FXUS62 KCHS 020931
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
431 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/...
POTENT WARM AIR ADVECTION AND STRONG ISENTROPIC LIFT UNDERWAY
EARLY THIS MORNING AND RAINS HAVE BROKEN OUT QUICKLY OVERNIGHT...
BECOMING HEAVY AT TIMES ACROSS THE FORECAST AREA N OF I-16 AND TO
THE W OF CHARLESTON. SURFACE LOW PRES WAS OVER SE LOUISIANA AT 08Z
AND THIS LOW WILL TRACK NE TODAY INTO THE EASTERN TENNESSEE VALLEY
REGION BY LATE DAY. A DEVELOPING WARM FRONT WAS MOVING TOWARD OUR
COASTAL AREAS IN SOUTH CAROLINA AND IS EXPECTED TO LIFT INTO THE
ALTAMAHA REGION IN THE NEXT FEW HOURS. THIS MORNING...ALL ATTENTION
IS ON PONDING WATER ON AREA ROADS AND A GOOD RISK FOR COASTAL
FLOODING. MODELS MAY BE A BIT TOO UNIFORM LIFTING THE WARM FRONT N
OVER OUR REGION TODAY AS A VERY SHALLOW WEDGE PATTERN WILL BE
FIGHTING TO HOLD ON ADJACENT TO THE SOUTH CAROLINA MIDLANDS UNDER
THE PCPN SHIELD THROUGH LATE MORNING.

BY MID TO LATE AFTERNOON WITH A WARM SECTOR SLOT OVER THE AREA...
STEADIER RAINS SHOULD BE SHIFTING TO THE N OF OUR CHARLESTON 
TRI-COUNTY ZONES LEAVING ALL OF OUR AREA IN A QUASI-MODIFIED WARM
SECTOR. WE THINK SEVERE THUNDERSTORMS INCLUDING A RISK FOR ISOLATED
TORNADOES WILL RAMP UP IN A LINEAR FASHION OVER S GEORGIA BY MID
TO LATE AFTERNOON AND BEGIN ACCELERATE E LATE IN THE DAY AS THE
UPPER CUT-OFF LOW LIFTS OUT AND BEGINS TO TILT NEGATIVELY OVER
NORTHERN ALABAMA AND NW GEORGIA TOWARD SUNSET. THE MID LEVEL
ATMOSPHERE WILL ONLY BECOME MODERATELY UNSTABLE BUT CERTAINLY GOOD
ENOUGH TO SUPPORT STRONG TO SEVERE TSTMS GIVEN THE UPWARD MOTION
ANTICIPATED THIS AFTERNOON. LOW LEVEL INSTABILITY WILL BE LACKING
AND MID 60S SURFACE DEW POINTS MAY BE CONFINED TO IMMEDIATE COASTAL
SECTIONS DURING THE AFTERNOON HOURS. JUST ABOUT ANY CONVECTIVE
ELEMENT WILL HAVE POTENTIAL FOR STRONG ROTATION GIVEN FAVORABLE
WIND FIELDS BUT WE THINK THE MAIN GAME FOR OUR FORECAST AREA WILL
BE A MID TO LATE AFTERNOON EVENT TODAY. A SIGNIFICANT SEVERE
WEATHER EVENT MAY CERTAINLY BE DEVELOPING LATER TODAY AS UPSTREAM
FORCING REACHES OUR REGION. AS FOR NOW...A HIGH-END SLIGHT RISK
FOR SEVERE WEATHER FROM SPC SEEMS REASONABLE GIVEN THE FORECAST
SURFACE BASED PATTERN AND QUESTIONABLE TRANSITION OF THE SYNOPTIC
SCALE WARM FRONT TODAY. NO CHANGE TO TEMPS TODAY AS WARM AIR
ALLOWS FOR SOME LOWER 70S ALONG THE COAST BY MID AFTERNOON. WE
HAVE HELD OFF ON WIND ADVISORIES TODAY AS MODELS SUGGEST ONLY A
SMALL POTENTIAL WINDOW FOR GUSTY WINDS ALONG THE CHARLESTON COUNTY
COAST. IT CERTAINLY WILL BECOME BREEZY AS LOW LEVEL WIND FIELDS
BUILD TODAY.

&&

.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 /09Z WEDNESDAY THROUGH SUNDAY/...
THROUGH THE OVERNIGHT HOURS AT BOTH KSAV AND KCHS...UPSTREAM MIXING
TRENDS AND LATEST SOUNDING WIND FIELDS SUGGEST LLWS WILL BECOME A 
FACTOR PRIOR TO DAWN AND CONTINUE AT LEAST THROUGH MID MORNING WHEN
SURFACE WIND GUSTS BECOME MORE OF A PREVAILING NATURE.

STRONG WARM AIR ADVECTION AND INCREASING LOW LEVEL CONVERGENCE WILL
ALLOW RAINFALL TO INCREASE IN COVERAGE AND INTENSITY OVERNIGHT WITH
MVFR CIGS AND VSBYS DEVELOPING THROUGH THE COASTAL CORRIDOR. IFR
CIGS/VSBYS ARE POSSIBLE LATE TONIGHT INTO ALMOST MIDDAY AROUND KCHS
IN CLOSER PROXIMITY TO THE LIFTING WARM FRONT.

THERE WILL LIKELY BE A BREAK FROM THE RAINS IN THE WHILE DURING THE
THE FIRST HALF 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.

EXTENDED AVIATION OUTLOOK...MVFR OR LOWER CIGS/VSBYS ALONG WITH 
GUSTY WINDS WILL BE POSSIBLE THROUGH WEDNESDAY NIGHT...AS A POTENT 
STORM SYSTEM MOVES THROUGH THE AREA AND BRINGS PERIODS OF HEAVY RAIN 
AND POSSIBLY TSTMS. VFR CONDITIONS ARE THEN EXPECTED THURSDAY 
THROUGH SUNDAY.

&&

.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.

&&

.TIDES/COASTAL FLOODING...
TIDAL DEPARTURES ARE INCREASING QUICKLY THIS MORNING AND WE HAVE
CONTINUED A COASTAL FLOOD WARNING THIS MORNING. MODERATE TO 
OCCASIONALLY HEAVY RAINFALL AND VERY HIGH TIDES MAY RESULT IN A
SIGNIFICANT COMBO OF FRESH AND SALT WATER FLOODING AROUND THE TIME
OF HIGH TIDE BETWEEN 7 AND 9 AM ALONG THE GEORGIA AND SOUTHERN 
SOUTH CAROLINA COAST. 

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...COASTAL FLOOD WARNING UNTIL 11 AM EST THIS MORNING FOR GAZ117-
     119-139-141.
     HIGH SURF ADVISORY UNTIL 5 AM EST THURSDAY FOR GAZ117-119-139-
     141.
SC...COASTAL FLOOD WARNING UNTIL 11 AM EST THIS MORNING FOR 
     SCZ048>051.
     HIGH SURF ADVISORY UNTIL 5 AM EST THURSDAY FOR SCZ048>051.
     LAKE WIND ADVISORY FROM NOON TODAY TO NOON EST THURSDAY FOR 
     SCZ045.
MARINE...SMALL CRAFT ADVISORY UNTIL NOON EST TODAY FOR AMZ350-352-374.
     GALE WARNING FROM NOON TODAY TO 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.

&&

$$