FXUS62 KCHS 221126
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
626 AM EST TUE DEC 22 2009
.SYNOPSIS...
HIGH PRESSURE LOCATED ACROSS THE SOUTHEASTERN STATES WILL BE
REINFORCED BY ANOTHER HIGH BUILDING IN FROM THE NORTH THROUGH
WEDNESDAY. A WARM FRONT IS EXPECTED TO LIFT NORTH THROUGH THE AREA
LATE THURSDAY NIGHT INTO FRIDAY...FOLLOWED BY A COLD FRONT MOVING
THROUGH FROM THE WEST LATE ON CHRISTMAS DAY. HIGH PRESSURE WILL
BUILD ACROSS THE AREA AGAIN NEXT WEEKEND.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
SKIES HAVE BECOME CLEAR EXCEPT FOR SOME THIN CIRRUS STILL CLOSE TO
THE GA COAST. TEMPS HAVE BEEN VERY SLOWLY FALLING ALONG WITH THE
TDS. SFC TDS HAVE GENERALLY BE ABOVE FREEZING...BUT ARE FALLING
WITH THE TEMPS. THERE IS SOME FROST MIXED IN WITH DEW ON THE CARS
HERE LOCALLY. FEEL THAT FROST WILL STRUGGLE TO FORM IN THE CURRENT
FROST ADVISORY REGION WHERE SFC TDS ARE STILL A FEW DEGS ABOVE
FREEZING. HOWEVER...DECIDED TO LET THE FROST ADVISORY STAND FOR
NOW GIVEN THAT FROST HAS BEEN DEVELOPING COINCIDENT WITH DEW HERE
LOCALLY.
EXPECT MORE SUN TODAY THAN YESTERDAY SINCE CIRRUS DECK HAS NOW
SHIFTED MAINLY OFFSHORE. CONTINUE TO GO NEAR OR SLIGHTLY BELOW
GUIDANCE FOR MAXES TODAY GIVEN A COLD START FOLLOWED BY VERY LIGHT
WINDS THIS AFTERNOON. THE LIGHT WINDS ARE A RESULT OF A SURFACE
RIDGE CENTERED RIGHT OVER THE REGION. THIS RIDGE WILL GRADUALLY
BECOME REINFORCED FROM THE NORTH TODAY AS HIGHER PRESSURE BUILDS
SOUTHWARD FROM A STRONGER CENTER OVER THE GREAT LAKES REGION. WITH
SUCH LIGHT WINDS FEEL IT WILL BE DIFFICULT TO MIX DOWN WARMER
TEMPS THIS AFTERNOON. HOWEVER...IF TEMPS DO REACH AROUND 60...THERE
COULD BE A WEAK AFTERNOON ONSHORE FLOW/SEABREEZE NEAR THE COAST.
CONFIDENCE IN THIS IS LOW.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/...
HIGHER PRESSURE AT THE SURFACE CONTINUES TO BUILD FROM NORTH TO
SOUTH OVER THE REGION. THIS WILL HELP TO FILTER SLIGHTLY DRIER AIR
AT LEAST INTO THE NORTHERN 2/3 OF THE REGION. THIS DRIER
AIR...ALONG WITH MOSTLY CLEAR SKIES COULD ALLOW TEMPS TO ACTUALLY
DROP A DEG OR TWO LOWER THAN THIS MORNING. HAVE INDICATED NEAR
FREEZING TEMPS OVER THE INLAND COUNTIES WITH MENTION OF PATCHY
FROST. WOULD NOT BE SURPRISED IF LATER FORECASTS NEED TO LOWER
MINS A LITTLE MORE AND MAYBE BRING PATCHY TO SCATTERED FROST
FURTHER EAST. ONE BIG VARIABLE IN THE EQUATION OF HOW COLD IT
COULD GET WILL BE THE LOW LEVEL WINDS. WITH THE SLIGHT BUILDING OF
HIGHER PRESSURE FROM THE NORTH...MODELS INDICATE THAT LIGHT NNE WINDS
OF 3-5 MPH COULD PERSIST MUCH OF THE NIGHT. IF THIS HAPPENS...THE
MINS WOULD STAY ABOVE FREEZING MOST AREAS AS GUIDANCE INDICATES.
&&
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
WEDNESDAY...FLAT RIDGING ALOFT WILL KEEP ANY SHORT WAVES NORTH AND
WEST OF THE FORECAST AREA...WHILE A HIGH PRESSURE WEDGE AT THE
SURFACE ESTABLISHES ITSELF TO THE LEE OF THE APPALACHIANS. THE LARGE
SCALE SUBSIDENCE AND OVERALL LACK OF ANY DEEP MOISTURE WILL LIKELY
PREVENT ANY COASTAL SHOWERS FROM MOVING ONSHORE. THUS WE LOOK TO
EXPERIENCE YET ANOTHER DAY TO DRY OUT FOR ALL THE RAINS SO FAR THIS
MONTH. EAST AND NE SYNOPTIC FLOW WILL HOWEVER ALLOW FOR SOME
STRATOCUMULUS TO EITHER DEVELOP OR ADVECT ONSHORE...RESULTING IN
PARTLY TO MOSTLY CLOUDY SKIES. TEMPS NEAR THE COAST WILL ONLY REACH
THE MID OR UPPER DUE TO THE ONSHORE FLOW...BUT INTERIOR AREAS WILL
REACH AS HIGH AS THE LOWER 60S SOUTH OF I-16 IN SE GA.
WEDNESDAY NIGHT...COASTAL WARM FRONT BEGINS TO FORM OVER THE NEARBY
ATLANTIC...AND WHILE THIS WILL PROVIDE SOME COASTAL CONVERGENCE AND
WEAK LIFT...A LARGER SCALE SUBSIDENCE ASSOCIATED WITH RIDGING BOTH
SURFACE AND ALOFT LOOKS TO KEEP ANY SHOWERS OVER THE ATLANTIC
WATERS. TEMPS NOWHERE NEAR AS COLD AS RECENT NIGHTS WITH SYNOPTIC
ONSHORE FLOW AND A FURTHER INCREASE IN CLOUDINESS. LOWEST READINGS
WILL RANGE FROM 38-40 ALONG THE NW TIER TO MID AND UPPER 40S AT THE
COAST.
THURSDAY/THURSDAY NIGHT...OUR LARGE SCALE SUBSIDENCE WILL SLOWLY
DIMINISH AS RIDGING ALOFT SHIFTS EAST. AT THE SAME TIME THE COASTAL
WARM FRONT WILL BEGIN TO PUSH NW TOWARD THE COAST. A DEEPENING
ONSHORE FLOW /FROM THE ATLANTIC IN THE LOWER LEVELS AND FROM THE
GULF OF MEXICO ALOFT/ WILL TRANSPORT INCREASING MOISTURE INTO THE
AREA. LOW LEVEL COASTAL CONVERGENCE WITH THE NEARBY FRONT WILL ALLOW
FOR SLIGHT CHANCE POPS IN THE MORNING...BUT AS DEEPER MOISTURE MOVES
IN FROM THE SW LATE WE HAVE SHOWN POPS INCREASING INTO THE CHANCE
RANGE NEAR THE ALTAMAHA RIVER. MOISTURE DEPTH AND AMOUNT INCREASES
THURSDAY NIGHT...AS LOW LEVEL WIND FIELDS INCREASE FROM OFF THE
ATLANTIC. THERE REMAINS UNCERTAINTY AS TO HOW FAR NW THE COASTAL
WARM FRONT WILL PROGRESS...WITH THE WEDGE STILL IN PLACE. BUT
WITH DEEPER MOISTURE...SHORT WAVES ALOFT AND PROXIMITY TO THE
FRONT WE LOOK FOR POPS TO INCREASE INTO THE LIKELY RANGE AFTER
MIDNIGHT FOR THE ENTIRE AREA. THIS COULD BE A CONCERN FOR THOSE
WHOM WILL BE OUT CHRISTMAS EVE. TEMPS WITHIN THE WEDGE ON THURSDAY
WILL RANGE FROM MID AND UPPER 50S NW TO MIDDLE 60S /AT LEAST/ OVER
THE SE. LOWS THURSDAY NIGHT WILL FALL ONLY ABOUT 8-12 DEGREES FROM
DAILY MAXES WITHIN THE WARM AIR ADVECTION REGIME. ANY
THUNDERSTORMS NEAR THE WARM FRONT LOOK TO REMAIN OVER THE
ATLANTIC.
FRIDAY...THERE DOES REMAIN SOME INDICATIONS THAT A WEAK SURFACE
LOW WILL FORM ALONG THE WARM FRONT OVER OR NEAR THE FORECAST
REGION. BUT THIS DOESN/T APPEAR TOO LIKELY GIVEN THE LACK OF ANY
STRONG SHORT WAVE AND HOW FAR REMOVED ANY TRIPLE POINT WOULD BE
FROM THE PARENT LOW OVER THE CENTRAL STATES. EVEN SO...ABUNDANT
MOISTURE AND LIFT WILL BE PROVIDED BY AN APPROACHING COLD FRONT
AND THE NEARBY WARM FRONT...SO WE HAVE MAINTAINED LIKELY POPS FOR
CHRISTMAS DAY. THE TRAILING COLD FRONT WILL SWEEP THROUGH THE
AREA IN THE AFTERNOON/EVENING...TAPERING POPS FROM WEST TO EAST AS A
RESULT. RISK OF THUNDER IS TOO LOW TO INCLUDE OVER LAND
AREAS. ANOTHER LARGE RANGE OF TEMPS FROM NW TO SE ACROSS THE
REGION FRIDAY ESPECIALLY IF WEDGE HOLDS IN PLACE.
SATURDAY...WHILE HIGH PRESSURE BUILDS FROM THE WEST IN WAKE OF THE
COLD FRONT...UPPER LEVEL JET WILL TRANSPORT CONSIDERABLE HIGH LEVEL
MOISTURE INTO THE REGION. DO NOT BELIEVE THERE IS ENOUGH LOW LEVEL
MOISTURE FOR ANY SHOWERS...BUT CERTAINLY ENOUGH CLOUD COVER TO LIMIT
MAX TEMPS TO NO HIGHER THAN UPPER 50S AND LOWER 60S.
SUNDAY AND MONDAY...SOME COLDER AIR WILL RETURN IN WAKE OF A LOW AND
MID LEVEL TROUGH THAT MOVES THROUGH EARLY NEXT WEEK. DRY NW FLOW
ALOFT AND SURFACE/LOW LEVEL HIGH PRESSURE WILL RESULT IN LARGE SCALE
SUBSIDENCE AND MOSTLY CLEAR SKIES WILL PREVAIL. TEMPS WILL BE BELOW
NORMAL BOTH DAYS.
&&
.AVIATION /11Z TUESDAY THROUGH SATURDAY/...
ALTHOUGH WE DID FORECAST VFR CONDITIONS WITH LITTLE TO NO WINDS
THROUGH 12Z WEDNESDAY...WE DO NEED TO KEEP WATCH FOR SHALLOW
GROUND FOG EARLY THIS MORNING WITH A FEW SITES NEARBY REPORTING
3-5SM. WE WILL ALSO APPROACH OUR CROSS-OVER TEMP LATE TONIGHT
WHICH MAY ALLOW FOR SHALLOW GROUND FOG TO TRY AND FORM.
EXTENDED AVIATION OUTLOOK...VFR WEATHER WILL CONTINUE THROUGH
WEDNESDAY. MVFR CONDITIONS ARE LIKELY...WITH PERHAPS EVEN EVENTUALLY
IFR IN LOW CLOUDINESS...RAIN/SHRA THURSDAY THROUGH FRIDAY. VFR
WEATHER LOOKS TO RETURN SATURDAY. ALSO A POTENTIAL FOR LOW LEVEL
WIND SHEAR LATE THIS WEEK IN ASSOCIATION WITH NEXT FRONTAL SYSTEM.
&&
.MARINE...
SIMILAR TO PAST FEW NIGHTS...BUOYS SHOWING A SURGE IN WINDS OF 15
TO 20 KTS WITH SEAS UP TO 3-4 FT. AS WE APPROACH SUNRISE...EXPECT
WINDS AND SEAS TO SETTLE BACK DOWN TO GENERALLY AROUND 10 KTS FROM
THE NORTH THROUGH TODAY. BY TONIGHT...WITH BETTER NOCTURNAL MIXING
AND A SLIGHTLY STRONGER PRESSURE GRADIENT AS HIGHER PRESSURE
BUILDS FROM THE NORTH...EXPECT SUSTAINED WINDS TO INCREASE BACK
TO 10 TO 15 KTS FROM THE NE. MAY SEE A PERIOD WHERE WINDS GO
CLOSER TO 15 KTS /ESPECIALLY OFFSHORE/ WITH SOME GUSTS CLOSE TO 20
KTS.
EXTENDED MARINE...
A REINFORCING AREA OF HIGH PRESSURE WILL CONTINUE TO BUILD FROM THE
NORTH ON WEDNESDAY...RESULTING IN THE HIGH PRESSURE WEDGE INLAND
BECOMING FIRMLY ESTABLISHED. A COASTAL WARM FRONT WILL THEN FORM AND
ATTEMPT TO PUSH NW INTO AT LEAST PARTS OF THE MARINE AREA THURSDAY.
HOWEVER...WITH THE HIGH PRESSURE WEDGE HOLDING INLAND...THE WARM
FRONT WILL STRUGGLE IN ITS NW PROGRESSION. WEAK LOW PRESSURE MAY
FORM ALONG THE FRONT OVER OR NEAR THE LOCAL WATERS THURSDAY NIGHT OR
FRIDAY...AND WILL MOVE NE...ALLOWING FOR A TRAILING COLD FRONT TO
CLEAR THE WATERS LATE FRIDAY AND FRIDAY NIGHT. THIS IS FOLLOWED BY
HIGH PRESSURE SATURDAY.
WE LOOK FOR A STEADY INCREASE IN NE WINDS WEDNESDAY THROUGH
WEDNESDAY NIGHT...AS A TIGHTER PRESSURE GRADIENT BEGINS TO FORM WITH
THE BUILDING WEDGE. WITH THE FAVORABLE NE FETCH WE COULD BE LOOKING
AT MARGINAL SCA CONDITIONS FOR SOME 6 FOOT SEAS ACROSS THE OUTER GA
WATERS BY 12Z THURSDAY. HOWEVER...AS GREATER PROBABILITY OF SCA/S
FOR ALL WATERS EXISTS THURSDAY AND THURSDAY NIGHT. THIS WILL BE THE
RESULT OF A PINCHED PRESSURE GRADIENT BETWEEN THE INLAND WEDGE AND
THE COASTAL WARM FRONT...AS WINDS AND SEAS CONTINUE TO BUILD. WITH
THE FAVORABLE ONSHORE FETCH...SOME DOUBLE DIGIT SEAS LOOK
PLAUSIBLE...ESPECIALLY ON THE OUTER GA WATERS.
ON FRIDAY THERE MAY BE TEMPORARY DECREASE IN WINDS AS THE PRESSURE
GRADIENT RELAXES...BEFORE WINDS INCREASE AGAIN WITH THE COLD AIR
ADVECTION IN WAKE OF THE NEXT COLD FRONT. SEAS WILL REMAIN ELEVATED
AHEAD OF THE COLD FRONT FRIDAY...THEN BEGIN TO DECREASE AS OFFSHORE
FETCH SETS IN. EVEN IF SOME DECREASE IN WINDS DO DEVELOP...SCA/S
STILL SEEM LIKELY DURING THIS TIME.
MARGINAL SCA/S ARE STILL POSSIBLE ACROSS PARTS OF THE MARINE AREA
SATURDAY WITH FLUCTUATIONS IN COLD AIR ADVECTION AND STILL A MODEST
PRESSURE GRADIENT TO PERSIST.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...FROST ADVISORY UNTIL 9 AM EST THIS MORNING FOR GAZ117-119-
139>141.
SC...FROST ADVISORY UNTIL 9 AM EST THIS MORNING FOR SCZ048-049-051.
MARINE...NONE.
&&
$$
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