FXUS62 KCHS 010025
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
725 PM EST MON NOV 30 2009

.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 /UNTIL 6 AM TUESDAY MORNING/...
REFLECTIVITIES HAVE ACTUALLY INCREASED A LITTLE AS THE LINE OF
SHOWERS HAS APPROACHED THE CWA. BASED ON RADAR TRENDS...I
INCREASED THE POPS TO CHANCE CATEGORY WITH THE FRONTAL PASSAGE. NO
OTHER CHANGES WERE MADE.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
HIGH PRESSURE WILL SETTLE OVER THE REGION AS THE COLD FRONT
BECOMES STATIONARY WELL TO THE SOUTH. DESPITE SUNNY SKIES...HIGHS
WILL STRUGGLE TO REACH THE MID 60S AS WEAK COLD AIR ADVECTION
CONTINUES DUE TO THE MAINLY NORTHEAST LOW-LEVEL WINDS.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
MODEL GUIDANCE IS IN GOOD AGREEMENT SHOWING A STRENGTHENING AREA
OF LOW PRESSURE TRACKING OUT OF THE CENTRAL GULF OF MEXICO AND
INTO SOUTHERN MISSISSIPPI TUESDAY NIGHT...THEN CONTINUING TO TRACK
OFF TO THE NORTHEAST THROUGH THE TENNESSEE VALLEY AND EASTERN OHIO
VALLEY WEDNESDAY AND WEDNESDAY NIGHT. AS THE STORM SYSTEM TRACKS
BY TO THE WEST OF THE FORECAST AREA...A WARM FRONT WILL LIFT
NORTHWARD THROUGH THE REGION WEDNESDAY MORNING. A STRONG COLD
FRONT WILL THEN APPROACH FROM THE WEST WEDNESDAY AFTERNOON AND
WEDNESDAY EVENING...AND SHIFTING EASTWARD TO THE ATLANTIC COAST
TOWARD DAYBREAK THURSDAY. RAIN SHOWERS ARE EXPECTED TO DEVELOP IN
WARM AIR ADVECTION PATTERN TUESDAY NIGHT FROM SOUTHWEST TO
NORTHEAST. WILL CARRY CHANCE POPS ACROSS THE SOUTH TUESDAY
EVENING...INCREASING TO LIKELY AFTER MIDNIGHT. ACROSS THE
NORTH...WILL KEEP THE FORECAST RAIN FREE IN THE EVENING...THEN
INCREASE POPS INTO THE SLIGHT CHANCE/LOW CHANCE RANGE AFTER
MIDNIGHT.

WARM AIR ADVECTION WILL CONTINUE THROUGH WEDNESDAY...WITH BEST 
CHANCES FOR RAIN EXPECTED ACROSS CENTRAL AND NORTHERN ZONES 
WEDNESDAY MORNING...AND WILL CARRY LIKELY POPS HERE. ACROSS SOUTHERN 
ZONES IT APPEARS THAT THE INITIAL WARM AIR ADVECTION PRECIP SHOULD 
BECOME MORE SCATTERED BY WEDNESDAY MORNING...SO WILL CARRY CHANCE 
POPS HERE. 

THINGS BECOME MUCH MORE INTERESTING WEDNESDAY AFTERNOON AND 
WEDNESDAY EVENING...AS THE FORECAST AREA SOLIDLY WARM SECTORS. 
TEMPERATURES ARE EXPECTED TO INCREASE INTO THE UPPER 60S TO LOWER 
70S ACROSS THE AREA...WHILE DEWPOINTS RISE INTO THE UPPER 60S TO 
AROUND 70 DEGREES. IF THE MODELS ARE ON THE RIGHT TRACK WITH THE 
TEMPERATURE AND BOUNDARY LAYER MOISTURE EVOLUTION...THIS WILL RESULT 
IN SURFACE BASED INSTABILITY OF AROUND 200-600 J/KG OF CAPE AND LI/S 
OF -2 TO -4 ACROSS THE ENTIRE FORECAST AREA...WITH NO CONVECTIVE 
INHIBITION. THAT SAID...DESPITE THE LACK OF GOOD INSTABILITY THE 
COMBINATION OF STRONG MID-LEVEL QG FORCING...ENTRANCE REGION FORCING 
FROM A 130+ KT H25 JET...MID-LEVEL LAPSE RATES STEEPENING TO BETWEEN 
6.5 AND 7.0 C/KM ALONG WITH 0-6 KM BULK SHEAR VALUES OF 65 TO 75 
KT...SUPPORTIVE OF ORGANIZED LINEAR AND SUPERCELLULAR 
CONVECTION...THE POTENTIAL FOR SEVERE THUNDERSTORMS IS BEGINNING TO 
LOOK MORE LIKELY. AS A RESULT...WILL CARRY LIKELY/CATEGORICAL POPS 
WEDNESDAY AFTERNOON/EVENING ACROSS THE ENTIRE FORECAST AREA...AND 
WILL ADD SEVERE THUNDERSTORM WORDING TO THE ZONES AS WELL. AS FAR AS 
HAZARDS GO...WITH H85 WINDS INCREASING TO AROUND 70 KT PROGGED BY 
BOTH THE GFS AND NAM...ENERGY HELICITY INDICES CLIMBING TO AROUND 
1...AND 0-1 KM HELICITY VALUES MAXING OUT IN THE 400-500 
M2/S2...DAMAGING STRAIGHT LINE WINDS AND TORNADOES APPEAR TO BE THE 
PRIMARY SEVERE WEATHER THREATS...WITH MARGINALLY SEVERE HAIL 
POSSIBLE AS WELL.

IN ADDITION TO THE SEVERE WEATHER POTENTIAL...WITH BOUNDARY LAYER 
WINDS INCREASING TO AROUND 50 KNOTS WEDNESDAY AFTERNOON AND 
WEDNESDAY EVENING...WIND ADVISORIES MAY BE NEEDED FOR PORTIONS OF 
THE FORECAST AREA...ESPECIALLY ALONG THE SOUTH CAROLINA COAST.

MEDIUM RANGE GUIDANCE IS IN FAIRLY GOOD AGREEMENT WITH OVERALL 
SYNOPTIC PATTERN EVOLUTION THROUGH THE EXTENDED PERIODS THIS 
AFTERNOON. AS THE POTENT STORM SYSTEM CONTINUES TO TRACK OFF TO THE 
NORTHEAST AND AWAY FROM THE REGION EARLY THURSDAY MORNING...A COLD 
FRONT WILL PUSH THROUGH THE AREA. HIGH PRESSURE WILL THEN BUILD IN 
BEHIND THE DEPARTING COLD FRONT THURSDAY AFTERNOON...AND REMAIN THE 
DOMINANT WEATHER FEATURE THROUGH THE WEEKEND AND INTO EARLY NEXT 
WEEK. GUIDANCE SUGGESTS THAT THERE MAY BE AN AREA OF LOW PRESSURE 
DEVELOPING OFF THE SOUTHEAST COAST IN THE FRIDAY NIGHT THROUGH 
SATURDAY TIME FRAME...BUT AT THIS TIME IT APPEARS THAT RAIN CHANCES 
WILL HOLD OFFSHORE. THEREFORE...WILL KEEP THE EXTENDED PERIODS RAIN 
FREE.

&&

.AVIATION /01Z TUESDAY THROUGH SATURDAY/...
I MADE A QUICK UPDATE TO THE TERMINALS TO INTRODUCE SOME WIND
GUSTS WITH THE FRONTAL PASSAGE LATER THIS EVENING AS PRESSURE
RISES ARE REMAINING FAIRLY STRONG IMMEDIATELY BEHIND THE FRONT. NO
OTHER CHANGES.

EXTENDED AVIATION OUTLOOK...VFR CONDITIONS ARE EXPECTED THROUGH
TUESDAY EVENING. MVFR OR LOWER CIGS/VSBYS ALONG WITH GUSTY WINDS
WILL BE POSSIBLE LATE TUESDAY NIGHT THROUGH WEDNESDAY NIGHT AS A
POTENT STORM SYSTEM MOVES THROUGH THE AREA. VFR CONDITIONS ARE
THEN EXPECTED THURSDAY THROUGH SATURDAY.

&&

.MARINE...
TONIGHT...SW WINDS WILL INCREASE THIS EVENING AHEAD OF AN
APPROACHING COLD FRONT...WHICH IS EXPECTED TO PUSH THROUGH THE
WATERS SHORTLY AFTER MIDNIGHT. AN INITIAL SHOT OF INTENSE CAA
WILL INCREASE WINDS QUICKLY AND WE THINK SMALL CRAFT ADVISORY
CONDITIONS WILL RESULT ACROSS THE CHARLESTON COUNTY COASTAL WATERS
AS WELL AS OFFSHORE GA WATERS. THERE IS A CHANCE OF MARGINAL
ADVISORY CONDITIONS IN CHS HARBOR AND THE SC COASTAL WATERS S OF
EDISTO BEACH BUT PREFER TO LET THE NEXT FORECAST SHIFT HAVE
ANOTHER LOOK. OFFSHORE WINDS WILL SEVERELY LIMIT THE
SEAS...ESPECIALLY NEAR THE COAST...BUT DO HAVE SEAS BUILDING TO 6
FT BEYOND 30 NM FROM SHORE. 

TUESDAY...IMPROVING CONDITIONS ON TAP TUE AS HIGH PRES BUILDS IN
FROM THE N...ALTHOUGH THE OUTER GA WATERS LOOK TO REMAIN IN
ADVISORY CONDITIONS...MAINLY FOR LINGERING 6 FT SEAS DUE TO THE
FAVORABLE NE FETCH.

TUESDAY NIGHT THROUGH SATURDAY...A STRENGTHENING AREA OF LOW
PRESSURE WILL TRACK OUT OF THE CENTRAL GULF OF MEXICO AND INTO
SOUTHERN MISSISSIPPI TUESDAY NIGHT...THEN CONTINUE TO TRACK
NORTHEAST THROUGH THE TENNESSEE VALLEY AND EASTERN OHIO VALLEY
WEDNESDAY AND WEDNESDAY NIGHT. THE PRESSURE GRADIENT IS EXPECTED
TO STRENGTHEN SIGNIFICANTLY OVER THE COASTAL WATERS WEDNESDAY AND
WEDNESDAY NIGHT...IN RESPONSE TO THE DEEPENING AREA OF LOW
PRESSURE TO THE WEST. AS A RESULT...SMALL CRAFT CONDITIONS ARE
EXPECTED ACROSS ALL WATERS WEDNESDAY AND WEDNESDAY NIGHT. GALE
FORCE WINDS APPEAR POSSIBLE OVER THE NORTHERN LEG OF THE SOUTH
CAROLINA NEARSHORE AS WELL AS ACROSS THE OUTER GEORGIA WATERS...SO
HAVE ISSUED A GALE WATCH FOR THESE MARINE ZONES IN THE
WEDNESDAY/WEDNESDAY NIGHT TIME FRAME AS WELL. IT REMAINS POSSIBLE
THAT THE REMAINING NEARSHORE MARINE ZONES INCLUDING CHARLESTON
HARBOR MAY SEE GALE FORCE WINDS...BUT CONFIDENCE IN SEEING
FREQUENT GUSTS TO GALE FORCE WHERE SEA SURFACE TEMPERATURES REMAIN
IN THE UPPER 50S TO LOWER 60S IS NOT HIGH ENOUGH TO WARRANT A GALE
WATCH AT THIS TIME.

AS THE STORM SYSTEM CONTINUES TO PULL OFF TO THE NORTHEAST AND AWAY 
FROM THE REGION LATE WEDNESDAY NIGHT AND THURSDAY MORNING...A COLD 
FRONT WILL PUSH THROUGH THE WATERS...WITH HIGH PRESSURE THEN 
BUILDING BACK INTO THE REGION FROM THE WEST THROUGH SATURDAY. SMALL 
CRAFT CONDITIONS ARE EXPECTED TO LINGER ACROSS PORTIONS OF THE 
WATERS THROUGH THURSDAY EVENING...WITH WINDS AND SEAS THEN REMAINING 
BELOW SMALL CRAFT THRESHOLDS FRIDAY THROUGH SATURDAY.

&&

.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 9.7
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...GALE WATCH FROM WEDNESDAY AFTERNOON THROUGH THURSDAY MORNING 
     FOR AMZ350-374.
     SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO NOON EST 
     WEDNESDAY FOR AMZ374.
     SMALL CRAFT ADVISORY UNTIL 5 AM EST TUESDAY FOR AMZ350.

&&

$$