FXUS62 KCHS 021654
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1154 AM EST WED DEC 2 2009

.SYNOPSIS...
A STRONG STORM SYSTEM DEVELOPING OVER THE NORTHERN GULF COAST
REGION EARLY THIS MORNING WILL TRACK NE ALONG THE APPALACHIANS
THROUGH THIS EVENING. A COLD FRONT WILL SWING THROUGH THE AREA 
LATE TONIGHT. HIGH PRES WILL BUILD OVER THE AREA THU INTO EARLY
FRI. LOW PRES OFF THE COAST WILL MOVE NE DURING THE FIRST PART OF
THE WEEKEND...THEN HIGH PRES WILL REBUILD LATE IN THE WEEKEND INTO
EARLY NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
CURRENTLY AT THE SURFACE...A BROAD AREA OF LOW PRESSURE IS
CENTERED OVER NORTHERN MISSISSIPPI AND ALABAMA...WITH A WARM
EXTENDING INTO CENTRAL GEORGIA THEN BENDING BACK TO THE NORTHEAST
THROUGH SOUTHERN PORTIONS OF THE FORECAST AREA AND UP ALONG THE
SOUTH CAROLINA COAST. MEANWHILE...THE CONTINUES TO HOLD STRONG
OVER THE MIDLANDS AND NORTHERN/WESTERN PORTIONS OF THE FORECAST
AREA. RADAR IMAGERY SHOWS CONVECTION INCREASING WEST OF THE AREA
WHICH IS BEGINNING TO FEEL THE INFLUENCE OF STRONG DYNAMIC FORCING
ALOFT. MAIN NEAR TERM CONCERNS REVOLVE AROUND POP TRENDS AND MORE
IMPORTANTLY SEVERE WEATHER POTENTIAL.

THIS AFTERNOON...
THE STRONG STORM SYSTEM WEST OF THE REGION WILL CONTINUE TO
INTENSIFY AS IT LIFTS NORTHWARD INTO THE SOUTHERN OHIO VALLEY
REGION. AS THIS HAPPENS...THE WARM FRONT WILL ACCELERATE NORTHWARD
THROUGH THE FORECAST AREA BY MID AFTERNOON...WHILE AT THE SAME
TIME WE BEGIN TO FEEL THE INFLUENCE OF STRONG DYNAMIC FORCING FOR
ASCENT. THE AREA WILL COME UNDER THE INFLUENCE OF ENTRANCE REGION
FORCING FROM A 120+ KNOT H25 JET...STRONG MID-LEVEL QG FORCING AS
THE UPPER TROUGH TAKES ON A NEGATIVE TILT...AND MID-LEVEL LAPSE
RATES WILL STEEPEN TO AROUND 6.5 C/KM. THE DYNAMIC FORCING IS
CERTAINLY NOT IN QUESTION...BUT THE AMOUNT OF SURFACE BASED
INSTABILITY THAT CAN BE REALIZED IS NOT AS CERTAIN. LATEST VISIBLE
SATELLITE IMAGES SHOW SOME BREAKS IN THE OVERCAST DEVELOPING
ACROSS NORTHERN FLORIDA AND SOUTHERN GEORGIA...WITH TEMPERATURES
RESPONDING...BY CLIMBING INTO THE MIDDLE 70S. IN FACT TEMPERATURES
ARE APPROACHING 70 DEGREES BEFORE NOON ACROSS SOUTHERN PORTIONS OF
THE FORECAST AREA ALONG THE ALTAMAHA. THAT SAID...WITH THE WARM
FRONT CONTINUING TO ACCELERATE NORTHWARD THROUGH THE FORECAST
AREA...EXPECT SURFACE BASED INSTABILITY TO DEVELOP BY MID
AFTERNOON ACROSS THE ENTIRE FORECAST AREA. WITH PLENTY OF LOW
LEVEL HELICITY IN PLACE ALONG WITH STRENGTHENING WIND FIELDS
ALOFT...THE POTENTIAL FOR SEVERE WEATHER STILL LOOKS ON TRACK
GIVEN THE HIGH SHEAR/LOW CAPE ENVIRONMENT WHICH IS ANTICIPATED.
THEREFORE...WILL CONTINUE TO MENTION THE STRONG DAMAGING WINDS AND
TORNADOES IN FORECAST PRODUCTS. UPDATE WILL BE OUT SHORTLY.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/...
THE FIRST HALF OF THIS EVENING PRIOR TO MIDNIGHT IS THE PERIOD
WHERE WE ARE MOST IMPRESSED WITH THE POTENTIAL FOR SEVERE
TSTMS AND POSSIBLE TORNADOES...ESPECIALLY ALONG TO THE E OF 
I-95 IN SOUTH CAROLINA AND SE GEORGIA. MODELS SHOW A WEDGE OF SURFACE-
BASED CAPES NEAR OR ABOVE 1000 J/KG SURGING N OFF THE ATLC AFTER
DARK TONIGHT AND THIS REGION IS EXPECTED TO MINGLE WITH A
DEVELOPING QUASI-LINEAR LINE OF BUILDING CONVECTION THAT SHOULD BE
RAPIDLY ACCELERATING E AHEAD OF A POWERFUL 130 KT UPPER JET
PUNCHING NE THROUGH N GEORGIA TO THE UPSTATE CAROLINAS THIS
EVENING. WE LIKE THE NAM FORECAST CONVECTION MODE DEPICTION BUT
THINK IT MAY BE A HOUR OR TWO SLOW BY 06Z. WE WILL BE WATCHING FOR
A POTENTIAL FOR WIDESPREAD DAMAGING WINDS ALONG THE COAST AND THE
POSSIBILITY OF ISOLATED TORNADOES AHEAD OF THE STRONG DRY SLOT
PUNCHING THROUGH THE AREA THIS EVENING. IF TIMING AND LOW LEVEL
INSTABILITY PAN OUT JUST RIGHT...THERE COULD BE A SWATH OF
WIDESPREAD WIND DAMAGE AND A STRONG TORNADO RISK. WE HAVE
CONTINUED TO MENTION SEVERE WEATHER IN OUR PRODUCTS WITH THIS
RELEASE. THE COLD FRONT WILL PASS OFF THE COAST LATE ENDING THE
RISK FOR RAINFALL AND SEVERE WEATHER...TEMPS AND DEW POINTS
FALLING AFTER MIDNIGHT MOST AREAS.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
IN THE WAKE OF THE COLD FRONTAL PASSAGE...MID AND UPPER LEVEL
MOISTURE WILL SHIFT NORTHEASTWARD AWAY FROM THE AREA AS SUBSIDENCE
OVERSPREADS THE AREA ON THU AND THU NIGHT. HOWEVER...WITH THE MAIN
UPPER LEVEL TROF EXPECTED TO REMAIN TO THE WEST...SOUTHWESTERLY
FLOW ALOFT IS EXPECTED TO KEEP THE POST FRONTAL COLD ADVECTION TO
A MINIMUM SO TEMPERATURES SHOULD REMAIN NEAR OR SLIGHTLY ABOVE
NORMAL VALUES. A SIGNIFICANT UPPER LEVEL SHORT WAVE IS EXPECTED TO
ROUND THE BASE OF THE CENTRAL UNITED STATES UPPER TROF TOWARDS THE
END OF THE WEEK AND THEN LIFT OUT NEGATIVELY TILTED ACROSS THE
AREA FRIDAY NIGHT AND SATURDAY. THE ECMWF AND GFS HAVE TRENDED 
FURTHER W WITH THE MOISTURE/QPF AND WE HAVE TRENDED HIGHER WITH POPS
ON SAT. WE ALSO TRENDED SLIGHTLY LOWER WITH HIGH TEMPS AND HIGHER WITH
LOW POPS OVER THE WEEKEND WITH POTENTIAL FOR SOME TRAPPED LOW
CLOUDS UNDER A DEVELOPING SUBSIDENCE INVERSION. HIGH PRES EARLY
NEXT WEEK...BUT IT MAY BE DIFFICULT TO SHAKE SOME COASTAL CLOUDS
IF A WEAK SURFACE TROF SETS UP OFF THE COAST.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
STRONG WARM AIR ADVECTION AND INCREASING LOW LEVEL CONVERGENCE
ENHANCING RAINFALL THIS MORNING AND WE HAVE SEEN AN INCREASE IN
COVERAGE AND INTENSITY OVERNIGHT WITH MVFR/IFR CIGS/VSBYS THROUGH
THE COASTAL CORRIDOR. LLWS IS IMPRESSIVE THIS MORNING WITH
LIGHT/VRBL SURFACE WINDS AT KSAV AND LIGHT N WINDS AT KCHS...
TOPPED BY INCREASING SE FLOW 25-40 KT ABOVE 1 KFT. WE THINK LLWS
WILL CONTINUE TO BE A PROBLEM UNTIL RAINS SUBSIDE LATER THIS
MORNING.

THERE WILL LIKELY BE A BREAK FROM THE RAINS FOR A WHILE DURING
PART OF THE AFTERNOON...ESPECIALLY AT KSAV. THERE IS SOME QUESTION
TO HOW LONG MORNING RAINS STICK AROUND AT KCHS AS ATLC MOISTURE
INFLUX LOOKS TO STAY QUITE STRONG THROUGH 18Z.

A POTENTIALLY SEVERE SQUALL LINE OR BROKEN LINE OF SHOWERS/TSTMS
WILL ACCOMPANY THE ONSET OF THE STRONGEST DYNAMICS THROUGH THE
REGION FROM LATE AFTERNOON THROUGH MID EVENING. WE HAVE USED
A BLENDED TIMING FROM OUR FIRST LOOK AT THE 00Z MODELS FOR OUR
TIMING ESTIMATION. ANYTIME AFTER MID AFTERNOON AT KSAV UNTIL MID
EVENING AND A COUPLE HOURS LATER AT KCHS. SEVERE CONVECTIVE
TURBULENCE APPEARS TO BE A LIKELIHOOD DURING THIS TIME.
AFTER 06Z/03...CONDITIONS SHOULD BECOME VFR AS THE CONVECTION
SHIFTS WELL OFFSHORE. THERE STILL MAY EITHER SOME SURFACE WIND
GUSTS OVERNIGHT OR POSSIBLY A BIT OF LLWS AGAIN LATE.

EXTENDED AVIATION OUTLOOK...VFR CONDITIONS ARE THEN EXPECTED
THU AND FRI. MVFR OR LOWER CIGS AND VSBYS POSSIBLE OVER PARTS
OF THE WEEKEND.

&&

.MARINE...
TODAY THROUGH TONIGHT...HAZARDOUS MARINE CONDITIONS ARE EXPECTED
TODAY AND TONIGHT AS A RAPIDLY INTENSIFYING GULF LOW SYSTEM
TRACKS NORTHEAST THROUGH THE TENNESSEE VALLEY...BEFORE SHIFTING
INTO THE EASTERN GREAT LAKES BY EARLY THURSDAY.

AN ASSOCIATED WARM FRONT WILL STEADILY SHIFT NORTHWARD THROUGH
THE COASTAL WATERS THIS MORNING...AHEAD OF A COLD FRONT APPROACHING
FROM THE WEST. AS THE WARM FRONT LIFTS NORTH...EXPECT THE TIGHTEST
PRESSURE GRADIENT TO BECOME SITUATED MAINLY ACROSS THE SOUTH
CAROLINA WATERS AND OFFSHORE GEORGIA WATERS THROUGH THE MORNING.
HOWEVER...CURRENT TRENDS SUPPORT ADVISORY WINDS AND SEAS BY LATE
MORNING ACROSS ALL MARINE ZONES. 

THERE CONTINUES TO BE TIMING DIFFERENCES BETWEEN THE MODELS
REGARDING PASSAGE OF THE COLD FRONT TONIGHT. PREFER TO LEAN TOWARD
THE SLOWER SOLUTION OF THE NAM MODEL...WHICH WOULD SUGGEST THE
MOST HAZARDOUS CONDITIONS WILL DEVELOP THIS EVENING AND OVERNIGHT
AS THE PRESSURE GRADIENT TIGHTENS SIGNIFICANTLY AHEAD OF THE COLD
FRONT. GALES STILL LOOK LIKELY FOR THE SOUTH CAROLINA WATERS AND
OFFSHORE GEORGIA ZONES THIS AFTERNOON AND OVERNIGHT...ALTHOUGH
BOTH MODELS HAVE TRENDED SLIGHTLY LOWER WITH WINDS IN THE 00Z RUN.
HAVE INDICATED THE STRONGEST SOUTHERLY SURGE WHEN THE FRONT CROSSES
INTO THE AREA AFTER 00Z...WITH COLD ADVECTION ENHANCING MIXING
OVER THE WATERS. THE CHARLESTON HARBOR AND THE NEARSHORE GEORGIA
WATERS SHOULD REMAIN JUST BELOW GALE CRITERIA...SO MAINTAINED SMALL
CRAFT ADVISORIES FOR THESE ZONES. SEAS WILL STEADILY BUILD THROUGH
THE DAY...PEAKING AROUND MIDNIGHT.

THURSDAY THROUGH SUNDAY...GALE CONDITIONS WILL END BY THURSDAY
MORNING...HOWEVER SMALL CRAFT ADVISORY CONDITIONS WILL LIKELY
PERSIST INTO THURSDAY MORNING FOR THE NORTHERN SOUTH CAROLINA
WATERS AND OFFSHORE GEORGIA WATERS WITHIN COLD ADVECTION IN THE
WAKE OF THE COLD FRONT. THE GRADIENT WILL STEADILY RELAX THROUGH
THURSDAY...ALLOWING WINDS AND SEAS TO DIMINISH/SUBSIDE.

MODELS ARE INDICATING THAT A WAVE OF LOW PRESSURE WILL DEVELOP
ALONG THE LINGERING COLD FRONT TO THE SOUTHEAST OF THE WATERS OVER
THE WEEKEND. THIS DEVELOPMENT COULD RESULT IN A STRONG NORTHEAST
SURGE SATURDAY AND SUNDAY AS THE SYSTEM PULLS NORTHEAST. DETAILS
REGARDING WINDS AND SEAS WILL BE HIGHLY DEPENDENT ON THE TRACK AND
STRENGTH OF THIS SYSTEM.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...HIGH SURF ADVISORY UNTIL 5 AM EST THURSDAY FOR GAZ117-119-139-
     141.
SC...HIGH SURF ADVISORY UNTIL 5 AM EST THURSDAY FOR SCZ048>051.
     LAKE WIND ADVISORY UNTIL NOON EST THURSDAY FOR SCZ045.
MARINE...SMALL CRAFT ADVISORY UNTIL NOON EST TODAY FOR AMZ350-352-374.
     GALE WARNING UNTIL 5 AM EST THURSDAY FOR AMZ350-352-374.
     SMALL CRAFT ADVISORY UNTIL 10 AM EST THURSDAY FOR AMZ354.
     SMALL CRAFT ADVISORY UNTIL 5 AM EST THURSDAY FOR AMZ330.

&&

$$

JRJ