FXUS62 KCHS 241206
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
706 AM 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 /THROUGH TONIGHT/...
SURFACE HIGH PRES WEDGE PATTERN HOLDING FIRM THIS MORNING WITH
PATCHY CLOUDINESS OVER OUR FORECAST AREA. SOME OF THE LOWER CLOUDS
MAY EXPAND OVER SE GEORGIA TOWARD DAWN WITH AREAS OF STRATOCUMULUS
ALONG THE SOUTH CAROLINA COAST. MODELS SHOW OUR AREAS TO THE W OF
I-95 REMAINING DRY TODAY WITH ISENTROPIC LIFT INCREASING THIS
AFTERNOON. THIS SHOULD ALLOW FOR A GENERAL INCREASE IN CLOUDS ALL
AREAS WITH A FEW LIGHT SHOWERS DEVELOPING OFF THE COAST AND MOVING
ONSHORE IN SOUTH CAROLINA 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 /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 /12Z THURSDAY THROUGH MONDAY/...
STRATOCUMULUS CLOUDS AT VARIOUS LAYERS WERE DEVELOPING ALONG THE
COASTAL CORRIDOR THIS MORNING. PRIOR TO 12Z...MVFR OR LOWER CIGS
WERE FAIRLY ISOLATED. WE STARTED OFF WITH PERIODS OF MVFR CIGS
AT TIMES THIS MORNING...TEMPO GROUPS AT BOTH TERMINALS. WE WOULD
NOT BE SURPRISED IF OUR TAFS WERE A BIT PESSIMISTIC TODAY OVERALL
BUT WE CONTINUED WITH A GENERAL PERSISTENCE AND SIMILAR GUIDANCE
FROM 06Z FORECAST SOUNDINGS AND MODEL DATA.
BY LATE AFTERNOON INTO EARLY AFTERNOON...WE THINK MVFR CIGS WILL
BECOMING MORE WIDESPREAD. SURFACE WINDS WILL ALSO BECOME GUSTY
THIS EVENING...IF NOT SOONER. THERE IS A POTENTIAL FOR LLWS THIS
EVENING OR TONIGHT BUT CONFIDENCE ON SURFACE WIND GUSTS AND
STRENGTH OF THE LOW LEVEL INVERSION QUITE LOW AT THIS JUNCTURE.
LATER TONIGHT...CONFIDENCE INCREASES THAT PREVAILING WIND GUSTS
INDEED DEVELOP AND CIGS REMAIN MVFR OR LOWER. WE HAVE INTRODUCED
SHOWERS NEAR THE END OF THE 12Z TAF CYCLE AT BOTH TERMS.
EXTENDED AVIATION OUTLOOK...MAINLY VFR FRI NIGHT THROUGH EARLY
NEXT WEEK.
&&
.MARINE...
NE WINDS HAVE BEEN AVERAGING 15 TO 20 KT OVERNIGHT AND SEAS HAVE
SLOWLY BEEN IN A BUILDING MODE WITH 3-4 FT SEAS WITHIN 20 NM AND
LIKELY A BIT HIGHER BEYOND 20 NM. SMALL CRAFT ADVISORY CONDITIONS
WILL DEVELOP TODAY OVER ALL WATERS THE HIGH PRES WEDGE HOLDS
FIRM INLAND WHILE PRES FALLS TO S INCREASE AHEAD OF THE IMPENDING
STORM SYSTEM. DEPENDENT ON WHERE THE TIGHTEST PINCHING OCCURS
TODAY...PARTS OF OUR NEAR SHORE WATERS N OF THE SAVANNAH RIVER
ENTRANCE MAY SEE A SOLID 25 KT DEVELOP. EVEN WHERE THE GRADIENT
DOES NOT BECOME PINCHED SOLIDLY...SEAS SHOULD BUILD INTO SMALL
CRAFT ADVISORY RANGE.
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 FROM 10 AM THIS MORNING TO 1 PM EST
FRIDAY FOR AMZ330.
SMALL CRAFT ADVISORY FROM NOON TODAY TO 9 PM EST FRIDAY FOR
AMZ352.
SMALL CRAFT ADVISORY FROM 10 AM THIS MORNING TO 5 AM EST
SATURDAY FOR AMZ350.
SMALL CRAFT ADVISORY FROM 10 AM THIS MORNING TO NOON EST
SATURDAY FOR AMZ374.
SMALL CRAFT ADVISORY FROM NOON TODAY TO 4 PM EST FRIDAY FOR
AMZ354.
&&
$$
