FXUS62 KCHS 080210
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
910 PM EST MON DEC 7 2009
.SYNOPSIS...
HIGH PRESSURE WILL REMAIN NORTH OF THE REGION THROUGH EARLY
TUE...WHILE A WEAK SURFACE TROUGH RESIDES OFFSHORE. A LOW PRESSURE
SYSTEM TO THE WEST WILL AFFECT THE REGION LATE TUESDAY INTO
WEDNESDAY. HIGH PRESSURE WILL THEN BUILD OVER THE REGION THROUGH FRI
BEFORE A GULF LOW PRESSURE SYSTEM AFFECTS THE AREA LATE FRI INTO THE
WEEKEND.
&&
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
THE FORECAST IS ON TRACK SO FAR. PINNING DOWN OVERNIGHT CLOUD
COVER IS PROVING DIFFICULT WITH THE VARIOUS SHORT TERM GUIDANCE
PACKAGES ESSENTIALLY SPLITTING THE DIFFERENCE ON THE DURATION AND
EXTENT OF LOW CLOUD COVERAGE AFTER MIDNIGHT. EITHER WAY INCOMING
MID-LEVEL CLOUDS OVER CENTRAL GEORGIA SHOULD KEEP THINGS RATHER
CLOUDY FOR MUCH OF THE NIGHT. ALTHOUGH THERE WILL BE PERIODS OF
PARTLY CLOUDY OR EVEN CLEAR CONDITIONS THIS EVENING...WE BELIEVE
MOSTLY CLOUDY WILL BE THE PRIMARY MODE AFTER MIDNIGHT...BUT IT
SHOULD BE NOTED THAT THIS IS A LOW CONFIDENCE FORECAST. WILL MAKE
SOME MINOR TEMPERATURE CHANGES...BUT NOTHING OF MAJOR CONSEQUENCE.
&&
.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
THE WEATHER PATTERN WILL BE IN A TRANSITION PERIOD ON TUESDAY...AS
THE INLAND WEDGE BEGINS TO BREAK DOWN AHEAD OF A COMPLEX LOW
SYSTEM DRIVING FROM THE CENTRAL PLAINS INTO THE OHIO VALLEY. THERE
IS QUITE A BIT OF DISAGREEMENT BETWEEN THE NAM AND GFS REGARDING
THE SPEED WITH WHICH A WARM FRONT WILL ERODE THE WEDGE...DIRECTLY
IMPACTING THE SENSIBLE WEATHER FORECAST. GFS IS MUCH MORE AGGRESSIVE
IN BREAKING DOWN THE HIGH PRESSURE WEDGE AND INTRODUCING RAIN
CHANCES INTO THE AREA TUESDAY MORNING...WHILE THE SLOWER NAM IS A
MUCH DRIER OUTLIER. 09Z SREF RUN SEEMS A GOOD BLEND OF THE TWO
MODELS...MORE CONSERVATIVE THAN THE GFS...WHILE STILL INDICATING
SOME CHANCE FOR RAIN LATE IN THE AFTERNOON ON TUESDAY. CONSIDERING
THAT COARSER RESOLUTION MODELS TEND TO ERODE THE WEDGE TOO
FAST...HAVE OPTED TO LEAN TOWARD THE NAM AS WELL AS THE SREF.
DELAYED THE INTRODUCTION OF RAIN CHANCES UNTIL 18Z ON TUESDAY.
ALTHOUGH A STRAY SHOWER OR TWO CANNOT BE RULED OUT BEFORE
THEN...FEEL THAT THE MAJORITY OF THE SHOWER ACTIVITY ASSOCIATED
WITH THE LIFTING WARM FRONT WILL OCCUR LATER IN THE DAY.
CONSIDERING THE MODEL DIVERGENCE REGARDING RAIN POTENTIAL...HAVE
OPTED TO MAINTAIN PERSISTENCE AND KEEP POPS IN THE 30 TO 40
PERCENT RANGE...HIGHEST FOR THE FAR INLAND LOCATIONS. HAVE KEPT
THUNDER OUT OF THE FORECAST FOR TUESDAY...AS INSTABILITY IS
INSUFFICIENT.
THE TEMPERATURE FORECAST FOR TUESDAY AFTERNOON COULD PROVE TO BE
VERY PROBLEMATIC...BEING GREATLY AFFECTED BY THE AMOUNT OF CLOUD
COVER AND THE TIMING OF SHOWERS. HAVE REFLECTED A LINGERING INLAND
WEDGE AND EARLIER SHOWER POTENTIAL ACROSS INLAND AREAS IN THE HIGH
TEMPERATURE GRADIENT...BY TRENDING FROM THE UPPER 50S INLAND TO
THE MID 60S FAR SOUTHEAST GEORGIA.
&&
.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
MEDIUM RANGE MODEL GUIDANCE IS IN RATHER GOOD AGREEMENT IN THE
OVERALL PATTERN THIS PERIOD BUT OF COURSE THERE ARE SOME SMALLER
SCALE DIFFERENCES THAT PRESENT MORE OF A CHALLENGE...ESPECIALLY LATE
IN THE WEEK.
A WARM FRONT IS EXPECTED TO PUSH N THROUGH THE AREA TUE NIGHT AS A
STRONG AREA OF LOW PRES MOVES NE INTO THE GREAT LAKES REGION. PREFER
THE SLOWER PROGRESSION OF THE WARM FRONTAL PASSAGE AS PER THE NAM12
DUE TO THE HIGH PRES WEDGE THAT WILL ALREADY BE IN PLACE.
HOWEVER...THE FRONT SHOULD BE N OF THE FORECAST AREA BY DAYBREAK WED
ALLOWING A RECOVERY OF DEWPOINTS BACK INTO THE MID 60S. THE TRAILING
COLD FRONT FROM THE LOW PRES MOVING THROUGH THE GREAT LAKES LOOKS TO
PUSH THROUGH OUR FORECAST AREA EARLY WED EVENING...ALTHOUGH IT LOOKS
TO BE IN A WEAKENING MODE AS THE BEST UPPER-LEVEL FORCING SHOULD BE
WELL REMOVED TO THE NW. THERE IS THE POTENTIAL FOR A FEW
THUNDERSTORMS BUT THERE DOES NOT APPEAR TO BE A BIG SEVERE WEATHER
THREAT ATTM. THE MAIN HAZARD WOULD MOST LIKELY BE STRONG GUSTY WINDS
WITH ANY CELL THAT CAN SUSTAIN AN UPDRAFT DUE TO THE STRONG
LOW-LEVEL JET IN PLACE. HAVE KEPT THE HIGHEST POPS /60S-70S/ WITH
THE WARM FRONTAL OVERRUNNING RAIN TUE NIGHT...MAINLY ACROSS NORTHERN
PORTIONS OF THE FORECAST AREA. POPS WILL BE NO HIGHER THAN 50
PERCENT WED...HIGHEST ACROSS INTERIOR PORTIONS OF THE FORECAST AREA.
DRIER/COOLER CONDITIONS EXPECTED TO MOVE IN BY THU AND PERSIST
THROUGH MUCH OF FRI BEFORE ANOTHER STORM SYSTEM COMES OUT OF THE
GULF OF MEXICO. RAIN LOOKS TO SPREAD INTO SE GA...POSSIBLY AS EARLY
AS LATE FRI...THEN UP INTO SE SC LATE FRI INTO SAT. TEMPERATURES
LOOK A BIT TOO WARM FOR FROZEN PRECIP INLAND SAT MORNING BUT WILL
CERTAINLY HAVE TO KEEP AN EYE ON THIS AS MID 30S ARE FORECAST.
OTHERWISE...POPS WILL REMAIN THROUGH SAT NIGHT FOR MOST OF THE
AREA...ALTHOUGH MAY LINGER ACROSS SE GA INTO EARLY SUN...AS THE LOW
PRES SYSTEM MOVES/RE-DEVELOPS ALONG THE SE US COAST. HIGH PRES
SHOULD THEN RETURN FROM THE N MON.
TEMPERATURES WILL BE AT OR ABOVE NORMAL THROUGH THU BEFORE DROPPING
BELOW NORMAL INTO EARLY NEXT WEEK.
&&
.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
LOW CONFIDENCE ON EXACTLY HOW CONDITIONS WILL PLAY OUT AT BOTH TAF
SITES FOR THE NEXT 24 HOURS. 18Z GUIDANCE CONTINUES TO OFFER A
NUMBER OF POSSIBILITIES WITH RESPECT TO LOW CLOUD DEVELOPMENT...
AREAL EXTENT AND TIMING. THE LATE FEW FRAMES OF VISIBLE SATELLITE
IMAGERY SHOWED THE SOUTHERN FLANK OF A LOW CLOUD DECK LURKING JUST
NORTH AND NORTHWEST OF KCHS TERMINAL. CIGS AT KMKS/KDYB AND KRBW
REMAIN LOW END MVFR AS OF 07/23Z WHICH COULD EASILY SPREAD INTO
THE KCHS TERMINAL OVER THE NEXT FEW HOURS. WILL CARRY A TEMPO
GROUP FOR BKN020 FROM 04-06Z TO COVER THIS POSSIBILITY. KSAV SHOULD
REMAIN VFR FOR THE NEXT FEW HOURS AT LEAST. WITH GUIDANCE CONTINUING
TO OFFER SOLUTIONS ANYWHERE FROM VFR TO IFR TONIGHT THINK IT BEST
TO CONTINUE A PERSISTENCE FORECAST FOR THE 00Z TAF CYCLE SHOWING
PREVAILING MVFR CIGS DEVELOPING AT BOTH TERMINALS BY 06Z.
THE PROBABILITIES FOR VFR ARE JUST ABOUT THE SAME AS MVFR AND IFR
TONIGHT SO AMENDMENTS WILL MOST CERTAINLY BE NEEDED OVERNIGHT AS
TRENDS BECOME CLEARER. CEILINGS...SHOULD THEY DEVELOP...WILL
LINGER INTO THE DAY TUESDAY WITH MVFR CONDITIONS POSSIBLE.
SHOWER ACTIVITY WILL BE ON THE INCREASE BY LATE AFTERNOON AS A
WARM FRONT TAKES SHAPE TO THE SOUTH AND ISENTROPIC ASSENT
INTENSIFIES OVER THE AREA. ITS A LITTLE TOO SOON TO INTRODUCE ANY
MENTION OF RAIN...BUT THIS MAY BE REEVALUATED WITH LATER TAF
CYCLES.
EXTENDED AVIATION OUTLOOK...MVFR OR LOWER CONDITIONS POSSIBLE WITH
THE NEXT STORM SYSTEM TUE NIGHT INTO WED. VFR SHOULD RETURN WED
NIGHT OR THU. MVFR OR LOWER CONDITIONS THEN RETURN SAT AS ANOTHER
LOW PRESSURE SYSTEM AFFECTS THE AREA.
&&
.MARINE...
INCOMING GUIDANCE SUGGESTS THE GRADIENT BETWEEN INLAND HIGH
PRESSURE AND A LINGERING COASTAL TROUGH WELL OFFSHORE WILL PINCH
THE GRADIENT A BIT MORE AFTER MIDNIGHT. WILL INCREASE WINDS TO
15-20 KT LATE FOR THE WATERS NORTH OF EDISTO BEACH WITH WINDS NO
HIGHER THAN 15 KT ELSEWHERE. SEAS GENERALLY 2-4 FT NEARSHORE
WATERS AND UP TO 5 FT OFFSHORE WATERS EXCEPT BUILDING 3-5 FT FOR
THE WATERS NORTH OF EDISTO.
MARINE CONDITIONS CONTINUE TO IMPROVE THROUGH THE AFTERNOON...WITH
NORTH TO NORTHEAST WINDS NOW AT OR BELOW 15 KT AND SEAS LESS THAN
5 FT. BUOY 4 HAS BECOME NORTH IN THE PAST FEW HOURS...SUGGESTING
THAT THE WEAK TROUGH HAS PUSHED FURTHER AWAY FROM THE COASTLINE.
WINDS WILL GRADUALLY VEER MORE ONSHORE TONIGHT THROUGH
TUESDAY...AS THE INLAND WEDGE SLOWLY ERODES AND A WARM FRONT LIFTS
NORTH INTO THE COASTAL WATERS. NORTHEAST TO EAST FLOW COULD
BRIEFLY SURGE BACK UP TO 15 OR 20 KT OVERNIGHT AND INTO
TUESDAY.
TUESDAY NIGHT THROUGH SATURDAY...A STRONG S/SW LOW-LEVEL JET WILL
DEVELOP ACROSS THE WATERS TUE NIGHT BEHIND A RETREATING WARM FRONT
AND AHEAD OF AN APPROACHING COLD FRONT. SOLID SMALL CRAFT
CONDITIONS SHOULD IMPACT ALL WATERS...EXCEPT POSSIBLY THE
NEARSHORE GA WATERS...LATE TUE NIGHT INTO WED NIGHT BEFORE A COLD
FRONT SWEEPS THROUGH AND WINDS BECOME OFFSHORE. CONDITIONS SHOULD
DROP BELOW ADVISORY CRITERIA THU MORNING...BUT MAY THEN RETURN
OVER THE OUTER GA WATERS SAT AS ANOTHER LOW PRES SYSTEM AFFECTS
THE AREA.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...NONE.
&&
$$
