Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 272337
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
637 PM EST FRI FEB 27 2015

.SYNOPSIS...
HIGH PRESSURE WILL BUILD NORTH OF THE REGION THROUGH TONIGHT AND
WEDGE SOUTHWARD OVER GEORGIA AND SOUTH CAROLINA OVER THE WEEKEND
WHILE A COASTAL TROUGH DEVELOPS OFF THE SOUTHEAST COAST. A COLD
FRONT WILL MOVE IN AND STALL OVER OR JUST SOUTH OF THE AREA ON
MONDAY...THEN LIFT NORTH AS A WARM FRONT ON TUESDAY. A COLD FRONT
WILL SHIFT THROUGH THE AREA LATE WEDNESDAY INTO THURSDAY...FOLLOWED
BY COOLER HIGH PRESSURE NEXT WEEKEND.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
A POWERFUL UPPER JET WILL REMAIN ANCHORED JUST TO THE WEST
OVERNIGHT AS SURFACE HIGH PRESSURE EXTENDS ACROSS THE REGION.
SATELLITE SHOWS THE CIRRUS CANOPY EXPANDING ONCE AGAIN ACROSS
FLORDIA...EASTERN GEORGIA...EASTERN SOUTH CAROLINA INTO THE NORTH
CAROLINA CRYSTAL COAST AS THE LEFT ENTRANCE REGION OF THE UPPER
JET STRENGTHENS SLIGHTLY. SATELLITE TRENDS SUGGEST THICK CIRRUS
WILL REMAIN IN PLACE FOR MUCH OF THE NIGHT...WHICH CORRESPONDS
WELL WITH THE LATEST SET OF HIGH RESOLUTION GUIDANCE. OVERNIGHT
LOWS MAY BE A BIT TOO COOL GIVEN THICK CIRRUS IS EXPECTED TO HOLD
FIRM...SO WILL NUDGE LOWS UP 1-3 DEGREES FOR MOST LOCATIONS. THESE
UPDATED VALUES MAY STILL PROVE TO BE TOO COOL...ESPECIALLY ACROSS
INTERIOR SOUTHEAST SOUTH CAROLINA. FURTHER ADJUSTMENTS MAY BE
NEEDED WITH THE LATE EVENING UPDATE. GUSTY CONDITIONS WILL DEVELOP
ACROSS THE COASTAL COUNTIES LATER THIS EVENING AND OVERNIGHT AS
THE PRESSURE GRADIENT BETWEEN INLAND HIGH PRESSURE AND A
DEVELOPING COASTAL TROUGH OFFSHORE TIGHTENS.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
SATURDAY AND SATURDAY NIGHT... SURFACE HIGH PRESSURE CENTERED OVER
THE MID-ATLANTIC REGION WILL WEDGE SOUTHWARD ALONG THE LEE OF THE
APPALACHIANS...WHILE A COASTAL TROUGH DEVELOPS OFF THE SOUTHEAST
COAST. INCREASING LOW AND MID LEVEL MOISTURE WILL SUPPORT SKIES
BECOMING CLOUDY ACROSS THE AREA. SHOWERS WILL INITIALLY BE LIMITED
TO THE COASTAL WATERS IN THE MORNING IN AN AREA OF ENHANCED LOW
LEVEL CONVERGENCE IN VICINITY OF THE COASTAL TROUGH...BUT
STRENGTHENING ISENTROPIC ASCENT WILL RESULT IN SOME RAIN DEVELOPING
OVER SOUTHEAST GEORGIA IN THE AFTERNOON. RAIN WILL THEN INCREASE IN
COVERAGE THROUGH THE NIGHT...WITH PROBABILITIES OF 30-50
PERCENT...HIGHEST ALONG THE COAST NEAR THE TROUGH AND TOWARD THE
MIDLANDS WHERE ISENTROPIC ASCENT WILL BE MAXIMIZED. LOW LEVEL
NORTHEAST FLOW WITHIN THE SURFACE WEDGE AND EXTENSIVE CLOUD COVER
WILL LIMIT HIGHS TO THE UPPER 40S TO AROUND 50 ACROSS THE AREA. LOWS
SATURDAY NIGHT WILL BE IN THE UPPER 30S TO LOWER 40S ACROSS MOST OF
THE AREA.

SUNDAY AND SUNDAY NIGHT...THE PARENT HIGH WILL BEGIN TO SHIFT OFF
THE MID-ATLANTIC COAST ON SUNDAY...WITH SOME INDICATION THAT THE
WEDGE MAY BEGIN TO ERODE LATE IN THE DAY OR SUNDAY NIGHT. DEEP
MOISTURE AND CONTINUED ISENTROPIC ASCENT WILL SUPPORT A 20-40
PERCENT CHANCE OF RAIN ACROSS THE AREA...WITH RAIN CHANCES TAPERING
OFF AT NIGHT AS THE COASTAL TROUGH LIFTS TO THE NORTH AND THE WEDGE
ERODES. THE TIMING OF THE WEDGE EROSION WILL BE CRITICAL FOR
TEMPERATURES...AS THERE ARE SIGNIFICANT DIFFERENCES IN FORECAST
HIGHS WITH THE VARIOUS NUMERICAL GUIDANCE. PLAN TO TAKE A BLEND OF
MODELS...WITH HIGHS IN THE UPPER 40S NORTHWEST TO THE UPPER 50S NEAR
THE GA COAST...BUT TEMPERATURES COULD BE 5-10 DEGREES WARMER/COOLER
DEPENDING ON HOW WELL ENTRENCHED THE WEDGE IS. LOWS SUNDAY NIGHT
SHOULD GENERALLY BE IN THE 40S AND LOWER 50S.

MONDAY...A BRIEF TRANSITION PERIOD IS EXPECTED AS WEAK HIGH PRESSURE
PASSES OVER THE REGION...FOLLOWED BY THE APPROACH AND EVENTUAL
PROGRESSION OF A BACKDOOR COLD FRONT INTO THE AREA LATE IN THE DAY.
THERE COULD BE SOME SHOWERS AROUND DURING THE DAY...BUT CERTAINLY
NOT A WASH OUT. TEMPERATURES COULD WARM INTO THE MID AND UPPER 60S
ACROSS SOUTHEAST SOUTH CAROLINA AND UPPER 60S TO LOWER 70S ACROSS
SOUTHEAST GEORGIA FOR HIGHS BEFORE THE BACKDOOR FRONT MOVES IN.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
A BACKDOOR COLD FRONT WILL STALL OVER OR NEAR THE AREA MONDAY
NIGHT...SUPPORTING CHANCES OF SHOWERS OVER THE AREA. THE STALLED
FRONT WILL THEN LIFT NORTH AS A WARM FRONT ON TUESDAY...BRINGING
WARMER CONDITIONS. IN GENERAL...EXPECT AFTERNOON HIGHS IN THE UPPER
60S/LOWER 70S ON TUESDAY. EVEN WARMER CONDITIONS WILL DEVELOP ON
WEDNESDAY AS A SOUTHERLY FLOW STRENGTHENS AND SOME COMPRESSIONAL
HEATING OCCURS AHEAD OF AN APPROACHING COLD FRONT FROM THE
WEST/NORTHWEST. STRONG FORCING WILL BE ASSOCIATED WITH THE
FRONT...SUPPORTING THE NEED FOR INCREASING SHOWERS AND SOME
THUNDERSTORMS IN THE FORECAST WEDNESDAY NIGHT INTO EARLY THURSDAY.
SHOWERS AND/OR THUNDERSTORMS WILL THEN SHIFT OFFSHORE WITH THE
COLD FRONT BY THURSDAY AFTERNOON...FOLLOWED BY DRY AND COOLER HIGH
PRESSURE ON FRIDAY.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
VFR...ALTHOUGH THE RISK FOR MVFR AND IFR CIGS WILL INCREASE AFTER
20Z THURSDAY...ESPECIALLY AT KSAV AS ISENTROPIC ASSENT
INTENSIFIES. GUSTY CONDITIONS ARE LIKELY AT KCHS/KSAV LATER THIS
EVENING AS THE PRESSURE GRADIENT TIGHTENS BETWEEN INLAND HIGH
PRESSURE AND A COASTAL TROUGH OFFSHORE.

EXTENDED AVIATION OUTLOOK...
FLIGHT RESTRICTIONS ARE LIKELY SATURDAY EVENING INTO SUNDAY AS A
WEDGE OF HIGH PRESSURE PERSISTS OVER THE AREA. VFR CONDITIONS
SHOULD RETURN FOR PART OF MONDAY...BEFORE FLIGHT RESTRICTIONS
BECOME POSSIBLE MONDAY NIGHT INTO EARLY TUESDAY AT EITHER TERMINAL
WITH THE PASSAGE OF ANOTHER COLD FRONT.

&&

.MARINE...
TONIGHT...HIGH PRESSURE WEDGING DOWN THE EASTERN SEABOARD TONIGHT
WILL PRODUCE A STRENGTHENING PRESSURE GRADIENT ALONG THE COAST.
THE TIGHTEST GRADIENT WILL BE ACROSS THE GA WATERS WHERE A COASTAL
TROUGH IS SETTING UP. WE HAVE SMALL CRAFT ADVISORIES IN EFFECT FOR
BOTH THE GA NEARSHORE AND OFFSHORE WATERS...WITH ADVISORIES FOR
THE SC WATERS STARTING AT VARIOUS INTERVALS LATER TONIGHT AS THE
GRADIENT TIGHTENS FROM SOUTH TO NORTH.

SATURDAY AND SUNDAY...HIGH PRESSURE WILL WEDGE INLAND ON SATURDAY
AND SUNDAY WHILE A COASTAL TROUGH DEVELOPS OFF THE GEORGIA COAST.
A STRONG PRESSURE GRADIENT IS EXPECTED TO DEVELOP BETWEEN THESE
TWO FEATURES...LEADING TO DETERIORATING CONDITIONS OVER ALL MARINE
WATERS SATURDAY AND SUNDAY. A GALE WARNING HAS BEEN ISSUED FOR
OFFSHORE GEORGIA WATERS ON SATURDAY/SATURDAY NIGHT WHERE PINCHING
BECOMES GREATEST ALONG THE NORTHERN EDGE OF THE COASTAL
TROUGH...AND SMALL CRAFT ADVISORIES WILL BE ONGOING FOR ALL
REMAINING WATERS THROUGH EARLY SUNDAY AFTERNOON. CONDITIONS WILL
BEGIN TO IMPROVE OVER THE WATERS SATURDAY NIGHT...PROMPTING AN END
TO A SMALL CRAFT ADVISORY IN THE CHS HARBOR...BUT WILL TAKE TIME
TO IMPROVE IN ALL REMAINING WATERS.

SUNDAY NIGHT THROUGH WEDNESDAY NIGHT...WINDS/SEAS SHOULD FALL
BELOW SMALL CRAFT ADVISORY LEVELS OVER ALL NEAR SHORE WATERS BY
SUNDAY EVENING...THEN BY MONDAY MORNING OVER THE OUTER GEORGIA
WATERS AS HIGH PRESSURE SLIDES OVER THE WATERS AND THE COASTAL
TROUGH WEAKENS. SMALL CRAFT ADVISORY CONDITIONS COULD RETURN LATE
WEDNESDAY INTO THURSDAY AS A COLD FRONT SWEEPS THROUGH THE
SOUTHEASTERN UNITED STATES.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 4 AM TO 11 PM EST SATURDAY FOR
     AMZ330.
     SMALL CRAFT ADVISORY UNTIL 1 PM EST SUNDAY FOR AMZ350-352-354.
     SMALL CRAFT ADVISORY UNTIL 9 AM EST SATURDAY FOR AMZ374.
     GALE WARNING FROM 9 AM TO 11 PM EST SATURDAY FOR AMZ374.

&&

$$


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