River Flood Warning 10, NWS Charleston, SC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1054 AM EDT THU APR 3 2008

.SYNOPSIS...
A HIGH PRES SURFACE WEDGE OVER THE FORECAST AREA WILL GRADUALLY
WEAKEN TODAY AS A COASTAL WARM FRONT APPROACHES FROM THE S AND SE.
THE FRONT WILL LIFT N OF THE AREA BY LATE TONIGHT AS ATLC HIGH
PRES EXPANDS ACROSS FLORIDA AND SOUTHERN GEORGIA FRI. A COLD
FRONT WILL PUSH THROUGH THE REGION LATE SAT. HIGH PRES WILL RETURN
FOR EARLY NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
THURSDAY MORNING...THE SURFACE FRONT WAS LOCATED WELL S/W OF THE
FORECAST AREA...AND A WEDGE OF HIGH PRESSURE WAS FIRMLY
ESTABLISHED WITH WIDESPREAD CLOUDS ACROSS THE REGION. ISENTROPIC
ASCENT DIAGNOSED WITHIN THE 295-300K LAYER...ELEVATED
INSTABILITY...PWATS AROUND 1.5 INCHES AND RELATIVELY WEAK/ZONAL
STEERING FLOW WERE CONTRIBUTING TO SLOW MOVING...BACKBUILDING/
TRAINING CONVECTION WITH LOCALLY HEAVY RAINFALL. THE FOCUS OF
SHOWERS/ISOLATED THUNDERSTORMS...WITH COVERAGE SUFFICIENT TO
JUSTIFY CATEGORICAL POPS ACROSS ALL BUT FAR SOUTHERN
COUNTIES...WILL SLOWLY SHIFT NORTH TODAY. THIS SLOW EVOLUTION WILL
MAINTAIN HIGH POPS AND THE THREAT FOR LOCALLY EXCESSIVE RAINFALL
INTO AT LEAST MID AFTERNOON.

MEANWHILE...LATEST MODEL GUIDANCE SUGGESTS THAT THE WEDGE WILL
GRADUALLY WEAKEN WITH TIME TODAY...ALLOWING SOME TEMPERATURE
RECOVERY. HOWEVER...AS OF LATE THURSDAY MORNING LOW LEVEL COOL
AIR WAS SO FIRMLY ESTABLISHED THAT THE PROSPECTS FOR A SIGNIFICANT
WARM UP APPEAR LIMITED. THUS...LOWERED HIGH TEMPERATURES
SIGNIFICANTLY ACROSS THE REGION. ADJUSTMENT STILL ALLOWS
TEMPERATURES TO RECOVER INTO THE 60S NORTH AND 70S SOUTH.
HOWEVER...TEMPERATURES MAY STRUGGLE TO REACH EVEN ADJUSTED VALUES
IN MANY LOCATIONS...POSSIBLY HOLDING IN THE 50S ACROSS THE
NORTH...AND HIGH TEMPERATURES MAY ACTUALLY OCCUR AFTER DARK AS A
WARM FRONT ADVANCES NORTH.

IF THE SURFACE BOUNDARY ADVANCES AS A WARM FRONT INTO S/SW
COUNTIES THIS AFTERNOON...INCREASED INSTABILITY AND ENHANCED LOW
LEVEL HELICITY NEAR THE BOUNDARY COULD SUPPORT A LOW END SEVERE
THUNDERSTORMS THREAT.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
MODELS INDICATE THE COASTAL TROUGH ADVANCING N TONIGHT WITH THE
REGION LOSING THE SFC WEDGE OVERNIGHT. MODEL TRENDS LOOK PRETTY
GOOD...BUT MAY BE A BIT FAST ON SFC VEERING PATTERN. POPS WILL
BE ON THE WANE TONIGHT AS THE WARM SECTOR ADVANCES. TEMPERATURES
COULD RISE OVERNIGHT MANY AREAS AFTER MIDNIGHT. WE RAISED MIN
TEMPS MANY AREAS CLOSER TO THE COAST AND SRN ZONES IN GEORGIA.

FRI IS A DIFFERENT ANIMAL FROM TODAY...TIGHT LOW LEVEL PRES
GRADIENT WITH A SSW FLOW AND DEEPER MIXING. WE SHOULD BECOME
PARTLY CLOUDY MOST AREAS AND SUNSHINE WILL QUICKLY WARM TEMPS
INTO THE 80S ALONG WITH BREEZY TO WINDY CONDITIONS E OF I-95
IN SOUTH CAROLINA. MANY AREAS COULD REMAIN DRY FRI...BUT THERE
IS FORECAST TO BE A WEAK LEE-SIDE SFC TROF AND THE SEA BREEZE
MOVING INTO THIS FEATURE MAY SPARK A FEW TSTMS TO THE W OF
I-95 MID TO LATE AFTN. FORECAST CONVERGENCE AND INSTABILITY
PROGS SUGGEST ISOLATED STRONG TSTMS POSSIBLE OVER AREAS LIKE
FAR INLAND COLLETON...DORECHESTER...AND BERKELEY.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
A MILD SLY FLOW WILL BE IN PLACE FRI NIGHT AND A FEW SHOWERS ARE
POSSIBLE. RAIN CHANCES INCREASE SIGNIFICANTLY SAT...MAINLY FROM W
TO E...AS A COLD FRONT APPROACHES FROM THE W AND THE AREA GETS
INTO THE RIGHT REAR QUADRANT OF A 130+ KT H25 JET. WITH THE FRONT
EXPECTED TO BE A BIT SLOWER THAN PREVIOUSLY THOUGHT...ALLOWING FOR
A BIT MORE INSTABILITY...WILL HAVE TO KEEP AN EYE OUT FOR THE
POTENTIAL FOR A FEW STRONG TO POSSIBLY SEVERE STORMS SAT AFTN/EVE.
SLOW CLEARING EXPECTED SAT NIGHT AS HIGH PRES TRIES TO BUILD IN N
OF THE AREA. HOWEVER... NUMERICAL GUIDANCE IS SUGGESTING AT LEAST
ONE AREA OF LOW WILL DEVELOP ON THE FRONT S OF THE AREA THROUGH
MID WEEK...POSSIBLY TRACKING CLOSE ENOUGH TO KEEP RAIN AT LEAST
ALONG THE COAST.

TEMPS WILL START THE PERIOD ABOVE NORMAL AHEAD OF THE FRONT...THEN
RETURN TO MORE NORMAL LEVELS THROUGH THE REMAINDER OF THE PERIOD.

&&

.AVIATION /14Z THURSDAY THROUGH MONDAY/...
IFR/MVFR CEILINGS WILL PERSIST TODAY...WITH THE MOST FREQUENT
SHOWERS AT KCHS. ISOLATED THUNDERSTORMS COULD DEVELOP OVER OR
CLOSE TO BOTH TAF SITES TODAY. WILL ASSESS THE POTENTIAL FOR
IFR OR LOWER CONDITIONS IN FOG AND STRATUS TONIGHT.

EXTENDED AVIATION OUTLOOK...MVFR OR LOWER CIGS/FOG POSSIBLE EARLY
FRI...THEN VFR CONDITIONS DEVELOPING FRI. MVFR OR LOWER CONDITIONS
POSSIBLE AGAIN SAT AND SAT NIGHT. VFR DEVELOPING SUN AND
CONTINUING MON.

&&

.MARINE...
THURSDAY MORNING PILOT BOAT REPORTS AND FIXED PLATFORM
OBSERVATIONS SUGGEST THAT ONGOING FORECASTS REMAIN ON TRACK...AND
ONGOING SCAS REMAIN IN EFFECT AND UNALTERED. THE TIGHT GRADIENT
BETWEEN THE WEDGE OF HIGH PRESSURE OVER LAND AND THE FRONTAL
TROUGH S/E OF THE REGION WILL MAINTAIN NE WINDS 20-30 KNOTS...WITH
SEAS AS HIGH AS 6-8 FT...INTO THIS AFTERNOON...BEFORE CONDITIONS
TEMPORARILY IMPROVE LATER TONIGHT INTO TONIGHT.

FRIDAY NIGHT THROUGH MONDAY...STRONG SLY FLOW WILL BE IN PLACE FRI
NIGHT AHEAD OF AN APPROACHING COLD FRONT...WHICH IS EXPECTED TO MOVE
THROUGH THE MARINE AREA SAT NIGHT. WILL LIKELY SEE SMALL CRAFT
ADVISORY /SCA/ CONDS IN CHS HARBOR SAT...AT LEAST FOR GUSTS TO 20
KT.  ELSEWHERE...SCA CONDS MAY BE EXPERIENCED ACROSS THE SC WATERS
FRI NIGHT DUE TO A COMBINATION OF WINDS AND SEAS...WHICH COULD
LINGER INTO SAT...ESPECIALLY N OF EDISTO BEACH. HIGH PRES BUILDS IN
FROM THE N SUN BUT ALL WATERS SHOULD SEE CONDS BELOW SCA LEVELS BY
THEN. THE OUTER GA WATERS MAY GET BACK INTO SCA CONDS MON FOR
SEAS...WHICH WILL BE BUILDING SLIGHTLY ON E/NE FLOW.

RIP CURRENTS...MODERATE RISK OF RIP CURRENTS ACROSS SOUTHEAST SOUTH
CAROLINA AND SOUTHEAST GEORGIA BEACHES ON TODAY DUE TO MODERATE
TO STRONG ONSHORE FLOW AND CONTINUED SWELLS.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 5 PM EDT THIS AFTERNOON FOR AMZ330-
     352-354.
     SMALL CRAFT ADVISORY UNTIL 11 PM EDT THIS EVENING FOR AMZ350.
     SMALL CRAFT ADVISORY UNTIL 11 PM EDT SATURDAY FOR AMZ374.

&&

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