FXUS62 KCHS 241752
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1252 PM EST THU DEC 24 2009
.SYNOPSIS...
A HIGH PRES WEDGE WILL CONTINUE INLAND TODAY. A COMPLEX STORM
SYSTEM WILL IMPACT THE REGION TONIGHT THROUGH FRIDAY. A COLD FRONT
WILL PUSH S AND E OF THE REGION FRI NIGHT. THEN...HIGH PRES WILL
BUILD INTO THE SOUTHEAST AND WILL REMAIN THE PARAMOUNT FEATURE
THROUGH THE MIDDLE OF NEXT WEEK.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
SURFACE HIGH PRESSURE WEDGE PATTERN HOLDING FIRM THIS
MORNING...BUT WILL BEGIN TO WEAKEN THIS AFTERNOON AS THE UPPER
CONFLUENCE DECREASES AHEAD OF A DEEP UPPER TROUGH MOVING OUT OF
THE SRN PLAINS AND INTO THE LWR MISSISSIPPI VALLEY. SATELLITE
INDICATES DIMINISHING SOUTH OF THE FORECAST AREA WITH SOME STRATUS
MOVING THROUGH OUR FORECAST AREA AND A GOOD DEAL OF STRATOCU
OFFSHORE WITH THE TROUGH OF LOW PRESSURE. RADAR IS PICKING UP ON
SOME RAIN BEYOND 20 NM FROM THE SC COAST AND WITH ISENTROPIC LIFT
INCREASING TODAY...SOME OF THIS ACTIVITY COULD MAKE IT ONSHORE.
THIS SHOULD ALLOW FOR A GENERAL INCREASE IN CLOUDS ALL AREAS WITH
LIGHT RAIN MOVING ONSHORE IN SC AFTER MIDDAY. OVERALL THE FORECAST
FOR TODAY REMAINS RELATIVELY UNCHANGED WITH HIGHS RANGING FROM THE
MID TO UPPER 50S ADJACENT TO THE SOUTH CAROLINA MIDLANDS TO THE
LOWER 60S ALONG THE COAST AND SOME MID 60S CLOSE TO THE ALTAMAHA.
NE TO E WINDS WILL BE INCREASING AND COASTAL AREAS WILL BECOME
BREEZY AT TIMES THIS AFTERNOON...ESPECIALLY FROM SAVANNAH
NORTHWARD.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
THE COMPLEX WINTER STORM SYSTEM OVER THE SOUTHERN PLAINS WILL POSE
A MYRIAD OF POTENTIAL WEATHER ISSUES FOR OUR AREA FROM LATE TONIGHT
INTO CHRISTMAS DAY. A STRONG UPPER LOW IN W TEXAS THIS MORNING WILL
MOVE TO THE ARKLATEX REGION BY THIS EVENING...THEN SHIFT MORE N
LATER TONIGHT...INDUCING A NEGATIVE TILTED SHORT WAVE TROUGH WHICH
WILL ACCELERATE THROUGH THE SE U.S. ON CHRISTMAS DAY. A WARM FRONT
WILL LIFT N THROUGH OUR FORECAST AREA LATE TONIGHT IN RESPONSE TO
THE UPPER SHORT WAVE AND LOW LEVEL WIND FIELDS WILL INCREASE
SHARPLY. MIXING PROFILES ARE DIFFICULT TO PIN DOWN GIVEN MODEL
DIFFERENCES IN PCPN TIMING AND WARM FRONTAL COMPLEXITY. WE THINK
WIDESPREAD RAINS WILL DEVELOP OVER E CENTRAL GEORGIA LATE THEN
SHIFT INTO OUR FORECAST AREA BY DAYBREAK FRI. CONVECTION WILL
LIKELY BE ELEVATED TO BEGIN THE DAY WITH A POCKET OF STEEPER LAPSE
RATES TRAVERSING AREAS JUST TO OUR SW-W PRIOR TO DAWN.
ALONG COASTAL AREAS...THE STRONG ONSHORE FLOW WILL BE PILING UP
WATER LEVELS WITH TIDAL ANOMALIES ON THE INCREASE OVERNIGHT. RAIN
IS EXPECTED TO COMMENCE SOMETIME CLOSER TO LOW TIDE LATE TONIGHT.
THIS NOSE OF INSTABILITY WILL ACCOMPANY A THETA-E RIDGE AND DYNAMICS
THROUGH OUR REGION DURING THE FIRST HALF OF CHRISTMAS DAY. STABILITY
FIELDS AND LAPSE RATES SUGGEST TSTMS ARE CERTAINLY POSSIBLE. WHILE
WIND FIELDS ARE CONCERNING...THE OVERALL LOW LEVEL ENVIRONMENT
DOES NOT APPEAR FAVORABLE FOR SEVERE WEATHER ALTHOUGH THE SLOWER
NAM TIMING IS A BIT CONCERNING. WITH THE DISPLACEMENT OF THE DEEP
SURFACE LOW AND VARIOUS FORECAST SOUNDINGS FOR OUR AREA...THE
POTENTIAL FOR SEVERE TSTMS WITH DAMAGING WIND GUSTS SEEMS MINIMAL
FROM OUR VANTAGE THIS MORNING BUT WE WILL CONTINUE TO MONITOR. OF
SOMEWHAT GREATER CONCERN SEEMS TO BE A PERIOD OF VERY HEAVY
CONVECTIVE RAINS WITH OUR ALREADY SATURATED SOILS. THE SITUATION
ALONG THE COAST WITH THE STRONG ONSHORE WINDS HOLDING IN WATER
LEVELS DURING A MID MORNING HIGH TIDE CYCLE MAKES THINGS EVEN MORE
INTERESTING. WE ARE IN AGREEMENT WITH THE HPC QPF IN THE 1-2 INCH
RANGE BUT THE TIMING OF THESE RAINS AND THE EVENTUAL STRENGTH OF
THE ONSHORE FLOW WILL BE DETERMINING FACTORS WHETHER WE SEE
LOCALIZED FLOODING IN ANY AREAS. THE OVERALL PROGRESSION AND
ACCELERATION OF THE OMEGA AND DEEP MOISTURE HAS SWAYED US AWAY
FROM ANY FLOOD WATCHES AT THIS POINT BUT THE SETUP HAS SOME
INTERESTING PROSPECTS IN SOUTH CAROLINA COASTAL ZONES.
CATEGORICAL MORNING POPS WERE TRIMMED DOWN TO CHANCE TO LIKELY
AFTER MIDDAY AND WITH THE WARM SECTOR...HIGH TEMPERATURES COULD
REACH 70 ALONG COASTAL AREAS. BREEZY CONDITIONS WILL BE MOST
NOTICEABLY ALONG THE SOUTH CAROLINA COAST THROUGH EARLY AFTERNOON.
CLEARING SKIES MAY EVEN TAKE HOLD IN OUR INLAND ZONES TO THE W OF
I-95 BY MID AFTERNOON IF SOME OF THE FASTER SOLUTIONS ARE
REALIZED.
&&
.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
LATEST GFS...GEM AND EUROPEAN GUIDANCE SUGGESTS THAT DEEP LAYER
MOISTURE WILL HAVE PUSHED OFFSHORE AND OUT OF THE FORECAST AREA
BY EARLY FRIDAY EVENING...WHILE THE SLOWER NAM DEPICTS A LESS
PROGRESSIVE SCENARIO. TRENDED FORECASTS TOWARD FASTER
DRYING...LIMITING SLIGHT CHANCE POPS TO FAR NORTHERN COUNTIES INTO
EARLY EVENING AND PUSHING POPS OUT OF COASTAL WATERS AROUND
MIDNIGHT. WOULD NOT BE SURPRISED IF THIS PRECIPITATION CLEARS THE
REGION EVEN EARLIER THAN INDICATED WITHIN THIS ADJUSTED FORECAST.
OTHERWISE...HIGH PRESSURE CENTERED W/NW OF THE REGION WILL RIDGE
INTO THE REGION FRIDAY NIGHT/SATURDAY AND WILL SPRAWL ACROSS THE
SOUTHEAST THROUGH THE MIDDLE OF NEXT WEEK. INITIALLY...TEMPERATURES
WILL RECOVER TO NEAR NORMAL SATURDAY...THEN ENHANCED COLD ADVECTION
BETWEEN THE HIGH PRESSURE AND LOW PRESSURE CENTERED NORTH OF THE
REGION WILL PUSH TEMPERATURES BELOW NORMAL LATE THIS WEEKEND...AND
TEMPERATURES WILL REMAIN BELOW NORMAL THROUGH THE REMAINDER OF THE
FORECAST PERIOD.
AN ENERGETIC AND MOISTURE-LADEN SUBTROPICAL JET WILL REMAIN
POSITIONED JUST SOUTH OF THE REGION...AND SEVERAL DISTURBANCES WILL
TRAVERSE THE JET LATE THIS WEEKEND THROUGH THE MIDDLE OF NEXT WEEK.
ASIDE FROM OCCASIONALLY PUSHING HIGH LEVEL CLOUDS INTO THE
REGION...WAVES OF LOW PRESSURE AND ASSOCIATED DEEP LAYER MOISTURE
SHOULD REMAIN SOUTH OF THE REGION...AND PRECIPITATION APPEARS
UNLIKELY THROUGH THE FIRST HALF OF NEXT WEEK. HOWEVER...IF ANY OF
THESE WAVES AMPLIFIES MORE VIGOROUSLY THAN EXPECTED...RAIN COULD
BRUSH THE REGION LATE THIS WEEKEND AND AGAIN EARLY NEXT WEEK. MORE
LIKELY...THE NEXT RAIN PRODUCING SYSTEM WILL EMERGE FROM THE GULF OF
MEXICO TO AFFECT THE REGION DURING THE LATTER HALF OF NEXT WEEK.
&&
.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
STRATOCUMULUS WILL CONTINUE TO PUSH ONSHORE THIS AFTERNOON BUT
CIGS SHOULD REMAIN VFR. LOOKS LIKE ANY LIGHT RAIN THROUGH EARLE
EVE WILL MOVE ONSHORE S OF KCHS AND N OF KSAV. THE MAIN IMPACT TO
THE TERMS THROUGH THIS AFTN WILL BE THE WIND GUSTS...WHICH WILL UP
NEAR 20 KT AT TIMES.
NOT CONFIDENT ATTM REGARDING HOW QUICK THE CIGS WILL LOWER TO MVFR
GIVEN THE DISAGREEMENT IN THE MOS GUIDANCE SO WAS PRETTY
CONSERVATIVE WITH THE 18Z TAFS. FOR NOW WILL FOLLOW THE LESS
PESSIMISTIC NAM MOS GUIDANCE. HAVE INCLUDED A TEMPO GROUP FOR MVFR
CIGS BETWEEN 00-06Z SINCE ALL GUIDANCE POINTS TOWARD THAT. AFTER
THAT TIME...MUCH WILL DEPEND ON HOW QUICK THE PRECIP ARRIVES. THERE
IS STILL A POTENTIAL FOR LLWS THIS EVENING OR TONIGHT BUT
CONFIDENCE ON SURFACE WIND GUSTS AND STRENGTH OF THE LOW LEVEL
WINDS IS QUITE LOW AT THIS JUNCTURE.
THERE IS HIGHER CONFIDENCE IN MVFR OR LOWER CIGS WITH RA/SH BY
AROUND 12Z FRI...A BIT EARLIER AT KSAV THAN KCHS...WITH GUSTY
CONDS CONTINUING. TSTMS ARE ALSO A POSSIBILITY BUT LOW CONFIDENCE
PRECLUDES MENTIONING ATTM.
EXTENDED AVIATION OUTLOOK...MAINLY VFR FRI NIGHT THROUGH EARLY
NEXT WEEK.
&&
.MARINE...
NE WINDS HAVE INCREASED TO 20 TO 25 KT AND SEAS HAVE BEEN BUILDING
AS WELL WITH 3-5 FT SEAS WITHIN 20 NM AND LIKELY A BIT HIGHER
BEYOND 20 NM. SMALL CRAFT ADVISORY CONDITIONS ARE EXPECTED ACROSS
ALL WATERS TODAY...AT LEAST FOR SEAS OF 6 FT.
STRONG ONSHORE WINDS WILL DEVELOP TONIGHT WITH SEAS BUILDING
ABOVE 6 FT CLOSE TO THE COAST BY DAYBREAK AS WINDS VEER TO SE
AND INCREASE TO 20 TO 25 KT AND EVEN CLOSE TO 30 KT POSSIBLE
OFF THE CHARLESTON COUNTY COAST.
ON FRIDAY...THE POTENT LOW LEVEL JET WILL MOVE FURTHER UP THE
CAROLINA COAST IN THE AFTERNOON AND WINDS WILL SHIFT TO A MORE
WSW COMPONENT IN THE WAKE OF A STRONG PRE-FRONTAL CONVERGENCE
BOUNDARY. WINDS AND SEAS SHOULD SUBSIDE DURING THE AFTERNOON...
BUT FOR MOST OF OUR WATERS SCA CONDITIONS WILL PERSIST.
IN THE WAKE OF COLD FROPA...EXPECT A SURGE OF W/NW WINDS AS COLD
ADVECTION OVERSPREADS THE WATERS. THIS SHOULD MAINTAIN SMALL CRAFT
ADVISORY SEAS WITHIN SOUTH CAROLINA NEARSHORE WATERS NORTH OF EDISTO
BEACH THROUGH THE NIGHT AND ACROSS THE OUTER GEORGIA WATERS THROUGH
SATURDAY MORNING. AN ENHANCED W/NW SURFACE PRESSURE GRADIENT AND
COLD ADVECTION/MARINE LAYER INSTABILITY WILL THEN SUPPORT ELEVATED
WINDS/SEAS SUNDAY THROUGH EARLY NEXT WEEK. HOWEVER...BECAUSE OF
THE OFFSHORE FETCH THE POTENTIAL FOR SMALL CRAFT ADVISORY SEAS WILL
REMAIN LIMITED TO AREAS BEYOND 20-40 NM...NEAR THE WEST WALL OF THE
GULF STREAM.
&&
.TIDES/COASTAL FLOODING...
STRONG ONSHORE WINDS COULD PRODUCE HIGH SURF...ELEVATED TIDES...
SHALLOW COASTAL FLOODING AND BEACH EROSION TONIGHT INTO FRI. THE
BEST CHANCE OF SHALLOW COASTAL FLOODING APPEARS TO BE EARLY
MORNING FRI WHEN THE TIDE LEVEL MAY APPROACH THE ADVISORY
CRITERIA OF 7.0 FEET MEAN LOWER LOW WATER IN CHS HARBOR. IF
THIS TIDE IS COINCIDENT WITH HEAVY RAINFALL...EXACERBATED
FLOODING PROBLEMS MAY OCCUR.
THERE IS ALSO A WINDOW FOR HIGH SURF TO DEVELOP ALONG THE SOUTH
CAROLINA COAST LATE TONIGHT AND CHRISTMAS MORNING BUT THE WINDOW
FOR CRITERIA APPEARS RATHER LIMITED. IF MODEL TRENDS CONTINUE TO
SHOW INCREASES IN FORECAST WINDS AND WAVES...A HIGH SURF ADVISORY
MAY BE REQUIRED. SEAS BEYOND 20 NM SHOULD BUILD ABOVE 10 FT BY FRI
MORNING WHILE BREAKERS BUILD TO AT LEAST 3-4 FT ALONG THE CHARLESTON
COUNTY COAST.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 1 PM EST FRIDAY FOR AMZ330.
SMALL CRAFT ADVISORY UNTIL 9 PM EST FRIDAY FOR AMZ352.
SMALL CRAFT ADVISORY UNTIL 5 AM EST SATURDAY FOR AMZ350.
SMALL CRAFT ADVISORY UNTIL NOON EST SATURDAY FOR AMZ374.
SMALL CRAFT ADVISORY UNTIL 4 PM EST FRIDAY FOR AMZ354.
&&
$$
