FXUS62 KCHS 222304
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
604 PM EST TUE DEC 22 2009
.SYNOPSIS...
A HIGH PRESSURE WEDGE WILL PERSIST INLAND INTO THURSDAY...THEN
WEAKEN AS AN ATLANTIC WARM FRONT SHIFTS NORTHWEST THROUGH THE
AREA. A WAVE OF LOW PRESSURE WILL LIKELY DEVELOP ALONG AN
APPROACHING COLD FRONT THURSDAY NIGHT INTO FRIDAY...THEN PUSH
NORTHEAST OF THE AREA. A TRAILING COLD FRONT WILL PASS LATE
FRIDAY...WITH COOLER HIGH PRESSURE RETURNING FOR THE WEEKEND.
&&
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
THE REGION REMAINS WITHIN A WEAK HIGH PRESSURE GRADIENT THIS
AFTERNOON THAT HAS MAINTAINED QUIET WEATHER CONDITIONS ACROSS THE
FORECAST AREA. HIGH PRESSURE TO THE NORTH WILL GRADUALLY BUILD
SOUTHWARD INTO AN INLAND WEDGE TONIGHT...WITH LIGHT WINDS BECOMING
NORTHEAST AS RESULT. EXPECT MOSTLY CLEAR SKIES AND ANOTHER COOL
NIGHT. LOW TEMPERATURES WILL RANGE FROM THE LOWER 30S FAR INLAND
TO THE MID TO UPPER 30S CLOSER TO THE COAST. COASTAL TEMPERATURES
WILL LIKELY BE TOO WARM FOR SCATTERED FROST DEVELOPMENT...AND
SINCE THESE COUNTIES ARE THE ONLY LOCATIONS STILL IN THE
FROST/FREEZE PROGRAM THIS SEASON...WILL NOT NEED TO ISSUE ANY
ADVISORIES FOR TONIGHT.
&&
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
THE INLAND WEDGE STRENGTHENS ALONG THE LEE OF THE APPALACHIANS ON
WEDNESDAY. FLAT UPPER RIDGING...NEGATIVE VORTICITY ADVECTION...AND
RELATIVELY DRY AIR AT THE LOW AND MID LEVELS SUGGESTS THAT RAIN
FREE CONDITIONS WILL AGAIN PREVAIL. SKY COVER WILL LIKELY INCREASE
LATER IN THE DAY...AS HIGH LEVEL CLOUDS BEGIN TO PUSH INTO THE
SOUTHEAST STATES AHEAD OF THE NEXT SYSTEM TO THE WEST.
EXPECT HIGH TEMPERATURES TO RANGE FROM THE UPPER 50S NORTH TO THE
LOWER 60S SOUTH WITHIN A TYPICAL WEDGE TYPE TEMPERATURE GRADIENT.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
PRETTY GOOD MODEL AGREEMENT THROUGH WED NIGHT...THEN FORECAST
CONFIDENCE LOWERS THU THROUGH FRI NIGHT REGARDING THE TIMING OF A
COLD FRONTAL PASSAGE.
A HIGH PRESSURE WEDGE WILL REMAIN IN PLACE WEDNESDAY NIGHT AS A
TROUGH OF LOW PRESSURE BEGINS TO TAKE SHAPE OFF THE COAST. EXPECT
THE ONLY POSSIBLE RAIN TO REMAIN OFF THE COAST THROUGH THE NIGHT.
LOWS WILL RANGE FROM THE UPPER 30S ACROSS THE INTERIOR TO LOWER/MID
40S ALONG THE SC COAST AND LOWER/MID 50S ALONG THE GA COAST.
MODELS BEGIN TO DIVERGE THU AS THE GFS/ECMWF/CANADIAN WANT TO PUSH
THE TROUGH OF LOW PRESSURE/COASTAL WARM FRONT INLAND THROUGH THE
AREA LATE THURSDAY/THURSDAY NIGHT. HOWEVER...THE NAM12 AND SREF SHOW
A SLOWER PROGRESSION OF THE WARM FRONT...NOT UNTIL LATE
FRIDAY/FRIDAY NIGHT. PREFER THE SLOWER PROGRESSION BASED ON
CLIMATOLOGY...ALTHOUGH DID NOT MAKE MUCH CHANGE TO THE FORECAST
BASED ON THE UNCERTAINTY.
CONTINUED TO LEAVE THUNDER OUT OF THE FORECAST OVER LAND AREAS FOR
THIS EVENT BUT WE MAY HAVE TO ADD IT IN AT SOME POINT AS EARLY AS
THURSDAY NIGHT BUT MOST LIKELY FRIDAY.
HIGH PRESSURE WILL THEN RETURN FRIDAY NIGHT INTO SATURDAY. WE MAY
HAVE TO END UP ADDING SOME RAIN CHANCES FRIDAY NIGHT IF THE FRONTAL
PASSAGE HOLDS OFF UNTIL LATE FRIDAY.
TEMPERATURES SHOULD REMAIN AT OR BELOW NORMAL THROUGH WED NIGHT
BEFORE RETURNING TO AT OR ABOVE NORMAL LEVELS THURSDAY THROUGH
FRIDAY NIGHT...THEN BACK TO NEAR OR BELOW NORMAL SATURDAY THROUGH
TUESDAY. FREEZING TEMPERATURES ARE POSSIBLE BEGINNING SATURDAY NIGHT
WELL INLAND...BECOMING MORE WIDESPREAD SUNDAY NIGHT AND MONDAY
NIGHT...ALTHOUGH PROBABLY NOT ENOUGH TO END THE GROWING SEASON
ACROSS THE ENTIRE FORECAST AREA.
&&
.AVIATION /23Z TUESDAY THROUGH SUNDAY/...
VFR CONDITIONS WILL PREVAIL FOR THE NEXT 24 HOURS. COULD SEE SOME
VERY SHALLOW GROUND FOG DEVELOP 06Z-12Z AT BOTH TERMINALS...BUT
DO NOT EXPECT ANY REDUCTIONS IN VSBYS.
EXTENDED AVIATION OUTLOOK...VFR WEATHER SHOULD PREVAIL INTO THU.
WIDESPREAD MVFR/IFR CONDITIONS ARE LIKELY TO BEGIN LATE THU NIGHT
DUE TO LOW CLOUDS/RAIN AND THEN PERSIST THROUGH FRI...AND POSSIBLY
FRI NIGHT...DEPENDING ON HOW QUICK A COLD FRONT PUSHES THROUGH THE
AREA. VFR WX SHOULD THEN RETURN BEHIND THE FRONT. THERE IS ALSO A
POTENTIAL FOR LOW LEVEL WIND SHEAR LATE THIS WEEK IN ASSOCIATION
WITH THE COLD FRONT.
&&
.MARINE...
LIGHT AND VARIABLE WINDS ARE CURRENTLY BEING REPORTED AT COASTAL
OBSERVATIONS THIS AFTERNOON. HIGH PRESSURE WILL CONTINUE TO BUILD
INLAND AND REINFORCE A MORE NORTHEAST SURFACE FLOW ACROSS THE
WATERS. THE PRESSURE GRADIENT WILL GRADUALLY TIGHTEN UNDER THE
BUILDING INLAND WEDGE...ALLOWING WIND SPEEDS TO STEADILY INCREASE
TO AROUND 15 KT LATE WEDNESDAY.
WEDNESDAY NIGHT THROUGH SUNDAY...A HIGH PRES WEDGE WILL BE IN PLACE
WED NIGHT INTO AT LEAST THU. A COASTAL WARM FRONT WILL ATTEMPT TO
PUSH NW INTO AT LEAST PARTS OF THE MARINE AREA THURSDAY BUT THE HIGH
PRESSURE WEDGE WILL LIKELY HOLD OFF THE FRONTAL PASSAGE UNTIL THU
NIGHT OR EVEN EARLY FRI. WEAK LOW PRESSURE MAY FORM ALONG THE FRONT
OVER OR NEAR THE LOCAL WATERS THURSDAY NIGHT OR FRIDAY...AND WILL
MOVE NE...ALLOWING FOR A TRAILING COLD FRONT TO CLEAR THE WATERS
LATE FRIDAY AND FRIDAY NIGHT. THIS IS FOLLOWED BY HIGH PRESSURE OVER
THE WEEKEND.
WE LOOK FOR A STEADY INCREASE IN NE WINDS THROUGH WEDNESDAY
NIGHT...AS A TIGHTER PRESSURE GRADIENT BEGINS TO FORM WITH THE
BUILDING WEDGE. WITH THE FAVORABLE NE FETCH WE COULD BE LOOKING AT
MARGINAL SCA CONDITIONS FOR SOME 6 FOOT SEAS ACROSS THE OUTER GA
WATERS BY 12Z THURSDAY. HOWEVER...A GREATER PROBABILITY OF SCA/S
FOR ALL WATERS EXISTS THURSDAY AND THURSDAY NIGHT. THIS WILL BE THE
RESULT OF A PINCHED PRESSURE GRADIENT BETWEEN THE INLAND WEDGE AND
THE COASTAL WARM FRONT...AS WINDS AND SEAS CONTINUE TO BUILD. WITH
THE FAVORABLE ONSHORE FETCH...SOME DOUBLE DIGIT SEAS LOOK
PLAUSIBLE...ESPECIALLY ON THE OUTER GA WATERS LATE THU INTO FRI.
ON FRIDAY THERE MAY BE TEMPORARY DECREASE IN WINDS AS THE PRESSURE
GRADIENT RELAXES...BEFORE WINDS INCREASE AGAIN WITH THE COLD AIR
ADVECTION IN WAKE OF THE NEXT COLD FRONT. SEAS WILL REMAIN ELEVATED
AHEAD OF THE COLD FRONT FRIDAY...THEN BEGIN TO DECREASE AS OFFSHORE
FETCH SETS IN. EVEN IF SOME DECREASE IN WINDS DOES DEVELOP...SCA/S
STILL SEEM LIKELY DURING THIS TIME.
MARGINAL SCA/S ARE STILL POSSIBLE ACROSS PARTS OF THE MARINE AREA
SATURDAY WITH FLUCTUATIONS IN COLD AIR ADVECTION AND STILL A MODEST
PRESSURE GRADIENT TO PERSIST. HOWEVER...CONDITIONS LOOK TO BE BELOW
ADVISORY THRESHOLDS SATURDAY NIGHT AND SUNDAY.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...NONE.
&&
$$
