Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 011740
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
140 PM EDT TUE SEP 1 2015

.SYNOPSIS...
A WEAK TROUGH OF LOW PRESSURE WILL PERSIST OVER THE SOUTHEAST THIS
WEEK. THIS WEEKEND INTO EARLY NEXT WEEK...HIGH PRESSURE WILL BUILD
INTO THE REGION FROM THE NORTH...AND A TROUGH OF LOW PRESSURE WILL
DEVELOP OVER OR CLOSE TO COASTAL WATERS.

&&

.NEAR TERM /THROUGH TONIGHT/...
MADE MINOR TWEAKS TO THE FORECAST FOR THE EARLY AFTERNOON
UPDATE...MAINLY ACCOUNTING FOR SLIGHT VARIATIONS IN OBSERVED
TEMPERATURE AND DEWPOINT TRENDS...BUT THINKING REMAINS THE SAME.
OBSERVATIONS NEAR THE COAST SHOW WINDS BEGINNING TO VEER...SHORTLY
BECOMING ONSHORE. ONCE THE SEABREEZE GETS GOING...SOME SHOWERS
AND ISOLATED TSTORMS ARE POSSIBLE...MAINLY SOUTH OF I-16 AND OVER
THE NEARSHORE WATERS SO GREATEST POPS REMAIN IN THIS AREA. THUNDERSTORMS
CONTINUE TO DRIFT NORTH INTO THE OUTER GEORGIA WATERS. ACROSS MUCH
OF SE SOUTH CAROLINA...MAINLY DRY WEATHER TODAY AS PWATS ARE LOWER
BUT MAINTAINED A SLIGHT AFTERNOON CHANCE FOR MOSTLY SPOTTY AND
SHALLOW CONVECTION ALONG THE SEABREEZE. SHOWERS INITIATED BY THE
SEABREEZE ARE EXPECTED TO QUICKLY DISSIPATE WITH THE LOSS OF
INSOLATION THIS EVENING.THE PLUME OF DEEP TROPICAL MOISTURE AND
THE ASSOCIATED STRONG MOISTURE GRADIENT ON IT/S NORTH FLANK ACROSS
EAST CENTRAL GEORGIA AND SOUTH CAROLINA WILL DRIFT VERY SLOWLY N
LATE TODAY AND TONIGHT.

TONIGHT...MODELS INDICATE DECREASING CONDENSATION PRES DEFICITS
INTO SE GEORGIA ALONG WITH WEAK UPPER DIFLUENCE AND THIS COULD
RESULT IN ISOLATE TO SCATTERED SHOWERS AND PERHAPS A FEW TSTMS
ACROSS SE GEORGIA WITH ISOLATED SHOWERS COASTAL SOUTH CAROLINA.
MODELS INDICATE PWATS WILL SURGE ABOVE 2.3 INCHES THUS WE
BUMPED POPS UP A BIT SOUTHERN ZONES.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
WEDNESDAY...A SHORTWAVE WILL TRACK ACROSS SOUTHERN COUNTIES OF THE
FORECAST AREA. WHILE MODELS DIFFER SOMEWHAT REGARDING
ORIENTATION/TIMING OF THIS FEATURE...IN GENERAL THE SCENARIO FAVORS
A NORTH TO SOUTH GRADIENT OF POPS...WITH A MAXIMUM OF ABOUT 50
PERCENT SOUTH OF I-16. PWATS EXCEEDING 2 INCHES AND WEAK LOW/MID
LEVEL WINDS SUGGEST A POTENTIAL FOR LOCALLY EXCESSIVE RAINFALL
ACROSS THIS AREA...AND LOCALLY GREATER POPS COULD EVENTUALLY BE
REQUIRED. OTHERWISE...TEMPERATURES SHOULD RECOVER INTO THE
UPPER80S/LOWER 90S MOST AREAS.

WEDNESDAY NIGHT...THE SHORTWAVE SHOULD PUSH OFFSHORE...ALTHOUGH
MODELS CONTINUE TO DISAGREE REGARDING THIS SCENARIO. THE 01/00Z EURO
MAINTAINS A FAIRLY WELL DEFINED AND PROGRESSIVE SYSTEM...WHILE THE
01/00Z GFS AND TO A LESSER EXTENT THE NAM DEPICT AN ELONGATED AXIS
OF VORTICITY WHICH PERSISTS OVER THE REGION WELL INTO THE NIGHT. THE
LATEST FORECAST DEPICTS DECREASING POPS WITH TIME...WITH OVERNIGHT
SLIGHT CHANCE/CHANCE POPS LIMITED TO SOUTHERN COASTAL COUNTIES AND
ADJACENT COASTAL WATERS. BY DAYBREAK THURSDAY...EXPECT LOWS IN THE
LOWER 70S INLAND AND IN THE MID/UPPER 70S CLOSER TO THE COAST.

THURSDAY...SUBSIDENCE/SHORTWAVE RIDGING IN THE WAKE OF THE DEPARTING
SHORTWAVE TROUGH SHOULD LIMIT DIURNAL POPS AND ALLOW TEMPERATURES TO
RECOVER INTO THE LOWER/MID 90S AWAY FROM THE COAST. MAX HEAT INDEX
VALUES OF 98-102F WILL BE COMMON THURSDAY AFTERNOON. POPS ARE
LIMITED TO SLIGHT CHANCE/CHANCE...MAINLY ALONG THE SEA BREEZE AND
HIGHEST ACROSS THE SOUTH...BUT EVEN THESE POPS COULD PROVE TO BE A
BIT HIGH.

THURSDAY NIGHT...POPS ARE LIMITED TO COASTAL WATERS. EXPECT LOW
TEMPERATURES IN THE LOWER-MID 70S INLAND AND MID TO UPPER 70S NEAR
THE COAST...EVEN AROUND 80F ON THE BEACHES.

FRIDAY...AN UPPER TROUGH WILL PUSH INTO THE REGION FROM THE NORTH
AND/OR WEST...DEPENDING ON YOUR MODEL OF CHOICE. POPS SHOULD
INCREASE INTO THE 30-40 PERCENT RANGE...ESPECIALLY DURING THE
AFTERNOON/EVENING. HIGH TEMPERATURES IN THE UPPER 80S WILL BE
COMMON.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
AT THE SURFACE...EXPANSIVE HIGH PRESSURE CENTERED NORTH OF THE
REGION WILL BUILD SOUTH NEXT WEEKEND INTO EARLY NEXT WEEK...AND A
COASTAL TROUGH SHOULD DEVELOP. ALOFT...A COMPLEX BLOCKING PATTERN
WILL DEVELOP...AND MEDIUM RANGE MODELS GENERALLY AGREE THAT THE
UPPER TROUGH WILL BECOME CUT OFF OVER THE SOUTHEAST THIS WEEKEND AND
WILL MEANDER OVER THE REGION INTO EARLY NEXT WEEK. THIS PATTERN
SHOULD FAVOR SLIGHTLY BELOW NORMAL TEMPS AND ABOVE NORMAL POPS.
UNCERTAINTY EXISTS REGARDING THE RELATIVE POSITIONS/STRENGTHS OF
CRITICAL FEATURES INCLUDING THE NORTH-SOUTH MOISTURE GRADIENT WHICH
TYPICALLY DEVELOPS IN THESE PATTERNS. THUS...CHANCE POPS ARE IN ORDER
DURING THE DAYTIME HOURS...HIGHEST SOUTH AND OVER COASTAL
WATERS...AND NIGHTTIME POPS ARE FOCUSED ACROSS SOUTHERN/COASTAL
COUNTIES AND ACROSS COASTAL WATERS. FORECAST ADJUSTMENTS WILL BE
NECESSARY AS DETAILS EMERGE OVER THE NEXT SEVERAL DAYS.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
VFR CONDITIONS ARE EXPECTED TO PREVAIL AT BOTH TERMINALS THROUGH
18Z WEDNESDAY. MOISTURE WILL INCREASE...PARTICULARLY NEAR KSAV
LATER TODAY AND ESPECIALLY TONIGHT. SOME SHOWERS ARE POSSIBLE IN
THE VICINITY OF EITHER TERMINAL DUE TO THE PROGRESSION OF THE
SEABREEZE BUT THE PROBABILITY FOR DIRECT IMPACTS IS TOO LOW TO
INCLUDE IN THE TAFS AT THIS TIME. THERE ARE ONLY A FEW INDICATIONS
THAT OVERNIGHT FLIGHT RESTRICTIONS IN MVFR CEILINGS AND/OR VSBYS
COULD OCCUR...AND THANKS TO THE INCREASED MOISTURE AND LIGHT AND
VARIABLE WINDS...MVFR CIGS ARE CERTAINLY POSSIBLE LATE TONIGHT AT
KSAV ALONG WITH A FEW SHOWERS BUT PROBABILITIES ARE LOW.

EXTENDED AVIATION OUTLOOK THROUGH SUNDAY...MAINLY VFR. THE
PROBABILITY FOR FLIGHT RESTRICTIONS WILL INCREASE THIS WEEKEND.

&&

.MARINE...
TODAY A WEAK PRESSURE PATTERN WILL PERSIST WITH SYNOPTIC FLOW
FAVORING A MAINLY SSE TO SSW COMPONENT. IN THE NEARSHORE WATERS A
LAND BREEZE WILL SHORTLY GIVE WAY TO A COMBINATION OF THIS
SYNOPTIC FLOW WITH A SEABREEZE LATER. SPEEDS MAINLY 10 KT OR LESS
AND SEAS 2 TO 3 FT THROUGH TONIGHT.

THROUGH LATE WEEK...A WEAK PRESSURE PATTERN WILL TRANSLATE
TO WINDS LESS THAN 15 KT DOMINATED BY THE SEA AND LAND BREEZES. BY
NEXT WEEKEND...HIGH PRESSURE BUILDING FROM THE NORTH AND A
DEVELOPING COASTAL TROUGH COULD PRODUCE INCREASING NE WINDS AND
BUILDING SEAS.

RIP CURRENTS...AN ELEVATED RISK FOR RIP CURRENTS COULD DEVELOP AGAIN
NEXT WEEKEND.

&&

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

&&

$$
SYNOPSIS...
NEAR TERM...
SHORT TERM...SPR
LONG TERM...SPR
AVIATION...
MARINE...SPR



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