FXUS62 KCHS 052331
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
631 PM EST SAT DEC 5 2009
.SYNOPSIS...
HIGH PRES WILL REMAIN NORTH OF THE REGION THROUGH MONDAY.
A COMPLEX STORM SYSTEM WILL IMPACT THE REGION TUE INTO WED. HIGH
PRES WILL BUILD OVER THE REGION FOR THE LATTER HALF OF NEXT WEEK.
A COLD FRONT WILL PUSH INTO THE AREA NEXT WEEKEND.
&&
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
WE CONTINUE TO EVALUATE THE POTENTIAL FOR FROST AND FREEZE
CONDITIONS TONIGHT. THE LATEST SHORT TERM MODEL GUIDANCE SUGGESTS
THE BOUNDARY LAYER WILL DECOUPLE ACROSS MUCH OF SOUTHEAST GEORGIA
LATER THIS EVENING AS HIGH PRESSURE NUDGES IN FROM THE WEST AND A
STRONG NOCTURNAL INVERSION FORMS. WITH WINDS NOW EXPECTED TO GO
CALM...WE BELIEVE THE RISK FOR FREEZING TEMPERATURES ACROSS FAR
INTERIOR SOUTHEAST GEORGIA HAS INCREASED ENOUGH TO JUSTIFY A
FREEZE WARNING FOR JENKINS-BULLOCH-EVANS-CANDLER AND TATTNALL
COUNTIES. EXPECT FREEZE DURATIONS OF 2-3 HOURS ALONG WITH
SCATTERED TO WIDESPREAD FROST.
WILL MAINTAIN THE FROST ADVISORY FOR THE I-95 CORRIDOR COUNTIES
FROM INLAND JASPER SOUTH TO INLAND MCINTOSH FOR SCATTERED
FROST...BUT THERE ARE SIGNS IN THE 18Z MODEL DATA THAT THE FROST
ADVISORY MAY NEED TO BE EXPANDED TO INCLUDE THE INTERIOR PARTS OF
OUR SOUTH CAROLINA COASTAL ZONES. WILL HAVE TO SEE HOW WINDS
TREND IN THESE AREAS LATER THIS EVENING SO WILL NOT EXPAND THE
FROST ADVISORY JUST YET...BUT THIS IS SOMETHING WE ARE CAREFULLY
WATCHING. FREEZING TEMPERATURES ARE EXPECTED FROM SCREVEN UP
THROUGH BERKELEY COUNTIES...BUT THE GROWING SEASON HAS ALREADY
ENDED IN THOSE AREAS. WILL NUDGE TEMPERATURES INTO THE UPPER 20S
ACROSS THE HIGHER TERRAIN AREAS FROM JENKINS OVER TO ALLENDALE PER
LATEST MODEL GUIDANCE.
&&
.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
COOL DRY HIGH PRESSURE CENTERED N OF THE REGION WILL EXTEND S OVER
THE AREA SUNDAY INTO SUNDAY NIGHT AS IT SLIDES OFF THE E COAST.
SOME HIGH CLOUDS OVER THE ENTIRE AREA AND MIDLVL CLOUDS NEAR THE
COAST WILL HOLD DOWN TEMPS A BIT...BUT THE MAIN EFFECT OF THE COLD
AIR ADVECTION WILL BE THE PRIMARY FACTOR KEEPING MAX TEMPS IN THE
MID 50S.
CLOUDS WILL GRADUALLY INCREASE SUN NIGHT AS THE HIGH PRESSURE
TAKES THE FORM OF AN INLAND WEDGE OVERNIGHT COMBINED WITH THE
FORMATION OF A WEAK COASTAL TROUGH. HAVE OPTED TO KEEP PRECIP OUT
OF THE FORECAST CONSIDERING THE AMOUNT OF LOW LEVEL MOISTURE
RECOVERY NEEDED TO PRODUCE MEASURABLE PRECIP. THE CLOUD DECK
OVERNIGHT WILL KEEP MIN TEMPS A BIT WARMER THAN SUNDAY MORNING...
WITH LOWS DROPPING TO THE MID 30S WELL INLAND...TO LWR 40S S OF
INTERSTATE 16 IN SE GA AND THE MID 40S ALONG THE ENTIRE SHORELINE.
&&
.LONG TERM /MONDAY THROUGH SATURDAY/...
HIGH PRESSURE WILL REMAIN CENTERED NORTH OF THE REGION
MONDAY...WHILE A SURFACE TROUGH WILL DEVELOP OVER THE COASTAL
WATERS. WITHIN A WEAK/ILL DEFINED OVERRUNNING REGIME FEATURING N
SURFACE FLOW AND WSW WINDS ALOFT...EXPECT MOSTLY CLOUDY SKIES.
HOWEVER...MODELS HAVE REMAINED INCONSISTENT REGARDING THE
POTENTIAL FOR LIGHT PRECIPITATION. THE FRIDAY MORNING NAM
DEPICTED SHOWERS ACROSS MUCH OF THE REGION...WHILE THE GFS
DEPICTED A DRY SCENARIO. SATURDAY MORNING...THESE MODELS HAVE
SWAPPED ROLES. GIVEN LIMITED DEEP LAYER MOISTURE AND WEAK TO NON-
EXISTENT ASCENT AM NOT IMPRESSED FOR PRECIPITATION...THUS SCALED
BACK COVERAGE SLIGHT CHANCE POPS TO ONLY INCLUDE NORTHERN
COUNTIES/COASTAL WATERS...AND EVEN THIS MAY BE OVERDONE.
AS DEEP LOW PRESSURE TRACKS ENE ACROSS THE US MIDSECTION
TUESDAY...OVERRUNNING PRECIPITATION WILL EXPAND IN COVERAGE AND
SPREAD N/NE OVER THE SOUTHEAST. THE 12Z NAM MAINTAINED THE
REMNANTS OF RELATIVELY DRY AIR OVER THE REGION...WHILE THE 12Z
GFS PUSHED DEEP LAYER MOISTURE IN THE REGION TUESDAY AFTERNOON.
DUE TO UNCERTAINTY REGARDING THE TIMING OF THE ONSET OF
PRECIPITATION... LIMITED POPS TO CHANCE TUESDAY...THEN BUMPED TO
LIKELY TUESDAY NIGHT WHICH MAY STILL BE CONSERVATIVE.
GIVEN THE SPC DAY 4-8 SEVERE WEATHER OUTLOOK AREA OVER THE
SOUTHEAST...A BRIEF SUMMARY OF THE MIDWEEK SEVERE WEATHER
POTENTIAL IS IN ORDER. A COMPLEX SCENARIO WILL EVOLVE TUESDAY
NIGHT AND WEDNESDAY. TO START...THE SURFACE WEDGE OF HIGH PRESSURE
WILL SHARPEN AND WILL PERSIST OVER MOST/ALL OF THE REGION
TUESDAY NIGHT...WHILE A WARM FRONT APPROACHES OR ADVANCES INTO
COASTAL WATERS. EVENTUALLY...A SECONDARY LOW PRESSURE WILL DEVELOP
ALONG THE MID ATLANTIC OR SOUTHEAST COAST LATER TUESDAY NIGHT OR
WEDNESDAY...PULLING A COLD FRONT THROUGH THE REGION. THERE REMAINS
MUCH UNCERTAINTY WHERE AND WHEN THE SECONDARY LOW WILL
DEVELOP...AND THIS IN TURN WILL DETERMINE IF/WHERE SURFACE BASED
INSTABILITY CAN PUSH INTO THE REGION BEFORE COLD FROPA WEDNESDAY.
THE PAST FEW MODEL RUNS HAVE SUGGESTED THAT SOME DEGREE OF SURFACE
BASED INSTABILITY COULD PUSH INTO SOUTHERN COUNTIES LATER TUESDAY
NIGHT THEN NE INTO COASTAL COUNTIES WEDNESDAY. HOWEVER...ONGOING
PRECIPITATION COULD DELAY OR PREVENT THE N/NE PROGRESS OF THE WARM
SECTOR...AND THE WINDOW OF OPPORTUNITY FOR DESTABILIZATION COULD
BE SHORTENED IF THE SECONDARY COASTAL LOW DEVELOPS BY EARLY
WEDNESDAY. THUS...DESPITE STRONG WIND FIELDS SUPPORTING A
TREMENDOUS AMOUNT OF SHEAR/HELICITY...THE SEVERE WEATHER POTENTIAL
COULD WELL BE OFFSET BY A LACK OF INSTABILITY AS WAS THE CASE WITH
THE DEC 2 EVENT. UNCERTAINTY REGARDING FORECAST DETAILS REMAINS
HIGH...AND FACTORS COULD YET FALL INTO PLACE TO SUPPORT
SIGNIFICANT SEVERE WEATHER LATE TUESDAY NIGHT INTO WEDNESDAY.
HOWEVER...AS OF SATURDAY AFTERNOON THE MIDWEEK SEVERE WEATHER
POTENTIAL APPEARS LIMITED.
AFTER COLD FROPA...HIGH PRESSURE SHOULD DRIER AIR INTO THE REGION
THROUGH LATE WEEK. IF HIGH PRESSURE ADVANCES OFFSHORE EARLIER THAN
EXPECTED...OVERRUNNING PRECIPITATION COULD AGAIN DEVELOP
THURSDAY-FRIDAY. HOWEVER...THIS SCENARIO DOES NOT APPEAR LIKELY
THUS MAINTAINED RAIN FREE FORECASTS THURSDAY AND FRIDAY.
ANOTHER COLD FRONT WILL APPROACH THE REGION FRIDAY NIGHT AND
SATURDAY...JUSTIFYING AT LEAST SLIGHT CHANCE TO CHANCE POPS.
&&
.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
VFR CONDITIONS WILL CONTINUE THROUGH THE 00Z TAF PERIOD
FOR KCHS AND KSAV. MAINLY CLEAR SKIES WILL PREVAIL OVERNIGHT AS HIGH
PRESSURE REMAINS ACROSS THE AREA. EXPECT LIGHT WINDS AT THE SURFACE
OVERNIGHT WHICH WILL RESULT IN POSSIBLE LLWS CONDITIONS FROM 00Z-04Z
FOR BOTH SITES. THE KCHS 00Z SOUNDING SHOWED 25 KNOT WINDS JUST OFF
THE SURFACE WHICH RESULTS IN MARGINAL CONDITIONS THUS WILL EXCLUDE
FROM THE TAFS. FEW TO SCATTERED CIRRUS WILL PUSH INTO THE REGION SUNDAY
AFTERNOON WITH WINDS SHIFTING TO THE NORTHEAST.
EXTENDED AVIATION OUTLOOK...OCCASIONAL MVFR CONDITIONS POSSIBLE
MONDAY THROUGH TUESDAY. IFR OR LOWER CONDITIONS POSSIBLE IN RAIN
TUESDAY NIGHT INTO WEDNESDAY. VFR SHOULD RETURN WEDNESDAY NIGHT OR
THURSDAY.
&&
.MARINE...
THE COASTAL LOW WILL CONTINUE SHIFTING NE INTO THE MID ATLC WATERS
THIS EVENING...ALLOWING HIGH PRESSURE TO MOVE IN FROM THE NW. A
RELATIVELY TIGHT PRESSURE GRADIENT COMBINED WITH DECENT POST-
FRONTAL SUBSIDENCE WILL PROMOTE FREQUENT GUSTS TO 25 KT OVER ALL
NEARSHORE WATERS AND SUSTAINED WINDS REACHING 25 KT OVER THE OUTER
GA WATERS TONIGHT. SMALL CRAFT ADVY HEADLINES WILL REMAIN THROUGH
THIS EVE FOR THE NEARSHORE GA WATERS BUT CONDITIONS SHOULD THEN
FALL BEFORE SCA THRESHOLDS DURING THE OVERNIGHT HOURS. WINDS WILL
BE SLOWER TO DROP OVER THE NRN SC WATERS AND THE OUTER GA WATERS
BUT WINDS LOOKS TO DROP BELOW SCA CRITERIA BY DAYBREAK SUN
MORNING. WINDS WILL CONTINUE TO SETTLE DOWN THROUGH THE DAY SUNDAY
AS THE PRESSURE GRADIENT RELAXES AND HIGH PRESSURE EXERTS BETTER
INFLUENCE OVER THE WATERS.
HIGH PRESSURE WILL REMAIN CENTERED N/NE OF THE COASTAL WATERS AND
WINDS/SEAS WILL REMAIN BELOW SMALL CRAFT ADVISORY THRESHOLDS
THROUGH AT LEAST TUESDAY. TUESDAY NIGHT AND WEDNESDAY...A
COMPLEX STORM SYSTEM WILL IMPACT THE COASTAL WATERS. IF A WARM
FRONT CAN ADVANCE THROUGH THE WATERS...WINDS COULD SHIFT TO THE
S/SW AND COULD SURGE TO SCA OR GALE LEVELS TUESDAY NIGHT INTO
WEDNESDAY. THEN...AS LOW PRESSURE DEVELOPS ALONG THE MID-ATLANTIC
OR SOUTHEAST COASTS WEDNESDAY...A COLD FRONT WILL PUSH THROUGH THE
WATERS WITH A WIND SHIFT TO THE W/NW. THE RESULTING SURGE OF
COLDER AIR WILL LIKELY SUPPORT SCA CONDITIONS INTO THURSDAY...AND
A PERIOD OF GALES WILL BE POSSIBLE ESPECIALLY BEYOND 20 NM.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...FROST ADVISORY FROM 1 AM TO 9 AM EST SUNDAY FOR GAZ101-116-118-
137-138-140.
FREEZE WARNING FROM 1 AM TO 9 AM EST SUNDAY FOR GAZ087-099-100-
114-115.
SC...FROST ADVISORY FROM 1 AM TO 9 AM EST SUNDAY FOR SCZ047.
MARINE...SMALL CRAFT ADVISORY UNTIL 10 PM EST THIS EVENING FOR AMZ352-
354.
SMALL CRAFT ADVISORY UNTIL 5 AM EST SUNDAY FOR AMZ350-374.
&&
$$
