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294
FXUS62 KCHS 202324
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
724 PM EDT SUN APR 20 2014

.SYNOPSIS...
LOW PRESSURE WELL OFF THE CAROLINA COAST WILL CONTINUE TO DEPART TO
THE NORTHEAST TONIGHT. OTHERWISE...HIGH PRESSURE WILL BUILD OVER
THE REGION INTO TUESDAY...BEFORE A WEAKENING COLD FRONT MOVES ACROSS
THE AREA TUESDAY NIGHT. HIGH PRESSURE WILL THEN PREVAIL THROUGH
LATE WEEK.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
LOW PRESSURE PILED ATOP ONE ANOTHER FROM THE SURFACE THROUGH THE
TROPOPAUSE OVER THE ATLANTIC NEAR 32N AND 76W WILL CONTINUE TO
EXIT FURTHER OUT TO SEA AS SHORT WAVE RIDGING ARRIVES FROM THE
WEST BY LATE TONIGHT. MEANWHILE...A FAIRLY STRONG HIGH PRESSURE
WEDGE EAST OF THE APPALACHIANS WILL HOLD IN PLACE. BUT GIVEN THAT
THE ATLANTIC CYCLONE WILL DROP A FEW MORE MILLIBARS THE ASSOCIATED
CYCLONIC CIRCULATION WILL EXTEND BACK TO THE WEST AND WILL COVER
MUCH OF THE REGION. THIS ALONG WITH A 2-3C NOCTURNAL INVERSION TO
FORM AND TRAPPING MOISTURE UNDERNEATH INDICATES THAT CLOUD COVER
WILL BE SLUGGISH IN DIMINISHING. THIS POSES A PROBLEM IN REGARDS
TO MINIMUM TEMPS. THE BOUNDARY LAYER NEVER FULLY DECOUPLES WHICH
KEEPS THINGS MIXED AND THAT ALONG WITH THE BLANKETING EFFECTS OF
THE CLOUDS WILL LIMIT HOW LOW WE GET. BUT WITH A NORTHERLY
SYNOPTIC FLOW TO USHER IN SOME COOLER UPSTREAM AIR...AND WHEN
COMPARING THE LOW LEVEL THICKNESS FORECAST WITH WHAT OCCURRED AT
SIMILAR VALUES LAST NIGHT...WE ARRIVE AT UPPER 40S/LOWER 50S
PRETTY MUCH ACROSS THE BOARD. THE EXCEPTION WILL BE FAR NW TIER
WITH LOWS IN THE MID 40S. OF COURSE THESE READINGS MIGHT NEED
ADJUSTMENTS IN UPCOMING FORECASTS PENDING SKY COVER TRENDS. WHILE
A COUPLE OF SPRINKLES CAN/T BE RULED OUT...NOTHING MEASURABLE WILL
OCCUR.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
MONDAY...LOW PRESSURE WELL OFF THE CAROLINA COAST WILL CONTINUE TO
DEPART TO THE NORTHEAST AS UPPER LEVEL RIDGING BUILDS EAST OVER THE
REGION AND HIGH PRESSURE AT THE SURFACE APPROACHES FROM THE WEST.
MODEL SOUNDINGS INDICATE THAT MOISTURE WILL REMAIN TRAPPED BENEATH
AN INVERSION TO START THE DAY...LIKELY RESULTING IN PARTLY TO MOSTLY
CLOUDY SKIES...BUT THEN CLEARING SHOULD TAKE PLACE IN THE LATE
MORNING AND AFTERNOON. DESPITE THE NORTHERLY FLOW...AFTERNOON
SUNSHINE COMBINED WITH RISING HEIGHTS ALOFT WILL RESULT IN
TEMPERATURES REACHING HIGHS IN THE MID TO UPPER 70S AWAY FROM THE
IMMEDIATE COAST.

MONDAY NIGHT...SURFACE HIGH PRESSURE WILL SETTLE OVER THE NORTHERN
GULF OF MEXICO...SETTING UP A WEAK RETURN FLOW ACROSS THE AREA.
DESPITE LIGHT WINDS...RADIATIONAL COOLING WILL BE LIMITED BY
INCREASING HIGH CLOUDS AS AN UPPER LEVEL JET SHIFTS OVER THE REGION.
LOWS SHOULD RANGE FROM AROUND 50 ACROSS INLAND SOUTHEAST SOUTH
CAROLINA TO THE LOWER AND MID 50S ELSEWHERE.

TUESDAY AND TUESDAY NIGHT...A MID AND UPPER LEVEL SHORT WAVE TROUGH
WILL MOVE ACROSS THE AREA TUESDAY AFTERNOON...FOLLOWED BY THE
PASSAGE OF A WEAK COLD FRONT FROM THE NORTHWEST OR NORTH TUESDAY
NIGHT. CLOUD COVER WILL BE ON THE INCREASE WITH THE APPROACH OF THE
UPPER TROUGH ON TUESDAY AND THE FORECAST WILL INDICATE A SLIGHT
CHANCE OF SHOWERS IN THE AFTERNOON INLAND FROM THE COAST. THEN...THE
POTENTIAL FOR SHOWERS INCREASES INTO THE CHANCE CATEGORY MAINLY
NORTH OF THE SAVANNAH RIVER TUESDAY EVENING...WITH A SLIGHT CHANCE
ELSEWHERE...AHEAD OF THE ACTUAL COLD FRONT. SURFACE BASED
INSTABILITY...WITH CAPE VALUES AS HIGH AS 500-900 J/KG AND LI/S DOWN
TO -2 OR -3...COULD SUPPORT SOME THUNDERSTORMS AHEAD OF THE FRONT AS
WELL. THE PRECIPITATION WILL END LATE EVENING OR DURING THE EARLY
OVERNIGHT HOURS AS THE FRONT PASSES. THE FLOW ALOFT WILL BECOME
DOWNSLOPE AS THE UPPER TROUGH MOVES THROUGH...AND COMBINED WITH SOME
COMPRESSIONAL HEATING AHEAD OF THE COLD FRONT WILL DRIVE
TEMPERATURES WELL INTO THE LOWER 80S FOR HIGHS AWAY FROM THE
IMMEDIATE COAST.

WEDNESDAY...HIGH PRESSURE WILL BUILD INTO THE REGION FROM THE
NORTHWEST WITH MOSTLY SUNNY SKIES ACROSS THE AREA. TEMPERATURES WILL
BE A BIT COOLER BEHIND THE FRONT...WITH HIGHS IN THE UPPER 70S TO
LOWER 80S IN MOST AREAS.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
AN UPPER LEVEL RIDGE OF HIGH PRESSURE WILL BUILD OVER THE SOUTHEAST
THROUGH THURSDAY SUPPORTING RAIN-FREE CONDITIONS AND HIGH
TEMPERATURES RANGING FROM THE UPPER 70S TO LOWER 80S THURSDAY. AS A
SURFACE RIDGE OF HIGH PRESSURE SHIFTS OFFSHORE FRIDAY THROUGH
SUNDAY...TEMPERATURES IN THE LOWER TO MID 80S WILL BE COMMON AWAY
FROM THE IMMEDIATE COAST. WITH MODERATE INSTABILITY EXPECTED FRIDAY
AND SATURDAY...INCLUDED A SLIGHT CHANCE FOR AFTERNOON THUNDERSTORMS.

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
ALTHOUGH WE HAVE INITIALIZED THE 00Z TAFS WITH VFR
CEILINGS...CONDITIONS APPEAR FAVORABLE FOR MVFR CEILINGS TO
DEVELOP OVERNIGHT AND PERSIST INTO MONDAY MORNING. THIS WILL BE
THE RESULT OF MOISTURE REMAINING TRAPPED BENEATH THE NOCTURNAL
INVERSION...AND THIS IDEA IS SUPPORTED BY RECENT
SATELLITE/OBSERVATIONAL TRENDS WHICH SHOW EXTENSIVE STRATOCUMULUS
SPREADING OUT ACROSS THE CENTRAL AND SOUTHERN PARTS OF SC AND SE
GA. CEILINGS WILL IMPROVE BACK TO VFR LATE MONDAY MORNING AND
PERSIST THROUGH THE REMAINDER OF THE TAF CYCLE. THE PLANETARY
BOUNDARY LAYER REMAINS MIXED ENOUGH THROUGH LATE MONDAY FOR
NORTHERLY WINDS TO AVERAGE 10-15 KT WITH OCCASIONAL HIGHER GUSTS
AT BOTH TERMINALS.

EXTENDED AVIATION OUTLOOK...VFR CONDITIONS ARE EXPECTED TO CONTINUE
INTO TUESDAY. THERE IS A SMALL CHANCE OF SOME IFR/MVFR CONDITIONS IN
CONVECTION LATE TUESDAY OR TUESDAY NIGHT...WITH CONDITIONS IMPROVING
BACK TO VFR BY WEDNESDAY.

&&

.MARINE...
TONIGHT...ALTHOUGH LOW PRESSURE EAST OF THE WATERS WILL CONTINUE
TO PULL FURTHER INTO THE ATLANTIC THROUGH THE NIGHT...IT/S CENTRAL
PRESSURE WILL DROP A FEW MORE MILLIBARS AS A HIGH PRESSURE WEDGE
REMAINS POSITIONED INLAND OVER THE SE. THE RESULTING PRESSURE
GRADIENT BETWEEN THESE TWO FEATURES WILL REMAIN PACKED...WITH THE
END RESULT THAT THE ONGOING SMALL CRAFT ADVISORIES WILL CONTINUE
FOR NORTHERLY WINDS OF 20-25 KT. SEAS WILL BE HELD IN CHECK
SOMEWHAT BY THE OFFSHORE FETCH...BUT GIVEN THAT UNDER THE WIND
WAVES THERE IS ALSO SOME SWELL ENERGY...COMBINED SEAS WILL BE AS
HIGH AS 4-6 FT WITHIN 20 NM AND 7-10 FT FURTHER OUT. IN CHARLESTON
HARBOR WAVES WILL BE 1-2 FT...EVEN A FOOT OR SO HIGHER AT THE
JETTIES.

WINDS AND SEAS WILL DIMINISH MONDAY AND MONDAY NIGHT AS COASTAL
LOW PRESSURE DEPARTS TO THE NORTHEAST AND HIGH PRESSURE BUILDS
FROM THE WEST. SMALL CRAFT ADVISORIES WILL PERSIST INTO MONDAY
MORNING FOR THE CHARLESTON COUNTY COASTAL WATERS AND THROUGH
MONDAY NIGHT FOR THE OUTER GA WATERS FOR LINGERING 6 FT SEAS. A
SOUTHWEST FLOW WILL STRENGTHEN TUESDAY AND TUESDAY EVENING AHEAD
OF AN APPROACHING COLD FRONT...WITH SPEEDS PEAKING AROUND 15 KT.
THE FRONT WILL MOVE OFFSHORE TUESDAY NIGHT...FOLLOWED BY HIGH
PRESSURE AND CONDITIONS BELOW SMALL CRAFT ADVISORY LEVELS THROUGH
THE REST OF THE WEEK.

&&

.TIDES/COASTAL FLOODING...
TIDES WILL CONTINUE TO RUN HIGH THIS EVENING. THERE IS A SMALL
CHANCE THAT SHALLOW COASTAL FLOODING WILL OCCUR AROUND HIGH TIDE
NEAR 1 AM MONDAY. DEPARTURES WOULD HAVE TO BE OVER 1 FT...THAT MAY
NOT BE ATTAINABLE...BUT IT CERTAINLY COULD BE CLOSE.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT MONDAY FOR AMZ330-352-354.
     SMALL CRAFT ADVISORY UNTIL 11 AM EDT MONDAY FOR AMZ350.
     SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT MONDAY NIGHT FOR
     AMZ374.

&&

$$

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







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