000
FXUS62 KCHS 220019
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
811 PM EDT SUN MAR 21 2010

.SYNOPSIS...
A COLD FRONT WILL APPROACHING FROM THE WEST WILL ADVANCE THROUGH
THE REGION TONIGHT. DEEP LOW PRESSURE TO THE NORTH WILL DOMINATE
CONDITIONS MONDAY AND TUESDAY...BEFORE HIGH PRESSURE EXPANDS OVER
THE REGION MID WEEK. ANOTHER COLD FRONT WILL LIKELY PASS THROUGH
THE AREA FRIDAY OR EARLY SATURDAY.

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
GRIDS AND TEXT PRODUCTS HAVE BEEN ISSUED TO REFLECT GOING SHORT
TERM TRENDS. THE MAIN CONCERN CONTINUES TO REVOLVE AROUND THE
CONVECTIVE POTENTIAL OVER THE NEXT SEVERAL HOURS. WATER VAPOR
IMAGERY SHOWS AN IMPRESSIVE UPPER LOW BARRELING EAST ACROSS THE
DEEP SOUTH THIS EVENING WITH A STRONG DIFLUENCE AXIS MOVING INTO
GEORGIA AND WESTERN SOUTH CAROLINA. IMPRESSIVE LIFT AHEAD OF THE
LOW IS SUPPORTING A HEALTHY LINE OF STRONG TSTMS ACROSS NORTH
GEORGIA WHICH HAVE HAD A HISTORY PRODUCING GUSTY WINDS AND SMALL
HAIL. SHOWERS AND TSTMS WILL CONTINUE TO DEVELOP ACROSS CENTRAL
GEORGIA...THE CSRA AND THE MIDLANDS OVER THE NEXT FEW HOURS AS THE
CORE OF THE STRONGEST LIFT INTERSECTS THE AXIS OF LOWER 60S
DEWPOINTS THAT ARE THE SLOWLY ADVECTING INLAND AHEAD OF AN
APPROACHING OCCLUDED FRONT. IN FACT...RADAR DATA FROM KJGX AND KCAE
INDICATE THIS DEVELOPMENT IS ALREADY IN PROGRESS. INCOMING MODEL
DATA SUGGEST THE COVERAGE OF SHOWERS AND TSTMS WILL LIKELY BE
LIMITED TO SEVERAL LINER BANDS WHICH WILL NOT LAST TOO LONG AT ANY
ONE LOCATIONS. WILL LOWER POPS TO 40-60 PERCENT WITH THE HIGHS POPS
CONFINED TO OUR INTERIOR SOUTH CAROLINA ZONES.

THERE CONTINUES TO BE ABOUT A 3-5 HOUR WINDOW FOR ISOLATED STRONG
TO SEVERE TSTMS TONIGHT...ROUGHLY IN THE 02Z-06Z TIME PERIOD.
MODIFIED RUC SOUNDINGS AS WELL AS THE 22/00Z SOUNDING FROM CHS
SUGGEST SOME WEAK SURFACE BASED INSTABILITY WILL DEVELOP OVER THE
NEXT 1-2 HOURS WITH LIFTED INDICES DROPPING TO -2 TO -3C WITH
SBCAPES AROUND 300 K/JG. ALREADY SEEING A GROWING AXIS OF SBCAPES
AROUND 200 J/KG EXTENDING FROM MACON TO NEAR WAYCROSS. ALTHOUGH
THESE THERMODYNAMIC VALUES ARE LESS THAN IMPRESSIVE...THE LACK OF
SURFACE BASED INSTABILITY WILL BE AUGMENTED BY IMPRESSIVE
KINEMATIC PROFILES WHICH ARE ALREADY IN PLACE. 0-6KM BULK SHEAR IN
EXCESS OF 50 KT WILL SUPPORT A RISK FOR ORGANIZED SHORT-DURATION
BOWING SEGMENTS WITH BRIEF SUPERCELL STRUCTURES POSSIBLE. ATTM WE
BELIEVE THE SEVERE TSTM RISK WILL BE FAIRLY ISOLATED. THE MAIN
HAZARDS WILL BE ISOLATED DAMAGING WIND GUSTS AND POSSIBLY AN
ISOLATED TORNADO. THERE WILL ALSO BE A RISK FOR SMALL
HAIL...ALTHOUGH THE LACK OF SIGNIFICANT INSTABILITY WILL LIKELY
LIMIT UPDRAFTS BELOW THE FAVORABLE HAIL GROWTH AREA.

.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
MONDAY...THE UPPER LEVEL LOW WILL MOVE ENE THROUGH THE SOUTHERN
APPALACHIANS. THERE MAY BE ENOUGH MOISTURE AND UPPER-LEVEL FORCING
FOR SOME SHOWERS...MAINLY ACROSS SOUTHERN SC AND INTERIOR SE GA.
GRAUPLE IS POSSIBLE WITH THESE SHOWERS DUE TO THE LOW FREEZING
LEVELS /AROUND 4-5K FT/. HIGHS SHOULD TOP OUT IN THE LOWER/MID 60S
UNDER MOSTLY CLOUDY SKIES. IT WILL ALSO BE BREEZY...WITH GUSTS UP
TO 30 MPH POSSIBLE FROM LATE MORNING ON.

MONDAY NIGHT...THE SHOWERS MAY LINGER INTO THE EARLY EVENING
AROUND THE CHARLESTON TRI-COUNTY AREA BEFORE CONDITIONS BEGIN TO
IMPROVE FROM THE SW. LOWS WILL DROP INTO THE LOWER 40S FOR MOST
LOCALES...POSSIBLY SLIGHTLY COOLER WELL INLAND AND SLIGHTLY WARMER
ALONG THE COAST.

TUESDAY...DEEP LOW PRESSURE WILL SLOWLY EXIT THE MID ATLANTIC
COAST. AFTER A CHILLY START WE SHOULD SEE TEMPERATURES REBOUND
INTO THE MID OR MAYBE EVEN UPPER 60S WITH BREEZY AFTERNOON
CONDITIONS.

TUESDAY NIGHT AND WEDNESDAY...HIGH PRESSURE WILL BUILD IN TUESDAY
NIGHT AND WEDNESDAY WITH TEMPERATURES MODERATING ABOVE NORMAL
WED WITH HIGHS IN THE MID 70S AWAY FROM THE COAST WHERE AN ONSHORE
FLOW WILL KEEP HIGHS NO WARMER THAN THE MID 60S.

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
WED NIGHT AND THU...SURFACE HIGH PRES OVER THE AREA WILL MAINTAIN
DRY WEATHER. A MODERATING TEMPERATURE TREND WITH HIGHS RETURNING
TO THE MID/UPPER 70S THU.

THU NIGHT THROUGH SUN...UNCERTAINTY BEGINS THU NIGHT AS THE 12Z/21
MODEL GUIDANCE IS IN DISAGREEMENT WITH RESPECT TO THE NEXT COLD
FRONT/LOW PRESSURE SYSTEM FRI INTO SAT AND ANOTHER COLD FRONT SUN.
DID NOT MAKE ANY CHANGES TO THIS PORTION OF THE FORECAST THROUGH
THIS PERIOD AS SLIGHT CHANCE POPS SHOULD COVER IT FOR NOW.

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
EXPECT CONDITIONS TO CONTINUE TO DETERIORATE THIS EVENING AND
OVERNIGHT FOR KCHS AND KSAV AS A DEEP LOW PRESSURE SYSTEM AFFECTS
THE AREA. HAVE INITIATED KSAV WITH MVFR CONDITIONS AS MAJORITY OF
THE SURROUNDING OBS CONTINUE TO SHOW PREVAILING MVFR CEILINGS. AS
MORE SHOWERS DEVELOP THIS EVENING AND MOVE ACROSS THE AREA...EXPECT
CEILINGS TO QUICKLY LOWER TO IFR LEVELS AT KSAV. EXPECT A ONE TO TWO
HOUR LAG IN DETERIORATING CONDITIONS AT KCHS DUE TO THE POSITIONING
OF THE LOW PRESSURE AND ITS ASSOCIATED COLD FRONT...BUT VFR
CONDITIONS SHOULD QUICKLY LOWER A COUPLE HOURS AFTER SUNSET AS WELL.
HAVE MAINTAINED A THREAT OF TSRA FOR BOTH SITES AS SOME ORGANIZED
CONVECTION COULD STILL MOVE THROUGH THE AREA THIS EVENING. MAY NEED
AMENDMENTS AS TIMING FOR THUNDER COULD BE SLIGHTLY OFF...ESPECIALLY
AT KSAV WHERE THE THUNDER RISK COULD PASS JUST NORTH OF THE TERMINAL.

00Z KCHS SOUNDING SHOWED MARGINAL LLWS CONDITIONS FOR KCHS WHICH
APPEARS ON TRACK WITH WHAT MOST MODEL SOUNDING ARE SHOWING.
THEREFORE...HAVE INCLUDED LLWS FOR BOTH SITES AS MODELS SHOW 40 TO
45 KNOT WINDS AROUND 2K FT...ESPECIALLY AT KCHS WHERE POTENTIAL FOR
SLIGHTLY STRONGER WINDS ARE POSSIBLE. AFTER 05Z/06Z...WINDS ALOFT
SHOULD START TO DIMINISH ENDING THE RISK OF LLWS CONDITIONS.

EXPECT CEILINGS TO LIFT AND SCATTER OUT PRIOR TO DAYBREAK MONDAY
MORNING. VFR CONDITIONS SHOULD THEN PREVAIL ALONG WITH GUSTY
SOUTHWESTERLY WINDS IN THE AFTERNOON DUE TO A TIGHT PRESSURE
GRADIENT.

EXTENDED AVIATION OUTLOOK...VFR THROUGH AT LEAST THU BEFORE MVFR
CONDS OR LOWER POSSIBLY AFFECT THE AREA WITH THE APPROACH OF THE
NEXT FRONTAL SYSTEM. GUSTY WINDS MON AND TUE AFTERNOON.

.MARINE...
SFC WINDS HAVE SHOWN A GRADUAL INCREASE SO FAR THIS AFTN AS THE
PRES GRADIENT TIGHTENS AHEAD OF AN INCOMING STRONG COLD FRONT.
STRONG LOW LEVEL WIND FIELDS MIXING DOWN PARTIALLY HAVE PUT WIND
SPEEDS IN THE 15 KT AREA...ON THEIR WAY TO NEAR AND POSSIBLY
EXCEEDING 20 KT. THIS IS A FAVORABLE DIRECTION TO SEE DISTURBED
CONDITIONS IN CHAS HARBOR SO HAVE OPTED TO RAISE SCA FLAGS FOR THE
REST OF TODAY AND TONIGHT FOR THE HARBOR. WITHIN THE COASTAL
WATERS...WINDS OUT OF THE SE THROUGH LATE THIS EVENING AND
BECOMING S LATE WILL BE THE FAVORABLE FETCH NEEDED TO STEADILY
INCREASE SEAS SUCH THAT ALL MARINE ZONES WILL HAVE SEAS IN EXCESS
OF 6 FEET OVERNIGHT. WILL KEEP THE REMAINING SCA HEADLINES IN
PLACE AS THEY ARE DELINEATED.

MONDAY THROUGH FRIDAY...THE RELATIVELY TIGHT PRES GRADIENT AND
STRONG LOW-LEVEL WINDS ARE EXPECTED OVER THE COASTAL WATERS
THROUGH TUE BEFORE DIMINISHING TUE NIGHT AS THE UPPER LEVEL LOW
PRES SYSTEM PUSHES FARTHER OFF THE COAST AND WELL NE OF THE AREA.
SCA CONDS...MAINLY FOR SEAS...WILL LINGER THROUGH MON FOR THE SC
COASTAL WATERS N OF EDISTO BEACH AND THE GA WATERS BEYOND 20 NM
FROM SHORE. HIGH PRES WILL THEN PROVIDE A MUCH MORE TRANQUIL
MARINE ENVIRONMENT WED INTO THU BEFORE CONDS POSSIBLY BEGIN TO GO
DOWNHILL AS A COLD FRONT/LOW PRES APPROACH FROM THE W.

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT MONDAY FOR AMZ330-354.
     SMALL CRAFT ADVISORY UNTIL 11 AM EDT MONDAY FOR AMZ352.
     SMALL CRAFT ADVISORY UNTIL 11 PM EDT MONDAY FOR AMZ350.
     SMALL CRAFT ADVISORY UNTIL 6 AM EDT TUESDAY FOR AMZ374.