Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 280617
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
117 AM EST SAT FEB 28 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 THIS MORNING/...TWEAKED SKY COVER AND
DEW POINT TRENDS JUST A BIT ON THE MIDNIGHT UPDATE...THE
REMAINDER OF THE FORECAST REMAINS ON TRACK.

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
FLORIDA...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 THIS 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 /06Z SATURDAY THROUGH WEDNESDAY/...
VFR...THE RISK FOR MVFR CIGS WILL INCREASE AFTER 20Z TODAY...ESPECIALLY
AT KSAV AS ISENTROPIC ASSENT INTENSIFIES. SCATTERED LIGHT RAINS
MAY ACCENTUATE IFR CIGS AROUND KSAV SOMETIME TONIGHT BUT
CONFIDENCE TOO LOW FOR ANY TAF INCLUSIONS THIS FAR OUT.

GUSTY NE WINDS ARE LIKELY AT KCHS/KSAV TODAY AND EVEN INTO
TONIGHT AS THE PRESSURE GRADIENT TIGHTENS BETWEEN INLAND HIGH
PRESSURE AND A COASTAL TROUGH OFFSHORE. MODELS COMING IN FAIRLY
ROBUST FOR RAIN CHANCES LATER TODAY ON THE 00Z RUN...WE INTRODUCED
VCSH AT KCHS BY THIS EVENING AND AFTERNOON VCSH AT KSAV TO
PREVAILING LIGHT SHOWERS BY LATE DAY OR EARLY EVENING. RAINS NOT
EXPECTED TO BE HEAVY OR PARTICULARLY WIDESPREAD.

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...
OVERNIGHT...CONDITIONS WILL STEADILY DETERIORATE ACROSS THE
WATERS AS THE PRESSURE GRADIENT BETWEEN INLAND HIGH PRESSURE AND A
DEVELOPING COASTAL TROUGH STRENGTHENS. SMALL CRAFT ADVISORY
CONDITIONS ARE LIKELY ALL AREAS LATER TONIGHT WITH WINDS 20-25 KT
WITH GUSTS TO 30 KT AND SEAS BUILDING TO 4-6 FT NEARSHORE WATERS
AND 5-7 FT OFFSHORE WATERS. TRENDS ARE BEING WATCHED CAREFULLY FOR
TOMORROW AS THE LATEST GUIDANCE SUGGESTS THE STRONGEST PINCHED
GRADIENT MAY OCCUR OVER THE SOUTH CAROLINA NEARSHORE WATERS WITH
GUSTS NEARING GALE FORCE. A GALE WARNING MAY BE NEEDED FOR THESE
ZONES LATER TONIGHT SHOULD THIS UPWARD TREND CONTINUE. WILL
INCLUDE A MENTION OF THIS IN THE HAZARDOUS WEATHER OUTLOOK.

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 UNTIL 11 PM EST THIS EVENING FOR AMZ330.
     SMALL CRAFT ADVISORY UNTIL 1 PM EST SUNDAY FOR AMZ350-352-354.
     SMALL CRAFT ADVISORY UNTIL 9 AM EST THIS MORNING FOR AMZ374.
     GALE WARNING FROM 9 AM THIS MORNING TO 11 PM EST THIS EVENING
     FOR AMZ374.

&&

$$
SYNOPSIS...
NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...


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