FXUS62 KCHS 250010
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
710 PM EST THU DEC 24 2009
.SYNOPSIS...
A HIGH PRES WEDGE WILL CONTINUE TO BREAK DOWN TONIGHT AS A COMPLEX
STORM SYSTEM IMPACTS THE REGION THROUGH FRIDAY. A COLD FRONT WILL
PUSH S AND E OF THE REGION FRI NIGHT. THEN...HIGH PRES WILL BUILD
INTO THE SOUTHEAST AND WILL REMAIN THE PARAMOUNT FEATURE THROUGH
THE MIDDLE OF NEXT WEEK.
&&
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
HAVE ISSUED A WIND ADVISORY FOR CHARLESTON AND COASTAL COLLETON
COUNTIES UNTIL 11 PM THIS EVENING. COASTAL OBSERVATIONS AND
DOWNTOWN CHARLESTON INDICATE WINDS ARE GETTING CLOSE TO WIND
ADVISORY CRITERIA. RUC MODEL WIND FIELDS SHOW WINDS OF 25-35 MPH
CONTINUING THROUGH 11 PM AFTER WHICH SPEEDS WILL DIMINISH SOMEWHAT
AS A COASTAL FRONT APPROACHES THE COAST. THE HIGHEST WINDS WILL BE
FOUND EAST OF HIGHWAY 17 WHERE GUSTS TO 40 MPH WILL BE POSSIBLE.
SURFACE HIGH PRESSURE WEDGE PATTERN CONTINUES TO BREAK DOWN AS THE
UPPER CONFLUENCE DECREASES AHEAD OF A DEEP UPPER TROUGH/CLOSED LOW
MOVING OUT OF THE SRN PLAINS AND INTO THE LWR MISSISSIPPI VALLEY.
INCREASING ISENTROPIC LIFT ASSOCIATED WITH A TROUGH OF LOW
PRESSURE OFFSHORE IS LEADING TO WIDESPREAD CLOUD COVER ACROSS THE
AREA AND EVEN SOME LIGHT RAIN...MAINLY ALONG THE BEAUFORT/SRN
CHARLESTON COUNTY COAST. OTHERWISE...RAIN CHANCES WILL BE ON THE
INCREASE FROM THE SOUTHWEST AS DEEP MOISTURE AND LIFT MOVE IN FROM
THE SOUTHWEST AHEAD OF A COLD FRONT. THINK MOST OF THE RAIN WILL
HOLD OFF UNTIL AFTER MIDNIGHT AND HAVE POPS RAMPING UP QUICKLY
FROM SOUTHWEST TO NORTHEAST BEYOND THAT TIME. AN AREA OF LOW
PRESSURE IS FORECAST TO BE SITUATED IN EAST CENTRAL GA AROUND 12Z
FRI AND THIS WILL HELP PULL THE COASTAL TROUGH/WARM FRONT N
THROUGH THE AREA LATE. INSTABILITY LOOKS TO REMAIN LOW ENOUGH
TONIGHT OVER LAND TO WARRANT KEEPING MENTION OF THUNDER OUT OF THE
FORECAST. HOWEVER...WILL HAVE TO WATCH HOW QUICKLY THE WARM FRONT
RETREATS N SINCE THIS WILL ULTIMATELY DETERMINE OUR INSTABILITY
AND SEVERE WX RISK LATE TONIGHT. LOW TEMPS SHOULD OCCUR THIS
EVE...THEN REMAIN STEADY OR SLOWLY RISE AS THE WARM FRONT BEGINS
TO LIFT N.
LAKE WINDS...A LAKE WIND ADVISORY IS BEING RAISED FOR LAKE
MOULTRIE WHERE 20 KT WINDS ARE EXPECTED LATE TONIGHT THROUGH
FRIDAY AFTERNOON IN ASSOCIATION WITH AN APPROACHING AREA OF LOW
PRESSURE AND COLD FRONT.
&&
.SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
TRICKY FORECAST ON TAP FOR CHRISTMAS DAY AS A WARM FRONT LIFTS N
THROUGH OUR FORECAST AREA WHILE AN AREA OF LOW PRESSURE MOVES NE
THROUGH THE SC MIDLANDS. THERE IS SOME UNCERTAINTY IN THE STRENGTH
OF THIS WAVE OF LOW PRESSURE AND THIS MAY IMPACT THE INTENSITY OF
ANY STORMS THAT DEVELOP. SINCE THE DAY TWO CONVECTIVE OUTLOOK FROM
SPC NOW PUTS OUR ENTIRE AREA IN A SLIGHT RISK FOR SEVERE WX...HAVE
ADDED THUNDER TO THE FORECAST BUT WITH LINGERING MODEL
DISAGREEMENT...HAVE NOT ADDED SEVERE WORDING TO THE FORECAST YET.
IT APPEARS AS THOUGH DAMAGING WINDS AND ISOLATED TORNADOES ARE THE
MAIN HAZARDS FROM AROUND DAYBREAK THROUGH MID AFTERNOON.
THE OTHER ASPECT OF THIS SYSTEM WILL BE SOME HEAVY RAINFALL AND WE
THINK 1-2 INCHES IS A GOOD BET. THIS SHOULD PRECLUDE INLAND
FLOODING ISSUES BUT OF COURSE HEAVY RAINFALL AROUND HIGH TIDE
EARLY IN THE AFTERNOON MAY PRESENT MORE PROBLEMS ALONG THE COAST DUE
TO COINCIDENT STRONG ONSHORE WINDS.
WE INCREASED MAX TEMPS A BIT...WITH SOME LOWER 70S POSSIBLE ALONG
THE COASTAL AREAS. BREEZY CONDITIONS ARE ALSO EXPECTED...MAINLY
ALONG THE SC COAST THROUGH MUCH OF THE DAY. SOME CLEARING SHOULD
BEGIN ACROSS OUR INTERIOR GA ZONES LATER IN THE DAY AS A TRAILING
COLD FRONT PUSHES THROUGH BEHIND THE DEPARTING AREA OF LOW PRESSURE.
&&
.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
A HIGHLY AMPLIFIED UPPER TROUGH WILL DOMINATE THE EAST COAST WEATHER
PATTERN FOR MUCH OF THE EXTENDED...MAINTAINING PREDOMINANTLY
BELOW-NORMAL TEMPERATURES. A STRONG COLD FRONT WILL MOVE OFF THE
COAST FRIDAY NIGHT...FOLLOWED BY COOL AND DRY WEATHER FOR SATURDAY.
THE COMBINATION OF A WEAK LOBE OF 850 MB MOISTURE AND INCREASING
UPPER JET DIVERGENCE MAY ALLOW FOR ISOLATED SHOWERS TO DEVELOP ON
SUNDAY BUT WE CONTINUED WITH A DRY FORECAST FOR NOW. STRONG NW FLOW
ON THE BACK SIDE OF PROGRESSIVE TROUGH WILL BRING A COLD AIRMASS TO
THE REGION SUNDAY NIGHT THROUGH WEDNESDAY. A HARD FREEZE IS POSSIBLE
IN MANY AREAS SUNDAY NIGHT AND MONDAY NIGHT WITH HIGH TEMPS SEVERAL
DEGREES BELOW NORMAL IN THE LOWER TO MIDDLE 50S.
WEDNESDAY NIGHT AND THURSDAY STILL LOOK MUDDLED AS A TROUGH DIGS
THROUGH THE GULF COAST STATES AND A SURFACE LOW POSSIBLY DEVELOPS
OFF THE SOUTHEAST COAST. ONLY CARRYING SLIGHT CHANCE POPS ALONG THE
COAST ON THURSDAY AT THIS POINT.
&&
.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
MAIN ISSUE WILL BE LOWERING CIGS TO MVFR AND POSSIBLY IFR
CONDITIONS ALONG WITH INCREASING WIND GUSTS AT BOTH CHS AND SAV
TERMINALS TONIGHT. MODERATE RAINS ARE THEN EXPECTED AS A SYSTEM
SHIFTS THROUGH THE SOUTHEAST SHORTLY AFTER DAYBREAK FRIDAY.
FOR CHS...LOW STRATUS WILL CONTINUE TO DRIFT ONSHORE AND OVER
THE TERMINAL TONIGHT LEADING TO PREVAILING MVFR CIGS. WINDS WILL
CONTINUE TO INCREASE OVERNIGHT AS A STRONG PRESSURE GRADIENT
FORMS OVER THE SOUTHEAST. EXPECT 15 TO 25 KT WINDS BY 09Z. RAIN
WILL THEN AFFECT THE TERMINAL BY 12Z FRIDAY. VSBYS ARE LIKELY TO
BECOME MVFR AND POSSIBLY IFR DURING MODERATE SHOWERS BETWEEN 14Z
TO 18Z FRIDAY. CONDITIONS WILL QUICKLY IMPROVE AS FROPA OCCURS BY
EARLY AFTERNOON AND WINDS BECOME SOUTHWEST. MVFR CIGS MAY BECOME
VFR BY 00Z SATURDAY. HAVE OPTED TO KEEP MVFR CIGS THROUGH
REMAINDER OF TAF GIVEN LOW CONFIDENCE FOR ENDING TIME OF EVENT.
FOR SAV...VFR CIGS WILL LIKELY BECOME MVFR BY 03Z FRIDAY AS
MOISTURE CONTINUES TO SHIFT NORTH AHEAD OF AN APPROACHING SYSTEM.
A BRIEF PERIOD OF 10 KNOT WINDS MAY ALLOW IFR CIGS TO CONTINUE
OVER THE SAV TERMINAL FOR THE NEXT HOUR OR TWO. HAVE OPTED TO KEEP
OUT OF TAF CURRENTLY AS DURATION OF EVENT IS EXPECTED TO BE SHORT
LIVED. AMENDMENT MAY BE NEEDED BY 01Z IF WINDS REMAIN 10 KNOTS.
WINDS WILL THEN INCREASE OVERNIGHT AS A STRONG PRESSURE GRADIENT
FORMS OVER THE SOUTHEAST. EXPECT 15 TO 20 KT WINDS BY 09Z. RAIN
WILL THEN AFFECT THE TERMINAL BY 09Z FRIDAY. VSBYS ARE LIKELY TO
BECOME MVFR AND POSSIBLY IFR DURING MODERATE SHOWERS BETWEEN 13Z
TO 17Z FRIDAY. CONDITIONS WILL QUICKLY IMPROVE AS FROPA OCCURS BY
EARLY AFTERNOON AND WINDS BECOME SOUTHWEST. MVFR CIGS MAY BECOME
VFR BY 22Z FRIDAY. HAVE OPTED TO KEEP MVFR CIGS THROUGH REMAINDER
OF TAF GIVEN LOW CONFIDENCE FOR ENDING TIME OF EVENT.
EXTENDED AVIATION OUTLOOK...MAINLY VFR FRI NIGHT THROUGH EARLY
NEXT WEEK.
&&
.MARINE...
A QUICK UPDATE WAS JUST ISSUED TO RAISE WINDS TO 25-30 KNOTS IN
THE CHARLESTON HARBOR THROUGH LATE EVENING. ITS NOT OUT OF THE
REALM OF POSSIBILITY THAT A SHORT FUSE GALE WARNING MAY BE NEEDED
IF WINDS BEGIN TO FREQUENTLY GUST TO 35 KNOTS.
TONIGHT...STRONG ONSHORE WINDS WILL CONTINUE AS AN INLAND HIGH
PRES WEDGE BREAKS DOWN AND A COASTAL TROUGH OF LOW PRES BEGINS TO
PUSH INLAND. EXPECT SOLID SCA CONDS ACROSS ALL WATERS TONIGHT WITH
FREQUENT GALE FORCE GUSTS AFTER MIDNIGHT ACROSS THE SC NEARSHORE
WATERS N OF EDISTO BEACH AND THE GA WATERS BEYOND 20 NM FROM
SHORE.
FRIDAY...THE LOW-LEVEL JET LOOKS TO STRENGTHEN OVER THE AREA EARLY
FRI AS A WAVE OF LOW PRES MOVES BY OVER THE SC MIDLANDS. ONSHORE
WINDS SHOULD BECOME MORE OFFSHORE LATER IN THE DAY...ALTHOUGH THE
TIMING IS STILL A BIT UNCERTAIN. AT LEAST SCA CONDITIONS ARE
EXPECTED ACROSS ALL WATERS THROUGH THE DAY.
FRIDAY NIGHT THROUGH TUESDAY...AN INITIAL SURGE OF COLD ADVECTION
FRIDAY NIGHT WILL KEEP WINDS AND SEAS UP OVER THE COASTAL WATERS
BUT CONDITIONS SHOULD STEADILY IMPROVE THROUGH SATURDAY AS HIGH
PRESSURE BUILDS FARTHER SOUTHEAST. A REINFORCING COLD FRONT MAY
PUSH WINDS AND SEAS TO SMALL CRAFT ADVISORY CRITERIA AT LEAST OVER
THE OFFSHORE GA WATERS LATE SUNDAY NIGHT THROUGH MONDAY.
&&
.TIDES/COASTAL FLOODING...
STRONG ONSHORE WINDS WILL PRODUCE HIGH SURF AND ELEVATED
TIDES...AND POSSIBLY SHALLOW COASTAL FLOODING AND BEACH EROSION...
TONIGHT INTO FRI. THE BEST CHANCE OF SHALLOW COASTAL FLOODING
APPEARS TO BE AROUND CHARLESTON DURING THE HIGH TIDE JUST AFTER
MIDNIGHT TONIGHT WHEN THE TIDE LEVEL MAY APPROACH THE ADVISORY
CRITERIA OF 7.0 FEET MEAN LOWER LOW WATER IN CHARLESTON HARBOR.
A HIGH SURF ADVISORY WILL BE RAISED FOR THE CENTRAL/LOWER SC COAST
WHERE BREAKERS OF AT LEAST 5 FT ARE ANTICIPATED FROM LATE TONIGHT
INTO FRIDAY AFTERNOON.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...LAKE WIND ADVISORY FROM MIDNIGHT TONIGHT TO 5 PM EST FRIDAY
FOR SCZ045.
HIGH SURF ADVISORY FROM MIDNIGHT TONIGHT TO 5 PM EST FRIDAY
FOR SCZ048>051.
WIND ADVISORY UNTIL 11 PM EST THIS EVENING FOR SCZ049-050.
MARINE...SMALL CRAFT ADVISORY UNTIL 9 PM EST FRIDAY FOR AMZ352.
GALE WARNING UNTIL 5 PM EST FRIDAY FOR AMZ350-374.
SMALL CRAFT ADVISORY UNTIL 5 PM EST FRIDAY FOR AMZ330-354.
&&
$$
