Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 201847
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
147 PM EST SAT DEC 20 2014

.SYNOPSIS...
UNSETTLED WEATHER IS EXPECTED THROUGH TUESDAY AS SEVERAL DISTURBANCES
MOVE OVER THE REGION. A STRONG COLD FRONT WILL APPROACH TUESDAY NIGHT...
THEN SHIFT THROUGH THE AREA ON WEDNESDAY. DRY HIGH PRESSURE WILL THEN
SETTLE OVER THE SOUTHEAST THROUGH LATE WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AN UPPER LEVEL SHORTWAVE IS PROGRESSING INTO NORTH GA AND THE SC
UPSTATE LATE THIS MORNING. MEANWHILE THE SUBTROPICAL JET STREAM
HAS SHIFTED EVER SO SLIGHTLY NORTH...MOVING THE REGION OF DIVERGENCE
TO OUR NORTH. WATER VAPOR IMAGERY SHOWS A LARGE AREA OF MID AND
HIGH LEVEL DRY AIR THAT WILL PUSH INTO THE REGION LATER THIS
AFTERNOON BEHIND THE SHORTWAVE. AT THE SURFACE WE HAVE WEAK HIGH
PRESSURE WEDGING DOWN THE EASTERN SEABOARD AND A SURFACE LOW
DEVELOPING OFF THE COAST. WE EXPECT FAIRLY WIDESPREAD LIGHT RAIN
TO CONTINUE INTO EARLY THIS AFTERNOON...ESPECIALLY ACROSS THE
NORTHERN HALF OF THE AREA CLOSER TO THE UPPER FORCING. BY MID TO
LATE AFTERNOON...ONCE PVA ASSOCIATED WITH THE SHORTWAVE SHIFTS OFF
THE COAST AND SOME DRIER AIR SHIFTS IN ALOFT...THE RAIN SHOULD
QUICKLY TAPER OFF FROM WEST TO EAST. CURRENT POP SCHEME LOOKS VERY
GOOD. CLOUDY SKIES SHOULD CONTINUE TODAY. TEMPS WILL REMAIN FAIRLY
STEADY THROUGH EARLY TO MID AFTERNOON DUE TO WEAK LOW-LEVEL COLD
ADVECTION AND EVAPORATIONAL COOLING. LATE IN THE DAY WE COULD SEE
A BRIEF REBOUND IN TEMPERATURES ONCE THE RAIN ENDS...BUT HIGHS
WILL NOT MAKE IT OUT OF THE 50S.

TONIGHT WE LIKE THE SREF REPRESENTATION OF LOW CLOUDS EXPANDING
INLAND THIS EVENING WITH STRATUS PERHAPS BUILDING DOWN IN SOME
AREAS BUT CONFIDENCE ONLY ENOUGH TO ADD PATCHY FOG TO THE FORECAST
OVERNIGHT AS LOW CLOUDS REMAIN MORE CERTAIN AT THIS POINT. LACK OF
FORCING SUGGESTS ANY LIGHT RAINS AROUND TONIGHT WOULD BE PATCHY
WITH SOME DRIZZLE AROUND THE REGION. POPS ONLY IN THE SLIGHT
CHANCE WERE MAINTAINED AND LOWS IN THE 40S ACROSS THE BOARD.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY/...
SUNDAY...THE DAY SHOULD START OFF SOMEWHAT DRY...BEFORE A PLUME OF
MOISTURE ADVECTS NORTH AS AN AREA OF LOW PRESSURE OVER THE NORTHEAST
GULF OF MEXICO SLOWLY SHIFTS OVER THE SOUTHEASTERN UNITED STATES
SUNDAY NIGHT. HAVE THEREFORE KEPT A GENERAL TREND OF RAMPING UP POPS
FROM SOUTHEAST GEORGIA TO SOUTHEAST SOUTH CAROLINA...WITH POPS
APPROACHING 80-90 SUNDAY NIGHT. GREATEST CHANCES OF PRECIP STILL
APPEAR TO BE OVER SOUTHEAST GEORGIA AND ALONG THE SOUTH CAROLINA
COAST AT THIS TIME...GIVEN THE LATEST TRACK ALONG THE SOUTHEAST
COAST. OVERALL HIGH TEMPS WILL BE DEPENDENT ON THE LOW TRACK...BUT
SHOULD REACH THE MID/UPPER 50S OVER MOST LOCATIONS AWAY FROM THE
COAST. TEMPS COULD PEAK NEAR 60 ALONG COASTAL AREAS IN SOUTHEAST
GEORGIA. OVERNIGHT LOWS SHOULD RANGE IN THE MID/UPPER 40S AWAY FROM
THE COAST...AND IN THE LOW 50S ALONG THE COAST.

MONDAY...SHOWERS WILL LIKELY BE ONGOING TO START OFF THE DAY AS AN
AREA OF LOW PRESSURE CONTINUES TO MAKE WAY TO THE NORTHEAST. MOST
PRECIP SHOULD SHIFT OFFSHORE DURING THE AFTERNOON...BUT ELEVATED
PRECIP CHANCES WILL REMAIN IN THE FORECAST THROUGH MUCH OF THE
EVENING WHILE ABUNDANT LOW-LVL MOISTURE LAGS BEHIND THE LOW TO THE
NORTHEAST. TEMPS WILL BE DEPENDENT ON WHAT IS LEFT OF THE HIGH
PRESSURE WEDGE INLAND...BUT SHOULD BE SLIGHTLY WARMER...IN THE UPPER
50S INLAND TO LOWER 60S IN SOUTHEAST GEORGIA AND ALONG THE SOUTH
CAROLINA COAST.

MONDAY NIGHT INTO TUESDAY...MODELS CONTINUE TO SUGGEST INCREASING
PRECIP CHANCES LATE MONDAY NIGHT INTO TUESDAY AS A COASTAL FRONT
LIFTS NORTH INTO A WEAKENING WEDGE OF HIGH PRESSURE AT THE SFC. A
PERIOD OF WARMING SHOULD OCCUR WITHIN A SOUTHERLY FLOW AHEAD OF THE
STRONG COLD FRONT TO THE WEST...WITH HIGH TEMPS APPROACHING THE
MID/UPPER 60S TUESDAY AFTERNOON. DEEPENING MOISTURE CHARACTERIZED BY
PWATS BETWEEN 1.8-1.9 INCHES ALONG WITH THE WARMER TEMPS SHOULD BE
SUFFICIENT FOR A FEW THUNDERSTORMS DURING THE AFTERNOON. GREATEST
CHANCES SHOULD OCCUR OVER SOUTHEAST GEORGIA WHERE SBCAPES APPROACH
800 J/KG AND MID LVL LAPSE RATES ARE NEAR 7 C/KM.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
TUESDAY NIGHT TEMPS WILL REMAIN RATHER MILD AHEAD OF A COLD FRONT TO
THE WEST. WE COULD SEE A FEW THUNDERSTORMS BEFORE THE FRONT SHIFTS
OFFSHORE WEDNESDAY AFTERNOON. GUSTY WINDS SHOULD ALSO ACCOMPANY THE
FRONT AS STRONG COLD AIR ADVECTION OCCURS BEHIND IT. A MUCH
QUIETER/DRY PERIOD OF WEATHER IS THEN ANTICIPATED AS HIGH PRESSURE
BUILDS OVER THE REGION BEHIND THE FRONT STARTING WEDNESDAY NIGHT.
TEMPS WILL BE SLOW TO WARM THROUGH THURSDAY...UNTIL HIGH PRESSURE
BECOMES MORE CENTERED OVER THE WESTERN ATLANTIC. OVERALL HIGH TEMPS
SHOULD RANGE IN THE MID/UPPER 50S THURSDAY...BEFORE SOUTHERLY FLOW
RETURNS TO THE AREA ALONG THE WESTERN EDGE OF HIGH PRESSURE ON
FRIDAY. TEMPS SHOULD PEAK INTO THE LOW/MID 60S BY LATE WEEK. ANOTHER
COLD FRONT COULD APPROACH NEXT WEEKEND...BRINGING THE NEXT CHANCE OF
PRECIP TO THE AREA.

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
CEILINGS WILL CONTINUE TO BOUNCE ALL OVER THE PLACE THIS AFTERNOON
AS POCKETS OF DRY AIR INTERACT WITH AN OTHERWISE DEEP MOIST LAYER
IN PLACE. SPORADIC IFR CONDITIONS THROUGH MID AFTERNOON WILL
RETURN TO VFR FOR MUCH OF THE EVENING AS DRIER MID AND HIGH LEVEL
AIR SHIFTS IN. OVERNIGHT...THE MODELS ARE SPLIT REGARDING THE
POTENTIAL FOR IFR CEILINGS AND BUILD-DOWN FOG. MODEL SOUNDINGS AND
SEASONAL CLIMATOLOGY BOTH SUPPORT PREVAILING IFR CEILINGS AND
3-4SM VSBYS FROM LATE THIS EVENING THROUGH DAYBREAK SUNDAY. AT
LEAST MVFR CEILINGS ARE LIKELY TO PERSIST THROUGH MUCH OF THE DAY
SUNDAY. RAIN WILL OVERSPREAD THE AREA FROM THE SOUTH DURING THE
DAY SUNDAY BUT THE BEST CHANCE WILL BE AFTER 18Z SO WE DID NOT
INCORPORATE INTO THE CURRENT TAF SET.

EXTENDED AVIATION OUTLOOK...PERIODS OF MVFR OR LOWER CONDITIONS
ARE LIKELY WITH RAIN/SHOWERS AND LOW STRATUS THROUGH MONDAY NIGHT
WHILE A WEDGE OF HIGH PRESSURE PERSISTS INLAND AND WAVES OF LOW
PRESSURE LIFT NORTHEAST ACROSS THE NEARBY ATLANTIC. ADDITIONAL
FLIGHT RESTRICTIONS APPEAR LIKELY TUESDAY INTO WEDNESDAY AFTERNOON
AS A STRONG COLD FRONT APPROACHES FROM THE WEST WITH SHOWERS AND
POSSIBLY THUNDERSTORMS. WINDY CONDITIONS SHOULD ALSO OCCUR NEAR
THE TIME OF FRONTAL PASSAGE ON WEDNESDAY.

&&

.MARINE...
PINCHED NORTHEAST GRADIENT ONGOING DUE TO INLAND SURFACE HIGH
PRESSURE AND LOW PRESSURE DEEPENING OFF OUR COAST. THE TIGHTEST
GRADIENT IS ACROSS THE CHARLESTON NEARSHORE WATERS BUT WILL RIPPLE
DOWN THE COAST THROUGH THIS EVENING. SEAS WILL GRADUALLY BUILD
THIS AFTERNOON BUT ALL AREAS WILL REMAIN BELOW ADVISORY CRITERIA.

SUNDAY THROUGH MONDAY NIGHT...CONDITIONS SHOULD REMAIN JUST BELOW
SMALL CRAFT ADVISORY LEVELS AS A WEDGE OF HIGH PRESSURE HOLDS INLAND
WHILE LOW PRESSURE SLOWLY DEVELOPS AND SHIFTS NORTHEAST ALONG THE
COAST. PERIODS OF RAIN/SHOWERS ARE ANTICIPATED OVER THE WATERS
THROUGH MONDAY NIGHT WHILE A COASTAL FRONT REMAINS ALONG THE COAST.
IN GENERAL...WINDS SHOULD BE NO HIGHER THAN 15-20 KT WITH SEAS UP TO
3-4 FT.

TUESDAY AND WEDNESDAY....CONDITIONS SHOULD BEGIN TO DETERIORATE AS A
COASTAL FRONT LIFTS NORTH WELL AHEAD OF A STRONG COLD FRONT THAT
EVENTUALLY SHIFTS OVER THE WATERS WEDNESDAY AFTERNOON. SHOWERS AND
THUNDERSTORMS WILL BE POSSIBLE OVER MOST WATERS AHEAD OF THE
FRONT...WHILE WINDS AND SEAS INCREASE/BUILD WITHIN A SOUTHERLY FLOW.
AT THIS TIME...CONDITIONS SHOULD REACH SMALL CRAFT ADVISORY LEVELS
NEAR DAYBREAK WEDNESDAY AS THE PRESSURE GRADIENT TIGHTENS AHEAD OF
THE APPROACHING FRONT. GALE FORCE WINDS ARE POSSIBLE AS THE COLD
FRONT SHIFTS OFFSHORE WITH STRONG COLD AIR ADVECTION BEHIND IT. A
GALE WATCH/WARNING COULD EVENTUALLY BE NEEDED FOR A PORTION OF THE
WATERS WEDNESDAY AFTERNOON AND NIGHT AS WINDS GUST TO 30-35 KT.
SEAS WILL ALSO BUILD UPWARDS TO 6-9 FT WEDNESDAY AFTERNOON INTO
EARLY WEDNESDAY NIGHT BEFORE IMPROVING LATE.

THURSDAY...CONDITIONS WILL IMPROVE QUICKLY OVER ALL WATERS AS HIGH
PRESSURE BECOMES CENTERED JUST SOUTH OF THE WATERS. WINDS/SEAS
SHOULD LOWER BELOW SMALL CRAFT ADVISORY LEVELS FOR ALL WATERS AROUND
DAYBREAK...THEN CONTINUE TO IMPROVE THROUGH LATE WEEK.

SEA FOG...LOW STRATUS DECKS COULD EQUATE TO REDUCED VISIBILITIES
TONIGHT INTO MONDAY. SEA FOG COULD DEVELOP AS SLIGHTLY WARMER AIR
ARRIVES ATOP MID/UPPER 50 SHELF WATER TEMPS WITHIN A SOUTH AND
SOUTHWEST FLOW LATE MONDAY INTO TUESDAY PRIOR TO WINDS INCREASING
ENOUGH TO SCOUR IT OUT LATER TUESDAY AND TUESDAY NIGHT.

&&

.TIDES/COASTAL FLOODING...
ALTHOUGH THERE ARE NO IMMEDIATE CONCERNS IN REGARDS TO TIDES...
GIVEN THE PERIGEAN SPRING TIDES EARLY NEXT WEEK...THERE IS AT
LEAST A MODERATE RISK OF SHALLOW COASTAL FLOODING CONCERNS MONDAY
AND TUESDAY AROUND THE TIME OF THE MORNING HIGH TIDE.

&&

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

&&

$$

NEAR TERM...JRL
SHORT TERM...DPB
LONG TERM...DPB
AVIATION...JRL
MARINE...DPB
TIDES/COASTAL FLOODING...





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