FXUS62 KCHS 260525
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1225 AM EST THU NOV 26 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 THIS MORNING/...
DENSE FOG IS QUICKLY BECOMING WIDESPREAD AS SKIES CLEAR IN THE
WAKE OF THE CIRRUS SHIELD. VSBYS ACROSS MUCH OF INTERIOR SOUTHEAST
GEORGIA HAVE ALREADY DROPPED TO LESS THAN 1/2 MILE AND CONDITIONS
SHOULD CONTINUE TO DETERIORATE AS THE NIGHT PROGRESSES. WILL ISSUE
A DENSE FOG ADVISORY FOR ALL BUT THE COASTAL ZONES. THE ADVISORY
MAY HAVE TO BE EXPANDED TO THE COAST OVER THE NEXT SEVERAL HOURS.
THERE IS SOME UNCERTAINLY ON HOW QUICKLY VSBYS WILL LIFT AS 1000MB
GEOSTROPHIC WINDS ARE FORECAST TO INCREASE AFTER 09Z...WHICH MAY
TRANSITION THE FOG TO STRATUS. WILL CARRY THE ADVISORY THROUGH 8
AM TO START...BUT MAY NEED TO BE MODIFIED LATER ONCE MORE
DEFINITIVE TRENDS ARE ESTABLISHED.
&&
.SHORT TERM /6 AM THIS MORNING THROUGH 6 AM FRIDAY/...
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 /05Z THURSDAY THROUGH MONDAY/...
THE BACK EDGE OF THE CIRRUS SHIELD WILL CLEAR THE KCHS TERMINAL
OVER THE NEXT 1-2 HOURS. FOG IS QUICKLY FILLING IN AS SKIES CLEAR
WITH MANY UPSTREAM OBSERVATIONS AT 26/05Z REPORTING VSBYS AS LOW
AS 1/4SM. GUIDANCE HAS BEEN SLOW TO PICKUP ON CURRENT VSBY TRENDS
AND WITH CLEAR SKIES AND FAIRLY LIGHT WINDS EXPECTED TO CONTINUE...
AREAS OF FOG SHOULD IMPACT THE TERMINALS THROUGH SUNRISE. HAVE
TRENDED VSBYS LOWER AT BOTH TERMINALS WITH THE 06Z TAFS...SHOWING
VSBYS PREVAILING IFR AT KSAV BY 08Z. CONDITIONS MAY STAY A BIT
HIGHER AT KCHS BUT STILL EXPECT AT LEAST A TEMPORARY STINT OF IFR
VSBYS FROM 09-12Z. THERE IS A REASONABLE POSSIBILITY THAT VSBYS
MAY CRATER TO SOLID LIFR AT EITHER SITE...BUT WITH 1000MB
GEOSTROPHIC WINDS FORECAST TO INCREASE AFTER 09Z...AM HESITANT TO
SHOW THOSE CONDITIONS JUST YET. AMENDMENTS WILL MOST CERTAINLY BE
NEEDED OVER THE NEXT FEW HOURS AS TRENDS BECOME MORE APPARENT. THE
FOG WILL BURN OFF FAIRLY QUICKLY AFTER SUNRISE WITH VFR CONDITIONS
PREVAILING THEREAFTER.
EXTENDED AVIATION OUTLOOK...VFR CONDITIONS ARE EXPECTED TO
PREVAIL THROUGH SUNDAY. MVFR CONDITIONS ARE POSSIBLE MONDAY AHEAD
OF A POTENT STORM SYSTEM.
&&
.MARINE...
WINDS WILL SWING AROUND TO THE NORTHWEST OVERNIGHT AS AN AREA OF LOW
PRESSURE OFF THE CAROLINA COAST CONTINUES TO TRACK NORTHEAST AND
AWAY FROM THE REGION...AND HIGH PRESSURE BEGINS TO BUILD IN FROM THE
WEST. WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT
THRESHOLDS THROUGH THE NIGHT.
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...DENSE FOG ADVISORY UNTIL 8 AM EST THIS MORNING FOR GAZ087-088-
099>101-114>116-118-137-138-140.
SC...DENSE FOG ADVISORY UNTIL 8 AM EST THIS MORNING FOR SCZ040-
042>045-047.
MARINE...SMALL CRAFT ADVISORY FROM 7 PM THIS EVENING TO 10 AM EST
FRIDAY FOR AMZ350-352.
SMALL CRAFT ADVISORY FROM 10 PM THIS EVENING TO 5 AM EST
FRIDAY FOR AMZ354.
SMALL CRAFT ADVISORY FROM 7 PM THIS EVENING TO 5 PM EST FRIDAY
FOR AMZ374.
&&
$$
