FXUS62 KCHS 051207
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
707 AM EST SAT DEC 5 2009
.SYNOPSIS...
LOW PRES WILL CONSOLIDATE OFF THE COAST THIS MORNING THEN RACE TO
THE NE LATER TODAY. HIGH PRES WILL BUILD N OF THE REGION FOR THE
REMAINDER OF THE WEEKEND. HIGH PRES WILL GIVE WAY TO A COMPLEX
MID WEEK STORM SYSTEM TUE NIGHT INTO WED. HIGH PRES WILL REBUILD
OVER THE REGION FOR THE LATTER HALF OF NEXT WEEK.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A CLASSIC LOOKING COOL SEASON SOUTHEAST U.S. STORM SYSTEM ON
SATELLITE IMAGERY THIS MORNING. RAIN HAS BEEN FAIRLY LIGHT BUT
STEADY OVER MOST OF OUR FORECAST AREA OVERNIGHT. RAINFALL AMOUNTS
HAVE AVERAGED 1/2 TO 3/4 INCH WITH LIGHTER AMOUNTS WELL INLAND AND
SLIGHTLY HIGHER AMOUNTS TO THE S OF SAVANNAH IN PARTS OF SOUTHEAST
GEORGIA AND OVER THE CHARLESTON TRI-COUNTY AREA.
OUR FORECAST PERSISTENCE IS STRONG THIS MORNING AND WE HAVE
MAINTAINED SIMILAR TIMING FOR RAINFALL TO TAPER OFF LATER TODAY.
MAINLY AROUND MIDDAY IN GEORGIA AND EARLY TO MID AFTERNOON IN SE
SOUTH CAROLINA. CLOUDS WILL BEGIN TO DECREASE FROM SW TO NE LATE
DAY AS DECREASING LOW LEVEL DEW POINTS ADVECT IN FROM WSW. WE
LOWERED HIGH TEMPERATURES A BIT TODAY...BUT STILL IN THE 50S JUST
ABOUT EVERYWHERE. WINDS WILL INCREASE THIS AFTERNOON AND WE MAY
SEEM SOME 15-20 MPH GUSTS IN THE MID AFTERNOON TO THE SW OF THE
SAVANNAH RIVER...ESPECIALLY IF CAN CLEAR OUT A BIT SOONER.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
SKIES WILL BECOME MOSTLY CLEAR ALL ZONES THIS EVENING AS NVA
TAKES OVER THE MID LEVELS AND DEEP LAYERED DRYING ENSUES. A TRICKY
TEMPERATURE FORECAST TONIGHT AS COLDER AIR FILTERS IN FROM THE NW
AND N OVERNIGHT. FROM HILLTONIA TO ALLENDALE TO ST. GEORGE WE
THINK A BRIEF FREEZE IS POSSIBLE LATE. SUNDAY SUNRISE TEMPERATURES
ELSEWHERE AWAY FROM THE IMMEDIATE COAST DOWN INTO THE MID 30S.
THESE READINGS ARE CONSISTENT WITH LATE NIGHT WINDS DECOUPLING AND
HIGH CLOUDS NOT REACHING THE AREA UNTIL AFTER DAWN. WE FORECASTED
SCATTERED AREAS OF FRONT INLAND FROM U.S. 17 TONIGHT AND ISSUED A
FROST ADVISORY FOR COUNTIES THAT HAVE NOT SEEN THE GROWING SEASON
END THUS FAR. COASTAL GEORGIA ZONES WERE NOT INCLUDED IN THE
ADVISORY.
ON SUNDAY...IT CONTINUES TO LOOK LIKE A COOL PATTERN AND WE
LOWERED HIGH TEMPERATURES JUST A TAD MOST PLACES. SUNSHINE WILL
BE FILTERED BY HIGH CLOUDS AT TIMES AND THERE MAY BE AN INCREASE
IN COASTAL CLOUDS TO THE S OF CHARLESTON ALONG THE COAST IF
THE GFS/ECMWF STAND CORRECT IN THEIR DEPICTION OF A DEVELOPING
COASTAL SURFACE TROUGH.
&&
.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
A PROGRESSIVE PATTERN WILL PERSIST THROUGH DAY 7 WITH SEVERAL
SYSTEMS AFFECTING THE REGION. SURFACE HIGH PRESSURE WILL PUSH OFF
THE COAST ON MONDAY BEFORE A SECONDARY HIGH FROM CANADA BUILDS DOWN
THE EASTERN SEABOARD ON TUESDAY. A SERIES OF SHORTWAVES MOVING
THROUGH THE SOUTHERN STREAM WILL MAINTAIN WEAK COASTAL TROUGHING
SUNDAY NIGHT THROUGH TUESDAY. ISOLATED LIGHT RAIN SHOWERS COULD
BEGIN TO DEVELOP IN MOISTURE CONVERGENCE OVER THE COASTAL WATERS
SUNDAY NIGHT...SPREADING ACROSS THE ENTIRE AREA MONDAY INTO MONDAY
NIGHT. BY TUESDAY A MORE POTENT UPPER LOW DROPS THROUGH THE CENTRAL
PLAINS AND INTO THE MID-MS VALLEY TUESDAY NIGHT. RAIN CHANCES LOOK
QUITE GOOD TUESDAY NIGHT INTO WEDNESDAY AS ISENTROPIC ASCENT
INCREASES AHEAD OF PRONOUNCED SHORTWAVE ENERGY...THEN A COLD FRONT
PUSHES THROUGH THE AREA. MAINTAINED SOLID CHANCE POPS DURING THIS
PERIOD. A GRADUAL WARM UP IS EXPECTED THROUGH WEDNESDAY BEFORE TEMPS
DROP BACK BELOW NORMAL THURSDAY AND FRIDAY.
&&
.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
AT KCHS...MVFR/IFR CIGS TO PREVAIL TODAY WITH MORNING RAIN ENDING
DURING THE AFTERNOON HOURS AS THE SYSTEM BEGINS TO PULL AWAY FROM
SOUTH CAROLINA. PERIODS OF MVFR VSBY IN LIGHT RAIN CAN ALSO BE
EXPECTED. GIVEN A POTENTIAL FOR LEE/BACK-SIDE LOW CLOUDS SHIFTING
SE FROM THE MIDLANDS THIS AFTERNOON...WE HAVE BEEN A LITTLE MORE
PESSIMISTIC THAN MUCH OF OUR NUMERICAL GUIDANCE IN LIFTING CIGS
TODAY. A RETURN TO VFR CONDITIONS ARE LIKELY AROUND OR SHORTLY
AFTER SUNSET.
AT KSAV...IFR CIGS/MVFR VSBYS IN LIGHT RAIN TO INITIALIZE THIS
MORNING. A TRICKY CIG FORECAST FROM LATE MORNING ON AS 06Z MODEL
SOUNDINGS SHOW DIFFERING SOLUTIONS IN A DOWNSLOPE REGIME. BOTH OUR
CONSCIOUS AND PRIOR EXPERIENCE WITH SIMILAR SYSTEMS TELL US THAT
PLAYING IMPROVING CONDITIONS A BIT SLOWER THAN EXPECTATIONS IS THE
WAY TO LEAN. DOWNSLOPE COMPONENT LOOKS STRONG HOWEVER AND WE HAVE
BASICALLY MAINTAINED PERSISTENCE WITH THE PREVIOUS 06Z TAF CYCLE.
AFTER SUNSET THIS EVENING...CONDITIONS WILL BE VFR.
EXTENDED AVIATION OUTLOOK...VFR LATE SUNDAY. PERIODIC MVFR/IFR CIGS
OR VSBYS POSSIBLE MON THROUGH WED.
&&
.MARINE...
IN THE WAKE OF DEPARTING LOW PRES TO THE NE TODAY...LOW LEVEL
COLD AIR ADVECTION AND PRES RISES ARE ON TAP FOR THE WATERS
AS THE EAST COAST STORM DEEPENS OFF THE MID ATLC COAST. THE PATTERN
IS VERY FAVORABLE FOR JETTING AND SURGING NW FLOW OFF OUR GEORGIA
COAST AND WE HAVE OPTED TO ISSUE SMALL CRAFT ADVISORIES OF ALL OF
OUR GEORGIA WATERS WATERS FROM LATE MORNING INTO TONIGHT. ALONG
THE SOUTH CAROLINA THE GRADIENT TIGHTENS A BIT LATER AND WEAKER
AND WE THINK SCA CONDITIONS WILL DEVELOP MAINLY BEYOND 20 NM OFF
THE COAST. SEAS WILL BUILD TO 2-4 FT WITHIN 20 NM TODAY AND 4-6
FT BEYOND.
ON SUNDAY...A DECENT NNE FLOW IN THE MORNING SHOULD PERSIST GIVEN
THE AVAILABLE THERMAL AND MOISTURE GRADIENTS FROM THE GULF STREAM
TO THE INTRACOASTAL. OVERALL...CONDITIONS WILL LIKELY FALL BELOW
SCA CRITERIA.
A FAIRLY WEAK PRESSURE GRADIENT WILL PREVAIL MON INTO TUE BEFORE A
WARM FRONT LIFTS NORTH AND A SOUTHERLY JET RAPIDLY INCREASES
WINDS/SEAS TUE NIGHT AND WED. WE WILL LIKELY REQUIRE SMALL CRAFT
ADVISORIES DURING THIS PERIOD.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...FROST ADVISORY FROM 3 AM TO 9 AM EST SUNDAY FOR GAZ087-099>101-
114>116-118-137-138-140.
SC...FROST ADVISORY FROM 3 AM TO 9 AM EST SUNDAY FOR SCZ047>051.
MARINE...SMALL CRAFT ADVISORY FROM 10 AM THIS MORNING TO 10 PM EST THIS
EVENING FOR AMZ354.
SMALL CRAFT ADVISORY FROM 10 AM THIS MORNING TO 5 AM EST
SUNDAY FOR AMZ374.
&&
$$
