FXUS62 KCHS 300840
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
340 AM EST MON NOV 30 2009
...SIGNIFICANT STORM SYSTEM POISED TO IMPACT THE REGION BY MID
WEEK BRINGING A NUMBER OF POTENTIAL HAZARDS...
.SYNOPSIS...
AN APPROACHING COLD FRONT WILL PUSH OFF THE COAST THIS EVENING AND
BECOME STATIONARY WELL TO THE SOUTH ON TUESDAY AS HIGH PRESSURE
BUILDS INTO THE REGION. A GULF LOW PRESSURE SYSTEM WILL DEVELOP
TUESDAY AND TUESDAY NIGHT...THEN TRACK NORTHEASTWARD ALONG THE
APPALACHIANS WEDNESDAY AND WEDNESDAY NIGHT. A COLD FRONT WILL
SWING THROUGH THE AREA THURSDAY...FOLLOWED BY HIGH PRESSURE FOR
THE END OF THE WEEK THROUGH NEXT WEEKEND.
&&
.NEAR TERM /THROUGH TODAY/...
THE WESTERN FLANKS OF ATLANTIC HIGH PRESSURE WILL GRADUALLY
BREAKDOWN TODAY AS A COLD FRONT APPROACHES FROM THE NORTHWEST.
WATER VAPOR IMAGERY AND UPSTREAM PROFILER DATA SHOW THE COLD
FRONT/S SUPPORTING SHORTWAVE EXTENDS FROM THE UPPER MISSISSIPPI
VALLEY INTO THE CENTRAL PLAINS WITH A PRONOUNCED CUT OFF LOW
SPINNING OVER THE NORTHERN BAJA. MODEL PROGS SHOW THE NORTHERN
STREAM SHORTWAVE CONTINUING TO DIG STEADILY SOUTHEAST TODAY AS AS
A SUBTROPICAL JET STRENGTHENS FROM EASTERN TEXAS THROUGH THE
MIDDLE ATLANTIC STATES.
FAVORABLE JET DYNAMICS ALOFT COUPLED WITH MODEST MID-LEVEL DPVA
WITH THE SHORTWAVE ITSELF IS ALREADY SUPPORTING A LARGE BAND OF
FRONTAL RAINS FROM THE OHIO VALLEY SOUTHWEST THROUGH EASTERN
TEXAS. THESE RAINS WILL MOVE RAPIDLY ACROSS THE DEEP SOUTH AS THE
DAY PROGRESSES AND WILL BE MOVING THROUGH THE MIDLANDS AND CENTRAL
GEORGIA BY MID AFTERNOON. THE VARIOUS MODEL GUIDANCE INCLUDING THE
LATEST SREF CONTINUES TO SUGGEST SHOWER ACTIVITY WILL PROGRESSIVELY
WEAKEN AS IT MOVES INTO THE EASTERN MIDLANDS/CSRA AS A LOWER THETA
AIRMASS IS ENCOUNTERED. THIS COMBINED WITH THE ATMOSPHERE BECOMING
INCREASING CONVERGENT ALOFT IN RESPONSE TO THE UPPER JET/S RIGHT
EXIT REGION ORIENTING ITSELF DIRECTLY OVERHEAD SUPPORTS
MAINTAINING A LOW POP FORECAST WITH SLIGHT CHANCE POPS GENERALLY
CONFINED TO THE FAR INLAND ZONES.
MOSTLY SUNNY SKIES EARLY WILL GIVE WAY TO INCREASING CLOUDS WITH
MOSTLY CLOUDY SKIES EXPECTED TO PREVAIL THIS AFTERNOON. HIGHS IN
THE LOWER 70S STILL LOOK ATTAINABLE AS TEMPERATURES SHOULD GET A
SOLID BOOST RIGHT AFTER SUNRISE. TEMPERATURES ALONG THE IMMEDIATE
BEACH FRONT WILL ONCE AGAIN REMAIN CONSIDERABLY COOLER WITH HIGHS
LIKELY TOPPING OUT ONLY IN THE MID 60S AT BEST.
&&
.SHORT TERM /TONIGHT THROUGH 6 PM TUESDAY/...
THE COLD FRONT WILL PUSH OFF THE COAST SHORTLY AFTER SUNRISE. ANY
LINGERING RAIN CHANCES WILL QUICKLY END BY MID-LATE EVENING AS
CONSIDERABLY DRIER AIR FILTERS IN FROM THE WEST. CLOUD COVER WILL
ALSO STEADILY DIMINISH WITH SKIES EXPECTED TO BECOME MOSTLY CLEAR
SHORTLY AFTER SUNSET ACROSS THE FAR WEST AND BY MIDNIGHT AT THE
COAST. LOWS WILL RANGE FROM THE LOWER 40S WELL INLAND TO THE UPPER
40S AT THE COAST.
HIGH PRESSURE WILL SETTLE OVER THE REGION TUESDAY AS THE COLD
FRONT BECOMES STATIONARY WELL TO THE SOUTH. DESPITE SUNNY SKIES...
HIGHS WILL STRUGGLE TO REACH THE 62-64 DEGREE RANGE UNDER WEAK CAA
AND NORTHEAST LOW-LEVEL TRAJECTORIES PREVAILING.
&&
.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
TRANSIENT HIGH PRESSURE TO THE NORTH WILL STEADILY SHIFT OFF THE
CAROLINA COAST TUESDAY NIGHT...WHILE A POTENT LOW SYSTEM TAKES SHAPE
OVER THE GULF OF MEXICO. MODELS HAVE CONSISTENTLY INDICATED THE
DEVELOPMENT OF THIS STORM SYSTEM FOR SEVERAL DAYS. NOW THAT THE
SYSTEM IS WITHIN DAY 3 OF THE FORECAST AND FINER DETAILS NEED TO
BE ADDRESSED...THERE IS MUCH MORE DIFFICULTY DUE TO TIMING AND
TRACK DIFFERENCES BETWEEN THE MODELS.
WHAT REMAINS CONSISTENT BETWEEN THE MODELS IS THAT A WARM FRONT WILL
LIFT NORTH THROUGH THE FORECAST AREA TUESDAY NIGHT...PLACING THE
REGION SOLIDLY WITHIN THE STRONG WARM SECTOR AHEAD OF THE SYSTEM.
EXPECT SHOWERS TO SPREAD FROM SOUTHWEST TO NORTHEAST ACROSS THE
AREA TUESDAY NIGHT AS A RESULT. ALL MODELS TRACK THE LOW SYSTEM
NORTHEAST GENERALLY ACROSS THE TENNESSEE/OHIO VALLEYS. GFS
SOLUTION IS STRONGER AND FASTER THAN ECMWF AND NAM AT THIS POINT.
PERHAPS THE MOST DIFFICULT DETAILS WILL INVOLVE RAIN POTENTIAL
BETWEEN THE WARM FRONT AND APPROACHING COLD FRONT FROM THE
WEST...AS WELL AS SEVERE POTENTIAL ON WEDNESDAY. NAM AND SREF BOTH
INDICATE A SLOT OF REDUCED QPF AS THE WARM FRONT LIFTS NORTH INTO
NORTH CAROLINA ON WEDNESDAY. THIS WOULD SUGGEST A LULL IN HEAVY
RAIN FOR A PERIOD DURING THE DAY BEFORE THE COLD FRONT CROSSES
INTO THE AREA. AS THIS SCENARIO HAS BEEN NOTED BEFORE...AM
HESITANT TO INDICATE A LARGE AREA OF CATEGORICAL POPS WITH THIS
FORECAST PACKAGE DUE TO UNCERTAINTY IN TIMING AND COVERAGE OF
PRECIP BETWEEN THE TWO FRONTS. HAVE NARROWED DOWN THE NORTHERN
THIRD OF THE FORECAST AREA WITH DEFINITE RAIN CHANCES WEDNESDAY
AFTERNOON...WHILE KEEPING LIKELY POPS ELSEWHERE. HAVE ALSO UPGRADED
PRECIP INTENSITY TO MODERATE...AS MODERATE TO HEAVY RAIN APPEARS
POSSIBLE WITHIN THE WARM FRONT.
SEVERE POTENTIAL WITH THE GULF LOW SYSTEM IS STILL DIFFICULT TO
DETERMINE...MAINLY DUE TO A LACK OF INSTABILITY OVER LAND AREAS.
THE SYSTEM IS HUGELY DYNAMICALLY DRIVEN...WITH IMPRESSIVE WIND
FIELDS AND SHEAR...STRONG UPPER LEVEL ENERGY...AND UNSEASONABLY
WARM TEMPERATURES/DEWPOINTS. HAVE MAINTAINED A CHANCE OF
THUNDERSTORMS ON WEDNESDAY...AND WILL CONTINUE TO MENTION SEVERE
POTENTIAL IN THE HAZARDOUS WEATHER OUTLOOK. IF THUNDERSTORMS DO
DEVELOP AND CAN TAP INTO THE IMPRESSIVE WIND PROFILE...THE MAIN
SEVERE HAZARD WOULD BE DAMAGING STRAIGHT LINE WINDS AND ISOLATED
TORNADOES.
PREFERRING TO FOLLOW THE SLOWER TRACK OF THE ECMWF...HAVE
CONTINUED LIKELY POPS INTO WEDNESDAY NIGHT. THE LOW SYSTEM WILL
TRACK TOWARD THE NEW ENGLAND STATES AND PULL A COLD FRONT THROUGH
THE AREA. RAIN WILL END BY THURSDAY MORNING...WITH A NOTICEABLE
COOLING TREND BEGINNING ON THURSDAY AND CONTINUING INTO THE
WEEKEND. EXPECT HIGH TEMPERATURES TO BE SUPPRESSED IN THE 50S TO
AROUND 60 FRIDAY INTO THE WEEKEND. MAINTAIN RAIN FREE WEATHER
THURSDAY THROUGH AT LEAST LATE WEEK.
&&
.AVIATION /07Z MONDAY THROUGH FRIDAY/...
VFR CONDITIONS WILL PREVAIL THROUGH 01/06Z. LIGHT WINDS AND ONLY
THIN CIRRUS PASSING OVERHEAD MAY SUPPORT SOME VERY SHALLOW GROUND
FOG LAYERS AT EITHER TERMINAL PRIOR TO SUNRISE...BUT WE DO NOT
EXPECT ANY SIGNIFICANT REDUCTIONS IN VSBYS. A COLD FRONT WILL
APPROACH FROM THE NW TODAY. CLOUD COVER WILL BE ON A STEADY
INCREASE AS THE DAY PROGRESSES WITH CEILINGS GRADUALLY LOWERING
DURING THE MID-LATE AFTERNOON AS THE FRONT DRAWS CLOSER. FROPA IS
EXPECTED AROUND 01Z AT KCHS AND AROUND 02Z AT KSAV. COULD SEE SOME
SPOTTY SHOWER ACTIVITY WITH THE FRONT ITSELF BUT PROBABILITIES ARE
TOO LOW TO JUSTIFY A MENTION IN EITHER TERMINAL ATTM. CEILINGS
MAY ALSO APPROACH MARGINAL MVFR THRESHOLDS...BUT ATTM WE BELIEVE
THEY WILL STAY ON THE LOWER END OF VFR. WILL SEE FAIRLY RAPID
CLEARING IN THE WAKE OF THE FRONT.
EXTENDED AVIATION OUTLOOK...VFR CONDITIONS ARE EXPECTED THROUGH
TUESDAY NIGHT. MVFR OR LOWER CIGS/VSBYS WILL BE POSSIBLE WEDNESDAY
THROUGH THURSDAY MORNING AS A POTENT STORM SYSTEM MOVES THROUGH THE
AREA.
&&
.MARINE...
SOUTHWEST WINDS WILL DOMINATE TODAY AS A COLD FRONT APPROACHES
FROM THE NORTHWEST. THE HIGHEST WINDS WILL BE FOUND ALONG THE
CHARLESTON COUNTY COASTAL WATERS WHERE SPEEDS WILL REACH AS HIGH
AS 15-20 KT AT TIMES. EXPECT 10-15 KT TO PREVAIL ELSEWHERE. SEAS
WILL GENERALLY REMAIN 3 FT OR LESS.
A COLD FRONT IS FORECAST TO PUSH THROUGH THE WATERS EARLY THIS
EVENING WITH WINDS BACKING TO THE W AND EVENTUALLY N/NW IN ITS
WAKE. AN INITIAL SHOT OF INTENSE CAA WILL INCREASE WINDS QUICKLY
AS THE SOUTHERN FLANK OF A PASSING SHORTWAVE PASSES OVERHEAD. ATTM
IT APPEARS THE HIGHEST WINDS WILL REMAIN OVER THE CHARLESTON COUNTY
COASTAL WATERS WHERE SPEEDS AS HIGH AS 20-25 KT WILL OCCUR. EXPECT
15-20 KT OVER THE REMAINDER OF THE LOCAL MARINE AREA. COULD SEE A
BRIEF SURGE AS HIGH AS 20 KT OVER THE GEORGIA OFFSHORE LEG FOR A
FEW HOURS LATE. LATER SHIFTS WILL NEED TO EVALUATE TO SEE WHETHER
SPEEDS TO BE INCREASED TO 20-25 KT THIS ZONE. PER COORDINATION
CHAT WITH WFO WILMINGTON...FLAGS WILL ONLY BE RAISED FOR THE
CHARLESTON COUNTY COASTAL WATERS. WILL LEAVE THE GEORGIA OFFSHORE
WATERS OUT OF THE ADVISORY FOR NOW GIVEN THE MARGINAL NATURE OF
THE EVENT...BUT SHOULD NEW DATA SUPPORT HIGHER WINDS...THEN THE
ADVISORY WILL NEED TO BE EXPANDED. OFFSHORE TRAJECTORIES WILL
SEVERELY LIMIT THE SEA GROWTH POTENTIAL WITHIN 10 NM OF THE COAST.
EXPECT SEAS OF 2-3 FT IN THIS AREA WITH SEA QUICKLY BUILDING TO
4-5 FT.
TUESDAY NIGHT THROUGH FRIDAY...PROGRESSIVE HIGH PRESSURE WILL
SHIFT OFF THE COAST TUESDAY NIGHT...WHILE A STRONG STORM SYSTEM
DEVELOPS OVER THE GULF OF MEXICO. THE COMBINATION OF A WARM FRONT
LIFTING NORTH THROUGH THE AREA...FOLLOWED BY A COLD FRONT LATER
WEDNESDAY...WILL RESULT IN HAZARDOUS MARINE CONDITIONS MID WEEK.
ALTHOUGH THE MIXING PROFILE WILL BE SOMEWHAT UNFAVORABLE GIVEN
STRONG WARM ADVECTION...THE EXTREMELY TIGHT PRESSURE GRADIENT
COULD SUPPORT GALE FORCE WINDS ACROSS AT LEAST THE OUTER WATERS.
FORECAST WINDS ARE JUST ABOVE THE MOST RECENT GFS AND NAM
WINDS...WHICH WERE SLIGHTLY WEAKER WITH THE 00Z RUNS. THIS REDUCED
CONFIDENCE JUST ENOUGH TO DELAY ISSUANCE OF A GALE WATCH FOR THE
FOURTH PERIOD OF THE FORECAST. AT THE VERY LEAST...HIGH END SMALL
CRAFT ADVISORIES ARE POSSIBLE FOR ALL WATERS INTO EARLY
THURSDAY...WHEN THE COLD FRONT SHIFTS AWAY FROM THE MARINE ZONES
AND WIND FIELDS DIMINISH.
&&
.TIDES/COASTAL FLOODING...
A POTENT STORM SYSTEM WILL DEVELOP IN THE GULF OF MEXICO TUESDAY
NIGHT AND TRACK WEST OF THE REGION WEDNESDAY AND WEDNESDAY NIGHT.
CONSIDERING THAT HIGH PREDICTED ASTRONOMICAL TIDE LEVELS WILL BE
OCCURRING DURING THIS PERIOD...THE COMBINATION OF STRONG ONSHORE FLOW
AND HEAVY RAINFALL COULD RESULT IN TIDAL DEPARTURES SIGNIFICANTLY
HIGHER THAN PREDICTED VALUES. THE GFS EXTRATROPICAL GUIDANCE
SHOWS TIDAL LEVELS REACHING 7.6 FEET IN CHARLESTON HARBOR AND 10.0
FEET AT FORT PULASKI DURING THE WEDNESDAY MORNING HIGH TIDE. THESE
LEVELS WOULD RESULT IN MODERATE TO SIGNIFICANT COASTAL FLOODING
CONCERNS ALONG THE SOUTH CAROLINA AND GEORGIA COASTS WEDNESDAY
MORNING...AND COASTAL FLOOD WATCHES AND/OR ADVISORIES MAY EVENTUALLY
BE NEEDED AS DETAILS BECOME MORE CLEAR.
ASTRONOMICAL TIDES ARE EXPECTED TO REMAIN HIGH THURSDAY MORNING AS
WELL...AND COASTAL FLOOD ADVISORIES MAY AGAIN BE NECESSARY FOR
THE SOUTH CAROLINA AND GEORGIA COAST.
IN ADDITION TO HIGH TIDES AND COASTAL FLOODING...STRONG WINDS OVER
THE ATLANTIC COASTAL WATERS MAY RESULT IN A NEED FOR A HIGH SURF
ADVISORY WITH BREAKERS BUILDING TO BETWEEN 5 AND 7 FEET IN THE SURF
ZONE. THIS COULD ALSO RESULT IN MODERATE TO SIGNIFICANT BEACH
EROSION ALONG THE SOUTH CAROLINA AND GEORGIA COAST.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 7 PM THIS EVENING TO 5 AM EST
TUESDAY FOR AMZ350.
&&
$$
