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000
FXUS62 KCHS 100024
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
724 PM EST TUE FEB 9 2010

...STRONG AND GUSTY WINDS TO IMPACT THE REGION...

.SYNOPSIS...
A STRONG COLD FRONT WILL PUSH OFFSHORE TONIGHT...WITH COLD
HIGH PRESSURE BUILDING IN WEDNESDAY AND THURSDAY. ANOTHER STORM
SYSTEM WILL PASS SOUTH OF THE AREA FRIDAY AND FRIDAY NIGHT...
POSSIBLY BRINGING SOME WINTRY PRECIPITATION TO THE REGION. HIGH
PRESSURE WILL BUILD OVER THE REGION FOR THE WEEKEND AND PERSIST
INTO EARLY NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
THE TUESDAY EVENING SURFACE ANALYSIS REVEALED A COMPLEX
SCENARIO...FEATURING LOW PRESSURE OVER THE SC MIDLANDS AND
NEAR THE SE NC COAST. AN INITIAL TRAILING COLD FRONT WAS POISED TO
ADVANCE INTO WESTERN COUNTIES...WHILE A MUCH STRONGER COLD FRONT
WAS SWEEPING INTO CENTRAL GA. AHEAD OF THESE SURFACE
BOUNDARIES...DEEP LAYER DRY AIR WAS OVERWHELMING
PRECIPITATION...THUS EXPECT ONLY SCATTERED SPRINKLES TO PUSH
THROUGH THE FORECAST AREA THIS EVENING. UPDATED FORECASTS TO LOWER
EVENING POPS AND TO REMOVE THE MENTION OF MEASURABLE
PRECIPITATION THIS EVENING.

IN THE WAKE OF THE STRONG COLD FROPA LATER THIS EVENING INTO THE
OVERNIGHT HOURS...MUCH COLDER AIR WILL PRESS INTO THE REGION
FROM THE NW AS HIGH PRESSURE BUILDS SOUTHEAST...AND CLOUDY SKIES
WILL GIVE WAY TO RAPID CLEARING FROM W TO E OVERNIGHT.

MEANWHILE...925 MB WINDS WILL INCREASE TO ABOUT 40 KT IN THE WAKE
OF STRONG COLD FROPA OVERNIGHT. POST FROPA PRESSURE RISES AND
BOUNDARY LAYER MIXING WILL SUPPORT BLUSTERY CONDITIONS ACROSS THE
REGION AFTER MIDNIGHT.

WATER TEMPERATURES ON LAKE MOULTRIE REMAIN IN THE UPPER 40S WHICH
SHOULD YIELD SIGNIFICANTLY DEEPER MIXING PROFILES WITH THE
INCOMING STRONG WINDS. SUSTAINED WINDS WILL PROBABLY BE IN THE
25-35 KT RANGE AFTER ABOUT 2 AM WITH GUSTS TO 40 KT. WITH
GEOSTROPHIC WINDS PROGGED AT 45 KT BY LATE TONIGHT...THE CHANCE
FOR SUSTAINED WINDS OF 35 KT OR HIGHER IS FAIRLY LOW.
HOWEVER...WITH CONSIDERABLE VARIABILITY BETWEEN MODELS REGARDING
WINDS ALOFT AND THE FACT THAT SUSTAINED WINDS ARE EXPECTED TO BE
AT LEAST 30 KT...MAINTAINED THE ONGOING HIGH WIND WARNING FOR LAKE
MOULTRIE TONIGHT.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY NIGHT/...
A CLOSED UPPER LEVEL LOW PRESSURE SYSTEM WILL QUICKLY TRACK ACROSS
THE MID-ATLANTIC REGION WEDNESDAY MORNING...ALLOWING SURFACE LOW
PRESSURE TO BOMB OFF THE MID-ATLANTIC COAST. VERY STRONG COLD AIR
ADVECTION WILL DEVELOP IN WAKE OF THIS SYSTEM ACROSS THE
REGION...AND PERSIST WELL INTO WEDNESDAY AFTERNOON. DURING THE SAME
TIME...IMPRESSIVE LOW LEVEL WIND FIELDS WILL BE IN PLACE OVER THE
AREA...WITH BUFR SOUNDINGS SHOWING WINDS AS HIGH AS 45 KT WITHIN THE
MIXED LAYER DURING THE DAY. AS A RESULT...EXPECT SUSTAINED WINDS AT
THE SURFACE TO REACH 20 TO 30 MPH WITH GUSTS UP TO 40 OR 45 MPH
DURING PEAK HEATING...GENERALLY FROM 9 AM TO 6 PM WEDNESDAY. GIVEN
THESE CONDITIONS...HAVE ISSUED A WIND ADVISORY FOR ALL OF SOUTHEAST
SOUTH CAROLINA AND SOUTHEAST GEORGIA. THE VERY WET GROUND CONDITIONS
COULD RESULT IN SOME DOWNED TREES AND POWER LINES GIVEN THE MAGNITUDE
OF FORECAST WINDS. WINDS COULD ALSO BE EVEN STRONGER ON BRIDGES AND
OVERPASSES.

SUNNY SKIES AND A DOWNSLOPE COMPONENT TO THE WINDS WOULD GENERALLY
FAVOR WARMER CONDITIONS ACROSS THE AREA ON WEDNESDAY...HOWEVER GIVEN
THE STRENGTH OF COLD AIR ADVECTION TEND TO FAVOR KEEPING HIGHS IN
THE UPPER 40S TO AROUND 50.

THE SURFACE PRESSURE GRADIENT WILL CONTINUE TO WEAKEN THROUGH
THURSDAY NIGHT AS THE UPPER LEVEL FLOW BECOMES ZONAL AND SURFACE
HIGH PRESSURE NEARS THE AREA FROM THE WEST. DRY CONDITIONS WILL
PREVAIL DURING THIS TIME...HOWEVER TEMPERATURES WILL REMAIN BELOW
NORMAL.

THE FOCUS THEN SHIFTS TO THE POTENTIAL SOUTHERN STREAM SYSTEM LATE
IN THE WEEK. 12Z MEDIUM RANGE GUIDANCE IS GENERALLY IN GOOD
AGREEMENT SHOWING A SHORT WAVE TROUGH MOVING ACROSS THE NORTHERN
GULF OF MEXICO ON FRIDAY...ALTHOUGH THERE ARE DIFFERENCES WITH
RESPECT TO THE LOCATION AND TIMING OF AN ASSOCIATED SURFACE LOW. THE
ECMWF...CANADIAN AND NAM ALL SHOW THE LOW TRACKING ACROSS THE
NORTHEAST GULF OF MEXICO FRIDAY TO A POSITION OFF THE SOUTHEAST U.S.
COAST FRIDAY NIGHT...ALTHOUGH THE NAM IS CONSIDERABLY SLOWER. THE
GFS APPEARS TO BE AN OUTLIER...WITH A MUCH MORE SUPPRESSED
SOLUTION...KEEPING THE LOW WELL TO THE SOUTH ACROSS THE EAST-CENTRAL
GULF OF MEXICO FRIDAY AND INTO THE CARIBBEAN FRIDAY NIGHT. THE GFS
IS TOO FAR SOUTH TO GENERATE ANY PRECIPITATION ACROSS THE AREA. THE
CANADIAN IS THE MOST ROBUST...SHOWING CONSIDERABLE PRECIPITATION
ACROSS THE AREA LATE FRIDAY AND FRIDAY NIGHT...WITH THE ECMWF
LOOKING LIKE THE BEST COMPROMISE AT THIS TIME.

AS FOR SENSIBLE WEATHER...EXPECT A SLIGHT CHANCE OR LOW CHANCE OF
RAIN ACROSS THE AREA ON FRIDAY...MAINLY SOUTH OF THE I-16 CORRIDOR
AND IN THE AFTERNOON. BY FRIDAY NIGHT...EXPECT A LOW CHANCE OF
PRECIPITATION ACROSS NEARLY THE ENTIRE FORECAST AREA...WITH
PROBABILITIES SLIGHTLY HIGHER TOWARD THE COAST. THERE DOES APPEAR TO
BE ENOUGH COLD AIR ALOFT TO THE NORTHWEST OF THE SURFACE LOW TO
RESULT IN PRECIPITATION TYPE ISSUES FOR THE AREA. GIVEN SOME
UNCERTAINTY...DO NOT WANT TO BE TOO SPECIFIC...BUT THE FORECAST
SHOWS A CHANCE FOR SNOW OR RAIN FRIDAY NIGHT WITH ALL SNOW POSSIBLE
IN THE NORTHWEST PART OF THE AREA OVERNIGHT AS THE COLDER AIR
FILTERS IN.

LAKE WINDS...A HIGH WIND WARNING WILL CONTINUE FOR LAKE MOULTRIE
THROUGH 9 AM WEDNESDAY...THEN MIXING PROFILES APPEAR TO BECOME MORE
FAVORABLE OVER THE LAND. AT THAT TIME...A WIND ADVISORY WILL BE IN
EFFECT FOR BERKELEY COUNTY AND INCLUDE LAKE MOULTRIE.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
DRY HIGH PRESSURE WILL MOVE INTO THE REGION AGAIN FOR THE
WEEKEND...ALLOWING A GRADUAL WARMING TREND FROM THE COOL
TEMPERATURES SEEN MID TO LATE WEEK.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
MVFR CIGS ARE EXPECTED THROUGH 06Z TONIGHT AT BOTH CHS AND SAV
TERMINALS. MVFR CIGS WILL QUICKLY IMPROVE TO VFR AS SKIES BECOME
CLEAR SHORTLY BETWEEN 06Z AND 12Z TONIGHT.

A STRONG PRESSURE GRADIENT WILL DEVELOP OVER BOTH TERMINALS
TONIGHT AS A COLD FRONT SWEEPS THROUGH THE SOUTHEAST AND HIGH
PRESSURE BUILDS INTO THE AREA. SOUTHWEST/WEST WINDS WILL RAPIDLY
RESPOND TO THE STRENGTHENING GRADIENT BY 06Z. WEST WINDS BETWEEN
15 TO 25 KNOTS ARE LIKELY BY 06Z THROUGH DAYBREAK AT BOTH
TERMINALS. WINDS WILL CONTINUE TO INCREASE TO 20 TO 30 KNOTS AT
BOTH TERMINALS THROUGH 1730Z AS CAA ALOFT AND SFC HEATING OCCURS.

EXPECT PEAK WINDS BETWEEN 25 TO 40 KNOTS BETWEEN 1730Z AND 2230Z
WEDNESDAY. THE CHS TERMINAL WILL LIKELY SEE THE HIGHEST SFC WINDS
GIVEN THE PROXIMITY TO THE STRONGEST LOW LVL WINDS MIXING TO THE
SFC. WIND CONDITIONS WILL SIGNIFICANTLY LOWER TO 15 TO 25 KNOTS AT
BOTH TERMINALS WITH DAYTIME HEAT LOSS BETWEEN 2230Z TO 00Z THURSDAY.

EXTENDED AVIATION OUTLOOK...MVFR CONDITIONS POSSIBLE FRIDAY
AFTERNOON THROUGH FRIDAY NIGHT. OTHERWISE...VFR CONDITIONS
EXPECTED TO PREVAIL. GUSTY WINDS COULD PERSIST INTO WED NIGHT.

&&

.MARINE...
A RELATIVELY WEAK PRESSURE PATTERN THIS EVENING WILL GIVE WAY TO A
MUCH SHARPER SURFACE PRESSURE GRADIENT AS A STRONG COLD FRONT
SWEEPS THROUGH THE WATER OVERNIGHT. THE ASSOCIATED STRONG COLD
ADVECTION AFTER MIDNIGHT TONIGHT...COUPLED WITH COASTAL WATER
TEMPERATURES RANGING FROM LOWER 50S TO UPPER 60S AND HOWLING
GEOSTROPHIC WINDS OF 40-50 KT...SHOULD YIELD SOLID GALE CONDITIONS
OVER ALL WATERS. WINDS SHOULD START CRANKING WELL AFTER MIDNIGHT
ONCE THE FRONT SHIFTS THROUGH AND COLD ADVECTION BEGINS. THE
HIGHEST 925 MB WINDS ARE PROGGED AT ABOUT 45 KT LATE
TONIGHT...WITH THE REMAINING GUIDANCE SHOWING SOMETHING A BIT
LOWER. BASED ON THIS INFORMATION AND A LOOK AT THE STABILITY
FACTOR CHART FOR MIXING PROFILES...STORM FORCE WINDS APPEAR
UNLIKELY OVER THE OFFSHORE GA WATERS DURING THIS EVENT.

SIGNIFICANT...HAZARDOUS MARINE WIND EVENT WILL CONTINUE INTO
WEDNESDAY. STRONG OFFSHORE WINDS WITHIN COLD ADVECTION WILL BE
ENHANCED BY MIXING THAT TAPS INTO A 35 TO 45 KT LOW LEVEL JET.
GUSTS TO 35 KT FOR THE NEARSHORE WATERS...AND 45 KT IN THE
OFFSHORE WATERS...COULD BE FREQUENT DURING THIS TIME. WILL KEEP
GALE WARNINGS GOING FOR ALL WATERS THROUGH WEDNESDAY MORNING. COLD
AIR ADVECTION MAY WANE A BIT WEDNESDAY AFTERNOON INTO WEDNESDAY
EVENING...AND EXPECT CONDITIONS TO FALL BELOW GALE CRITERIA OVER
THE NEARSHORE GEORGIA WATERS AND CHARLESTON HARBOR BY THE
AFTERNOON...THEN ACROSS THE REMAINDER OF THE NEARSHORE WATERS
DURING THE AFTERNOON OR EVENING. STRONG GUSTS TO GALE FORCE WILL
CONTINUE OVER THE OUTER GEORGIA WATERS THROUGH THE NIGHT HOWEVER.

CONSIDERING THE VERY STRONG OFFSHORE FLOW...WAVE HEIGHTS WILL BE
SOMEWHAT SUPPRESSED. OUTER WATERS WILL LIKELY PEAK AT 10 TO 12 KT
WITHIN THE BETTER FETCH.

GRADUALLY IMPROVING CONDITIONS ARE EXPECTED ON THURSDAY AS THE
PRESSURE GRADIENT WEAKENS WITHIN BUILDING HIGH PRESSURE.

LOW PRESSURE WILL DEVELOP IN THE GULF OF MEXICO AND TRACK ACROSS
CENTRAL FLORIDA ON FRIDAY. AS THE COASTAL WATERS REMAIN IN THE COLD
SECTOR OF THIS SYSTEM...NORTHEAST WINDS COULD INCREASE AGAIN FRIDAY
AND SATURDAY. HOWEVER...WITH THE LOW DISPLACED SO FAR SOUTH...THE
STRENGTH OF THE COLD ADVECTION IS QUESTIONABLE. WILL THUS KEEP WINDS
BELOW ADVISORY CRITERIA THURSDAY THROUGH THE REMAINDER OF THE
FORECAST PERIOD.

&&

.FIRE WEATHER...
CRITICAL HUMIDITY AND WINDS EXPECTED ON WEDNESDAY ACROSS MUCH OF
THE AREA. HOWEVER...WFO COLUMBIA COORDINATED WITH THE FORESTRY
COMMISSION AND US FOREST SERVICE AND DETERMINED THAT FUEL
MOISTURES ARE TOO HIGH TO WARRANT ANY RED FLAG PRODUCTS.

&&

.TIDES/COASTAL FLOODING...
A CONSIDERABLE BLOWOUT TIDE IS POSSIBLE ALONG THE SC/GA COAST ON
WEDNESDAY WITH STRONG OFFSHORE WINDS OF 20-30 KT AND ALREADY LOW
ASTRONOMICAL TIDE PREDICTIONS. THE LOWEST TIDE LEVELS WILL
PROBABLY OCCUR DURING THE LATE WED MORNING LOW TIDE. WILL CONTINUE
TO MENTION IN THE HAZARDOUS WEATHER OUTLOOK DUE TO SOME CONCERNS
FOR MARITIME NAVIGATION.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...WIND ADVISORY FROM 9 AM TO 6 PM EST WEDNESDAY FOR GAZ087-088-
     099>101-114>119-137>141.
SC...WIND ADVISORY FROM 9 AM TO 6 PM EST WEDNESDAY FOR SCZ040-
     042>045-047>051.
     HIGH WIND WARNING UNTIL 9 AM EST WEDNESDAY FOR SCZ045.
MARINE...GALE WARNING UNTIL 5 PM EST WEDNESDAY FOR AMZ352.
     GALE WARNING UNTIL MIDNIGHT EST WEDNESDAY NIGHT FOR AMZ350.
     GALE WARNING UNTIL 11 AM EST WEDNESDAY FOR AMZ330-354.
     GALE WARNING UNTIL 6 AM EST THURSDAY FOR AMZ374.

&&

$$