FXUS62 KCHS 160557
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1257 AM EST WED DEC 16 2009

.SYNOPSIS...
A COLD FRONT WILL CONTINUE TO PUSH OFFSHORE TODAY. HIGH PRESSURE
WILL THEN BUILD INTO THE AREA THROUGH THURSDAY. A SLOW MOVING STORM
SYSTEM WILL MOVE FROM THE NORTHEAST GULF OF MEXICO ON FRIDAY TO
OFF THE GEORGIA AND SOUTH CAROLINA COAST ON SATURDAY. HIGH
PRESSURE IS THEN EXPECTED TO BUILD BACK INTO THE AREA FOR THE TAIL
END OF THE WEEKEND INTO EARLY NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
AS OF TUE EVE...
NO MAJOR CHANGES ARE PLANNED TO THE FORECAST THIS EVENING. COLD
FRONT IS MOVING RAPIDLY ACROSS THE WESTERN CAROLINAS AND GEORGIA
THIS EVENING BEING AIDED BY POST FRONTAL ISALLOBARIC RISES ON THE
ORDER OF 3-4MB/3HRS. THE SURFACE FLOW HAS ALREADY VEERED WESTERLY
AHEAD OF THE FRONT WHICH IS HELPING TO SCOUR OUT LOW-LEVEL
MOISTURE. SHOWER ACTIVITY HAS DIMINISHED OVER THE PAST FEW HOURS
AND THIS TREND WILL CONTINUE AS THE FRONT APPROACHES. WILL KEEP
SLIGHT CHANCE POPS THROUGH MIDNIGHT FOR MAINLY THE COASTAL AND FAR
SOUTHERN ZONES...OTHERWISE EXPECT DRY CONDITIONS TO DOMINATE.

LIGHT WESTERLY WINDS WILL BACK QUICKLY TO THE NORTH AFTER FROPA
WITH GUSTY WINDS DEVELOPING WITH THE ONSET OF STRONG POST FRONTAL 
COLD AIR ADVECTION. THE FRONT WILL ENTER THE NORTHWEST ZONES
AROUND MIDNIGHT AND CLEAR THE NORTH GEORGIA COAST BY 4-5 AM. LOWS
TONIGHT WILL RANGE FROM AROUND 45 WELL INLAND TO THE LOWER-MID 50S
ALONG THE GEORGIA COAST. CLOUDY SKIES THIS EVENING WILL GRADUALLY
THIN AS THE FRONT SURGES SOUTH...BUT EXTENSIVE CIRRUS WILL KEEP
SKIES MOSTLY CLOUDY THROUGH SUNRISE. IN FACT...200-400MB LAYERED
RH FIELDS SUGGEST A BAND OF CIRRUS COULD REMAIN OVER MUCH OF THE
AREA WEDNESDAY...SO WILL GO AHEAD AND UPDATE THE FORECAST TO SHOW
SLIGHTLY HIGHER CLOUD COVER DURING THAT TIME.

LAKE WINDS...A LAKE WIND ADVISORY REMAINS IN EFFECT FOR LAKE
MOULTRIE. STRONG POST FRONTAL COLD AIR ADVECTION COUPLED WITH THE 
RELATIVELY WARMER LAKE WATERS WILL SUPPORT VIGOROUS MIXING OVER
THE OPEN LAKE WATERS. SHOULD SEE WINDS AS HIGH AS 20 KT DEVELOP
AFTER MIDNIGHT AND CONTINUE THROUGH WEDNESDAY MORNING. WAVES WILL
BUILD AS HIGH AS 2-3 FT...MAINLY OVER THE CENTRAL AND SOUTHERN
PARTS OF THE LAKE.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM TODAY/...
A DRY...COOL AND MOSTLY SUNNY DAY IS EXPECTED WEDNESDAY AS A LARGE
RIDGE OF HIGH PRESSURE BUILDS IN. SUSTAINED COLD ADVECTION
THROUGHOUT THE DAY SHOULD OFFSET SOME WEAK DOWNSLOPE COMPRESSION.
WE TRIED TO ACCOUNT FOR THE USUAL WARM BIAS IN THE STATISTICAL
GUIDANCE DURING POST-FROPA COLD ADVECTION EVENTS AND THEREFORE
UNDERCUT FORECAST HIGHS BY A FEW DEGREES. THIS YIELDS UPPER 50S
FOR MOST AREAS.

&&

.LONG TERM /TONIGHT THROUGH TUESDAY/...
MEDIUM RANGE GUIDANCE HAS COME INTO MUCH BETTER AGREEMENT WITH THE 
SURFACE PRESSURE PATTERN THROUGH THE EXTENDED PERIODS THIS 
AFTERNOON...BUT THE HIGHLY ANOMALOUS PATTERN CONTINUES TO LEAD TO 
SLIGHTLY BELOW NORMAL FORECAST CONFIDENCE.

MODEL SOLUTIONS ALL AGREE THAT HIGH PRESSURE WILL BUILD OVER THE 
AREA WEDNESDAY NIGHT THROUGH THURSDAY...RESULTING IN RAIN FREE 
WEATHER. CONDITIONS THEN DETERIORATE THURSDAY NIGHT AS DEEP MOISTURE 
AND PLENTY OF FORCING FOR ASCENT FROM UPPER LEVEL SHORTWAVE ENERGY 
AND THE ENTRANCE REGION OF A 140+ KNOT H25 JET SPREADS OVER THE 
FORECAST AREA. COULD SEE SOME LIGHT PRECIPITATION DEVELOP IN THE 
EVENING ACROSS PRIMARILY SOUTHEAST GEORGIA...SO HAVE INCLUDED SLIGHT 
CHANCE POPS HERE. AFTER MIDNIGHT...AS THE DEEPER MOISTURE AND BETTER 
FORCING ARRIVE HAVE BUMPED POPS TO HIGH CHANCE SOUTH AND SLIGHT 
CHANCE ACROSS THE FAR NORTH. OF CONCERN IS HOW DRY THE AIRMASS IN 
PLACE WILL BE AS THE PRECIPITATION ARRIVES...WITH MODEL SOUNDINGS 
SHOWING MOISTURE EXTENDING PLENTY HIGH ENOUGH FOR ICE NUCLEATION. AT 
THE SAME TIME...WITH THE DRY LOW LEVEL AIRMASS IN PLACE AS SEEN IN 
MODEL SOUNDINGS...CAN/T RULE OUT A PERIOD OF GRAUPLE OR SLEET 
ESPECIALLY ACROSS FAR INTERIOR PORTIONS OF THE FORECAST AREA PRIOR 
TO PRECIPITATION TRANSITIONING TO RAIN. FOR NOW...WILL KEEP ANY 
MENTION OF WINTRY PRECIP OUT OF THE FORECAST...BUT THIS WILL NEED TO 
BE CLOSELY MONITORED OVER THE NEXT COUPLE OF DAYS.

ANY POTENTIAL WINTRY PRECIP SHOULD CHANGE OVER TO ALL RAIN QUICKLY 
FRIDAY MORNING AS WARMER AIR ALOFT AND WINDS SHIFTING SLIGHTLY MORE 
ONSHORE ALLOW FOR TEMPERATURES TO WARM THROUGHOUT THE BOUNDARY 
LAYER. EXPECT A FAIRLY STEADY RAIN FRIDAY AND FRIDAY NIGHT AS AN 
AREA OF LOW PRESSURE TRACKS FROM THE NORTHWEST GULF OF MEXICO TO OFF 
THE SOUTH CAROLINA COAST BY DAYBREAK SATURDAY. HAVE BUMPED POPS UP 
ACCORDINGLY INTO THE LIKELY RANGE AREA WIDE. 

MODEL GUIDANCE IS IN GOOD AGREEMENT LIFTING THE AREA OF LOW PRESSURE 
NORTHEAST AND AWAY FROM THE AREA SATURDAY AND SATURDAY NIGHT...BUT 
DO SO AT VARYING SPEEDS. GIVEN PLENTY OF WRAP AROUND MOISTURE IN 
PLACE ACROSS THE AREA SATURDAY...HAVE BUMPED POPS UP INTO THE CHANCE 
RANGE ALL AREAS...AND HAVE KEPT SLIGHT CHANCE/LOW CHANCE POPS IN 
PLACE SATURDAY NIGHT.  

HIGH PRESSURE IS THEN EXPECTED TO BUILD BACK INTO THE AREA SUNDAY 
THROUGH TUESDAY...WITH RAIN FREE WEATHER EXPECTED.

TEMPERATURES ARE EXPECTED TO RUN WELL BELOW NORMAL THROUGHOUT THE 
EXTENDED PERIODS.

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
A COLD FRONT IS MOVING QUICKLY THROUGH THE TERMS AT THE START OF
THE 06Z TAF PERIOD AND WILL CONTINUE TO SHIFT WINDS TO THE N/NNE.
WINDS WILL BE GUSTY DUE TO STRONG COLD AIR ADVECTION BEHIND THE
FRONT...POSSIBLY REACHING 20 KT...ESPECIALLY AT KCHS. THE
STRONGEST GUSTS ARE EXPECTED UNTIL AROUND DAYBREAK...WHEN WINDS
MAY DIMINISH A BIT BEFORE INCREASING AGAIN. GUSTS SHOULD SUBSIDE
THIS AFTERNOON AS THE LOW-LEVEL WINDS DIMINISH. WE WILL SEE SOME
MVFR CIGS AT BOTH TERMS WITH THE FROPA FOR AT LEAST A FEW
HOURS...THEN VFR CONDS SHOULD PREVAIL BY DAYBREAK ON THROUGH THE
REST OF THE TAF PERIOD.

EXTENDED AVIATION OUTLOOK...VFR CONDITIONS ARE EXPECTED WEDNESDAY
NIGHT THROUGH THURSDAY NIGHT. MVFR OR LOWER CIGS AND/OR VSBYS ARE
LIKELY FRIDAY AND FRIDAY NIGHT...AND POSSIBLE SATURDAY AND
SATURDAY NIGHT AS A STORM SYSTEM PASSES BY OFF THE SOUTHEAST
COAST. VFR CONDITIONS ARE EXPECTED TO RETURN FOR SUNDAY.

&&

.MARINE...
AS OF TUE EVE...
MOVED THE INITIAL TIMES FOR THE SMALL CRAFT ADVISORY AND
GALE WARNING TO CURRENT TIME...OTHERWISE NO MAJOR CHANGES. RUC AND
NAM BOUNDARY LAYER WINDS SHOW 30-35 KT DEVELOPING OVER THE GEORGIA
OFFSHORE WATERS WHERE WATER TEMPERATURES ARE STILL IN THE UPPER
60S TO LOWER 70S. THIS SHOULD SUPPORT AT LEAST FREQUENT GUSTS TO
GALE FORCE...SO THE GALE WARNING FOR AMZ374 WILL REMAIN IN FORCE.
BASED ON MODEL WIND PROGS...THIS EVENT LOOKS FAIRLY SHORT-LIVED
AND BY WED AFTERNOON WINDS AND SEAS SHOULD BE SUBSIDING.

HIGH PRESSURE WILL BUILD BACK INTO THE REGION WEDNESDAY NIGHT AND
THURSDAY...BEFORE A DEVELOPING STORM SYSTEM IN THE GULF OF MEXICO
BEGINS TO TAKE AIM ON THE AREA THURSDAY NIGHT AND FRIDAY. THIS
STORM SYSTEM WILL THEN LIFT NORTHEAST OFF THE SOUTH CAROLINA AND
GEORGIA COAST FRIDAY NIGHT AND SATURDAY...WITH HIGH PRESSURE
BUILDING BACK INTO THE REGION FOR SUNDAY. SMALL CRAFT CONDITIONS
FOR WINDS/SEAS OR A COMBINATION OF THE TWO MAY LINGER ACROSS THE
OUTER GEORGIA WATERS THROUGH SUNDAY.

THE BIGGER STORY MAY BE A NEED FOR GALE WARNINGS OVER PORTIONS OF 
THE WATERS FRIDAY THROUGH SATURDAY...MUCH DEPENDENT ON THE STRENGTH 
AND TRACK OF THE LOW HOWEVER. GIVEN THE UNCERTAINTY...HAVE KEPT 
WINDS AND WIND GUSTS BELOW GALE FORCE...BUT FUTURE SHIFTS WILL NEED 
TO CLOSELY MONITOR THIS DEVELOPING WEATHER SITUATION.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...LAKE WIND ADVISORY UNTIL NOON EST TODAY FOR SCZ045.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EST THIS EVENING FOR AMZ350-
     352.
     SMALL CRAFT ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR AMZ354.
     GALE WARNING UNTIL NOON EST TODAY FOR AMZ374.
     SMALL CRAFT ADVISORY UNTIL NOON EST TODAY FOR AMZ330.

&&

$$