Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 230315
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1015 PM EST MON DEC 22 2014

.SYNOPSIS...
AN INLAND WEDGE OF HIGH PRESSURE WILL PREVAIL THROUGH TONIGHT...
BEFORE BEGINNING TO ERODE ON TUESDAY AS A WARM FRONT LIFTS NORTH
INTO THE AREA. A STRONG COLD FRONT WILL THEN APPROACH FROM THE
WEST ON WEDNESDAY AND MOVE THROUGH EARLY WEDNESDAY NIGHT. HIGH
PRESSURE WILL THEN BUILD FROM THE GULF COAST REGION ON THURSDAY
AND SETTLE OVER THE SOUTHEAST UNITED STATES FRIDAY INTO SATURDAY.
ANOTHER COLD FRONT COULD SHIFT THROUGH LATE IN THE WEEKEND.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
A DEEP AND RICH FEED OF TROPICAL-LIKE MOISTURE CONTINUES TO STREAM
IN FROM THE SW...ALTHOUGH THE MAIN CONVEYOR BELT IS JUST A TAD
SOUTH AND SE OF THE FORECAST AREA. IT ACTUALLY HAS IT/S ORIGINS IN
THE EASTERN PACIFIC...AND WILL EVENTUALLY TIP BACK INTO THE AREA
BEYOND THE TONIGHT PERIOD.

THE IN-SITU WEDGE IS VERY RELUCTANT TO MOVE TONIGHT...ALTHOUGH THE
COASTAL WARM FRONT OUT STUCK JUST EAST OF THE SHELF WATERS OFF THE
GA COAST AND EXTENDING TO NEAR THE WEST WALL OF THE GULF STREAM
OFF THE SC WATERS WILL ATTEMPT TO NUDGE WESTWARD INTO THE WEDGE.
THIS FRONT COULD MAKE IT A LITTLE CLOSER TO THE COAST BY
DAYBREAK...BUT FOR THE MOST PART THE WEDGE WILL HOLD FIRM.

CONSIDERABLY WARMER AIR ATOP THE SHALLOW COOL AIR WEDGE WILL RESULT
IN A FURTHER BUILD DOWN OF THE ALREADY LOW STRATUS DECKS. THIS
ALONG WITH A LITTLE DRIER AIR WITHIN THE LAYER FROM ABOUT 700 TO
400 MB SITTING ATOP THE EXTREMELY SATURATED LOWER LEVELS...WILL
COMBINE WITH THE DAMP GROUND CONDITIONS FROM RECENT RAINS TO
PRODUCE AN EXPANSION OF FOG THROUGH THE NIGHT. FOG WILL BECOME
DENSE IN MANY SECTIONS AND THUS A CONTINUATION OF THE DENSE FOG
ADVISORY FOR ALL ZONES.

THERE IS A ENOUGH ISENTROPIC LIFT TO GENERATE PATCHY DRIZZLE...BUT
ALSO A SLIGHT CHANCE OR CHANCE OF LITTLE LIGHT RAIN. BUT WE WILL
NEED TO CLOSELY WATCH THE SHORT WAVE HEADING INTO THE FLORIDA BIG
BEND FROM THE SW THAT COULD SKIRT OUR SE SECTIONS LATE. THIS COULD
LEAD TO SLIGHTLY HIGHER COVERAGE OF SHOWERS AND EVEN TREND TO
LIMIT THE FOG COVERAGE TO THE SOUTH/SE OF HINESVILLE.

TEMPS WON/T BUDGE MUCH...ACTUALLY EVEN RISING A COUPLE OF DEGREES.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
TUESDAY AND TUESDAY NIGHT...THE MID AND UPPER LEVEL PATTERN WILL
BEGIN TO AMPLIFY AS A TROUGH DIGS ACROSS THE PLAINS STATES THEN
SLOWLY ADVANCES EASTWARD OVER THE MISSISSIPPI VALLEY. MEANWHILE AT
THE SURFACE AN INLAND WEDGE OF HIGH PRESSURE WILL BEGIN TO
ERODE...LIKELY SLOWER THAN MODELS DEPICT...AS A WARM FRONT GRADUALLY
LIFTS INTO THE AREA ON TUESDAY AND TO THE NORTH OF THE AREA TUESDAY
NIGHT. UNSETTLED CONDITIONS WILL PREVAIL AS DEEP MOISTURE PUSHES
PRECIPITABLE WATER VALUES UPWARDS OF 1.75 INCHES AND NUMEROUS
DISTURBANCES ALOFT CROSS THE AREA WITHIN A DEEP SOUTH-SOUTHWEST
FLOW. THERE APPEARS TO BE A BIT OF A LULL IN TERMS OF PRECIPITATION
AROUND DAYBREAK...BUT THEN RAIN/SHOWERS WILL INCREASE IN COVERAGE
THROUGH THE MORNING...BECOMING WIDESPREAD TUESDAY AFTERNOON AND
TUESDAY NIGHT. MODELS INDICATE THERE THERE COULD BE SOME MAINLY
ELEVATED INSTABILITY...SO HAVE MENTION OF SLIGHT CHANCE
THUNDERSTORMS ACROSS COASTAL AND SOUTHERN PORTIONS OF THE FORECAST
AREA IN THE AFTERNOON. THERE IS EXPECTED TO BE A SIGNIFICANT
GRADIENT IN TEMPERATURES ON TUESDAY...WITH HIGHS IN THE UPPER 60S TO
AROUND 70 NEAR THE COAST AND ACROSS SOUTHERN AREAS...AND IN THE MID
50S TO AROUND 60 IN NORTHWEST PARTS OF THE FORECAST AREA WHERE THE
WEDGE IS LIKELY TO PERSIST. LOWS TUESDAY NIGHT SHOULD BE IN THE MID
50S TO LOWER 60S...WITH TEMPERATURES POTENTIALLY RISING IN NORTHWEST
PORTIONS OF THE AREA AS THE WARM FRONT LIFTS NORTH.

WEDNESDAY AND WEDNESDAY NIGHT...A DEEP MID AND UPPER LEVEL TROUGH
WILL ADVANCE EAST OF THE MISSISSIPPI VALLEY...DRIVING A STRONG COLD
FRONT AT THE SURFACE TOWARD THE SOUTHEAST COAST. THE FRONT IS
EXPECTED TO MOVE THROUGH THE AREA WEDNESDAY EVENING INTO THE EARLY
OVERNIGHT HOURS. DEEP MOISTURE AND ENHANCED FORCING FOR ASCENT WILL
SUPPORT WIDESPREAD SHOWERS WITH EMBEDDED THUNDERSTORMS WEDNESDAY
AHEAD OF THE FRONT. DESPITE IMPRESSIVE WIND FIELDS ALOFT...LIMITED
INSTABILITY AT THE SURFACE DUE TO WIDESPREAD RAINFALL WILL
SIGNIFICANTLY REDUCE THE SEVERE WEATHER POTENTIAL AND THE STORM
PREDICTION CENTER ONLY HAS THE AREA HIGHLIGHTED IN A MARGINAL RISK
FOR SEVERE THUNDERSTORMS AT THIS TIME. IF FOR SOME REASON SOME
SURFACE BASED INSTABILITY CAN DEVELOP...THEN THERE WOULD BE A SMALL
POTENTIAL FOR ISOLATED DAMAGING WIND GUSTS WEDNESDAY AFTERNOON INTO
WEDNESDAY EVENING. SHOWERS WILL THEN BEGIN TO TAPER OFF FROM THE
WEST-SOUTHWEST OVERNIGHT AS THE COLD FRONT SHIFTS OFFSHORE.
TEMPERATURES ON WEDNESDAY SHOULD SURGE INTO THE LOWER 70S AS THE
SOUTHERLY FLOW STRENGTHENS AND SOME COMPRESSIONAL HEATING OCCURS
AHEAD OF THE FRONT. LOWS WEDNESDAY NIGHT WILL BE IN THE UPPER 40S TO
LOWER 50S.

THURSDAY...SURFACE HIGH PRESSURE WILL BUILD INTO THE REGION FROM THE
GULF COAST REGION...WITH WESTERLY WINDS RESULTING IN RAIN-FREE
CONDITIONS. SKIES WILL GRADUALLY CLEAR THROUGH THE DAY...WITH HIGHS
REACHING THE MID AND UPPER 50S.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
QUIET WEATHER WILL PREVAIL INTO THE WEEKEND AS HIGH PRESSURE BECOMES
CENTERED OVER THE SOUTHEASTERN UNITED STATES. OVERALL HIGH TEMPS
SHOULD GRADUALLY WARM EACH DAY AS HIGH PRESSURE CONTINUES TO SLIDE
EAST LATE WEEKEND...ALLOWING A LIGHT SOUTHERLY FLOW TO RETURN TO THE
AREA. IN GENERAL...TEMPS WILL REACH THE LOWER 60S ON FRIDAY...THEN
TO THE MID 60S ON SATURDAY. OVERNIGHT LOWS SHOULD RANGE IN THE THE
LOW/MID 40S INTO THE WEEKEND. THE NEXT BEST CHANCE OF PRECIP SHOULD
OCCUR EARLY NEXT WEEK WITH A COLD FRONT THAT APPROACHES THE REGION.
HOWEVER...CONFIDENCE IN TIMING AND STRENGTH OF PATTERN IS QUITE LOW
GIVEN LARGE DISCREPANCIES IN MODEL SOLUTIONS.

&&

.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
BOTH KSAV AND KCHS LOOKED TO REMAIN LOCKED IN LOW STRATUS AND
IFR/LIFR CEILINGS THROUGH 00Z WEDNESDAY. AS THE STRATUS SINKS
LOWER THROUGH TONIGHT INTO TUESDAY MORNING THERE WILL BECOME MORE
OF A REDUCTION IN SURFACE VISIBILITIES AS MIST AND EVENTUALLY FOG
DEVELOP. SOME OF THE FOG WILL BE DENSE AT TIMES INTO TUESDAY
MORNING BEFORE SOME IMPROVEMENT OCCURS IN REGARDS TO VISIBILITY
TUESDAY BY AFTERNOON. PERIODIC RAIN AND DRIZZLE WILL ALSO OCCUR
THROUGH THE VALID FORECAST CYCLE. THE EVER PESKY HIGH PRESSURE
WEDGE WILL STILL HOLD IN PLACE TONIGHT...GRADUALLY ERODING TUESDAY
AND GIVING WAY TO A COASTAL WARM FRONT ALLOWING FOR LIGHT NE WINDS
TO EVENTUALLY VEER AROUND TO LIGHT SE. WHILE THE PROSPECTS ARE NOT
TOO HIGH...THERE MIGHT BE ENOUGH INSTABILITY TO PRODUCE A LITTLE
THUNDER AND LIGHTNING NEAR THE ADVANCING WARM FRONT TUESDAY.

EXTENDED AVIATION OUTLOOK...MVFR OR LOWER CONDITIONS ARE LIKELY
TUESDAY NIGHT INTO WEDNESDAY EVENING DUE TO LOW CEILINGS AND
OCCASIONALLY REDUCED VISIBILITIES IN FOG AND SHOWERS. LLWS WILL BE
A POSSIBILITY TUESDAY NIGHT AS STRONGER WIND FIELDS SHIFT OVER THE
AREA IN ADVANCE OF AN APPROACHING COLD FRONT. VFR CONDITIONS
SHOULD PREVAIL THURSDAY THROUGH SATURDAY.

&&

.MARINE...
TONIGHT...THE COASTAL WARM FRONT IS TRYING TO MAKE SOME HEADWAY
TOWARD THE SHORELINE...BUT HAS GOTTEN STUCK EAST OF THE SHELF
WATERS. IT WILL BE A STRUGGLE TO PENETRATE ACROSS THESE COOLER
WATERS...AND THUS WINDS WITHIN ABOUT 10-15 NM WITH STAY MAINLY NE OR
EAST. FURTHER OUT THEY SHOULD BE ABLE TO VEER MORE SE OR EVEN
SOUTH BY LATE. SPEEDS ON AVERAGE WILL BE NO MORE THAN 10 OR 15 KT
AND SEAS WILL HOLD STEADY AROUND 2-4 FT...GREATEST ACROSS AMZ374.

OF GREATER IMPORTANCE TONIGHT WILL BE THE FORMATION OF
FOG...MAINLY THE RESULT OF THE BUILDING DOWN OF THE ALREADY LOW
CLOUDS AND THE RELATIVELY WARMER AIR ARRIVING JUST OFF THE COOLER
WATERS AND ASSOCIATED AMBIENT AIR TEMPS. WE HAVE A DENSE FOG
ADVISORY FOR CHARLESTON HARBOR VALID THROUGH 10 AM...AND WE MAY
EVENTUALLY NEED TO EXPAND ON THIS TO INCLUDE PARTS OF ALL OF THE
0-20 NM WATERS OVERNIGHT. FOR NOW WE ARE SHOWING AREAS OF FOG OVER
AMZ350-352-354.

FINALLY...THERE IS JUST ENOUGH SURFACE BASED INSTABILITY AND STEEP
MID LEVEL LAPSE RATES OUT ACROSS PARTS OF AMZ374 TO PRODUCE
ISOLATED T-STORMS BEYOND 20 NM OFF THE SE GA COAST. OCCASIONAL
LIGHTNING STRIKES...WIND GUSTS UP NEAR 30 KT AND BRIEF HEAVY RAINS
WILL ACCOMPANY THE STRONGEST STORMS AS THEY RIDE TOWARD THE EAST/NE.

TUESDAY...A WARM FRONT WILL BEGIN TO LIFT NORTH AND WEST OF THE
WATERS AS AN INLAND WEDGE ERODES. THIS WILL ALLOW FOR A SOUTHERLY
FLOW WITH WINDS LESS THAN 15 KT.

TUESDAY NIGHT THROUGH EARLY THURSDAY...CONDITIONS WILL DETERIORATE
LATE TUESDAY NIGHT INTO EARLY WEDNESDAY AS THE PRESSURE GRADIENT
TIGHTENS AND STRONG LOW LEVEL WIND FIELDS SPREAD OVER THE WATERS
AHEAD OF AN APPROACHING COLD FRONT. SMALL CRAFT ADVISORY CONDITIONS
ARE EXPECTED TO DEVELOP ACROSS ALL WATERS WEDNESDAY...THEN CONTINUE
INTO WEDNESDAY NIGHT AS THE COLD FRONT MOVES OFFSHORE AND STRONG
COLD AIR ADVECTION DEVELOPS IN ITS WAKE. WINDS WILL REACH UPWARDS OF
AROUND 20 KT ACROSS THE NEAR SHORE WATERS AND 25 KT ACROSS THE OUTER
GEORGIA WATERS...WITH HIGHER GUSTS. THERE IS A SMALL POTENTIAL FOR A
PERIOD OF GALE FORCE GUSTS OVER THE OUTER GEORGIA WATERS WEDNESDAY
NIGHT INTO EARLY THURSDAY AS THE COLD AIR ADVECTION PEAKS. SEAS WILL
BUILD UP TO 5-8 FT WEDNESDAY BEFORE WINDS SHIFT OFFSHORE.

THURSDAY AFTERNOON THROUGH SATURDAY...CONDITIONS WILL IMPROVE
QUICKLY OVER ALL WATERS AS HIGH PRESSURE BECOMES CENTERED OVER THE
SOUTHEAST. WINDS/SEAS SHOULD LOWER BELOW SMALL CRAFT ADVISORY LEVELS
FOR ALL WATERS THURSDAY AFTERNOON...THEN CONTINUE TO IMPROVE
THROUGH THE WEEKEND AS THE CENTER OF HIGH PRESSURE SLIDES OFFSHORE.

SEA FOG...MARINERS ARE ADVISED THAT LOW STRATUS DECKS AND PERIODS OF
RAIN OR DRIZZLE WILL EQUATE TO REDUCED VISIBILITIES TUESDAY UNTIL
WEDNESDAY...BUT THE BEST CHANCE OF CLASSIC SEA FOG COULD DEVELOP AS
WARMER AIR ARRIVES ATOP MID/UPPER 50 DEGREE SHELF WATER TEMPS
EARLY TUESDAY PRIOR TO WINDS INCREASING ENOUGH TO SCOUR IT OUT
LATE TUESDAY NIGHT.

&&

.TIDES/COASTAL FLOODING...
TIDAL DEPARTURES HAVE BEEN RUNNING AROUND 1 FT MLLW OR GREATER OF
LATE AND ALTHOUGH DEPARTURES WILL COME DOWN SOME BY MORNING...IT
ON/T TAKE MUCH TO GENERATE AT LEAST SHALLOW COASTAL FLOODING. AS A
RESULT A COASTAL FLOOD ADVISORY APPEARS VERY LIKELY. WE WILL CONTINUE
TO HIGHLIGHT THE POTENTIAL IN THE HAZARDOUS WEATHER OUTLOOK.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...DENSE FOG ADVISORY UNTIL 10 AM EST TUESDAY FOR GAZ087-088-
     099>101-114>119-137>141.
SC...DENSE FOG ADVISORY UNTIL 10 AM EST TUESDAY FOR SCZ040-042>045-
     047>052.
MARINE...DENSE FOG ADVISORY UNTIL 10 AM EST TUESDAY FOR AMZ330.

&&

$$

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






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