Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 180542
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
142 AM EDT THU SEP 18 2014

.SYNOPSIS...
A COLD FRONT WILL CONTINUE TO MOVE SOUTH ACROSS THE REGION
OVERNIGHT. AN INLAND WEDGE OF HIGH PRESSURE WILL THEN PREVAIL IN
THE WAKE OF THE FRONT INTO THE WEEKEND. ANOTHER COLD FRONT WILL
APPROACH FROM THE WEST EARLY NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
THERE IS STILL SOME CONVECTION ONGOING AS OF EARLY THURSDAY
MORNING...DRIVEN MAINLY BY A SHORT WAVE ALOFT AIDED BY THE RIGHT
REAR QUAD OF AN UPPER JET STREAK. MOST OF THE CONVECTION WAS NOW
OFFSHORE BUT ISOLATED SHOWERS REMAIN REMAIN POSSIBLE FOR A COUPLE
MORE HOURS.

THE MAIN FORECAST PROBLEM FOR LATER TONIGHT WILL BE THE FORMATION
OF FOG...GIVEN SOME DRY AIR ALOFT...THE SATURATED GROUNDS FROM
RECENT RAINS AND CALM WINDS. WE HAVE INCLUDED PATCHY FOG FOR MOST
LOCATIONS OVER LAND AFTER 3 OR 4 AM...BUT ALSO A STRIP WHERE AREAS
OF FOG WILL OCCUR ALONG THE WEST/NW ZONES. THIS IS WHERE WE FIND
THE LOWEST CONDENSATION PRESSURE DEFICITS...THE MOST FAVORABLE
FOG STABILITY INDICES AND ALSO WHERE CROSS-OVER TEMPS WILL EASILY
BE MET. IF SKIES CLEAR OUT ENOUGH THERE WOULD BE A RISK FOR SOME
DENSE FOG.

WHERE WE HAVE SEEN SOME TEMPORARY CLEARING OF SKIES WE HAVE SOME
TEMPS ALREADY DOWN INTO THE UPPER 60S. THIS IS A DEFINITE
INDICATION THAT A CHANGE IN AIR MASS IS FORTHCOMING AND ALTHOUGH
THE TEMP CURVE WILL BOUNCE AROUND A COUPLE OF DEGREES...WE DO LOOK
FOR FAIRLY COMFORTABLE OVERNIGHT LOWS DOWN INTO THE 65-70 DEGREE
JUST ABOUT EVERYWHERE EXCEPT THE IMMEDIATE COAST WHERE LOWER 70S
WILL BE COMMON.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH SATURDAY/...
THURSDAY...AN AMPLIFIED UPPER PATTERN STARTS THE PERIOD WITH A
BROAD...FULL LATITUDE UPPER TROUGH OVER THE EAST U.S. AND RIDGE OVER
THE WEST. AT THE SURFACE...A MODERATELY STRONG HIGH PRESSURE...
CENTERED OVER THE NORTHERN GT. LAKES...WILL MOVE EAST INTO NORTHERN
NEW ENGLAND BY THE END OF THE DAY. THE RIDGE OF HIGH PRESSURE WILL
FORM A WEDGE DOWN INTO THE SOUTHEAST U.S.. THIS WILL PRODUCE LOW
LEVEL ENE FLOW. ALL MODELS SHOW ONLY MARGINAL DEEP LAYER MOISTURE
OVER THE LAND AREA...BUT WITH SOME WEAK OVER-RUNNING WITH THE
WEDGE...KEPT SLIGHT CHANCE POPS EASTERN 1/3 OF LAND AND INTO MARINE
AREA. HIGHS IN THE LOWER 80S NORTH...UPPER 80S SOUTH.  BY THURSDAY
NIGHT...THINK ANY PRECIP WILL BE MAINLY CONFINED TO ATLANTIC WATERS
AND IMMEDIATE COASTAL AREAS...WHERE SOME COASTAL LOW LEVEL
CONVERGENCE OCCURS. KEPT SLIGHT CHANCE POPS NEAR THE COAST...AND
CHANCE OUT INTO ATLANTIC. LOWS IN THE MID TO UPPER 60S.

FRIDAY...THE UPPER PATTERN BECOMES MUCH LESS AMPLIFIED...WITH THE
MAIN JET CONFINED OVER THE NORTHERN TIER OF STATES. HOWEVER...AT THE
SURFACE...A MODERATELY STRONG HIGH PRESSURE WEDGE REMAINS IN
PLACE...STRETCHING FROM NEW ENGLAND...SOUTHWARD TO GEORGIA.
EAST-NORTHEAST LOW LEVEL FLOW AND MODERATE DEEP LAYER MOISTURE WILL
KEEP THE THREAT FOR ISOLATED TO SCATTERED SHOWERS AND
THUNDERSTORMS...ESPECIALLY CLOSER TO THE COAST AND ATLANTIC WATERS.
HIGHS A LITTLE COOLER...IN THE LOWER 80S UNDER MOSTLY CLOUDY SKIES.
SIMILAR TO THE PREVIOUS NIGHT...THINK BEST CHANCES FOR ANY
SHOWERS/THUNDERSTORMS WILL BE OVER THE ATLANTIC AND IMMEDIATE
COASTAL AREAS AS A WEAKER HIGH PRESSURE RIDGE REMAINS OVER THE LAND
AND WEAK LOW PRESSURE SYSTEM TRIES TO DEVELOP WELL OFFSHORE OVER THE
ATLANTIC.

SATURDAY...THE UPPER FLOW BEGINS TO SLOWLY AMPLIFY AGAIN WITH A
SHARPENING TROUGH OVER THE EAST...WHICH HELPS TO KICK OUT A WEAK LOW
OVER THE COASTAL WATERS TO THE NORTHEAST BY THE END OF THE PERIOD.
THE BULK OF THE DEEP LAYER MOISTURE AGAIN RESIDES OVER THE IMMEDIATE
COAST AND ATLANTIC WATERS. KEPT CHANCE POPS COAST...AND SLIGHT
CHANCE INLAND. HIGHS IN THE LOWER 80S.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
A COASTAL TROUGH ON THE PERIPHERY OF INLAND HIGH PRESSURE WILL
LIFT NORTH/NORTHEAST ACROSS THE ATLANTIC WATERS SUNDAY...WHILE
THE INLAND WEDGE EVENTUALLY ERODES AHEAD OF A STRONG COLD FRONT
UPSTREAM. PRECIPITATION POTENTIAL ON SUNDAY WILL BE SIMILAR TO
PREVIOUS DAYS...MAINLY FOCUSED ACROSS THE COASTAL COUNTIES WITH
RAIN-FREE CONDITIONS FARTHER INLAND. THE COLD FRONT WILL CONTINUE
TO APPROACH FROM THE NORTHWEST ON MONDAY...AS A PRE-FRONTAL SURFACE
TROUGH SHIFTS OVER THE EAST COAST STATES. THE COLD FRONT THEN
STEADILY MOVES THROUGH THE FORECAST AREA EARLY TUESDAY...FOLLOWED
BY EXPANSIVE HIGH PRESSURE WITH ORIGINS FROM THE NORTHERN PLAINS.
MEDIUM RANGE MODEL SOLUTIONS ARE NOT INDICATING SIGNIFICANT
PRECIPITATION ASSOCIATED WITH THE FRONTAL PASSAGE...AND HAVE THUS
CAPPED RAIN CHANCES GENERALLY BELOW 30 PERCENT FOR THE EARLY WEEK
PERIOD. TEMPERATURES COULD REBOUND AHEAD OF THE FRONT ON MONDAY AND
PEAK IN THE MID TO UPPER 80S...BEFORE A NOTABLE COOLING TREND
OCCURS IN THE WAKE OF THE FRONT TUESDAY AND WEDNESDAY.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
BOTH SITES HAVE THE POTENTIAL FOR LATE NIGHT STRATUS AND/OR
FOG...WITH MVFR OR LOWER CONDITIONS TO OCCUR FROM AROUND 09-13Z.
WHILE MOST OF THE REST OF THURSDAY WILL BE VFR...ISOLATED
SHRA/TSRA WILL OCCUR IN THE AFTERNOON AND LATER TAF ISSUANCES MAY
NEED TO ADDRESS THE CONCERN FOR IMPACTS ON BOTH OF EITHER
TERMINAL.

EXTENDED AVIATION OUTLOOK...LOW CLOUDS/FOG WILL BE POSSIBLE WITH
PERIODS OF MVFR OR LOWER CIGS EACH MORNING THROUGH AT LEAST
SATURDAY. OTHERWISE...MAINLY VFR OUTSIDE OF ANY ISOLATED SHOWERS
EACH DAY. IMPROVING CONDITIONS WITH MAINLY VFR SUNDAY AND MONDAY.

&&

.MARINE...
OVERNIGHT...A POORLY DEFINED COLD FRONT WILL SLIDE SOUTH THROUGH
THE WATERS AS WEAK LOW PRESSURE EAST OF THE GULF STREAM OFF THE SC
COAST MOVES EAST/NE. THERE WILL BE...WITH VARYING WIND DIRECTIONS
AT NO MORE THAN 10 KT OR SO...THEN BECOMING MORE NORTHERLY LATE
ACROSS THE SC WATERS. STRONG TSTMS WITH WIND SIGNATURES EXCEEDING
40 KT WERE PLOWING OFFSHORE OF THE SAVANNAH RIVER ENTRANCE AND
BEAUFORT COUNTY. SPECIAL MARINE WARNINGS WERE IN PLACE AS OF 130 AM.

ANOTHER ISSUE WILL BE IN REGARDS TO LONG PERIOD SWELLS GENERATED
FROM DISTANT HURRICANE EDOUARD WHICH WILL CONTINUE TO IMPACT THE
COASTAL WATERS. SWELL PERIODS WILL AVERAGE 12-15 SECONDS...AND
DOMINANT WAVE HEIGHTS WILL HOLD AROUND 2-3 FT WITHIN 20 NM BUT UP
TO 3-4 FT FURTHER OFFSHORE.

THURSDAY THROUGH SUNDAY...NO HIGHLIGHTS EXPECTED THROUGH THE PERIOD.
A LOW PRESSURE SYSTEM MAY DEVELOP AND MOVE ACROSS THE OUTER
WATERS SATURDAY AND EARLY SUNDAY. THERE IS STILL UNCERTAINTY WITH
THE STRENGTH AND POSITION OF THIS SYSTEM. LATEST GUIDANCE
INCREASES WINDS FROM THE NORTHEAST POSSIBLY AS HIGH AS 15 TO 20
KT WITH SEAS 3 TO 5 FEET SATURDAY...THEN WEAKEN AGAIN BY SUNDAY
THROUGH MONDAY.

RIP CURRENTS...LONG PERIOD SWELL FROM HURRICANE EDOUARD WILL OCCUR
ALONG THE BEACHES THROUGH THURSDAY. DESPITE ONLY LIGHT ONSHORE
WINDS...1-2 FT SWELLS WITH PERIODS NEAR 14 SECONDS SUPPORT AN
ENHANCED PERIOD OF RIP CURRENTS ALONG THE SOUTH CAROLINA AND
GEORGIA BEACHES. A MODERATE RISK OF RIP CURRENTS IS THEREFORE IN
PLACE THROUGH THURSDAY EVENING.

&&

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

&&

$$

NEAR TERM...
SHORT TERM...RFM
LONG TERM...WMS
AVIATION...
MARINE...





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