Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 232008
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
408 PM EDT TUE SEP 23 2014

.SYNOPSIS...
A HIGH PRESSURE WEDGE WILL BUILD INLAND...WHILE A COASTAL TROUGH
DEVELOPS OFFSHORE INTO MID WEEK. THE REGION WILL THEN REMAIN
SITUATED BETWEEN HIGH PRESSURE TO THE NORTH AND A STATIONARY
FRONT TO THE SOUTH AND EAST THROUGH EARLY NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
THE PATTERN AT THE SURFACE AND ALOFT IS FAIRLY ANOMALOUS FOR LATE
SEPTEMBER. A NEARLY STATIONARY UPPER LOW IS FILLING OVER THE
CAROLINAS...WHILE A WEDGE OF SURFACE HIGH PRESSURE BUILDS INLAND AND
A COASTAL TROUGH DEVELOPS OFFSHORE. SOLID NORTHEAST FLOW PREVAILS
ON THE PERIPHERY OF THE INLAND WEDGE...AND WHEN COMBINED WITH
THICK CLOUD COVER...HAS SIGNIFICANTLY SUPPRESSED TEMPERATURES
ACROSS THE FORECAST AREA.

DEEP MOISTURE STREAMING UP THE EASTERN AND NORTHERN EDGES OF THE
UPPER LOW...COMBINED WITH CONVERGENCE ALONG THE COASTAL TROUGH
ANCHORED ALONG AN OFFSHORE FRONT...WILL SUPPORT PERSISTENT RAIN
CHANCES OVERNIGHT. WILL CONTINUE TO INDICATE A NOTABLE
PRECIPITATION GRADIENT ACROSS THE AREA...WITH SCATTERED TO
NUMEROUS SHOWERS IMPACTING THE COASTLINE AND CHARLESTON TRI COUNTY
REGION...WHILE MORE ISOLATED ACTIVITY OCCURS INLAND ASSOCIATED
WITH THE CORE OF THE UPPER LOW.

THE COASTAL TROUGH WILL AMPLIFY OVERNIGHT AND TIGHTEN THE GRADIENT
BETWEEN THE INLAND WEDGE...SUPPORTING A SURGE IN NORTHEAST WINDS.
CONDITIONS COULD GET BREEZY INLAND AND WINDY ALONG THE
COAST...POSSIBLY GUSTING UP TO 25 TO 30 MPH AT TIMES. THE
COMBINATION OF THESE COOL WINDS AND PERSISTENT CLOUD COVER WILL
ALLOW TEMPERATURES TO FALL BELOW SEASONAL NORMALS...RANGING FROM
THE UPPER 50S INLAND TO THE MID 60S NEAR THE COAST.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
WEDNESDAY...THE CORE OF THE UPPER LOW WILL REMAIN CENTERED JUST
WEST OF THE FORECAST AREA...WHILE A SURFACE TROUGH WILL PERSIST OVER
OR CLOSE TO THE COASTAL WATERS. THROUGH AT LEAST THE MORNING
HOURS...THE UPPER LOW WILL CONTINUE TO DRAW A N-S PLUME OF DEEP
MOISTURE OVER THE COASTAL TROUGH AND INTO COASTAL COUNTIES
ESPECIALLY ALONG THE SC COAST. FARTHER SOUTH/WEST THE UPPER LOW...A
MID-LEVEL DRY SLOT WILL PERSIST CLOSER TO THE UPPER LOW...AND THIS
SHOULD GREATLY LIMIT THE COVERAGE/PERSISTENCE OF ANY SHOWERS.
THUS...MORNING POPS ARE GRADUATED FROM LIKELY ALONG THE SOUTH
CAROLINA COAST...WHERE LOCALLY HEAVY RAIN IS POSSIBLE...TO SLIGHT
CHANCE INLAND. DURING THE AFTERNOON...23/12Z GUIDANCE SUGGESTS THAT
THE UPPER LOW WILL GRADUALLY UNRAVEL/WEAKEN...AND FORCING FOR
ASCENT/ASSOCIATED POPS SHOULD DIMINISH ALONG THE SC COAST.
OTHERWISE...HIGH TEMPS ARE EXPECTED TO REMAIN BELOW NORMAL...RANGING
FROM THE LOWER/MID 70S NORTH/NEAR THE SC COAST TO UPPER 70S/NEAR 80F
INLAND.

WEDNESDAY NIGHT THROUGH FRIDAY...23/12Z GUIDANCE AGREES THAT THE
UPPER LOW WILL CONTINUE TO DISSIPATE WEST OF THE REGION IN FAVOR OF
AN OFFSHORE UPPER RIDGE EXPANDING OVER THE REGION. THE SURFACE
TROUGH WILL LIKELY LINGER OVER OR CLOSE TO THE COASTAL WATERS...AND
MOISTURE WILL REMAIN SUFFICIENT FOR POPS TAPERED FROM CHANCE ALONG
THE COAST TO SLIGHT CHANCE INLAND...HIGHEST DURING THE AFTERNOON.
MEAGER INSTABILITY JUSTIFIES NO MENTION OF THUNDERSTORMS OVER LAND
THROUGH THE PERIOD.

TEMPERATURES SHOULD GRADUALLY MODERATE AND HIGH TEMPS COULD APPROACH
NORMAL VALUES AS EARLY AS FRIDAY.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
CONSIDERABLE DISAGREEMENT BETWEEN MODELS IN THE LONG TERM THOUGH IT
LOOKS AS THOUGH THE EXPANSIVE HIGH WILL REMAIN NORTH OF THE AREA
THROUGH SUNDAY. ENOUGH MOISTURE AND LIFT WILL EXIST FOR ISOLATED TO
SCATTERED SHOWERS ACROSS THE AREA. POTENTIAL FOR INCREASING RAIN
CHANCES EARLY NEXT WEEK IF A FRONT LIFTS NORTH OUT OF THE GULF PER
THE 00Z ECMWF. TEMPS RETURN TO NEAR NORMAL FOR LATE SEPT BY THE
WEEKEND.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
LATEST RADAR IMAGERY SHOWS SCATTERED RAIN CONTINUING TO STREAM
ACROSS THE CHARLESTON TRI COUNTY REGION AND JUST OFF THE SOUTH
CAROLINA/GEORGIA WATERS THIS AFTERNOON. HAVE INITIALIZED THE KSAV
TAF WITH DRY WEATHER...AS THE MAJORITY OF ACTIVITY WILL LIKELY
REMAIN TO THE EAST AND NORTH. DETERMINING TIMING AND DURATION OF
LIGHT RAIN AT KCHS WILL BE MORE DIFFICULT DUE TO ITS CLOSER
PROXIMITY TO THE FLUX OF MOISTURE FROM THE MARINE ZONES. PREFER
TO INDICATE VCSH THROUGH THE NIGHTTIME PERIOD...WITH A TEMPO GROUP
FOR -RA AND BROKEN MVFR CONDITIONS DURING THE NEXT FEW HOURS.

THE PRESSURE GRADIENT WILL BEGIN TO TIGHTEN BETWEEN AN INLAND
WEDGE OF HIGH PRESSURE AND A TROUGH OFFSHORE...SUPPORTING AN
INCREASE IN NORTHEAST WINDS. STRONGEST WINDS COULD ACTUALLY OCCUR
OVERNIGHT...WHEN THE GRADIENT IS THE TIGHTEST. BROKEN TO OVERCAST
SKY COVER WILL LIKELY VARY BETWEEN LOW VFR AND MVFR THROUGH THE
PERIOD...AND ADJUSTMENTS WILL LIKELY BE NEEDED. WILL INDICATE
CONDITIONS PREVAILING MVFR BY DAYBREAK WEDNESDAY...AS WIND SPEEDS
DIMINISH SLIGHTLY AND THE INLAND WEDGE INVERSION HOLDS IN PLACE.

EXTENDED AVIATION OUTLOOK...MVFR OR LOWER CIGS POSSIBLE AT TIMES
INTO THE END OF THE WEEK WITH A LINGERING WEDGE PATTERN AND AMPLE
LOW LEVEL MOISTURE.

&&

.MARINE...
TONIGHT...A STRONG COOL SEASON STYLE INLAND WEDGE/COASTAL TROUGH
PATTERN WILL CONTINUE TO EVOLVE...CHARACTERIZED BY A TIGHTENING
GRADIENT AS HIGH PRESSURE BUILDS IN FROM THE NORTH. SMALL CRAFT
ADVISORIES ARE ACTIVE FOR ALL THE COASTAL WATERS...AS CONDITIONS
STEADILY DETERIORATE. SOLID ADVISORY CONDITIONS ARE EXPECTED
ACROSS ALL WATERS BY TONIGHT...WITH SEAS BUILDING TO 6 TO 8
FT...HIGHEST OFFSHORE. THERE COULD BE SOME LOCAL PINCHING AND A
FEW GUSTS NEARING GALES AT TIMES...BUT HAVE CAPPED ALL WINDS AT 30
KT FOR NOW.

THROUGH LATE WEEK....STRONG HIGH PRESSURE WILL REMAIN CENTERED TO
THE NORTH...A STATIONARY FRONT WILL REMAIN SOUTH AND EAST OF THE
AREA...AND A COASTAL TROUGH WILL MEANDER OVER OR CLOSE TO THE
WATERS. THIS PATTERN SHOULD SUPPORT A PROLONGED PERIOD OF ELEVATED
NORTHEAST WINDS AND ASSOCIATED ELEVATED SEAS. HOWEVER...23/12Z
GUIDANCE HAS REDUCED WINDS/SEAS DURING THE WEDNESDAY-FRIDAY TIME
FRAME...AND THIS INTRODUCES FORECAST UNCERTAINTY. PERHAPS HIGHEST
WINDS/SEAS WILL PERIODICALLY SURGE INTO THE REGION...AS OPPOSED TO
THE RELATIVELY STEADY STATE CONDITIONS DEPICTED BY THE ONGOING
FORECAST. FOR NOW...SIGNIFICANT CHANGES ARE NOT JUSTIFIED...AND
SMALL CRAFT ADVISORIES WILL CONTINUE INTO WEDNESDAY NIGHT FOR ALL
MARINE ZONES OUTSIDE CHARLESTON HARBOR.

NEXT WEEKEND...HIGH PRESSURE WILL REMAIN TO THE NORTH AND THE
STATIONARY FRONT WILL REMAIN SOUTH/EAST OF THE WATERS. HOWEVER...THE
HIGH PRESSURE COULD EXPAND ACROSS THE REGION...PERHAPS SUPPORTING A
SUBTLE RELAXATION OF THE SURFACE PRESSURE GRADIENT AND ASSOCIATED
WIND/SEAS.

RIP CURRENTS...LOCAL GUIDANCE YIELDED A BORDERLINE LOW/MODERATE RISK
FOR RIP CURRENTS ON AREA BEACHES WEDNESDAY. GIVEN SOME UNCERTAINTY
REGARDING WIND DIRECTION/SPEED...WITHOUT A SIGNIFICANT CHANGE IN THE
ONGOING PATTERN...OPTED FOR A PERSISTENCE FORECAST OF MODERATE
RISK FOR WEDNESDAY. AN ELEVATED RISK FOR RIP CURRENTS WILL LIKELY
CONTINUE THROUGH AT LEAST LATE THIS WEEK...AND PERHAPS EVEN INTO
THE WEEKEND.

&&

.TIDES/COASTAL FLOODING...
A PROLONGED NORTHEAST FLOW WITH MODERATE WIND SPEEDS WILL RESULT IN
ELEVATED TIDE LEVELS THROUGH THE UPCOMING WEEKEND. ALTHOUGH THE
POSITIVE ANOMALY WOULD NEED TO BE A LITTLE MORE THAN 1.0
FEET...THERE IS A MODERATE CHANCE OF THE TIDE REACHING 7 FT MLLW
ALONG THE SOUTH CAROLINA COAST THAT WOULD NECESSITATE COASTAL FLOOD
ADVISORIES AROUND THE TIMES OF HIGH TIDE.

&&

.EQUIPMENT...
THE DOWNTOWN CHARLESTON WEATHER SENSOR AT WATERFRONT PARK /KCXM/
REMAINS OUT OF SERVICE...AND HOURLY OBSERVATIONS AND DAILY CLIMATE
INFORMATION WILL NOT BE AVAILABLE UNTIL FURTHER NOTICE. IT IS
UNKNOWN AT THIS TIME WHEN THE SENSOR WILL BE RETURNED TO SERVICE.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 5 AM EDT WEDNESDAY FOR AMZ330.
     SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT WEDNESDAY NIGHT FOR
     AMZ350-352-354-374.

&&

$$

NEAR TERM...WMS
SHORT TERM...SPR
LONG TERM...JRL
AVIATION...WMS/SPR
MARINE...WMS/SPR/JRL
TIDES/COASTAL FLOODING...
EQUIPMENT...





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