIFT GRADUALLY INCREASES DURING THE AFTERNOON...ALL KIND OF DOWNSTREAM OF THAT SHORTWAVE DROPPING INTO MONTANA. SHOULD SEE SOME MID/HIGH CLOUDS DEVELOP AS A RESULT OF THIS LIFT...BUT THINKING THE MAJORITY OF THESE CLOUDS ANY PRECIPITATION POTENTIAL WITH THEM WILL STAY WEST/SOUTHWEST OF THE AREA. THIS AGREES WELL WITH THE 03.12Z GFS/ECMWF. COOLER PERIOD ANTICIPATED. MAY HAVE TO WATCH FOR VALLEY FOG POTENTIAL IF THE SURFACE RIDGE OF HIGH PRESSURE COMING IN WEDNESDAY NIGHT BUILDS IN FASTER. .LONG TERM...THURSDAY NIGHT THROUGH MONDAY 256 PM CDT MON SEP 3 2012 THROUGH SATURDAY...MODELS REMAIN IN GOOD AGREEMENT WITH THE HANDLING OF THE POTENT SHORTWAVE OVER MONTANA...HOW IT ENDS UP FORMING A FAIRLY DEEP TROUGH OVER THE UPPER AND MID MISSISSIPPI RIVER VALLEYS BY 12Z SATURDAY. AS THIS TROUGH FORMS...FRONTOGENESIS DOWNSTREAM WILL LIKELY SPREAD MID/HIGH CLOUDS ACROSS THE AREA THURSDAY NIGHT AND FRIDAY...SOME OF WHICH COULD PRODUCE A FEW SHOWERS. OVERALL... BULK OF PRECIPITATION IS ANTICIPATED TO STAY TO THE SOUTH...CLOSER TO A DEVELOPING LOW PRESSURE SYSTEM LIFTING OUT OF THE CENTRAL PLAINS. BY FRIDAY NIGHT...AS THE TROUGHING MOVES IN...THE CLOUDS AND POTENTIAL FOR SHOWERS GET PUSHED EAST. HIGH PRESSURE THEN BUILDS IN FOR SATURDAY. MUCH OF THIS PERIOD THROUGH SATURDAY WILL BE BELOW NORMAL...DUE TO FIRST CLOUDS ON FRIDAY AND THEN 850MB TEMPS FALLING TO 6-8C FOR SATURDAY. HIGHS MAY STRUGGLE TO CLIMB TO OR MUCH ABOVE 70. BEYOND SATURDAY...MODELS HANDLE THE TROUGHING DIFFERENTLY...WITH THE 03.12Z ECMWF AND CANADIAN CLOSING IT OFF AND PERHAPS MOVING IT SOUTHEAST...WHEREAS THE 03.12Z GFS AND ITS ENSEMBLES REMAIN MORE PROGRESSIVE. FOR THE FORECAST AREA...EITHER SCENARIO DOESNT MATTER MUCH...AS ALL MODELS END UP HAVING UPPER RIDGING BUILDING UP OVER THE PLAINS AND INTO THE FORECAST AREA LATE MONDAY. THIS WILL KEEP CONDITIONS DRY WITH A GRADUAL WARMING TREND. BY MONDAY...850MB TEMPS ARE BACK UP TO 12-14C...YIELDING HIGHS AT LEAST AROUND NORMAL. && .AVIATION...TONIGHT AND TUESDAY 636 PM CDT MON SEP 3 2012 SHOWERS AND STORMS WERE SOUTH OF THE TAF SITES EARLY THIS EVENING...WITH VISIBLE SATELLITE IMAGERY SHOWING BACK EDGE OF CLOUDS PUSHING INTO SOUTHEAST MINNESOTA. BIGGEST CONCERN FOR THE TAF PERIOD IS THE POTENTIAL FOR DENSE FOG OVERNIGHT INTO EARLY TUESDAY MORNING. SKIES ARE EXPECTED TO CLEAR THIS EVENING AND WITH THE RECENT RAIN/HIGHER DEW POINTS AND LIGHT WINDS CONDITIONS CONDUCIVE TO DENSE FOG DEVELOPMENT. THE BIGGEST CAVEAT IS WEAK SHORTWAVES IN THE FLOW NOW KICKING OFF CONVECTION OVER THE DAKOTAS. 04.18Z NAM DOES SHOW SOME CLOUDS AND SHOWERS FRONT THIS AFFECTING THE TAF SITES LATE TONIGHT...WHILE THE 04.12Z ECMWF AND ARXLAPS KEEPING THINGS DRY. GIVEN CURRENT TEMPERATURE/DEW POINT SPREADS IT WILL NOT TAKE MUCH TO GET FOG FORMATION. DID ADD A TEMPO 1SM BR TO BOTH THE TAF SITES LATE TONIGHT. WILL MONITOR THROUGH THE EVENING HOURS FOR THE POTENTIAL FOR LOWER VISIBILITIES. WITH INSTABILITIES REMAINING ON TUESDAY CANNOT RULE OUT SOME CONVECTION IN THE UNSTABLE AIR MASS. HOWEVER...DIFFICULT TO DISCERN ANY TIMING AND THUS DID NOT MENTION AT THIS TIME AS COVERAGE EXPECTED TO BE ISOLATED AT BEST. && .ARX WATCHES/WARNINGS/ADVISORIES... 256 PM CDT MON SEP 3 2012 WI...NONE. MN...NONE. IA...NONE. && $$ SHORT TERM...AJ LONG TERM...AJ AVIATION...JLR
AREA FORECAST DISCUSSION
NWS LA CROSSE WI
239 PM CDT SUN SEP 2 2012 .SHORT TERM...TONIGHT THROUGH WEDNESDAY 239 PM CDT SUN SEP 2 2012 MAIN FORECAST CONCERNS ARE ON PRECIPITATION CHANCES THROUGHOUT AND ANY SEVERE WEATHER POTENTIAL FOR MONDAY/LABOR DAY. CURRENTLY AS OF 20Z...WATER VAPOR LOOP AND RAP 500MB HEIGHT ANALYSIS SHOWED A DEEP UPPER LOW OVER SASKATCHEWAN....RIDGING OVER THE WESTERN GREAT LAKES REGION...AND THE REMNANTS OF ISAAC IN SOUTHWEST INDIANA. WITHIN THE SOUTHWEST FLOW BETWEEN THE UPPER LOW AND THE RIDGING...A SHORTWAVE WAS PRESENT FROM LAKE WINNIPEG TO CENTRAL SOUTH DAKOTA. THE COMBINATION OF DPVA AHEAD OF THIS SHORTWAVE AND LOW TO MID LEVEL MOISTURE TRANSPORT SURGING NORTH HAS KEPT SOME SHOWERS AND THUNDERSTORMS GOING OVER NORTHWEST MINNESOTA. THIS MOISTURE TRANSPORT CAN BE SEEN IN SOME OF THE GOES DERIVED PRECIPITABLE WATER IMAGERY...WHERE VALUES ARE IN THE 1-1.3 INCH RANGE FROM EASTERN NEBRASKA INTO WESTERN MINNESOTA. ASSOCIATED WITH THIS SHORTWAVE AT THE SURFACE IS A COLD FRONT THAT STRETCHES FROM NORTH CENTRAL MINNESOTA BACK INTO SOUTHEAST SOUTH DAKOTA. OVER OUR AREA...PLENTY OF SUNSHINE CONTINUES...THANKS TO DRY AIR PRESENT AS SEEN ON THE 12Z MPX SOUNDING. MIXING FROM THE SUN COMBINED WITH 850MB TEMPS AROUND 18C PER 12Z SOUNDINGS ALLOWING TEMPERATURES TO CLIMB INTO THE LOW TO MID 80S. SOME CUMULUS HAS FORMED OVER THE SOUTHEAST HALF OF THE AREA...THOUGH...REFLECTIVE OF ISAAC MOISTURE BEGINNING TO GET PULLED NORTHWEST AHEAD OF THE SHORTWAVE/FRONT. THAT MOISTURE CAN BE SEEN TOO ON GOES PRECIPITABLE WATER IMAGERY. TONIGHT AND MONDAY...THE SHORTWAVE SEEN OVER THE DAKOTAS IS PROGGED TO PUSH EAST-NORTHEAST IN RESPONSE TO THE DEEP UPPER LOW IN CANADA HEADING EAST. AS THE SHORTWAVE HEADS INTO THE RIDGE OVER THE FORECAST AREA...IT LOOKS LIKE IT WILL WEAKEN...BUT COME THROUGH NORTHERN SECTIONS OF THE FORECAST AREA AT A GOOD TIME FOR CONVECTIVE INITIATION...I.E. MONDAY AFTERNOON. WITH THE SHORTWAVE WEAKENING... SO DOES THE FRONT ASSOCIATED WITH IT. HOWEVER...ALSO OF INTEREST IS MOST MODELS SHOWING A SHORTWAVE COMING OUT OF UTAH/COLORADO RIGHT NOW. THIS SHORTWAVE GETS PICKED UP BY THE SOUTHWEST FLOW AND ENTERS THE SOUTHERN PORTION OF THE FORECAST AREA DURING THE AFTERNOON. SO ALTHOUGH THE SURFACE FRONTAL FEATURE IS WEAKENING...THERE ARE A COUPLE OF AIDES ALOFT FOR CONVECTION. BEFORE DISCUSSING MONDAY FURTHER...BACK TO TONIGHT. ANTICIPATING CONVECTIVE DEVELOPMENT ALONG THE FRONT LATE THIS AFTERNOON OR DURING THE EVENING IN WESTERN MINNESOTA. THIS ACTIVITY SHOULD WEAKEN OVERNIGHT WITH LOSS OF HEATING...BUT SOME COULD LINGER AND SCRAPE THE NORTHWEST SECTION OF THE FORECAST AREA VERY LATE IN THE NIGHT. CERTAINLY THE MOISTURE TRANSPORT THROUGHOUT THE 925-700MB LAYER STAYING FOCUSED UP WELL TO THE NORTH DOESNT HELP TO MAINTAIN CONVECTION. IT IS ENTIRELY POSSIBLE MONDAY MORNING THAT NO PRECIPITATION IS AROUND...A BREAK BETWEEN THE TONIGHT ACTIVITY DIMINISHING AND AFTERNOON ACTIVITY STARTING UP. FOR THE AFTERNOON...BUILDING INSTABILITY WITH MLCAPES OF 1000-2000 J/KG COMBINED WITH THE TWO SHORTWAVES SHOULD INITIATE CONVECTION. IN FACT...THE ONE SHORTWAVE COMING FROM THE SOUTHWEST MAY END UP HAVING MOST OF THE CONVECTION...AS NOTED BY THE 02.12Z SPCWRF-NMM...HIRESW-ARW AND NAM. AS SUCH...HAVE INCREASED PRECIPITATION CHANCES TO 50 PERCENT SOUTH OF I-90. REGARDING SEVERE RISK...ONLY AREA OF CONCERN IS AHEAD OF THAT SHORTWAVE...WHERE LOCALIZED 0-6KM SHEAR VALUES JUMP UP TO 25-30KT. OUTSIDE OF THAT...0-3KM AND 0-6KM SHEAR VALUES ARE GENERALLY BELOW 20 KTS. THEREFORE...THINKING MOST CONVECTION NORTH OF I-90 SHOULD STAY SUB-SEVERE WHILE THERE COULD BE A RISK SOUTH OF I-90. FOR TEMPERATURES...INCREASING SOUTHERLY FLOW AND CLOUDS WILL RESULT IN A WARMER NIGHT TONIGHT. SOME CLOUDS AROUND ON MONDAY MAKE HIGHS A LITTLE DIFFICULT...BUT WITH 850MB TEMPS STILL NEAR 18C AND SOME SUN...HIGHS SHOULD AT LEAST GET BACK UP INTO THE LOW TO EVEN MID 80S. MONDAY NIGHT AND TUESDAY...A WEST-SOUTHWEST 500MB FLOW CONTINUES... AHEAD OF WHAT IS FORECAST TO BE A POTENT SHORTWAVE DROPPING DOWN INTO SOUTH CENTRAL CANADA AND THE NORTHWEST DAKOTAS BY 00Z WEDNESDAY. THERE ARE NO REAL DISCERNIBLE SHORTWAVES COMING THROUGH THE FLOW AND IMPACTING THE FORECAST AREA ACCORDING TO THE MODELS. LOOKING AT MOISTURE TRANSPORT AND ISENTROPIC LIFT FIELDS...THERE IS NOTHING REALLY TO NOTE EITHER THAT SUGGEST PRECIPITATION...AT LEAST FROM THE 02.12Z NAM/GFS. THEREFORE...ONCE WHATEVER CONVECTION OCCURS MONDAY AFTERNOON PUSHES OFF TO THE EAST...LIKELY EARLY IN THE EVENING...DRY CONDITIONS COULD OCCUR RIGHT THROUGH TUESDAY. THIS IS A DEFINITE CHANGE FROM PREVIOUS MODEL RUNS...EVEN THE 02.00Z ECMWF...WHICH HAD SOME BETTER MOISTURE TRANSPORT AHEAD OF THAT POTENT SHORTWAVE COMING DOWN TO INITIATE CONVECTION. FOR NOW WILL LOWER PRECIPITATION CHANCES INTO THE 15-25 PERCENT RANGE...BUT FUTURE FORECASTS MAY BE ABLE TO PULL THESE CHANCES ENTIRELY IF TRENDS CONTINUE. ANOTHER ITEM TO WATCH IS FOG TUESDAY MORNING. IF SKIES CAN CLEAR OUT...DECOUPLING OF WINDS AND ANY RAIN FROM MONDAY WOULD LEAD TO FOG DEVELOPMENT. DUE TO UNCERTAINTY ON CLOUDS...HAVE LEFT OUT FOG. DESPITE THE SHORTWAVE PASSAGE MONDAY EVENING...850MB TEMPS STAY WARM IN THE 18-20C RANGE THROUGH TUESDAY. IN ADDITION... DEWPOINTS DO NOT LOOK TO DROP MUCH IF AT ALL. THEREFORE... ANTICIPATING SIMILAR LOW AND HIGH TEMPERATURES TO TONIGHT AND MONDAY. TUESDAY NIGHT AND WEDNESDAY...THAT POTENT SHORTWAVE TROUGH COMING INTO THE NORTHWEST DAKOTAS LATE TUESDAY IS WELL AGREED UPON BY MODELS TO MOVE OVER MINNESOTA BY 12Z WEDNESDAY...THEN CONTINUE ITS FAST MOTION EAST AND REACH WESTERN LOWER MICHIGAN BY 00Z THURSDAY. PRETTY STRONG FORCING THIS TROUGH...NOTED IN 500-300MB PV FIELDS...THOUGH MOST OF IT STAYS NORTH OF THE FORECAST AREA. THERE IS SOME MOISTURE TRANSPORT AND ISENTROPIC LIFT ACCOMPANYING THE TROUGH...SO WITH THE WEAK HEIGHT FALLS IN OUR AREA WE SHOULD SEE SOME PRECIPITATION MOVE THROUGH. MOST LIKELY TIME PERIOD APPEARS TO OCCUR BETWEEN 06Z-18Z WEDNESDAY. PREVIOUS FORECAST PRECIPITATION CHANCES REFLECT THIS WELL. STRONG ISENTROPIC DESCENT AND SUBSIDENCE BEHIND THE TROUGH WILL ALLOW FOR DRYING AND CLEARING CONDITIONS AFTER 18Z WEDNESDAY. THEREFORE...HAVE DRIED OUT THE FORECAST AREA FOR THE AFTERNOON. NOTE...IT COULD ALSO BE PRETTY BREEZY IN THE AFTERNOON AS PRESSURE GRADIENT BRIEFLY TIGHTENS...DEEP MIXING AND COLD ADVECTION OCCUR. REGARDING TEMPERATURES...850MB TEMPS HOLD BETWEEN 18-20C TUESDAY NIGHT...BUT ONCE THE FRONT MOVES THROUGH WITH THE SHORTWAVE WEDNESDAY MORNING...THESE TEMPS FALL TO 10-12C BY 00Z THURSDAY. STILL...HIGHS ON WEDNESDAY SHOULD BE ABLE TO TOP OUT IN THE MID 70S TO LOW 80S WITH THE SUN IN THE AFTERNOON. WARM NIGHT LIKELY TUESDAY NIGHT AHEAD OF THE FRONT AND RELATIVELY HIGH DEWPOINTS. .LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY 239 PM CDT SUN SEP 2 2012 SURPRISINGLY...THE 02.12Z ECMWF/GFS/CANADIAN AND GFS ENSEMBLES ARE ALL IN REALLY GOOD AGREEMENT WITH THE UPPER AIR AND SURFACE PATTERNS THROUGH SATURDAY. SOME DIFFERENCES START TO SHOW UP ON SUNDAY...BUT GIVEN THE AMPLIFICATION FORECAST TO OCCUR...IT IS SURPRISING TO SEE THE GOOD AGREEMENT. THE LONG TERM PERIOD STARTS OFF WITH UPPER TROUGHING OVER MUCH OF CENTRAL CANADA WITH A POTENT SHORTWAVE DROPPING DOWN THROUGH ALBERTA. THIS SHORTWAVE ENDS UP CARVING OUT A FAIRLY DEEP TROUGH AS IT DIGS SOUTHEAST...REACHING THE OHIO VALLEY SATURDAY MORNING. AS THIS SHORTWAVE DIGS...A FRONTOGENESIS ZONE LOOKS TO FORM ACROSS THE FORECAST AREA. THIS APPEARS TO OCCUR THURSDAY NIGHT AND LASTS THROUGH FRIDAY NIGHT. OVERALL...THE BEST MOISTURE AND FRONTOGENESIS FORCING STAYS SOUTH...THEREFORE PRECIPITATION CHANCES ARE ONLY IN THE 20-30 RANGE. ON SATURDAY... BOTH THE 02.00Z AND 02.12Z ECMWF END UP DEVELOPING A RELATIVELY STRONG SURFACE LOW IN INDIANA...PARTIALLY CAUSED BY THE UPPER TROUGH BEGINNING TO CLOSE OFF. THE 02.00Z ECMWF HAD DEFORMATION SHOWERS INTO THE SOUTHEASTERN HALF OF THE FORECAST AREA FOR SATURDAY. HOWEVER...THE NEW 02.12Z ECMWF HAS SHOVED THEM OFF TO THE EAST. FOR NOW...JUST PLACED A 20 PERCENT CHANCE IN THE AREA AROUND GRANT COUNTY. THE GFS AND CANADIAN ARE MOSTLY DRY. THE REST OF THE WEEKEND AND GOING INTO EARLY NEXT WEEK WILL ALL HINGE ON WHAT HAPPENS WITH THE UPPER TROUGH/LOW. THE NEW 02.12Z ECMWF KEEPS IT OVER INDIANA...LIKE SOME OF THE 02.12Z GFS ENSEMBLES. THE 02.12Z GFS HAS IT MORE PROGRESSIVE. EITHER SOLUTION LOOKS DRY FOR THE FORECAST AREA...BUT CLOUDS AND TEMPERATURES WOULD BE GREATLY AFFECTED...WITH THE FARTHER WEST SOLUTION HOLDING MORE CLOUDS AND COOLER AIR IN THE FORECAST AREA. SOME OF THE MOVEMENT OF THE UPPER TROUGH/LOW WILL DEPEND ON TROPICAL STORM LESLIE WHICH IS FORECAST TO MOVE THROUGH THE WESTERN ATLANTIC AND STRENGTHEN...LIKELY BLOCKING UP THE FLOW. REGARDING TEMPERATURES...THEY WILL BE ON THE COOL DOWN AS THE UPPER TROUGH FORMS. 850MB TEMPS FALL FROM THE 10-12C ON THURSDAY TO 6-8C ON SATURDAY. AS SUCH...HIGHS ARE ONLY FORECAST TO PERHAPS REACH 70 ON SATURDAY. SATURDAY NIGHT COULD BE QUITE COOL...DEPENDING ON CLOUDS...WITH HIGH PRESSURE POSSIBLY MOVING IN AT THE SURFACE FROM THE NORTHWEST. SOME SLIGHT REBOUND IN TEMPERATURES ARE ANTICIPATED ON SUNDAY. && .AVIATION...THIS AFTERNOON THROUGH MONDAY 1205 PM CDT SUN SEP 2 2012 MODEL SOUNDINGS SHOWING DIURNAL WARMING PRODUCING MIXING TO NEAR 850MB THIS AFTERNOON. WITH AN INCREASE OF LOWER LEVEL MOISTURE ON SOUTHEAST LOW LEVEL FLOW...A FEW VFR CUMULUS EXPECTED THIS AFTERNOON NEAR THE TOP OF THE MIXING...DISSIPATING LATE THIS AFTERNOON/EARLY THIS EVENING. APPROACHING TROUGH/COLD FRONT FROM THE NORTHERN PLAINS EXPECTED TO TRIGGER SCT SHRA/TSRA LATE THIS AFTERNOON/EVENING. MID/HIGH LEVEL DEBRIS CLOUDS FROM THIS CONVECTION TO THEN SPREAD ACROSS THE TAF SITES LATER THIS EVENING/OVERNIGHT INTO MON MORNING. MODELS INDICATING IFR FOG POTENTIAL AT BOTH KRST/KLSE TONIGHT. WITH THE BKN-OVC HIGHER LEVEL DEBRIS CLOUDS EXPECTED LATER TONIGHT ALONG WITH SOUTH TO SOUTHEAST GRADIENT WINDS IN THE 5-10KT RANGE...TONIGHT IS NOT SHAPING UP TO BE AN OVERLY FAVORABLE RADIATIONAL IFR FOG NIGHT. DID INCLUDE SOME 5SM BR AT BOTH KRST/KLSE IN THE 09-13Z TIME-FRAME TO ACCOUNT FOR THE MORE MOIST AIRMASS MOVING INTO THE AREA AHEAD OF THE TROUGH/FRONT. APPEARS CONVECTION IN THE FCST AREA WITH THE FRONT WILL MAINLY OCCUR AFTER 18Z MON. LATER TAF CYCLES WILL HAVE TO CONSIDER SHRA/TSRA CHANCES FOR MON AFTERNOON AND ANY NEED FOR VCSH/SHRA/TSRA/CB MENTIONS IN KRST/KLSE TAFS. AT THIS TIME IT APPEARS CONVECTION MON AFTERNOON WOULD BE SCT AND TAFS MAY ONLY NEED VCSH/VCTS FOR A PORTION OF THE 18-00Z MON TIME-FRAME AS THE FRONT/LINE OF SCT CONVECTION PASSES. && .ARX WATCHES/WARNINGS/ADVISORIES... 239 PM CDT SUN SEP 2 2012 WI...NONE. MN...NONE. IA...NONE. && $$ SHORT TERM...AJ LONG TERM...AJ AVIATION.....RRS
AREA FORECAST DISCUSSION
NWS LA CROSSE WI
617 AM CDT SUN SEP 2 2012 .SHORT TERM...TODAY THROUGH WEDNESDAY 300 AM CDT SUN SEP 2 2012 THE MAIN FOCUS IN THE SHORT TERM IS ON THE PRECIPITATION CHANCES MONDAY INTO WEDNESDAY. CURRENTLY...CLEAR SKIES ARE THE RULE THROUGHOUT MUCH OF THE REGION WITH THE CIRRUS FROM ISAAC DRIFTING EAST ACROSS SOUTHERN WISCONSIN/NORTHERN ILLINOIS AND THE NEXT SYSTEM STILL WELL OFF TO THE WEST IN EASTERN MONTANA. DRY LOW LEVEL AIR AND LIGHT WINDS ARE IN PLACE DUE TO A RIDGE OF HIGH PRESSURE THAT EXTENDS ACROSS SOUTHEAST CANADA THROUGH THE GREAT LAKES. ANOTHER PLEASANT DAY IS ON TAP FOR THE UPPER MISSISSIPPI RIVER VALLEY AS THE WESTERN PERIPHERY OF THE SURFACE RIDGE AXIS REMAINS ACROSS THE REGION WITH THE NEXT SYSTEM MOVING ACROSS THE DAKOTAS. WITH THIS FRONT APPROACHING FROM THE WEST AND THE RIDGE AXIS DRIFTING EAST...THE LOW LEVEL WIND FLOW WILL BECOME MORE SOUTHERLY AND WILL HELP TO USHER IN SOME SLIGHTLY WARMER AIR INTO THE REGION. SKIES WILL MAINLY BE SUNNY...THOUGH 02.00Z NAM/GFS BUFKIT SOUNDINGS ARE SHOWING SOME MOISTURE AROUND 4KFT THAT COULD LEAD TO SOME FAIR WEATHER CU DEVELOPING IN THE LATE MORNING/AFTERNOON HOURS. THE 02.00Z NAM/GFS/GEM/ECMWF ARE ALL IN DECENT AGREEMENT WITH THE TIMING OF THE FRONT AND CONVECTION ENTERING THE REGION EARLY MONDAY MORNING TOWARD DAYBREAK ACROSS WESTERN WISCONSIN AND SOUTHERN MINNESOTA/NORTHERN IOWA. THIS FRONT WILL MOVE THROUGH FROM MONDAY MORNING INTO THE EVENING AND DECAY AS IT TRACKS EAST. DESPITE THIS WEAKENING LOW LEVEL FORCING...A MID LEVEL SHORTWAVE TROUGH WILL BE PROPAGATING THROUGH AND PROVIDE ENOUGH LIFT TO WORK WITH THE UNCAPPED INSTABILITY AHEAD OF THE FRONT TO PRODUCE SOME SHOWERS AND THUNDERSTORMS...PARTICULARLY ACROSS WESTERN WISCONSIN IN THE AFTERNOON. THE 02.00Z NAM IS A LITTLE STRONGER WITH ITS 0-3KM SHEAR COMPARED TO THE 02.00Z GFS WHICH KEEPS THE BETTER SHEAR BEHIND THE FRONT. A FEW STRONG STORMS STILL CAN NOT BE RULED OUT GIVEN THE INSTABILITY...FORCING AND IDEAL TIMING OF THE FRONTAL PASSAGE IN THE MIDDLE OF THE AFTERNOON IN WESTERN WISCONSIN THOUGH IT SHOULD NOT BE A WIDESPREAD EVENT. AFTER THIS FEATURE PASSES...THE FORECAST BECOMES A BIT MORE MUDDLED GOING INTO MID WEEK AS DIFFERENCES ARISE BETWEEN THE GUIDANCE. MONDAY NIGHT INTO TUESDAY APPEARS TO BE THE BIGGEST CHALLENGE WITH THE 02.00Z NAM KEEPING THE LOW LEVEL MOISTURE TRANSPORT FIXED TO THE SOUTH WITH RIDGING OVERHEAD WHILE THE 02.00Z GFS IS STRONGER WITH IT AND SPREADS PRECIPITATION ACROSS THE REGION THROUGH MUCH OF THE DAY...WHICH IS LIKELY OVERDONE. STILL THINK THAT A MENTION OF PRECIPITATION IS WARRANTED ON TUESDAY...BUT CONFIDENCE IS NOT HIGH ENOUGH TO KEEP THE 40-50 PERCENT CHANCES IN THERE. THE NAM/GFS/ECMWF DO APPEAR TO DROP ANOTHER WEAK COLD FRONT DOWN ACROSS CENTRAL WISCONSIN TUESDAY NIGHT BEFORE THE MAIN SHOW ARRIVES ON WEDNESDAY AS THE COLD FRONT COMES THROUGH THAT WILL PUSH TEMPERATURES BACK DOWN TO NORMAL. THE ASSOCIATED DEEP MID LEVEL TROUGH WILL SPLIT A SHORTWAVE TROUGH OFF OF IT ON WEDNESDAY AS THE COLD FRONT COMES THROUGH. THIS APPEARS TO BE THE BEST COMBINATION OF FORCING...MOISTURE AVAILABILITY AND INSTABILITY OVER THE NEXT FEW DAYS AND THUS WARRANTS THE HIGHEST CHANCES FOR PRECIPITATION INTO THE AFTERNOON. .LONG TERM...WEDNESDAY NIGHT THROUGH SATURDAY 300 AM CDT SUN SEP 2 2012 COOLER AIR WILL MOVE INTO THE REGION BEHIND THE COLD FRONT THAT COMES THROUGH ON WEDNESDAY WITH NORTHWESTERLY FLOW ALOFT THAT WILL PERSIST INTO NEXT WEEKEND. TEMPERATURES WILL BE AT OR JUST BELOW SEASONAL VALUES WITH HIGHS IN THE LOW TO MID 70S. THE NEXT CHANCES FOR PRECIPITATION WILL COME ON FRIDAY AS A MID LEVEL TROUGH DIVES TO THE SOUTH ACROSS THE NORTHERN PLAINS/UPPER MISSISSIPPI RIVER VALLEY. THE 02.00Z ECMWF APPEARS TO BE THE ODD MODEL OUT AT THIS POINT WITH KEEPING A SECONDARY CLOSED LOW DROPPING DOWN ON SATURDAY WHILE THE 02.00Z GFS/GEM ARE FASTER WITH BUILDING A RIDGE IN BY SATURDAY MORNING. THE BETTER FORCING WITH THIS SYSTEM APPEARS TO GO TO THE SOUTH WHERE A SURFACE LOW SPINS UP ACROSS THE SOUTHERN PLAINS AND HEADS EAST TOWARD THE OHIO RIVER VALLEY. && .AVIATION...TODAY AND TONIGHT 617 AM CDT SUN SEP 2 2012 HIGH PRESSURE EXTENDING FROM LAKE SUPERIOR INTO SOUTHERN MN KEEPING SKIES MOSTLY CLEAR ACROSS THE AREA THIS MORNING. EAST FLOW AND REMNANTS OF ISAAC OVER IL BRINGING A FEW MVFR LEVEL STRATOCUMULUS INTO FAR SOUTHERN WI/NORTHEAST IA. RAP MODEL INDICATING SOME INCREASE IN LOWER LEVEL MOISTURE WHICH MAY PRODUCE FEW-SCT020-025 AS FAR NORTH AS KLSE THROUGH THIS MORNING. AS SUCH...ADDED FEW022 IN THE KLSE FROM 13-17Z. MODEL SOUNDINGS THEN SHOW MIXING/DRYING THROUGH THE LOWEST 3-4KFT DISSIPATING THIS CLOUD. FOR THE REST OF THE DAY...MAY SEE A FEW DAYTIME HEATING CUMULUS FLOATING AROUND WITH BASES IN THE 4-5KFT RANGE...THEN DISSIPATING BY SUNSET. NEXT CONCERN WILL BE INCOMING COLD FRONT FROM MN LATE TONIGHT. EXPECTING AN INCREASE IN ALTOCUMULUS WITH BASES AOA 12KFT IN ADVANCE OF THE FRONT REACHING THE KRST/KLSE TAF SITES AFTER 06Z. ANY SHRA/TS ACTIVITY WITH THE FRONT EXPECTED TO REMAIN NORTHWEST OF THE TAF SITES THROUGH 12Z. SOME MODEL GUIDANCE SUGGESTING VALLEY FOG POTENTIAL AT KLSE TOWARD MORNING...BUT FEEL THIS IS OVERDONE AND WILL NOT BE REALIZED DUE TO AN INCREASE IN MID-CLOUD WHICH WILL INHIBIT NEEDED RADIATIONAL COOLING. ANOTHER NEGATIVE FACTOR IN FOG FORMATION WILL BE INCREASING PRESSURE GRADIENT/STIRRING WINDS IN ADVANCE OF THE COLD FRONT. WILL HAVE TO WATCH SHRA/TS POTENTIAL FOR MONDAY. APPEARS RIGHT NOW THAT THE HIGHEST POTENTIAL FOR CONVECTION WILL BE NORTH OF TH TAF SITES...BUT NEEDS TO BE WATCHED CLOSELY. WILL PASS THIS CONCERN ONTO THE DAYSHIFT FOR FURTHER ASSESSMENT. && .ARX WATCHES/WARNINGS/ADVISORIES... 300 AM CDT SUN SEP 2 2012 WI...NONE. MN...NONE. IA...NONE. && $$ SHORT TERM...HALBACH LONG TERM...HALBACH AVIATION...DAS
AREA FORECAST DISCUSSION
NWS MILWAUKEE/SULLIVAN WI
1130 PM CDT SAT SEP 1 2012 .UPDATE... DRY AIR FROM THE NORTHEAST HAS ERODED THE PRECIPITATION ACROSS FAR SOUTHEAST WISCONSIN AND SOUTHERN LAKE MICHIGAN. THE LATEST NAM AND THE HRRR KEEP US DRY THROUGH THE NIGHT...WITH SOME LIGHT PRECIPITATION SUNDAY MORNING BEFORE NOON.. WILL TRIM BACK THE CHANCES OF RAIN TONIGHT A LITTLE WITH ONLY THE FAR SOUTHEAST TIP IN A SLIGHT CHANCE OF SHOWERS. && .AVIATION/06Z TAFS/... MVFR CIGS SHOULD EXPAND ESPECIALLY SOUTHEAST. SOME MVFR FOG ALSO EXPECTED WITH THE HIGHER DEWPOINTS SOUTHEAST AND FAR SOUTH CENTRAL. THE LATEST NAM AND THE HRRR KEEP US DRY THROUGH THE NIGHT. LOW WILL TRACK ACROSS SOUTHERN ILLINOIS TONIGHT THEN REACH FAR SOUTHERN INDIANA SUNDAY EVENING. && .PREV DISCUSSION... /ISSUED 302 PM CDT SAT SEP 1 2012/ TONIGHT - CONFIDENCE...MEDIUM FAR SOUTHERN AREAS STILL VULNERABLE TO NORTHERN PERIPHERY OF ISAAC. CONVECTION HAS DEVELOPED NORTH OF THE MAIN RAIN SHIELD IN BETTER FRONTOGENETICAL FORCING ZONE AND HAS TRENDED NW A BIT TOWARDS SRN TIER OF COUNTIES. 12Z 850 ANALYSIS SHOWED 3C DEW POINT AT GRB WITH STEADY NE WIND WITH 16C DEW POINT IN CENTRAL IL WITH A SOUTH WIND AT 30 KNOTS. SO FAIR AMOUNT OF LOWER LEVEL CONVERGENCE WITH LIMITED ELEVATED INSTABILITY. WILL KEEP HIGHEST POPS IN THE SOUTHERN COUNTIES THROUGH 00Z. AXIS OF MAIN RAIN AREA FURTHER SOUTH OF THE CONVECTIVE BAND IS BREAKING UP WITH A SUBTLE SHIFT TO THE NORTH. UPPER LOW IN CENTRAL MO WILL BE TRACKING DUE EAST WITH LOW LEVEL EASTERLY FLOW MAINTAINING A PRETTY DECENT DRY FEED. LOW LEVEL RH PROGS DO SHOW A BUMP NORTH IN THE BETTER 925-850 RH AS THE NIGHT WEARS ON. CLOUDS AND EAST WINDS WILL LIKELY KEEP TEMPS FROM FALLING AS MUCH AS IN THE NORTHERN CWA WHERE MORE IN THE WAY OF SCT THIN CIRRUS EXPECTED. SUNDAY - CONFIDENCE...MEDIUM UPPER LOW TRACKS FROM SRN IL TOWARDS KENTUCKY WITH 500 MILLIBAR RIDGE AXIS TAKING HOLD DURING THE AFTERNOON. APPEARS BEST CHANCE OF ANY SHRA WILL BE IN THE MORNING AND AGAIN IN THE FAR SOUTH BEFORE INFLUENCE OF CIRCULATION SHIFTS AWAY. LOW LEVEL RH PROGS SUGGEST IMPROVEMENT IN THE AFTERNOON AS 90 PCT PLUS LOWERS. SUNDAY NIGHT...FORECAST CONFIDENCE IS HIGH. A NARROW HIGH PRESSURE RIDGE SETTLES OVER THE AREA...EXTENDING ACROSS THE GREAT LAKES FROM ITS PARENT HIGH OVER NEW ENGLAND. THE LOW PRESSURE SYSTEM THAT WAS ISAAC HAS WEAKENED AND MOVED TO THE OHIO VALLEY. SO QUIET THIS PERIOD. MONDAY AND TUESDAY...FORECAST CONFIDENCE IS MEDIUM. NOW THAT THE UPPER LOW ASSOCIATED WITH ISAAC HAS OPENED UP AND PUSHED INTO THE SOUTHEAST U.S...THE MID LEVEL FLOW OVER THE UPPER MIDWEST BECOMES FAST AND ZONAL. QUEUE THE SHORT WAVE TRAIN. THE FIRST OF THESE PUSHES IN TO OUR NORTH WITH AN ATTENDANT WEAK...AND WEAKENING...COLD FRONT. THIS COULD SET OFF SOME SHOWERS AND STORMS IN THE WEST MONDAY AFTERNOON. THE DAY 3 SPC OUTLOOK HAS THE SLIGHT RISK PUSHING INTO MUCH OF OUR NORTHERN TIER ON MONDAY. THIS LOOKS TOO AGGRESSIVE GIVEN THE TIMING...THE AVAILABLE FORCING AND MASS FIELDS. I SUSPECT AN ADJUSTMENT FARTHER NORTH AND WEST IS LIKELY WHEN IT BECOMES THE DAY 2 OUTLOOK...OR DROPPED ENTIRELY. ANOTHER SHORT WAVE WITH BETTER DEFINITION AND A SHARPER TROF ARRIVES LATE MONDAY NIGHT AND TUESDAY. THIS SHOULD BRING A HIGHER CHANCE OF SHOWERS AND STORMS. SOUNDINGS SHOW PLENTY OF AVAILABLE CAPE WITH THE MID LEVELS COOLING AND SURFACE TEMPS STILL HITTING THE MID 80S. WEDNESDAY...FORECAST CONFIDENCE IS MEDIUM TO HIGH. ALL THE MODELS AGREE ON A MUCH STRONGER SHORT WAVE DIGGING INTO THE GREAT LAKES ON WEDNESDAY. SHOWERS AND STORMS LIKELY MOST PLACES. CAPE VALUES SHOULD CLOSE IN ON THE 1500-2000J/KG RANGE. TIMING IS GOOD WITH A STRONG COLD FRONT PUSHING IN DURING THE LATE AFTERNOON. DEEP LAYER SHEAR ON THE ORDER OF 30 TO 40KTS. THURSDAY THROUGH FRIDAY...FORECAST CONFIDENCE IS LOW TO MEDIUM. THINGS QUIET DOWN...BUT THE UPPER FLOW REMAINS ZONAL AND FAST WITH HEIGHTS GRADUALLY FALLING AS A LARGE SCALE...EAST-WEST TROF SLOWLY DROPS OUT OF SOUTHERN CANADA...ROTATING AROUND A HUGE UPPER LOW OVER HUDSON BAY CANADA. WE/LL BE SUSCEPTIBLE TO MORE WEAK SHORT WAVE ENERGY PRODUCING A CHANCE FOR SHOWERS FROM TIME TO TIME. BUT NAILING THAT DOWN THIS FAR OUT IS NEAR IMPOSSIBLE. AVIATION/00Z TAFS/...DECENT CIRCULATION IN CENTRAL MO PER WATER VAPOR IMAGERY. 1008MB SURFACE LOW. MID/HIGH CLOUDS WRAPPING INTO SRN WI ON NORTHERN PERIPHERY OF THIS CIRCULATION. LOW LEVEL EASTERLY FLOW HELPING TO KEEP LOWER LAYERS DRY FOR NOW. LOW LEVEL RH PROGS/BUFKIT/MOS ALL SUGGEST POTENTIAL FOR MVFR CONDITIONS SPREADING NORTH LATER TONIGHT INTO SUNDAY MORNING. WILL MAINTAIN TREND OF PRIOR TAFS IN LEANING IN THIS DIRECTION. SURFACE UPPER LOW WILL SLOWLY SHIFT TO SRN IL VICINITY BY MIDDAY SUNDAY. LOW LEVEL EASTERLY PERSISTS. MARINE...WILL RETAIN SMALL CRAFT FOR THE SOUTHERN TIER AS WINDS REMAIN GUSTY WITH THE TIGHTER PRESSURE GRADIENT ASSOCIATED WITH REMNANTS OF HURRICANE ISAAC. DECENT FETCH WILL ALLOW FOR HIGHER WAVE HEIGHTS. CORRESPONDING THREAT FOR RIP CURRENTS. && .MKX WATCHES/WARNINGS/ADVISORIES... WI...NONE. LM...SMALL CRAFT ADVISORY UNTIL 4 PM CDT SUNDAY FOR LMZ646. && $$ UPDATE...HENTZ TONIGHT/SUNDAY AND AVIATION/MARINE...COLLAR SUNDAY NIGHT THROUGH SATURDAY...DAVIS
AREA FORECAST DISCUSSION...CORRECTED
NWS PHOENIX AZ
300 AM MST TUE SEP 4 2012 .UPDATE...UPDATED AVIATION SECTION... .SYNOPSIS... HIGH PRESSURE ALOFT WILL REMAIN CENTERED OVER OR NEAR NEW MEXICO THROUGH MUCH OF THE UPCOMING WEEK. VERY MOIST AND MODERATELY UNSTABLE AIR OVER THE AREA WILL LEAD TO STORM CHANCES ACROSS THE REGION FOR MUCH OF THIS WEEK. LOCALLY HEAVY RAINFALL AND STRONG WINDS ARE LIKELY WITH THE STRONGER STORMS. && .DISCUSSION... STORM ACTIVITY FOR THE NIGHT CONTINUES OVER FAR SOUTHEAST ARIZONA BUT IS NOT WIDESPREAD. MADE UPDATES TO THE FORECAST TO DROP THE POPS FROM MOST AREAS. A STRAY ECHO OR TWO LIE CLOSE ENOUGH TO SOUTHWEST MARICOPA/NORTHWEST PINAL/SOUTHERN GILA COUNTIES THAT A SLIGHT CHANCE WAS LEFT FOR THIS EVENING...GOING TO ZERO FOR THE OVERNIGHT HOURS. DEEPER MOISTURE IS PROGGED TO SHIFT OVER SOUTHEAST ARIZONA TUESDAY FOR A BETTER CHANCE OF STORMS OVER THE CENTRAL DESERTS. AS USUAL THOUGH...FORECAST SOUNDINGS SUGGEST THAT OUTFLOWS WILL BE NECESSARY TO OVERCOME SOME CONVECTIVE INHIBITION. SIMILAR SITUATION WEDNESDAY. SOUTHEASTERLY STEERING FLOW WEDNESDAY MAY BE BEST OPPORTUNITY FOR PHOENIX AREA. MEANWHILE...LOWER LEVELS OVER SOUTHEAST CALIFORNIA START TO LOSE MOISTURE. && .PREVIOUS DISCUSSION ISSUED 300 PM... LATEST RAP ANALYZED A DIFFUSE TROUGH EXTENDING FROM SOUTHERN NM TO HERMOSILLO MEXICO...THOUGH THIS IS DIFFICULT TO IDENTIFY ON WV IMAGERY. STRONG STORMS HAVE DEVELOPED IN THE DIFLUENT REGION BETWEEN THIS TROUGH AND AN ANTICYCLONE CENTERED NEAR THE WHITE MOUNTAINS. FURTHER NORTH ACROSS THE MOGOLLON RIM...OROGRAPHICALLY-INDUCED SHOWERS AND THUNDERSTORMS HAVE ALSO FORMED BUT CONTINUE TO DRIFT NORTHEASTWARD TOWARDS THE CO PLATEAU WITHIN A 10 KT MEAN LAYER FLOW. EARLIER MOISTURE SURGE ALONG THE GOC AND ACROSS YUMA AND THE IMPERIAL VALLEY YIELDED HEAT INDICES BETWEEN 110 AND 115 DEGREES...BUT HAVE SINCE LOWERED AS THE ATMOSPHERE MIXES OUT. LATEST MESOANALYSIS SHOWS MODERATELY STRONG CONVECTIVE INHIBITION ACROSS MUCH OF THE FORECAST AREA...LARGELY DUE TO A RIDGE AND THE ASSOCIATED WARM/DRY AIR IN THE 800-700 MB LAYER. MODEL SOUNDINGS INDICATE THAT THIS LAYER WILL MOISTEN ACROSS WESTERN AZ THIS AFTERNOON...WHICH WILL HELP TO ERODE THE CIN AND INITIATE ISOLATED CONVECTION. NMM-B BASED WRF FROM UNIV OF AZ APPEARS TO HAVE THE BEST HANDLE ON THE SHORT-TERM EVOLUTION AND SUGGESTS STORMS WILL FIRE ACROSS YUMA AND LA PAZ COUNTIES THIS AFTERNOON. ISOLATED ACTIVITY IN THE IMPERIAL VALLEY ALSO CANNOT BE RULED OUT...GIVEN THE SOUTHWESTERLY STEERING FLOW AND PRESENCE OF CB/TCU ON VISIBLE SATELLITE ALONG THE BAJA SPINE. ACROSS THE PHOENIX METRO AREA...THE MAIN IMPACT APPEARS TO BE THE POTENTIAL BLOWING DUST FROM THUNDERSTORMS TO THE SOUTH...THOUGH POPS REMAIN 5 TO 10 PERCENT ABOVE THE CLIMATOLOGICAL AVERAGE. IN THE SHORT TERM (MONDAY-WEDNESDAY)...EXPECT A DAY TO DAY INCREASE IN STORM ACTIVITY...ESPECIALLY OVER AZ PORTION OF THE CWA. VERY MOIST AIR MASS CURRENTLY EXISTS OVER NORTHWEST MEXICO. SYNOPTIC PATTERN...WITH RATHER STRONG TROUGH OF LOW PRESSURE MOVING EAST ACROSS SOUTH-CENTRAL CANADA WHILE A TROPICAL DISTURBANCE (NOW TS JOHN) MOVES WEST JUST OFF THE SOUTHERN END OF BAJA CALIFORNIA...CERTAINLY SUPPORTS A MOISTURE INCREASE OVER OUR AREA...AND THE GFS/ECMWF/NAM CERTAINLY AGREE THE ATMOSPHERE WILL MOISTEN SIGNIFICANTLY DURING THE NEXT 36 HRS. WITH ATMOSPHERIC MOISTENING CONTINUING ON TUESDAY (ANOMALOUSLY HIGH PRECIPITABLE WATER NEAR 2" BY THEN) AND MORE DIFLUENT UPPER LEVEL FLOW OVER SOUTHEAST AZ BY TUESDAY AFTN...PRECIP CHANCE WILL BE A BIT GREATER TUESDAY EVENING...ESPECIALLY OVER SOUTH-CENTRAL AZ. VERY MOIST AND MODERATELY UNSTABLE ATMOSPHERE REMAINS IN PLACE ON WEDNESDAY...AND PRECIP CHANCES WILL BE ENHANCED AS A WEAK WEATHER DISTURBANCE MOVES WEST ACROSS SONORA. WITH SUCH HIGH ATMOSPHERIC MOISTURE CONTENT...DECENT CAPE...AND WEAK STEERING FLOW...LOCALLY HEAVY RAINFALL CAN BE EXPECTED...THOUGH STRONG/DAMAGING WINDS WILL ALSO BE POSSIBLE. IN THE EXTENDED PERIOD(THURSDAY-SUNDAY)...NUMERICAL MODELS INDICATE ATMOSPHERE WILL REMAIN ANOMALOUSLY MOIST AND MODERATELY UNSTABLE WHILE WEAK WEATHER DISTURBANCE CONTINUE TO AFFECT THE DESERT SOUTHWEST. WENT WITH SLIGHT CHANCE POPS DURING THE LATE AFTN/EVENING HOURS FOR SOUTH-CENTRAL AZ EACH DAY...BUT WOULD NOT BE SURPRISED IF PRECIP CHANCES WILL ACTUALLY BE SOMEWHAT HIGHER THAN CURRENTLY PORTRAYED. && .AVIATION... SOUTH-CENTRAL ARIZONA...INCLUDING KPHX...KIWA...AND KSDL... ISOLATED THUNDERSTORMS THAT ARE NOW AFFECTING THE PHOENIX AREA ARE EXPECTED TO DISSIPATE BY 400 AM. THESE STORMS ARE CURRENTLY TURNING THE WINDS TO AN EASTERLY TO SOUTHEASTERLY DIRECTION. LIGHTER WINDS ARE EXPECTED TO PREVAIL AFTER 400 AM WITH WESTERLY WINDS LIKELY TO RETURN BY THIS AFTERNOON. SOUTHEAST CA AND SOUTHWEST AZ...INCLUDING KIPL AND KBLH... NO THUNDERSTORM ACTIVITY EXPECTED OVER FAR SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA THE REST OF THE NIGHT...THOUGH A STRAY LIGHT SHOWER CANT BE RULED OUT. OTHERWISE JUST SOME MINOR DEBRIS CLOUDS AND WINDS FAVORING SOUTH AND SOUTHEAST DIRECTIONS. STORM ACTIVITY TUESDAY AFTERNOON MAY IMPACT TAF SITES BUT TOO LOW A PROBABILITY TO MENTION IN TAFS AT THIS POINT. AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS. && .FIRE WEATHER... THURSDAY THROUGH MONDAY... SIGNIFICANT MONSOON MOISTURE WILL COVER THE REGION. A SLIGHT CHANCE OF AFTERNOON AND EVENING THUNDERSTORMS WILL CONTINUE MAINLY OVER SOUTH CENTRAL ARIZONA...PARTICULARLY MOUNTAINS. MINIMUM RELATIVE HUMIDITIES WILL RANGE FROM 20 TO 25 PERCENT...EXCEPT 15 TO 20 PERCENT IN IN SOUTHEAST CALIFORNIA. RELATIVELY LIGHT WINDS ARE EXPECTED. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...NONE. CA...NONE. && $$ VISIT US ON FACEBOOK...TWITTER...AND AT WEATHER.GOV/PHOENIX DISCUSSION...AJ PREVIOUS DISCUSSION...HIRSCH/DG AVIATION...PERCHA/AJ FIRE WEATHER...VASQUEZ
AREA FORECAST DISCUSSION...CORRECTED
NWS PHOENIX AZ
1010 PM MST MON SEP 3 2012 .SYNOPSIS... HIGH PRESSURE ALOFT WILL REMAIN CENTERED OVER OR NEAR NEW MEXICO THROUGH MUCH OF THE UPCOMING WEEK. VERY MOIST AND MODERATELY UNSTABLE AIR OVER THE AREA WILL LEAD TO STORM CHANCES ACROSS THE REGION FOR MUCH OF THIS WEEK. LOCALLY HEAVY RAINFALL AND STRONG WINDS ARE LIKELY WITH THE STRONGER STORMS. && .DISCUSSION... STORM ACTIVITY FOR THE NIGHT CONTINUES OVER FAR SOUTHEAST ARIZONA BUT IS NOT WIDESPREAD. MADE UPDATES TO THE FORECAST TO DROP THE POPS FROM MOST AREAS. A STRAY ECHO OR TWO LIE CLOSE ENOUGH TO SOUTHWEST MARICOPA/NORTHWEST PINAL/SOUTHERN GILA COUNTIES THAT A SLIGHT CHANCE WAS LEFT FOR THIS EVENING...GOING TO ZERO FOR THE OVERNIGHT HOURS. DEEPER MOISTURE IS PROGGED TO SHIFT OVER SOUTHEAST ARIZONA TUESDAY FOR A BETTER CHANCE OF STORMS OVER THE CENTRAL DESERTS. AS USUAL THOUGH...FORECAST SOUNDINGS SUGGEST THAT OUTFLOWS WILL BE NECESSARY TO OVERCOME SOME CONVECTIVE INHIBITION. SIMILAR SITUATION WEDNESDAY. SOUTHEASTERLY STEERING FLOW WEDNESDAY MAY BE BEST OPPORTUNITY FOR PHOENIX AREA. MEANWHILE...LOWER LEVELS OVER SOUTHEAST CALIFORNIA START TO LOSE MOISTURE. && .PREVIOUS DISCUSSION ISSUED 300 PM... LATEST RAP ANALYZED A DIFFUSE TROUGH EXTENDING FROM SOUTHERN NM TO HERMOSILLO MEXICO...THOUGH THIS IS DIFFICULT TO IDENTIFY ON WV IMAGERY. STRONG STORMS HAVE DEVELOPED IN THE DIFLUENT REGION BETWEEN THIS TROUGH AND AN ANTICYCLONE CENTERED NEAR THE WHITE MOUNTAINS. FURTHER NORTH ACROSS THE MOGOLLON RIM...OROGRAPHICALLY-INDUCED SHOWERS AND THUNDERSTORMS HAVE ALSO FORMED BUT CONTINUE TO DRIFT NORTHEASTWARD TOWARDS THE CO PLATEAU WITHIN A 10 KT MEAN LAYER FLOW. EARLIER MOISTURE SURGE ALONG THE GOC AND ACROSS YUMA AND THE IMPERIAL VALLEY YIELDED HEAT INDICES BETWEEN 110 AND 115 DEGREES...BUT HAVE SINCE LOWERED AS THE ATMOSPHERE MIXES OUT. LATEST MESOANALYSIS SHOWS MODERATELY STRONG CONVECTIVE INHIBITION ACROSS MUCH OF THE FORECAST AREA...LARGELY DUE TO A RIDGE AND THE ASSOCIATED WARM/DRY AIR IN THE 800-700 MB LAYER. MODEL SOUNDINGS INDICATE THAT THIS LAYER WILL MOISTEN ACROSS WESTERN AZ THIS AFTERNOON...WHICH WILL HELP TO ERODE THE CIN AND INITIATE ISOLATED CONVECTION. NMM-B BASED WRF FROM UNIV OF AZ APPEARS TO HAVE THE BEST HANDLE ON THE SHORT-TERM EVOLUTION AND SUGGESTS STORMS WILL FIRE ACROSS YUMA AND LA PAZ COUNTIES THIS AFTERNOON. ISOLATED ACTIVITY IN THE IMPERIAL VALLEY ALSO CANNOT BE RULED OUT...GIVEN THE SOUTHWESTERLY STEERING FLOW AND PRESENCE OF CB/TCU ON VISIBLE SATELLITE ALONG THE BAJA SPINE. ACROSS THE PHOENIX METRO AREA...THE MAIN IMPACT APPEARS TO BE THE POTENTIAL BLOWING DUST FROM THUNDERSTORMS TO THE SOUTH...THOUGH POPS REMAIN 5 TO 10 PERCENT ABOVE THE CLIMATOLOGICAL AVERAGE. IN THE SHORT TERM (MONDAY-WEDNESDAY)...EXPECT A DAY TO DAY INCREASE IN STORM ACTIVITY...ESPECIALLY OVER AZ PORTION OF THE CWA. VERY MOIST AIR MASS CURRENTLY EXISTS OVER NORTHWEST MEXICO. SYNOPTIC PATTERN...WITH RATHER STRONG TROUGH OF LOW PRESSURE MOVING EAST ACROSS SOUTH-CENTRAL CANADA WHILE A TROPICAL DISTURBANCE (NOW TS JOHN) MOVES WEST JUST OFF THE SOUTHERN END OF BAJA CALIFORNIA...CERTAINLY SUPPORTS A MOISTURE INCREASE OVER OUR AREA...AND THE GFS/ECMWF/NAM CERTAINLY AGREE THE ATMOSPHERE WILL MOISTEN SIGNIFICANTLY DURING THE NEXT 36 HRS. WITH ATMOSPHERIC MOISTENING CONTINUING ON TUESDAY (ANOMALOUSLY HIGH PRECIPITABLE WATER NEAR 2" BY THEN) AND MORE DIFLUENT UPPER LEVEL FLOW OVER SOUTHEAST AZ BY TUESDAY AFTN...PRECIP CHANCE WILL BE A BIT GREATER TUESDAY EVENING...ESPECIALLY OVER SOUTH-CENTRAL AZ. VERY MOIST AND MODERATELY UNSTABLE ATMOSPHERE REMAINS IN PLACE ON WEDNESDAY...AND PRECIP CHANCES WILL BE ENHANCED AS A WEAK WEATHER DISTURBANCE MOVES WEST ACROSS SONORA. WITH SUCH HIGH ATMOSPHERIC MOISTURE CONTENT...DECENT CAPE...AND WEAK STEERING FLOW...LOCALLY HEAVY RAINFALL CAN BE EXPECTED...THOUGH STRONG/DAMAGING WINDS WILL ALSO BE POSSIBLE. IN THE EXTENDED PERIOD(THURSDAY-SUNDAY)...NUMERICAL MODELS INDICATE ATMOSPHERE WILL REMAIN ANOMALOUSLY MOIST AND MODERATELY UNSTABLE WHILE WEAK WEATHER DISTURBANCE CONTINUE TO AFFECT THE DESERT SOUTHWEST. WENT WITH SLIGHT CHANCE POPS DURING THE LATE AFTN/EVENING HOURS FOR SOUTH-CENTRAL AZ EACH DAY...BUT WOULD NOT BE SURPRISED IF PRECIP CHANCES WILL ACTUALLY BE SOMEWHAT HIGHER THAN CURRENTLY PORTRAYED. && .AVIATION... SOUTH-CENTRAL ARIZONA...INCLUDING KPHX...KIWA...AND KSDL... NO THUNDERSTORM ACTIVITY EXPECTED FOR THE PHOENIX AREA THE REST OF THE NIGHT. A WEAK OUTFLOW FROM SOUTHEAST CALIFORNIA MAY AFFECT KIWA BUT KPHX AND KSDL EXPECTED TO STAY WEST. OTHERWISE EXPECT WEST WINDS TO CONTINUE THROUGH AT LEAST 08Z BEFORE BECOMING LIGHT AND VARIABLE WITH JUST SOME MINOR DEBRIS CLOUDS. BETTER CHANCE OF AT LEAST SOME OUTFLOWS REACHING THE METRO AREA TUESDAY EVENING. SOUTHEAST CA AND SOUTHWEST AZ...INCLUDING KIPL AND KBLH... NO THUNDERSTORM ACTIVITY EXPECTED OVER FAR SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA THE REST OF THE NIGHT...THOUGH A STRAY LIGHT SHOWER CANT BE RULED OUT. OTHERWISE JUST SOME MINOR DEBRIS CLOUDS AND WINDS FAVORING SOUTH AND SOUTHEAST DIRECTIONS. STORM ACTIVITY TUESDAY AFTERNOON MAY IMPACT TAF SITES BUT TOO LOW A PROBABILITY TO MENTION IN TAFS AT THIS POINT. AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS. && .FIRE WEATHER... THURSDAY THROUGH MONDAY... SIGNIFICANT MONSOON MOISTURE WILL COVER THE REGION. A SLIGHT CHANCE OF AFTERNOON AND EVENING THUNDERSTORMS WILL CONTINUE MAINLY OVER SOUTH CENTRAL ARIZONA...PARTICULARLY MOUNTAINS. MINIMUM RELATIVE HUMIDITIES WILL RANGE FROM 20 TO 25 PERCENT...EXCEPT 15 TO 20 PERCENT IN IN SOUTHEAST CALIFORNIA. RELATIVELY LIGHT WINDS ARE EXPECTED. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...NONE. CA...NONE. && $$ VISIT US ON FACEBOOK...TWITTER...AND AT WEATHER.GOV/PHOENIX DISCUSSION...AJ PREVIOUS DISCUSSION...HIRSCH/DG AVIATION...AJ FIRE WEATHER...VASQUEZ
AREA FORECAST DISCUSSION
NWS GRAND JUNCTION CO
1055 PM MDT MON SEP 3 2012 .SHORT TERM...(TODAY THROUGH TUESDAY NIGHT) ISSUED AT 252 PM MDT MON SEP 3 2012 JET STREAM REMAINS OVERHEAD WITH STRONGEST JET STREAK HAVING MOVED WELL EAST OVER SRN MN/NRN IA. CONVECTION CONTINUES TO FAVOR THE ROAN/TAVAPUTS THIS AFTN IN RESPONSE TO DISTURBANCES MOVING THROUGH MEAN FLOW AND ALSO FAVORABLE OROGRAPHICS. POT VORT FIELDS ALSO FAVOR THIS AREA SO EVENTS PLAYING OUT AS EXPECTED. AS HAS BEEN THE CASE LAST FEW DAYS...BIGGEST CONCERN WILL BE GUSTY OUTFLOW WINDS REACHING 40 TO 45 MPH AND ALSO SOME SMALL HAIL. DID EXPECT MORE CONVECTION DOWN SOUTH SINCE AVAILABLE PRECIP TABLE WATER IS MUCH HIGHER. BELIEVE CONVECTION IS LIMITED FOR TWO REASONS. FIRST...STEERING FLOW IS ALMOST FROM DUE WEST WHICH IS NOT THE BEST DIRECTION FOR OROGRAPHICALLY INDUCED CONVECTION. SECOND...AND MORE IMPORTANTLY...THERE IS NO REAL TRIGGER TO KICK OFF SOME LIFT LIKE THERE IS UP NORTH. SO FOR THE REMAINDER OF THE AFTERNOON...SOME MINOR DISCREPANCIES HAVE CROPPED UP BETWEEN MODELS BUT HRRR IS DOING A REMARKABLE JOB NAILING DOWN WHERE CONVECTION HAS AND IS OCCURRING. LATEST HRRR GUIDANCE SUGGESTS SHOWERS AND STORMS WILL DIE DOWN BY 6PM WITH VERY LITTLE IN THE WAY OF PRECIPITATION AFTER THAT. THIS DOES MAKE SENSE AS MODELS ALSO CONTINUE TO DRY OUT ATMOSPHERE. FORECAST FOLLOWS SUIT THOUGH NOT SO DRAMATICALLY WITH CONVECTION ENDING AROUND SUNSET. CLEAR SKIES WILL BE DOMINANT OVERNIGHT ALLOWING LOW TEMPS TO BE A BIT COOLER THAN SEEN THE LAST FEW DAYS THOUGH STILL A DEGREE OR TWO ABOVE NORMAL. ON TUESDAY ZONAL FLOW SETS UP FROM THE H3 LEVEL TO H7 WHICH EFFECTIVELY CUTS OFF THE FLOW OF MOISTURE FROM THE SOUTH. THE MUCH TOUTED DRIER AIR WILL FINALLY ARRIVE IF THE NAM12/GFS40 ARE TO BE BELIEVED WHICH WILL GREATLY INHIBIT CONVECTION. KEPT POPS AS THEY WERE WITH SOME VERY ISOLD SHOWERS AND STORMS POSSIBLE OVER SAN JUANS AND TO SOME EXTENT CENTRAL MOUNTAINS THOUGH TREND IS TO KEEP LOWERING POP AND QPF AMTS AND COVERAGE. THE REMAINDER OF THE FORECAST AREA WILL SEE PLENTY OF SUNSHINE WITH SEASONAL TEMPERATURES EXPECTED. OVERNIGHT...CLEAR SKIES EXPECTED WITH NEAR NORMAL LOW TEMPERATURES. .LONG TERM...(WEDNESDAY THROUGH SUNDAY) ISSUED AT 252 PM MDT MON SEP 3 2012 SOMEWHAT ACTIVE NORTHERN STREAM THE LAST HALF OF THE WEEK AS SHORTWAVES ROTATING AROUND A CENTRAL CANADA LOW DROP INTO THE NRN TIER STATES. FIRST SHORTWAVE MOVES INTO THE UPPER MIDWEST ON WEDNESDAY... A SECOND DROPS DOWN ACROSS MT WED NIGHT...AND A THIRD AND STRONGER ONE CLIPS NE CO LATE FRI. A RATHER WEAK WESTERLY UPPER JET OVERHEAD ON WED STRENGTHENS THU-FRI AS THAT THIRD WAVE APPROACHES...AND MAY RESULT IN STRONGER SURFACE WINDS ACROSS NE UT/NW CO. BROAD HIGH PRESSURE DOMINATES THE SOUTHWEST STATES AND FOUR CORNERS AND WILL BE MAIN INFLUENCE ON SE UT/SW CO. MODELS KEEP ENOUGH MOISTURE PRESENT FOR ISOLATED TO PERHAPS SCATTERED THUNDERSTORMS MAINLY OVER THE CENTRAL AND SOUTHERN MTNS THURSDAY. THE SOUTHWEST UPPER HIGH BUILDS NORTHWEST INTO THE GREAT BASIN FRI AND SAT AND SHOULD RESULT IN DRIER NW FLOW FOR OUR FORECAST AREA THIS WEEKEND. MODELS SHOW A PACIFIC TROUGH REACHING THE NORTHWEST COAST BY MONDAY...SHIFTING THE HIGH EAST AND ALLOWING MONSOONAL MOISTURE TO RETURN NEXT MONDAY. CONFIDENCE BELOW AVERAGE ON THIS... HOWEVER...GIVEN MODEL AND RUN-TO-RUN INCONSISTENCIES...SO WILL STAY CONSERVATIVE WITH POPS FOR MONDAY. && .AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT) ISSUED AT 1054 PM MDT MON SEP 3 2012 DRY WEST TO NORTHWEST FLOW WILL KEEP VFR CONDITIONS IN PLACE ACROSS THE REGION THROUGH LATE TUESDAY NIGHT. && .FIRE WEATHER... ISSUED AT 252 PM MDT MON SEP 3 2012 WIND IN GENERAL LOOKS TO REMAIN JUST BELOW CRITICAL LEVELS ACROSS DAGGETT COUNTY AND NORTHERN DUCHESNE COUNTY /FWX ZONES 481 AND 485/ IN NE UT AND MOFFAT COUNTY /FWX ZONE 200/ IN NW CO TUESDAY AFTERNOON. WIND GUSTS 20-25 MPH ARE PROBABLE DURING PEAK HEATING TUESDAY AFTERNOON. WHILE LOCAL AREAS MAY SEE CRITICAL CONDITIONS BELOW 8000-9000 FT DUE TO WIND GUSTS AND LOW RH...DO NOT THINK AREAL COVERAGE OR DURATION IS ENOUGH TO WARRANT A FIRE WEATHER HIGHLIGHT FOR NE UT/NW CO AT THIS TIME. SOME CONCERN THAT WIND GUSTS COULD APPROACH/EXCEED CRITICAL LEVELS ACROSS NE UT/NW CO ON THU AS A DISTURBANCE APPROACHING FROM THE NW BEGINS TO STRENGTHEN WINDS ALOFT...WHICH COULD THEN MIX DOWN DURING PEAK HEATING. HOWEVER...IT APPEARS THAT HUMIDITY WILL REMAIN ABOVE CRITERIA THU AS MODELS CURRENTLY SHOWING SOME INCREASE IN MOISTURE. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...NONE. UT...NONE. && $$ SHORT TERM...TGR LONG TERM...JAD AVIATION...JDC
AREA FORECAST DISCUSSION
NWS MOUNT HOLLY NJ
510 AM EDT TUE SEP 4 2012 .SYNOPSIS... A WARM FRONT EXTENDED EASTWARD FROM LOW PRESSURE IN THE OHIO RIVER VALLEY TO MARYLAND AND DELAWARE AND THE ADJACENT COASTAL WATERS EARLY THIS MORNING. THE LOW IS FORECAST TO DRIFT TO THE NORTHEAST AND IT SHOULD PULL THE FRONT SLOWLY TO THE NORTH DURING TODAY AND TONIGHT. AS THE LOW REACHES THE VICINITY OF MAINE AND CANADA`S MARITIME PROVINCES ON WEDNESDAY NIGHT, IT IS EXPECTED TO PULL A TRAILING FRONTAL BOUNDARY THROUGH OUR REGION. A COLD FRONT FROM THE NORTHWEST IS FORECAST TO ARRIVE EARLY ON FRIDAY FOLLOWED BY WEAK HIGH PRESSURE. SLOW MOVING LOW PRESSURE AND A FRONTAL BOUNDARY FROM THE WEST MAY INFLUENCE OUR REGION OVER THE WEEKEND AND INTO MONDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... CNVTV ACTVTY DEFINITELY INCREASED DURG LATE EVE INTO THE OVERNIGHT HOURS. IT HAS BEEN ORIENTED IN A MAINLY W-E BAND ACROSS SRN AND SE PA INTO SRN NJ. NOT EXACTLY CLEAR WHAT IS DRIVING THIS LATEST ROUND EXCEPT THAT THE AMS CONTS TO BE VERY MOIST AND SMWHT UNSTABLE... ESPCLY ACRS THE CNTRL AND SRN PARTS OF OUR FCST AREA. LATEST RAP MODEL DOES SHOW GOOD UVV OVER THE AREA. STORMS ARE PRODUCING LCLLY HVY RAIN AND SOME FLOODING...BUT FORTUNATELY THE WORST OF IT SEEMS TO BE OVER SMWHT SPARSELY POPULATED AREAS IN SRN NJ. CNVTN IS EXPECTED TO CONT FOR A FEW MORE HRS WITH PERHAPS A SLOW NWD SHIFT. OTRW HAVE GENLY MAINTAINED THE CURRENT FCST WITH LIKELY POPS FOR MOST OF THE AREA THROUGH TUESDAY. ELY WINDS EARLY THIS MORN SHOULD INCR AND BECOME SLY BY AFTN. MAX TEMPS ARE A BLEND OF MAV/MET GUIDANCE. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/... LOW PRES OVER ERN OH IS FCST TO TRACK NEWD INTO UPSTATE NY DURG THIS PD...WITH A CDFNT TRAILING SWWD. HWVR OUR FCST AREA WILL REMAIN IN THE MOIST TROPICAL AMS AHD OF THE FNT AND THUS THE POTENTIAL FOR HEAVY SHOWERS AND TSTMS WILL CONT. THERE SHOULD BE ENOUGH OF A PRES GRADIENT TO MAINTAIN LIGHT SLY WINDS OVERNIGHT. MIN TEMPS SHOULD BE SIMILAR TO EARLY THIS MORNING. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... ON WEDNESDAY MORNING, THE AXIS OF DEEP MOISTURE WILL EXTEND THROUGH OUR FORECAST AREA. PRECIPITABLE WATER VALUES SHOULD BE IN EXCESS OF 2 INCHES AT MOST LOCATIONS. A LOW LEVEL JET IS EXPECTED TO EXTEND FROM THE CAROLINAS TO NEW ENGLAND AT THAT TIME. BOTH FEATURES ARE ANTICIPATED TO DRIFT EASTWARD ON WEDNESDAY. HOWEVER, THE THREAT OF HEAVY RAIN WILL REMAIN THROUGH MUCH OF THE DAY, DECREASING SLOWLY FROM WEST TO EAST. AS A RESULT, THE FLASH FLOOD WATCH WILL BE EXTENDED INTO WEDNESDAY EVENING. A MID LEVEL SHORT WAVE OVER THE DAKOTAS EARLY THIS MORNING IS FORECAST TO WORK ITS WAY TO THE EAST. THE FEATURE IS EXPECTED TO PASS OVERHEAD FROM WEDNESDAY AFTERNOON INTO WEDNESDAY EVENING. IT WILL HELP TO KICK THE DEEP MOISTURE OFF THE COAST ON WEDNESDAY NIGHT, FURTHER DECREASING THE POTENTIAL FOR HEAVY RAIN IN OUR REGION. FOR THURSDAY, THERE WILL REMAIN SOME INSTABILITY IN OUR REGION AS ANOTHER MID LEVEL SHORT WAVE APPROACHES FROM THE NORTHWEST. AS A RESULT, WE WILL KEEP THE MENTION OF A CHANCE OF SHOWERS AND THUNDERSTORMS. THE SHORT WAVE IS EXPECTED TO PASS OVERHEAD ON THURSDAY AFTERNOON. A SURFACE COLD FRONT ASSOCIATED WITH THE FEATURE SHOULD ARRIVE FOR LATE THURSDAY NIGHT AND EARLY FRIDAY. WEAK HIGH PRESSURE AND DRY AIR ARE EXPECTED TO FOLLOW FOR FRIDAY INTO FRIDAY NIGHT. A MID LEVEL TROUGH IS ANTICIPATED TO DIG OVER THE EASTERN HALF OF THE COUNTRY FOR THE WEEKEND AND INTO THE EARLY PART OF THE NEW WEEK. CONDITIONS ARE FORECAST TO BECOME UNSETTLED AGAIN DURING THAT PERIOD WITH A CHANCE OF PRECIPITATION. TEMPERATURES MAY BE SLIGHTLY ABOVE NORMAL FOR WEDNESDAY THROUGH FRIDAY AND NEAR NORMAL FOR SATURDAY THROUGH MONDAY. && .AVIATION /09Z TUESDAY THROUGH SATURDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. IFR CIGS SHOULD PREVAIL OVERNIGHT BUT VSBYS WILL REMAIN HIGH... EXCEPT IN HEAVY SHOWERS OR ISOLD TSTMS. THESE CONDS WILL PERSIST INTO TUE MORNING BUT SHOULD IMPROVE SMWHAT BY MID MORNING. MAINLY VFR CONDS ARE EXPECTED BY TUE AFTN. HWVR...SHWRS/TSTMS FROM TIME TO TIME WILL RESULT IN PERIODS OF MVFR TO IFR CIGS/VSBYS BUT IN GENERAL THESE SHOULD NOT LAST VERY LONG AT ANY GIVEN SITE. TAFS WILL BE UPDATED BASED ON SHORT-TERM FCSTS WITH AS MUCH LEAD TIME AS POSSIBLE. WINDS OVERNIGHT WILL BE LIGHT ELY BUT ARE FCST TO BECOME SLY BY MID DAY TUE AND BECOME A LITTLE STRONGER. OUTLOOK... WEDNESDAY...SHOWERS LIKELY WITH A CHANCE OF THUNDERSTORMS. THERE IS THE POTENTIAL FOR PERIODS OF MODERATE TO HEAVY RAIN ACCOMPANIED BY MVFR OR IFR CONDITIONS. MVFR OR IFR CONDITIONS ARE ALSO POSSIBLE IN MORNING FOG, HAZE AND LOW CLOUDS. WEDNESDAY NIGHT AND THURSDAY...MAINLY VFR WITH A CHANCE OF SHOWERS AND THUNDERSTORMS. MVFR OR IFR CONDITIONS ARE ALSO POSSIBLE IN LATE NIGHT AND EARLY MORNING FOG, HAZE AND LOW CLOUDS. THURSDAY NIGHT THROUGH FRIDAY NIGHT...MAINLY VFR. SATURDAY...MAINLY VFR WITH A CHANCE OF SHOWERS AND THUNDERSTORMS. && .MARINE... AFTER FURTHER REVIEW...DECIDED TO GO AHEAD AND ISSUE A SCA FOR COASTAL WATERS BEGINNING THIS EVE AND CONTG THROUGH WED. THIS WILL BE PRIMARILY FOR SEAS DUE TO A COMBO OF WIND WAVES AND INCRG SELY SWELL...ALTHO THERE COULD BE OCNL GUSTS TO 25 KT IN SW FLOW. THE WW3 SHOWS SEAS UP TO 7 FT AT THE OUTER EDGE OF OUR COASTAL WATERS ON WED MORN...WHICH COULD BE A BIT OVERDONE BUT IT SEEMS PRUDENT AT THIS POINT TO GO AHEAD WITH THE SCA. SCATTERED SHOWER AND TSTM ACTVTY WILL CONT WITH LCLY POOR VSBYS AND HIGHER WINDS NEAR TSTMS. OUTLOOK... A WARM FRONT IS FORECAST TO LIFT SLOWLY OVER THE COASTAL WATERS OF DELAWARE AND NEW JERSEY DURING TODAY WITH ANOTHER FRONTAL BOUNDARY ARRIVING FROM THE WEST ON WEDNESDAY NIGHT. A COLD FRONT FROM THE NORTHWEST IS ANTICIPATED FOR EARLY FRIDAY. WIND SPEEDS AND GUSTS SHOULD REMAIN LESS THAN 25 KNOTS THROUGH THE PERIOD. FROM WEDNESDAY THROUGH SATURDAY, LONG PERIOD SWELLS FROM DISTANT TROPICAL SYSTEM LESLIE ARE FORECAST TO AFFECT THE COASTAL WATERS OF DELAWARE AND NEW JERSEY. WAVE HEIGHTS ON OUR OCEAN WATERS SHOULD BE 5 FEET OR GREATER DURING THAT PERIOD WITH A SMALL CRAFT ADVISORY LIKELY. && .RIP CURRENTS... LONG PERIOD SWELLS FROM DISTANT TROPICAL SYSTEM LESLIE ARE FORECAST TO AFFECT THE COASTS OF DELAWARE AND NEW JERSEY INTO AT LEAST THE EARLY PART OF NEXT WEEK. AS A RESULT, A PROLONGED PERIOD WITH A MODERATE TO HIGH RISK OF RIP CURRENTS IS ANTICIPATED. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...FLASH FLOOD WATCH THROUGH WEDNESDAY EVENING FOR PAZ067>071. NJ...FLASH FLOOD WATCH THROUGH WEDNESDAY EVENING FOR NJZ015>019. DE...FLASH FLOOD WATCH THROUGH WEDNESDAY EVENING FOR DEZ001. MD...NONE. MARINE...SMALL CRAFT ADVISORY FROM 8 PM THIS EVENING TO 8 PM EDT WEDNESDAY FOR ANZ450>455. && $$ SYNOPSIS...IOVINO NEAR TERM...AMC SHORT TERM...AMC LONG TERM...IOVINO AVIATION...AMC/IOVINO MARINE...AMC/IOVINO RIP CURRENTS...
AREA FORECAST DISCUSSION
NWS MOUNT HOLLY NJ
430 AM EDT TUE SEP 4 2012 .SYNOPSIS... A WARM FRONT EXTENDED EASTWARD FROM LOW PRESSURE IN THE OHIO RIVER VALLEY TO MARYLAND AND DELAWARE AND THE ADJACENT COASTAL WATERS EARLY THIS MORNING. THE LOW IS FORECAST TO DRIFT TO THE NORTHEAST AND IT SHOULD PULL THE FRONT SLOWLY TO THE NORTH DURING TODAY AND TONIGHT. AS THE LOW REACHES THE VICINITY OF MAINE AND CANADA`S MARITIME PROVINCES ON WEDNESDAY NIGHT, IT IS EXPECTED TO PULL A TRAILING FRONTAL BOUNDARY THROUGH OUR REGION. A COLD FRONT FROM THE NORTHWEST IS FORECAST TO ARRIVE EARLY ON FRIDAY FOLLOWED BY WEAK HIGH PRESSURE. SLOW MOVING LOW PRESSURE AND A FRONTAL BOUNDARY FROM THE WEST MAY INFLUENCE OUR REGION OVER THE WEEKEND AND INTO MONDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... CNVTV ACTVTY DEFINITELY INCREASED DURG LATE EVE INTO THE OVERNIGHT HOURS. IT HAS BEEN ORIENTED IN A MAINLY W-E BAND ACROSS SRN AND SE PA INTO SRN NJ. NOT EXACTLY CLEAR WHAT IS DRIVING THIS LATEST ROUND EXCEPT THAT THE AMS CONTS TO BE VERY MOIST AND SMWHT UNSTABLE... ESPCLY ACRS THE CNTRL AND SRN PARTS OF OUR FCST AREA. LATEST RAP MODEL DOES SHOW GOOD UVV OVER THE AREA. STORMS ARE PRODUCING LCLLY HVY RAIN AND SOME FLOODING...BUT FORTUNATELY THE WORST OF IT SEEMS TO BE OVER SMWHT SPARSELY POPULATED AREAS IN SRN NJ. CNVTN IS EXPECTED TO CONT FOR A FEW MORE HRS WITH PERHAPS A SLOW NWD SHIFT. OTRW HAVE GENLY MAINTAINED THE CURRENT FCST WITH LIKELY POPS FOR MOST OF THE AREA THROUGH TUESDAY. ELY WINDS EARLY THIS MORN SHOULD INCR AND BECOME SLY BY AFTN. MAX TEMPS ARE A BLEND OF MAV/MET GUIDANCE. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/... LOW PRES OVER ERN OH IS FCST TO TRACK NEWD INTO UPSTATE NY DURG THIS PD...WITH A CDFNT TRAILING SWWD. HWVR OUR FCST AREA WILL REMAIN IN THE MOIST TROPICAL AMS AHD OF THE FNT AND THUS THE POTENTIAL FOR HEAVY SHOWERS AND TSTMS WILL CONT. THERE SHOULD BE ENOUGH OF A PRES GRADIENT TO MAINTAIN LIGHT SLY WINDS OVERNIGHT. MIN TEMPS SHOULD BE SIMILAR TO EARLY THIS MORNING. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... ON WEDNESDAY MORNING, THE AXIS OF DEEP MOISTURE WILL EXTEND THROUGH OUR FORECAST AREA. PRECIPITABLE WATER VALUES SHOULD BE IN EXCESS OF 2 INCHES AT MOST LOCATIONS. A LOW LEVEL JET IS EXPECTED TO EXTEND FROM THE CAROLINAS TO NEW ENGLAND AT THAT TIME. BOTH FEATURES ARE ANTICIPATED TO DRIFT EASTWARD ON WEDNESDAY. HOWEVER, THE THREAT OF HEAVY RAIN WILL REMAIN THROUGH MUCH OF THE DAY, DECREASING SLOWLY FROM WEST TO EAST. AS A RESULT, THE FLASH FLOOD WATCH WILL BE EXTENDED INTO WEDNESDAY EVENING. A MID LEVEL SHORT WAVE OVER THE DAKOTAS EARLY THIS MORNING IS FORECAST TO WORK ITS WAY TO THE EAST. THE FEATURE IS EXPECTED TO PASS OVERHEAD FROM WEDNESDAY AFTERNOON INTO WEDNESDAY EVENING. IT WILL HELP TO KICK THE DEEP MOISTURE OFF THE COAST ON WEDNESDAY NIGHT, FURTHER DECREASING THE POTENTIAL FOR HEAVY RAIN IN OUR REGION. FOR THURSDAY, THERE WILL REMAIN SOME INSTABILITY IN OUR REGION AS ANOTHER MID LEVEL SHORT WAVE APPROACHES FROM THE NORTHWEST. AS A RESULT, WE WILL KEEP THE MENTION OF A CHANCE OF SHOWERS AND THUNDERSTORMS. THE SHORT WAVE IS EXPECTED TO PASS OVERHEAD ON THURSDAY AFTERNOON. A SURFACE COLD FRONT ASSOCIATED WITH THE FEATURE SHOULD ARRIVE FOR LATE THURSDAY NIGHT AND EARLY FRIDAY. WEAK HIGH PRESSURE AND DRY AIR ARE EXPECTED TO FOLLOW FOR FRIDAY INTO FRIDAY NIGHT. A MID LEVEL TROUGH IS ANTICIPATED TO DIG OVER THE EASTERN HALF OF THE COUNTRY FOR THE WEEKEND AND INTO THE EARLY PART OF THE NEW WEEK. CONDITIONS ARE FORECAST TO BECOME UNSETTLED AGAIN DURING THAT PERIOD WITH A CHANCE OF PRECIPITATION. TEMPERATURES MAY BE SLIGHTLY ABOVE NORMAL FOR WEDNESDAY THROUGH FRIDAY AND NEAR NORMAL FOR SATURDAY THROUGH MONDAY. && .AVIATION /09Z TUESDAY THROUGH SATURDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. IFR CIGS SHOULD PREVAIL OVERNIGHT BUT VSBYS WILL REMAIN HIGH... EXCEPT IN HEAVY SHOWERS OR ISOLD TSTMS. THESE CONDS WILL PERSIST INTO TUE MORNING BUT SHOULD IMPROVE SMWHAT BY MID MORNING. MAINLY VFR CONDS ARE EXPECTED BY TUE AFTN. HWVR...SHWRS/TSTMS FROM TIME TO TIME WILL RESULT IN PERIODS OF MVFR TO IFR CIGS/VSBYS BUT IN GENERAL THESE SHOULD NOT LAST VERY LONG AT ANY GIVEN SITE. TAFS WILL BE UPDATED BASED ON SHORT-TERM FCSTS WITH AS MUCH LEAD TIME AS POSSIBLE. WINDS OVERNIGHT WILL BE LIGHT ELY BUT ARE FCST TO BECOME SLY BY MID DAY TUE AND BECOME A LITTLE STRONGER. OUTLOOK... WEDNESDAY...SHOWERS LIKELY WITH A CHANCE OF THUNDERSTORMS. THERE IS THE POTENTIAL FOR PERIODS OF MODERATE TO HEAVY RAIN ACCOMPANIED BY MVFR OR IFR CONDITIONS. MVFR OR IFR CONDITIONS ARE ALSO POSSIBLE IN MORNING FOG, HAZE AND LOW CLOUDS. WEDNESDAY NIGHT AND THURSDAY...MAINLY VFR WITH A CHANCE OF SHOWERS AND THUNDERSTORMS. MVFR OR IFR CONDITIONS ARE ALSO POSSIBLE IN LATE NIGHT AND EARLY MORNING FOG, HAZE AND LOW CLOUDS. THURSDAY NIGHT THROUGH FRIDAY NIGHT...MAINLY VFR. SATURDAY...MAINLY VFR WITH A CHANCE OF SHOWERS AND THUNDERSTORMS. && .MARINE... SELY WINDS OVER THE COASTAL WATERS WILL BECOME MORE SLY TODAY AS THE FNTL BNDRY ACROSS DELMARVA GRDLY LIFTS NWD. WINDS AND SEAS ARE EXPECTED TO INCREASE A BIT TONIGHT AND COULD APPROACH SCA CONDS AT TIMES. SITN APPEARS MARGINAL HWVR SO WILL HOLD OFF ISSUING ANY ADVISORIES FOR NOW. SCATTERED SHOWER AND TSTM ACTVTY WILL CONT WITH LCLLY POOR VSBYS AND HIGHER WINDS NEAR TSTMS. OUTLOOK... A WARM FRONT IS FORECAST TO LIFT SLOWLY OVER THE COASTAL WATERS OF DELAWARE AND NEW JERSEY DURING TODAY WITH ANOTHER FRONTAL BOUNDARY ARRIVING FROM THE WEST ON WEDNESDAY NIGHT. A COLD FRONT FROM THE NORTHWEST IS ANTICIPATED FOR EARLY FRIDAY. WIND SPEEDS AND GUSTS SHOULD REMAIN LESS THAN 25 KNOTS THROUGH THE PERIOD. FROM WEDNESDAY THROUGH SATURDAY, LONG PERIOD SWELLS FROM DISTANT TROPICAL SYSTEM LESLIE ARE FORECAST TO AFFECT THE COASTAL WATERS OF DELAWARE AND NEW JERSEY. WAVE HEIGHTS ON OUR OCEAN WATERS SHOULD BE 5 FEET OR GREATER DURING THAT PERIOD WITH A SMALL CRAFT ADVISORY LIKELY. && .RIP CURRENTS... LONG PERIOD SWELLS FROM DISTANT TROPICAL SYSTEM LESLIE ARE FORECAST TO AFFECT THE COASTS OF DELAWARE AND NEW JERSEY INTO AT LEAST THE EARLY PART OF NEXT WEEK. AS A RESULT, A PROLONGED PERIOD WITH A MODERATE TO HIGH RISK OF RIP CURRENTS IS ANTICIPATED. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...FLASH FLOOD WATCH THROUGH WEDNESDAY EVENING FOR PAZ067>071. NJ...FLASH FLOOD WATCH THROUGH WEDNESDAY EVENING FOR NJZ015>019. DE...FLASH FLOOD WATCH THROUGH WEDNESDAY EVENING FOR DEZ001. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...IOVINO NEAR TERM...AMC SHORT TERM...AMC LONG TERM...IOVINO AVIATION...AMC/IOVINO MARINE...AMC/IOVINO RIP CURRENTS...IOVINO
AREA FORECAST DISCUSSION
NWS TAMPA BAY RUSKIN FL
405 AM EDT TUE SEP 4 2012 .SYNOPSIS... 07Z WATER VAPOR AND H4 RAP ANALYSIS SHOW A COMPLEX UPPER LEVEL PATTERN OVER THE SOUTHEAST CONUS THIS MORNING. FORECAST AREA IS SITUATED BETWEEN A DISTURBANCE/SHORTWAVE DROPPING SOUTHWARD OUT OF AL/GA/MS...AND A POTENT CLOSED UPPER LOW SPINNING JUST OFF THE FLORIDA EAST COAST. UPPER LEVEL MOISTURE FIELDS ARE ALSO QUITE COMPLEX WITH WV IMAGERY SHOWING A BAND OF SIGNIFICANTLY LOWER UPPER TROPOSPHERIC MOISTURE WRAPPING AROUND THE NORTHERN AND WESTERN SIDES OF THE UPPER LOW CIRCULATION. THE POSITION AND STRENGTH OF THIS DRY AIR WILL PLAY A PART IN WHERE THE BEST CHANCES FOR SHOWERS/STORMS WILL OCCUR LATER TODAY. AT THE SURFACE...SUBTROPICAL RIDGE IS A BIT UNDEFINED...HOWEVER BEST GUESS ANALYSIS WOULD PLACE THE AXIS THROUGH THE CENTRAL FL PENINSULA. VERY LITTLE IN THE WAY OF RADAR RETURNS ACROSS THE FORECAST AREA THIS MORNING. MOST OF THE ACTIVITY IS LOCATED TO OUR NORTH AND SOUTH ASSOCIATED WITH THE 2 DISTURBANCES MENTIONED ABOVE. && .SHORT TERM (TODAY THROUGH THURSDAY)... TODAY...UPPER LEVEL ENERGY TO OUR NORTHWEST WILL CONTINUE TO SINK SOUTHWARD OVER THE FL PANHANDLE AND OVER THE NORTH-CENTRAL GULF OF MEXICO BY THE END OF THE DAY. AT THE SAME TIME WILL BE WATCHING THE UPPER LOW CENTERED JUST EAST OF MIAMI BEGIN TO VERY SLOWLY MIGRATE NORTHWARD. OUR FORECAST AREA WILL REMAIN SOMEWHERE IN THE MIDDLE MAKING THE FORECAST A BIT CHALLENGING...ESPECIALLY IN REGARDS TO RAIN CHANCES. IN GENERAL EXPECTING THE BEST SYNOPTIC SUPPORT FOR LIFT ASSOCIATED WITH THE NORTHERN ENERGY TO REMAIN TO THE NORTH OF LEVY COUNTY TOWARD THE WESTERN BIG BEND/PANHANDLE AREAS. AT THE SAME TIME...THE MOST SUPPORTIVE MOISTURE FIELDS AND MID-LEVEL COLD POOL ASSOCIATED WITH THE UPPER LOW WILL BE ALONG THE FLORIDA EAST COAST. WITH THIS IN MIND...WONT DEVIATE FAR FROM THE MAV RAIN CHANCES FOR THE NATURE COAST/TAMPA BAY AREA ZONES. WILL BUMP RAIN CHANCES UP 10-20% FURTHER INLAND AND SOUTHWARD DOWN TOWARD FORT MYERS IN CLOSER PROXIMITY TO THE INSTABILITY UNDER THE COLD POOL. WEDNESDAY...THE OVERALL SYNOPTIC PATTERN IN THE UPPER LEVELS WILL NOT CHANGE SIGNIFICANTLY WITH OUR REGION REMAINING IN THE SQUEEZE BETWEEN 2 PIECES OF UPPER LEVEL ENERGY. THE SUBTROPICAL RIDGE AXIS IS FORECAST TO DROP A BIT FURTHER SOUTHWARD WHICH WILL ACT TO TURN OUR LOW LEVEL FLOW MORE TO AN ONSHORE SOUTHWEST DIRECTION. GLOBAL GUIDANCE IS ALSO HINTING THAT SOME OF DRY AIR ALOFT WILL BE DIMINISHING MAKING THE COLUMN LESS HOSTILE TO DEEP CONVECTION. THE LOW LEVEL SW FLOW IS CLIMO FAVORED FOR THE DEVELOPMENT OF WIDELY SCT NOCTURNAL SHOWERS OVER THE COASTAL WATERS AND WILL ADD THIS POTENTIAL TO THE GRIDS DURING THE SECOND HALF OF WEDNESDAY NIGHT. THURSDAY...FORECAST IS OF LOWER CONFIDENCE THAN USUAL FOR THE DAY THREE PERIOD AS GLOBAL GUIDANCE IS NOT IN GOOD AGREEMENT REGARDING THE EVENTUAL EVOLUTION OF THE DISTURBANCE DROPPING OFF THE FL PANHANDLE IN THE NORTH-CENTRAL GULF. GFS HAS A MORE SHEARED SYSTEM WITH ONLY AN OPEN TROUGH AT THE SURFACE. THE ECMWF ON THE OTHER HAND HOLDS ONTO A STRONGER VORTICITY LOBE IN THE UPPER LEVELS WHICH SUPPORTS A CLOSED SURFACE LOW REFLECTION. THESE 2 SOLUTIONS PRODUCE VERY DIFFERENT WIND/MOISTURE FIELDS OVER THE EASTERN GULF AND FL PENINSULA. VERY DIFFICULT TO SAY WHICH MODEL HAS A BETTER HANDLE ON THE SITUATION. UNTIL THINGS BECOME MORE CERTAIN...WILL RUN A BLEND OF THE MAV/SREF FOR THE THURSDAY FORECAST. && .LONG TERM (FRIDAY THROUGH NEXT MONDAY)... A TROUGH AXIS WITH ORIGINS BACK TO THE REMNANTS OF ISAAC PHASED W/ NRN STREAM STREAM ENERGY WILL DIG INTO THE NE GULF THROUGH THE END OF THE WEEK. MODELS ARE NOT IN GOOD AGREEMENT ON WHAT HAPPENS BEYOND THAT. THE ECMWF HAS CONSISTENTLY SPUN UP A SFC LOW PRESSURE SYSTEM JUST NE OF THE REGION WHILE THE GFS SHEARS THE ENERGY APART AND KEEPS MORE OF A DISORGANIZED TROUGH. THE NAM 12 SEEMS ON BOARD WITH THE ECMWF AS IT ALSO SHOWS A CLOSED LOW BY FRI. EITHER WAY...MOISTURE POOLED ALONG AND SOUTH OF THIS SYSTEM WILL MOVE IN OFF THE NE GULF LEADING TO INCREASE IN TROPICAL SHRA AND TSTMS FOR THE WEEKEND...BUT WHICH SOLN PANS OUT WILL OBVIOUSLY HAVE MAJOR IMPLICATIONS ON EXACTLY HOW MUCH IMPACT THIS SYSTEM WILL HAVE. GIVEN THE UNCERTAINTY...WILL HOLD CLOSER TO A GFS SOLN WITH POPS INCREASING INTO THE SCT RANGE FOR THE WEEKEND. A MUCH STRONGER AND MORE AMPLIFIED MID LEVEL TROUGH WILL DEVELOP OVER THE WEEKEND ACROSS THE ERN HALF OF THE COUNTRY. THE 00Z GFS HAS TRENDED MORE TOWARDS A LARGE CLOSED LOW SIMILAR TO THE ECMWF AND THIS WOULD ACTUALLY BRING THE FIRST COLD FRONT OF THE SEASON THROUGH THE AREA BEFORE STALLING. PREVIOUS RUNS STALLED THE BOUNDARY A BIT FURTHER NORTH BUT STILL BROUGHT THE BOUNDARY INTO THE CEN FL...AND CLIMATOLOGICALLY THIS IS PROBABLY A BETTER SOLN FOR DAY 7-8 OF THE FORECAST. SO WILL KEEP SCT/CHC POPS GOING INTO MON FOR NOW...AT LEAST ACROSS SRN HALF OF THE CWA. INCREASE IN PRECIP AND ONSHORE WINDS WILL HELP KEEP HIGHS DOWN SOME OVER THE WEEKEND AND WILL ALSO PROVIDE AN INCREASED RISK OF RIP CURRENTS TO THE AREA. && .AVIATION... WILL INCLUDE VCTS FOR LATE AFTN AND EARLY EVENING FOR LAL AND SRN SITES TO COVER ISOLD TO SCT TSTMS IN THESE AREAS. THERE IS AN OUTSIDE CHC OF MVFR VSBYS IN SRN SITES THIS MORNING AND WED MORNING...BUT PROBS ARE TO LOW TO RESTRICT TAFS AND WILL THEREFORE STICK WITH VFR FORECAST FOR THE NEXT 24 HOURS. && .MARINE... THE SUBTROPICAL RIDGE AXIS WILL SETTLE SOUTHWARD THE NEXT COUPLE OF DAYS. WINDS AND SEAS WILL REMAIN LOW THROUGH WEDNESDAY...THEN BEING TO INCREASE DURING THURSDAY AND FRIDAY AS A TROUGH OR WEAK AREA OF LOW PRESSURE APPROACHES FROM THE WEST. && .FIRE WEATHER... THE FORECAST THROUGH MIDWEEK WILL FEATURE A MORE TYPICAL SUMMER PATTERN WITH WIDELY SCATTERED AFTERNOON/EVENING STORMS. RELATIVE HUMIDITY VALUES WILL REMAIN ABOVE CRITICAL VALUES AND NO SIGNIFICANT FIRE WEATHER CONCERNS ARE ANTICIPATED. && .PRELIMINARY POINT TEMPS/POPS... TPA 90 75 90 76 / 20 10 30 20 FMY 92 75 90 74 / 30 20 40 20 GIF 93 73 91 73 / 30 20 30 10 SRQ 89 75 89 76 / 20 10 30 20 BKV 92 70 91 70 / 20 10 30 20 SPG 91 78 89 77 / 20 10 30 20 && .TBW WATCHES/WARNINGS/ADVISORIES... FL...NONE. GULF WATERS...NONE. && $$ SYNOPSIS/SHORT TERM/MARINE/FIRE WX...MROCZKA LONG TERM/AVIATION...GITTINGER
AREA FORECAST DISCUSSION
NWS PEACHTREE CITY GA
201 AM EDT TUE SEP 4 2012 .PREV DISCUSSION... /ISSUED 952 PM EDT MON SEP 3 2012/ UPDATE... HAVE MADE SEVERAL UPDATES TO THE GRIDS THROUGH THE EVENING... MAINLY TO ADJUST POPS TO ACCOUNT FOR CONVECTIVE TRENDS. REDUCED POPS NORTHWEST AND INCREASED IN A LINE ROUGHLY FROM AHN TO CSG WHERE CONVECTION LINGERED THROUGH THE EVENING...WITH A SLOW INCREASING TREND NORTHWEST OVER NIGH. HRRR AND OTHER HIRES GUIDANCE STILL INDICATING THAT CONVECTION FROM ALABAMA WILL WORK ITS WAY INTO GEORGIA...ESPECIALLY WHAT HAS BEEN DEVELOPING IN NORTHEAST ALABAMA. DID REDUCE THUNDER WORDING FOR THE OVERNIGHT PERIOD. TEMPS THROUGH THE EVENING DUE TO THE RAIN...AND OVERNIGHT LOWS MAY BE A LITTLE TOO HIGH. HAVE MADE SOME MINOR ADJUSTMENTS BUT WITH DEWPOINTS SO HIGH DO NOT FEEL COMFORTABLE LOWERING MINS ANY MORE. TDP SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/... /ISSUED 334 PM EDT MON SEP 3 2012/ REMNANTS OF ISAAC STILL SPINNING NEAR THE IN/KY BORDER THIS AFTERNOON. TWO RAIN BANDS MOVING THROUGH GA AT THE MOMENT. THE FIRST ONE IS DOWN ALONG THE GA COAST WITH THE SECOND NOW MOVING THROUGH THE ATL/AHN AREAS. MAINLY SHOWERS WITH THIS BAND BUT THERE ARE SOME ISOLATED THUNDERSTORMS . THESE STORMS ARE NOT SEVERE BUT THEY ARE INCREASING IN INTENSITY AS THEY MOVE INTO MORE UNSTABLE AIR ACROSS CENTRAL GA. INSTABILITIES HAVE INCREASED INTO THE 1500-2500 J/KG RANGE ACROSS CENTRAL GA AND WILL SUPPORT SOME STRONG STORMS. MODELS INDICATING POSSIBLE MCS DEVELOPMENT OVERNIGHT JUST WEST OF THE CWA. HAVE KEPT POPS HIGH THROUGH TUESDAY...WITH GENERALLY LIKELY ACROSS MUCH OF THE CWA. ALTHOUGH BEST DESTABILIZATION IS OCCURRING RIGHT NOW...THERE SHOULD BE ENOUGH INSTABILITY TO SUPPORT ISOLATED TO SCATTERED THUNDERSTORMS THROUGH THE OVERNIGHT HOURS. MOST PLACES WILL SEE PRECIPITATION AMOUNTS OF 1-2 INCHES THROUGH THE SHORT TERM. FLASH FLOOD GUIDANCE WELL ABOVE THIS SO DO NOT ANTICIPATE ANY ISSUES. AS FOR TEMPERATURES...MAV GUIDANCE HA BEEN RUNNING A BIT COLD ON MIN TEMPS AND A BIT WARM ON MAX TEMPS. HAVE MADE SLIGHT ADJUSTMENTS TO COMPENSATE FOR THIS. 01 LONG TERM /WEDNESDAY THROUGH MONDAY/... /ISSUED 334 PM EDT MON SEP 3 2012/ LATEST EXTENDED GUIDANCE SHOWS BEST MOISTURE HANGING AROUND A LITTLE LONGER INTO WEDNESDAY AND THURSDAY AND ONLY CHANGE WAS TO BUMP UP INTO LOW LIKELY/HIGH CHANCE RANGE. REMAINDER OF THE EXTENDED REMAINS UNCHANGED. DEESE TROPICAL MOISTURE BECOMES STRETCHED OUT ACROSS THE CWA THROUGH WEDNESDAY WITH SOME HINT AT DRYING THURSDAY INTO FRIDAY AS THE UPPER RIDGE NOSES EASTWARD. HAVE NOT REMOVED POPS FOR THE BRIEF DRIER PERIOD...JUST REDUCED THEM OVER MUCH OF THE CWA. BY THE WEEKEND BOTH MODELS SHOW A SIGNIFICANT CLOSED LOW DEVELOPING VICINITY OF THE OHIO VALLEY. THIS KEEPS THE UNSETTLED WEATHER OVER THE CWA AND HAVE CONTINUED WITH CHANCE OR SLIGHT CHANCE POPS. MODEL MAX TEMPERATURES LOOKED A BIT HIGH GIVEN THE UPPER PATTERN SO HAVE TWEAKED THEM DOWN A BIT MOST AREAS. 41 && .AVIATION... 06Z UPDATE... SCATTERED LIGHT TO MODERATE RAIN SHOWERS CONTINUE THIS MORNING ACROSS MUCH OF THE AREA. IFR CIGS BEGINNING TO DEVELOP...AND EXPECT WIDESPREAD IFR CIGS BY 09Z. CIGS IMPROVE TO MVFR BY 15Z...AND SHOULD REMAIN LOW END VFR THROUGH THE AFTERNOON. -SHRA EXPECTED OFF AND ON THROUGH THE DAY...WITH BEST CHANCE FOR TS AFTER 18Z. HAVE GONE PREVAILING TS AT THIS TIME...BUT WILL LIKELY CHANGE THIS TO TEMPO FOR 12Z TAF...AS PER DIRECTIVE. SW WINDS THROUGH THE PERIOD...EXCEPT AHN WITH SSE WINDS. SPEEDS SHOULD BE 7-9KTS THROUGH THE DAY...THEN 5KTS OR LESS OVERNIGHT. //ATL CONFIDENCE...06Z UPDATE... MEDIUM ON ALL ELEMENTS. 31 && .PRELIMINARY POINT TEMPS/POPS... ATHENS 86 71 87 71 / 60 50 50 30 ATLANTA 84 72 86 73 / 60 40 40 30 BLAIRSVILLE 79 65 82 65 / 70 50 40 20 CARTERSVILLE 85 71 86 68 / 70 50 40 20 COLUMBUS 88 73 89 74 / 70 40 50 30 GAINESVILLE 82 71 85 71 / 70 50 50 30 MACON 89 72 89 72 / 60 40 50 30 ROME 86 71 87 69 / 70 40 30 20 PEACHTREE CITY 85 71 86 69 / 60 40 40 30 VIDALIA 91 73 90 74 / 60 40 40 30 && .FFC WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...31 LONG TERM....41 AVIATION...31
AREA FORECAST DISCUSSION
NWS LINCOLN IL
330 AM CDT TUE SEP 4 2012 .DISCUSSION... ISSUED 330 AM CDT TUE SEP 4 2012 SHORT TERM...TODAY THROUGH FRIDAY NIGHT SOME FOG PRESENT OVER EASTERN IL EAST OF I-55 WHERE SKIES CURRENTLY CLEAR AND WILL CONTINUE PATCHY FOG UNTIL 9 AM OVER EASTERN IL. MID/HIGH CLOUDS SPREADING EAST FROM IA AND NORTHERN MO INTO CENTRAL/NW IL EARLY THIS MORNING WITH A CLUSTER OF SHOWERS AND THUNDERSTORMS OVER NORTHERN MO AND OVER SOUTHERN LAKE MI AND NEAR CHICAGO. HRRR MODELS WAS HANDLING QPF THE BEST THIS MORNING WHICH BRINGS THE CONVECTION FROM NORTHERN MO EASTWARD INTO CENTRAL IL AND WEAKENS IT THIS MORNING. WILL CARRY POPS OF 20-40% TODAY AND HIGHEST WEST OF SPRINGFIELD. ISOLATED SHOWERS AND THUNDERSTORMS POSSIBLE THIS AFTERNOON IN UNSTABLE HUMID AIRMASS WITH DEWPOINTS STILL IN THE LOWER 70S. SPC KEEPS SLIGHT RISK NW OF IL TODAY. HIGHS IN THE UPPER 80S AND LOWER 90S AGAIN TODAY. HAVE 20-30% CHANCE OF SHOWERS AND THUNDERSTORMS INTO WESTERN AREAS OVERNIGHT WHILE PATCHY FOG POSSIBLE OVER EASTERN IL AGAIN AFTER MIDNIGHT. MODELS HAVE TRENDED A BIT SLOWER WITH A STRONGER COLD FRONT MOVING SE INTO CENTRAL IL WED AFTERNOON/EVENING. SPC CONTINUES SLIGHT RISK ACROSS MUCH OF CENTRAL IL NW OF I-70 WED AFTERNOON AND EARLY EVENING UNTIL SUNSET. AIRMASS GETS UNSTABLE AGAIN BY WED AFTERNOON WITH CAPES 2000-3000 J/KG WHILE BEST WIND SHEAR AND SHORT WAVE ENERGY IS NORTH OF CENTRAL IL. ADDED 20-30% CHANCE OF CONVECTION OVER EASTERN IL WED EVENING ESPECIALLY EARLY WED EVENING UNTIL SUNSET. ANOTHER VERY WARM AND HUMID DAY WED WITH HIGHS IN THE UPPER 80S AND LOWER 90S. DRY CONDITIONS EXPECTED THU WITH A FAIR AMOUNT OF SUNSHINE AS WEAK HIGH PRESSURE SETTLES INTO IL BY SUNSET THU...WITH SOME INCREASING CLOUDS FROM THE WEST LATER IN THE DAY. HIGHS IN THE LOW TO MID 80S AND WARMEST BY LAWRENCEVILLE WITH 87F. ANOTHER FAIRLY STRONG NORTHERN STREAM SHORT WAVE DIVES INTO THE MIDWEST BY FRI RETURNING A GOOD CHANCE OF SHOWERS AND A FEW THUNDERSTORMS. THIS TO ALSO BRING COOLER WEATHER LATER THIS WEEK. LONG TERM...SATURDAY THROUGH MONDAY NIGHT THE ENSEMBLE MODELS CONTINUE TO SHOW A STRONG UPPER LEVEL TROF DIGGING SOUTHEAST THROUGH THE MIDWEST AND GREAT LAKES REGION LATE THIS WEEK. THERE ARE STILL DIFFERENCES AMONG THE INDIVIDUAL MEMBERS ON WHAT HAPPENS WITH THIS TROUGH THIS WEEKEND...WITH SOME MEMBERS KEEPING THE TROUGH MORE PROGRESSIVE AND PUSHING IT EAST OF THE AREA BY SUNDAY MORNING...WHILE OTHERS CUTOFF THE TROUGH OVER THE OHIO VALLEY INTO NEXT MONDAY. FOR NOW WILL USE A BLEND OF MODEL SOLUTIONS AND STICK CLOSE TO ALLBLEND POPS IN THE EXTENDED FOR THIS WEEKEND...WITH HIGHER POPS SAT AND SHIFTING MORE INTO EASTERN IL SUNDAY...AND DRY MONDAY. BELOW NORMAL TEMPERATURES BY 5-10 DEGREES FOR THE HIGHS EXPECTED THIS WEEKEND AND GRADUALLY MODIFY DURING NEXT WORK WEEK. KH && .AVIATION... ISSUED 1154 PM CDT MON SEP 3 2012 NONE OF THE SHORT RANGE MODELS HAVE A VERY GOOD HANDLE ON THE CLOUDS OR PRECIPITATION THAT WAS OCCURRING JUST BEFORE 05Z. THE BIGGEST QUESTION OVERNIGHT WILL BE THE VISIBILITY AFTER 10Z. MOST TAF SITES IN CENTRAL AND EASTERN IL WILL HAVE PLENTY OF LOW LEVEL MOISTURE AND CALM/VERY LIGHT WIND. THE CLOUD COVER MAY NOT BE AS EXTENSIVE AS PREVIOUSLY THOUGHT. THUS...MOST AREAS SHOULD SEE THEIR VISIBILITY DROP TO MVFR LEVELS BY 10-11Z. ACROSS EASTERN IL THE MID/UPPER LEVEL CLOUDS WILL ARRIVE LATER AND THE CROSSOVER TEMPS INDICATE A BETTER CHANCE FOR FOG OVERNIGHT. THUS...THE VSBY SHOULD DROP TO MVFR LEVELS FIRST...THEN INTO THE IFR CATEGORY JUST BEFORE DAYBREAK. THE BEST CHANCE FOR WIDELY SCATTERED SHOWERS WILL BE AFTER DAYBREAK AS A WEAK SHORTWAVE MOVES TOWARD THE AREA...SO PUSHED BACK THE VCSH A FEW HOURS TO REFLECT THIS. MILLER && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$
AREA FORECAST DISCUSSION
NWS GOODLAND KS
1119 PM MDT MON SEP 3 2012 .UPDATE... ISSUED AT 841 PM MDT MON SEP 3 2012 JUST COMPLETED AN UPDATE. PRECIPITATION FORECAST APPEARS TO BE ON TRACK. EARLIER PRECIPITATION HAS DECREASED OR ENDED. HOWEVER...ENTRANCE REGION OF UPPER JET REMAINS IN THE AREA THROUGH THE NIGHT AS ANOTHER SHORTWAVE TROUGH MOVES THROUGH. ALSO SOME SURFACE CONVERGENCE AROUND MAINLY IN THE NORTHWEST. CURRENT ANALYSIS HAS INCREASING ELEVATED CINH AND DECREASING ELEVATED CAPE. NAM SHOWS NO INSTABILITY DURING THE NIGHT WITH GFS MAINTAINING A DECENT AMOUNT OF ELEVATED CAPE WITH NOT A LOT OF CINH. MODELS INSISTING ON KEEPING OR REDEVELOPING PRECIPITATION OVER THE SOUTHERN PORTION OF THE AREA THROUGH THE NIGHT. AFTER SAYING ALL THAT CURRENT GRIDS DO HAVE THIS DEPICTION AND FEEL COMFORTABLE IN KEEPING THIS FORECAST AT THIS TIME. WEST WINDS AND LOWER DEWPOINTS LOOK TO SPREAD FROM WEST TO EAST ACROSS THE AREA THROUGH THE NIGHT WITH THE THICKEST CLOUD COVER OVER THE SOUTH. AS A RESULT LOWERED DEWPOINTS OVER THE ENTIRE AREA AND LOWERED MINS OVER THE NORTHERN HALF TO TWO THIRDS. && .SHORT TERM...(THIS EVENING THROUGH TUESDAY) ISSUED AT 200 PM MDT MON SEP 3 2012 LATEST WV IMAGERY SHOWS A NARROW BAND OF SUBSIDENCE OVER EASTERN COLORADO MOVING INTO THE TRI-STATE AREA BEHIND THE UPPER LEVEL TROUGH THAT BROUGHT LIGHT RAINFALL TODAY. RUC ANALYSIS HAS A SECOND SHORT WAVE TROUGH FOLLOWING THE SUBSIDENCE BEHIND THE INITIAL SHORT WAVE. AT THE SURFACE THE COLD FRONT FROM YESTERDAY EXTENDS FROM SOUTHWEST KANSAS NORTHEAST TO IOWA. ANY STORM ACTIVITY THAT DEVELOPS ALONG THE FRONT SHOULD BE WELL SOUTH OF THE AREA. OTHERWISE A SUBTLE SURFACE TROUGH WAS LOCATED BETWEEN WRAY AND SAINT FRANCIS...WHICH MAY SERVE TO HELP FOCUS CONVECTION OVER THE NORTHWEST LATE THIS AFTERNOON AND THIS EVENING. EARLY THIS EVENING SURFACE CONVERGENCE WILL DEVELOP OVER THE NORTHWEST PART OF THE AREA BELOW A 700-500MB SHORT WAVE TROUGH. THE DEEP LIFTING WILL GIVE THE BEST SHOT FOR RAINFALL TO REACH THE GROUND. MEANWHILE THERE MAY BE SOME LINGERING STORMS IN THE HILL CITY TO MCCOOK AREA...AS THE 700-500MB SHORT WAVE TROUGH THAT BROUGHT RAIN EARLIER TODAY DEPARTS THE AREA. AS THE NIGHT PROGRESSES PRECIP. CHANCES SHIFT FROM THE NORTHWEST TO THE SOUTH AS A ANOTHER SHORT WAVE TROUGH MOVES ACROSS THE AREA. WITH A DEEP DRY LAYER IN PLACE...AM NOT TOO CONFIDENT ANYTHING WILL REACH THE GROUND. TUESDAY ANOTHER SHORT WAVE TROUGH WILL MOVE THROUGH THE AREA. DURING THE LATE MORNING THROUGH THE AFTERNOON A PRE-FRONTAL TROUGH WILL DEVELOP AT THE SURFACE BELOW THE SHORT WAVE TROUGH. LIFT ALONG THE SURFACE AND MID LEVEL TROUGH INCREASE THROUGH THE DAY. WITH STRONGER LIFT OCCURRING DURING THE AFTERNOON HAVE INCREASED PRECIP. CHANCES ALONG AND EAST OF THE SURFACE TROUGH. THESE AREAS WILL BE MORE LIKELY TO HAVE STRONG TO SEVERE THUNDERSTORMS DUE TO THE BETTER INSTABILITY. THE 0-6KM SHEAR WILL BE AROUND 30 TO 35 KTS FOR THE PERIOD...WHICH WILL SUPPORT ORGANIZED STORM STRUCTURE WITH PROLONGED UPDRAFTS. AM THINKING THE MAIN THREAT WITH THESE STORMS WILL BE STRONG TO SEVERE WIND GUSTS DUE TO THE HIGH CLOUD BASES. TEMPERATURES WILL BE SIMILAR TO LAST NIGHT AND TODAY...WITH LOWS IN UPPER 50S TO LOW 60S AND HIGHS IN THE 90S. .LONG TERM...(TUESDAY NIGHT THROUGH MONDAY) ISSUED AT 131 PM MDT MON SEP 3 2012 TUESDAY NIGHT-THURSDAY...WILL KEEP A SMALL CHANCE OF PRECIPITATION IN THE FORECAST EARLY TUESDAY NIGHT BEFORE DRIER AIR WORKS INTO THE AREA UNDER NORTHWEST FLOW ALOFT THROUGH EARLY THURSDAY MORNING. NOT TERRIBLY EXCITED ABOUT PRECIPITATION CHANCES THURSDAY AFTERNOON DESPITE MOISTURE AVAILABILITY AS DYNAMICS RATHER WEAK. TRIMMED POPS DOWN JUST A BIT. HIGH TEMPERATURES WEDNESDAY IN THE LOW TO MID 80S...WARMING INTO THE UPPER 80S TO LOW 90S THURSDAY. LOWS IN THE 50S TO LOW 60S. THURSDAY NIGHT-FRIDAY NIGHT...PRECIPITATION CHANCES WILL SLOWLY INCREASE THROUGH FRIDAY AS AN UPPER TROUGH AND COLD FRONT APPROACH THEN MOVE THROUGH THE AREA. PRECIP CHANCES DECREASE FROM NORTH TO SOUTH FRIDAY NIGHT AS THE SYSTEM MOVES OUT OF THE AREA AND STABLE HIGH PRESSURE MOVES IN. HIGH TEMPERATURES FRIDAY 75-80. LOWS THURSDAY NIGHT IN THE LOW 60S COOLING INTO THE LOW TO MID 50S FRIDAY NIGHT BEHIND THE FRONT. SATURDAY-MONDAY...DRY. HIGH TEMPERATURES SATURDAY IN THE MID TO UPPER 70S...WARMING INTO THE MID 80S TO AROUND 90 BY MONDAY. OVERNIGHT LOWS NEAR TO SLIGHTLY ABOVE NORMAL. && .AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT) ISSUED AT 1115 PM MDT MON SEP 3 2012 MODELS HAVING DIFFICULTY DURING THIS TIME PERIOD. WITH NUMEROUS SHORTWAVE TROUGHS MOVING THROUGH MODELS ARE ALL OVER THE PLACE WITH THE WIND FIELD AND PLACEMENT OF PRECIPITATION. AT THIS TIME VFR CONDITIONS ARE EXPECTED THROUGH THE PERIOD. CURRENT THUNDERSTORM ACTIVITY SHOULD STAY SOUTH OF KGLD THROUGH THE NIGHT. TOMORROW...DEPENDING ON POSITION OF PREFRONTAL TROUGH...HIGH BASED THUNDERSTORMS COULD AFFECT EITHER SITE BEGINNING IN THE MID TO LATE AFTERNOON HOURS. AS A RESULT OF THE UNCERTAINTY AND PRECIPITATION CHANCES NOT OCCURRING UNTIL THE QUARTER TO HALF OF THE PERIOD...CHOSE TO HANDLE THE CHANCES WITH VCTS. FURTHER REFINEMENTS OF THE WIND FIELD AND THUNDERSTORM CHANCE WILL CONTINUE TO BE NEEDED. && .FIRE WEATHER... ISSUED AT 200 PM MDT MON SEP 3 2012 TUESDAY AFTERNOON AREAS NORTH OF A KIT CARSON TO MCCOOK LINE WILL HAVE RELATIVE HUMIDITIES DROP TO AROUND 15 PERCENT DURING THE AFTERNOON. IN ADDITION WIND GUSTS AROUND 20 MPH CAN BE EXPECTED. WHILE THIS IS BELOW ISSUANCE CRITERIA...CARE SHOULD BE TAKEN FOR ANY OUTDOOR BURNING. && .GLD WATCHES/WARNINGS/ADVISORIES... KS...NONE. CO...NONE. NE...NONE. && $$ UPDATE...BULLER SHORT TERM...JTL LONG TERM...99 AVIATION...BULLER FIRE WEATHER...JTL
AREA FORECAST DISCUSSION
NWS MARQUETTE MI
440 AM EDT TUE SEP 4 2012 .SHORT TERM...(TODAY AND TONIGHT) ISSUED AT 438 AM EDT TUE SEP 4 2012 00Z RAOBS/LATEST WV IMAGERY AND RUC ANALYSIS SHOW FAST ZONAL FLOW OVER THE NRN TIER CONUS TO THE S OF DEEP OCCLUDED LO CENTERED OVER NRN MANITOBA. DISTURBANCE/AREA OF DEEPER MSTR RESPONSIBLE FOR SHRA/TS YDAY HAS PUSHED TO THE E AND GIVEN WAY TO WEAK HI PRES AND DRIER AIR. SOME AREAS OF DENSE FOG HAVE DVLPD OVER MAINLY THE ERN AND CNTRL CWA WITH LGT WINDS WHERE THE DRYING ALF HAS OUTRUN THE NEAR SFC DRYING. FOG APPEARS LESS PREVALENT OVER THE W WHERE DRIER LLVL AIR APRNT ON THE 00Z INL/MPX RAOBS HAS MADE GREATER INROADS. DESPITE THE PRESENCE OF THIS DRY AIR...SOME SHRA/A FEW TS ARE NOTED OVER NW MN NEAR AN INCOMING SHRTWV/SFC LO PRES TROF IN AREA WHERE NAM/GFS SHOW SOME H85 THETA E ADVECTION. SOME PATCHY MID/HI CLDS AHEAD OF THIS DISTURBANCE ARE DRIFING INTO THE WRN CWA. FARTHER TO THE NW...ANOTHER STRONGER SHRTWV IS OVER SASKATCHEWAN AND MOVING SEWD ON THE SRN FLANK OF CLOSED LO IN MANITOBA. EARLY THIS MORNING...OPTED TO ISSUE AN SPS FOR MUCH OF THE E AND CNTRL CWA TO HIGHLIGHT LOCALLY DENSE FOG. TODAY...EXPECT FOG TO BURN OFF THIS MRNG WITH ONSET OF DAYTIME HEATING. CONCERN THEN TURNS TO IMPACT OF SHRTWV NOW MOVING E THRU NRN MN. SEVERAL MODELS...ESPECIALLY THE 00Z NAM/CNDN...SHOW SOME FAIRLY SHARP DEEP LYR QVECTOR CNVGC/H3-2 DVGC/AXIS OF HIER H85-5 RH ASSOCIATED WITH DPVA/H85 THETA E ADVECTION IMPACTING THE WRN ZNS THIS AFTN INTO THE EARLY EVNG. IN FACT...RECENT SPC CONVECTIVE OUTLOOK HAS THE FAR W IN A SLIGHT RISK FOR SVR STORMS LATE THIS AFTN/EARLY EVNG. MODIFIED GFS FCST SDNG FOR IWD LATE IN THE AFTN YIELDS SBCAPE NEAR 1900 J/KG FOR SFC T/TD 84/60 UNDER STEEP MID LVL LAPSE RATES. THE NAM INDICATES 2000-2500 J/KG MUCAPE IN THIS AREA. A POSITIVE FOR SVR STORMS IS THE STEEP MID LVL LAPSE RATES/PRESENCE OF DRY AIR IN THE MID LVLS WITH SFC-10K FT DELTA THETA E 15-20C AND INVERTED V LOOK TO THE LLVL TEMP/DEWPT PROFILES THAT WOULD ENHANCE THE THREAT OF GUSTY WINDS. ON THE OTHER HAND...GENERALY DRYNESS OF THE ATMOSPHERE WL TEND TO LIMIT THE COVERAGE OF THE STORMS. ALSO DEEP LYR SHEAR IS FCST TO BE UP TO 30 KTS...A BIT MARGINAL BUT PROBABLY ENUF TO ALLOW FOR AT LEAST PULSE SVR STORMS. OTRW...EXPECT ANOTHER WARM DAY WITH H85 TEMPS IN THE 16-18C RANGE SUPPORTING HI TEMPS IN THE 80S AWAY FM LK BREEZES THAT WL TEND TO FORM OFF MAINLY LK MI WITH SSE H925 FLOW. TNGT...EXPECT BAND OF SCT SHRA/TS MOVING W-E INTO THE E HALF TO SLOWLY DIMINISH WITH LOSS OF DAYTIME HEATING/SHIFT OF SUPPORTING DEEP LYR QVECTOR CNVGC TO THE N INTO ONTARIO. WITH SOME DNVA/ NEGATIVE H85 THETA E ADVECTION/DEEP LYR QVECTOR DVGC FOLLOWING THIS BAND... EXPECT A PERIOD OF DRY WX. HOWEVER...APRCH OF SHARPER SHRTWV NOW MOVING SEWD THRU SASKATCHEWAN AND VIGOROUS DPVA/DEEP LYR QVECTOR CNVGC/SOME UPR DVGC WILL BRING BACK A THREAT OF SHRA/TS OVER THE W LATE. LIMITING FACTORS WILL BE LIMITED MSTR RETURN...SOME GUIDANCE ACTUALLY SHOWS NEGATIVE H85 THETA E ADVECTION...AND ARRIVAL OF THE DYNAMICS AT TIME OF MIN DIURNAL HEATING. .LONG TERM...(WEDNESDAY THROUGH MONDAY) ISSUED AT 438 AM EDT TUE SEP 4 2012 STARTING WITH WEDNESDAY...MOST OF THE GUIDANCE BRINGS A MODEST COLD FRONT THROUGH UPPER MI LATE WEDNESDAY MORNING INTO THE AFTERNOON. AS FOR MOISTURE AND INSTABILITY...850MB THETA E RIDGE SPRAWLS ITSELF ACROSS THE CWA TUESDAY NIGHT. PLENTY OF MOIST AIR WILL BE IN PLACE AS THE NOSE OF AN 850MB JET AIMS INTO SOUTHWESTERN UPPER MI...WITH PWATS EXPECTED TO BE 130-150 PERCENT OF NORMAL. SFC BASED CAPE DURING THE EARLY AFTERNOON IS AROUND 1000-1500 J/KG...AND MUCAPE IS UPWARDS OF 1800 J/KG. HIGHEST VALUES ARE IN THE SOUTH-SOUTH CENTRAL PORTIONS OF THE CWA. LOOKING AT FORECAST SOUNDINGS IT SEEMS WITH SHORTWAVE MOVING THROUGH DURING PEAK HEATING WE SHOULD HAVE ENOUGH GUSTO TO BREAK THE WEAK CAP THAT WILL BE IN PLACE. AS FAR AS ANY SUPPORT GOES...300MB JET STREAK SLIDES ACROSS THE CWA IN THE AFTERNOON...WITH RIGHT ENTRANCE REGION DYNAMICS IN PLAY ACROSS MAINLY THE SOUTH CENTRAL PORTION OF THE CWA. ECMWF HAS 500MB VORT MAXIMUM SLIDING INTO THE WEST HALF OF UPPER MI BY 18Z. WITH THE 300/850 MB JET STREAKS MOVING THROUGH 0-6 KM SHEAR IS AROUND 25-35 KNOTS. OVERALL THIS GIVES US A MODERATE CAPE/SHEAR ENVIRONMENT AND POTENTIAL FOR A SEVERE LINE OF STORMS...LIKELY DEVELOPING ACROSS THE SOUTHERN PORTIONS OF THE CWA WHERE LIFT AND INSTABILITY IS MAXIMIZED. THURSDAY WE DEAL WITH COOLER DRY AIR BEHIND THE FRONT/IN THE WAKE OF THE LOW PRESSURE SYSTEM NEAR JAMES BAY. DRY AIR PUNCHES IN ALOFT OVERNIGHT ON WEDNESDAY...SO IT LOOKS LIKE THURSDAY WILL BE RELATIVELY QUIET IN TERMS OF PRECIPITATION. PWATS DROP DOWN TO NEAR 70 PERCENT OF NORMAL AT TIMES AS SURFACE HIGH PRESSURE MOVING ACROSS THE MIDWEST TRIES TO RIDGE INTO UPPER MI. BY FRIDAY THE LOW BEGINS TO OCCLUDE NEAR JAMES BAY...SWINGING AN UPPER LEVEL TROUGH ACROSS UPPER MICHIGAN ONCE MORE. ECMWF GENERATES PRECIPITATION ACROSS CENTRAL AND EASTERN PRECIPITATION FOR THE DAY ON FRIDAY...SUPPORTED BY MODERATE 850-500MB QVECTOR CONVERGENCE AND LINGERING MOISTURE /PWATS AROUND 110 PERCENT OF NORMAL/. WITH NORTHWEST FLOW AND LAKE-850MB TEMP DIFFERENCES AROUND 15-18C...EXPECT A LAKE EFFECT COMPONENT TO PRECIPITATION NEAR LAKE SUPERIOR. ADDITIONALLY...STRONG ONSHORE FLOW WILL GENERATE WAVES AS HIGH AS 3 TO 5 FEET IN THE ALGER AND EASTERN MARQUETTE COUNTY SURF ZONE FRIDAY INTO SATURDAY MORNING...LEADING TO THE POSSIBILITY FOR RIP CURRENT DEVELOPMENT. WITH THE COLD FRONT PASSING WEDNESDAY AFTERNOON/EVENING TEMPERATURES WILL BE MORE FALL LIKE...WITH HIGHS IN THE 60S AND LOW 70S THROUGH THE REMAINDER OF THE PERIOD. ALONG WITH FALL LIKE TEMPERATURES...WE CAN EXPECT FALL-LIKE FEATURES. FRIDAY THERE IS AN ELEVATED POTENTIAL FOR WATERSPOUT DEVELOPMENT AS COOLER TEMPERATURES ALOFT MOVE IN OVER THE STILL WARM LAKE. FORECASTS PER THE INTERNATIONAL CENTRE FOR WATERSPOUT RESEARCH ARE STILL INDICATING THAT CONDITIONS WILL BE FAVORABLE FOR THEIR DEVELOPMENT. AS THE SFC/500MB HIGH PRESSURE RIDGE OVER THE NORTHERN PLAINS BUILDS INTO UPPER MICHIGAN FOR THE WEEKEND AND THROUGH THE FIRST PORTION OF THE WORK WEEK...EXPECT CONDITIONS TO REMAIN FAIRLY DRY. THE ONLY EXCEPTION IS THE LOW PRESSURE SYSTEM THAT DEVELOPS IN THE OHIO VALLEY FRIDAY...LINGERING OVER LOWER MI THROUGH THE EXTENDED. THIS COULD BRING SLIGHT CHANCE POPS OVER THE EASTERN U.P. FOR SATURDAY INTO MONDAY. FOR NOW WITH MODEL DIFFERENCES IN LOCATION AND TIMING OF THIS PRECIP WILL KEEP THE MODEL CONSENSUS IN FORECAST UNTIL THE FINER DETAILS CAN BE NARROWED DOWN. && .AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT) ISSUED AT 137 AM EDT TUE SEP 4 2012 EXPECT VLIFR CONDITIONS/FOG THRU SUNRISE AT SAW BEFORE DAYTIME HEATING BURNS THIS FOG OFF AND BRINGS A RETURN OF VFR CONDITIONS. DRY LLVL AIR SHOWN ON THE 00Z MPX/INL RAOBS HAS MADE GREATER INROADS INTO WRN UPR MI...SO LOOK FOR ONLY PTCHY FOG/POSSIBLE MVFR VSBYS AT THESE LOCATIONS. THE APRCH OF A LO PRES TROF THIS AFTN IN TANDEM WITH DAYTIME HEATING MAY RESULT IN SOME SHRA/EVEN A TS AT ALL 3 SITES THIS AFTN/EVNG...BUT RELATIVE DRYNESS OF THE LLVLS SHOULD MAINTAIN VFR CONDITIONS. SOME FOG MAY DVLP AT IWD LATER THIS EVNG WITH SOME DRYING ALF OVER LINGERNIG LLVL MSTR. && .MARINE...(FOR THE 4 AM LAKE SUPERIOR FORECAST ISSUANCE) ISSUED AT 438 AM EDT TUE SEP 4 2012 EXPECT SSW WINDS TO INCREASE UP TO 20 KTS TODAY MAINLY OVER THE E HALF IN ADVANCE OF AN APPROACHING LO PRES TROF. THESE STRONGER WINDS WILL BRING DRIER AIR OVER THE E HALF OF THE LAKE AND DISSIPATE FOG THAT DEVELOPED DURING THE NIGHT IN THE WAKE OF SHOWERS THAT FELL ON MON. ALTHOUGH WINDS WILL DIMINISH FOR A TIME WITH THE PASSAGE OF THE TROF...EXPECT W TO NW WINDS IN ITS WAKE LATE WED THRU THU TO INCREASE UP TO 20 TO 25 KTS AS COOLER AIR ARRIVES OVER THE RELATIVELY WARM LAKE WATERS AND ENHANCES MIXING. ALTHOUGH WINDS MAY DIMINISH FOR A TIME ON THU NIGHT AS ANOTHER TROF SWINGS OVER LAKE SUPERIOR...PLAN ON ANOTHER ROUND OF STRONGER NW WINDS UP TO 25 KTS ON FRI IN ITS WAKE. THE APPROACH OF HIGH PRESSURE/A WEAKENING PRES GRADIENT THIS WEEKEND WILL CAUSE WINDS TO SLOWLY DIMINISH. && .MQT WATCHES/WARNINGS/ADVISORIES... UPPER MICHIGAN... NONE. LAKE SUPERIOR... NONE. LAKE MICHIGAN... NONE. && $$ SHORT TERM...KC LONG TERM...MCD AVIATION...KC MARINE...KC
AREA FORECAST DISCUSSION
NWS MARQUETTE MI
138 AM EDT TUE SEP 4 2012 .SHORT TERM...(THIS EVENING THROUGH TUESDAY) ISSUED AT 517 PM EDT MON SEP 3 2012 WATER VAPOR IMAGERY AND RUC ANALYSIS SHOW WSW FLOW OVER THE UPPER GREAT LAKES BTWN UPPER RIDGE EXTENDING FROM THE PLAINS TO THE LWR LAKES AND A DEEP...OCCLUDED LOW OVER NRN MANITOBA. NARROW MOISTURE RIBBON HAS SHIFTED INTO THE UPPER LAKES IN ASSOCIATION WITH DISSIPATING SFC TROF ORIGINALLY ASSOCIATED WITH DEEP SYSTEM IN NRN MANITOBA. LEFT EXIT OF UPPER JET STREAK AIDED EARLY MORNING CONVECTION OVER NW UPPER MI/LAKE SUPERIOR. BASED ON LATEST RUC ANALYSIS...IT APPEARS CONVECTION THAT HAS BEEN DEVELOPING MAY BE GETTING SOME SUPPORT FROM THE RIGHT ENTRANCE OF JET STREAK NOW. ONGOING CONVECTION OVER ROUGHLY THE SE HALF OF THE FCST AREA WILL CONTINUE SETTLE SE INTO THE EVENING HRS. WITH MUCAPE ON THE ORDER OF 1000-2000J/KG AND DEEP LAYER SHEAR AROUND 40KT...ORGANIZED STORMS WILL CONTINUE ALONG WITH THE POTENTIAL OF SVR FOR THE NEXT SEVERAL HRS. SHRA/TSRA SHOULD BE OUT OF THE SE/SCNTRL FCST AREA MID TO LATE EVENING. HEALTHY DRYING ALOFT (NOTE UPSTREAM 12Z KINL SOUNDING) WILL THEN OCCUR THRU THE NIGHT...ENDING ANY THREAT OF ADDITIONAL PCPN. CONSIDERING DRYNESS OF INCOMING AIR MASS AND LIGHT/CALM WIND UNDER BUBBLE SFC HI PRES BUILDING INTO THE AREA...FAVORED THE LOWER SIDE OF AVBL GUIDANCE FOR MIN TEMPS. VIGOROUS DRYING ALOFT/LIGHT WINDS FAVOR FOG DEVELOPMENT...ESPECIALLY SINCE THERE HAS BEEN RAINFALL TODAY. THUS...MAINTAINED MENTION OF AREAS OF FOG OVER MUCH OF THE INTERIOR. ON TUE...ATTENTION TURNS TO A COUPLE OF SHORTWAVES EXTENDING FROM ND INTO MT. ONE OR BOTH OF THESE WAVES WILL REACH THE UPPER LAKES TUE AND WILL LIKELY PROVIDE SUFFICIENT FORCING FOR ISOLD/SCT CONVECTION. GIVEN THAT CONVECTION IS CURRENTLY BEING OBSERVED OVER THE ERN DAKOTAS AHEAD OF THE FIRST WAVE...BUMPED POPS UP INTO THE CHC CATEGORY OVER ROUGHLY THE W HALF OF THE FCST AREA TUE. ALTHOUGH NAM/GFS MLCAPES ARE IN THE 1500-2500J/KG RANGE...DEEP LAYER SHEAR IS UNDER 30KT WHICH WILL WORK TO LIMIT MORE WIDESPREAD SVR POTENTIAL. NONETHELESS...IF STORMS DO DEVELOP...MAY SEE SOME ISOLD/PULSE TYPE SVR STORMS TUE AFTN. .LONG TERM...(TUESDAY NIGHT THROUGH MONDAY) ISSUED AT 517 PM EDT MON SEP 3 2012 BASIC OUTLOOK OF THE LONG TERM NOT TOO DIFFERENT FROM YESTERDAY. WV LOOP AND 12Z RAOBS INDICATE PAIR OF UPPER LOWS IN CANADA FROM NORTHERN MANITOBA INTO NORTHERN BRITISH COLUMBIA. MANITOBA LOW STAYS FAIRLY STATIONARY THROUGH WEDNESDAY WHILE THE BRITISH COLUMBIA LOW DIGS TO ITS SOUTH AND EVENTUALLY SOUTHEAST INTO NORTHERN ONTARIO. AS THIS OCCURS...STRONG SFC-H85 COLD FRONT MARCHES ACROSS UPPER GREAT LAKES WEDNESDAY AFTERNOON AND EVENING. DYNAMICS PROVIDED BY 12-HR H5 HEIGHT FALLS TO 60M AND A COUPLED JET STRUCTURE COMBINE WITH SFC-H85 FRONT AND SURGE OF H85 MOISTURE TRANSPORT TO GENERATE SHRA ALONG AND AHEAD OF THE FRONT. DEPENDING ON TIMING OF FRONT AND HEATING AHEAD OF FRONT...TSRA COULD BE STRONG GIVEN 0-6KM CAPES UP TO 1500 J/KG AND AS H85 JET INCREASES OVER CWA AND BECOMES PARALLEL TO THE H5 FLOW. SETUP IS FAVORABLE FOR DYNAMICALLY DRIVEN BOW-ECHO SOMEWHERE OVER THE AREA AS THERE IS A DRY H7-H5 LAYER PUNCHING INTO THE AREA FROM THE WEST WITH DWPNT DEPRESSIONS OVR 20C BY LATER AFTN. BEST CHANCE FOR SEVERE PROBABLY ENDS UP SOUTH AND EAST OF CWA WHERE GREATEST MLCAPES ARE FORECAST IN THE AFTN. AT THE LEAST...LIKELY POPS ARE CERTAINLY WARRANTED AS THE SFC-H85 FRONT WORKS ACROSS THE CWA. ONCE FRONT PLOWS THROUGH MAY SEE HIGHER WIND GUSTS WEDNESDAY NIGHT INTO THURSDAY AS SFC LOW WRAPS UP BTWN LAKE SUPERIOR AND HUDSON BAY. GFS/ECMWF H85 WINDS NOT THAT STRONG...MAYBE UP TO 30 KTS...SO DOES NOT APPEAR THAT WINDS WILL BECOME TOO STRONG. IF THE SFC LOW ENDS UP DEEPENING CLOSER TO LK SUPERIOR...COULD SEE NORTHWESTERLY WIND GUSTS ALONG LK SUPERIOR 40-45 MPH. AT THIS POINT...WX ON THURSDAY SHOULD END UP QUIET AS UPR MICHIGAN IS BTWN THE STRONG SHORTWAVE TROUGH THAT MOVES THROUGH MID WEEK AND RE-INFORCING TROUGH THAT IS FORECAST TO ROTATE THROUGH ON FRIDAY. FORECAST SOUNDINGS FROM GFS AND OUTPUT FROM GEM-NHEM INDICATE SOME POTENTIAL FOR LIGHT SHRA OVER THE EASTERN CWA IN WEAK AREA OF LOW-LEVEL CONVERGENCE. SEEMS GREATER CHANCE OF SHRA ARRIVES ON FRIDAY WITH THE INCOMING TROUGH AND INDICATION OF SHORTWAVE RIDING THROUGH IN WEST/NORTHWEST FLOW ALOFT. THIS FORCING ALONG WITH INCREASING OVER-WATER INSTABILITY WITH LAKE EFFECT CAPES PUSHING AOA 500J/KG SUGGESTS HYBRID LATE SUMMER AND EARLY FALL TYPE SHRA AND MAYBE EVEN MENTION OF TSRA GIVEN LAKE INDUCED EQL OVER 20KFT WHICH PUSHES CONVECTIVE DEPTH BLO 0C. GIVEN LAKE-H85 DELTA T AOA 15C...DEEP LAKE INDUCED CLOUD DEPTH...AND WINDS WITHIN THE MIXED LAYER STAYING BLO 25 KTS...PARAMETERS STILL LINE UP FOR WATERSPOUT POTENTIAL ON FRIDAY...ESPECIALLY IF SUBTLE LOW-LEVEL TROUGH THAT IS SHOWING UP IN MODELS OVER EASTERN LK SUPERIOR/EASTERN CWA DOES INDEED VERIFY. TOUGH TO INCLUDE MENTION OF WATERSPOUTS THIS FAR OUT IN THE FORECAST BUT WILL BE INTERESTING TO SEE OUTPUT IN THE NEXT COUPLE DAYS FROM THE NEW EXPERIMENTAL GREAT LAKES WATERSPOUT FORECAST BASED ON THE SZILAGYI WATERSPOUT INDEX /SWI/ THAT COMES OUT OF THE INTERNATIONAL CENTRE FOR WATERSPOUT RESEARCH /ICWR/. IN ADDITION TO WATERSPOUTS...WILL ALSO LIKELY HAVE INCREASED RISK OF RIP CURRENTS ALONG LK SUPERIOR BEACHES...MAINLY IN ALGER COUNTY WITH THE EXPECTED NORTHWEST WINDS. UPPER TROUGH SLOWLY MOVES EAST THROUGH NEXT WEEKEND. THIS PLACES UPPER LAKES WITHIN ZONE OF SHARP CONFLUENCE AND ASSOCIATED SFC RIDGING. ECMWF HAS DEFINITELY TRENDED FARTHER EAST WITH TROUGH AND KEEPS QPF OUT OF UPR MICHIGAN FOR THE WEEKEND. GFS IS SLIGHTLY FARTHER WEST WITH THE TROUGH AND WOULD KEEP THREAT OF SHRA OVER EASTERN CWA ON SATURDAY. BASED ON AMPLIFIED PATTERN CANNOT RULE THIS IDEA OUT AND WILL AT THE LEAST KEEP CONSENSUS SLIGHT CHANCE POPS AND BUMP UP SKY COVER. SUNDAY INTO MONDAY IS TOUGH TO FIGURE OUT AS ECMWF CONTINUES TO INDICATE STRONGER SHORTWAVE WITHIN BASE OF TROUGH LIFTING NORTH AND AFFECTING THE EASTERN PORTIONS OF CWA WITH SOME SHRA WHILE THE GFS KEEPS ALL THIS TOO FAR TO THE EAST TO AFFECT THE AREA. NO REAL CONSISTENT SIGNAL FOR EITHER SOLUTION SO HAVE TO KEEP CONSENSUS POPS AT THIS TIME. && .AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT) ISSUED AT 137 AM EDT TUE SEP 4 2012 EXPECT VLIFR CONDITIONS/FOG THRU SUNRISE AT SAW BEFORE DAYTIME HEATING BURNS THIS FOG OFF AND BRINGS A RETURN OF VFR CONDITIONS. DRY LLVL AIR SHOWN ON THE 00Z MPX/INL RAOBS HAS MADE GREATER INROADS INTO WRN UPR MI...SO LOOK FOR ONLY PTCHY FOG/POSSIBLE MVFR VSBYS AT THESE LOCATIONS. THE APRCH OF A LO PRES TROF THIS AFTN IN TANDEM WITH DAYTIME HEATING MAY RESULT IN SOME SHRA/EVEN A TS AT ALL 3 SITES THIS AFTN/EVNG...BUT RELATIVE DRYNESS OF THE LLVLS SHOULD MAINTAIN VFR CONDITIONS. SOME FOG MAY DVLP AT IWD LATER THIS EVNG WITH SOME DRYING ALF OVER LINGERNIG LLVL MSTR. && .MARINE...(FOR THE 4 AM LAKE SUPERIOR FORECAST ISSUANCE) ISSUED AT 429 AM EDT MON SEP 3 2012 EXPECT S WINDS UP TO 20 KTS IN ADVANCE OF AN APPROACHING COLD FRONT TO DIMINISH THIS EVENING AS THE FRONT TENDS TO WEAKEN. LIGHT WINDS WILL THEN PREVAIL THRU TONIGHT AS A WEAK HI PRES SYSTEM MOVES INTO THE UPPER GREAT LAKES. A SERIES OF LOW PRESSURE SYSTEMS AND COLD FRONTS WILL MOVE NEAR LAKE SUPERIOR TUESDAY THROUGH SUNDAY...LEADING TO PERIODS OF INCREASED WINDS. HOWEVER...AT THIS TIME WINDS ARE EXPECTED TO REMAIN BELOW 25KTS. && .MQT WATCHES/WARNINGS/ADVISORIES... UPPER MICHIGAN... NONE. LAKE SUPERIOR... NONE. LAKE MICHIGAN... NONE. && $$ SHORT TERM...ROLFSON LONG TERM...JLA AVIATION...KC MARINE...ROLFSON
AREA FORECAST DISCUSSION
NWS NORTH PLATTE NE
345 AM CDT TUE SEP 4 2012 .DISCUSSION... ONE MORE DAY OF 90S BEFORE A COOL DOWN CAN BE EXPECTED. RIDGE ACROSS THE SOUTHERN PLAINS WITH SOUTHWEST FLOW IN TRANSITION TO A MORE ZONAL FLOW AS A TROUGH PUSHES ACROSS THE NORTHERN ROCKIES AND NORTHERN PLAINS. SURFACE TROUGH ACROSS THE CWA THIS MORNING WITH VERY DRY AIR...DEW PTS IN THE 30S...WEST OF THE TROUGH...A KVTN TO KTIF TO KOGA LINE. TO THE EAST OF THE TROUGH DEW PTS IN THE 50S AND 60S AND A FEW SITES ACROSS CENTRAL NEB STARTING TO REPORT SOME FOG. COLD FRONT HEADING SOUTH ACROSS THE NORTHERN ROCKIES. TROUGH WILL REMAIN NEARLY STATIONARY THIS AFTERNOON ACROSS THE AREA WITH VERY DRY CONDITIONS AND RH PERCENTAGES NEAR OR BELOW 15 PERCENT TO THE WEST. WINDS ARE MARGINAL...AROUND 15 TO 20 MPH...FOR RFW CRITERIA...HOWEVER DUE TO DROUGHT AND LOW RH VALUES...WILL HAVE A RFW FOR MUCH OF NW NEB. AS FOR TEMPS...THE DRY AIR WILL COMBINE WITH SOME PREFRONTAL COMPRESSIONAL HEATING TO PUSH HIGHS ONCE AGAIN INTO THE 90S. LATE THIS AFTERNOON ALONG AND EAST OF THE TROUGH...WHERE BETTER LOW LEVEL MOISTURE...SOME ISOLATED THUNDERSTORMS ARE POSSIBLE WITH PEAK HEAT...SIMILAR TO YESTERDAY. BETTER SHEAR/HIGHER CAPE/AND SPC SLIGHT RISK IS EAST OF THE CWA...HOWEVER EXPECT DEVELOPMENT ALONG TO EAST OF THE TROUGH...WHICH SHOULD STILL BE OVER THE CWA...AND CANNOT RULE OUT A STRAY STORM BECOMING STRONG. ONCE THE COLD FRONT MOVES ACROSS THE AREA THIS EVENING INTO THE OVERNIGHT HOURS...THE CONVECTION WILL QUICKLY MOVE EAST. DRY AND COOL AIR WILL SPREAD ACROSS THE AREA. WED HIGHS AROUND 80 ACROSS ALL BUT THE SW...WHICH SHOULD PUSH INTO THE LOWER 80S. THESE HIGHS ARE FAIRLY CLOSE TO NORMAL FOR THIS TIME OF YEAR. HOWEVER DEW PTS IN THE 30S TO LOWER 40S WILL CONTINUE TO CREATE A HIGH DANGER HOWEVER WINDS NOT EXPECTED TO BE MUCH OVER 10 MPH. THURSDAY ANOTHER COLD FRONT WILL APPROACH FROM THE NW. AHEAD OF THE FRONT WINDS BECOME SOUTHERLY AND BRING A RETURN OF WARMER TEMPERATURES AND POSSIBLY SOME LL MOISTURE. WILL HAVE TO MONITOR HIGHS AS THE MODELS HAVE TRENDED UP TODAY...WITH THE NAM SEEING AN INCREASE BACK CLOSE TO 90. HAVE NOT JUMPED TO THIS WARM YET...HOWEVER IF WE DO WARM TO THIS...NEAR CRITICAL FIRE WEATHER CONDITIONS WILL BE POSSIBLE AS DEW PTS SLOW TO RISE. AS THE FRONT PASSES THURSDAY NIGHT INTO FRIDAY MOISTURE WILL CONTINUE TO BE A LIMITING FACTOR ON SHOWER AND THUNDERSTORM DEVELOPMENT. HAVE TRENDED DRIER AS RETURN MOISTURE LOOKS TO BE ONLY TO CURRENT LEVELS...AT BEST...ACCORDING TO LATEST GUIDANCE...WITH A GOOD POSSIBILITY THIS TREND WILL CONTINUE OVER THE NEXT FEW FORECAST UPDATES. FRIDAY INTO SATURDAY WILL BE THE COOLEST OF THE FORECAST PERIOD AS COOL HIGH PRESSURE SETTLES OVER THE HIGH PLAINS. GUIDANCE AND FORECAST HAVE HIGHS ONLY IN THE 70S...WITH LOWS IN THE 40S. BY SUNDAY THE HIGH WILL PUSH TO THE EAST WITH SOUTHERLY FLOW RETURNING AND BRINGING A SLOW WARMUP INTO THE START OF NEXT WEEK. STILL NO MOISTURE AND FORECAST REMAINS DRY. && .AVIATION... VFR IS EXPECTED MOST AREAS TODAY AND TONIGHT. PATCHY MORNING FOG WILL DEVELOP ALONG AND EAST OF HIGHWAY 183 THROUGH 14Z. ISOLATED THUNDERSTORMS ARE EXPECTED LATE THIS AFTERNOON AND THIS EVENING ALONG AND EAST OF HIGHWAY 83. WINDY CONDITIONS ARE EXPECTED TONIGHT BEHIND A STRONG COLD FRONT. && .FIRE WEATHER... HOT DRY AIR WILL SURGE EAST THROUGH WESTERN AND NORTH CENTRAL NEBRASKA AHEAD OF A STRONG COLD FRONT WHICH WILL MOVE THROUGH TONIGHT. CRITICAL FIRE DANGER IS EXPECTED ALONG AND NORTH OF INTERSTATE 80 AND GENERALLY ALONG AND WEST OF HIGHWAY 83. THE 20Z HRRR AND THE 00Z GEM REGIONAL MODELS SUGGEST SIMILAR CONDITIONS WILL DEVELOP ACROSS SWRN NEB AND PERHAPS INTO AREAS EAST OF HIGHWAY 83. GIVEN THE DIFFERENCES BETWEEN HRRR AND GEM REGIONAL VERSUS THE NAM AND ECM WILL HOLD OFF ON AN EXPANSION OF THE RED FLAG WARNING FOR NOW. && .LBF WATCHES/WARNINGS/ADVISORIES...RED FLAG WARNING FROM 11 AM CDT /10 AM MDT/ THIS MORNING TO 10 PM CDT /9 PM MDT/ THIS EVENING FOR NEZ204-206-208. && $$ DISCUSSION...MASEK AVIATION/FIRE WEATHER...CDC
AREA FORECAST DISCUSSION
NWS RALEIGH NC
253 AM EDT TUE SEP 4 2012 .SYNOPSIS... UNSETTLED WEATHER WILL PERSIST THROUGH WEDNESDAY AS THE REMNANTS OF TROPICAL CYCLONE ISAAC SLOWLY WEAKEN ALONG THE CENTRAL AND SOUTHERN APPALACHIANS. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1005 PM MONDAY... TONIGHT: FORECAST RATIONALE RELATIVELY UNCHANGED FROM EARLIER THINKING. ONE WEAKENING BAND OF CONVECTION AND EMBEDDED MCV/S NEAR KFVX AND KLHZ WILL CONTINUE TO CROSS THE FAR NORTHEAST PIEDMONT AND NORTHERN COASTAL PLAIN THROUGH MIDNIGHT. HEAVY RAIN WILL BE THE PRIMARY HAZARD WITH THIS CONVECTION. THE MAIN FOCUS FOR SCATTERED CONVECTION OVERNIGHT WILL THEN OCCUR OVER THE WESTERN HALF OF THE RAH CWFA....PARTICULARLY OVER THE WESTERN PIEDMONT...WHERE DEEP LAYER MOISTURE TRANSPORT AND GLANCING FORCING FOR ASCENT ASSOCIATED WITH WEAK PERTURBATIONS IN SOUTHWESTERLY FLOW ALOFT -- EVIDENT ON 02Z WV IMAGERY AND RAP ANALYZED VORTICITY FIELDS FROM EASTERN AL TO THE SC UPSTATE -- ARE FORECAST TO BE MAXIMIZED. PERSISTENCE LOWS GENERALLY IN THE LOWER 70S...WITH AREAS OF STRATUS AND/OR FOG LATE. THESE SHOWERS AND ISOLATED STORMS TOO WILL POSE A RISK OF HEAVY RAIN...BUT THE SCATTERED NATURE AND DIMINISHED INSTABILITY SUGGEST A MINIMAL THREAT OF FLOODING. AS OF 340 PM MONDAY... OVERVIEW: THE REMNANTS OF TROPICAL CYCLONE ISAAC WILL GET STRETCHED AND SHEARED APART DURING THE DAY ON TUESDAY...LEAVING BEHIND A WEAK MID/UPPER LEVEL TROUGHINESS ACROSS THE CAROLINAS. TUESDAY AND TUESDAY NIGHT: THE MOIST AIRMASS FEATURING PWATS AT OR ABOVE 2.0" WILL REMAIN IN PLACE ACROSS THE CAROLINAS ON TUESDAY. THERE REMAINS SOME QUESTIONS/UNCERTAINTY REGARDING PENDING DEVELOPMENT AND EVOLUTION OF A SOUTHWARD PROPAGATING MCS TOWARDS THE GULF COAST STATES THAT COULD AUGMENT/DISTURB MOISTURE CONVERGENCE OVER THE AREA...BUT OVERALL THINKING IS THAT WE WILL SEE DIURNAL ENHANCEMENT IN CONVECTIVE COVERAGE TUESDAY AFTERNOON...ESPECIALLY OVER THE WESTERN PIEDMONT INVOF OF THE BROAD TROUGHINESS AND CONTINUED UPSLOPE REGIME ALONG THE EASTERN SLOPES. ELSEWHERE...MUCH LIKE TODAY...FORCING WILL BE MOSTLY CONFINED TO VIA MESOSCALE BOUNDARIES SUCH AS DIFFERENTIAL HEATING...OUTFLOW OR SEABREEZE. POPS RANGING FROM LIKELY WEST TO CHANCE POPS EAST. HIGHS TUESDAY SHOULD BE VERY SIMILAR TO TODAY...DEPENDENT ON HOW EARLY CONVECTION/RAIN MOVES INTO WESTERN PORTIONS OF THE FORECAST AREA. HIGHS IN THE LOWER TO MID 80S WEST TO NEAR 90 CENTRAL AND EASTERN AREAS. LOWS 69 TO 73. SEVERE THREAT...ORGANIZED SEVERE WEATHER APPEARS UNLIKELY THIS AFTERNOON AND AGAIN TOMORROW WITH INSTABILITY TEMPERED BY CLOUD COVER AND WEAK MID-LEVEL LAPSE RATES. HOWEVER...AN ISOLATED SEVERE THREAT CANNOT BE RULED OUT WHERE MESOSCALE PROCESSES LOCALLY ENHANCE LOW/MID LEVEL SHEAR AND ASCENT. THE MAIN CONCERN WILL BE FROM HEAVY RAINFALL AND FLASH FLOODING...PRIMARILY IN THE WESTERN PIEDMONT WHERE A SLOW MOVING NORTH-SOUTH ORIENTED LINE OF CONVECTION COULD PERSIST FOR SEVERAL HOURS. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... AS OF 240 AM TUESDAY... LOCALLY HEAVY RAIN WEDNESDAY AFTERNOON AND EVENING... THE COMBINATION OF THE RESIDUAL MID-UPPER LEVEL TROUGH AND A WEAK COLD FRONT WILL COMBINE WITH DEEP BOUNDARY LAYER MOISTURE AND SURFACE HEATING TO BRING ANOTHER GOOD CHANCE OF MAINLY AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS ON WEDNESDAY. QPF ON THE ORDER OF 0.25 TO 0.50 WILL BE FORECAST... WHICH IS AN AREAL AVERAGE FOR THE REGION. HOWEVER... LOCALLY 1-2 INCHES OF RAIN ARE EXPECTED WHICH MAY LEAD AGAIN TO MAINLY URBAN AND SMALL STREAM FLOODING. FORECAST SOUNDINGS INDICATE MORE LOW STRATUS TO START THE DAY BEFORE BURNING OFF TO PARTLY SUNNY SKIES BY MID MORNING. HIGHS SHOULD TOP OUT A FEW DEGREES ABOVE THE EARLY SEP AVERAGE. EXPECT MID TO UPPER 80S OVER THE PIEDMONT WITH AROUND 90 ACROSS THE SANDHILLS AND COASTAL PLAIN. EXPECT THE CONVECTION TO BECOME MORE ISOLATED OVERNIGHT WITH ADDITIONAL STRATUS LATE. LOWS AGAIN WEDNESDAY NIGHT WILL BE IN THE LOWER 70S AS THE DEW POINTS WILL CONTINUE VERY OPPRESSIVE. THE WEAK COLD FRONT IS FORECAST TO STALL OVER OUR AREA THURSDAY INTO THURSDAY NIGHT. WE WILL MAINTAIN A GOOD CHANCE OF MAINLY AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS THURSDAY. HIGHS ONCE AGAIN SHOULD BE IN THE MID TO UPPER 80S NW AND AROUND 90 SE. && .LONG TERM /FRIDAY THROUGH MONDAY/... AS OF 250 AM TUESDAY... MORE OPPRESSIVE HUMIDITY ALONG WITH SHOWERS AND THUNDERSTORMS EXPECTED INTO EARLY NEXT WEEK. ANOTHER STRONG MID-UPPER LEVEL TROUGH/CUT OFF LOW EXPECTED TO DEVELOP OVER THE OHIO/TENNESSEE VALLEY REGION THIS WEEKEND AND EARLY NEXT WEEK. JUST HOW FAR SOUTH THE UPPER LOW DEVELOPS WILL DETERMINE THE COVERAGE AND AMOUNTS OF RAIN FOR OUR REGION SAT-MON. THE LATEST TRENDS SUPPORT A DEEPER AND MORE CUT-OFF H5 LOW AS FAR SOUTH AS THE SOUTHERN APPALACHIANS SUN-MON. THIS WOULD SUGGEST ANOTHER VERY WET PERIOD FOR THE CENTRAL AND SOUTHERN APPALACHIANS EAST ACROSS NC/VA WITH LOCALLY HEAVY RAIN. HOWEVER... THERE CONTINUED TO BE ENOUGH SPREAD IN THE MODEL SOLUTIONS TO INFER ONLY LOW TO MEDIUM CONFIDENCE IN THE DETAILS THIS FAR OUT. THEREFORE... WE WILL MAINTAIN INCREASING CHANCES OF SHOWERS/STORMS SAT-SUN. THE WARM AND MOIST PATTERN MAY PERSIST INTO EARLY NEXT WEEK BEFORE THE UPPER TROUGH/LOW PULL OUT TO THE NE TUE-WED. FRIDAY... WE WILL CARRY 20-30 POP AS THE LOW LEVEL BOUNDARY WILL BE IN THE REGION (MORE LIKELY STALLING OVER THE EASTERN PIEDMONT OR COASTAL PLAIN). PARTLY SUNNY OTHERWISE WITH HIGHS IN THE MID 80S NW TO AROUND 90 SE. SAT-MON... WE WILL CARRY 40-50 POP WITH MAINLY AFTERNOON AND EVENING SHOWERS AND STORMS. DEPENDING ON THE EVOLUTION OF THE UPPER TROUGH... LOCALLY HEAVY RAIN MAY BE A THREAT AGAIN. HIGHS WILL BE MOSTLY IN THE 80S. LOWS IN THE 70-73 RANGE...EXCEPT UPPER 60S NW. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... AS OF 115 AM TUESDAY... 24-HR TAF PERIOD: INT/GSO: THE BEST CHANCE FOR ADVERSE AVIATION CONDITIONS TODAY WILL BE IN WESTERN PORTIONS OF THE STATE (INT/GSO TERMINALS) WHERE LOW-LEVEL MOISTURE AND UPPER LEVEL FORCING ASSOCIATED WITH THE REMNANTS OF TC ISAAC WILL BE MAXIMIZED. EXPECT IFR/LIFR STRATUS AND SCATTERED CONVECTION AT THE INT/GSO TERMINALS BETWEEN 06-15Z...WITH CEILINGS IMPROVING TO MVFR BY EARLY/MID AFTERNOON (~18Z) AND SCATTERED/ PERIODIC CONVECTION THROUGH THE REMAINDER OF THE TAF PERIOD. RDU: EXPECT A CHANCE FOR ISOLATED CONVECTION AND IFR/LIFR CEILINGS OR VISBYS BETWEEN 06-12Z AT THE RDU TERMINAL...WITH ANY IFR/LIFR CEILINGS IMPROVING TO MVFR AND EVENTUALLY VFR BY 15-18Z. PERIODIC CONVECTION WILL REMAIN POSSIBLE THROUGHOUT THE TAF PERIOD...THOUGH THE BEST OVERALL CHANCES ARE EXPECTED FURTHER WEST AT THE INT/GSO TERMINALS AS MENTIONED ABOVE. FAY/RWI: DRIER LOW-LEVEL (2500-5000 FT AGL) CONDITIONS WILL BE PRESENT OVER EASTERN PORTIONS OF THE AREA TODAY...AND IT WOULD APPEAR THAT SUB-VFR VISBYS ASSOCIATED WITH FOG ARE MORE LIKELY THAN SUB-VFR CEILINGS BETWEEN 06-12Z THIS MORNING. LOCALLY DENSE FOG AND IFR/LIFR VISBYS CANNOT BE RULED OUT IN THE 10-12Z TIME FRAME WHERE CLOUD COVER IS THINNER AND WINDS GO CALM PRIOR TO SUNRISE. ANY FOG WOULD BE EXPECTED TO LIFT TO VFR BY 12-14Z. ISOLD CONVECTION WILL BE POSSIBLE AT THE FAY/RWI TERMINALS THROUGHOUT THE TAF PERIOD...THOUGH UNCERTAINTY IN THE TIMING AND COVERAGE OF CONVECTION IS GREATER AT THESE SITES THAN POINTS FURTHER WEST. WEDNESDAY-SUNDAY: GIVEN LITTLE CHANGE IN THE OVERALL PATTERN WED/WED NIGHT... ANTICIPATE SIMILAR CONDITIONS TO TODAY AND MONDAY...CHARACTERIZED BY MORNING FOG/STRATUS AND PERIODIC SHOWERS/STORMS...WITH THE BEST CHANCE AND GREATEST COVERAGE DURING THE AFTERNOON AND EVENING HOURS. DRIER/VFR CONDITIONS WILL BE MORE LIKELY THU/FRI AS THE REMNANTS OF TC ISAAC WASH OUT AND A DRIER AIRMASS BUILDS TOWARD THE AREA FROM THE WEST. HOWEVER...ADVERSE AVIATION CONDITIONS ARE EXPECTED TO RETURN OVER THE WEEKEND AS UN UNSEASONABLY DEEP UPPER LEVEL TROUGH DIGS INTO THE TN VALLEY AND DEEP SOUTH. -VINCENT && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...VINCENT NEAR TERM....MWS/CBL SHORT TERM...BADGETT LONG TERM...BADGETT AVIATION...VINCENT
AREA FORECAST DISCUSSION
NWS RALEIGH NC
118 AM EDT TUE SEP 4 2012 .SYNOPSIS... UNSETTLED WEATHER WILL PERSIST THROUGH WEDNESDAY AS THE REMNANTS OF TROPICAL CYCLONE ISAAC SLOWLY WEAKEN ALONG THE CENTRAL AND SOUTHERN APPALACHIANS. && .NEAR TERM /THROUGH TUESDAY NIGHT/... AS OF 1005 PM MONDAY... TONIGHT: FORECAST RATIONALE RELATIVELY UNCHANGED FROM EARLIER THINKING. ONE WEAKENING BAND OF CONVECTION AND EMBEDDED MCV/S NEAR KFVX AND KLHZ WILL CONTINUE TO CROSS THE FAR NORTHEAST PIEDMONT AND NORTHERN COASTAL PLAIN THROUGH MIDNIGHT. HEAVY RAIN WILL BE THE PRIMARY HAZARD WITH THIS CONVECTION. THE MAIN FOCUS FOR SCATTERED CONVECTION OVERNIGHT WILL THEN OCCUR OVER THE WESTERN HALF OF THE RAH CWFA....PARTICULARLY OVER THE WESTERN PIEDMONT...WHERE DEEP LAYER MOISTURE TRANSPORT AND GLANCING FORCING FOR ASCENT ASSOCIATED WITH WEAK PERTURBATIONS IN SOUTHWESTERLY FLOW ALOFT -- EVIDENT ON 02Z WV IMAGERY AND RAP ANALYZED VORTICITY FIELDS FROM EASTERN AL TO THE SC UPSTATE -- ARE FORECAST TO BE MAXIMIZED. PERSISTENCE LOWS GENERALLY IN THE LOWER 70S...WITH AREAS OF STRATUS AND/OR FOG LATE. THESE SHOWERS AND ISOLATED STORMS TOO WILL POSE A RISK OF HEAVY RAIN...BUT THE SCATTERED NATURE AND DIMINISHED INSTABILITY SUGGEST A MINIMAL THREAT OF FLOODING. AS OF 340 PM MONDAY... OVERVIEW: THE REMNANTS OF TROPICAL CYCLONE ISAAC WILL GET STRETCHED AND SHEARED APART DURING THE DAY ON TUESDAY...LEAVING BEHIND A WEAK MID/UPPER LEVEL TROUGHINESS ACROSS THE CAROLINAS. TUESDAY AND TUESDAY NIGHT: THE MOIST AIRMASS FEATURING PWATS AT OR ABOVE 2.0" WILL REMAIN IN PLACE ACROSS THE CAROLINAS ON TUESDAY. THERE REMAINS SOME QUESTIONS/UNCERTAINTY REGARDING PENDING DEVELOPMENT AND EVOLUTION OF A SOUTHWARD PROPAGATING MCS TOWARDS THE GULF COAST STATES THAT COULD AUGMENT/DISTURB MOISTURE CONVERGENCE OVER THE AREA...BUT OVERALL THINKING IS THAT WE WILL SEE DIURNAL ENHANCEMENT IN CONVECTIVE COVERAGE TUESDAY AFTERNOON...ESPECIALLY OVER THE WESTERN PIEDMONT INVOF OF THE BROAD TROUGHINESS AND CONTINUED UPSLOPE REGIME ALONG THE EASTERN SLOPES. ELSEWHERE...MUCH LIKE TODAY...FORCING WILL BE MOSTLY CONFINED TO VIA MESOSCALE BOUNDARIES SUCH AS DIFFERENTIAL HEATING...OUTFLOW OR SEABREEZE. POPS RANGING FROM LIKELY WEST TO CHANCE POPS EAST. HIGHS TUESDAY SHOULD BE VERY SIMILAR TO TODAY...DEPENDENT ON HOW EARLY CONVECTION/RAIN MOVES INTO WESTERN PORTIONS OF THE FORECAST AREA. HIGHS IN THE LOWER TO MID 80S WEST TO NEAR 90 CENTRAL AND EASTERN AREAS. LOWS 69 TO 73. SEVERE THREAT...ORGANIZED SEVERE WEATHER APPEARS UNLIKELY THIS AFTERNOON AND AGAIN TOMORROW WITH INSTABILITY TEMPERED BY CLOUD COVER AND WEAK MID-LEVEL LAPSE RATES. HOWEVER...AN ISOLATED SEVERE THREAT CANNOT BE RULED OUT WHERE MESOSCALE PROCESSES LOCALLY ENHANCE LOW/MID LEVEL SHEAR AND ASCENT. THE MAIN CONCERN WILL BE FROM HEAVY RAINFALL AND FLASH FLOODING...PRIMARILY IN THE WESTERN PIEDMONT WHERE A SLOW MOVING NORTH-SOUTH ORIENTED LINE OF CONVECTION COULD PERSIST FOR SEVERAL HOURS. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... AS OF 300 PM MONDAY... UNSETTLED WEATHER WILL LIKELY PERSIST ACROSS CENTRAL NC THROUGH THE SHORT TERM PERIOD AS WEAK TROUGHING ALOFT REMAINS OVER THE AREA. AT THE SURFACE...A WEAK BOUNDARY WILL APPROACH THE AREA LATE WEDNESDAY INTO THURSDAY. ALL OF THIS COMBINED WITH AMPLE MOISTURE (PWAT VALUES EXCEEDING 2 INCHES) AND A MODERATELY UNSTABLE AIR MASS WILL RESULT IN SCATTERED SHOWERS AND THUNDERSTORMS...MAINLY DURING THE AFTERNOON AND EVENING HOURS. AT THIS TIME...AM EXPECTING THE BEST COVERAGE TO BE ACROSS THE WEST ON WEDNESDAY AS THERE WILL BE SLIGHTLY DRIER AIR ACROSS THE EAST AND THEN THE BEST FOCUS SHOULD SHIFT TO THE EAST FOR THURSDAY AS SLIGHTLY DRIER AIR MOVES IN BEHIND THE AFOREMENTIONED SURFACE BOUNDARY. THE MAIN THREAT IS EXPECTED TO BE HEAVY RAIN THAT COULD LEAD TO SOME FLOODING...ESPECIALLY IN URBAN AREAS. HIGH TEMPS WILL BE NEAR NORMAL...GENERALLY IN THE MID/UPPER 80S...WITH OVERNIGHT LOWS RUNNING SLIGHTLY ABOVE NORMAL...GENERALLY IN THE UPPER 60S TO LOWER 70S. && .LONG TERM /FRIDAY THROUGH MONDAY/... AS OF 300 PM MONDAY... AN UNSETTLED WEATHER PATTERN IS EXPECTED TO CONTINUE THROUGH MUCH OF THE LONG TERM PERIOD. FOR FRIDAY...THE BROAD TROUGH ALOFT WILL STILL BE OVER THE AREA...WHILE AT THE SURFACE A WEAK SURFACE BOUNDARY (SEE ABOVE SHORT TERM DISCUSSION) WILL LIKELY BE WASHING OUT OVER THE AREA. NEVERTHELESS...WITH MOISTURE CONTENT STILL EXPECTED TO BE HIGH ACROSS THE REGION...AM EXPECTING ANOTHER GOOD CHANCE OF SHOWERS AND THUNDERSTORMS. BY THE WEEKEND...A SHORT WAVE COMING OUT OF CENTRAL CANADA WILL RESULT IN A TROUGH AMPLIFYING AS IT MOVES ACROSS THE MIDWEST ON SATURDAY AND TOWARDS THE EAST COAST BY SUNDAY. AS THIS RATHER DEEP TROUGH AND ITS ASSOCIATED SURFACE FRONT APPROACHES THE REGION...THIS SHOULD RESULT IN A PROLONGED PERIOD OF GOOD PRECIP CHANCES THROUGH AT LEAST THE END OF THE WEEKEND. AS CAN BE EXPECTED THIS FAR OUT...THERE ARE TIMING AND STRENGTH DIFFERENCES....BUT WILL BEGIN TO TAPER POPS DOWNWARD LATE SUNDAY AND INTO EARLY NEXT WEEK. THERE ARE STILL FAIRLY STRONG INDICATIONS THAT COOLER AND DRIER AIR SHOULD ARRIVE SOMETIME EARLY NEXT WEEK AS A RATHER DEEP TROUGH/CUT OFF LOW DEVELOPS. OVERALL...TEMPS WILL BE NEAR NORMAL EARLY ON IN THE PERIOD BEFORE TRENDING BELOW NORMAL AS INCREASED PRECIP CHANCES AND THE DEEP TROUGH/ASSOCIATED SURFACE FRONT APPROACH AND MOVE THROUGH THE REGION. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... AS OF 115 AM TUESDAY... 24-HR TAF PERIOD: INT/GSO: THE BEST CHANCE FOR ADVERSE AVIATION CONDITIONS TODAY WILL BE IN WESTERN PORTIONS OF THE STATE (INT/GSO TERMINALS) WHERE LOW-LEVEL MOISTURE AND UPPER LEVEL FORCING ASSOCIATED WITH THE REMNANTS OF TC ISAAC WILL BE MAXIMIZED. EXPECT IFR/LIFR STRATUS AND SCATTERED CONVECTION AT THE INT/GSO TERMINALS BETWEEN 06-15Z...WITH CEILINGS IMPROVING TO MVFR BY EARLY/MID AFTERNOON (~18Z) AND SCATTERED/ PERIODIC CONVECTION THROUGH THE REMAINDER OF THE TAF PERIOD. RDU: EXPECT A CHANCE FOR ISOLATED CONVECTION AND IFR/LIFR CEILINGS OR VISBYS BETWEEN 06-12Z AT THE RDU TERMINAL...WITH ANY IFR/LIFR CEILINGS IMPROVING TO MVFR AND EVENTUALLY VFR BY 15-18Z. PERIODIC CONVECTION WILL REMAIN POSSIBLE THROUGHOUT THE TAF PERIOD...THOUGH THE BEST OVERALL CHANCES ARE EXPECTED FURTHER WEST AT THE INT/GSO TERMINALS AS MENTIONED ABOVE. FAY/RWI: DRIER LOW-LEVEL (2500-5000 FT AGL) CONDITIONS WILL BE PRESENT OVER EASTERN PORTIONS OF THE AREA TODAY...AND IT WOULD APPEAR THAT SUB-VFR VISBYS ASSOCIATED WITH FOG ARE MORE LIKELY THAN SUB-VFR CEILINGS BETWEEN 06-12Z THIS MORNING. LOCALLY DENSE FOG AND IFR/LIFR VISBYS CANNOT BE RULED OUT IN THE 10-12Z TIME FRAME WHERE CLOUD COVER IS THINNER AND WINDS GO CALM PRIOR TO SUNRISE. ANY FOG WOULD BE EXPECTED TO LIFT TO VFR BY 12-14Z. ISOLD CONVECTION WILL BE POSSIBLE AT THE FAY/RWI TERMINALS THROUGHOUT THE TAF PERIOD...THOUGH UNCERTAINTY IN THE TIMING AND COVERAGE OF CONVECTION IS GREATER AT THESE SITES THAN POINTS FURTHER WEST. WEDNESDAY-SUNDAY: GIVEN LITTLE CHANGE IN THE OVERALL PATTERN WED/WED NIGHT... ANTICIPATE SIMILAR CONDITIONS TO TODAY AND MONDAY...CHARACTERIZED BY MORNING FOG/STRATUS AND PERIODIC SHOWERS/STORMS...WITH THE BEST CHANCE AND GREATEST COVERAGE DURING THE AFTERNOON AND EVENING HOURS. DRIER/VFR CONDITIONS WILL BE MORE LIKELY THU/FRI AS THE REMNANTS OF TC ISAAC WASH OUT AND A DRIER AIRMASS BUILDS TOWARD THE AREA FROM THE WEST. HOWEVER...ADVERSE AVIATION CONDITIONS ARE EXPECTED TO RETURN OVER THE WEEKEND AS UN UNSEASONABLY DEEP UPPER LEVEL TROUGH DIGS INTO THE TN VALLEY AND DEEP SOUTH. -VINCENT && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...VINCENT NEAR TERM....MWS/CBL SHORT TERM...KRR LONG TERM...KRR AVIATION...VINCENT
AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NWS SIOUX FALLS SD
1100 PM CDT MON SEP 3 2012 .DISCUSSION... WILL VERY LIKELY BE ABLE TO LET THE REMAINDER OF THE SEVERE THUNDERSTORM WATCH EXPIRE AT 03Z. TOWARD SUNSET...THE STORMS BECAME INCREASINGLY LOW CENTROID...AND ELIMINATED THE WESTERN ZONES FROM THE WATCH. OTHERWISE HAVE ADJUSTED THE GRIDS BASED ON CURRENT TRENDS...INCREASING LATE EVENING POPS ALONG THE I 90 CORRIDOR... EAST CENTRAL SD AND EVEN INTO PARTS OF SW MN. CONVERSELY... BASICALLY ELIMINATED POPS IN OUR SOUTHERN ZONES AS AT LEAST AT THE MOMENT...THEY ARE GENERALLY CAPPED OFF WITH THE SHORT WAVE DYNAMICS ALONG AND NORTH OF I 90. THE INDIVIDUAL CELLS CONTINUE TO BUILD SLIGHTLY TO THE SOUTH...SO IT IS POSSIBLE THAT SIOUX FALLS ITSELF MAY BE GET HIT AROUND 04Z...AND THUS INCREASED POPS TO A STRONG SCATTERED. IT IS A BIT SURPRISING THAT THE STORMS HAVE HELD THIS INTENSITY FOR THIS LONG...KNOWING THAT THEY WERE LIKELY TIED TO THE SURFACE BOUNDARY EARLIER THIS EVENING. BUT THE SHORT WAVE MAY BE STRONGER THAN THE EARLIER MODELS WERE INDICATING. FOR OTHER ELEMENTS...LOW TEMPERATURES STILL LOOK GOOD. GRID UPDATE IS OUT AND WILL UPDATE THE ZFP VERY SHORTLY. /MJF && .AVIATION.../FOR THE 06Z TAF ISSUANCE/ ISOLATED HIGH BASED THUNDERSTORMS FROM KFSD-KMML AS OF 04Z WILL MOVE EAST THROUGH MN/IA NORTH OF HIGHWAY 18 THROUGH 08Z. ERRATIC GUSTY WINDS POSSIBLE WITH THE STORMS...WHICH SHOULD BE EAST OF TAF SITES BY START OF 06Z TAF PERIOD. WITH LOW LEVEL MOISTURE AND LIGHT WINDS WITHIN WEAK SURFACE RIDGE AXIS OVER NORTHWEST IOWA...COULD SEE SOME POCKETS OF MVFR FOG DEVELOP TOWARD DAYBREAK AND WILL KEEP SOME LIGHT FOG FOR KSUX 10-14Z. CONVECTIVE CHANCES INCREASE INTO THE MISSOURI RIVER VALLEY LATE TUESDAY AFTERNOON...AND EXPAND DURING THE EVENING AS UPPER WAVE/ASSOCIATED COLD FRONT APPROACHES. WILL ADD MENTION OF THUNDER INTO KFSD/KSUX TUESDAY EVENING...HOWEVER CONFIDENCE IN TIMING/LOCATION SOMEWHAT UNCERTAIN AND SUBJECT TO CHANGE IN FUTURE TAF ISSUANCES. && .PREV DISCUSSION.../ISSUED AT 315 PM CDT/ LIGHT SHOWERS MAINLY CONFINED TO NORTHWEST IOWA SO FAR THIS AFTERNOON. MID LEVEL CLOUDS ALSO DISSIPATING IN OUR WEST ALLOWING FOR DECENT HEATING. DEWPOINTS HAVE FALLEN RAPIDLY ONCE MIXING COMMENCED...WITH DRY AIR ALOFT. THIS WAS SHOWN WELL BY THE HRRR AND NAM. BOTH OF THESE MODELS SHOW SOME DEWPOINT RECOVERY BY LATER THIS AFTERNOON RIGHT AHEAD OF THE APPROACHING FRONTAL BOUNDARY. THE QUESTION IS WHETHER THEY RECOVER ENOUGH TO HELP BREAK THE CAP. HRRR HAS BACKED OFF SOME OF ITS EARLIER IDEA OF SCATTERED TO NUMEROUS STORMS FORMING AS THE BOUNDARY ENTERED OUR CWA. STILL THINKING WE POSSIBLY GET SOME ISOLATED DEVELOPMENT AFTER 4 OR 5 PM WEST OF THE JAMES RIVER. FULL SUN COMBINED WITH CONVERGENCE ALONG THE FRONT AND AN APPROACHING SHORTWAVE...MAY BE ENOUGH TO AT LEAST GET ISOLATED DEVELOPMENT. CAPE COULD BE AROUND 1500 J/KG NEAR THE BOUNDARY...AND A VEERING WIND PROFILE WITH DECENT WINDS ALOFT SHOULD RESULT IN AROUND 40 KTS EFFECTIVE SHEAR. SO ANY STORM THAT IS ABLE TO FORM COULD BE SEVERE...WITH STRONG WINDS AND LARGE HAIL. STORMS WOULD MOVE EAST OR EAST SOUTHEAST...BUT THINKING MOST ACTIVITY WILL BE DIURNALLY DRIVEN AND THUS DIE AS THE EVENING PROGRESSES. KEPT CHANCE POPS MAINLY ALONG AND WEST OF THE JAMES RIVER....WITH SLIGHT CHANCE THROUGH THE REST OF THE CWA...JUST IN CASE STORMS PERSIST ALONG THERE OUTFLOW LONGER THAN EXPECTED. SKIES SHOULD CLEAR LATER TONIGHT...WITH LOWS IN THE 50S AND 60S. COULD SEE SOME FOG DEVELOPMENT IN THE SOUTH...ESPECIALLY WHERE RAIN HAS FALLEN TODAY IN NORTHWEST IOWA. TUESDAY SHOULD START MOSTLY SUNNY WITH HIGHS IN THE 80S AND 90S. TRICKY PART OF TUESDAYS FORECAST WILL BE HOW FAR SOUTH THE BOUNDARY MAKES IT LATE TONIGHT...AND HOW QUICKLY IT PUSHES BACK NORTH AS A WARM FRONT TOMORROW BEFORE THE COLD FRONT PUSHES THROUGH. WITH STABLE DRIER AIR NORTH OF THIS BOUNDARY...CONVECTION CHANCES WILL BE CONFINED TO ALONG AND SOUTH OF IT DURING THE DAY...AS ANOTHER SHORTWAVE PUSHES ACROSS. NAM IS THE FURTHEST SOUTH WITH THE BOUNDARY...ONLY PUSHING AS FAR NORTH AS SPENCER TO YANKTON BY AFTERNOON. THE GFS IS FURTHEST NORTH...WITH THE ECMWF IN BETWEEN. NAM HAS BEEN A LITTLE TOO AGGRESSIVE WITH FRONTS...BUT GENERALLY HAS BEEN THE BEST. THUS TEND TO THINK A SOLUTION SOMEWHERE BETWEEN THE ECMWF AND NAM WILL BE CLOSEST. THIS WOULD GENERALLY KEEP THE THUNDERSTORM THREAT SOUTH OF INTERSTATE 90 THROUGH 7 PM TUESDAY. STORMS THAT DO FORM IN THE AFTERNOON WILL HAVE THE POTENTIAL OF BEING SEVERE...WITH AROUND 2000 J/KG OF CAPE AND DEEP LAYER SHEAR OF 40 KTS. LARGE HAIL AND STRONG WINDS WILL BE POSSIBLE IN ANY STORM THAT DOES FORM. CAP SHOULD HOLD STRONG FOR MUCH OF THE AFTERNOON...HOWEVER CONTINUED HEATING AND THE APPROACHING WAVE SHOULD BREAK IT AT SOME POINT EITHER LATE AFTERNOON OR EVENING. /CHENARD THAT APPROACHING WAVE AND FRONT SHOULD BRING MORE NUMEROUS SHOWERS AND THUNDERSTORMS TUESDAY EVENING...MAINLY TO THE EASTERN PART OF THE AREA WHERE MOISTURE POOLING AND INFLOW WILL BE GOOD. SYSTEM MOVING FAST ENOUGH AND MID TO UPPER FLOW IS STRONG ENOUGH SO THAT RAINFALL AMOUNTS SHOULD NOT BE TOO HIGH. FRONT WILL BE MOVING ACROSS AREA WITH COOLER AIR SPREADING IN BEHIND IT...AND PRECIPITATION DECREASING STEADILY AFTER MIDNIGHT. GUIDANCE SEEMS OK AT THIS POINT ON COOLING FOR LOW TEMPERATURES. MOVEMENT LOOKS FAST ENOUGH TO KEEP OUT ANY MENTION OF LINGERING SHOWERS FOR WEDNESDAY AND DRYING CERTAINLY LOOKS STRONG...SO WE SHOULD BE HEADING TO A SUNNY/MOSTLY SUNNY DAY WEDNESDAY AFTER MORNING CLOUDS SOUTHEAST DECREASE. LATE THURSDAY INTO FRIDAY LOOKS LIKE ANOTHER THREAT OF SHOWERS AND STORMS AS NEXT WAVE AND COLD FRONT IS PRECEDED BY FAVORABLY THERMAL ADVECTION PATTERN. WILL GO WITH LOW POPS AS PER GUIDANCE FOR NOW BUT OVERALL THREAT SEEMS A LITTLE HIGHER AND WHEN WE CAN NARROW DOWN THE TIMING BETTER...THE POPS FOR AT LEAST PART OF THAT TIME...PERHAPS THURSDAY NIGHT...MAY GO UP. THIS SYSTEM WILL BRING IN EVEN COOLER AIR FOR FRIDAY AND SATURDAY. SOLIDLY DRY PATTERN WILL ALSO DEVELOP BEHIND THIS SYSTEM...AND THE DRY PATTERN WILL REMAIN IN PLACE AS SLOW BUT STEADY WARMING SETS IN SUNDAY AFTERNOON THROUGH MONDAY. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...NONE. MN...NONE. IA...NONE. NE...NONE. $$
AREA FORECAST DISCUSSION
NWS LA CROSSE WI
1150 PM CDT MON SEP 3 2012 .SHORT TERM...TONIGHT THROUGH THURSDAY 256 PM CDT MON SEP 3 2012 MAIN FORECAST CONCERNS ARE ON PRECIPITATION CHANCES THROUGH WEDNESDAY. CURRENTLY AS OF 20Z...WATER VAPOR LOOP AND RAP 500MB HEIGHT ANALYSIS SHOWED BROAD TROUGHING OVER SOUTHWEST AND SOUTH CENTRAL CANADA... WITH NEARLY ZONAL FLOW ON ITS SOUTH SIDE ACROSS MUCH OF THE NORTHERN U.S.. WITHIN THE BROAD UPPER TROUGHING...A PORTENT SHORTWAVE IS EVIDENT OVER CENTRAL ALBERTA. IN THE ZONAL FLOW...THERE ARE NUMEROUS WEAK SHORTWAVES...WHICH DURING THIS MORNING PRETTY MUCH ALL HAD AT LEAST ACCAS OR CONVECTION WITH THEM: ONE IN NORTH DAKOTA...ANOTHER IN WESTERN MINNESOTA...ONE IN WESTERN NEBRASKA AND LASTLY ONE IN CENTRAL IOWA. DPVA AHEAD OF THE SHORTWAVE IN CENTRAL IOWA COMBINED WITH A WEAKENING SURFACE COLD FRONT EXTENDING FROM CENTRAL UPPER MICHIGAN TO NEAR DES MOINES...AS WELL AS MLCAPE VALUES THAT HAVE CLIMBED TO 1500-2000 J/KG WITH LITTLE CIN PER RAP ANALYSIS...HAS ALLOWED FOR SHOWER AND THUNDERSTORM DEVELOPMENT. MOST OF THE ACTIVITY HAS BEEN DISORGANIZED...DUE TO 0-6KM SHEAR BELOW 30 KT WHERE STORMS ARE IN THE FORECAST AREA. ALSO...A SURGE OF MONSOONAL MID-CLOUDS THROUGH THE UPPER FLOW IS HELPING TO PUT A LID ON THE AMOUNT OF INSTABILITY. THERE ARE EVEN SOME SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS COMING OUT OF THESE MID CLOUDS. WITH THE VARYING CLOUD COVER AND PRECIPITATION...TEMPERATURES TODAY ARE ALL OVER THE PLACE IN THE FORECAST AREA. MOST LOCATIONS REACHED 80...WHILE BOSCOBEL GOT CLOSE TO 90. ABNORMALLY HIGH DEWPOINTS PERSIST TOO...WITH MOST OF THE AREA SEEING READINGS AROUND 70F. TONIGHT AND TUESDAY...VERY TRICKY FORECAST TO SAY THE LEAST. THE NEAR ZONAL FLOW WILL PERSIST THROUGH THIS PERIOD AS THE POTENT ALBERT SHORTWAVE DIGS DOWN INTO THE NORTHERN PLAINS. MODELS CONTINUE TO INDICATE WEAK SHORTWAVES MOVING THROUGH THIS FLOW...LIKE THOSE AROUND THE DAKOTAS TODAY. WITH MUCAPE VALUES PROGGED TO NOT DROP MUCH BELOW 1000 J/KG...HIGHLY CONCERNED THERE COULD BE OFF AND ON SHOWERS AND THUNDERSTORMS THROUGHOUT THIS PERIOD. THIS HAS BEEN SUGGESTED THE PAST FEW DAYS...ESPECIALLY BY THE ECMWF...THOUGH THE LATEST 03.12Z ECMWF IS NOT AS ACTIVE. NOW SOME HI RESOLUTION MODEL RUNS HAVE SUGGESTED THAT THE CURRENT AFTERNOON CONVECTION DROPS SOUTHEAST THIS EVENING...WHILE OTHER CONVECTION DEVELOPS IN IOWA AND DROPS SOUTHEAST. THIS ALLOWS THE FORECAST AREA TO END UP DRY AFTER MIDNIGHT. FOR NOW HOLDING ON TO SOME LOW CHANCES OF PRECIPITATION BECAUSE OF TOO MUCH UNCERTAINTY TO GO DRY BASED ON THE ENVIRONMENT. IF SKIES CLEAR OUT TONIGHT...THE HIGH AMOUNT OF SURFACE MOISTURE AROUND AND WEAK WIND FIELD WOULD LIKELY RESULT IN WIDESPREAD RADIATION FOG. NOT ENTIRELY CONFIDENT WE WILL HAVE A LONG PERIOD OF CLEAR SKIES...THOUGH. SO IN SUMMARY...THERE APPEARS TO BE TWO SCENARIOS FOR TONIGHT: 1. SKIES CLEAR AND WE END UP WITH DENSE FOG 2. PERIODS OF ACCAS AND ISOLATED SHOWERS/STORMS RIGHT NOW...BANKING ON NUMBER 2 AND ACKNOWLEDGING THE FOG BY ADDING AT LEAST A PATCHY MENTION AFTER MIDNIGHT INTO TUESDAY MORNING. WITH THE HIGH AMOUNT OF SURFACE MOISTURE...ANTICIPATING TEMPERATURES OUTSIDE OF THE TYPICAL COLD SPOTS TO NOT DROP BELOW THE MID 60S. DEPENDING ON AMOUNT OF SUN ON TUESDAY...WITH 850MB TEMPS BETWEEN 18-20C...HIGHS COULD GET CLOSE TO 90. TUESDAY NIGHT AND WEDNESDAY...THE POTENT SHORTWAVE TROUGH COMING INTO THE NORTHERN PLAINS AT 00Z WEDNESDAY IS FORECAST TO DIG INTO MINNESOTA BY 12Z...THEN RAPIDLY SHOOT EAST OVER MUCH OF MICHIGAN BY 00Z THURSDAY. THIS RAPID MOVEMENT MEANS AN OVERALL SHORT TIME WINDOW FOR PRECIPITATION FORCED BY THE TROUGH. NOTE THAT THE BEST 500-300MB PV ADVECTION IS STILL SUGGESTED TO STAY TO THE NORTH OF THE FORECAST AREA. HOWEVER...THE COMBINATION OF WEAK 500MB HEIGHT FALLS...A SURGE OF LOW TO MID LEVEL MOISTURE TRANSPORT...AS WELL AS AT LEAST 1000-1500 J/KG OF MUCAPE ACCOMPANYING THE MOISTURE TRANSPORT SHOULD PRODUCE SHOWERS AND THUNDERSTORMS ACROSS MUCH OF THE AREA. SOME OF THESE COULD GET GOING AS EARLY AS THE EVENING...BUT BETTER CHANCES ARE EXPECTED AFTER MIDNIGHT THROUGH ABOUT 15Z WEDNESDAY...WHEN THE TROUGH IS HAVING ITS BIGGEST FORCING INFLUENCE. 1-6KM SHEAR IS GENERALLY 15-25KT...WHICH SHOULD KEEP CONVECTION SUB-SEVERE. AFTER 15Z...STRONG SUBSIDENCE WILL WORK IN WEST TO EAST...CLEARING SKIES OUT. WINDS SHOULD PICK UP TOO AS THE PRESSURE GRADIENT TIGHTENS... COLD ADVECTION AND DEEP MIXING OCCUR. NOTING ABOUT THE COLD ADVECTION...850MB TEMPS WHICH LOOK TO HOVER BETWEEN 16-20C TUESDAY NIGHT END UP FALLING TO 12-14C OR SLIGHTLY COOLER BY 00Z WEDNESDAY. THUS...EXPECT COOLER HIGHS FOR WEDNESDAY ON THE ORDER OF MID 70S TO LOWER 80S. TUESDAY NIGHT WILL STILL BE WARM WITH LOWS IN THE 60S...THANKS TO SOUTH FLOW AHEAD OF THE SHORTWAVE/ASSOCIATED COLD FRONT AND HIGHER DEWPOINTS. WEDNESDAY NIGHT AND THURSDAY...IN THE WAKE OF WEDNESDAYS POTENT SHORTWAVE...UPPER FLOW TURNS ZONAL OVER THE AREA. BUT THIS IS BRIEF...WITH ATTENTION TURNING BACK TO ALBERTA WHERE YET ANOTHER POTENT SHORTWAVE IS PROGGED TO DROP SOUTH INTO MONTANA BY 00Z FRIDAY. WEDNESDAY NIGHT STILL LOOKS DRY THANKS TO LINGERING DRY AIR AND SUBSIDENCE IN THE WAKE OF WEDNESDAYS TROUGH. THURSDAY IS A LITTLE MORE PROBLEMATIC. TO THE NORTH...MODELS ARE INDICATING A COUPLE OF SHORTWAVES CROSSING NORTHERN MINNESOTA AND WISCONSIN... WHICH BRING DOWN A COLD FRONT INTO NORTHWEST WI BY 00Z. BOTH THE 03.12Z NAM AND 03.06Z GFS DEPICT SOME LIGHT QPF ACROSS TAYLOR COUNTY WITH THIS FEATURE IN THE AFTERNOON. SOUNDINGS SUGGEST VERY LITTLE MUCAPE WITH THIS FRONT AND A FAIRLY DRY BOUNDARY LAYER BELOW 750MB. NEW 03.12Z GFS HAS CAME IN DRY. THEREFORE...HAVE HELD OFF ON MENTION ANY PRECIPITATION CHANCES UP AROUND TAYLOR COUNTY. FOR THE REST OF THE AREA...300-305K ISENTROPIC LIFT GRADUALLY INCREASES DURING THE AFTERNOON...ALL KIND OF DOWNSTREAM OF THAT SHORTWAVE DROPPING INTO MONTANA. SHOULD SEE SOME MID/HIGH CLOUDS DEVELOP AS A RESULT OF THIS LIFT...BUT THINKING THE MAJORITY OF THESE CLOUDS ANY PRECIPITATION POTENTIAL WITH THEM WILL STAY WEST/SOUTHWEST OF THE AREA. THIS AGREES WELL WITH THE 03.12Z GFS/ECMWF. COOLER PERIOD ANTICIPATED. MAY HAVE TO WATCH FOR VALLEY FOG POTENTIAL IF THE SURFACE RIDGE OF HIGH PRESSURE COMING IN WEDNESDAY NIGHT BUILDS IN FASTER. .LONG TERM...THURSDAY NIGHT THROUGH MONDAY 256 PM CDT MON SEP 3 2012 THROUGH SATURDAY...MODELS REMAIN IN GOOD AGREEMENT WITH THE HANDLING OF THE POTENT SHORTWAVE OVER MONTANA...HOW IT ENDS UP FORMING A FAIRLY DEEP TROUGH OVER THE UPPER AND MID MISSISSIPPI RIVER VALLEYS BY 12Z SATURDAY. AS THIS TROUGH FORMS...FRONTOGENESIS DOWNSTREAM WILL LIKELY SPREAD MID/HIGH CLOUDS ACROSS THE AREA THURSDAY NIGHT AND FRIDAY...SOME OF WHICH COULD PRODUCE A FEW SHOWERS. OVERALL... BULK OF PRECIPITATION IS ANTICIPATED TO STAY TO THE SOUTH...CLOSER TO A DEVELOPING LOW PRESSURE SYSTEM LIFTING OUT OF THE CENTRAL PLAINS. BY FRIDAY NIGHT...AS THE TROUGHING MOVES IN...THE CLOUDS AND POTENTIAL FOR SHOWERS GET PUSHED EAST. HIGH PRESSURE THEN BUILDS IN FOR SATURDAY. MUCH OF THIS PERIOD THROUGH SATURDAY WILL BE BELOW NORMAL...DUE TO FIRST CLOUDS ON FRIDAY AND THEN 850MB TEMPS FALLING TO 6-8C FOR SATURDAY. HIGHS MAY STRUGGLE TO CLIMB TO OR MUCH ABOVE 70. BEYOND SATURDAY...MODELS HANDLE THE TROUGHING DIFFERENTLY...WITH THE 03.12Z ECMWF AND CANADIAN CLOSING IT OFF AND PERHAPS MOVING IT SOUTHEAST...WHEREAS THE 03.12Z GFS AND ITS ENSEMBLES REMAIN MORE PROGRESSIVE. FOR THE FORECAST AREA...EITHER SCENARIO DOESNT MATTER MUCH...AS ALL MODELS END UP HAVING UPPER RIDGING BUILDING UP OVER THE PLAINS AND INTO THE FORECAST AREA LATE MONDAY. THIS WILL KEEP CONDITIONS DRY WITH A GRADUAL WARMING TREND. BY MONDAY...850MB TEMPS ARE BACK UP TO 12-14C...YIELDING HIGHS AT LEAST AROUND NORMAL. && .AVIATION...THROUGH 06Z WEDNESDAY 1150 PM CDT MON SEP 3 2012 RATHER COMPLICATED FORECAST SCENARIO FOR THIS TAF CYCLE. INFRARED SATELLITE IMAGERY SHOWING A BAND OF CLEARING WORKING ITS WAY INTO SOUTHEAST MINNESOTA. VISIBILITIES HAVE ALREADY DROPPED TO 2 1/2 MILES AT KRST AND EXPECT VISIBILITIES TO DROP INTO THE IFR CATEGORY AT KRST AT TAF ISSUANCE TIME AND INTO THE MVFR CATEGORY AT KLSE A FEW HOURS LATER. QUESTION WILL BE HOW FAR THEY DROP BEFORE MID AND HIGH LEVEL CLOUDS FROM THE CONVECTION OVER THE DAKOTAS MAKES IT WAY OVERHEAD. HAVE INCLUDED A TEMPO 1/4SM AT KRST AND 1SM AT KLSE AS CONDITIONS LOOKS FAVORABLE TO SEE AT LEAST SOME IFR CONDITIONS FOR A WHILE AND CANNOT RULE OUT A PERIOD OF DENSE FOG AS WELL AT KSLE. AFTER ANY FOG LIFTS TUESDAY MORNING...THE NEXT SHORTWAVE WILL APPROACH THE AREA. THE 03.21Z SREF INCREASES PROBABILITIES DURING THE AFTERNOON HOURS...ESPECIALLY EAST OF THE MISSISSIPPI RIVER. THIS CONSISTENT WITH INCREASING MOISTURE TRANSPORT AND AN UNSTABLE AIR MASS. DID MENTION SHRA AT KLSE AND JUST VCSH AT KRST. && .ARX WATCHES/WARNINGS/ADVISORIES... 256 PM CDT MON SEP 3 2012 WI...NONE. MN...NONE. IA...NONE. && $$ SHORT TERM...AJ LONG TERM...AJ AVIATION...JLR
AREA FORECAST DISCUSSION
NWS LINCOLN IL
937 AM CDT TUE SEP 4 2012 .DISCUSSION... ISSUED 937 AM CDT TUE SEP 4 2012 WEAKENING SHORT-WAVE TROUGH HAS SPREAD A BAND OF MID-LEVEL CLOUDINESS INTO CENTRAL AND WESTERN ILLINOIS THIS MORNING. DESPITE THE PRESENCE OF THIS FORCING MECHANISM...PREVAILING HIGH PRESSURE HAS PREVENTED MUCH PRECIP FROM REACHING THE AREA. 14Z/9AM RADAR MOSAIC SHOWS A LINE OF SHOWERS/STORMS EXTENDING FROM NORTH OF SAINT LOUIS WESTWARD ACROSS CENTRAL MISSOURI...HOWEVER THIS PRECIP IS DISSIPATING AS IT PUSHES FURTHER EAST INTO THE SURFACE RIDGE AXIS. NEITHER THE 11Z HRRR NOR THE 12Z NAM ARE HANDLING THE CURRENT SITUATION VERY WELL AT ALL...WITH BOTH MODELS INDICATING A GOOD DEAL OF PRECIP ACROSS THE WESTERN KILX CWA THIS MORNING. BASED ON CURRENT SATELLITE/RADAR AND THE PRESENCE OF SURFACE HIGH PRESSURE...HAVE REJECTED THE HIGH-RES MODEL SOLUTION IN FAVOR OF ONLY ISOLATED SHOWERS/THUNDER TODAY. HAVE ALREADY SENT A ZONE UPDATE TO LOWER POPS AND REMOVE MENTION OF MORNING FOG ACROSS THE E/SE. BARNES && .AVIATION... ISSUED 605 AM CDT TUE SEP 4 2012 COVERAGE OF MVFR AND LOCAL IFR VSBYS IN FOG OVER THE NEXT COUPLE OF HOURS...AND THEN THE TSRA THREAT TODAY THE MAIN FORECAST CONCERNS. A WEAK WEATHER DISTURBANCE TRACKING ACROSS THE LOWER GREAT LAKES THIS MORNING HAS PRODUCED SOME SCATTERED SHOWERS AND THUNDERSTORMS ACROSS THE SOUTHERN GREAT LAKES WITH A SECONDARY AREA OF STORMS OVER PARTS OF NORTHERN MISSOURI. SHORT RANGE MODELS SUGGEST AS THE UPPER WAVE MOVES ACROSS OUR AREA THIS MORNING...IT WILL BRING A FEW OF THE SHOWERS AND THUNDERSTORMS INTO OUR AREA BUT COVERAGE LOOKS TO BE QUITE LIMITED...NOT MUCH MORE THAN A VCSH/VCTS MENTION AT THIS POINT. WHAT FOG WE DO SEE OVER THE NEXT COUPLE OF HOURS SHOULD BE GONE BY 14 OR 15Z...WITH SOME SCATTERED CUMULUS WITH BASES AROUND 4000 FEET AND SCT-BKN AC INTO THE AFTERNOON HOURS. WINDS WILL BE LIGHT FROM A SOUTHERLY DIRECTION TODAY WITH SPEEDS OF 10KTS OR LESS...WITH LIGHT AND VARIABLE WINDS AGAIN FOR TONIGHT. MAY SEE VSBYS DROP AGAIN TO MVFR LATER TONIGHT AS SOME PATCHY FOG FORMS AFTR 05Z. SMITH && .PREV DISCUSSION... ISSUED 330 AM CDT TUE SEP 4 2012 SHORT TERM...TODAY THROUGH FRIDAY NIGHT SOME FOG PRESENT OVER EASTERN IL EAST OF I-55 WHERE SKIES CURRENTLY CLEAR AND WILL CONTINUE PATCHY FOG UNTIL 9 AM OVER EASTERN IL. MID/HIGH CLOUDS SPREADING EAST FROM IA AND NORTHERN MO INTO CENTRAL/NW IL EARLY THIS MORNING WITH A CLUSTER OF SHOWERS AND THUNDERSTORMS OVER NORTHERN MO AND OVER SOUTHERN LAKE MI AND NEAR CHICAGO. HRRR MODELS WAS HANDLING QPF THE BEST THIS MORNING WHICH BRINGS THE CONVECTION FROM NORTHERN MO EASTWARD INTO CENTRAL IL AND WEAKENS IT THIS MORNING. WILL CARRY POPS OF 20-40% TODAY AND HIGHEST WEST OF SPRINGFIELD. ISOLATED SHOWERS AND THUNDERSTORMS POSSIBLE THIS AFTERNOON IN UNSTABLE HUMID AIRMASS WITH DEWPOINTS STILL IN THE LOWER 70S. SPC KEEPS SLIGHT RISK NW OF IL TODAY. HIGHS IN THE UPPER 80S AND LOWER 90S AGAIN TODAY. HAVE 20-30% CHANCE OF SHOWERS AND THUNDERSTORMS INTO WESTERN AREAS OVERNIGHT WHILE PATCHY FOG POSSIBLE OVER EASTERN IL AGAIN AFTER MIDNIGHT. MODELS HAVE TRENDED A BIT SLOWER WITH A STRONGER COLD FRONT MOVING SE INTO CENTRAL IL WED AFTERNOON/EVENING. SPC CONTINUES SLIGHT RISK ACROSS MUCH OF CENTRAL IL NW OF I-70 WED AFTERNOON AND EARLY EVENING UNTIL SUNSET. AIRMASS GETS UNSTABLE AGAIN BY WED AFTERNOON WITH CAPES 2000-3000 J/KG WHILE BEST WIND SHEAR AND SHORT WAVE ENERGY IS NORTH OF CENTRAL IL. ADDED 20-30% CHANCE OF CONVECTION OVER EASTERN IL WED EVENING ESPECIALLY EARLY WED EVENING UNTIL SUNSET. ANOTHER VERY WARM AND HUMID DAY WED WITH HIGHS IN THE UPPER 80S AND LOWER 90S. DRY CONDITIONS EXPECTED THU WITH A FAIR AMOUNT OF SUNSHINE AS WEAK HIGH PRESSURE SETTLES INTO IL BY SUNSET THU...WITH SOME INCREASING CLOUDS FROM THE WEST LATER IN THE DAY. HIGHS IN THE LOW TO MID 80S AND WARMEST BY LAWRENCEVILLE WITH 87F. ANOTHER FAIRLY STRONG NORTHERN STREAM SHORT WAVE DIVES INTO THE MIDWEST BY FRI RETURNING A GOOD CHANCE OF SHOWERS AND A FEW THUNDERSTORMS. THIS TO ALSO BRING COOLER WEATHER LATER THIS WEEK. LONG TERM...SATURDAY THROUGH MONDAY NIGHT THE ENSEMBLE MODELS CONTINUE TO SHOW A STRONG UPPER LEVEL TROF DIGGING SOUTHEAST THROUGH THE MIDWEST AND GREAT LAKES REGION LATE THIS WEEK. THERE ARE STILL DIFFERENCES AMONG THE INDIVIDUAL MEMBERS ON WHAT HAPPENS WITH THIS TROUGH THIS WEEKEND...WITH SOME MEMBERS KEEPING THE TROUGH MORE PROGRESSIVE AND PUSHING IT EAST OF THE AREA BY SUNDAY MORNING...WHILE OTHERS CUTOFF THE TROUGH OVER THE OHIO VALLEY INTO NEXT MONDAY. FOR NOW WILL USE A BLEND OF MODEL SOLUTIONS AND STICK CLOSE TO ALLBLEND POPS IN THE EXTENDED FOR THIS WEEKEND...WITH HIGHER POPS SAT AND SHIFTING MORE INTO EASTERN IL SUNDAY...AND DRY MONDAY. BELOW NORMAL TEMPERATURES BY 5-10 DEGREES FOR THE HIGHS EXPECTED THIS WEEKEND AND GRADUALLY MODIFY DURING NEXT WORK WEEK. KH && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$
AREA FORECAST DISCUSSION
NWS LINCOLN IL
611 AM CDT TUE SEP 4 2012 .DISCUSSION... ISSUED 330 AM CDT TUE SEP 4 2012 SHORT TERM...TODAY THROUGH FRIDAY NIGHT SOME FOG PRESENT OVER EASTERN IL EAST OF I-55 WHERE SKIES CURRENTLY CLEAR AND WILL CONTINUE PATCHY FOG UNTIL 9 AM OVER EASTERN IL. MID/HIGH CLOUDS SPREADING EAST FROM IA AND NORTHERN MO INTO CENTRAL/NW IL EARLY THIS MORNING WITH A CLUSTER OF SHOWERS AND THUNDERSTORMS OVER NORTHERN MO AND OVER SOUTHERN LAKE MI AND NEAR CHICAGO. HRRR MODELS WAS HANDLING QPF THE BEST THIS MORNING WHICH BRINGS THE CONVECTION FROM NORTHERN MO EASTWARD INTO CENTRAL IL AND WEAKENS IT THIS MORNING. WILL CARRY POPS OF 20-40% TODAY AND HIGHEST WEST OF SPRINGFIELD. ISOLATED SHOWERS AND THUNDERSTORMS POSSIBLE THIS AFTERNOON IN UNSTABLE HUMID AIRMASS WITH DEWPOINTS STILL IN THE LOWER 70S. SPC KEEPS SLIGHT RISK NW OF IL TODAY. HIGHS IN THE UPPER 80S AND LOWER 90S AGAIN TODAY. HAVE 20-30% CHANCE OF SHOWERS AND THUNDERSTORMS INTO WESTERN AREAS OVERNIGHT WHILE PATCHY FOG POSSIBLE OVER EASTERN IL AGAIN AFTER MIDNIGHT. MODELS HAVE TRENDED A BIT SLOWER WITH A STRONGER COLD FRONT MOVING SE INTO CENTRAL IL WED AFTERNOON/EVENING. SPC CONTINUES SLIGHT RISK ACROSS MUCH OF CENTRAL IL NW OF I-70 WED AFTERNOON AND EARLY EVENING UNTIL SUNSET. AIRMASS GETS UNSTABLE AGAIN BY WED AFTERNOON WITH CAPES 2000-3000 J/KG WHILE BEST WIND SHEAR AND SHORT WAVE ENERGY IS NORTH OF CENTRAL IL. ADDED 20-30% CHANCE OF CONVECTION OVER EASTERN IL WED EVENING ESPECIALLY EARLY WED EVENING UNTIL SUNSET. ANOTHER VERY WARM AND HUMID DAY WED WITH HIGHS IN THE UPPER 80S AND LOWER 90S. DRY CONDITIONS EXPECTED THU WITH A FAIR AMOUNT OF SUNSHINE AS WEAK HIGH PRESSURE SETTLES INTO IL BY SUNSET THU...WITH SOME INCREASING CLOUDS FROM THE WEST LATER IN THE DAY. HIGHS IN THE LOW TO MID 80S AND WARMEST BY LAWRENCEVILLE WITH 87F. ANOTHER FAIRLY STRONG NORTHERN STREAM SHORT WAVE DIVES INTO THE MIDWEST BY FRI RETURNING A GOOD CHANCE OF SHOWERS AND A FEW THUNDERSTORMS. THIS TO ALSO BRING COOLER WEATHER LATER THIS WEEK. LONG TERM...SATURDAY THROUGH MONDAY NIGHT THE ENSEMBLE MODELS CONTINUE TO SHOW A STRONG UPPER LEVEL TROF DIGGING SOUTHEAST THROUGH THE MIDWEST AND GREAT LAKES REGION LATE THIS WEEK. THERE ARE STILL DIFFERENCES AMONG THE INDIVIDUAL MEMBERS ON WHAT HAPPENS WITH THIS TROUGH THIS WEEKEND...WITH SOME MEMBERS KEEPING THE TROUGH MORE PROGRESSIVE AND PUSHING IT EAST OF THE AREA BY SUNDAY MORNING...WHILE OTHERS CUTOFF THE TROUGH OVER THE OHIO VALLEY INTO NEXT MONDAY. FOR NOW WILL USE A BLEND OF MODEL SOLUTIONS AND STICK CLOSE TO ALLBLEND POPS IN THE EXTENDED FOR THIS WEEKEND...WITH HIGHER POPS SAT AND SHIFTING MORE INTO EASTERN IL SUNDAY...AND DRY MONDAY. BELOW NORMAL TEMPERATURES BY 5-10 DEGREES FOR THE HIGHS EXPECTED THIS WEEKEND AND GRADUALLY MODIFY DURING NEXT WORK WEEK. KH && .AVIATION... ISSUED 605 AM CDT TUE SEP 4 2012 COVERAGE OF MVFR AND LOCAL IFR VSBYS IN FOG OVER THE NEXT COUPLE OF HOURS...AND THEN THE TSRA THREAT TODAY THE MAIN FORECAST CONCERNS. A WEAK WEATHER DISTURBANCE TRACKING ACROSS THE LOWER GREAT LAKES THIS MORNING HAS PRODUCED SOME SCATTERED SHOWERS AND THUNDERSTORMS ACROSS THE SOUTHERN GREAT LAKES WITH A SECONDARY AREA OF STORMS OVER PARTS OF NORTHERN MISSOURI. SHORT RANGE MODELS SUGGEST AS THE UPPER WAVE MOVES ACROSS OUR AREA THIS MORNING...IT WILL BRING A FEW OF THE SHOWERS AND THUNDERSTORMS INTO OUR AREA BUT COVERAGE LOOKS TO BE QUITE LIMITED...NOT MUCH MORE THAN A VCSH/VCTS MENTION AT THIS POINT. WHAT FOG WE DO SEE OVER THE NEXT COUPLE OF HOURS SHOULD BE GONE BY 14 OR 15Z...WITH SOME SCATTERED CUMULUS WITH BASES AROUND 4000 FEET AND SCT-BKN AC INTO THE AFTERNOON HOURS. WINDS WILL BE LIGHT FROM A SOUTHERLY DIRECTION TODAY WITH SPEEDS OF 10KTS OR LESS...WITH LIGHT AND VARIABLE WINDS AGAIN FOR TONIGHT. MAY SEE VSBYS DROP AGAIN TO MVFR LATER TONIGHT AS SOME PATCHY FOG FORMS AFTR 05Z. SMITH && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$
AREA FORECAST DISCUSSION
NWS GRAND RAPIDS MI
1126 AM EDT TUE SEP 4 2012 .SYNOPSIS... ISSUED AT 1125 AM EDT TUE SEP 4 2012 CLOUDS WILL DECREASE THIS AFTERNOON BEHIND SHOWERS AND THUNDERSTORMS EXITING THE THE AREA. STRONG OR SEVERE THUNDERSTORMS ASSOCIATED WITH A COLD FRONT ARE EXPECTED WEDNESDAY AFTERNOON AND EVENING. BEHIND THE FRONT...SEASONABLY COOL TEMPERATURES AND SCATTERED SHOWERS WILL FINISH THE WORK WEEK AND LAST INTO THE WEEKEND. && .UPDATE... ISSUED AT 1125 AM EDT TUE SEP 4 2012 UPDATED THE TIMING OF PRECIPITATION EXITING THE AREA. WE CONTINUE TO ADVERTISE GRADUAL CLEARING THIS AFTERNOON WITH GREATLY REDUCED PRECIPITATION CHANCES. WE HAVE MODERATE CONFIDENCE ABOUT THE CLEARING AND SOMEWHAT BETTER CONFIDENCE ABOUT THE DECREASED CHANCES FOR RAIN THIS AFTERNOON. WE WILL HAVE TO WATCH FOR LINGERING CLOUDS THIS AFTERNOON... PARTICULARLY OVER OUR NW ZONES. METARS AND VISIBLE SATELLITE INDICATE A WEAK COLD FRONT SURGING SE FROM THE GREEN BAY AREA WITH SIGNIFICANT CLOUDINESS BEHIND THIS FRONT. LATEST HRRR GUIDANCE WASHES OUT THE FRONT THIS AFTERNOON WHEN A DIURNALLY FORCED LOW PRESSURE AREA FORMS ACROSS LOWER MICHIGAN. THIS WOULD HELP TO DECREASE CLOUD COVERAGE AREAWIDE...BUT OF COURSE ALSO ASSUMES LIMITED CLOUDINESS IN THE FIRST PLACE TO HELP THE DIURNAL FORCING. CLOUD TRENDS OVER THE NEXT FEW HOURS WILL THEREFORE BE IMPORTANT. UPDATE ISSUED AT 610 AM EDT TUE SEP 4 2012 I UPDATED THE GRIDS AND ZONE TO PUT CONDITIONAL POPS FOR THE NEXT FEW HOURS AS THE BAND OR RAIN AND EMBEDDED THUNDERSTORMS ASSOCIATE WITH THE MID LEVEL TROUGH CONTINUE TO MOVE EAST ACROSS THE CWA. I ALSO SERIOUSLY INCREASED THE QPF SINCE I HAVE RECEIVED MESONET REPORTS LIKE .67 INCHES IN JENISON. THE INDIANA TRAILS GOLF COURSE JUST SOUTH OF THE CITY OF GRAND RAPIDS HAD 1.01 INCHES IN 15 MINUTES. IN ANY EVENT THIS AREA OF SHOWERS IS ASSOCIATED WITH THE 700 MB TROUGH AND THERE IS STRONG SUBSIDENCE BEHIND IT. I BELIEVE SKIES WILL CLEAR BEHIND THIS AND ADDITIONAL CONVECTION IS UNLIKELY MID TO LATER AFTERNOON OVER OUR CWA SUE TO THE SUBSIDENCE BEHIND THE SHORTWAVE. && .SHORT TERM...(TODAY THROUGH THURSDAY) ISSUED AT 320 AM EDT TUE SEP 4 2012 FORECAST CONCERNS DEAL WITH CONVECTIVE TRENDS TODAY AND WEDNESDAY. NOT MANY CHANGES WERE MADE TO THE GOING FORECAST. MODEL TRENDS THE PAST 24 HRS HAVE SLOWED THE TIMING OF THE COLD FRONT WEDNESDAY BY A FEW HOURS AND INSTEAD OF MOVING ACROSS THE CWA DURING THE AFTERNOON...THE FRONT MAY MOVE THROUGH DURING THE EVENING. DUE TO DIURNAL INSTABILITY FADE...THE SEVERE THREAT HAS EFFECTIVELY SHIFTED A BIT WWD AND THE SERN CWA HAD BEEN REMOVED FROM THE DAY2 OUTLOOK. LATEST REGIONAL RADAR SHOWS A BROKEN LINE OF SHOWERS AND ISOLATED STORMS STRETCHING FROM NE LWR TO NEAR CHICAGO. THIS PCPN IS ASSOCIATED WITH A WEAKENING FRONTAL BOUNDARY AND WILL CROSS THE CWA TODAY. MESO ANALYSIS SHOWS EFFECTIVE SHEAR NEAR 40KTS ALONG THE I-96 CORRIDOR ATTM. INSTABILITY HOWEVER IS LOW AND SO SVR STORMS ARE NOT EXPECTED. THERE IS A LOW LEVEL DEW POINT GRADIENT THAT STRETCHES ALONG I-69/96 AND WE MAY SEE A FLAREUP OF CONVECTION AS THE ONGOING PCPN INTERACTS WITH IT. SKIES WILL BECOME PT/MO SUNNY BEHIND THE CONVECTION TODAY AND TEMPS WILL ONCE AGAIN CLIMB INTO THE MID TO UPPER 80S. A STRONGER COLD FRONT WILL APPROACH WEDNESDAY LATE IN THE DAY. AS MENTIONED ABOVE TIMING APPEARS A BIT SLOWER THAN PREVIOUS MODEL RUNS. THE STRONGEST DYNAMICS APPEAR OVER NRN LWR MI. HIRES ECMWF SHOWS STRONGEST MOISTURE TRANSPORT AND GREATEST SHEAR ACROSS THE NRN CWA AND NRN LWR. ADDITIONALLY...THE LLJ IS POINTED IN THAT DIRECTION LATE IN THE DAY AND THE ACCOMPANYING SHORT WAVE IS PROGD TO MOVE OVER NRN LWR AS WELL. AS SUCH HIGHEST POPS WERE DIRECTED NWD. PWATS INCREASE TO AROUND 1.75 INCHES LATE IN THE DAY AND SO WE COULD SEE SOME HEAVY RAIN DUMPED OUT OF THEM. WE/RE RUNNING WITH A DRY FCST THURSDAY. LATEST NAM DOES SHOW A DECENT SHORT WAVE MOVING ACROSS THE CWA THEN. HOWEVER THE GFS DOES NOT. CONFIDENCE WASN/T HIGH ENOUGH YET TO ADD POPS TO THE THURSDAY GRIDS. .LONG TERM...(THURSDAY NIGHT THROUGH MONDAY) ISSUED AT 320 AM EDT TUE SEP 4 2012 THERE ARE TWO PRIMARY CONCERNS FOR THIS PART OF THE FORECAST. THE FIRST THE CHANCE FOR RAIN WITH DEVELOPING SYSTEM OVER THE OHIO VALLEY FOR FRIDAY INTO SUNDAY. THE SECOND ISSUE IS JUST HOW CHILLY DOES IT GET THIS WEEKEND? CONSIDERABLE UNCERTAINTY REMAINS IN FORECAST FOR THE FRI THROUGH SUNDAY PART OF THE FORECAST. THE PRIMARY ISSUE IS JUST WHAT HAPPENS THE SYSTEM THAT DIGS INTO THE OHIO VALLEY FRIDAY INTO SATURDAY? FOR THREE RUNS IN A ROW THE ECMWF WAS RATHER CONSISTENT WITH THE DEVELOPING SYSTEM OVER THE SOUTHERN GREAT LAKES THEN THE 12Z RUN OF THE ECMWF DEVELOPS THE SYSTEM FARTHER SOUTH RESULTING IN THE RAIN MOSTLY MISSING US TO THE SOUTH. MEANWHILE THE GFS IS NOW TRACKING THE SYSTEM FARTHER NORTH AND WOULD BRING SOME RAIN INTO THE AREA LATER FRIDAY INTO SATURDAY BEFORE IT SINKS THE SYSTEM SOUTH OF THE AREA SATURDAY NIGHT. GIVEN THE UNCERTAINLY I LARGELY CONTINUED OUR GOING FORECAST AND CALLED GOOD. THE ONE THINK THAT IS CLEAR... WE WILL NOT BE SEEING HIGHS IN THE 80S AGAIN FRI THROUGH MONDAY AS SOUTHWEST MICHIGAN && .AVIATION...(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING) ISSUED AT 610 AM EDT TUE SEP 4 2012 I WILL TIME THE CONVECTION ACROSS THE TAF SITES THIS MORNING AND HAVE CLEARING FROM WEST TO EAST AT THE TAF SITES THIS AFTERNOON DUE TO THE 700 MB TROUGH MOVING EAST OF THE AREA. I DO NOT EXPECT ANY DEVELOPMENT OF THE STORMS THIS AFTERNOON. INCREASING WINDS IN THE BOUNDARY LAYER AFTER 06Z SHOULD KEEP FOG FROM DEVELOPING AT THE TAF SITES TONIGHT. THE NEXT AREA OF RAIN WILL MOVE IN WEDNESDAY AFTERNOON WITH THE CONVECTION ON THE COLD FRONT. && .MARINE... ISSUED AT 320 AM EDT TUE SEP 4 2012 WEAK PRESSURE GRADIENT WILL AGAIN RESULT IN LIGHT WINDS AND LOW WAVES TODAY. THUNDERSTORMS AND RESULTANT HIGHER WINDS/WAVES WILL REMAIN A THREAT THROUGH WEDNESDAY. && .HYDROLOGY... ISSUED AT 320 AM EDT TUE SEP 4 2012 LOCALLY HEAVY RAINFALL WILL BE POSSIBLE WITH SCT STORMS TODAY AND MORE SO LATE WEDNESDAY. WIDESPREAD FLOODING IS NOT ANTICIPATED. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...NONE. LM...NONE. && $$ UPDATE...TJT SYNOPSIS...TJT SHORT TERM...93 LONG TERM...WDM AVIATION...WDM HYDROLOGY...93 MARINE...93
AREA FORECAST DISCUSSION
NWS MARQUETTE MI
728 AM EDT TUE SEP 4 2012 .SHORT TERM...(TODAY AND TONIGHT) ISSUED AT 438 AM EDT TUE SEP 4 2012 00Z RAOBS/LATEST WV IMAGERY AND RUC ANALYSIS SHOW FAST ZONAL FLOW OVER THE NRN TIER CONUS TO THE S OF DEEP OCCLUDED LO CENTERED OVER NRN MANITOBA. DISTURBANCE/AREA OF DEEPER MSTR RESPONSIBLE FOR SHRA/TS YDAY HAS PUSHED TO THE E AND GIVEN WAY TO WEAK HI PRES AND DRIER AIR. SOME AREAS OF DENSE FOG HAVE DVLPD OVER MAINLY THE ERN AND CNTRL CWA WITH LGT WINDS WHERE THE DRYING ALF HAS OUTRUN THE NEAR SFC DRYING. FOG APPEARS LESS PREVALENT OVER THE W WHERE DRIER LLVL AIR APRNT ON THE 00Z INL/MPX RAOBS HAS MADE GREATER INROADS. DESPITE THE PRESENCE OF THIS DRY AIR...SOME SHRA/A FEW TS ARE NOTED OVER NW MN NEAR AN INCOMING SHRTWV/SFC LO PRES TROF IN AREA WHERE NAM/GFS SHOW SOME H85 THETA E ADVECTION. SOME PATCHY MID/HI CLDS AHEAD OF THIS DISTURBANCE ARE DRIFING INTO THE WRN CWA. FARTHER TO THE NW...ANOTHER STRONGER SHRTWV IS OVER SASKATCHEWAN AND MOVING SEWD ON THE SRN FLANK OF CLOSED LO IN MANITOBA. EARLY THIS MORNING...OPTED TO ISSUE AN SPS FOR MUCH OF THE E AND CNTRL CWA TO HIGHLIGHT LOCALLY DENSE FOG. TODAY...EXPECT FOG TO BURN OFF THIS MRNG WITH ONSET OF DAYTIME HEATING. CONCERN THEN TURNS TO IMPACT OF SHRTWV NOW MOVING E THRU NRN MN. SEVERAL MODELS...ESPECIALLY THE 00Z NAM/CNDN...SHOW SOME FAIRLY SHARP DEEP LYR QVECTOR CNVGC/H3-2 DVGC/AXIS OF HIER H85-5 RH ASSOCIATED WITH DPVA/H85 THETA E ADVECTION IMPACTING THE WRN ZNS THIS AFTN INTO THE EARLY EVNG. IN FACT...RECENT SPC CONVECTIVE OUTLOOK HAS THE FAR W IN A SLIGHT RISK FOR SVR STORMS LATE THIS AFTN/EARLY EVNG. MODIFIED GFS FCST SDNG FOR IWD LATE IN THE AFTN YIELDS SBCAPE NEAR 1900 J/KG FOR SFC T/TD 84/60 UNDER STEEP MID LVL LAPSE RATES. THE NAM INDICATES 2000-2500 J/KG MUCAPE IN THIS AREA. A POSITIVE FOR SVR STORMS IS THE STEEP MID LVL LAPSE RATES/PRESENCE OF DRY AIR IN THE MID LVLS WITH SFC-10K FT DELTA THETA E 15-20C AND INVERTED V LOOK TO THE LLVL TEMP/DEWPT PROFILES THAT WOULD ENHANCE THE THREAT OF GUSTY WINDS. ON THE OTHER HAND...GENERALY DRYNESS OF THE ATMOSPHERE WL TEND TO LIMIT THE COVERAGE OF THE STORMS. ALSO DEEP LYR SHEAR IS FCST TO BE UP TO 30 KTS...A BIT MARGINAL BUT PROBABLY ENUF TO ALLOW FOR AT LEAST PULSE SVR STORMS. OTRW...EXPECT ANOTHER WARM DAY WITH H85 TEMPS IN THE 16-18C RANGE SUPPORTING HI TEMPS IN THE 80S AWAY FM LK BREEZES THAT WL TEND TO FORM OFF MAINLY LK MI WITH SSE H925 FLOW. TNGT...EXPECT BAND OF SCT SHRA/TS MOVING W-E INTO THE E HALF TO SLOWLY DIMINISH WITH LOSS OF DAYTIME HEATING/SHIFT OF SUPPORTING DEEP LYR QVECTOR CNVGC TO THE N INTO ONTARIO. WITH SOME DNVA/ NEGATIVE H85 THETA E ADVECTION/DEEP LYR QVECTOR DVGC FOLLOWING THIS BAND... EXPECT A PERIOD OF DRY WX. HOWEVER...APRCH OF SHARPER SHRTWV NOW MOVING SEWD THRU SASKATCHEWAN AND VIGOROUS DPVA/DEEP LYR QVECTOR CNVGC/SOME UPR DVGC WILL BRING BACK A THREAT OF SHRA/TS OVER THE W LATE. LIMITING FACTORS WILL BE LIMITED MSTR RETURN...SOME GUIDANCE ACTUALLY SHOWS NEGATIVE H85 THETA E ADVECTION...AND ARRIVAL OF THE DYNAMICS AT TIME OF MIN DIURNAL HEATING. .LONG TERM...(WEDNESDAY THROUGH MONDAY) ISSUED AT 438 AM EDT TUE SEP 4 2012 STARTING WITH WEDNESDAY...MOST OF THE GUIDANCE BRINGS A MODEST COLD FRONT THROUGH UPPER MI LATE WEDNESDAY MORNING INTO THE AFTERNOON. AS FOR MOISTURE AND INSTABILITY...850MB THETA E RIDGE SPRAWLS ITSELF ACROSS THE CWA TUESDAY NIGHT. PLENTY OF MOIST AIR WILL BE IN PLACE AS THE NOSE OF AN 850MB JET AIMS INTO SOUTHWESTERN UPPER MI...WITH PWATS EXPECTED TO BE 130-150 PERCENT OF NORMAL. SFC BASED CAPE DURING THE EARLY AFTERNOON IS AROUND 1000-1500 J/KG...AND MUCAPE IS UPWARDS OF 1800 J/KG. HIGHEST VALUES ARE IN THE SOUTH-SOUTH CENTRAL PORTIONS OF THE CWA. LOOKING AT FORECAST SOUNDINGS IT SEEMS WITH SHORTWAVE MOVING THROUGH DURING PEAK HEATING WE SHOULD HAVE ENOUGH GUSTO TO BREAK THE WEAK CAP THAT WILL BE IN PLACE. AS FAR AS ANY SUPPORT GOES...300MB JET STREAK SLIDES ACROSS THE CWA IN THE AFTERNOON...WITH RIGHT ENTRANCE REGION DYNAMICS IN PLAY ACROSS MAINLY THE SOUTH CENTRAL PORTION OF THE CWA. ECMWF HAS 500MB VORT MAXIMUM SLIDING INTO THE WEST HALF OF UPPER MI BY 18Z. WITH THE 300/850 MB JET STREAKS MOVING THROUGH 0-6 KM SHEAR IS AROUND 25-35 KNOTS. OVERALL THIS GIVES US A MODERATE CAPE/SHEAR ENVIRONMENT AND POTENTIAL FOR A SEVERE LINE OF STORMS...LIKELY DEVELOPING ACROSS THE SOUTHERN PORTIONS OF THE CWA WHERE LIFT AND INSTABILITY IS MAXIMIZED. THURSDAY WE DEAL WITH COOLER DRY AIR BEHIND THE FRONT/IN THE WAKE OF THE LOW PRESSURE SYSTEM NEAR JAMES BAY. DRY AIR PUNCHES IN ALOFT OVERNIGHT ON WEDNESDAY...SO IT LOOKS LIKE THURSDAY WILL BE RELATIVELY QUIET IN TERMS OF PRECIPITATION. PWATS DROP DOWN TO NEAR 70 PERCENT OF NORMAL AT TIMES AS SURFACE HIGH PRESSURE MOVING ACROSS THE MIDWEST TRIES TO RIDGE INTO UPPER MI. BY FRIDAY THE LOW BEGINS TO OCCLUDE NEAR JAMES BAY...SWINGING AN UPPER LEVEL TROUGH ACROSS UPPER MICHIGAN ONCE MORE. ECMWF GENERATES PRECIPITATION ACROSS CENTRAL AND EASTERN PRECIPITATION FOR THE DAY ON FRIDAY...SUPPORTED BY MODERATE 850-500MB QVECTOR CONVERGENCE AND LINGERING MOISTURE /PWATS AROUND 110 PERCENT OF NORMAL/. WITH NORTHWEST FLOW AND LAKE-850MB TEMP DIFFERENCES AROUND 15-18C...EXPECT A LAKE EFFECT COMPONENT TO PRECIPITATION NEAR LAKE SUPERIOR. ADDITIONALLY...STRONG ONSHORE FLOW WILL GENERATE WAVES AS HIGH AS 3 TO 5 FEET IN THE ALGER AND EASTERN MARQUETTE COUNTY SURF ZONE FRIDAY INTO SATURDAY MORNING...LEADING TO THE POSSIBILITY FOR RIP CURRENT DEVELOPMENT. WITH THE COLD FRONT PASSING WEDNESDAY AFTERNOON/EVENING TEMPERATURES WILL BE MORE FALL LIKE...WITH HIGHS IN THE 60S AND LOW 70S THROUGH THE REMAINDER OF THE PERIOD. ALONG WITH FALL LIKE TEMPERATURES...WE CAN EXPECT FALL-LIKE FEATURES. FRIDAY THERE IS AN ELEVATED POTENTIAL FOR WATERSPOUT DEVELOPMENT AS COOLER TEMPERATURES ALOFT MOVE IN OVER THE STILL WARM LAKE. FORECASTS PER THE INTERNATIONAL CENTRE FOR WATERSPOUT RESEARCH ARE STILL INDICATING THAT CONDITIONS WILL BE FAVORABLE FOR THEIR DEVELOPMENT. AS THE SFC/500MB HIGH PRESSURE RIDGE OVER THE NORTHERN PLAINS BUILDS INTO UPPER MICHIGAN FOR THE WEEKEND AND THROUGH THE FIRST PORTION OF THE WORK WEEK...EXPECT CONDITIONS TO REMAIN FAIRLY DRY. THE ONLY EXCEPTION IS THE LOW PRESSURE SYSTEM THAT DEVELOPS IN THE OHIO VALLEY FRIDAY...LINGERING OVER LOWER MI THROUGH THE EXTENDED. THIS COULD BRING SLIGHT CHANCE POPS OVER THE EASTERN U.P. FOR SATURDAY INTO MONDAY. FOR NOW WITH MODEL DIFFERENCES IN LOCATION AND TIMING OF THIS PRECIP WILL KEEP THE MODEL CONSENSUS IN FORECAST UNTIL THE FINER DETAILS CAN BE NARROWED DOWN. && .AVIATION...(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING) ISSUED AT 728 AM EDT TUE SEP 4 2012 EXPECT FOG IMPACTING SAW/CMX TO BURN OFF BY MID MRNG WITH THE ONSET OF DAYTIME HEATING. AN APRCHG LO PRES TROF WILL BRING THE THREAT OF SHRA/SOME TS TO ALL 3 SITES THIS AFTN/EVNG BEFORE THE TROF MOVES TO THE E THIS EVNG AND ENDS THE THREAT W-E. SINCE IWD HAS THE BEST SHOT TO SEE SOME TS...ADDED AN EXPLICIT FCST FOR TS TIMING THERE FOR 20Z-22Z. WITH LGT WINDS/DRYING ALF IN THE WAKE OF THE TROF...MORE FOG MAY FORM OVERNGT. BUT THE APRCH OF ANOTHER LO PRES TROF MAY BRING MORE CLDS/-SHRA TO IWD LATE IN THE FCST PERIOD. && .MARINE...(FOR THE 4 AM LAKE SUPERIOR FORECAST ISSUANCE) ISSUED AT 438 AM EDT TUE SEP 4 2012 EXPECT SSW WINDS TO INCREASE UP TO 20 KTS TODAY MAINLY OVER THE E HALF IN ADVANCE OF AN APPROACHING LO PRES TROF. THESE STRONGER WINDS WILL BRING DRIER AIR OVER THE E HALF OF THE LAKE AND DISSIPATE FOG THAT DEVELOPED DURING THE NIGHT IN THE WAKE OF SHOWERS THAT FELL ON MON. ALTHOUGH WINDS WILL DIMINISH FOR A TIME WITH THE PASSAGE OF THE TROF...EXPECT W TO NW WINDS IN ITS WAKE LATE WED THRU THU TO INCREASE UP TO 20 TO 25 KTS AS COOLER AIR ARRIVES OVER THE RELATIVELY WARM LAKE WATERS AND ENHANCES MIXING. ALTHOUGH WINDS MAY DIMINISH FOR A TIME ON THU NIGHT AS ANOTHER TROF SWINGS OVER LAKE SUPERIOR...PLAN ON ANOTHER ROUND OF STRONGER NW WINDS UP TO 25 KTS ON FRI IN ITS WAKE. THE APPROACH OF HIGH PRESSURE/A WEAKENING PRES GRADIENT THIS WEEKEND WILL CAUSE WINDS TO SLOWLY DIMINISH. && .MQT WATCHES/WARNINGS/ADVISORIES... UPPER MICHIGAN... NONE. LAKE SUPERIOR... NONE. LAKE MICHIGAN... NONE. && $$ SHORT TERM...KC LONG TERM...MCD AVIATION...KC MARINE...KC
AREA FORECAST DISCUSSION
NWS OMAHA/VALLEY NE
1032 AM CDT TUE SEP 4 2012 .DISCUSSION... MAIN CONCERN FOR LATE THIS AFTERNOON AND EVENING WILL BE CONVECTIVE POTENTIAL ALONG/NORTH OF A SURFACE TROUGH THAT EXTENDS FROM WESTERN NEBRASKA THROUGH SOUTHEAST NEBRASKA. NAM CONTINUES TO BE THE MOST AGGRESSIVE MODEL IN DEVELOPING CONVECTION BY 21-00Z ALONG AND NORTH OF I80...THEN CONTINUING THAT THROUGH THE EVENING BEFORE PUSHING OFF TO THE NORTHEAST. THIS SEEMS REASONABLE GIVE WEAK ZONAL FLOW ALOFT WITH SUBTLE ALBEIT WEAK HEIGHT FALLS NOTED ON 12Z OBJECTIVE UPPER AIR ANALYSIS. THIS IS ALSO WITHIN AN AREA WHERE THE CAP SHOULD BE THE WEAKEST GIVEN 10-11 DEGREES AT H70. INTERESTING...THE HRRR DOES NOT DEVELOP ANY CONVECTION AT ALL... AND THE RAP13 HOLDS OFF UNTIL ABOUT 23Z BETWEEN OMAHA AND SIOUX CITY. MADE MINOR TWEAKS TO THE FORECAST...PULLING POPS JUST A LITTLE BIT FURTHER SOUTH 21-23Z...OTHERWISE NO OTHER CHANGES MADE. DEWALD && .PREV DISCUSSION... /ISSUED 643 AM CDT TUE SEP 4 2012/ AVIATION... 12Z TAFS FOR KOFK...KLNK AND KOMA. AREAS OF MVFR FOG WILL LIFT BY 15Z THIS MORNING. VSBYS AT KOFK MAY DROP TO BELOW A MILE FOR A BRIEF TIME AS WELL. THEN SOUTHERLY WINDS NEAR 10 TO 15KTS WILL PREVAIL WITH SCATTERED CLOUDS NEAR FL040. THERE IS A CHANCE FOR THUNDERSTORMS OVER ALL OF EASTERN NEBRASKA AFTER 21Z AS A LOW PRESSURE SYSTEM MOVES INTO THE AREA. THINKING BEST INSTABILITY WILL FOCUS STORMS NEAR THE MISSOURI RIVER...TO KOMA WILL HAVE BEST CHANCE FOR STORMS. A COLD FRONT SHOULD MOVE THROUGH EASTERN NEBRASKA AFTER 06Z...WITH WINDS TURNING TO NORTHWEST AND THUNDERSTORM CHANCES ENDING BY 10Z ALL SITES. DERGAN PREV DISCUSSION... /ISSUED 343 AM CDT TUE SEP 4 2012/ DISCUSSION... MAIN FORECAST CONCERNS ARE THUNDERSTORM CHANCES THIS AFTERNOON/EVENING AND AGAIN ON THURSDAY INTO FRIDAY. WESTERLY UPPER LEVEL FLOW CONTINUES OVERHEAD WITH SEVERAL WEAK EMBEDDED SHORTWAVES PASSING THROUGH THE FLOW. AT THE SFC...WEAK AREA OF LOW PRESSURE IS CENTERED OVER CENTRAL SOUTH DAKOTA/CENTRAL NEBRASKA WITH RICH DEWPOINTS IN THE UPPER 60S TO LOWER 70S RESIDING OVER MUCH OF EASTERN NEBRASKA AND WESTERN IOWA. THIS MAY LEAD TO PATCHY FOG FOR THE MORNING COMMUTE AND WILL CONTINUE TO KEEP AN EYE ON ANY DETERIORATING CONDITIONS THIS MORNING. AN UPPER LEVEL TROF WILL SWING THROUGH THE CANADIAN PRAIRIE PROVINCES AND NORTHERN PLAINS TODAY. AHEAD OF THIS...A STRONG COLD FRONT WILL PUSH SOUTHEAST THROUGH THE PLAINS. AHEAD OF THIS FRONT THUNDERSTORMS COULD DEVELOP LATE THIS AFTERNOON ALONG THE MOIST AXIS ACROSS NORTHEAST NEBRASKA AS AFTERNOON HEATING PEAKS. UPPER LEVEL SUPPORT WILL BE WEAK THROUGHOUT THE LATE AFTERNOON BUT IS FORECAST TO INCREASE INTO THE EVENING HOURS AHEAD OF A WEAK SHORTWAVE AHEAD OF THE UPPER TROF. A MAJORITY OF MODEL GUIDANCE SOLUTIONS DEVELOP AN AREA OF QPF OVER NORTHEAST NEBRASKA...CLOSER TO UPPER LEVEL FORCING...AROUND 21Z AND SPREAD IT SOUTHEAST WELL AHEAD OF THE SFC FRONT THRU 06Z. STEEPENING MID LEVEL LAPSE RATES ALONG WITH MODERATE INSTABILITY AND 0-6KM BULK SHEAR AROUND 40KTS COULD LEAD TO SOME SEVERE STORMS...MAINLY IN THE NORTHERN CWA. STRONG SUBSIDENCE IS FORECAST BEHIND THE FRONT SO WILL QUICKLY END POPS AFTER FROPA WHICH SHOULD BE THRU THE ENTIRE CWA BY 12-15Z WED. COOLER TEMPERATURES FOLLOW BEHIND THE BOUNDARY WITH HIGHS IN THE UPPER 70S TO LOWER 80S FOR WEDNESDAY AS HIGH PRESSURE BUILDS INTO THE CENTRAL PLAINS. RETURN FLOW SETS UP LATER IN THE DAY THURSDAY SO WL LEAVE MUCH OF THE DAY DRY WITH POPS RETURNING TO THE FORECAST THURSDAY NIGHT IN LLVL WARM AIR ADVECTION REGIME. IN ADDITION...ANOTHER UPPER LEVEL SHORTWAVE WILL BE APPROACHING THE REGION AS A COLD FRONT SLIDES EAST ACROSS THE FORECAST AREA. NOCTURNAL LOW LEVEL JET MAY SUSTAIN ACTIVITY THRU THE OVERNIGHT HOURS AS WELL AS INTO FRIDAY MORNING. A STRENGTHENING UPPER LEVEL TROF MOVING TOWARD THE GREAT LAKES REGION WILL BRING COOLER TEMPERATURES FOR THE WEEKEND BEFORE THE TROF CLOSES OFF OVER THE OHIO VALLEY REGION. A LARGE AREA OF SFC HIGH PRESSURE WILL BE IN PLACE SUNDAY INTO MONDAY. A BIT OF A WARM UP IS EXPECTED EARLY NEXT WEEK AS AN UPPER LEVEL RIDGE BUILDS INTO THE CENTRAL PLAINS. KERN && .OAX WATCHES/WARNINGS/ADVISORIES... NE...NONE. IA...NONE. && $$
AREA FORECAST DISCUSSION...UPDATED
NWS NORTH PLATTE NE
636 AM CDT TUE SEP 4 2012 .UPDATE... .AVIATION... VFR IS EXPECTED MOST AREAS TODAY AND TONIGHT. PATCHY MORNING FOG WILL DISSIPATE ALONG AND EAST OF HIGHWAY 183 BY 14-15Z. ISOLATED THUNDERSTORMS ARE EXPECTED LATE THIS AFTERNOON THROUGH EARLY EVENING ALONG AND EAST OF HIGHWAY 83. WINDY CONDITIONS ARE EXPECTED TONIGHT BEHIND A STRONG COLD FRONT. && .PREV DISCUSSION... /ISSUED 345 AM CDT TUE SEP 4 2012/ DISCUSSION... ONE MORE DAY OF 90S BEFORE A COOL DOWN CAN BE EXPECTED. RIDGE ACROSS THE SOUTHERN PLAINS WITH SOUTHWEST FLOW IN TRANSITION TO A MORE ZONAL FLOW AS A TROUGH PUSHES ACROSS THE NORTHERN ROCKIES AND NORTHERN PLAINS. SURFACE TROUGH ACROSS THE CWA THIS MORNING WITH VERY DRY AIR...DEW PTS IN THE 30S...WEST OF THE TROUGH...A KVTN TO KTIF TO KOGA LINE. TO THE EAST OF THE TROUGH DEW PTS IN THE 50S AND 60S AND A FEW SITES ACROSS CENTRAL NEB STARTING TO REPORT SOME FOG. COLD FRONT HEADING SOUTH ACROSS THE NORTHERN ROCKIES. TROUGH WILL REMAIN NEARLY STATIONARY THIS AFTERNOON ACROSS THE AREA WITH VERY DRY CONDITIONS AND RH PERCENTAGES NEAR OR BELOW 15 PERCENT TO THE WEST. WINDS ARE MARGINAL...AROUND 15 TO 20 MPH...FOR RFW CRITERIA...HOWEVER DUE TO DROUGHT AND LOW RH VALUES...WILL HAVE A RFW FOR MUCH OF NW NEB. AS FOR TEMPS...THE DRY AIR WILL COMBINE WITH SOME PREFRONTAL COMPRESSIONAL HEATING TO PUSH HIGHS ONCE AGAIN INTO THE 90S. LATE THIS AFTERNOON ALONG AND EAST OF THE TROUGH...WHERE BETTER LOW LEVEL MOISTURE...SOME ISOLATED THUNDERSTORMS ARE POSSIBLE WITH PEAK HEAT...SIMILAR TO YESTERDAY. BETTER SHEAR/HIGHER CAPE/AND SPC SLIGHT RISK IS EAST OF THE CWA...HOWEVER EXPECT DEVELOPMENT ALONG TO EAST OF THE TROUGH...WHICH SHOULD STILL BE OVER THE CWA...AND CANNOT RULE OUT A STRAY STORM BECOMING STRONG. ONCE THE COLD FRONT MOVES ACROSS THE AREA THIS EVENING INTO THE OVERNIGHT HOURS...THE CONVECTION WILL QUICKLY MOVE EAST. DRY AND COOL AIR WILL SPREAD ACROSS THE AREA. WED HIGHS AROUND 80 ACROSS ALL BUT THE SW...WHICH SHOULD PUSH INTO THE LOWER 80S. THESE HIGHS ARE FAIRLY CLOSE TO NORMAL FOR THIS TIME OF YEAR. HOWEVER DEW PTS IN THE 30S TO LOWER 40S WILL CONTINUE TO CREATE A HIGH DANGER HOWEVER WINDS NOT EXPECTED TO BE MUCH OVER 10 MPH. THURSDAY ANOTHER COLD FRONT WILL APPROACH FROM THE NW. AHEAD OF THE FRONT WINDS BECOME SOUTHERLY AND BRING A RETURN OF WARMER TEMPERATURES AND POSSIBLY SOME LL MOISTURE. WILL HAVE TO MONITOR HIGHS AS THE MODELS HAVE TRENDED UP TODAY...WITH THE NAM SEEING AN INCREASE BACK CLOSE TO 90. HAVE NOT JUMPED TO THIS WARM YET...HOWEVER IF WE DO WARM TO THIS...NEAR CRITICAL FIRE WEATHER CONDITIONS WILL BE POSSIBLE AS DEW PTS SLOW TO RISE. AS THE FRONT PASSES THURSDAY NIGHT INTO FRIDAY MOISTURE WILL CONTINUE TO BE A LIMITING FACTOR ON SHOWER AND THUNDERSTORM DEVELOPMENT. HAVE TRENDED DRIER AS RETURN MOISTURE LOOKS TO BE ONLY TO CURRENT LEVELS...AT BEST...ACCORDING TO LATEST GUIDANCE...WITH A GOOD POSSIBILITY THIS TREND WILL CONTINUE OVER THE NEXT FEW FORECAST UPDATES. FRIDAY INTO SATURDAY WILL BE THE COOLEST OF THE FORECAST PERIOD AS COOL HIGH PRESSURE SETTLES OVER THE HIGH PLAINS. GUIDANCE AND FORECAST HAVE HIGHS ONLY IN THE 70S...WITH LOWS IN THE 40S. BY SUNDAY THE HIGH WILL PUSH TO THE EAST WITH SOUTHERLY FLOW RETURNING AND BRINGING A SLOW WARMUP INTO THE START OF NEXT WEEK. STILL NO MOISTURE AND FORECAST REMAINS DRY. AVIATION... VFR IS EXPECTED MOST AREAS TODAY AND TONIGHT. PATCHY MORNING FOG WILL DEVELOP ALONG AND EAST OF HIGHWAY 183 THROUGH 14Z. ISOLATED THUNDERSTORMS ARE EXPECTED LATE THIS AFTERNOON AND THIS EVENING ALONG AND EAST OF HIGHWAY 83. WINDY CONDITIONS ARE EXPECTED TONIGHT BEHIND A STRONG COLD FRONT. FIRE WEATHER... HOT DRY AIR WILL SURGE EAST THROUGH WESTERN AND NORTH CENTRAL NEBRASKA AHEAD OF A STRONG COLD FRONT WHICH WILL MOVE THROUGH TONIGHT. CRITICAL FIRE DANGER IS EXPECTED ALONG AND NORTH OF INTERSTATE 80 AND GENERALLY ALONG AND WEST OF HIGHWAY 83. THE 20Z HRRR AND THE 00Z GEM REGIONAL MODELS SUGGEST SIMILAR CONDITIONS WILL DEVELOP ACROSS SWRN NEB AND PERHAPS INTO AREAS EAST OF HIGHWAY 83. GIVEN THE DIFFERENCES BETWEEN HRRR AND GEM REGIONAL VERSUS THE NAM AND ECM WILL HOLD OFF ON AN EXPANSION OF THE RED FLAG WARNING FOR NOW. && .LBF WATCHES/WARNINGS/ADVISORIES...RED FLAG WARNING FROM 11 AM CDT /10 AM MDT/ THIS MORNING TO 10 PM CDT /9 PM MDT/ THIS EVENING FOR NEZ204-206-208. && $$ SHORT TERM/EXTENDED...CDC AVIATION...CDC
AREA FORECAST DISCUSSION
NWS SAN JOAQUIN VALLEY - HANFORD CA
324 PM PDT TUE SEP 4 2012 .SYNOPSIS... MOISTURE FROM THE TROPICS WILL STREAM INTO THE REGION THROUGH THURSDAY PRODUCING ISOLATED SHOWERS AND THUNDERSTORMS TO PARTS OF THE AREA. BY FRIDAY, DRIER AIR WILL MOVE IN FROM THE WEST, BRINGING AN END TO THE THUNDERSTORM THREAT. && .DISCUSSION... SCT TO BKN CLOUDS ACROSS THE CENTRAL SJV AND INTO THE TULARE COUNTY MOUNTAINS TODAY. TEMPERATURES ACROSS THE SJV ARE APPROACHING THE CENTURY MARK IN A FEW LOCATIONS. NO PRECIP HAS BEEN REPORTED WITH THE CLOUD COVER THIS AFTERNOON IN THE VALLEY AND ONLY A FEW HUNDREDTHS IN THE TULARE COUNTY FOOTHILLS AND MOUNTAINS. THE FORECAST CALLS FOR PARTLY CLOUDY SKIES TONIGHT OVER THE CENTRAL CA INTERIOR. VISIBLE SATELLITE IMAGERY INDICATES A LINE OF SHOWERS OFF THE NRN BAJA COAST THAT IS MOVING NORTH. SOME SHOWERS HAVE DEVELOPED IN THE SOUTH LAND THIS AFTERNOON. THE KERN DESERT AND MOUNTAINS REMAIN RAIN FREE THIS AFTERNOON AS RUC SHOWS STABLE ATMS. A FEW LIGHTNING STRIKES ARE OCCURRING IN THE FRESNO COUNTY MOUNTAINS ATTM AS A CLUSTER OF STORMS QUICKLY MOVES EAST. SW FLOW ALOFT IS FORECAST TO CONTINUE THIS WEEK WITH RISING HEIGHTS AND TEMPERATURES CONTINUING ABOVE NORMAL THROUGH THE WEEKEND. THE UPPER RIDGE WILL MOVE INTO SRN CA BY SAT AND REMAIN THERE UNTIL MONDAY BEFORE IT DRIFTS BACK TO THE EAST AS ANOTHER SURGE OF MOISTURE APPROACHES THE AREA BY NEXT TUESDAY. THE ECMWF IS MORE AGGRESSIVE WITH THE MOISTURE ON NEXT TUESDAY THAN THE GFS. && .AVIATION... VFR CONDITIONS WILL PREVAIL ACROSS THE CENTRAL CALIFORNIA INTERIOR THROUGH 18Z WEDNESDAY. && .AIR QUALITY ISSUES... NONE. && .CERTAINTY... THE LEVEL OF CERTAINTY FOR DAYS 1 AND 2 IS MEDIUM. THE LEVEL OF CERTAINTY FOR DAYS 3 THROUGH 7 IS MEDIUM. THIS INFORMATION IS PROVIDED AS PART OF A TRIAL PROJECT CONDUCTED BY THE NATIONAL WEATHER SERVICE SAN JOAQUIN VALLEY - HANFORD. CERTAINTY LEVELS INCLUDE LOW...MEDIUM...AND HIGH. PLEASE VISIT WWW.WEATHER.GOV/HNX/CERTAINTY.PHP /ALL LOWER CASE/ FOR ADDITIONAL INFORMATION AND/OR TO PROVIDE FEEDBACK. && .HNX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ PUBLIC...JDB AVN/FW...MOLINA SYNOPSIS...WP WEATHER.GOV/HANFORD
AREA FORECAST DISCUSSION
NWS GRAND JUNCTION CO
238 PM MDT TUE SEP 4 2012 .SHORT TERM...(TODAY THROUGH WEDNESDAY NIGHT) ISSUED AT 238 PM MDT TUE SEP 4 2012 WATER VAPOR IMAGERY CLEARLY SHOWING MUCH DRIER AIR THAT HAS FILTERED DOWN FROM THE NORTH OVERNIGHT WITH RH VALUES ACROSS TOP THIRD OF THE FORECAST AREA IN THE TEENS. PWATS REMAIN NEAR .7 INCH FOR THE SAN JUANS AND AREAS SOUTH SO SOME LIGHT SHOWERS OR QUICK POP AND DROP STORM IS NOT OUT OF THE QUESTION THROUGH THE EVENING HOURS. WATER VAPOR IS ALSO SHOWING SOME SMALL DISTURBANCES MOVING THROUGH THE MEAN FLOW CAUSING SOME CONVECTION ACROSS ARIZONA AND CENTRAL UTAH...POSSIBLY REACHING SOUTHEASTERN UTAH IN THE NEXT HOUR OR TWO. DID INCREASE POPS FOR THAT AREA THROUGH THE EVENING HOURS AS WELL AS KEEPING CURRENT POPS IN PLACE FOR THE SAN JUANS. PLENTY OF SUNSHINE TO CONTINUE FOR THE REST OF THE FORECAST AREA WHICH WILL PERSIST THROUGH REMAINDER OF SHORT TERM. ANY CONVECTION SHOULD END NEAR SUNSET WITH CLEAR SKIES EXPECTED OVERNIGHT. TEMPS SHOULD DROP TO PLEASANT CLIMATOLOGICAL NORMS FOR MOST LOCALES. NOT MUCH CHANGE WEDNESDAY WITH CHANCES FOR PRECIP CONTINUING TO DECREASE WITH ONLY VERY ISOLD POPS OVER THE HIGHEST TERRAIN OF THE SAN JUANS. SUNNY SKIES WILL BE THE RULE WITH TEMPS RUNNING ABOUT 4 TO 6 DEGREES ABOVE NORMAL. OVERNIGHT LOWS WILL STAY NEAR NORMAL. .LONG TERM...(THURSDAY THROUGH TUESDAY) ISSUED AT 238 PM MDT TUE SEP 4 2012 A SHORTWAVE DISTURBANCE IS EXPECTED TO DROP ACROSS ID/MT ON THURSDAY AND CLIP NE CO BY MIDDAY FRIDAY. AN ASSOCIATED COLD FRONT SHOULD REACH NE UT/NW CO THU EVENING AND PUSH ACROSS THE REMAINDER OF THE FORECAST AREA THURSDAY NIGHT. AS THE SHORTWAVE APPROACHES...MOISTURE IS PULLED IN AHEAD OF IT FROM THE WEST FOR INCREASING CLOUDS THURSDAY...WITH ISOLATED TO SCATTERED SHOWERS DEVELOPING BY LATE AFTERNOON INTO EVENING. SOME INITIAL STORMS MAY BE DRY...BUT MODELS FORECAST PRECIPITABLE WATER VALUES BETWEEN 1/2 TO 3/4 INCH BY THU EVENING...SO EXPECT STORMS TO WET UP. DRIER AIR WILL BE MOVING IN ON NORTHWEST FLOW BY FRI AFTERNOON AND CONTINUE THROUGH SATURDAY AS A HIGH PRESSURE RIDGE BUILDS OVER THE GREAT BASIN. A PACIFIC TROUGH MOVES INLAND LATE THIS WEEKEND PULLING UP A SLUG OF MOISTURE AHEAD OF IT AND PUSHING THE RIDGE EAST. THIS SHOULD INCREASE THE CHANCE OF SHOWERS MONDAY AND TUESDAY. && .AVIATION...(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING) ISSUED AT 238 PM MDT TUE SEP 4 2012 VFR CONDITIONS FOR ALL TAF SITES TODAY WITH KASE AND KEGE HAVING A REMOTE CHANCE FOR A WEAK CELL TO MOVE CLOSE TO THE TERMINALS. SOME GUSTY WINDS UP TO 40 MPH ARE POSSIBLE FROM THE CELLS. ASIDE FROM THAT...PLENTY OF SUN EXPECTED WITH VFR PERSISTING THROUGH TOMORROW. && .FIRE WEATHER... ISSUED AT 238 PM MDT TUE SEP 4 2012 WIND GUSTS IN THE 20-25 MPH RANGE ACROSS THE NORTH THIS AFTERNOON WITH A FEW SITES SHOWING A BIT STRONGER GUSTS. LOCALIZED AREAS LIKELY TO SEE A BRIEF PERIOD OF CRITICAL RH AND/OR WIND GUSTS BUT WIDESPREAD CRITICAL CONDITIONS ARE NOT EXPECTED. HIGH-RESOLUTION HRRR AND RUC13 MODELS SHOW WIND GUSTS DIMINISHING QUICKLY EARLY THIS EVENING. NE UT/NW CO SHOULD CONTINUE TO REMAIN ON THE SOUTHERN FRINGE OF THE STRONGER WINDS THROUGH WEDNESDAY. THURSDAY AFTERNOON MAY SEE A BIT STRONGER WINDS ACROSS THE NORTH...20-30 MPH GUSTS...AS A SHORTWAVE AND ASSOCIATED SURFACE COLD FRONT APPROACH FROM THEN NORTH. HOWEVER...MOISTURE WILL ALSO BE INCREASING WITH AFTERNOON HUMIDITY EXPECTED TO BOTTOM OUT RIGHT AROUND 15 PERCENT. WITH INCREASING CLOUDS...WILL CONTINUE TO HOLD OFF ON ANY FIRE WEATHER HIGHLIGHTS FOR NE UT/NW CO ALTHOUGH ISOLATED AREAS COULD SEE CRITICAL WIND/RH CONDITIONS DEVELOP FOR A FEW HOURS THURS AFTERNOON. WILL CONTINUE KEEPING A WATCH ON THIS. ISOLATED TO SCATTERED THUNDERSTORMS MAY BE DRY INITIALLY THURS AFTERNOON BUT SHOULD WET UP BY THURS EVENING. THE COLD FRONT SHOULD PUSH THROUGH THURS NIGHT. && GJT WATCHES/WARNINGS/ADVISORIES... CO...NONE. UT...NONE. && $$ SHORT TERM...TGR LONG TERM...JAD AVIATION...TGR FIRE WEATHER...JAD
AREA FORECAST DISCUSSION
NWS LINCOLN IL
1236 PM CDT TUE SEP 4 2012 .DISCUSSION... ISSUED 937 AM CDT TUE SEP 4 2012 WEAKENING SHORT-WAVE TROUGH HAS SPREAD A BAND OF MID-LEVEL CLOUDINESS INTO CENTRAL AND WESTERN ILLINOIS THIS MORNING. DESPITE THE PRESENCE OF THIS FORCING MECHANISM...PREVAILING HIGH PRESSURE HAS PREVENTED MUCH PRECIP FROM REACHING THE AREA. 14Z/9AM RADAR MOSAIC SHOWS A LINE OF SHOWERS/STORMS EXTENDING FROM NORTH OF SAINT LOUIS WESTWARD ACROSS CENTRAL MISSOURI...HOWEVER THIS PRECIP IS DISSIPATING AS IT PUSHES FURTHER EAST INTO THE SURFACE RIDGE AXIS. NEITHER THE 11Z HRRR NOR THE 12Z NAM ARE HANDLING THE CURRENT SITUATION VERY WELL AT ALL...WITH BOTH MODELS INDICATING A GOOD DEAL OF PRECIP ACROSS THE WESTERN KILX CWA THIS MORNING. BASED ON CURRENT SATELLITE/RADAR AND THE PRESENCE OF SURFACE HIGH PRESSURE...HAVE REJECTED THE HIGH-RES MODEL SOLUTION IN FAVOR OF ONLY ISOLATED SHOWERS/THUNDER TODAY. HAVE ALREADY SENT A ZONE UPDATE TO LOWER POPS AND REMOVE MENTION OF MORNING FOG ACROSS THE E/SE. BARNES && .AVIATION... ISSUED 1236 PM CDT TUE SEP 4 2012 VFR CONDITIONS WILL PREVAIL THROUGH THE ENTIRE 18Z TAF PERIOD. A BAND OF MID/HIGH CLOUDS WILL CONTINUE TO DRIFT EASTWARD ACROSS THE AREA THIS AFTERNOON...WHILE A CU-FIELD DEVELOPS AT LOW-LEVELS. CU-RULE AND LATEST SATELLITE IMAGERY SUGGEST BKN CEILINGS AOA 4000FT POSSIBLE ACROSS THE EAST. HAVE INCLUDED A TEMPO GROUP FOR BKN CU AT KCMI...BUT HAVE KEPT SKIES SCT FURTHER WEST AT THE REMAINING TERMINALS. ONCE MID/HIGH CLOUDS SHIFT FURTHER EAST AND DIURNAL CU DISSIPATES...CLEAR SKIES WILL BE THE RULE TONIGHT. FORECAST SOUNDINGS SHOW INCREASING MID/HIGH CLOUDS ONCE AGAIN BY WEDNESDAY MORNING...AS A COLD FRONT APPROACHES FROM THE WEST. ANY LOWER CLOUDS AND SCATTERED CONVECTION WILL LIKELY HOLD OFF UNTIL AFTER 18Z. WINDS WILL INITIALLY BE LIGHT/VARIABLE THIS AFTERNOON AND TONIGHT...BUT WILL BECOME S/SE AT 5 TO 10KT AHEAD OF THE APPROACHING FRONT WEDNESDAY MORNING. BARNES && .PREV DISCUSSION... ISSUED 330 AM CDT TUE SEP 4 2012 SHORT TERM...TODAY THROUGH FRIDAY NIGHT SOME FOG PRESENT OVER EASTERN IL EAST OF I-55 WHERE SKIES CURRENTLY CLEAR AND WILL CONTINUE PATCHY FOG UNTIL 9 AM OVER EASTERN IL. MID/HIGH CLOUDS SPREADING EAST FROM IA AND NORTHERN MO INTO CENTRAL/NW IL EARLY THIS MORNING WITH A CLUSTER OF SHOWERS AND THUNDERSTORMS OVER NORTHERN MO AND OVER SOUTHERN LAKE MI AND NEAR CHICAGO. HRRR MODELS WAS HANDLING QPF THE BEST THIS MORNING WHICH BRINGS THE CONVECTION FROM NORTHERN MO EASTWARD INTO CENTRAL IL AND WEAKENS IT THIS MORNING. WILL CARRY POPS OF 20-40% TODAY AND HIGHEST WEST OF SPRINGFIELD. ISOLATED SHOWERS AND THUNDERSTORMS POSSIBLE THIS AFTERNOON IN UNSTABLE HUMID AIRMASS WITH DEWPOINTS STILL IN THE LOWER 70S. SPC KEEPS SLIGHT RISK NW OF IL TODAY. HIGHS IN THE UPPER 80S AND LOWER 90S AGAIN TODAY. HAVE 20-30% CHANCE OF SHOWERS AND THUNDERSTORMS INTO WESTERN AREAS OVERNIGHT WHILE PATCHY FOG POSSIBLE OVER EASTERN IL AGAIN AFTER MIDNIGHT. MODELS HAVE TRENDED A BIT SLOWER WITH A STRONGER COLD FRONT MOVING SE INTO CENTRAL IL WED AFTERNOON/EVENING. SPC CONTINUES SLIGHT RISK ACROSS MUCH OF CENTRAL IL NW OF I-70 WED AFTERNOON AND EARLY EVENING UNTIL SUNSET. AIRMASS GETS UNSTABLE AGAIN BY WED AFTERNOON WITH CAPES 2000-3000 J/KG WHILE BEST WIND SHEAR AND SHORT WAVE ENERGY IS NORTH OF CENTRAL IL. ADDED 20-30% CHANCE OF CONVECTION OVER EASTERN IL WED EVENING ESPECIALLY EARLY WED EVENING UNTIL SUNSET. ANOTHER VERY WARM AND HUMID DAY WED WITH HIGHS IN THE UPPER 80S AND LOWER 90S. DRY CONDITIONS EXPECTED THU WITH A FAIR AMOUNT OF SUNSHINE AS WEAK HIGH PRESSURE SETTLES INTO IL BY SUNSET THU...WITH SOME INCREASING CLOUDS FROM THE WEST LATER IN THE DAY. HIGHS IN THE LOW TO MID 80S AND WARMEST BY LAWRENCEVILLE WITH 87F. ANOTHER FAIRLY STRONG NORTHERN STREAM SHORT WAVE DIVES INTO THE MIDWEST BY FRI RETURNING A GOOD CHANCE OF SHOWERS AND A FEW THUNDERSTORMS. THIS TO ALSO BRING COOLER WEATHER LATER THIS WEEK. LONG TERM...SATURDAY THROUGH MONDAY NIGHT THE ENSEMBLE MODELS CONTINUE TO SHOW A STRONG UPPER LEVEL TROF DIGGING SOUTHEAST THROUGH THE MIDWEST AND GREAT LAKES REGION LATE THIS WEEK. THERE ARE STILL DIFFERENCES AMONG THE INDIVIDUAL MEMBERS ON WHAT HAPPENS WITH THIS TROUGH THIS WEEKEND...WITH SOME MEMBERS KEEPING THE TROUGH MORE PROGRESSIVE AND PUSHING IT EAST OF THE AREA BY SUNDAY MORNING...WHILE OTHERS CUTOFF THE TROUGH OVER THE OHIO VALLEY INTO NEXT MONDAY. FOR NOW WILL USE A BLEND OF MODEL SOLUTIONS AND STICK CLOSE TO ALLBLEND POPS IN THE EXTENDED FOR THIS WEEKEND...WITH HIGHER POPS SAT AND SHIFTING MORE INTO EASTERN IL SUNDAY...AND DRY MONDAY. BELOW NORMAL TEMPERATURES BY 5-10 DEGREES FOR THE HIGHS EXPECTED THIS WEEKEND AND GRADUALLY MODIFY DURING NEXT WORK WEEK. KH && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$
AREA FORECAST DISCUSSION
NWS NORTHERN INDIANA
339 PM EDT TUE SEP 4 2012 .SHORT TERM...TONIGHT THROUGH WEDNESDAY NIGHT. SEVERAL CONCERNS TO DEAL WITH OVER THE NEXT 36 HOURS FROM CONVECTION/SVR WX TO FOG. WEAK FRONTAL BOUNDARY WAS ROUGHLY LOCATED FROM MONTICELLO TO FORT WAYNE TO DEFIANCE WITH ISOL TO SCT SHOWERS STRUGGLING TO TAKE SHAPE ALONG WITH GIVEN WEAK CONVERGENCE AND LIMITED INSTABILITY. WILL KEEP A PRE 1ST PERIOD TO ADDRESS THIS ACTIVITY WHICH SHOULD EXIT BY 00Z. WITH MOIST BOUNDARY LAYER AND LITTLE CHANCE FOR MIXING ACROSS THE AREA TODAY...FOG/STRATUS POTENTIAL WILL REMAIN HIGH ACROSS MOST IF NOT ALL OF THE FORECAST AREA. COULD SEE WIDESPREAD DENSE FOG LATER TONIGHT IN MANY SPOTS WITH TEMPS FALLING PASS CROSSOVER TEMPS IN THE UPPER 60S TO AROUND 70 AND CALM WINDS/CLEAR SKIES. POTENTIAL ISSUES ARISE FROM ANTICIPATED UPSTREAM CONVECTION ACROSS MINN/WI/IOWA. SEVERAL RUNS OF THE HRRR HAVE SHOWN DEVELOPMENT ACROSS THIS AREA DROPPING TOWARDS POSSIBLE WESTERN PARTS OF THE FORECAST AREA LATER TONIGHT/WEDS MORNING...POSSIBLY CAUSING ISSUES WITH FOG DEVELOPMENT. FOR NOW...HAVE BUMPED UP WORDING IN ZONES TO PATCHY DENSE FOG AND WILL DEFER TO EVENING/OVERNIGHT SHIFTS TO ADJUST BASED ON UPSTREAM TRENDS. STRONGER UPPER LEVEL TROUGH AND SFC COLD FRONT STILL POISED TO MOVE INTO THE REGION WEDS/WEDS NGT. STRONG DYNAMICS WILL ACCOMPANY THE SYSTEM WITH A FAVORABLE TIMING OF LIFT AND MSTR CONVERGENCE IN THE LATE AFTERNOON/EARLY EVENING. GIVEN 0-6 KM SHEAR IN THE 30 TO 40 KT RANGE SVR THREAT IS STILL POSSIBLE...IF SUFFICIENT HEATING CAN OCCUR AHEAD OF THE ACTUAL FRONT. THE FLY IN THE OINTMENT FOR THIS MAY BE ANY LATE NIGHT/MORNING CONVECTION NOTED ABOVE THAT COULD STABILIZE THE AREA THROUGH OPTIMAL PEAK HEATING...THEREBY REDUCING CHANCES FOR SVR WX. DO STILL FEEL THAT CONVECTION WILL FIRE TO THE WEST ALONG THE FRONT IN ILLINOIS DURING THE AFTERNOON AND MOVE EAST TOWARDS THE AREA. HAVE THEREFORE CAUTIOUSLY HELD WITH LIKELY POPS IN NW AREAS WEDS AFTERNOON BUT FOR NOW BACKED OFF ON POP TIMING EARLIER IN THE DAY ASSUMING THAT MODEL INDICATIONS OF IA/WI/MN COMPLEX DYING AS IT APPROACHES OCCUR. THIS SAME REASONING WARRANTS A SLIGHT INCREASE IN POPS WEDS NGT WITH POTENTIAL FOR SOMEWHAT SLOWER DEPARTURE OF PRECIP...BUT NOT A RAMP UP TO LIKELY IN EASTERN AREAS GIVEN LESS FAVORABLE TIME FRAME FOR CONVECTION TO MAINTAIN ITSELF UNLESS ALREADY WELL ESTABLISHED. && .LONG TERM... THURSDAY THROUGH TUESDAY...THE MAIN CHALLENGES THIS PERIOD CONCERN THE CHANCES FOR THE DEVELOPMENT OF A CUT OFF LOW OVER THE OHIO VALLEY REGION THIS WEEKEND. ADDITIONAL CHALLENGES INCLUDE THE TIMING AND EXTENT OF PRECIPITATION AND THE EFFECT ON TEMPERATURES IF THE LOW DEVELOPS AND LINGERS OVER OR NEAR THE REGION. FOR THIS PACKAGE...FAVOR THE ECMWF...ALTHOUGH THE 12Z RUN WAS AN OUTLIER COMPARED TO THE PAST SEVERAL RUNS. THE 12Z ECMWF RUN WAS NOT USED FOR THIS PACKAGE. THE PAST SEVERAL ECMWF RUNS HAVE HAD REASONABLE RUN TO RUN CONSISTENCY. AS A WHOLE THE NEW 12Z GFS SOLUTION HAS TRENDED TOWARD THE SLOWER...FARTHER WEST 00Z ECMWF SOLUTION. ALSO...THE 00Z ECMWF HAS HAD BETTER SUPPORT WITH THE SURFACE LOW/SURFACE REFLECTION CLOSER TO THE UPPER LOW THAN THE GFS. HAVE RAISED RAIN CHANCES FRIDAY NIGHT GIVEN REASONABLE CONFIDENCE IN THE TIMING OF THE SHORT WAVE TROF AND ASSOCIATED COLD FRONT. FOR THE REST OF THE PERIOD...WENT WITH PERSISTENCE AND ATTEMPTED TO HOLD TO THE PREVIOUS FORECAST WITH DRY CONDITIONS STARTING SUNDAY NIGHT. && .AVIATION... MVFR CIGS WERE MOVING BACK INTO BOTH SITES...AT KSBN IN THE WAKE OF THE FRONT WITH STRATUS DECK FORMING...AND AT KFWA ALONG AN ADVANCING FRONTAL BOUNDARY. CONTINUED WITH VCTS AT KFWA FOR A FEW HORUS BUT SHORTLY AFTER ISSUING CONVECTION BEGAN TO FIRE JUST TO SE OF AIRPORT. MAY AMEND TO REMOVE SOONER THAN 20Z BUT WILL MONITOR FOR NOW. OTHERWISE...MAIN FOCUS WILL BE LOW CLOUDS/FOG POTENTIAL OVERNIGHT AT BOTH SITES. STRATUS DECK CURRENTLY AFFECTING KSBN COULD CAUSE ISSUES WITH FOG DEVELOPMENT TONIGHT IF IT WE TO REMAIN AROUND. HOWEVER...THIS SHOULD SCOUR OUT DURING THE AFTERNOON HOURS. CIGS/VSBY TANKED RATHER RAPIDLY AT KFWA LAST NIGHT WITH DROP TO NEAR 0SM VSBY RIGHT AROUND 12Z. SIMILAR CONDITIONS ARE POSSIBLE TONIGHT AT BOTH SITES WITH EMPHASIS ON KFWA. HAVE INTRODUCED FOG AND EVENTUAL IFR/LIFR CONDITIONS AT BOTH SITES LATER TONIGHT. FOG SHOULD BURN OFF BY MID MORNING ONCE AGAIN. REMNANTS OF CONVECTION THAT IS EXPECTED TO DEVELOP TO THE NW OF THE AREA TONIGHT MAY SNEAK INTO KSBN IN THE 15 TO 18Z WINDOW. FOR NOW NO MENTION OF PRECIP. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...NONE. MI...NONE. OH...NONE. LM...NONE. && $$ SHORT TERM...FISHER LONG TERM...SKIPPER AVIATION...FISHER
AREA FORECAST DISCUSSION
NWS DES MOINES IA
345 PM CDT TUE SEP 4 2012 .SHORT TERM /TONIGHT/... PRIMARY CONCERN TONIGHT WILL BE CONVECTIVE TRENDS BUT CONFIDENCE IN THAT EVOLUTION IS DECREASING AS MOST MODELS...HIGH RES EXPLICIT AND PARAMETERIZED...ARE CURRENTLY OVERZEALOUS IN THEIR DEPICTION OF PRECIP. PRESENT SITUATION HAS 80KT JET FROM ROCKIES INTO IA ENHANCING DEEP/EFFECTIVE SHEAR. LITTLE IN THE WAY OF LARGE SCALE FORCING NOTED IMMEDIATELY UPSTREAM HOWEVER WITH RAP ANALYSIS AND WATER VAPOR IMAGERY FAIRLY BENIGN. ONLY SIGN OF LARGER SCALE UPWARD VERTICAL MOTION /UVM/ SEEMS TO BE ACROSS CENTRAL NE NEAR H85/H7 SHORT WAVE PER VISIBLE IMAGERY. OUR FORECAST AREA SEEMS PRIMED FOR DEVELOPMENT THERMODYNAMICALLY WITH UNCAPPED 2000-4000 J/KG MLCAPES. HOWEVER SPOTTY CONVERGENCE AND LITTLE TO NO UVM OVERHEAD HAVE RESULTED IN NO DEVELOPMENT AS OF YET. SMALL CELL ALONG HIGHWAY 20 DISSIPATED WHICH IS A SIGNAL THAT WE ARE NOT READY TO GO SURFACE BASED AND/OR HAVE INSUFFICIENT UPPER LEVEL SUPPORT. AT THE MOMENT FEEL THAT CONVECTIVE INITIATION IS GOING TO WAIT FOR AFOREMENTIONED NE UVM ALONG WITH INCREASED SYNOPTIC SCALE FORCING AHEAD OF MT/DAKOTAS SHORT WAVE AS IT MOVES EAST THIS EVENING. ECMWF/GFS QG FORCING INCREASES AS IT REACHES MN BY 06Z. 18Z RAP SUGGESTS WEAKLY CAPPED ELEVATED CAPES 2000 J/KG OR MORE WILL BE IN PLACE AND CERTAINLY CAPABLE OF SUPPORTING SEVERE WEATHER CONSIDERING OUR PROXIMITY TO THE JET. DCAPES SHOULD REMAIN QUITE HIGH OVERNIGHT WITH SOUNDINGS SHOWING PLENTY OF DRY AIR BELOW 3KM. THUS EXPECT NE CONVECTION TO SLOWLY DEVELOP AND MATURE AS IT REACHES IA MUCAPE AXIS WITH DAMAGING WINDS AND HAIL QUITE POSSIBLE. .LONG TERM /WEDNESDAY THROUGH TUESDAY/... FORECAST CONCERNS FOR WEDNESDAY WILL DEAL WITH A STRONG COLD FRONT PUSHING ACROSS THE FORECAST AREA DURING THE MORNING AIDED BY A POTENT SHORT WAVE SWEEPING ACROSS THE NORTHERN PLAINS INTO IA. MOST OF THE CAPE AND SHEAR ARE AHEAD OF THE BOUNDARY SO ONGOING CONVECTION FROM THE OVERNIGHT WILL AFFECT THE EASTERN HALF OR SO OF THE FORECAST AREA. BEHIND THE FRONT MUCH COOLER AND DRIER AIR WILL PUSH INTO CENTRAL IOWA DURING THE AFTERNOON SO ANY THUNDERSTORM THREAT IN THE AFTERNOON WILL BE CONFINED TO THE FAR SOUTHEAST PORTION OF CENTRAL IOWA ON EAST. BEYOND WEDNESDAY WE BEGIN OUR SLIDE IN TEMPS AS HIGH PRESSURE BUILDS IN WEDNESDAY NIGHT THROUGH LATE THURSDAY. WARM ADVECTION OCCURS THURSDAY NIGHT AHEAD OF THE NEXT SYSTEM TO AFFECT THE AREA. ON FRIDAY THETA ADVECTION INCREASES AND A SECOND SHORT WAVE ROTATES THROUGH THE NORTHERN AND CENTRAL PLAINS BRINGING AND ANOTHER FRONT WILL PUSH ACROSS IOWA BRINGING A REINFORCING SHOT OF COLD AIR. SHOWERS AND ISOLATED THUNDERSTORMS WILL OCCUR WITH THIS FOLLOWED BY SOME VERY COOL AIR. TEMPERATURES OVER THE WEEKEND WILL ACTUALLY BE BELOW NORMAL BUT IT WILL BE DRY. && .AVIATION...04/12Z VFR CONDITIONS ARE NOTED THROUGH THE PERIOD...BUT THAT IS MORE DUE TO A LACK OF CONFIDENCE IN TIMING THAN OCCURRENCE. MODELS SUGGEST CONVECTION WILL DEVELOP LATER THIS AFTERNOON OR THIS EVENING...BUT DECIDED TO JUST MENTION VFR VCSH WORDING FOR NOW RATHER THAN TRY TO TAKE A STAB AT A DIFFICULT TO PREDICT CONVECTIVE WINDOW. CHANCES FOR CONVECTION DIMINISH OVERNIGHT AND THERE MAY BE A PERIOD OF REDUCED VSBYS IN FOG...BUT AGAIN PREDICTABILITY IN THIS REGARD IS LOW DUE TO CONVECTIVE TRENDS SO IT IS OMITTED FOR NOW. FRONT WILL PASS THROUGH SITES WED MORNING ENDING PRECIP AND FOG THREAT. && .DMX WATCHES/WARNINGS/ADVISORIES...NONE. && $$ SHORT TERM/AVIATION...SMALL LONG TERM...FAB
AREA FORECAST DISCUSSION
NWS SHREVEPORT LA
1111 AM CDT TUE SEP 4 2012 .DISCUSSION... SO FAR JUST ABOUT A REPEAT PERFORMANCE OF YESTERDAY/S EFFORT WITH SIMILAR READINGS AT THIS TIME. PARTLY CLOUDY CONDITIONS ARE NOTED ON SATELLITE IMAGERY OVER DEEP EAST TEXAS WITH LITTLE IF ANY CLOUDS ELSEWHERE OVER THE FOUR STATE AREA. WATER VAPOR SHOWS THE RIDGE OVERHEAD. ALREADY MANY READINGS AT 90 DEGREES WITH A BIT LESS WIND THAN YESTERDAY SO LIKEWISE MIXING MAY DELAY INTO THE MID AFTERNOON TODAY. THE ONLY CHANGE OF NOTE IS IN THE RAP MODEL WHICH SHOWS SOME TENTHS OF QPF ALONG AND SOUTH OF I-20 OVER NORTH CENTRAL LOUISIANA. PERHAPS ATTENDANT TO THE MCV OVER AL THIS MORNING. SFC WINDS ARE COMING AROUND OVER NORTHERN MS TO THE NE AND ANY SORT OF BOUNDARY THAT MAY RESULT WOULD HAVE A CHANCE IN THE MOIST DELTA REGION FOR FURTHER INITIATION OF CONVECTION. THE CURRENT FORECAST HAS NO WORDING FOR SUCH...BUT OUT OF RESPECT FOR THIS MODELS PERFORMANCE OVER THE LAST COUPLE MONTHS HAVE INCREASED POP HERE WITH NO MENTION OF WEATHER AT THIS TIME. NEXT TEXT PRODUCTS SENT WITH ONLY SLIGHT CHANCES TO A FEW ZONES FOR SKY. ALSO WE HAVE BLENDED LAPS WITH SOME NEW NAM WIND DATA. /24/ && .AVIATION... SIMILAR SCENARIO THIS MORNING...AS VFR FLIGHT CATEGORIES WILL REMAIN COMMON ACROSS THE AREA TODAY. SKC WILL BE POPULAR IN MANY AREA METARS. HOWEVER SOME MVFR CIGS STILL LINGER IN DEEP EAST TEXAS AS SEEN BY KLFK...BUT THESE CLOUDS ARE SCATTERING OUT QUICKLY. SOUTHWEST WINDS OF 10 TO 15 KTS WILL BE OBSERVED THIS AFTERNOON...THEN DIMINISH TO 5 TO 10 KTS WITH SUNSET. NO VSBY CONCERNS ARE EXPECTED IN THE 18Z TAF PERIOD. /11/ && .PREV DISCUSSION... /ISSUED 408 AM CDT TUE SEP 4 2012/ DISCUSSION... WV IMAGERY THIS MORNING CONTINUES TO SHOW UPPER RIDGING OVER OUR REGION...WITH A TROF OVER THE SERN U.S. AND ANOTHER TROF SWEEPING OVER THE TOP OF THE RIDGE ACROSS THE NRN PLAINS. THE INFLUENCE OF THE UPPER RIDGE WILL MAKE FOR ANOTHER HOT DAY ACROSS THE REGION. HAVE GONE WITH ANOTHER HEAT ADVISORY ACROSS EXTREME NE TX...SE OK...SW AR...NW AND N CENTRAL LA WHERE EITHER 100+ TEMPS OR 72+ DEWPOINTS WILL FORCE HEAT INDICES TO EXCEED 105 DEGREES. A FEW OTHER LOCATIONS ACROSS E TX MAY BRIEFLY SEE 105 DEGREE HEAT INDICES...BUT THESE OCCURRENCES SHOULD REMAIN TOO ISOLATED TO WARRANT BEING INCLUDED IN THE HEAT ADVISORY. AT ANY RATE...THE HEAT IS EXPECTED TO CONTINUE THROUGH THU...BEFORE THE RIDGE BEGINS TO BREAK DOWN. UPPER TROF MOVING INTO THE NRN PLAINS WILL FORCE THE RIDGE SWD AND BRING SOME RAIN CHANCES TO THE NRN PORTIONS OF THE REGION THU...BEFORE ANOTHER TROF DIGS SEWD FRI AND FORCES THE RIDGE TO RETREAT WELL TO THE W. RAIN CHANCES WILL BE ON THE INCREASE FOR THE WEEKEND...AS THIS FALL-LIKE UPPER TROF/COLD FRONT MOVE ACROSS THE WRN GULF STATES. SIGNIFICANTLY COOLER AND DRIER AIR IS FCST TO FOLLOW AS SFC HIGH PRESSURE BUILDS IN BEHIND THE FRONT...WITH TEMPS EXPECTED TO DIP SEVERAL DEGREES BELOW NORMAL FOR THE EARLY PART OF NEXT WORK WEEK. /12/ AVIATION... MOSTLY VFR FLIGHT WEATHER TODAY. PATCHY CIGS BETWEEN 7 HUNDRED AND 15 HUNDRED FEET THIS MORNING ACROSS DEEP EAST TEXAS INTO NORTHCENTRAL LOUISIANA...SOUTH OF INTERSTATE 20...WILL GIVE WAY TO MOSTLY CLEAR SKIES BY 15Z. SURFACE WIND SOUTH TO SOUTHWEST 5 TO 10 KTS EARLY THIS MORNING BECOMING WEST TO SOUTHWEST 8 TO 12 KTS AFTER 16Z. /14/ && .PRELIMINARY POINT TEMPS/POPS... SHV 99 76 100 75 99 / 10 10 10 10 10 MLU 100 76 99 72 97 / 10 10 10 10 20 DEQ 103 71 103 72 99 / 10 10 10 20 20 TXK 100 76 100 75 98 / 10 10 10 10 10 ELD 98 73 99 72 98 / 10 10 10 10 20 TYR 98 77 99 75 98 / 10 10 10 10 10 GGG 98 76 100 73 99 / 10 10 10 10 10 LFK 98 74 99 73 98 / 10 10 10 10 10 && .SHV WATCHES/WARNINGS/ADVISORIES... AR...HEAT ADVISORY UNTIL 7 PM CDT THIS EVENING FOR THE FOLLOWING ZONES: ARZ050-051-059>061-070>073. LA...HEAT ADVISORY UNTIL 7 PM CDT THIS EVENING FOR THE FOLLOWING ZONES: LAZ001>006-010>014-017>022. OK...HEAT ADVISORY UNTIL 7 PM CDT THIS EVENING FOR THE FOLLOWING ZONES: OKZ077. TX...HEAT ADVISORY UNTIL 7 PM CDT THIS EVENING FOR THE FOLLOWING ZONES: TXZ096-097. && $$ 24/11
AREA FORECAST DISCUSSION
NWS MARQUETTE MI
128 PM EDT TUE SEP 4 2012 .SHORT TERM...(TODAY AND TONIGHT) ISSUED AT 438 AM EDT TUE SEP 4 2012 00Z RAOBS/LATEST WV IMAGERY AND RUC ANALYSIS SHOW FAST ZONAL FLOW OVER THE NRN TIER CONUS TO THE S OF DEEP OCCLUDED LO CENTERED OVER NRN MANITOBA. DISTURBANCE/AREA OF DEEPER MSTR RESPONSIBLE FOR SHRA/TS YDAY HAS PUSHED TO THE E AND GIVEN WAY TO WEAK HI PRES AND DRIER AIR. SOME AREAS OF DENSE FOG HAVE DVLPD OVER MAINLY THE ERN AND CNTRL CWA WITH LGT WINDS WHERE THE DRYING ALF HAS OUTRUN THE NEAR SFC DRYING. FOG APPEARS LESS PREVALENT OVER THE W WHERE DRIER LLVL AIR APRNT ON THE 00Z INL/MPX RAOBS HAS MADE GREATER INROADS. DESPITE THE PRESENCE OF THIS DRY AIR...SOME SHRA/A FEW TS ARE NOTED OVER NW MN NEAR AN INCOMING SHRTWV/SFC LO PRES TROF IN AREA WHERE NAM/GFS SHOW SOME H85 THETA E ADVECTION. SOME PATCHY MID/HI CLDS AHEAD OF THIS DISTURBANCE ARE DRIFING INTO THE WRN CWA. FARTHER TO THE NW...ANOTHER STRONGER SHRTWV IS OVER SASKATCHEWAN AND MOVING SEWD ON THE SRN FLANK OF CLOSED LO IN MANITOBA. EARLY THIS MORNING...OPTED TO ISSUE AN SPS FOR MUCH OF THE E AND CNTRL CWA TO HIGHLIGHT LOCALLY DENSE FOG. TODAY...EXPECT FOG TO BURN OFF THIS MRNG WITH ONSET OF DAYTIME HEATING. CONCERN THEN TURNS TO IMPACT OF SHRTWV NOW MOVING E THRU NRN MN. SEVERAL MODELS...ESPECIALLY THE 00Z NAM/CNDN...SHOW SOME FAIRLY SHARP DEEP LYR QVECTOR CNVGC/H3-2 DVGC/AXIS OF HIER H85-5 RH ASSOCIATED WITH DPVA/H85 THETA E ADVECTION IMPACTING THE WRN ZNS THIS AFTN INTO THE EARLY EVNG. IN FACT...RECENT SPC CONVECTIVE OUTLOOK HAS THE FAR W IN A SLIGHT RISK FOR SVR STORMS LATE THIS AFTN/EARLY EVNG. MODIFIED GFS FCST SDNG FOR IWD LATE IN THE AFTN YIELDS SBCAPE NEAR 1900 J/KG FOR SFC T/TD 84/60 UNDER STEEP MID LVL LAPSE RATES. THE NAM INDICATES 2000-2500 J/KG MUCAPE IN THIS AREA. A POSITIVE FOR SVR STORMS IS THE STEEP MID LVL LAPSE RATES/PRESENCE OF DRY AIR IN THE MID LVLS WITH SFC-10K FT DELTA THETA E 15-20C AND INVERTED V LOOK TO THE LLVL TEMP/DEWPT PROFILES THAT WOULD ENHANCE THE THREAT OF GUSTY WINDS. ON THE OTHER HAND...GENERALY DRYNESS OF THE ATMOSPHERE WL TEND TO LIMIT THE COVERAGE OF THE STORMS. ALSO DEEP LYR SHEAR IS FCST TO BE UP TO 30 KTS...A BIT MARGINAL BUT PROBABLY ENUF TO ALLOW FOR AT LEAST PULSE SVR STORMS. OTRW...EXPECT ANOTHER WARM DAY WITH H85 TEMPS IN THE 16-18C RANGE SUPPORTING HI TEMPS IN THE 80S AWAY FM LK BREEZES THAT WL TEND TO FORM OFF MAINLY LK MI WITH SSE H925 FLOW. TNGT...EXPECT BAND OF SCT SHRA/TS MOVING W-E INTO THE E HALF TO SLOWLY DIMINISH WITH LOSS OF DAYTIME HEATING/SHIFT OF SUPPORTING DEEP LYR QVECTOR CNVGC TO THE N INTO ONTARIO. WITH SOME DNVA/ NEGATIVE H85 THETA E ADVECTION/DEEP LYR QVECTOR DVGC FOLLOWING THIS BAND... EXPECT A PERIOD OF DRY WX. HOWEVER...APRCH OF SHARPER SHRTWV NOW MOVING SEWD THRU SASKATCHEWAN AND VIGOROUS DPVA/DEEP LYR QVECTOR CNVGC/SOME UPR DVGC WILL BRING BACK A THREAT OF SHRA/TS OVER THE W LATE. LIMITING FACTORS WILL BE LIMITED MSTR RETURN...SOME GUIDANCE ACTUALLY SHOWS NEGATIVE H85 THETA E ADVECTION...AND ARRIVAL OF THE DYNAMICS AT TIME OF MIN DIURNAL HEATING. .LONG TERM...(WEDNESDAY THROUGH MONDAY) ISSUED AT 438 AM EDT TUE SEP 4 2012 STARTING WITH WEDNESDAY...MOST OF THE GUIDANCE BRINGS A MODEST COLD FRONT THROUGH UPPER MI LATE WEDNESDAY MORNING INTO THE AFTERNOON. AS FOR MOISTURE AND INSTABILITY...850MB THETA E RIDGE SPRAWLS ITSELF ACROSS THE CWA TUESDAY NIGHT. PLENTY OF MOIST AIR WILL BE IN PLACE AS THE NOSE OF AN 850MB JET AIMS INTO SOUTHWESTERN UPPER MI...WITH PWATS EXPECTED TO BE 130-150 PERCENT OF NORMAL. SFC BASED CAPE DURING THE EARLY AFTERNOON IS AROUND 1000-1500 J/KG...AND MUCAPE IS UPWARDS OF 1800 J/KG. HIGHEST VALUES ARE IN THE SOUTH-SOUTH CENTRAL PORTIONS OF THE CWA. LOOKING AT FORECAST SOUNDINGS IT SEEMS WITH SHORTWAVE MOVING THROUGH DURING PEAK HEATING WE SHOULD HAVE ENOUGH GUSTO TO BREAK THE WEAK CAP THAT WILL BE IN PLACE. AS FAR AS ANY SUPPORT GOES...300MB JET STREAK SLIDES ACROSS THE CWA IN THE AFTERNOON...WITH RIGHT ENTRANCE REGION DYNAMICS IN PLAY ACROSS MAINLY THE SOUTH CENTRAL PORTION OF THE CWA. ECMWF HAS 500MB VORT MAXIMUM SLIDING INTO THE WEST HALF OF UPPER MI BY 18Z. WITH THE 300/850 MB JET STREAKS MOVING THROUGH 0-6 KM SHEAR IS AROUND 25-35 KNOTS. OVERALL THIS GIVES US A MODERATE CAPE/SHEAR ENVIRONMENT AND POTENTIAL FOR A SEVERE LINE OF STORMS...LIKELY DEVELOPING ACROSS THE SOUTHERN PORTIONS OF THE CWA WHERE LIFT AND INSTABILITY IS MAXIMIZED. THURSDAY WE DEAL WITH COOLER DRY AIR BEHIND THE FRONT/IN THE WAKE OF THE LOW PRESSURE SYSTEM NEAR JAMES BAY. DRY AIR PUNCHES IN ALOFT OVERNIGHT ON WEDNESDAY...SO IT LOOKS LIKE THURSDAY WILL BE RELATIVELY QUIET IN TERMS OF PRECIPITATION. PWATS DROP DOWN TO NEAR 70 PERCENT OF NORMAL AT TIMES AS SURFACE HIGH PRESSURE MOVING ACROSS THE MIDWEST TRIES TO RIDGE INTO UPPER MI. BY FRIDAY THE LOW BEGINS TO OCCLUDE NEAR JAMES BAY...SWINGING AN UPPER LEVEL TROUGH ACROSS UPPER MICHIGAN ONCE MORE. ECMWF GENERATES PRECIPITATION ACROSS CENTRAL AND EASTERN PRECIPITATION FOR THE DAY ON FRIDAY...SUPPORTED BY MODERATE 850-500MB QVECTOR CONVERGENCE AND LINGERING MOISTURE /PWATS AROUND 110 PERCENT OF NORMAL/. WITH NORTHWEST FLOW AND LAKE-850MB TEMP DIFFERENCES AROUND 15-18C...EXPECT A LAKE EFFECT COMPONENT TO PRECIPITATION NEAR LAKE SUPERIOR. ADDITIONALLY...STRONG ONSHORE FLOW WILL GENERATE WAVES AS HIGH AS 3 TO 5 FEET IN THE ALGER AND EASTERN MARQUETTE COUNTY SURF ZONE FRIDAY INTO SATURDAY MORNING...LEADING TO THE POSSIBILITY FOR RIP CURRENT DEVELOPMENT. WITH THE COLD FRONT PASSING WEDNESDAY AFTERNOON/EVENING TEMPERATURES WILL BE MORE FALL LIKE...WITH HIGHS IN THE 60S AND LOW 70S THROUGH THE REMAINDER OF THE PERIOD. ALONG WITH FALL LIKE TEMPERATURES...WE CAN EXPECT FALL-LIKE FEATURES. FRIDAY THERE IS AN ELEVATED POTENTIAL FOR WATERSPOUT DEVELOPMENT AS COOLER TEMPERATURES ALOFT MOVE IN OVER THE STILL WARM LAKE. FORECASTS PER THE INTERNATIONAL CENTRE FOR WATERSPOUT RESEARCH ARE STILL INDICATING THAT CONDITIONS WILL BE FAVORABLE FOR THEIR DEVELOPMENT. AS THE SFC/500MB HIGH PRESSURE RIDGE OVER THE NORTHERN PLAINS BUILDS INTO UPPER MICHIGAN FOR THE WEEKEND AND THROUGH THE FIRST PORTION OF THE WORK WEEK...EXPECT CONDITIONS TO REMAIN FAIRLY DRY. THE ONLY EXCEPTION IS THE LOW PRESSURE SYSTEM THAT DEVELOPS IN THE OHIO VALLEY FRIDAY...LINGERING OVER LOWER MI THROUGH THE EXTENDED. THIS COULD BRING SLIGHT CHANCE POPS OVER THE EASTERN U.P. FOR SATURDAY INTO MONDAY. FOR NOW WITH MODEL DIFFERENCES IN LOCATION AND TIMING OF THIS PRECIP WILL KEEP THE MODEL CONSENSUS IN FORECAST UNTIL THE FINER DETAILS CAN BE NARROWED DOWN. && .AVIATION...(FOR THE 18Z TAFS THROUGH 12Z WEDNESDAY MORNING) ISSUED AT 128 PM EDT TUE SEP 4 2012 AN APRCHG LO PRES TROF WILL BRING THE THREAT OF SHRA/SOME TS TO MAINLY IWD THIS AFTN/EVNG BEFORE THE TROF MOVES TO THE E THIS EVNG. WITH LGT WINDS/DRYING ALF IN THE WAKE OF THE TROF...MORE FOG MAY FORM OVERNGT. BUT THE APRCH OF ANOTHER LO PRES TROF SHOULD BRING MORE CLDS/-SHRA TO IWD TOWARDS DAYBREAK AND TO CMX AND SAW DURING THE MORNING WEDNESDAY. PRIOR TO THIS SAW WILL HAVE THE BEST CHANCE OF EXPERIENCING IFR CONDITIONS IN FOG BEFORE SUNRISE. && .MARINE...(FOR THE 4 AM LAKE SUPERIOR FORECAST ISSUANCE) ISSUED AT 438 AM EDT TUE SEP 4 2012 EXPECT SSW WINDS TO INCREASE UP TO 20 KTS TODAY MAINLY OVER THE E HALF IN ADVANCE OF AN APPROACHING LO PRES TROF. THESE STRONGER WINDS WILL BRING DRIER AIR OVER THE E HALF OF THE LAKE AND DISSIPATE FOG THAT DEVELOPED DURING THE NIGHT IN THE WAKE OF SHOWERS THAT FELL ON MON. ALTHOUGH WINDS WILL DIMINISH FOR A TIME WITH THE PASSAGE OF THE TROF...EXPECT W TO NW WINDS IN ITS WAKE LATE WED THRU THU TO INCREASE UP TO 20 TO 25 KTS AS COOLER AIR ARRIVES OVER THE RELATIVELY WARM LAKE WATERS AND ENHANCES MIXING. ALTHOUGH WINDS MAY DIMINISH FOR A TIME ON THU NIGHT AS ANOTHER TROF SWINGS OVER LAKE SUPERIOR...PLAN ON ANOTHER ROUND OF STRONGER NW WINDS UP TO 25 KTS ON FRI IN ITS WAKE. THE APPROACH OF HIGH PRESSURE/A WEAKENING PRES GRADIENT THIS WEEKEND WILL CAUSE WINDS TO SLOWLY DIMINISH. && .MQT WATCHES/WARNINGS/ADVISORIES... UPPER MICHIGAN... NONE. LAKE SUPERIOR... NONE. LAKE MICHIGAN... NONE. && $$ SHORT TERM...KC LONG TERM...MCD AVIATION...KC MARINE...KC
AREA FORECAST DISCUSSION
NWS GRAND RAPIDS MI
122 PM EDT TUE SEP 4 2012 .SYNOPSIS... ISSUED AT 1125 AM EDT TUE SEP 4 2012 CLOUDS WILL DECREASE THIS AFTERNOON BEHIND SHOWERS AND THUNDERSTORMS EXITING THE THE AREA. STRONG OR SEVERE THUNDERSTORMS ASSOCIATED WITH A COLD FRONT ARE EXPECTED WEDNESDAY AFTERNOON AND EVENING. BEHIND THE FRONT...SEASONABLY COOL TEMPERATURES AND SCATTERED SHOWERS WILL FINISH THE WORK WEEK AND LAST INTO THE WEEKEND. && .UPDATE... ISSUED AT 1125 AM EDT TUE SEP 4 2012 UPDATED THE TIMING OF PRECIPITATION EXITING THE AREA. WE CONTINUE TO ADVERTISE GRADUAL CLEARING THIS AFTERNOON WITH GREATLY REDUCED PRECIPITATION CHANCES. WE HAVE MODERATE CONFIDENCE ABOUT THE CLEARING AND SOMEWHAT BETTER CONFIDENCE ABOUT THE DECREASED CHANCES FOR RAIN THIS AFTERNOON. WE WILL HAVE TO WATCH FOR LINGERING CLOUDS THIS AFTERNOON... PARTICULARLY OVER OUR NW ZONES. METARS AND VISIBLE SATELLITE INDICATE A WEAK COLD FRONT SURGING SE FROM THE GREEN BAY AREA WITH SIGNIFICANT CLOUDINESS BEHIND THIS FRONT. LATEST HRRR GUIDANCE WASHES OUT THE FRONT THIS AFTERNOON WHEN A DIURNALLY FORCED LOW PRESSURE AREA FORMS ACROSS LOWER MICHIGAN. THIS WOULD HELP TO DECREASE CLOUD COVERAGE AREA-WIDE...BUT OF COURSE ALSO ASSUMES LIMITED CLOUDINESS IN THE FIRST PLACE TO HELP THE DIURNAL FORCING. CLOUD TRENDS OVER THE NEXT FEW HOURS WILL THEREFORE BE IMPORTANT. UPDATE ISSUED AT 610 AM EDT TUE SEP 4 2012 I UPDATED THE GRIDS AND ZONE TO PUT CONDITIONAL POPS FOR THE NEXT FEW HOURS AS THE BAND OR RAIN AND EMBEDDED THUNDERSTORMS ASSOCIATE WITH THE MID LEVEL TROUGH CONTINUE TO MOVE EAST ACROSS THE CWA. I ALSO SERIOUSLY INCREASED THE QPF SINCE I HAVE RECEIVED MESONET REPORTS LIKE .67 INCHES IN JENISON. THE INDIANA TRAILS GOLF COURSE JUST SOUTH OF THE CITY OF GRAND RAPIDS HAD 1.01 INCHES IN 15 MINUTES. IN ANY EVENT THIS AREA OF SHOWERS IS ASSOCIATED WITH THE 700 MB TROUGH AND THERE IS STRONG SUBSIDENCE BEHIND IT. I BELIEVE SKIES WILL CLEAR BEHIND THIS AND ADDITIONAL CONVECTION IS UNLIKELY MID TO LATER AFTERNOON OVER OUR CWA SUE TO THE SUBSIDENCE BEHIND THE SHORTWAVE. && .SHORT TERM...(TODAY THROUGH THURSDAY) ISSUED AT 320 AM EDT TUE SEP 4 2012 FORECAST CONCERNS DEAL WITH CONVECTIVE TRENDS TODAY AND WEDNESDAY. NOT MANY CHANGES WERE MADE TO THE GOING FORECAST. MODEL TRENDS THE PAST 24 HRS HAVE SLOWED THE TIMING OF THE COLD FRONT WEDNESDAY BY A FEW HOURS AND INSTEAD OF MOVING ACROSS THE CWA DURING THE AFTERNOON...THE FRONT MAY MOVE THROUGH DURING THE EVENING. DUE TO DIURNAL INSTABILITY FADE...THE SEVERE THREAT HAS EFFECTIVELY SHIFTED A BIT WWD AND THE SERN CWA HAD BEEN REMOVED FROM THE DAY2 OUTLOOK. LATEST REGIONAL RADAR SHOWS A BROKEN LINE OF SHOWERS AND ISOLATED STORMS STRETCHING FROM NE LWR TO NEAR CHICAGO. THIS PCPN IS ASSOCIATED WITH A WEAKENING FRONTAL BOUNDARY AND WILL CROSS THE CWA TODAY. MESO ANALYSIS SHOWS EFFECTIVE SHEAR NEAR 40KTS ALONG THE I-96 CORRIDOR ATTM. INSTABILITY HOWEVER IS LOW AND SO SVR STORMS ARE NOT EXPECTED. THERE IS A LOW LEVEL DEW POINT GRADIENT THAT STRETCHES ALONG I-69/96 AND WE MAY SEE A FLAREUP OF CONVECTION AS THE ONGOING PCPN INTERACTS WITH IT. SKIES WILL BECOME PT/MO SUNNY BEHIND THE CONVECTION TODAY AND TEMPS WILL ONCE AGAIN CLIMB INTO THE MID TO UPPER 80S. A STRONGER COLD FRONT WILL APPROACH WEDNESDAY LATE IN THE DAY. AS MENTIONED ABOVE TIMING APPEARS A BIT SLOWER THAN PREVIOUS MODEL RUNS. THE STRONGEST DYNAMICS APPEAR OVER NRN LWR MI. HIRES ECMWF SHOWS STRONGEST MOISTURE TRANSPORT AND GREATEST SHEAR ACROSS THE NRN CWA AND NRN LWR. ADDITIONALLY...THE LLJ IS POINTED IN THAT DIRECTION LATE IN THE DAY AND THE ACCOMPANYING SHORT WAVE IS PROGGED TO MOVE OVER NRN LWR AS WELL. AS SUCH HIGHEST POPS WERE DIRECTED NWD. PWATS INCREASE TO AROUND 1.75 INCHES LATE IN THE DAY AND SO WE COULD SEE SOME HEAVY RAIN DUMPED OUT OF THEM. WE/RE RUNNING WITH A DRY FCST THURSDAY. LATEST NAM DOES SHOW A DECENT SHORT WAVE MOVING ACROSS THE CWA THEN. HOWEVER THE GFS DOES NOT. CONFIDENCE WASN/T HIGH ENOUGH YET TO ADD POPS TO THE THURSDAY GRIDS. .LONG TERM...(THURSDAY NIGHT THROUGH MONDAY) ISSUED AT 320 AM EDT TUE SEP 4 2012 THERE ARE TWO PRIMARY CONCERNS FOR THIS PART OF THE FORECAST. THE FIRST THE CHANCE FOR RAIN WITH DEVELOPING SYSTEM OVER THE OHIO VALLEY FOR FRIDAY INTO SUNDAY. THE SECOND ISSUE IS JUST HOW CHILLY DOES IT GET THIS WEEKEND? CONSIDERABLE UNCERTAINTY REMAINS IN FORECAST FOR THE FRI THROUGH SUNDAY PART OF THE FORECAST. THE PRIMARY ISSUE IS JUST WHAT HAPPENS THE SYSTEM THAT DIGS INTO THE OHIO VALLEY FRIDAY INTO SATURDAY? FOR THREE RUNS IN A ROW THE ECMWF WAS RATHER CONSISTENT WITH THE DEVELOPING SYSTEM OVER THE SOUTHERN GREAT LAKES THEN THE 12Z RUN OF THE ECMWF DEVELOPS THE SYSTEM FARTHER SOUTH RESULTING IN THE RAIN MOSTLY MISSING US TO THE SOUTH. MEANWHILE THE GFS IS NOW TRACKING THE SYSTEM FARTHER NORTH AND WOULD BRING SOME RAIN INTO THE AREA LATER FRIDAY INTO SATURDAY BEFORE IT SINKS THE SYSTEM SOUTH OF THE AREA SATURDAY NIGHT. GIVEN THE UNCERTAINLY I LARGELY CONTINUED OUR GOING FORECAST AND CALLED GOOD. THE ONE THINK THAT IS CLEAR... WE WILL NOT BE SEEING HIGHS IN THE 80S AGAIN FRI THROUGH MONDAY AS SOUTHWEST MICHIGAN && .AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON) ISSUED AT 122 PM EDT TUE SEP 4 2012 CONDITIONS WERE GRADUALLY IMPROVING EARLY THIS AFTERNOON...BEHIND THE MORNING RAINS. THERE WAS A MIX OF VFR AND MVFR CONDITIONS AS OF 17Z...AND A TREND MORE TOWARD VFR IS EXPECTED THROUGH THE REMAINDER OF THE AFTERNOON. AREAS OF MVFR CEILINGS COULD LINGER UNTIL 20-21Z. MORE FOG DEVELOPMENT IS EXPECTED TONIGHT WITH HIGH DEWPOINTS LINGERING OVER THE REGION UNDER PARTLY CLOUDY SKIES. WILL INTRODUCE IFR VSBYS TO THE TAFS MAINLY AFTER 08Z. LOCALLY DENSE FOG WILL AGAIN BE POSSIBLE. THE FOG SHOULD LIFT AROUND 14Z WED. THUNDERSTORMS WILL BE POSSIBLE BY LATE WED MORNING INTO THE EARLY AFTERNOON OVER WESTERN AND CENTRAL LOWER. HAVE ADDED VCTS TO MKG AND GRR. THIS THREAT WILL MOVE TOWARD THE OTHER TAF SITES AFTER 18Z WED. && .MARINE... ISSUED AT 320 AM EDT TUE SEP 4 2012 WEAK PRESSURE GRADIENT WILL AGAIN RESULT IN LIGHT WINDS AND LOW WAVES TODAY. THUNDERSTORMS AND RESULTANT HIGHER WINDS/WAVES WILL REMAIN A THREAT THROUGH WEDNESDAY. && .HYDROLOGY... ISSUED AT 320 AM EDT TUE SEP 4 2012 LOCALLY HEAVY RAINFALL WILL BE POSSIBLE WITH SCT STORMS TODAY AND MORE SO LATE WEDNESDAY. WIDESPREAD FLOODING IS NOT ANTICIPATED. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...NONE. LM...NONE. && $$ UPDATE...TJT SYNOPSIS...TJT SHORT TERM...93 LONG TERM...WDM AVIATION...JK HYDROLOGY...93 MARINE...93
AREA FORECAST DISCUSSION
NWS NORTH PLATTE NE
1231 PM CDT TUE SEP 4 2012 .AVIATION... VFR IS EXPECTED MOST AREAS TODAY AND THROUGH THE OVERNIGHT. ONE EXCEPTION BEING ACROSS FAR NORTH CENTRAL NEBRASKA...GENERALLY ALONG AND EAST OF A KBBW TO KONL LINE...WHERE TSTMS ARE POSSIBLE. MODEL SOUNDINGS INDICATE DRY LOWER LEVELS...THUS HIGH BASED STORMS CAPABLE OF ERRATIC GUSTY WIND WOULD BE THE EXPECTED STORM THREAT. OTHERWISE...A FRONT IS PROGGED TO CROSS THE REGION LATER THIS EVENING...PASSING OVER THE KVTN TERMINAL AROUND 01Z...THEN OVER KLBF AFTER 05Z. A DISTINCT NORTHERLY WIND SHIFT IS ANTICIPATED ALONG THE FRONTAL PASSAGE...WITH WIND SPEEDS GUSTING AOA 20KTS POSSIBLE. && PREV DISCUSSION... /ISSUED 345 AM CDT TUE SEP 4 2012/ DISCUSSION... ONE MORE DAY OF 90S BEFORE A COOL DOWN CAN BE EXPECTED. RIDGE ACROSS THE SOUTHERN PLAINS WITH SOUTHWEST FLOW IN TRANSITION TO A MORE ZONAL FLOW AS A TROUGH PUSHES ACROSS THE NORTHERN ROCKIES AND NORTHERN PLAINS. SURFACE TROUGH ACROSS THE CWA THIS MORNING WITH VERY DRY AIR...DEW PTS IN THE 30S...WEST OF THE TROUGH...A KVTN TO KTIF TO KOGA LINE. TO THE EAST OF THE TROUGH DEW PTS IN THE 50S AND 60S AND A FEW SITES ACROSS CENTRAL NEB STARTING TO REPORT SOME FOG. COLD FRONT HEADING SOUTH ACROSS THE NORTHERN ROCKIES. TROUGH WILL REMAIN NEARLY STATIONARY THIS AFTERNOON ACROSS THE AREA WITH VERY DRY CONDITIONS AND RH PERCENTAGES NEAR OR BELOW 15 PERCENT TO THE WEST. WINDS ARE MARGINAL...AROUND 15 TO 20 MPH...FOR RFW CRITERIA...HOWEVER DUE TO DROUGHT AND LOW RH VALUES...WILL HAVE A RFW FOR MUCH OF NW NEB. AS FOR TEMPS...THE DRY AIR WILL COMBINE WITH SOME PREFRONTAL COMPRESSIONAL HEATING TO PUSH HIGHS ONCE AGAIN INTO THE 90S. LATE THIS AFTERNOON ALONG AND EAST OF THE TROUGH...WHERE BETTER LOW LEVEL MOISTURE...SOME ISOLATED THUNDERSTORMS ARE POSSIBLE WITH PEAK HEAT...SIMILAR TO YESTERDAY. BETTER SHEAR/HIGHER CAPE/AND SPC SLIGHT RISK IS EAST OF THE CWA...HOWEVER EXPECT DEVELOPMENT ALONG TO EAST OF THE TROUGH...WHICH SHOULD STILL BE OVER THE CWA...AND CANNOT RULE OUT A STRAY STORM BECOMING STRONG. ONCE THE COLD FRONT MOVES ACROSS THE AREA THIS EVENING INTO THE OVERNIGHT HOURS...THE CONVECTION WILL QUICKLY MOVE EAST. DRY AND COOL AIR WILL SPREAD ACROSS THE AREA. WED HIGHS AROUND 80 ACROSS ALL BUT THE SW...WHICH SHOULD PUSH INTO THE LOWER 80S. THESE HIGHS ARE FAIRLY CLOSE TO NORMAL FOR THIS TIME OF YEAR. HOWEVER DEW PTS IN THE 30S TO LOWER 40S WILL CONTINUE TO CREATE A HIGH DANGER HOWEVER WINDS NOT EXPECTED TO BE MUCH OVER 10 MPH. THURSDAY ANOTHER COLD FRONT WILL APPROACH FROM THE NW. AHEAD OF THE FRONT WINDS BECOME SOUTHERLY AND BRING A RETURN OF WARMER TEMPERATURES AND POSSIBLY SOME LL MOISTURE. WILL HAVE TO MONITOR HIGHS AS THE MODELS HAVE TRENDED UP TODAY...WITH THE NAM SEEING AN INCREASE BACK CLOSE TO 90. HAVE NOT JUMPED TO THIS WARM YET...HOWEVER IF WE DO WARM TO THIS...NEAR CRITICAL FIRE WEATHER CONDITIONS WILL BE POSSIBLE AS DEW PTS SLOW TO RISE. AS THE FRONT PASSES THURSDAY NIGHT INTO FRIDAY MOISTURE WILL CONTINUE TO BE A LIMITING FACTOR ON SHOWER AND THUNDERSTORM DEVELOPMENT. HAVE TRENDED DRIER AS RETURN MOISTURE LOOKS TO BE ONLY TO CURRENT LEVELS...AT BEST...ACCORDING TO LATEST GUIDANCE...WITH A GOOD POSSIBILITY THIS TREND WILL CONTINUE OVER THE NEXT FEW FORECAST UPDATES. FRIDAY INTO SATURDAY WILL BE THE COOLEST OF THE FORECAST PERIOD AS COOL HIGH PRESSURE SETTLES OVER THE HIGH PLAINS. GUIDANCE AND FORECAST HAVE HIGHS ONLY IN THE 70S...WITH LOWS IN THE 40S. BY SUNDAY THE HIGH WILL PUSH TO THE EAST WITH SOUTHERLY FLOW RETURNING AND BRINGING A SLOW WARMUP INTO THE START OF NEXT WEEK. STILL NO MOISTURE AND FORECAST REMAINS DRY. FIRE WEATHER... HOT DRY AIR WILL SURGE EAST THROUGH WESTERN AND NORTH CENTRAL NEBRASKA AHEAD OF A STRONG COLD FRONT WHICH WILL MOVE THROUGH TONIGHT. CRITICAL FIRE DANGER IS EXPECTED ALONG AND NORTH OF INTERSTATE 80 AND GENERALLY ALONG AND WEST OF HIGHWAY 83. THE 20Z HRRR AND THE 00Z GEM REGIONAL MODELS SUGGEST SIMILAR CONDITIONS WILL DEVELOP ACROSS SWRN NEB AND PERHAPS INTO AREAS EAST OF HIGHWAY 83. GIVEN THE DIFFERENCES BETWEEN HRRR AND GEM REGIONAL VERSUS THE NAM AND ECM WILL HOLD OFF ON AN EXPANSION OF THE RED FLAG WARNING FOR NOW. && .LBF WATCHES/WARNINGS/ADVISORIES...RED FLAG WARNING UNTIL 10 PM CDT /9 PM MDT/ THIS EVENING FOR NEZ204-206-208. && $$ SHORT TERM/EXTENDED...MASEK AVIATION...JACOBS
AREA FORECAST DISCUSSION
NWS OMAHA/VALLEY NE
1212 PM CDT TUE SEP 4 2012 .AVIATION...18Z TAFS FOR KOMA...KLNK AND KOFK. PRIMARY CONCERN WILL BE CHANCES FOR THUNDERSTORMS AS A FRONT LIFTS THROUGH THE REGION. BELIEVE BEST CHANCE WOULD AT 21-23Z AT KLNK...AND 23-02Z AT KOFK AND KOMA. OTHERWISE...VFR CONDITIONS EXPECTED UNTIL THEN WITH MID BASED CUMULUS CLOUDS EITHER MOVING IN OR DEVELOPING AROUND 6000-8000 FEET. SECONDARY CONCERN IS THE PLACEMENT OF A STRONG COLD FRONT SWEEPING FROM NORTHWEST TO SOUTHEAST OVERNIGHT WITH AN ABRUPT WIND SHIFT TO THE NORTH NORTHWEST AND SUBSTANTIAL INCREASE IN SPEEDS BEHIND THE FRONT WITH WINDS 15 TO 25 KNOTS. INITIAL FORECAST PUTS THIS FRONT IN THE KOFK VICINITY BY ABOUT 11Z...AND KLNK/KOMA BY ABOUT 13Z. DEWALD && .PREV DISCUSSION... /ISSUED 1032 AM CDT TUE SEP 4 2012/ DISCUSSION... MAIN CONCERN FOR LATE THIS AFTERNOON AND EVENING WILL BE CONVECTIVE POTENTIAL ALONG/NORTH OF A SURFACE TROUGH THAT EXTENDS FROM WESTERN NEBRASKA THROUGH SOUTHEAST NEBRASKA. NAM CONTINUES TO BE THE MOST AGGRESSIVE MODEL IN DEVELOPING CONVECTION BY 21-00Z ALONG AND NORTH OF I80...THEN CONTINUING THAT THROUGH THE EVENING BEFORE PUSHING OFF TO THE NORTHEAST. THIS SEEMS REASONABLE GIVE WEAK ZONAL FLOW ALOFT WITH SUBTLE ALBEIT WEAK HEIGHT FALLS NOTED ON 12Z OBJECTIVE UPPER AIR ANALYSIS. THIS IS ALSO WITHIN AN AREA WHERE THE CAP SHOULD BE THE WEAKEST GIVEN 10-11 DEGREES AT H70. INTERESTING...THE HRRR DOES NOT DEVELOP ANY CONVECTION AT ALL... AND THE RAP13 HOLDS OFF UNTIL ABOUT 23Z BETWEEN OMAHA AND SIOUX CITY. MADE MINOR TWEAKS TO THE FORECAST...PULLING POPS JUST A LITTLE BIT FURTHER SOUTH 21-23Z...OTHERWISE NO OTHER CHANGES MADE. DEWALD PREV DISCUSSION... /ISSUED 343 AM CDT TUE SEP 4 2012/ DISCUSSION... MAIN FORECAST CONCERNS ARE THUNDERSTORM CHANCES THIS AFTERNOON/EVENING AND AGAIN ON THURSDAY INTO FRIDAY. WESTERLY UPPER LEVEL FLOW CONTINUES OVERHEAD WITH SEVERAL WEAK EMBEDDED SHORTWAVES PASSING THROUGH THE FLOW. AT THE SFC...WEAK AREA OF LOW PRESSURE IS CENTERED OVER CENTRAL SOUTH DAKOTA/CENTRAL NEBRASKA WITH RICH DEWPOINTS IN THE UPPER 60S TO LOWER 70S RESIDING OVER MUCH OF EASTERN NEBRASKA AND WESTERN IOWA. THIS MAY LEAD TO PATCHY FOG FOR THE MORNING COMMUTE AND WILL CONTINUE TO KEEP AN EYE ON ANY DETERIORATING CONDITIONS THIS MORNING. AN UPPER LEVEL TROF WILL SWING THROUGH THE CANADIAN PRAIRIE PROVINCES AND NORTHERN PLAINS TODAY. AHEAD OF THIS...A STRONG COLD FRONT WILL PUSH SOUTHEAST THROUGH THE PLAINS. AHEAD OF THIS FRONT THUNDERSTORMS COULD DEVELOP LATE THIS AFTERNOON ALONG THE MOIST AXIS ACROSS NORTHEAST NEBRASKA AS AFTERNOON HEATING PEAKS. UPPER LEVEL SUPPORT WILL BE WEAK THROUGHOUT THE LATE AFTERNOON BUT IS FORECAST TO INCREASE INTO THE EVENING HOURS AHEAD OF A WEAK SHORTWAVE AHEAD OF THE UPPER TROF. A MAJORITY OF MODEL GUIDANCE SOLUTIONS DEVELOP AN AREA OF QPF OVER NORTHEAST NEBRASKA...CLOSER TO UPPER LEVEL FORCING...AROUND 21Z AND SPREAD IT SOUTHEAST WELL AHEAD OF THE SFC FRONT THRU 06Z. STEEPENING MID LEVEL LAPSE RATES ALONG WITH MODERATE INSTABILITY AND 0-6KM BULK SHEAR AROUND 40KTS COULD LEAD TO SOME SEVERE STORMS...MAINLY IN THE NORTHERN CWA. STRONG SUBSIDENCE IS FORECAST BEHIND THE FRONT SO WILL QUICKLY END POPS AFTER FROPA WHICH SHOULD BE THRU THE ENTIRE CWA BY 12-15Z WED. COOLER TEMPERATURES FOLLOW BEHIND THE BOUNDARY WITH HIGHS IN THE UPPER 70S TO LOWER 80S FOR WEDNESDAY AS HIGH PRESSURE BUILDS INTO THE CENTRAL PLAINS. RETURN FLOW SETS UP LATER IN THE DAY THURSDAY SO WL LEAVE MUCH OF THE DAY DRY WITH POPS RETURNING TO THE FORECAST THURSDAY NIGHT IN LLVL WARM AIR ADVECTION REGIME. IN ADDITION...ANOTHER UPPER LEVEL SHORTWAVE WILL BE APPROACHING THE REGION AS A COLD FRONT SLIDES EAST ACROSS THE FORECAST AREA. NOCTURNAL LOW LEVEL JET MAY SUSTAIN ACTIVITY THRU THE OVERNIGHT HOURS AS WELL AS INTO FRIDAY MORNING. A STRENGTHENING UPPER LEVEL TROF MOVING TOWARD THE GREAT LAKES REGION WILL BRING COOLER TEMPERATURES FOR THE WEEKEND BEFORE THE TROF CLOSES OFF OVER THE OHIO VALLEY REGION. A LARGE AREA OF SFC HIGH PRESSURE WILL BE IN PLACE SUNDAY INTO MONDAY. A BIT OF A WARM UP IS EXPECTED EARLY NEXT WEEK AS AN UPPER LEVEL RIDGE BUILDS INTO THE CENTRAL PLAINS. KERN && .OAX WATCHES/WARNINGS/ADVISORIES... NE...NONE. IA...NONE. && $$
AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NWS SIOUX FALLS SD
325 PM CDT TUE SEP 4 2012 .DISCUSSION.../ISSUED AT 325 PM CDT/ DIFFUSE BOUNDARY IN NORTHWEST IOWA BEGINNING TO LIFT NORTHWARD AS A WARM FRONT THIS AFTERNOON AS SURFACE LOW PRESSURE STRENGTHENS OVER THE BLACK HILLS. MIXING HAS ALLOWED DEWPOINTS TO DRAMATICALLY FALL THIS AFTERNOON ACROSS THE NORTHWESTERN TWO THIRDS OF THE CWA...WHILE DEEPER MOISTURE HAS ALLOWED DEWPOINTS TO REMAIN IN THE 60S ACROSS NORTHWEST IOWA. INSTABILITY CONTINUES TO INCREASE THIS AFTERNOON...ESPECIALLY ACROSS OUR SOUTHEASTERN HALF OF THE FORECAST AREA WHERE CAPE VALUES ARE GREATER THAN 1500 J/KG...WITH INCREASING LAPSE RATES AND STRENGTHENING WESTERLIES BRINGING SHEAR UP AROUND 40 KT. SO FAR...CAPPING IS PREVENTING CONVECTION FROM DEVELOPING...HOWEVER WITH KSUX ALREADY 95/65 EXPECT THE CAPPING TO BE SURPASSED SOON. THE HRRR AND NAM CONTINUE TO DEPICT CONVECTION MOVING NORTHEASTWARD INTO THE MISSOURI VALLEY...EXTREME SOUTHEAST SOUTH DAKOTA AND NORTHWEST IOWA LATE THIS AFTERNOON THROUGH THE EVENING. IF CONVECTION DOES MANAGE TO FIRE IN THIS AREA...STORMS COULD POTENTIALLY BECOME SEVERE WITH LARGE HAIL TO AROUND WALNUT SIZE AND WIND GUSTS TO 70 MPH. FURTHER WEST...HIGH BASED CUMULUS FIELD NOW MOVING INTO OUR WESTERN BORDER. ISOLATED HIGH BASED CONVECTION WILL BE POSSIBLE IN OUR WESTERN HALF THIS AFTERNOON AND EVENING...BUT EXPECT LITTLE TO NO SEVERE WEATHER IN THIS AREA WITH SUCH DRY LOW AND MID LEVELS. AS THE LOW BEGINS TRACKING EAST NORTHEAST ACROSS THE FORECAST AREA THIS EVENING AND OVERNIGHT...THE TRAILING COLD FRONT WILL SHIFT THE CONVECTION INTO CENTRAL AND EASTERN PORTIONS OF THE FORECAST AREA WHERE CONDITIONS ARE MORE FAVORABLE FOR PRECIPITATION. WINDS WILL LIKELY BECOME FAIRLY BREEZY FROM THE WEST NORTHWEST LATE TONIGHT. LOWS TONIGHT WILL RANGE FROM THE MID 50S FAR NORTHWEST TO THE MID 60S FAR SOUTHEAST. RELATIVELY QUIET WEATHER WITH MILDER TEMPERATURES EXPECTED FOR WEDNESDAY AS SURFACE HIGH PRESSURE SETTLES IN BEHIND THE EXITING SYSTEM. NORTH NORTHWEST WINDS WILL REMAIN A LITTLE BREEZY THROUGH THE DAY...BUT SKIES WILL BE SUNNY AND HIGHS ARE EXPECTED IN THE 70S. / HIGH PRESSURE WILL BUILD IN OVER THE AREA FOR WEDNESDAY NIGHT. THUS TRENDED LOWS TOWARDS THE COOLER SIDE OF GUIDANCE...GENERALLY UPPER 40S TO LOWER 50S. A MID LEVEL WAVE AND SOME CLOUD COVER MAY BEGIN ENTERING OUR WEST BY LATE NIGHT...THUS DID NOT GO QUITE AS COOL AS I WOULD HAVE IF COMPLETELY CLEAR SKIES WERE MORE LIKELY. MID LEVEL FORCING OVERHEAD ON THURSDAY OUT AHEAD OF OUR NEXT WAVE...ALSO SHOULD SEE DECENT ISENTROPIC LIFT. ATMOSPHERE WILL BE ON THE DRY SIDE THOUGH...THUS FOLLOWED THE NAM AND GFS IDEA OF A DRY DAY. HOWEVER SHOULD SEE AT LEAST SOME MID LEVEL CLOUD COVER...AND WITH DECENT MID LEVEL LAPSE RATES...WOULD NOT BE SURPRISED TO SEE A FEW ELEVATED SHOWERS AND THUNDERSTORMS. THINK THE ECMWF IS PROBABLY OVERDOING CONVECTION THURSDAY...BUT LOW POPS MAY NEED TO BE ADDED ON FUTURE SHIFTS IF MODELS TREND A LITTLE MOISTER IN THE MID LEVELS. WITH UNCERTAINTY ON CLOUD COVER...FOLLOWED A BLEND OF THE COOLER MOS AND THE WARMER BIAS CORRECTED NAM FOR HIGHS...GENERALLY MID 70S SOUTHWEST MINNESOTA TO LOW TO MID 80S ELSEWHERE. SURFACE LOW TO OUR WEST ON THURSDAY WILL PRODUCE BLUSTERY SOUTH SOUTHEAST WINDS WEST OF THE JAMES RIVER...WITH GUSTS AROUND 25 TO 30 MPH POSSIBLE. THE BETTER MOISTURE AND DEEP LAYER FORCING MOVES ACROSS THE CWA THURSDAY NIGHT. THUS LOOKS LIKE A GOOD CHANCE OF SEEING SOME SHOWERS IN MOST AREAS. INSTABILITY IS ON THE LOW SIDE...BUT SHOULD SEE AT LEAST A COUPLE HUNDRED J/KG OF ELEVATED CAPE. SO THINKING WE SEE AT LEAST SOME EMBEDDED THUNDER. WITH THE CLOUDS AND SHOWERS AROUND...LOWS WILL STAY A BIT WARMER THAN WEDNESDAY NIGHT...MAINLY IN THE 50S. COULD SEE SOME LINGERING SHOWERS ACROSS NORTHWEST IOWA FRIDAY MORNING...BUT THESE SHOULD EXIT THE AREA BY AFTERNOON AS THE TROUGH AXIS AND DEEPER MOISTURE PUSHES EAST. EXPECT TO SEE GRADUAL CLEARING FROM NORTH TO SOUTH DURING THE DAY. MUCH COOLER AIR WILL BE ADVECTED IN BEHIND THE FRONT FOR FRIDAY...AND THIS COMBINED WITH THE LINGERING CLOUD COVER...SHOULD HOLD HIGHS IN THE MID 60S TO LOWER 70S. AS WE HEAD INTO THE WEEKEND...OUR UPPER LEVEL LOW WILL PUSH EAST AND DIG A DEEP TROUGH INTO THE EASTERN PART OF THE COUNTRY. MEANWHILE A STRONG RIDGE WILL BUILD INTO THE ROCKIES. OUR AREA WILL REMAIN IN BETWEEN THE TWO MAKING TEMPERATURES A BIT TRICKY. WE WILL TEND TO SEE A WARMING TREND INTO EARLY NEXT WEEK...BUT HOW WARM DEPENDS ON THE STRENGTH AND POSITION OF THE ABOVE MENTIONED FEATURES. TRENDED HIGHS A BIT ABOVE CONSENSUS SUNDAY THROUGH TUESDAY CLOSER TO THE 0Z ECMWF AND HPC GUIDANCE. THIS GIVES 70S ON SATURDAY...AND UPPER 70S TO MID 80S SUNDAY THROUGH TUESDAY. THE NEW 12Z ECMWF HAS TRENDED STRONGER WITH THE RIDGE AND THUS WARMER WITH TEMPERATURES...SO WILL HAVE TO MONITOR MODEL TRENDS THIS PERIOD. LOWS FRIDAY AND SATURDAY NIGHT LOOK TO BE ON THE COOL SIDE...WITH LIGHT WINDS AND CLEAR SKIES EXPECTED. LOWERED THEM A LITTLE BELOW CONSENSUS...WITH MAINLY MID AND UPPER 40S EXPECTED. AS THE RIDGE BUILDS CLOSER...LOWS SHOULD WARM INTO THE 50S BY SUNDAY NIGHT. LOOKS DRY SATURDAY THROUGH TUESDAY. PROBABLY WILL SEE OUR NEXT COLD FRONT APPROACH SOMETIME AROUND TUESDAY...HOWEVER AT THIS TIME DOES NOT UPPER TO BE MUCH MOISTURE WITH IT. /CHENARD && .AVIATION.../FOR THE 18Z TAF ISSUANCE/ VFR CONDITIONS EXPECTED THROUGH 18Z WEDNESDAY. SCATTERED THUNDERSTORMS WILL DEVELOP AFTER 22Z IN THE 129 CORRIDOR AND EASTWARD AHEAD OF A COLD FRONT. TEMPORARY MVFR CONDITIONS IN THE THUNDERSTORMS ARE POSSIBLE AFTER 00Z. GUSTY NORTHWEST WINDS OF 10 TO 20 KNOTS WILL FOLLOW BEHIND THE FRONT OVERNIGHT AND INTO WEDNESDAY MORNING. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...NONE. MN...NONE. IA...NONE. NE...NONE. $$
AREA FORECAST DISCUSSION
NWS LA CROSSE WI
256 PM CDT TUE SEP 4 2012 .SHORT TERM...TONIGHT THROUGH WEDNESDAY NIGHT 256 PM CDT TUE SEP 4 2012 MAIN FORECAST CONCERNS ARE ON CONVECTION THROUGH WEDNESDAY MORNING AND ASSOCIATED SEVERE WEATHER POTENTIAL. CURRENTLY AS OF 20Z...WATER VAPOR LOOP AND RAP 500MB HEIGHT ANALYSIS SHOWED A POTENT SHORTWAVE TROUGH OVER SOUTHERN SASKATCHEWAN INTO EASTERN MONTANA...THEN NEAR ZONAL TO SLIGHT SOUTHWEST FLOW STREAMING EAST INTO NEW ENGLAND. WITHIN THIS FLOW...A SHORTWAVE WAS PRESENT OVER FAR WESTERN WISCONSIN...WITH SOME WEAK RIDGING RIGHT BEHIND IT OVER MINNESOTA. MOSTLY SUNNY SKIES AFTER THE FOG BURNED OFF THIS MORNING HAS ALLOWED FOR STRONG HEATING ACROSS THE AREA. WITH 12Z RAOBS HAVING 850MB TEMPS AROUND 18C...TEMPERATURES HAVE CLIMBED INTO THE MID TO UPPER 80S. DEWPOINTS REMAIN MUGGY FOR THIS TIME OF YEAR...IN THE MID 60S TO AROUND 70. THE COMBINATION OF THE TEMPERATURES AND DEWPOINTS HAS RESULTED IN MLCAPE VALUES OF 2000-3000 J/KG WITH LITTLE CIN. AT THE SURFACE...LOW PRESSURE WAS NEAR AITKIN MN WITH A DRY-LINE ARCING THROUGH NORTHWEST WI INTO SOUTHEAST MN. PLENTY OF CUMULUS GOING UP AHEAD OF THIS DRY LINE. STORMS ARE EXPECTED TO DEVELOP IN THE NEXT HOUR OR TWO OUT OF THIS CUMULUS FIELD. BIG CONCERN FOR SEVERE WEATHER IS WIND GIVEN MID-LEVEL DRY AIR PRESENT...SEEN ON BOTH WATER VAPOR AND THE 12Z MPX SOUNDING. TO THE WEST...FAIRLY QUIET ACROSS THE DAKOTAS AHEAD OF THE POTENT TROUGH. HOWEVER...ANOTHER SURFACE LOW HAS DEVELOPED AHEAD OF IT NEAR PIERRE. IN ADDITION... GOES PRECIPITABLE WATER IMAGERY SHOWS MOISTURE BEGINNING TO SURGE TO THE NORTHWEST THROUGH EASTERN NEBRASKA AHEAD OF THE SURFACE LOW/UPPER TROUGH. REST OF THE AFTERNOON...ASSUMING CONVECTION FIRES IN THE CUMULUS FIELD...WHICH IS INDICATED BY MANY MESO-MODELS...EXPECTING IT TO PROPAGATE EAST-SOUTHEAST QUICKLY DURING THE NEXT FEW HOURS. THIS IS DUE TO THE DRY MID LEVEL AIR ALLOWING FOR RAPID MOVING OUTFLOW AS WELL AS THE MAIN SHORTWAVE ACCOMPANYING IT SHIFTING INTO EASTERN WISCONSIN BY 00Z. THEREFORE...THINKING THE SEVERE THREAT AND PROBABLY MUCH OF THE PRECIPITATION WILL END BY 00Z. ONLY CAVEAT COULD BE IN FAR SOUTHWEST WI AND FAR NORTHEAST IA WHERE THERE ARE HINTS THE TAIL END OF CONVECTION COULD STALL OUT. KEPT SOME HIGHER CHANCES OF PRECIPITATION DOWN THERE JUST IN CASE. TONIGHT AND WEDNESDAY...THE POTENT SHORTWAVE OVER EASTERN MONTANA IS FORECAST TO MOVE INTO WESTERN MINNESOTA BY 12Z WEDNESDAY. AS THIS OCCURS...THE MOISTURE SEEN LIFTING UP THROUGH EASTERN NEBRASKA RIGHT NOW IS GOING TO GET ISENTROPICALLY LIFTED UP TOWARDS US. SO AFTER SOME BRIEF SHORTWAVE RIDGING AND SUBSIDENCE THIS EVENING...ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS LOOKS LIKELY. DEVELOPMENT MAY OCCUR SOUTH OF I-90 AS EARLY AS 03Z AS SUGGESTED BY THE 04.12Z NAM/GFS. BETTER POTENTIAL FOR PRECIPITATION FOR THE ENTIRE AREA IS AFTER MIDNIGHT AS THE SHORTWAVE APPROACHES AND 850MB MOISTURE TRANSPORT REALLY INCREASES. MID-LEVEL FLOW IS NICELY DIFFLUENT TOO AHEAD OF THE WAVE...AIDING IN FORCING. MCS DEVELOPMENT IS CERTAINLY POSSIBLE...AS NOTED BY THE 04.12Z ECMWF/UKMET/CANADIAN/NAM. REGARDING SEVERE CONCERN...1-6KM SHEAR VALUES VARY FROM MODEL TO MODEL. NAM IS ON THE ORDER OF 30-40 KT WHILE THE GFS IS 20-30KT. THE NAM WOULD DEFINITELY GIVE A SEVERE WEATHER CONCERN...WITH BOTH HAIL AND DAMAGING WINDS POSSIBLE. THE GFS NOT AS MUCH SO. THEREFORE... THINK THE SPCS DAY 1 OUTLOOK SLIGHT RISK IDEA IS APPROPRIATE. A BIG NOTE...THERE IS A POSSIBILITY MCS DEVELOPMENT COULD OCCUR FARTHER SOUTH SAY MORE OVER IOWA. IF IT DOES...CORFIDI VECTORS WOULD TAKE IT SOUTHEAST...LIMITING SOME OF THE CONVECTIVE ACTIVITY OVER THE FORECAST AREA. SHORTWAVE TROUGH IS PROGGED TO HEAD EAST TO CENTRAL UPPER MICHIGAN AND LAKE MICHIGAN BY 18Z...ALLOWING STRONG ISENTROPIC DESCENT TO FILTER INTO THE AREA AND CLEAR OUT THE PRECIPITATION/CLOUDS. COLD FRONTAL BOUNDARY TOO LOOKS TO BE THROUGH THE AREA AROUND 18Z. 850MB TEMPS FALL QUITE A BIT WITH THE PASSAGE OF THE TROUGH. THROUGH 12Z WEDNESDAY...THEY HOVER BETWEEN 18-20C. BY 00Z THURSDAY...THOUGH... THEY FALL TO 12-14C. THUS...ANTICIPATE A COOLER DAY TOMORROW...MORE AROUND SEASONABLE NORMALS. WEDNESDAY NIGHT AND THURSDAY...TROUGHING OVER THE FORECAST AREA AS A RESULT OF THAT POTENT SHORTWAVE MOVING THROUGH WEDNESDAY LOOKS TO BE SHORT-LIVED. THAT IS BECAUSE ANOTHER POTENT TROUGH IS PROGGED TO DROP SOUTH INTO MONTANA BY 12Z THURSDAY. THERE WILL BE ENOUGH SUBSIDENCE AND DRY AIR PERSISTING IN THE WAKE OF WEDNESDAYS SHORTWAVE SUCH THAT WEDNESDAY NIGHT STAYS DRY. AT THE SURFACE...A HIGH PRESSURE RIDGE IS PROGGED TO BUILD INTO WESTERN PORTIONS OF THE FORECAST AREA BY 12Z THURSDAY. GIVEN THE RIDGE POSITION...ENOUGH OF A NORTHWESTERLY BREEZE SHOULD OCCUR TO PREVENT ANY FOG AT LEAST IN THE MISSISSIPPI RIVER VALLEY. OTHER SMALLER VALLEYS LIKE THE WISCONSIN MAY STILL BE SUSCEPTIBLE...THOUGH. COOLER NIGHT LIKELY WITH WINDS LIGHTENING UP THROUGH THE NIGHT AS WELL AS CLEAR SKIES. SOME OF THE TYPICAL COLD SPOTS COULD FALL INTO THE MID 40S. ON THURSDAY...THAT POTENT TROUGH DIGS DOWN A LITTLE MORE THROUGH MONTANA...SETTING UP WEST-SOUTHWEST MID LEVEL FLOW OVER THE AREA. WITHIN THIS FLOW...THERE COULD BE A SHORTWAVE SKIMMING ACROSS NORTHERN WISCONSIN IN THE AFTERNOON...BUT OTHERWISE MODELS DO NOT SHOW ANY OTHER SHORTWAVES OF SIGNIFICANCE. HOWEVER..WITH THAT POTENT TROUGH DIGGING A LITTLE MORE...IT SETS UP A 310-315K ISENTROPIC LIFT/MID-LEVEL FRONTOGENESIS ZONE DOWNSTREAM ACROSS THE NORTHERN PLAINS INTO OUR REGION. LOOKS LIKE ANY PRECIPITATION RESULTING FROM THIS FORCING WILL STAY WEST OF OUR AREA...BUT AN INCREASE IN MID/HIGH CLOUDS IS LIKELY...ESPECIALLY IN THE AFTERNOON. 850MB TEMPS OF 12-14C COMBINED WITH A DECENT AMOUNT OF SUN AND THE DRY AIR SHOULD ALLOW FOR TEMPERATURES TO CLIMB INTO THE MID TO UPPER 70S. THURSDAY NIGHT AND FRIDAY...THE POTENT TROUGH OVER MONTANA IS FORECAST TO DIG SOUTHEAST DURING THIS PERIOD...BEING PUSHED BY RIDGING DROPPING DOWN INTO SOUTH CENTRAL CANADA. BY 00Z SATURDAY...A LONG WAVE TROUGH SHOULD EXTEND FROM NORTHEAST ONTARIO...INTO THE FORECAST AREA AND INTO NEBRASKA. THE MAIN ISSUE WITH THIS POTENT TROUGH COMING TOWARDS THE AREA IS WHERE DOES THE FRONTOGENESIS ZONE AHEAD OF IT LAY UP...AND THUS THE ASSOCIATED PRECIPITATION. THE 04.00Z ECMWF KEPT THE BULK OF IT ACROSS IOWA THURSDAY NIGHT AND INTO ILLINOIS AND MISSOURI ON FRIDAY...THUS FOR THE MOST PART OUR FORECAST AREA ENDS UP DRY. THE 04.12Z NAM IS FARTHER NORTH...HAVING PRECIPITATION FALL SOUTH OF INTERSTATE 94 AFTER MIDNIGHT THURSDAY NIGHT AND FRIDAY. 04.12Z GFS IS A LITTLE MORE INTERESTING. THE MODEL SUGGESTS SOME HIGHER LEVEL FRONTOGENESIS PRODUCING A BAND OF MOSTLY LIGHT RAIN...WHICH SLOWLY DROPS SOUTH THROUGH THE AREA AFTER MIDNIGHT THURSDAY NIGHT THROUGH FRIDAY. THESE BANDS SOMETIMES VERIFY AND OTHER TIMES NOT. OVERALL...THE BULK OF THE PRECIPITATION IN THE GFS FALLS TO THE SOUTH. IN ANY EVENT...ALL MODELS SUGGEST A NEED TO INCREASE PRECIPITATION CHANCES UP TO 40 FOR NOW...MAINLY SOUTH OF I-90. FURTHER REFINEMENTS WILL BE NEEDED AS WE GET CLOSER TO THIS PERIOD. WITH MORE CLOUDS AS WELL AS COOLER AIR COMING IN WITH THE UPPER TROUGH...ANTICIPATE THIS PERIOD TO BE MUCH COOLER THAN AS OF LATE. THIS WILL BE ESPECIALLY TRUE ON FRIDAY AS 850MB TEMPS FALL TO 6-9C. HIGHS ON FRIDAY MAY GET STUCK IN THE 60S...ESPECIALLY IF IT RAINS ALL DAY LIKE THE NAM. .LONG TERM...FRIDAY NIGHT THROUGH TUESDAY 256 PM CDT TUE SEP 4 2012 04.12Z ECMWF/GFS/CANADIAN AND GFS ENSEMBLES ARE A LITTLE DIFFERENT AMONGST EACH OTHER TODAY COMPARED TO YESTERDAY...MOSTLY WITH REGARDS TO HANDLING WHETHER THE UPPER TROUGH COMING THROUGH THE FORECAST AREA FRIDAY ENDS UP CLOSING OFF IN THE OHIO RIVER VALLEY. INTERESTINGLY...THE 04.12Z ECMWF/CANADIAN AND GFS HAVE NOW FLIP-FLOPPED WITH EACH OTHER...WITH THE ECMWF/CANADIAN NOW MORE PROGRESSIVE AND THE GFS CLOSING OFF. FOR OUR AREA...THOUGH...WHICH EVER SOLUTION PANS OUT REALLY DOESNT MATTER...AS BOTH SCENARIOS BUILD HIGH PRESSURE INTO THE FORECAST AREA FOR THE WEEKEND. SO MAYBE AFTER A FEW LINGERING SHOWERS IN NORTHEAST IA/SOUTHWEST WI FRIDAY NIGHT...EXPECT DECREASING CLOUDS AND DRY WEATHER FOR THE WEEKEND. CERTAINLY LOOKS COOL COMPARED TO WHAT HAS BEEN SEEN RECENTLY... THANKS TO 850MB TEMPS OF 6-8C ON SATURDAY AND 10-12C ON SUNDAY. WOULD NOT BE SURPRISED IF SOME OF THE TYPICAL COLD SPOTS END UP SEEING SOME UPPER 30S. FOR EARLY NEXT WEEK...UPPER RIDGING OVER THE WESTERN U.S. IS FORECAST TO BUILD UP INTO THE FORECAST AREA...BUT FLATTEN PRETTY QUICKLY BY TUESDAY AS A SHORTWAVE TROUGH CROSSING SOUTHERN CANADA. WILL SEE A WARM UP WITH THE RIDGING COMING IN...AT LEAST BACK TO NORMAL. DRY CONDITIONS SHOULD CONTINUE AS WELL WITH THE HIGH PRESSURE OVER THE WEEKEND BLOCKING GULF OF MEXICO MOISTURE RETURN. && .AVIATION...THROUGH 18Z WEDNESDAY 1217 PM CDT TUE SEP 4 2012 CHALLENGING FORECAST PERIOD WITH A COUPLE ROUNDS OF SHOWERS/STORMS POSSIBLY AFFECTING KRST/KLSE OVER THE NEXT 24 HOURS. FIRST WAVE ENTERING MINNESOTA AND COMBINED WITH STRONG SURFACE HEATING AND A MOIST AIRMASS...SHOWERS/STORMS ARE EXPECTED TO FIRE UP ACROSS EASTERN MINNESOTA BETWEEN 20 AND 22Z AND THEN QUICKLY TRACK EAST/SOUTHEAST THROUGH AROUND OR SHORTLY AFTER 00Z. AT THIS TIME...CONFIDENCE IS HIGHER THAT KLSE WILL BE IMPACTED AND HAVE CONTINUED PRECIP MENTION STARTING 22Z THROUGH 00Z. AT KRST...CONDITIONS SHOULD REMAIN VFR AS BULK OF STORMS ARE EXPECTED TO BE EAST OF THE AIRPORT. 850 MB MOISTURE TRANSPORT REALLY RAMPS UP ACROSS SOUTHERN MINNESOTA STARTING AFTER 06Z TONIGHT AHEAD OF A POTENT SHORTWAVE THAT WILL MOVE ACROSS THE UPPER MIDWEST. CONFIDENCE HAS INCREASED THAT STORMS WILL DEVELOP...MOST LIKELY IMPACTING KRST AFTER 06Z AND THEN KLSE AFTER 09Z. A COLD FRONT WILL THEN SWEEP ACROSS THE AREA BETWEEN 15 AND 18Z WEDNESDAY..BRINGING AN END TO PRECIP AND A SHIFT TO NORTHERLY WINDS. && .ARX WATCHES/WARNINGS/ADVISORIES... 256 PM CDT TUE SEP 4 2012 WI...NONE. MN...NONE. IA...NONE. && $$ SHORT TERM...AJ LONG TERM...AJ AVIATION...ZT