FXUS64 KBMX 081626
AFDBMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
1026 AM CST TUE DEC 8 2009
.UPDATE...MORNING UPDATE.
CONVECTION HAS BEGUN UPSTREAM...OVER WEST CENTRAL MISSISSIPPI AND
IS MOVING RAPIDLY TOWARD CENTRAL ALABAMA...WITH WIDESPREAD SHOWERS
SHIFTING OUT OF SOUTHWESTERN ALABAMA. DEWPOINTS HAVE RISEN 5 TO 10
DEGREES ACROSS CENTRAL ALABAMA SINCE 12Z HAVING CLIMBED INTO THE
MIDDLE 50S IN SOUTHERN AND SOUTHWESTERN PORTIONS OF CENTRAL ALABAMA.
THIS MOISTURE RETURN IS THE KEY TO THE POTENTIAL OF SEVERE WEATHER
THIS EVENING AND OVERNIGHT. GUIDANCE CONTINUES TO BRING IMPRESSIVE
COLD SEASON/NIGHTTIME THERMODYNAMIC INSTABILITY TO THE AREA
OVERNIGHT WITH LI'S IN THE -1 TO -2 RANGE AND CAPES IN EXCESS OF
500 J/KG. BASED ON WHAT WE HAVE SEEN SO FAR TODAY...FEEL LIKE
DEWPOINTS IN THE 62 TO 67 DEGREE RANGE WILL MAKE IT INTO AT LEAST
A POTION OF CENTRAL ALABAMA OVERNIGHT JUST AHEAD OF THE COLD
FRONT. SEVERE POTENTIAL WILL INCREASE PROGRESSIVELY SOUTHWARD OF A
LINE FROM TUSCALOOSA TO CLANTON TO ROANOKE. DYNAMICS ALOFT ARE
EQUALLY IF NOT MORE IMPRESSIVE. ONE FLY IN THE SEVERE POTENTIAL
OINTMENT IS MORE UNIDIRECTIONAL SHEAR EXPECTED BY MIDNIGHT AS
WINDS SHIFT MORE SOUTHWESTERLY. NEVERTHELESS...ANY WATCHES WILL MOST
LIKELY BE TORNADO WATCHES.
12/SIRMON
&&
.SHORT TERM...TODAY THROUGH WEDNESDAY.
ACTIVE WEATHER PERIOD IN STORE WITH SEVERAL HAZARDS POSSIBLE. THE
NAM IS STILL JUST A TAD SLOWER BUT IT SEEMS TO SPEED THINGS UP TOWARD
THE END OF THE EVENT. BUT THE REST OF THE 00Z GUIDANCE INCLUDING THE
ECMWF/GFS/SREF ARE ALL IN PRETTY GOOD AGREEMENT. STRONG SHORT WAVE
TROUGH NEAR THE FOUR CORNERS REGION QUICKLY MIGRATES INTO THE OHIO
VALLEY/GREAT LAKES TONIGHT AND BECOMES NEGATIVELY TILTED NORTH OF THE
AREA. SURFACE CYCLONE DEEPENS RAPIDLY AS IT MOVES FROM OKLAHOMA
TOWARDS MICHIGAN. SIGNIFICANT 500 MB HEIGHT FALLS STAY NORTH OF THE
AREA BUT WE STILL RECEIVE A 5 TO 9 DAM DROP TONIGHT. SURFACE
PRESSURES DROP SOME 5 TO 10 MB IN A 6 HOUR PERIOD BEGINNING THIS
AFTERNOON AND LASTING INTO TONIGHT. IT APPEARS THAT THE MOST
INTENSE DEEPENING OF THE LOW WILL OCCUR OVERNIGHT NORTH OF THE
REGION. BOUNDARY THAT IS PROGGED TO MOVE THROUGH OVERNIGHT DOES NOT
HAVE A GREAT DEAL OF THICKNESS PACKING AND LOOKS MORE LIKE A DRY
LINE...SOMETIMES ENHANCING THUNDERSTORM ACTIVITY ALONG IT.
STRONG JET MAXIMUM (100KT +) APPROACHES WESTERN ALABAMA OVERNIGHT AS
MODELS INDICATE A BIT MORE DIVERGENCE THAN PREVIOUS RUNS...ALTHOUGH
WE ARE NOT ORIENTED IN THE PREFERRED QUADRANT. MID LEVEL WINDS
INCREASE TO 50-70KTS LATE THIS AFTERNOON. LOW LEVEL JET DEVELOPING
AS WE SPEAK SOUTHWEST OF THE AREA WITH WINDS INCREASING ALL DAY.
MAX LOW LEVEL JET MOVES IN AROUND SUNSET.
THE MAIN CONCERN HERE IS THE TIMING OF THE WARM FRONT MOVING INTO
CENTRAL ALABAMA AND HOW FAR NORTH IT ACTUALLY GOES. THIS WILL PROVIDE
THE INSTABILITY AND MOISTURE FOR SURFACE BASED THUNDERSTORMS AND
INCREASE THREAT OF SEVERE WEATHER. WILL GO WITH THE IDEA THAT SURFACE
STABLE LAYER WILL HANG ON MUCH OF THE DAY...BUT RELATIVELY WARM RAIN
AND AN INCREASE IN SOUTHERLY WINDS ALOFT WILL EVENTUALLY SCOUR OUT
THE STABLE LAYER AND EXPECT A RATHER QUICK SURGE OF THE WARM FRONT
AROUND SUNSET. FAR NORTHERN AND EASTERN AREAS WILL BE THE LAST
AREAS TO INCREASE THE MOISTURE.
SHORT TERM MODEL CONSENSUS CONTINUES TO ADVERTISE PLENTY OF SURFACE
BASED INSTABILITY FOR WINTER TIME SEVERE CONVECTION. THEREFORE...
WILL GO WITH THE FOLLOWING SCENARIO. SOUTHERLY WINDS INCREASE JUST
ABOVE THE SURFACE THIS AFTERNOON AND WILL ADD MENTION OF ELEVATED
THUNDER AREA-WIDE...NO SEVERE. THE WARM FRONT SURGES NORTHWARD AROUND
SUNSET WITH A CHANCE OF ISOLATED SEVERE ALONG AND SOUTH OF THE WARM
FRONT INTO THE WARM SECTOR. THE MAIN FORCING OCCURS IN THE VICINITY
OF THE DRY LINE FRONT AND COINCIDING WITH THE LARGE SCALE PRESSURE
DROPS. THIS FORCING ENTERS NORTHWESTERN SECTIONS JUST AFTER SUNSET
AROUND 8 PM...MOVES TO NEAR THE INTERSTATE 20 CORRIDOR AROUND
MIDNIGHT...AND EXITS SOUTHEASTERN AREAS AROUND SUNRISE. LAPSE RATES
ARE A BIT BETTER ON THE 00Z RUNS AND CAPES ARE ALSO A TAD HIGHER
(300-800 OR SO) AND WILL RE-INTRODUCE MENTION OF SOME HAIL. THERE
WILL BE TREMENDOUS SHEAR AND SRH AROUND 300. MODEL HODOGRAPHS START
OFF CURVED AND TREND TOWARD STRAIGHT WITH THE DRY LINE. TORNADOES AND
DAMAGING WINDS REMAIN AS THREATS OVERNIGHT. MUCH LESSER CONFIDENCE ON
THE PLACEMENT OF ANY HEAVY RAINFALL. PRECIP WATER VALUES ARE A FEW
STANDARD DEVIATIONS ABOVE NORMAL AND SOME TRAINING THUNDERSTORMS MAY
OCCUR...BUT OVERALL A FAST MOVING SYSTEM.
SURFACE WINDS WILL BE GUSTY AND A LAKE WIND ADVISORY HAS BEEN ISSUED
AREA-WIDE FROM 18Z TODAY THROUGH 18Z WEDNESDAY. SUSTAINED WINDS OF
10 TO 20 MPH ARE EXPECTED WITH WIND GUSTS OF 25 MPH POSSIBLE. THIS
MAY NEED TO BE UPGRADED AS A FEW HIGHER GUSTS MAY MATERIALIZE.
.LONG TERM...THURSDAY THROUGH MONDAY.
ONCE THIS FIRST SYSTEM GETS OUT OF THE AREA ON WEDNESDAY...CLEARING
SKIES AND MUCH COOLER TEMPERATURES ARE IN STORE FOR THURSDAY THROUGH
FRIDAY MORNING. WILL LIKELY SEE 20S AREA WIDE AGAIN FRIDAY MORNING.
ATTENTION NOW TURNS TO THE NEXT SYSTEM THAT WILL BE MOVING INTO THE
AREA ON FRIDAY AFTERNOON. THIS SYSTEM WILL BE A GULF LOW THAT WILL
DEVELOP. CONTINUE TO FEEL AS THOUGH THIS LOW WILL SLIDE NORTH INLAND
TOWARD CENTRAL ALABAMA. THIS SOLUTION IS SUPPORTED BY THE EUROPEAN
AND OVERALL GFS ENSEMBLES. THE GFS ITSELF IS MUCH FURTHER NORTH THAN
YESTERDAYS RUN...SO FEEL COMFORTABLE ABOUT THE COLD AIR REMAINING TO
THE NORTH. IN FACT WILL START THE MENTION OF RAIN AFTER NOON ON
FRIDAY. THIS IS HEDGING TOWARD THE EUROPEAN WHICH IS A GOOD 12 HOURS
SLOWER ON THE START TIME.
OVERALL THE SYSTEM ON FRIDAY INTO SATURDAY IS TRENDED TOWARD THE
EUROPEAN...THUS TEMPERATURES ARE A TOUCH HIGHER THAN GFS MOS THROUGH
THE WEEKEND. POPS ARE ALSO TRENDED THAT WAY AS WELL. WILL KEEP A
SLIGHT CHANCE OF RAIN THROUGH SUNDAY AFTERNOON WITH THIS SLOWER
SOLUTION.
ANOTHER ROUND OF SHOWERS MOVE IN MONDAY AS THE SOUTHERN STREAM
REMAINS ACTIVE OVER THE AREA.
16
&&
.AVIATION...12Z TAF DISCUSSION.
AS PREVIOUSLY MENTIONED...THE LOWER CLOUDS ARE BEGINNING TO SET IN
AHEAD OF THE WARM FRONT. GENERAL TREND WILL CONTINUE TO BE FOR
LOWERING CLOUD DECK THROUGH THE MORNING ACROSS ALL OF CENTRAL
ALABAMA WITH IFR CIGS DEVELOPING BY 14 TO 15Z.
RAIN WILL SPREAD FROM WEST TO EAST ACROSS AREA WITH WIDESPREAD VSBYS
3-5 MILES DEVELOPING BETWEEN 13Z AND 15Z. ONCE LOW CLOUDS AND RAIN
SET IN...THERE WILL LIKELY BE NO IMPROVEMENT IN FLIGHT CATEGORY
THROUGHOUT THE DAY. IN FACT COULD SEE EVEN LOWERED WITH PERIODS OF
LIFR DURING THE AFTERNOON. MODELS ARE NOW HINTING THAT THE WARM
FRONT WILL NOT LIFT THROUGH THE TAF SITES UNTIL AFTER 00Z.
CONFIDENCE REMAINS LOW BUT WENT MORE WITH THE PESSIMISTIC FORECAST
AS THE COLD AIR WEDGE WILL KEEP THE WARM FRONT IN CHECK UNTIL THIS
EVENING. HEAVIER SHOWERS AND STORMS WILL BEGIN TO AFFECT NORTHERN
TAF SITES BY 00 TO 03Z...AND INCLUDED IN TAFS THROUGH 9Z. COLD FRONT
WILL MOVE THROUGH LATER ON WEDNESDAY...BUT THE THUNDERSTORM THREAT
MAY BE ENDING CLOSER TO 12Z WEDNESDAY.
SURFACE WINDS WILL GRADUALLY VEER FROM FROM EAST TO SOUTHEAST TO
SOUTH...AND INCREASE IN SPEED AS DEEP LOW PRESSURE AREA PASSES
NORTHWEST OF ALABAMA TUESDAY NIGHT.
16
&&
.BMX WATCHES/WARNINGS/ADVISORIES...
LAKE WIND ADVISORY IN EFFECT FROM NOON TODAY THROUGH NOON
WEDNESDAY FOR ALL OF CENTRAL ALABAMA.
&&
$$
12/75/16
