FXUS62 KCHS 281122
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
622 AM EST SAT NOV 28 2009
...FREEZING TEMPERATURES OCCURRING WELL INLAND THIS MORNING...
.SYNOPSIS...
HIGH PRESSURE WILL EXTEND ACROSS THE REGION THROUGH MONDAY. A
COLD FRONT WILL MOVE INTO THE AREA FROM THE NORTHWEST MONDAY
NIGHT...THEN STALL SOUTH OF THE AREA ON TUESDAY. A GULF LOW
PRESSURE SYSTEM WILL DEVELOP TUESDAY AND MOVE UP THE COAST
WEDNESDAY THROUGH THURSDAY...FOLLOWED BY HIGH PRESSURE LATE
IN THE WEEK.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
THE FREEZE WARNING AND FROST ADVISORY APPEAR TO BE WORKING OUT
VERY WELL. COMPLETE BOUNDARY LAYER DECOUPLING HAS OCCURRED FOR
MOST LOCATIONS EXCEPT ALONG THE IMMEDIATE COAST WHERE WINDS HAVE
TIPPED MORE NORTHERLY AT 5-10 MPH. CURRENT DATA SUGGEST WE WILL
BE ABLE TO END THE GROWING SEASON FOR A NUMBER OF INLAND COUNTIES
LATER THIS MORNING. THE DECISIONS ON WHICH COUNTIES CAN BE
CLEARED WILL BE LEFT TO THE DAY SHIFT AND WILL BE COORDINATED WITH
WFOS COLUMBIA AND WILMINGTON AFTER THE MORNING COOPERATIVE
OBSERVER REPORTS ARE RECEIVED.
PRELIMINARY LOW TEMPERATURES AS OF 6 AM...
SUMMERVILLE AIRPORT... 30
WITHERBEE RAWS........ 31
ROUND O............... 31
SMOAKS................ 31
MONCKS CORNER AIRPORT. 32
WALTERBORO AIRPORT.... 32
SYLVANIA AIRPORT...... 32
CHARLESTON AIRPORT.... 34
SAVANNAH AIRPORT...... 37
HIGH PRESSURE CENTERED OVER THE WESTERN FLORIDA PANHANDLE WILL
MOVE SLOWLY EAST TODAY AS HEIGHTS BUILD ALOFT. CIRRUS WILL BE ON
THE INCREASE THROUGHOUT THE DAY AS A SOUTHERN STREAM SHORTWAVE
OVER LOUISIANA MOVES NORTHEAST ACROSS THE LOWER MISSISSIPPI
VALLEY. THE CIRRUS SHOULD REMAIN FAIRLY THIN THIS MORNING...BUT
WILL GRADUALLY THICKEN FROM SOUTHWEST TO NORTHEAST AS THE DAY
PROGRESSES IN RESPONSE TO 300MB WINDS BACKING AHEAD OF THE
APPROACHING SHORTWAVE. EXPECT SKIES TO BECOME PARTLY CLOUDY
ACROSS MUCH OF SOUTHEAST GEORGIA WITH MOSTLY SUNNY SKIES
PREVAILING UNTIL LATE IN THE AFTERNOON FOR SOUTHEAST SOUTH
CAROLINA. LOW-LEVEL THICKNESSES AND FORECAST SOUNDINGS SUPPORT
HIGHS IN THE LWR-MID 60S.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
SURFACE HIGH PRESSURE WILL BUILD EAST TONIGHT AND BE CENTERED
ALONG THE LOWER SOUTH CAROLINA COAST BY SUNRISE SUNDAY. ALTHOUGH
CALM WINDS ARE EXPECTED AS THE BOUNDARY LAYER DECOUPLES...300MB RH
PROGS SHOW CIRRUS HOLDING OVER MUCH OF THE REGION UNTIL WELL AFTER
MIDNIGHT. THIS WILL LIKELY HAVE AN IMPACT ON OVERNIGHT LOWS WITH
LOWS RANGING FROM AROUND 36-37 WELL INLAND TO THE MID 40S CLOSER
TO THE BEACHES. THE BEST CHANCES FOR PATCHY FROST WILL BE CONFINED
TO AREAS WELL INLAND...ROUGHLY FROM JENKINS COUNTY EAST TO THE
NORTHERN PARTS OF BERKELEY COUNTY AWAY FROM LAKE MOULTRIE. SHOULD
THE CIRRUS THIN QUICKER THAN EXPECTED AND TEMPERATURES DROP MORE
THAN FORECAST...THE RISK FOR SCATTERED FROST MAY INCREASE. ITS TOO
SOON TO TELL WHETHER THE GROWING SEASON WILL COME TO AN END FOR
THIS AREA WITH THIS MORNING/S FROST-FREEZE EVENT...BUT IF IT DOES
NOT...THEN A FROST ADVISORY MAY BE CONSIDERED.
HIGH PRESSURE WILL SLOWLY SHIFT OFFSHORE SUNDAY AS THE UPPER RIDGE
FLATTENS ALOFT THE THE FLOW BECOMES MORE ZONAL. EXPECT A MAINLY
SUNNY SKY AND DRY CONDITIONS WITH HIGHS IN THE LOWER 70S.
&&
.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
AN UPPER LEVEL SHORTWAVE WILL PROGRESS FROM THE OHIO VALLEY INTO
THE MID ATLANTIC STATES SUNDAY NIGHT THROUGH MONDAY...ALLOWING A
COLD FRONT TO SHIFT SOUTHEAST TOWARD THE FORECAST AREA. TIMING OF
THE COLD FRONT IS FAIRLY UNIFORM BETWEEN THE MODELS...WITH THE
BOUNDARY PUSHING INTO THE COASTAL WATERS MONDAY NIGHT. TEMPERATURES
THAT WERE UNSEASONABLY WARM ON MONDAY WITHIN SOUTHWEST FLOW AHEAD
OF THE FRONT WILL BE NOTICEABLY COOLER BY TUESDAY...AS FLOW VEERS
TO THE NORTH-NORTHEAST. WILL MAINTAIN A 30 PERCENT CHANCE OF RAIN
MONDAY NIGHT WITH THE COLD FRONT PASSAGE...THEN INDICATE POPS
BRIEFLY DECREASING ON TUESDAY FROM NORTHWEST TO SOUTHEAST AS THE
FRONT STALLS SOUTH OF THE FORECAST AREA.
AS THE FRONT DIPS SOUTH AND HIGH PRESSURE BRIEFLY BUILDS IN FROM
THE NORTH...A POTENT SOUTHERN STREAM SHORTWAVE WILL DEVELOP OVER
TEXAS AND ASSIST IN THE SPIN-UP OF A GULF LOW PRESSURE SYSTEM BY
WEDNESDAY. ECMWF AND GFS HAVE BEEN FAIRLY CONSISTENT WITH EACH
OTHER FOR THE PAST SEVERAL MODEL RUNS CONCERNING THE GENERAL
EVOLUTION OF THIS SYSTEM...LENDING SOME CONFIDENCE TO THE MID
RANGE FORECAST.
THE LINGERING BOUNDARY TO THE SOUTH WILL LIFT NORTH AS A WARM
FRONT LATE TUESDAY...SUPPORTING STRONG WARM ADVECTION AND SOLID
RAIN CHANCES TUESDAY NIGHT INTO WEDNESDAY. THERE ARE SOME
DIFFERENCES IN THE PRESSURE PATTERN AS THE SURFACE LOW SHIFTS
NORTHEAST FROM THE GULF OF MEXICO...HOWEVER QPF FIELDS BETWEEN
MEDIUM RANGE MODELS SOLIDLY SUGGEST HEAVY RAIN WILL OCCUR OVER THE
AREA WEDNESDAY. HAVE THEREFORE RAISED POPS INTO THE LIKELY RANGE
FOR THE DAYTIME HOURS ON WEDNESDAY DUE TO THIS MODEL CONSISTENCY.
PERHAPS THE MAIN QUESTION REMAINS WHETHER THE DOMINANT LOW CENTER
WILL PROGRESS MORE INLAND BEFORE SHIFTING OFF THE MID ATLANTIC
COASTLINE...OR WHETHER THE LOW WILL BECOME MORE FOCUSED ALONG THE
GEORGIA/CAROLINA COAST AND TRACK ENTIRELY ALONG THE SOUTHEAST
COAST.
EITHER WAY...THE STORM SYSTEM WILL DRAG ANOTHER COLD FRONT THROUGH
THE AREA ON THURSDAY...AND HAVE DECREASED RAIN CHANCES BEHIND THE
FRONT ACCORDINGLY. HIGH PRESSURE WILL THEN MOVE INTO THE REGION
AND MAINTAIN A PERIOD OF RAIN FREE WEATHER LATER IN THE WEEK.
EXPECT TEMPERATURES TO COOL BEHIND THE SECOND COLD FRONT ON
THURSDAY...WITH OVERNIGHT LOWS FALLING INTO THE UPPER 30S INLAND
FRIDAY MORNING.
&&
.AVIATION /11Z SATURDAY THROUGH WEDNESDAY/...
VFR CONDITIONS WILL DOMINATE THROUGH 12Z AT KCHS AND KSAV.
EXTENDED AVIATION OUTLOOK...MVFR OR LOWER CIGS/VSBYS POSSIBLE MON
NIGHT THROUGH WED DUE TO RAIN CHANCES WITHIN UNSETTLED WEATHER.
&&
.MARINE...
WINDS ARE STARTING TO SUBSIDE ACROSS THE WATERS THIS MORNING AS
HIGH PRESSURE DRAWS CLOSER. OBSERVATIONS FROM 41004 AND 41008
SUGGEST WINDS REMAIN ELEVATED ENOUGH OVER THE GEORGIA OFFSHORE LEG
TO EXTEND THE SMALL CRAFT ADVISORY THERE THROUGH 8 AM. OTHERWISE
WILL CANCEL THE SMALL CRAFT ADVISORY FOR THE GEORGIA NEARSHORE
WATERS WITH THIS FORECAST PACKAGE. BOTH WINDS AND SEAS WILL
STEADILY DIMINISH TODAY WITH WINDS EXPECTED TO BECOME LIGHT AND
VARIABLE ACROSS MUCH OF THE NEARSHORE WATERS SOUTH OF EDISTO
BEACH.
LIGHT AND VARIABLE WINDS WILL CONTINUE INTO TONIGHT WITH HIGH
PRESSURE CENTERED ALONG THE LOWER SOUTH CAROLINA COAST. WINDS MAY
BACK TO THE SOUTHWEST CLOSER TO SUNRISE SUNDAY BUT SPEEDS WILL BE
5 KT OR LESS. SOUTHERLY WINDS WILL FINALLY INCREASE SUNDAY AS
HIGH PRESSURE SHIFTS FARTHER OFFSHORE AND A RESULTANT SEA BREEZE
DEVELOPS ALONG THE LAND/SEA INTERFACE.
SUNDAY NIGHT THROUGH WEDNESDAY...THE PRESSURE GRADIENT WILL
TIGHTEN SUNDAY NIGHT INTO MONDAY AS A COLD FRONT APPROACHES THE
REGION. ALTHOUGH SOUTHWEST WINDS WILL INCREASE AS A
RESULT...CURRENT THINKING IS THAT CONDITIONS WILL REMAIN BELOW
ADVISORY CRITERIA PRIOR TO FRONTAL PASSAGE.
THE FRONT WILL DROP THROUGH THE AREA MONDAY NIGHT...WITH COLD
ADVECTION BEHIND THE FRONT CREATING A SURGE IN NORTH TO NORTHEAST
WINDS ON TUESDAY. ADVISORIES ARE POSSIBLE FOR THE OFFSHORE GEORGIA
WATERS DUE TO A COMBINATION OF FREQUENT 25 KT WIND GUSTS AND SEAS
BUILDING ABOVE 6 FT.
MARINE CONDITIONS WILL THEN DETERIORATE RAPIDLY LATE TUESDAY
NIGHT INTO WEDNESDAY...AS A GULF LOW PRESSURE SYSTEM MOVES UP THE
SOUTHEAST COAST AND FURTHER TIGHTENS THE PRESSURE GRADIENT OVER
THE WATERS. THE EXACT STRENGTH AND TRACK OF THE SYSTEM WILL HAVE A
HUGE IMPACT ON WIND SPEEDS AND WAVE HEIGHTS OVER THE WATERS. AT
LEAST SMALL CRAFT ADVISORY CONDITIONS ARE POSSIBLE FOR ALL WATERS
MID WEEK WITHIN STRONG SOUTH TO SOUTHWEST FLOW. HAVE USED A BLEND
OF ECMWF AND GFS FOR THE MORNING FORECAST PACKAGE.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...FROST ADVISORY UNTIL 9 AM EST THIS MORNING FOR GAZ099>101-
114>116-118-137-138-140.
FREEZE WARNING UNTIL 9 AM EST THIS MORNING FOR GAZ087-088.
SC...FROST ADVISORY UNTIL 9 AM EST THIS MORNING FOR SCZ047>051.
FREEZE WARNING UNTIL 9 AM EST THIS MORNING FOR SCZ040-042>045.
MARINE...SMALL CRAFT ADVISORY UNTIL 8 AM EST THIS MORNING FOR AMZ374.
&&
$$
