Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 281148
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
748 AM EDT TUE APR 28 2015

.SYNOPSIS...
A WEAK AND DRY COLD FRONT WILL PUSH SOUTH THROUGH THE AREA THIS
MORNING WHILE HIGH PRESSURE REMAINS TO THE NORTH TODAY. A STORM
SYSTEM LIFTING OUT OF THE GULF COAST REGION WILL MOVE ACROSS THE
NORTHERN FLORIDA PENINSULA TONIGHT AND JUST OFFSHORE OF THE GEORGIA
AND SOUTH CAROLINA COAST ON WEDNESDAY. AS THE LOW PULLS AWAY
WEDNESDAY NIGHT AND THURSDAY...HIGH PRESSURE WILL BEGIN TO BUILD
BACK IN FROM THE NORTHWEST...GRADUALLY SETTLING OVER THE AREA FOR
THE WEEKEND INTO EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
TODAY...WEAK MID AND UPPER LEVEL RIDGING WILL PREVAIL OVER THE
REGION AHEAD OF A POSITIVELY TILTED TROUGH SHIFTING ACROSS THE
PLAINS STATES. AT THE SURFACE...HIGH PRESSURE WILL SETTLE JUST
NORTH OF THE AREA DURING THE DAY AS LOW PRESSURE TRACKS ALONG THE
NORTHERN GULF COAST REGION AHEAD OF THE UPPER TROUGH. ISENTROPIC
ASCENT AND MOISTURE DEPTH WILL GRADUALLY RAMP UP FROM THE SOUTH
TODAY...ALL WHILE UPPER LEVEL DIFLUENCE STRENGTHENS. THE RESULT
WILL BE AN INCREASING PROBABILITY FOR RAINFALL THROUGH THE PERIOD.
THE FORECAST INDICATES 20-30 PERCENT RAIN CHANCES MAINLY ACROSS
SOUTHEAST GEORGIA AND THE SOUTHERN TIP OF SOUTH CAROLINA BY THE
END OF THE DAY. GENERALLY CLOUDY SKIES WILL MAKE IT TOUGH TO WARM
MUCH...PROBABLY ONLY INTO THE LOWER 70S MOST PLACES.

TONIGHT...RAIN CHANCES RAMP UP FROM SOUTHWEST TO NORTHEAST AS DEEP
MOISTURE COMBINES WITH UPPER FORCING FOR ASCENT FROM THE
APPROACHING UPPER TROUGH AND NEARBY JET. THE SURFACE LOW AND
ASSOCIATED WARM FRONT SHOULD BE OVER SOUTHERN GEORGIA BY
DAYBREAK...LIKELY NOT GETTING MUCH MORE NORTH THAN THE ALTAMAHA
RIVER. THIS WILL KEEP THE BULK OF THE INSTABILITY SOUTH OF THE
AREA AND THUS THE RISK FOR THUNDERSTORMS IS PRETTY LOW...MAINLY
ELEVATED IN NATURE. HOWEVER...GIVEN THE STRONG DEEP LAYER SHEAR
AND ENHANCED HELICITY NEAR THE WARM FRONT SOME STRONGER STORMS MAY
NOT BE TOO FAR AWAY SO WILL HAVE TO KEEP AN EYE ON THE PROGRESSION
OF THE WARM FRONT LATE TONIGHT. LOWS SHOULD GET INTO THE 50S MOST
LOCALES AWAY FROM THE COAST ALTHOUGH TEMPS COULD RISE NEAR THE GA
COAST LATE AS THE WARM FRONT APPROACHES.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
WEDNESDAY AND WEDNESDAY NIGHT...AN UPPER LEVEL LOW MOVING ACROSS THE
TENNESSEE VALLEY AT THE START OF THE PERIOD WILL WEAKEN AND BECOME
ABSORBED BY A MUCH STRONGER CLOSED LOW DROPPING SOUTHWARD ACROSS THE
GREAT LAKES REGION. MEANWHILE UPPER DIVERGENCE ASSOCIATED WITH AN
UNSEASONABLY STRONG SOUTHERN STREAM JET WILL MAINTAIN A SURFACE LOW
PRESSURE SYSTEM ALONG THE SOUTHEAST PERIPHERY OF THE WEAKENING UPPER
LOW. MODELS ARE NOW COMING INTO MUCH BETTER AGREEMENT WITH THE TRACK
OF THE SURFACE LOW...AS THE NAM12 AND ECMWF HAVE TRENDED TOWARD THE
GFS SOLUTION BY KEEPING THE LOW SOUTH AND EAST OF THE AREA. MODELS
GENERALLY TRACK THE LOW ACROSS THE NORTHERN FLORIDA PENINSULA OR FAR
SOUTHERN GEORGIA EARLY WEDNESDAY MORNING...THEN MOVE IT JUST
OFFSHORE OF THE GEORGIA AND SOUTH CAROLINA COASTS THROUGH WEDNESDAY
AFTERNOON. THE LOW THEN BEGINS PULLING AWAY TO THE NORTHEAST
WEDNESDAY NIGHT.

AS THE LOW PASSES JUST TO THE SOUTH WEDNESDAY MORNING...SHOWERS WILL
BE WIDESPREAD ACROSS THE AREA GIVEN DEEP MOISTURE...ALONG WITH
STRONG ISENTROPIC ASCENT...UPPER DIVERGENCE AND FORCING FOR ASCENT
AHEAD OF THE APPROACHING/WEAKENING UPPER LOW. AS THE SURFACE LOW
TRANSITIONS TO A POSITION JUST OFF THE SOUTHEAST COAST...THE
GREATEST SHOWER COVERAGE WILL BEGIN LIFTING OUT WITH DECREASING RAIN
CHANCES THROUGH THE AFTERNOON FROM THE SOUTHWEST. THE POTENTIAL FOR
SHOWERS WILL CONTINUE TO DIMINISH FROM THE SOUTHWEST WEDNESDAY NIGHT
AS THE COASTAL LOW PULLS AWAY TO THE NORTHEAST. GIVEN THE MODEL
CONSENSUS OF KEEPING THE AREA SOLIDLY ON THE COLD SIDE OF THE
LOW...HAVE REMOVED MENTION OF THUNDERSTORMS FOR NEARLY ALL AREAS.
THE EXCEPTION IS MCINTOSH COUNTY AND THE ADJACENT COASTAL
WATERS...WHERE A SLIGHT CHANCE OF THUNDERSTORMS HAVE BEEN MAINTAINED
ON WEDNESDAY TO ACCOUNT FOR ANY UNEXPECTED ENCROACHMENT OF THE WARM
SECTOR OR EVEN SOME ELEVATED THUNDERSTORMS. THE SEVERE WEATHER
THREAT APPEARS GREATLY REDUCED AT THIS TIME AS WELL. AS FOR
TEMPERATURES...THE NORTHEAST FLOW COMBINED WITH WIDESPREAD SHOWERS
WILL RESULT IN A VERY COOL DAY...WITH HIGHS IN THE MID 60S TOWARD
THE MIDLANDS AND CSRA AND IN THE UPPER 60S TO AROUND 70 FARTHER
SOUTH AND EAST. LOWS AT NIGHT SHOULD BE IN THE LOWER TO MID 50S.

THURSDAY AND THURSDAY NIGHT...AN UNUSUALLY STRONG UPPER LEVEL LOW
FOR THIS TIME OF YEAR WILL DROP ACROSS THE OHIO VALLEY AND OVER THE
CENTRAL APPALACHIANS. MEANWHILE...SURFACE LOW PRESSURE WILL
STRENGTHEN OFF THE MID-ATLANTIC COAST AS HIGH PRESSURE BUILDS FROM
THE MISSISSIPPI VALLEY. A FEW INSTABILITY SHOWERS COULD OCCUR ALONG
THE SOUTHERN PERIPHERY OF THE DEEP CLOSED LOW...AND THE FORECAST
INDICATES A SLIGHT CHANCE OF SHOWERS ACROSS MOST OF THE
AREA...MAINLY NORTH OF I-16. TEMPERATURES WILL REMAIN UNSEASONABLY
COOL...WITH HIGHS IN THE LOWER 70S MOST AREAS. LOWS WILL REMAIN IN
THE LOWER TO MID 50S.

FRIDAY...THE STRONG UPPER LEVEL LOW WILL SHIFT TO THE MID-ATLANTIC
COAST...WITH SURFACE HIGH PRESSURE CONTINUING TO BUILD INTO THE
REGION FROM THE NORTHWEST. A DRY NORTHWEST FLOW WILL RESULT IN RAIN-
FREE CONDITIONS...BUT COOL TEMPERATURES WILL PREVAIL ONCE AGAIN WITH
HIGHS IN THE LOWER TO MID 70S.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
MEDIUM RANGE GUIDANCE IS IN VERY GOOD AGREEMENT WITH THE OVERALL
SYNOPTIC PATTERN...LEADING TO A HIGH CONFIDENCE FORECAST IN THE LONG
TERM PERIOD. DEEP LAYERED RIDGING WILL BUILD FROM THE WEST THROUGH
THE WEEKEND...THEN TRANSITION TO OVER THE WESTERN ATLANTIC EARLY
NEXT WEEK. STRONG SUBSIDENCE WILL RESULT IN RAIN-FREE CONDITIONS
THROUGH THE LONG TERM PERIOD...ALTHOUGH WITH A RETURN FLOW BRINGING
IN SOME ADDITIONAL MOISTURE AND A MORE PRONOUNCED SEA BREEZE EARLY
NEXT WEEK...ISOLATED DIURNAL CONVECTION CERTAINLY COULD NOT BE RULED
OUT. TEMPERATURES WILL MODERATE ON SATURDAY...RETURN TO NEAR NORMAL
SUNDAY...THEN CLIMB TO SLIGHTLY ABOVE NORMAL BY EARLY NEXT WEEK.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
KCHS...VFR CONDITIONS WILL PREVAIL INTO THIS EVENING...THEN
CONDITIONS WILL DETERIORATE OVERNIGHT AS SHOWERS DEVELOP AHEAD OF
LOW PRESSURE PASSING TO THE SOUTH. EXPECT MVFR...OR POSSIBLY
LOWER...CEILINGS AFTER 05Z ALONG WITH LIGHT SHOWERS.

KSAV...SHOWERS WILL SPREAD TOWARD THE TERMINAL THROUGH THE DAY
AHEAD OF LOW PRESSURE TRACKING ACROSS THE NORTHERN GULF COAST
REGION. HAVE ADDED VICINITY SHOWERS TO THE TAF AFTER 16Z...ALONG
WITH GUSTY EASTERLY WINDS. CONDITIONS WILL DETERIORATE THIS
EVENING AND OVERNIGHT AS THE LOW PASSES TO THE SOUTH...CAUSING
SHOWERS TO OVERSPREAD THE TERMINAL AND CEILINGS TO LOWER TO MVFR
OR LOWER LEVELS.

EXTENDED AVIATION OUTLOOK...MVFR OR LOWER CONDITIONS ARE PROBABLE
WEDNESDAY INTO WEDNESDAY NIGHT AS LOW PRESSURE PASSES TO THE
SOUTH AND EAST AND SHOWERS OVERSPREAD THE AREA. VFR CONDITIONS ARE
EXPECTED TO PREVAIL THURSDAY THROUGH SATURDAY.

&&

.MARINE...
TODAY AND TONIGHT...HIGH PRESSURE WILL REMAIN IN PLACE NORTH OF
THE AREA WHILE A DEVELOPING AREA OF LOW PRESSURE ALONG THE GULF
COAST SHIFTS TOWARD SOUTHEAST GEORGIA TONIGHT. THIS WILL LEAD TO A
TIGHTENING OF THE PRESSURE GRADIENT AND ENHANCED
WINDS/SEAS...CLOSE TO ADVISORY LEVELS. LOW CONFIDENCE AND THE
MARGINAL NATURE OF THE EVENT PRECLUDES ANY ADVISORIES AT THIS TIME
BUT CAN/T RULE THEM OUT EVENTUALLY DEPENDING ON WHERE THE BEST
GRADIENT SETS UP...WHICH SEEMS MOST LIKELY ALONG THE LOWER SC AND
NORTHERN GA NEARSHORE WATERS.

WEDNESDAY THROUGH SUNDAY...CONDITIONS WILL DETERIORATE AS A LOW
PRESSURE SYSTEM PASSES JUST EAST OF THE COASTAL WATERS
WEDNESDAY...THEN BEGINS TO LIFT OFF TO THE NORTHEAST WEDNESDAY
NIGHT. A PERIOD OF SMALL CRAFT ADVISORY CONDITIONS ARE EXPECTED FOR
ALL WATERS WEDNESDAY AND/OR WEDNESDAY NIGHT IN ASSOCIATION WITH A
TIGHT SURFACE PRESSURE GRADIENT AROUND THE LOW. WINDS/SEAS SHOULD
THEN SLOWLY IMPROVE ON THURSDAY AS THE LOW PRESSURE SYSTEM SHIFTS
FARTHER NORTH/NORTHEAST AND AWAY FROM THE AREA...BEFORE IMPROVING
FURTHER AS WEAK HIGH PRESSURE SETTLES OVER THE WATERS THROUGH THE
WEEKEND.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...
NEAR TERM...RJB
SHORT TERM...JAQ
LONG TERM...JAQ
AVIATION...JAQ
MARINE...JAQ/RJB



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