Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 180816
AFDCHS

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

.SYNOPSIS...
HIGH PRESSURE WILL BUILD NORTH OF GEORGIA AND SOUTH CAROLINA INTO THE
WEEKEND. A COLD FRONT WILL APPROACH FROM THE WEST EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
PRE-DAWN...ISOLATED CONVECTION LINGERED ACROSS PARTS OF AREA THROUGH
1 AM BEFORE GATHERING OFFSHORE AND MOVING OUT INTO THE GULF STREAM.
LATEST EMC RAP ANALYSIS INDICATES INCREASING CIN AND NOT MUCH
RESIDUAL INSTABILITY LEFT THUS WE ARE EXPECTING MAINLY DRY WEATHER
FOR DAWN. AREAS OF STRATUS AND FOG WERE DEVELOPING INLAND AND SOME
SPOTS COULD SEE SOME LOCALLY DENSE FOG. AT THIS TIME...NO REGION
TO SINGLE OUT FOR VSBY PROBLEMS...ALTHOUGH SOUTH OF I-16 IN
GEORGIA WILL BE AN AREA TO WATCH.

MID AND UPPER LEVEL TROUGHING CONTINUES THROUGH TONIGHT ACROSS THE
SOUTHEASTERN SEABOARD WITH A POORLY DEFINED SURFACE FRONT CAMPING
OUT ALONG OR SOUTH OF THE SAVANNAH RIVER ENTRANCE. LOW CLOUDS AND
INLAND FOG SHOULD DISSIPATE AFTER MID MORNING WITH WEAK 850 MB
THETA-E ADVECTION FROM W TO E LIKELY TO GENERATE EXPANDING LATE
MORNING AND AFTERNOON CUMULUS/STRATOCU FIELDS. IN ADDITION...UPPER
JET STRUCTURE APT TO DEVELOP SOME HIGHER LEVEL CLOUDS AT TIMES.

CONVECTION PROGNOSIS TODAY POINTS TO AREAS MAINLY ALONG AND E OF I-95
IN SOUTH CAROLINA AS A WEAK LOW PRES REGION IN THE BOUNDARY LAYER
TAKES SHAPE ALONG THE SAVANNAH RIVER THIS AFTERNOON. A WEAK LOBE OF
MID LEVEL VORTICITY IS FORECAST TO TRAVERSE THE CAROLINAS WITH BETTER
THERMODYNAMICS AND MUCAPES PROGGED ALONG THE SEA BREEZE CORRIDOR
NORTH OF SAVANNAH. WHILE MODELS DO NOT SHOW QUITE AS MUCH OVERALL
INSTABILITY AS WEDNESDAY...A FEW STRONGER TSTMS WITH DOWNPOURS AND
FQT LIGHTNING ARE POSSIBLE. WE BUMPED POPS INTO THE CHANCE RANGE
ALONG AND E OF I-95 IN SOUTH CAROLINA THIS AFTERNOON AND ALONG THE
SE GEORGIA COASTAL ZONES EARLY THIS EVENING AS STORMS DRAIN DOWN THE
SEA BREEZE. INTERESTING TO NOTE THAT THE NSSL WRF HINTS AT SOME
DEVIANT/SPLITTING CELLS AGAIN TODAY...SIMILAR TO YESTERDAY. THE
00Z OPERATIONAL NAM APPEARED TO SUFFER FROM CONVECTIVE FEEDBACK AT
TIMES IN THROUGH TONIGHT.

HIGH TEMPS TODAY DEPENDENT ON HOW LONG THE SUN STAYS OUT MANY
AREAS AND WE BUMPED UP TEMPS CLOSER TO 90 SOUTH OF I-16 IN
GEORGIA.

TONIGHT...THERE COULD BE SOME LINGERING CONVECTION ONCE AGAIN WITH
BEACHES AND BARRIER ISLANDS SUSPECT AFTER MIDNIGHT. INLAND AREAS
MAY ALSO SEE YET ANOTHER BOUT OF LOW CLOUDS AND FOG.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY/...
FRIDAY...THE CENTER OF SURFACE HIGH PRESSURE WILL STEADILY TRACK
OVER THE NEW ENGLAND STATES DURING THE DAY...THEN OFF THE
NORTHERN COAST THROUGH THE EVENING AND NIGHTTIME PERIOD. THE
MOVEMENT OF THE HIGH WILL ALLOW AN INLAND WEDGE TO STRENGTHEN DOWN
THE APPALACHIANS...STRETCHING FROM THE MID ATLANTIC STATES
THROUGH THE CAROLINAS AND GEORGIA. THIS PATTERN WILL MAINTAIN
SOLID NORTHEAST FLOW ACROSS THE FORECAST AREA...WITH HIGH
TEMPERATURES REFLECTING THE ASSOCIATED COOLING TREND BY ONLY
PEAKING IN THE LOW TO MID 80S. MOISTURE AND CONVERGENCE ALONG THE
PERIPHERY OF THE INLAND WEDGE NEAR A DEVELOPING TROUGH...AS WELL
AS SHORTWAVE ENERGY EMBEDDED WITHIN THE WEAKENING UPPER
TROUGH...WILL STILL BE SUFFICIENT TO SUPPORT SCATTERED CONVECTION.
EXPECT INITIAL ACTIVITY TO BE FOUND OVER THE WATERS AND COASTLINE
DURING THE MORNING...EVENTUALLY SPREADING INLAND THROUGH THE
AFTERNOON HOURS WITHIN ONSHORE FLOW. BEST SHOWER/THUNDERSTORM
COVERAGE WILL THEN RETURN TO THE COASTLINE AFTER SUNSET. LOW
TEMPERATURES WILL CONTINUE TO TREND COOLER...FALLING INTO THE MID
60S INLAND AND UPPER 60S ALONG THE COAST.

SATURDAY...THE UPPER TROUGH ALONG THE EAST COAST WILL BE IN A
DAMPENING STATE LATE IN THE WEEK...EVENTUALLY TRANSITIONING INTO
A BAGGY UPPER LOW FEATURE AT THE START OF THE WEEKEND. ENERGY
WITHIN THIS LOW ALOFT WILL SUPPORT THE STRENGTHENING OF A COASTAL
TROUGH INTO A SURFACE WAVE OF LOW PRESSURE. THERE IS SOME
DISAGREEMENT BETWEEN MODEL SOLUTIONS REGARDING THE STRENGTH OF
THESE FEATURES...WITH CONSENSUS IN ITS GENERAL TRACK TO THE
NORTH/NORTHEAST OVER THE WATERS AS THE DAY PROGRESSES. INLAND
AREAS WITHIN THE WEDGE OF HIGH PRESSURE WILL REMAIN UNDER A DRIER
REGIME...AS THE BEST CHANCE FOR PRECIPITATION IS FOCUSED ACROSS
THE EASTERN HALF OF THE FORECAST AREA CLOSEST TO MOISTURE AND
CONVERGENCE OFFSHORE. HAVE THUS INDICATED SLIGHT CHANCE POPS FAR
INLAND...INCREASING TO 30 TO 40 PERCENT CLOSER TO THE COASTLINE.
RAIN COVERAGE WILL THEN TRANSITION BACK TO THE COASTLINE AND
MARINE ZONES OVERNIGHT. TEMPERATURES WILL BE EVEN COOLER ON
SATURDAY...AS AFTERNOON HIGHS ARE SUPPRESSED IN THE LOW 80S AND
NIGHTTIME MINIMUMS FALL INTO THE MID 60S.

SUNDAY...THE OFFSHORE SURFACE WAVE WILL CONTINUE TO LIFT
NORTH/NORTHEAST ACROSS THE ATLANTIC WATERS...AS THE WEAK UPPER
LOW BECOMES ABSORBED IN A DEEPENING TROUGH TO THE NORTH. THE
INLAND WEDGE WILL STEADILY BREAK DOWN THROUGH THE DAY AHEAD OF A
RAPIDLY APPROACHING COLD FRONT. THE FORECAST AREA COULD BECOME
LOCATED WITHIN A BAND OF DRY DEEP LAYER AIR BETWEEN THE OFFSHORE
LOW TO THE NORTHEAST AND THE COLD FRONT TO THE WEST. HAVE THUS
INDICATED ONLY A SLIGHT CHANCE FOR RAIN ALONG THE
COASTLINE...EXCEPT FOR A SMALL AREA OF CHANCE POPS SOUTH OF
INTERSTATE 16 IN SOUTHEAST GEORGIA. EXPECT MOST
LOCATIONS...ESPECIALLY INLAND...TO OTHERWISE REMAIN DRY.
TEMPERATURES WILL MODERATE UNDER TRANSITIONING SURFACE FLOW WITHIN
THE ERODING INLAND WEDGE...WITH HIGH TEMPERATURES REACHING THE LOW
TO MID 80S.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
A STRONG SHORTWAVE TROUGH WILL SWEEP ACROSS THE NEW ENGLAND AND
MID ATLANTIC STATES ON MONDAY...HELPING TO DRIVE A COLD FRONT
THROUGH THE FORECAST AREA. MEDIUM RANGE MODELS ARE IN DECENT
AGREEMENT THAT THE FRONT WILL BE ASSOCIATED WITH LITTLE SIGNIFICANT
PRECIPITATION...AND WILL THUS CONTINUE TO CAP RAIN CHANCES IN THE
SLIGHT CHANCE RANGE DURING FRONTAL PASSAGE. EXPANSIVE SURFACE HIGH
PRESSURE FOLLOWING IN THE WAKE OF THE COLD FRONT WILL HAVE ORIGINS
FROM THE NORTHERN PLAINS STATES...AND WILL BE ACCOMPANIED BY A
MORE NOTABLE CHANGE IN AIR MASS. AHEAD OF THE FRONT...TEMPERATURES
ON MONDAY WILL ACTUALLY WARM SEVERAL DEGREES WITHIN FRONTAL
COMPRESSION AND DOWNSLOPE FLOW. CONDITIONS WILL THEN QUICKLY
COOL...WITH LOW TEMPERATURES MONDAY NIGHT FALLING INTO THE LOW TO
MID 60S. EXPECT HIGH TEMPERATURES TUESDAY THROUGH MID WEEK TO ONLY
PEAK IN THE LOW 80S. NIGHTTIME LOWS WILL RANGE FROM THE LOW TO
MID 60S. WITH DRY HIGH PRESSURE POSSIBLY LINGERING THROUGH THE
EXTENDED PERIOD...HAVE GENERALLY KEPT RAIN CHANCES IN THE SLIGHT
CHANCE RANGE...HIGHEST ALONG THE COAST AND OFFSHORE.

&&

.AVIATION /07Z 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...
FAIRLY STRAIGHTFORWARD FORECAST THROUGH TONIGHT WITH WIND SPEEDS
MAINLY 10 KT OR LESS TODAY BUT INCREASING A BIT IN ONSHORE FLOW
TONIGHT...NOTHING SUBSTANTIAL. SEAS 2 TO 3 FT IN SWELL WAVE FOR
THE MOST PART. SYNOPTIC PATTERN FAVORS SOME NOCTURNAL CONVECTION
OVER THE WATERS AGAIN TONIGHT.

FRIDAY THROUGH MONDAY...MODERATE NORTHEAST FLOW IS EXPECTED
SATURDAY AND SUNDAY...AS PRESSURE GRADIENT REMAINS TIGHT BETWEEN
INLAND HIGH PRESSURE AND A WAVE OF LOW PRESSURE FARTHER OFFSHORE.
WINDS COULD PEAK AT 15 TO 20 KT WITH SEAS 3 TO 5 FEET
SATURDAY...BEFORE DIMINISHING SUNDAY AND MONDAY AS THE INLAND
WEDGE WEAKENS AHEAD OF AN APPROACHING COLD FRONT.

RIP CURRENTS...LONG PERIOD SWELL FROM HURRICANE EDOUARD WILL OCCUR
ALONG THE BEACHES TODAY. 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 TODAY.

&&

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

&&

$$

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





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