754
FXUS62 KCHS 252337
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
637 PM EST WED NOV 25 2009
SYNOPSIS
HIGH PRESSURE WILL BUILD IN FROM THE WEST TONIGHT. A DRY COLD
FRONT WILL MOVE THROUGH THE AREA THURSDAY...WITH HIGH PRESSURE
THEN BUILDING INTO THE REGION THROUGH SUNDAY. ANOTHER STORM SYSTEM
WILL APPROACH THE REGION EARLY NEXT WEEK.
NEAR TERM /UNTIL 6 AM THURSDAY MORNING/
AS LOW PRESSURE OFF THE NC/SC COAST SHIFTS OFF TO THE NE
TONIGHT...HIGH PRESSURE WILL START TO MOVE IN FROM THE W.
LINGERING SHOWERS WILL SHIFT OFFSHORE AND CLOUDS WILL CONTINUE TO
LIFT AND DISSIPATE THROUGH THE OVERNIGHT HOURS AS DRIER AIR ENTERS
THE REGION. SKIES WILL BE MOSTLY CLEAR BY EARLY MORNING THURSDAY
FOR MUCH OF THE CHS CWFA. MOST AREAS WILL HAVE WINDS SETTLE DOWN
DUE TO DECOUPLING FROM THE NIGHTLY INVERSION...SETTING UP GROUND
FOG DEVELOPMENT WITH THE LOW LEVEL MOISTURE TRAPPED UNDER THE
INVERSION. MET MOS GUIDANCE AND SREF FORECAST PROGS HINT AT THIS
SCENARIO SO HAVE INCLUDED PATCHY FOG FOR LATE TONIGHT.
LOWS WELL INLAND WILL DROP INTO THE UPPER 30S WHILE LOW-MID 40S
WILL BE MORE COMMON AWAY FROM THE COAST. NEAR THE SHORES...LOWS
WILL ONLY DROP TO THE LWR 50S.
SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/
MODEL SOLUTIONS SHOW A DRY BUT POTENT COLD FRONT PUSHING THROUGH
THE AREA LATE THANKSGIVING DAY...BRINGING A NOTICEABLE PUNCH OF
COLD AIR TO THE REGION FOR THURSDAY NIGHT. THE LACK OF ANY
MOISTURE WITH THE FRONT WILL MAKE FOR A PRECIPITATION-FREE AND
MOSTLY CLEAR THURSDAY FOLLOWED BY HIGH PRESSURE MOVING IN
THURSDAY NIGHT...MAINTAINING CLEAR SKIES.
WITH COLD AIR ADVECTION NOT KICKING IN UNTIL THURSDAY NIGHT... MAX
TEMPS FOR THANKSGIVING WILL BE RIGHT AROUND NORMAL...GENERALLY IN
THE MID TO UPR 60S WITH A FEW 70-DEGREE READINGS POSSIBLE IN ERN
PORTIONS OF THE AREA. TEMPS WILL DROP OFF QUICKLY TMRW NIGHT AS
STRONG NOCTURNAL DOWNSLOPING WILL FORCE MIN TEMPS INTO THE MID 30S
WELL INLAND AND LWR 40S ALONG THE COAST. WITH WINDS NOT QUITE
CALMING DOWN AND A VERY DRY AIRMASS ENTERING THE AREA...EVEN
PATCHY FROST DOES NOT LOOK FAVORABLE TO DEVELOP SO HAVE NOT
INCLUDED IT IN THE FORECAST FOR THU NIGHT.
LONG TERM /FRIDAY THROUGH WEDNESDAY/
MEDIUM RANGE GUIDANCE IS IN RATHER GOOD AGREEMENT THROUGH SUNDAY
NIGHT LEADING TO NORMAL TO ABOVE NORMAL FORECAST CONFIDENCE...THEN
CONFIDENCE LOWERS THROUGH MID WEEK AS MODELS DIFFER WITH RESPECT
TO A LOW PRESSURE SYSTEM MOVING INTO THE GREAT LAKES.
HIGH PRESSURE WILL SLIDE WEST TO EAST OVER THE AREA FRIDAY THROUGH
THE WEEKEND PROVIDING DRY BUT UNSEASONABLY COOL CONDITIONS. IN
FACT...FROST/FREEZE CONDITIONS ARE EXPECTED ACROSS INLAND AREAS
FRIDAY...SATURDAY AND SUNDAY MORNINGS.
RETURN FLOW ON THE WESTERN SIDE OF THE HIGH WILL SET UP ACROSS THE
FORECAST AREA SUNDAY. MODEL DIFFERENCES BEGIN SUNDAY NIGHT INTO
MONDAY REGARDING A DEVELOPING AREA OF LOW PRESSURE MOVING FROM THE
LOWER MISSISSIPPI VALLEY NORTHEAST INTO THE GREAT LAKES REGION.
FOR NOW HAVE FOLLOWED THE SLOWER ECMWF/HPC SOLUTION...MAINLY FOR
CONSISTENCY PURPOSES. THIS KEEPS DEEP MOISTURE OVER THE AREA
THROUGH WEDNESDAY AND THUS WILL MAINTAIN A CHANCE FOR SHOWERS
MONDAY THROUGH WEDNESDAY...WITH HIGHEST CHANCES MONDAY NIGHT INTO
TUESDAY. WE MAY EVEN BE DEALING WITH SOME THUNDERSTORMS DURING
THIS PERIOD BUT KEPT CHANCES MINIMAL FOR NOW DUE TO THE
UNCERTAINTY IN THE AMOUNT OF INSTABILITY THAT CAN DEVELOP.
BELOW AVERAGE TEMPERATURES WILL PERSIST THROUGH SUNDAY
MORNING...THEN SHOULD RETURN ABOVE NORMAL SUNDAY THROUGH
WEDNESDAY.
AVIATION /00Z THURSDAY THROUGH MONDAY/
OVERCAST HIGH LEVEL CLOUD COVER WILL CLEAR AS DRIER AIR FILTERS
IN FROM THE WEST OVERNIGHT. THE CLEAR SKIES...MOIST GROUND
CONDITIONS FROM EARLIER RAINFALL...AND WINDS BELOW 5 KT WILL
SUPPORT SOME PATCHY FOG FORMATION AT THE TERMINALS DURING THE PRE-
DAWN HOURS. AS A RESULT...THE FORECAST WILL REFLECT TEMPORARY
VISIBILITY REDUCTIONS TO MVFR LEVELS IN THE 08-12Z TIME FRAME.
OTHERWISE...VFR CONDITIONS WILL PREVAIL AT BOTH KCHS AND KSAV
THROUGH 00Z FRIDAY.
EXTENDED AVIATION OUTLOOK...VFR CONDITIONS ARE EXPECTED TO
PREVAIL THROUGH SUNDAY. MVFR CONDITIONS ARE POSSIBLE MONDAY AHEAD
OF A POTENT STORM SYSTEM.
MARINE
AS HIGH PRESSURE ENTERS FROM THE W BEHIND THE DEPARTING COASTAL
LOW PRESSURE SYSTEM...WINDS WILL BACK TO WNW WITH SPEEDS NO HIGHER
THAN 15 KT. SEAS WITHIN 20 NM OF SHORE WILL BE CAPPED AT 2 FT
WHILE THE OUTER GA WATERS WILL SEE 3-4 FOOT WAVES.
A COLD FRONT WILL MOVE THROUGH THE WATERS LATE THURSDAY...WITH
STRONG COLD AIR ADVECTION TO FOLLOW THURSDAY NIGHT. SPEEDS WILL
LIKELY RISE ABOVE 20 KT FOR ALL MARINE ZONES /EXCEPT CHAS HARBOR/
BY LATE THU EVENING. THE STRONG SURGE LOOKS TO LAST FOR MUCH OF
THE NIGHT SO HAVE ISSUED SMALL CRAFT ADVISORIES FOR ALL NEARSHORE
ZONES AND THE OUTER GA WATERS STARTING THU EVENING. THE OFFSHORE
FETCH WILL PREVENT MUCH RISE IN THE NEARSHORE WATERS BUT THE OUTER
GA WATERS WILL SEE SEAS REACH THE 6-7 FOOT RANGE.
FRIDAY THROUGH MONDAY...SMALL CRAFT ADVISORY CONDITIONS SHOULD
CONTINUE INTO FRIDAY MORNING AS COLD AIR ADVECTION AND A TIGHT
PRES GRADIENT LINGER OVER THE AREA. OTHERWISE...HIGH PRES WILL
BUILD INTO THE AREA THROUGH THE WEEKEND WITH RATHER BENIGN MARINE
CONDITIONS.
AN APPROACHING COLD FRONT WILL LEAD TO AN INCREASE IN WINDS MONDAY
BUT CONDITIONS SHOULD REMAIN BELOW ADVISORY THRESHOLDS.
CHS WATCHES/WARNINGS/ADVISORIES
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 7 PM THURSDAY TO 10 AM EST FRIDAY
FOR AMZ350-352.
SMALL CRAFT ADVISORY FROM 7 PM THURSDAY TO 5 PM EST FRIDAY FOR
AMZ374.
SMALL CRAFT ADVISORY FROM 10 PM THURSDAY TO 5 AM EST FRIDAY
FOR AMZ354.
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