Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 010322
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1022 PM EST SAT FEB 28 2015

.SYNOPSIS...
HIGH PRESSURE WILL CONTINUE TO WEDGE SOUTHWARD OVER THE REGION
THROUGH SUNDAY WHILE A COASTAL TROUGH LINGERS OFF THE SOUTHEAST
COAST. A COLD FRONT WILL DEVELOP OVER THE AREA LATE MONDAY THEN
STALL JUST TO THE SOUTH OF THE AREA MONDAY NIGHT AS HIGH PRESSURE
BUILDS FROM THE NORTH. THE FRONT WILL LIFT BACK NORTH THROUGH THE
AREA AS A WARM FRONT LATE 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 SUNDAY MORNING/...
A ZONAL WEST-SW FLOW WILL PREVAIL ALOFT WHILE AT THE SURFACE WE
FIND A STRONG HIGH PRESSURE WEDGE INLAND AND A WELL PRONOUNCED
COASTAL TROUGH OUT NEAR THE WESTERN SIDE OF THE GULF STREAM. THE
LARGE SCALE FLOW CHANGES LITTLE OVERNIGHT...WHILE THE WEDGE
WEAKENS SLIGHTLY BUT HOLDS FIRM...WHILE THE COASTAL TROUGH
ATTEMPTS TO BREAK THROUGH THE COOLER SHELF WATERS BUT STRUGGLES TO
DO SO.

FORCING FOR ASCENT IS PROVIDED BY A 40-45 KT LOW LEVEL JET PASSING
DIRECTLY THROUGH THE CWFA AND A 50-60 KT MID LEVEL JET PASSING
JUST NORTH OF THE AREA. THIS ALONG WITH THE PROXIMITY TO THE
TROUGH OFFSHORE AND ISENTROPIC UPGLIDE ON VARIOUS LEVELS WILL
SUPPORT LIKELY TO CATEGORICAL POPS THROUGH THE NIGHT. MUCH OF THE
RAIN WILL BE LIGHT AND FOR NOW WE DON/T SEE ANYTHING MORE THAN A
FEW HUNDREDTHS TO MAYBE ONE OR TWO TENTHS OF IN INCH. EARLY ON THE
BEST CHANCES WILL BE ALONG THE NW TIER IN CONJUNCTION WITH THE LOW
LEVEL JET PASSING THROUGH...BUT PROBABILITIES ARE THEN DIVIDED
INTO TWO QUADS LATE. THE FIRST WILL BE AGAIN ALONG THE NW TIER
WERE THE BEST ISENTROPIC LIFT IS FOUND...WITH A SECOND AREA ON THE
BEACHES WHERE THE BEST LOW LEVEL CONVERGENCE IS EXPECTED.

TEMPS WON/T CHANGE MUCH GIVEN BOUNDARY LAYER MIXING AND THE
INSULATING EFFECTS OF THE OVERCAST CLOUD COVER. THIS EQUATES TO
MIN TEMPS IN THE LOWER AND MIDDLE 40S FOR THE BULK OF THE REGION.
HOWEVER...A FEW UPPER 30S WILL SNEAK INTO THE NW ZONES.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/...
SUNDAY...A WEST-SOUTHWEST FLOW WILL PREVAIL ALOFT OVER MUCH OF THE
EASTERN UNITED STATES...CAUSING SURFACE HIGH PRESSURE TO SHIFT OFF
THE SOUTHERN NEW ENGLAND/NORTHERN MID-ATLANTIC COAST. AS THIS
OCCURS...A COASTAL TROUGH OFF THE SOUTHEAST COAST WILL SHIFT A BIT
CLOSER TO THE SHORELINE...WITH A FEW MODELS SHOWING IT MOVING JUST
INLAND LATE IN THE DAY. HOWEVER...THE HIGH SHOULD CONTINUE TO WEDGE
INTO THE REGION ALONG THE LEE OF THE APPALACHIANS THROUGH MUCH OF
THE DAY.

ISENTROPIC ASCENT AND DEEP MOISTURE WILL SUPPORT A GOOD COVERAGE OF
RAIN IN THE MORNING AND EARLY AFTERNOON...WITH PROBABILITIES AS HIGH
AS 60-80 PERCENT. THE ASSOCIATED DIABATIC COOLING WILL KEEP THE
WEDGE WELL ENTRENCHED OVER THE AREA DURING THIS TIME...POSSIBLY
RESULTING IN FALLING TEMPERATURES IN THE MORNING WHEN PRECIPITATION
WILL BE MOST WIDESPREAD. LATE DAY HIGHS SHOULD RANGE FROM THE
MID/UPPER 40S IN NORTHWEST PARTS OF THE AREA AND LOWER/MID 50S NEAR
THE COAST AND OVER MUCH OF SOUTHEAST GEORGIA...ALTHOUGH IF THE
COASTAL TROUGH DOES MOVE INLAND TEMPERATURES NEAR THE COAST COULD BE
EVEN WARMER.

SUNDAY NIGHT...THE WEDGE OF HIGH PRESSURE WILL BEGIN TO ERODE AS THE
COASTAL TROUGH LIFTS OFF TO THE NORTHEAST. CONTINUED ISENTROPIC
ASCENT WILL SUPPORT A CHANCE OF RAIN IN THE EVENING...BUT THE
DEVELOPING WESTERLY FLOW ALOFT WILL BEGIN TO DRY OUT THE MID-LEVELS
OF THE ATMOSPHERE LATER IN THE EVENING AND OVERNIGHT BRINGING AN END
TO THE RAIN. HOWEVER...LOW LEVEL MOISTURE WILL REMAIN ABUNDANT AND
COULD RESULT IN PATCHY FOG AND DRIZZLE. LOWS WILL GENERALLY BE IN
THE LOWER TO MID 40S.

MONDAY AND MONDAY NIGHT...EARLY MONDAY WILL BE A TRANSITION PERIOD
BEFORE A FRONT DEVELOPS OVER THE AREA LATE IN THE DAY THEN DROPS
SOUTH AS A BACKDOOR COLD FRONT MONDAY NIGHT AND STALLS SOUTH OF THE
AREA. SURFACE HIGH PRESSURE WILL THEN BEGIN TO WEDGE FROM THE NORTH.
THERE IS A SLIGHT CHANCE FOR RAIN IN NORTH AND NORTHWESTERN PORTIONS
OF THE FORECAST AREA IN CLOSER PROXIMITY TO THE DEVELOPING FRONT
MONDAY AFTERNOON. RAIN CHANCES WILL INCREASE A BIT MONDAY NIGHT AS
LOW LEVEL CONVERGENCE INCREASES IN VICINITY OF THE DESCENDING
FRONT...WITH THE HIGHEST PROBABILITIES ACROSS INTERIOR SOUTHEAST
GEORGIA. HIGHS WILL BE IN THE MID 60S ACROSS SOUTHEAST SOUTH
CAROLINA AND UPPER 60S TO NEAR 70 IN SOUTHEAST GEORGIA. LOWS MONDAY
NIGHT WILL RANGE FROM THE MID/UPPER 40S NORTH TO THE MID 50S SOUTH.

TUESDAY...HIGH PRESSURE WILL CONTINUE TO WEDGE FROM THE NORTH...BUT
AS THE PARENT HIGH SHIFTS OFF THE MID-ATLANTIC COAST THE STALLED
FRONT TO THE SOUTH WILL LIFT BACK NORTHWARD INTO THE AREA LATE IN
THE DAY AS A WARM FRONT. THERE COULD BE SOME SHOWERS AROUND DURING
THE DAY WITH PROBABILITIES IN THE 20-30 PERCENT RANGE...HIGHEST
NORTH AHEAD OF THE LIFTING WARM FRONT. HIGH TEMPERATURES WILL BE
HIGHLY DEPENDENT ON HOW QUICKLY THE WEDGE ERODES AND THE WARM FRONT
LIFTS NORTH. FOR NOW...THE FORECAST INDICATES HIGHS IN THE LOWER TO
MID 60S ACROSS SOUTHEAST SOUTH CAROLINA AND UPPER 60S TO LOWER 70S
ACROSS SOUTHEAST GEORGIA.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
WARMER CONDITIONS ARE EXPECTED THROUGH WEDNESDAY AS A SOUTHERLY FLOW
STRENGTHENS AHEAD OF A COLD FRONT APPROACHING FROM THE NORTHWEST.
SFC HEATING AS WELL AS SOME COMPRESSIONAL HEATING SUPPORT OVERALL
HIGH TEMPS IN THE MID/UPPER 70S WEDNESDAY AFTERNOON BEFORE THE ONSET
OF SHOWERS AHEAD OF THE APPROACHING COLD FRONT. STRONG FORCING WILL
BE ASSOCIATED WITH THE FRONT...SUPPORTING THE NEED FOR A FEW
THUNDERSTORMS OVER INLAND AREAS EARLY WEDNESDAY NIGHT. THE COLD
FRONT WILL THEN PUSH THROUGH THE AREA ON THURSDAY...WITH PERIODS OF
MODERATE SHOWERS UNTIL EARLY FRIDAY. DRY AND COOLER HIGH PRESSURE
WILL FOLLOW THE FRONT ON FRIDAY...THEN PERSIST ON SATURDAY. OVERALL
TEMPS WILL REMAIN BELOW NORMAL INTO THE WEEKEND...WITH AFTERNOON
HIGHS IN THE MID/UPPER 50S AND LOWS IN THE MID/UPPER 30S.

&&

.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
BOTH AIRFIELDS WILL BEGIN THE EVENING WITH MVFR CEILINGS...WHICH
WILL GRADUALLY LOWER INTO THE IFR RANGE OVERNIGHT OR EARLY
SUNDAY...THEN PERSIST THROUGH THE REMAINDER OF THE VALID CYCLE.
THIS IS THE RESULT OF ABUNDANT MOISTURE TRAPPED BENEATH THE WEDGE
INVERSION...AIDED BY ISENTROPIC LIFT AT VARIOUS LEVELS. IN
ADDITION...LARGE SCALE FORCING FOR ASCENT DUE TO STRONGER VERTICAL
WIND FIELDS AND THE PROXIMITY TO A NEARBY COASTAL TROUGH WILL
GENERATE PERIODS OF RAIN AND DRIZZLE THROUGH 00Z MONDAY. WINDS
WILL BE A LITTLE GUSTY TONIGHT AS THE PRESSURE PATTERN TIGHTENS
BETWEEN AN INLAND HIGH PRESSURE WEDGE AND THE TROUGH OVER THE
NEARBY ATLANTIC. BASED ON RECENT VWP DATA AND MOST RECENT SOUNDING
INFORMATION WE HAVE INCLUDED LOW LEVEL WIND SHEAR AT BOTH SITES
OVERNIGHT.

EXTENDED AVIATION OUTLOOK...FLIGHT RESTRICTIONS ARE LIKELY THROUGH
MUCH OF SUNDAY NIGHT AS A WEDGE OF HIGH PRESSURE PERSISTS OVER THE
AREA. VFR CONDITIONS SHOULD THEN RETURN ON MONDAY. A BACKDOOR COLD
FRONT COULD PRODUCE ANOTHER ROUND OF FLIGHT RESTRICTIONS MONDAY
AFTERNOON/EVENING...FOLLOWED BY MORE CHANCES OF FLIGHT RESTRICTIONS
ON TUESDAY AS THE FRONT RETURNS AS A WARM FRONT. VFR CONDITIONS
SHOULD RETURN FOR WEDNESDAY. THE NEXT COLD FRONT SHOULD BRING
ADDITIONAL FLIGHT RESTRICTIONS THURSDAY.

&&

.MARINE...
TONIGHT...THERE HAS BEEN AND WILL REMAIN A TIGHT PINCHING BETWEEN
A ROBUST INLAND WEDGE AND A SHARP COASTAL TROUGH NEAR THE WESTERN
SIDE OF THE GULF STREAM. AS A RESULT WE HAVE SEEN GUSTS TO NEAR
OR GREATER THAN GALE FORCE AT BUOY 41008...FT. PULASKI AND TYBEE
ISLAND SINCE MID AFTERNOON. BASED ON THIS AND RECENT SOUNDING DATA
WE CONTINUED THE GALE WARNING FOR AMZ352-354-374. SOLID SCA/S
REMAIN FOR THE CHARLESTON HARBOR AND CHARLESTON COUNTY 0-20 NM
ATLANTIC WATERS. BUT THE PINCHING WILL TIGHTEN FURTHER THOSE
WATERS LATER THIS EVENING AND A GALE WARNING STILL MAY BE REQUIRED
FOR AMZ350 LATER ON. THE TROUGH WILL ATTEMPT TO BREAK ACROSS THE
COOLER SHELF WATERS BUT WILL STRUGGLE TO DO SO WITH THE WEDGE
STILL IN PLACE. THUS WE HAVE EXTENDED THE GALES UNTIL 5 AM FOR
AMZ253-354. THE OUTER GA WATERS SHOULD SEE THE TROUGH PASS
OVERNIGHT...THUS THE GALE WILL END BY 2 AM AND WILL TRANSITION TO
A SMALL CRAFT ADVISORY AFTER THAT TIME. MARINERS ARE ADVISED THAT
LOW STRATUS DECKS LATE THIS EVENING AND OVERNIGHT WILL COMBINE
WITH THE RAIN TO REDUCE VISIBILITIES UNDER 2 NM AT TIMES.

SUNDAY...HIGH PRESSURE WILL WEDGE INLAND ON SUNDAY WHILE A COASTAL
TROUGH LIFTS NORTH ALONG THE SOUTHEAST COAST. A STRONG PRESSURE
GRADIENT IS EXPECTED TO DEVELOP BETWEEN THESE TWO FEATURES...WITH
SMALL CRAFT ADVISORY LEVEL CONDITIONS OVER ALL NEARSHORE WATERS
THROUGH SUNDAY MORNING. WINDS/SEAS SHOULD THEN FALL BELOW SMALL
CRAFT ADVISORY LEVELS IN NEAR SHORE WATERS SUNDAY AFTERNOON AS
WEAKER HIGH PRESSURE SLIDES OVER THE WATERS AND THE COASTAL TROUGH
SHIFTS NORTH OF THE AREA. LINGERING 6-7 FT SEAS WILL LIKELY KEEP
OFFSHORE GEORGIA WATERS IN A SMALL CRAFT ADVISORY TO AROUND MIDNIGHT
SUNDAY NIGHT.

MONDAY AND TUESDAY...CONDITIONS SHOULD REMAIN BELOW ADVISORY LEVELS
AS A BACKDOOR COLD FRONT STALLS OVER OR JUST SOUTH OF THE COASTAL
WATERS ON MONDAY...BUT A BRIEF NORTHEAST SURGE IS EXPECTED MONDAY
NIGHT. THE FRONT WILL THEN LIFT BACK NORTH AS A WARM FRONT ON
TUESDAY. AS THE FRONT LIFTS NORTH...DEWPTS SHOULD RISE INTO THE
UPPER 50S TO AROUND 60...POSSIBLY RESULTING IN SOME SEA FOG OVER
SOUTHERN WATERS.

WEDNESDAY THROUGH FRIDAY...SEA FOG COULD BE AN ISSUE AS DEEP
MOISTURE ADVECTS OVER COOLER WATERS WEDNESDAY AND THURSDAY AHEAD OF
AN APPROACHING COLD FRONT. WINDS AND SEAS WILL ALSO GRADUALLY
INCREASE/BUILD AHEAD OF A COLD FRONT...LIKELY SUPPORTING THE NEED
FOR ADDITIONAL SMALL CRAFT ADVISORIES THAT START WEDNESDAY NIGHT AND
PERSIST INTO FRIDAY AS THE COLD FRONT SHIFTS OVER THE WATERS AND IS
FOLLOWED BY COOLER HIGH PRESSURE.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 5 AM EST SUNDAY FOR AMZ330.
     GALE WARNING UNTIL 5 AM EST SUNDAY FOR AMZ352-354.
     SMALL CRAFT ADVISORY UNTIL 1 PM EST SUNDAY FOR AMZ350.
     GALE WARNING UNTIL 2 AM EST SUNDAY FOR AMZ374.

&&

$$
SYNOPSIS...
NEAR TERM...JRL
SHORT TERM...JAQ
LONG TERM...DPB
AVIATION...
MARINE...



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