Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 221912
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
312 PM EDT FRI MAY 22 2015

.SYNOPSIS...
HIGH PRESSURE WILL EXTEND ACROSS THE REGION THROUGH EARLY NEXT WEEK.
A WEAK COASTAL TROUGH WILL PUSH TO THE GEORGIA COAST SATURDAY INTO
SUNDAY.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
TONIGHT...THE CENTER OF THE SURFACE HIGH WILL SLIDE EASTWARD AWAY
FROM THE GREAT LAKES AND TOWARD THE MID ATLANTIC REGION. THIS WILL
HELP MAINTAIN THE COOL AND DRY NORTHEAST FLOW ACROSS THE REGION. THE
FORECAST IS DRY UNDER THE INFLUENCE OF DEEP DRY AIR AND A STRONG
SUBSIDENCE INVERSION. GIVEN THE WAY THE PRESSURE GRADIENT
ALIGNS...AREAS WELL INLAND HAVE THE BEST CHANCE OF COMPLETE
DECOUPLING WHILE LOCATIONS CLOSER TO THE COAST MAY STAY A BIT MIXED.
THE RESULT WILL BE OUR COOLEST NIGHT IN ABOUT A WEEK WITH SOME MID
50S POSSIBLE WELL INLAND...RANGING TO LOW TO MID 60S RIGHT AT THE
COAST.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
SATURDAY AND SUNDAY...HIGH PRESSURE OVER THE MID-ATLANTIC STATES
WILL STEADILY SHIFT OFFSHORE DURING THE PERIOD. MODELS SHOW A
WEAK/SUBTLE COASTAL TROUGH FEATURE DEVELOPING OFF THE SOUTHEAST
GEORGIA AND NORTHEAST FLORIDA COASTS, WHICH WILL SLOWLY SHIFT TO THE
BEACHES BY SUNDAY. THE 22/12Z NAM/GFS ARE SIMILAR IN SHOWING
ISOLATED-SCATTERED SHOWERS/TSTMS DEVELOPING OVER THE COASTAL WATERS
AND PUSHING ONSHORE SOUTH OF THE SAVANNAH RIVER ENTRANCE SATURDAY
NIGHT INTO SUNDAY, BUT THIS LOOKS A BIT BULLISH WITH THE ASSOCIATED
SREF MEMBERS AND THE 22/00Z ECMWF SHOWING MUCH DRIER SOLUTIONS.
PREFER TO LEAN CLOSER TO THE DRIER ECMWF/SREF ENSEMBLE MEAN, WHICH
IS ALSO SIMILAR THE PREVIOUS FORECAST. THIS KEEPS MENTIONABLE POPS
OUT OF THE FORECAST WITH SLIGHT CHANCE POPS CONFINED TO THE ADJACENT
GEORGIA COASTAL WATERS. IF THE 22/12Z ECMWF AND 22/21Z SREF TREND
WETTER...THAN THE INTRODUCTION OF MENTIONABLE POPS MAY BE NEEDED
WITH THE FULL FORECAST PACKAGE SATURDAY MORNING. HIGHS WILL RANGE
FROM LOWER-MID 80S BOTH DAY, POSSIBLY WARMING INTO THE UPPER 80S
WELL INLAND BY SUNDAY AFTERNOON. LOWS WILL RANGE FROM THE UPPER
50/NEAR 60 WELL INLAND TO THE LOWER 70S AT THE BEACHES SUNDAY
MORNING.

MONDAY...LOW-LEVEL MOISTURE WILL INCREASE MONDAY AFTERNOON AS HIGH
PRESSURE SHIFTS FARTHER OUT INTO THE ATLANTIC, HELPING TO ADVECT
HIGHER MEAN BOUNDARY LAYER-700 HPA THETA-E INTO THE REGION. THE BEST
LOW-LEVEL MOISTURE RETURN LOOKS TO BE CONFINED TO SOUTHEAST GEORGIA
WHERE A RISK FOR ISOLATED SHOWERS/TSTMS WILL OCCUR DURING THE
AFTERNOON AND EARLY EVENING HOURS. UPPER LEVEL RIDING WILL BE
SUBSTANTIAL WITH 500 HPA HEIGHTS REACHING 593 DM AND THE CENTER OF
THE 850 HPA ANTICYCLONE CENTERED DIRECTLY OVERHEAD. THIS WILL TEND TO
LIMIT THE OVERALL AMOUNT OF SHOWER/TSTM ACTIVITY WITH FAIRLY WARM
MID-LEVEL THERMAL PROFILES. SLIGHT CHANCE POPS WERE MAINTAINED FOR
ALL OF SOUTHEAST GEORGIA WITH POPS BELOW MENTIONABLE THRESHOLDS OVER
SOUTHEAST GEORGIA. HIGHS WILL RANGE FROM THE MID-UPPER 80S; COOLER
AT THE BEACHES.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
A STRONG DEEP LAYERED RIDGE WILL REMAIN THE DOMINANT WEATHER FEATURE
DURING THE LONG TERM PERIOD. INCREASING LOW-LEVEL THICKNESSES
SUPPORT A WARMING TREND WITH TEMPS SEVERAL DEGREES ABOVE NORMAL
THROUGH THE PERIOD. A STRONG MID-LEVEL CAP WILL MINIMIZE RAIN
CHANCES THROUGH WEDNESDAY. SOME SHORTWAVE ENERGY WILL BEGIN TO ERODE
THE RIDGE FROM THE WEST THURSDAY INTO FRIDAY...POTENTIALLY ALLOWING
FOR ISOLATED SHOWERS AND TSTMS TO MOVE INTO INLAND AREAS DURING THE
AFTERNOON HOURS.

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
VFR CONDITIONS WILL PREVAIL THROUGH 18Z SATURDAY.

EXTENDED AVIATION OUTLOOK...VFR.

&&

.MARINE...
REST OF AFTERNOON AND TONIGHT...HIGH PRESSURE WILL CROSS THE GREAT
LAKES THIS EVENING AND MOVE TOWARD THE MID ATLANTIC REGION THROUGH
THE OVERNIGHT. THIS WILL MAINTAIN THE ONGOING MODESTLY PINCHED
GRADIENT ALONG THE COAST AND CONTINUE TO FEED ELEVATED NORTHEAST
FLOW. WINDS ALONG THE LAND/SEA INTERFACE MAY BRIEFLY TURN MORE
EASTERLY THIS AFTERNOON AND EVENING...BEFORE BECOMING NORTHEASTERLY
AGAIN OVERNIGHT. THE TIGHTEST GRADIENT WILL BE ACROSS THE GEORGIA
WATERS WHICH WILL SUPPORT 15-20 KT THROUGH THE NIGHT.
ELSEWHERE...WINDS MAY DIMINISH BACK TO 10-15 KT THIS EVENING BEFORE
INCREASING BACK INTO THE 15-20 KT RANGE LATE TONIGHT. GIVEN THAT THE
MAIN WIND DRIVER IS PRESSURE GRADIENT RELATED AND NOT MIXING...FEEL
PRETTY CONFIDENT THAT GUSTS WILL BE LIMITED TO THE LOW 20 KT RANGE
AT TIME AND SMALL CRAFT ADVISORIES WILL NOT BE NEEDED. SEAS WILL BE
UP TO 4 FT OUT AROUND 20 NM MAINLY OFF THE GEORGIA COAST...AND 4-5
FT BEYOND 20 NM.

SATURDAY...AN ENHANCED PRESSURE GRADIENT WILL MAINTAIN LESS THAN
IDEAL CONDITIONS OVER THE COASTAL WATERS INTO SATURDAY. NORTHEAST
WINDS OF 15-20 KT WILL KEEP THE SEA STATE RATHER CHOPPY WITH SEA
BUILDING TO 3-4 FT NEARSHORE WATERS AND 4-5 FT BY SATURDAY AFTERNOON
AND 4-5 FT NEARSHORE WATERS WITH 5-6 FT OFFSHORE WATERS SATURDAY
NIGHT. A SMALL CRAFT ADVISORY MAY EVENTUALLY BE NEEDED...MAINLY FOR
THE GEORGIA OFFSHORE LEG WHERE SEA BREACH THE 6 FT ADVISORY
CRITERIA.

SUNDAY...WINDS WILL DIMINISH A BIT AS THE PRESSURE GRADIENT RELAXES
A BIT IN RESPONSE TO HIGH PRESSURE SHIFTING OUT INTO THE ATLANTIC.
WINDS WILL TURN MORE EASTERLY AS A RESULT WITH SPEEDS GENERALLY 15
KT OR SO. SEAS WILL REMAIN ELEVATED WITH 3-4 FT NEARSHORE WATERS AN
5-6 FT OFFSHORE WATERS.

MONDAY THROUGH WEDNESDAY...THERE ARE NO SIGNIFICANT CONCERNS WITH
WINDS GENERALLY 15 KT OR LESS AND SEAS 4 FT OR LESS.

&&

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

&&

$$

NEAR TERM...BSH
SHORT TERM...ST
LONG TERM...JRL
AVIATION...BSH
MARINE...BSH/ST



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