Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 070356
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1056 PM EST FRI MAR 6 2015

.SYNOPSIS...
HIGH PRESSURE WILL PREVAIL ACROSS THE AREA THROUGH EARLY
SUNDAY...BEFORE IT SHIFTS INTO THE ATLANTIC FOR EARLY NEXT WEEK.
AN UNSETTLED PATTERN WILL THEN DEVELOP BETWEEN A STATIONARY FRONT
SOUTH AND EAST OF THE REGION AND HIGH PRESSURE CENTERED TO THE
NORTH FROM LATE MONDAY OR MONDAY NIGHT THROUGH MUCH OF NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
AS EXPECTED...CLOUD COVER CONTINUE TO DECREASE AND EXCELLENT
RADIATIONAL COOLING CONDITIONS ARE SPREADING ACROSS THE REGION.
THUS...MAINTAINED ONGOING FREEZE WARNINGS/FROST ADVISORIES WITH
ONLY MINOR ADJUSTMENTS MAINLY TO SHORTED THE DURATION OF FREEZING
TEMPS BY AN HOUR OR TWO MOST AREAS.

MEANWHILE...DEWPOINTS HAVE REMAINED SOMEWHAT ELEVATED ESPECIALLY
ALONG/SOUTH OF THE SAVANNAH RIVER...AND RECENT HIGH RESOLUTION
MODELS SUGGEST THAT AT LEAST PATCHY GROUND FOG COULD DEVELOP AWAY
FROM THE COAST OVERNIGHT. WHERE TEMPERATURES ARE EXPECTED TO FALL
TO NEAR OR BELOW FREEZING...INTRODUCED A MENTION OF PATCHY
FREEZING FOG. AS OF LATE FRIDAY EVENING...LATEST THINKING IS THAT
FOG COVERAGE/IMPACTS WILL REMAIN LIMITED. HOWEVER...MORE
EXTENSIVE FOG DEVELOPMENT COULD EITHER PRODUCE SOME LOCALIZED
TRAVEL ISSUES ON ELEVATED ROAD SURFACES OR COULD HOLD
TEMPERATURES A BIT ABOVE FORECAST VALUES...IN SOME CASES JUST
ABOVE FREEZING. NO ADVISORIES OR STATEMENTS ARE JUSTIFIED AS OF
THE LATE EVENING UPDATE.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
SATURDAY...QUASI-ZONAL FLOW ALOFT ATOP WILL CAUSE THE COLD ARCTIC
HIGH PRESSURE ANCHORED ACROSS THE LOCAL AREA IN THE MORNING TO SLIDE
TOWARD THE COAST BY NIGHTFALL...SUPPORTING A QUIET WEATHER PATTERN.
AN EXTREMELY DRY VERTICAL COLUMN WITH PWATS NO MORE THAN 1/4 OR 1/3
INCH WILL SUPPORT PLENTY OF SUNSHINE /ASIDE FROM A FEW LINGERING JET
STREAM CIRRUS EARLY IN THE MORNING/. FULL INSOLATION AND LOW LEVEL
THICKNESS EXPANDS TO 1336-1345 METERS...PLUS SOME MODIFICATION OF
THE AIR MASS WILL GENERATE A WARMER DAY. ALTHOUGH WE/LL STILL BE
SOME 5-8F BELOW CLIMATOLOGICAL NORMS...HIGHS WILL RANGE FROM UPPER
50S OR NEAR 60 NORTH TO 62-64 SOUTH. AFTERNOON SEA BREEZE
CIRCULATIONS WILL LIMIT THE COASTAL SECTIONS TO THE LOWER 50S NORTH
AND MID-UPPER 50S CENTRAL AND SOUTH.

SATURDAY NIGHT...SURFACE HIGH PRESSURE WILL PERSIST OVERHEAD
ALLOWING FOR RAPID DECOUPLING WITH SUNSET. UNDER MAINLY CLEAR SKIES
AND DEW POINTS DOWN IN THE LOWER AND MIDDLE 30S WILL LEAD TO ALMOST
PERFECT RADIATIONAL COOLING INLAND FROM THE BARRIER ISLANDS. THIS IN
TURN WILL PRODUCE AT LEAST SCATTERED FROST NEAR AND WEST OF US-
17...AND A FROST ADVISORY WILL LIKELY BE REQUIRED. LOWS WILL RANGE
FROM 34-37 INLAND TO THE LOWER-MIDDLE 40S ON THE COASTAL COMMUNITIES.

SUNDAY...THE SYNOPTIC SITUATION IS CHARACTERIZED BY ZONAL FLOW
UPSTAIRS AND THE SURFACE HIGH TO PULL EAST INTO THE ATLANTIC. WARM
ADVECTION STARTS TO CRANK UP AS A SOUTH-SW FLOW IN THE LOWER LAYERS
DEVELOPS WITH THIS TRANSITIONS...WITH 1000-850 MB THICKNESS TO
STRETCH TO 1355-160 METERS. WHILE WE DO SEE AN INCREASE IN MID/HIGH
LEVEL CLOUDS...THERE IS STILL SUFFICIENT INSOLATION TO YIELD MAX
TEMPS OF 70-72 ACROSS THE MAJORITY OF THE CWFA. THE EXCEPTION WILL
BE THE ATLANTIC SEABOARD WHERE HIGHS ARE RESTRICTED TO THE LOWER 60S
WITH SEA BREEZE AND ONSHORE SYNOPTIC FLOW.

SUNDAY NIGHT AND MONDAY...A SOUTHERN STREAM PERTURBATION WILL
PROGRESS THROUGH THE SOUTHERN PLAINS...AS A SUB-TROPICAL RIDGE FROM
THE ATLANTIC EXPANDS WEST/NW. THIS WILL INDUCE SLIGHTLY RISING
HEIGHTS ALOFT AND ITS ACCOMPANYING WARM ADVECTION. HIGH PRESSURE AT
THE SURFACE WILL PULL FURTHER OFFSHORE AS THE OLD BAROCLINIC ZONE
AND STATIONARY FRONT TO THE SOUTH BEGINS TO CREEP CLOSER. ISENTROPIC
ASCENT WILL DEVELOP AS THIS OCCURS...INITIALLY CAUSING AN INCREASE
IN CLOUDINESS. IT/LL TAKE AWHILE FOR THE LOWEST LEVELS TO MOISTEN
UP...SO WE HAVE DELAYED THE ONSET OF THE NEXT RAIN EVENT. AT LEAST
THE FIRST HALF OF SUNDAY NIGHT WILL BE DRY...BUT WE HAVE SHOWN 20
POPS SOUTH OF I-16 OVERNIGHT. THEN ON MONDAY THE RAIN CHANCES CLIMB
FROM SW TO NE...PEAKING IN THE 20 PERCENTILE NORTH AND 30 PERCENTILE
SOUTH. NOTICEABLY WARMER SUNDAY NIGHT WITH INSULATING EFFECTS OF THE
CLOUDS AND WARM ADVECTION. TEMPS ON MONDAY MIGHT NEED SOME
ADJUSTMENTS PENDING HOW QUICKLY THE CLOUDS THICKEN/LOWER AND ARRIVAL
OF THE RAIN. FOR NOW WE ARE SHOWING MID AND UPPER 60S INLAND AND
CLOSER 60 ON THE BEACHES.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
CONFIDENCE IN THE DETAILS OF THE EXTENDED FORECAST REMAIN RATHER LOW
CONSIDERING PERSISTENT MODEL DISCREPANCIES WITHIN A RELATIVELY
CHANGEABLE PATTERN. RAIN CHANCES WILL BE DRIVEN BY THE LOCATION OF A
LINGERING STATIONARY FRONT AND ANY WAVES OF LOW PRESSURE....AS WELL
AS A RIBBON OF DEEP MOISTURE ENHANCED BY CONTINUAL SHORTWAVE ENERGY
MOVING UP FROM THE GULF OF MEXICO. WITH THE SOUTHEAST COAST ALONG
THE PERIPHERY OF THE SUBTROPICAL RIDGE...THE AXIS OF DEEP MOISTURE
WILL LIKELY BE HELD JUST TO THE WEST AND NORTH OF THE FORECAST
AREA...WITH BEST RAIN CHANCES ACROSS INLAND AND NORTHERN ZONES AS A
RESULT. HAVE INCLUDED RAIN CHANCES IN THE FORECAST FOR THE ENTIRE
WEEK...HIGHEST MONDAY NIGHT INTO TUESDAY. OTHERWISE...PREFER TO
REMAIN SOMEWHAT GENERIC AND FLEXIBLE REGARDING THE FORECAST...AS
RAIN POTENTIAL AND COVERAGE EXPECTATIONS FOR THE MID TO LATE WEEK
PERIOD WILL LIKELY CHANGE AS MODELS HOPEFULLY COME INTO BETTER
AGREEMENT.

HIGH TEMPERATURES WILL GENERALLY REACH THE 60S EACH
AFTERNOON...EXCEPT FOR LOW 70S SOUTHEAST GEORGIA ZONES WEDNESDAY AND
THURSDAY. LOW TEMPERATURES WILL BE WARMER THAN NORMAL...MAINLY A
RESULT OF THE INSULATING EFFECTS OF CLOUD COVER THAT IS EXPECTED TO
LINGER THROUGH THE MAJORITY OF THE WEEK.

&&

.AVIATION /04Z SATURDAY THROUGH WEDNESDAY/...
VFR THROUGH SATURDAY. LOW PROBABILITY FOR GROUND FOG IN THE KSAV
VICINITY LATE TONIGHT INTO EARLY SATURDAY.

EXTENDED AVIATION OUTLOOK...VFR WILL CONTINUE FROM SATURDAY
AFTERNOON INTO MONDAY. OCCASIONAL WAVES OF LOW PRESSURE RIDING
ALONG A NEARBY STATIONARY FRONT MONDAY NIGHT THROUGH WEDNESDAY
COULD BRING PERIODS OF MVFR AND IFR CONDITIONS IN LOW CEILINGS AND
RAIN.

&&

.MARINE...
OVERNIGHT...ELEVATED WINDS/SEAS WILL PERSIST ON THE PERIPHERY OF
INLAND HIGH PRESSURE...OUTSIDE CHARLESTON HARBOR. N/NE WINDS WILL
RANGE FROM 15-20 KT WITHIN NEAR SHORE WATERS TO 20-25 KT BEYOND 20
NM. SEAS WILL RANGE FROM AS HIGH AS 405 FT WITHIN 20 NM TO AS HIGH
AS 6-8 FT BEYOND.

SATURDAY...THE REMAINING SMALL CRAFT ADVISORY ON THE OUTER GA WATERS
IN THE MORNING WILL EXPIRE BY 16Z...AS THE CONTINENTAL HIGH OVER THE
SE IN THE MORNING SLIDES TOWARD THE COAST AND COLD ADVECTION FADES
IN THE AFTERNOON. NE WINDS WILL PEAK AS HIGH AS 8-12 KT IN
CHARLESTON HARBOR AND 13-19 KT OVER THE OPEN ATLANTIC IN THE
MORNING...VEERING SOME 20-50 DEGREES IN THE AFTERNOON AS SPEEDS
DIMINISH TO LESS THAN 10 OR 15 KT. SEAS UP TO 6 FT BEYOND 40 NM OFF
THE GA COAST IN THE MORNING...DROPPING TO 5 FT OR LESS. ELSEWHERE
SEAS WILL BE AT OR BELOW 3 OR 4 FT THROUGH THE DAY.

SATURDAY NIGHT THROUGH SUNDAY...CONDITIONS WILL BE BENIGN ACROSS THE
MARINE COMMUNITY AS THE SURFACE HIGH REMAINS ACROSS THE WATERS. THE
END RESULT IS FOR WINDS OF VARYING DIRECTIONS /DRIVEN MAINLY BY LAND
BREEZE AND SEA BREEZE CIRCULATIONS/ AT LESS THAN 10 KT AND SEAS
RESTRICTED TO MAINLY 3 FT OR LESS.

SUNDAY NIGHT AND MONDAY...THE SURFACE HIGH SLIDES FURTHER EAST
ACROSS THE ATLANTIC AS A STATIONARY FRONT TAKES SHAPE TO OUR SOUTH.
THIS CAUSES S SLOW BUT STEADY TIGHTENING OF THE PRESSURE GRADIENT
FROM LATE SUNDAY NIGHT INTO MONDAY...ENOUGH SO THAT NE WINDS CLIMB
TO AT LEAST A SOLID 12-18 KT ON MONDAY...MAYBE HIGHER. SEAS WILL
HOLD AT 4 FT OR LOWER.

FORECAST CONFIDENCE REMAINS RATHER LOW EARLY INTO THE MIDDLE OF NEXT
WEEK DUE TO THE UNCERTAINTY REGARDING A FLUCTUATING STATIONARY FRONT
AND POSSIBLE WAVES OF LOW PRESSURE TRACKING ALONG THE FEATURE. WILL
CONTINUE TO KEEP WINDS/SEAS BELOW ADVISORY LEVELS...HOWEVER ANY
CHANGES TO THE LOCATION OF THE FRONT AND/OR THE STRENGTH OF LOW
PRESSURE WAVES COULD SUPPORT STRONGER WINDS AND HIGHER SEAS.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...FREEZE WARNING UNTIL 9 AM EST SATURDAY FOR GAZ099>101.
     FREEZE WARNING FROM 4 AM TO 9 AM EST SATURDAY FOR GAZ114>116-
     118-137-138-140.
     FROST ADVISORY FROM 4 AM TO 9 AM EST SATURDAY FOR GAZ117-119-
     139-141.
     FREEZE WARNING UNTIL 9 AM EST SATURDAY FOR GAZ087-088.
SC...FREEZE WARNING UNTIL 9 AM EST SATURDAY FOR SCZ047>052.
     FREEZE WARNING UNTIL 9 AM EST SATURDAY FOR SCZ040-042>045.
MARINE...SMALL CRAFT ADVISORY UNTIL NOON EST SATURDAY FOR AMZ374.

&&

$$
SYNOPSIS...
NEAR TERM...SPR
SHORT TERM...
LONG TERM...WMS
AVIATION...SPR
MARINE...BSH/SPR



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