Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 211810
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
110 PM EST FRI NOV 21 2014

.SYNOPSIS...
HIGH PRESSURE WILL PREVAIL INTO THE UPCOMING WEEKEND BEFORE A
WARM FRONT MOVES NORTH THROUGH THE AREA SUNDAY. A COLD FRONT WILL
MOVE THROUGH THE AREA MONDAY NIGHT...FOLLOWED BY HIGH PRESSURE
INTO THE MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
TEMPS WARMING UP MORE THAN EXPECTED...LIKELY DUE TO THE VERY DRY
ATMOSPHERE...FRONTAL COMPRESSION AND DOWNSLOPE WARMING. WE INCREASED
HIGHS A BIT MORE INTO THE MID 60S NORTH/NEAR 70 SOUTH.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH MONDAY/...
TONIGHT...HIGH PRESSURE WILL SINK INTO THE VIRGINIA TIDEWATER AND
NORTH CAROLINA PIEDMONT TONIGHT...WEDGING SOUTH INTO SOUTH
CAROLINA AND GEORGIA AS UPPER RIDGING STRENGTHENS ALOFT. MODELS
SHOW A SUBTLE COASTAL TROUGH DEVELOPING LATE TONIGHT...WHICH
COULD PRODUCE A FEW LIGHT SPRINKLES OVER PORTIONS OF THE COASTAL
WATERS...BUT NOTHING SIGNIFICANT. ISENTROPIC 4-PANELS SUGGEST THE
STRONGEST ISENTROPIC ASSENT WILL LIKELY REMAIN DISPLACED WELL TO
THE SOUTH AND OFFSHORE ALONG THE WESTERN WALL OF THE GULF STREAM
THROUGH MUCH OF THE NIGHT AS 925-850 HPA WINDS WILL NOT VEER AHEAD
OF THE NEXT STORM SYSTEM UNTIL WELL AFTER MIDNIGHT. CLEAR TO
MOSTLY CLEAR CONDITIONS WILL THEREFORE DOMINATE FOR MUCH OF THE
NIGHT WITH SOME CLOUDS FORECAST TO CREEP IN FROM THE SOUTH AND
OFFSHORE CLOSER TO SUNRISE AS THE NOSE OF THE STRONGEST ISENTROPIC
ASSENT DRAWS CLOSER TO THE GEORGIA COAST. THERE WILL BE QUITE A
GRADIENT IN TEMPERATURES WITH LOWS RANGING FROM THE LOWER 30S
ACROSS FAR INTERIOR AREAS TO THE LOWER 50S ALONG THE GEORGIA
COAST. BREEZY CONDITIONS WILL ALSO MATERIALIZE ALONG THE BEACHES...
MAINLY FROM HILTON HEAD SOUTH TO TYBEE AND SAPELO ISLANDS...AS THE
SURFACE PRESSURE GRADIENT BEGINS TO PINCH BETWEEN IN THE INLAND
WEDGE AND THE WEAK COASTAL TROUGH OFFSHORE.

SATURDAY AND SATURDAY NIGHT...STRONG HIGH PRESSURE CENTERED TO
THE NORTH OF THE AREA WILL TRACK OFF THE COAST AND INTO THE
ATLANTIC WATERS. LOW LEVEL FLOW WILL VEER MORE ONSHORE...KEEPING
HIGH TEMPERATURES SEVERAL DEGREES BELOW NORMAL IN THE LOW TO MID
60S...WHILE ALLOWING DEWPOINTS TO STEADILY INCREASE. FORECAST
MODEL SOUNDINGS STILL SHOW SIGNIFICANT MID LEVEL DRY AIR LINGERING
FOR MUCH OF THE DAYTIME HOURS...AND HAVE THUS REMAINED RATHER
CONSERVATIVE REGARDING ANY RAIN CHANCES UNTIL THE LATE NIGHT TIME
FRAME. EXPECT PRECIPITATION COVERAGE TO THEN INCREASE RAPIDLY FROM
SOUTHWEST TO NORTHEAST SATURDAY NIGHT...AS SHORTWAVE ENERGY IN THE
EASTERN GULF OF MEXICO ASSISTS IN THE NORTHWARD PROGRESSION OF A
WARM FRONT INTO THE FORECAST AREA BY DAYBREAK SUNDAY. INCREASING
CLOUD COVER AND LOW LEVEL MOISTURE WILL MITIGATE NIGHTTIME
COOLING...KEEPING LOW TEMPERATURES IN THE UPPER 40S FAR NORTHWEST
ZONES TO THE MID 50S SOUTHEAST.

SUNDAY...A ROBUST SOUTHERN STREAM SHORTWAVE WILL BECOME NEGATIVELY
TILTED AS IT LIFTS FROM THE GULF COAST STATES INTO THE EASTERN
TENNESSEE VALLEY. THE WARM FRONT ON THE PERIPHERY OF RETREATING
ATLANTIC HIGH PRESSURE WILL CONTINUE TO MOVE NORTHWARD THROUGH THE
CAROLINAS...PLACING THE FORECAST AREA SOLIDLY WITHIN THE WARM
SECTOR OF A LOW PRESSURE SYSTEM FAR TO THE WEST/NORTHWEST. WILL
ADVERTISE WIDESPREAD SHOWERS WITH POTENTIALLY HEAVY RAINFALL
THROUGHOUT THE DAY...AS PRECIPITABLE WATER VALUES INCREASE TO AN
UNSEASONABLY HIGH 2 INCHES. DESPITE THICK CLOUD COVER AND NOTABLE
RAIN COVERAGE...TEMPERATURES WILL BE ABLE TO RISE INTO THE UPPER
60S TO LOWER 70S WITHIN STRONG SOUTHERLY FLOW...WHILE DEWPOINTS
REACH THE LOW 60S INLAND TO THE UPPER 60S SOUTHEAST COAST. STRONG
WIND FIELDS EVIDENT IN A 40 KT LOW LEVEL JET...AND SUBSEQUENTLY
IMPRESSIVE 0-6 KM BULK SHEAR VALUES FROM 40 TO 50 KT...SUGGEST
THAT SOME CONVECTIVE ORGANIZATION IS POSSIBLE. STORM PREDICTION
CENTER HAS PLACED THE FORECAST AREA WITHIN A SLIGHT RISK ZONE FOR
SUNDAY CONSIDERING THE IMPRESSIVE SYNOPTIC SCALE FORCING
AVAILABLE. MARGINAL INSTABILITY WILL STILL ADD SOME UNCERTAINTY TO
THE SEVERE POTENTIAL...HOWEVER WILL INDICATE A CHANCE FOR THUNDER
GIVEN THE WARMER TEMPERATURES AND RISING DEWPOINT VALUES. LOCALLY
HEAVY RAIN WILL BE POSSIBLE WITH STORM TOTAL RAINFALL AMOUNTS OF
1-3 INCHES--LOCALLY HIGHER.

SUNDAY NIGHT INTO MONDAY...AS THE SHORTWAVE ENERGY RAPIDLY PULLS
TO THE NORTH...SHOWERS AND ISOLATED THUNDERSTORMS WILL DIMINISH IN
COVERAGE FROM SOUTH TO NORTH. LOW TEMPERATURES SUNDAY NIGHT WILL
BE QUITE MILD IN THE UPPER 50S TO LOWER 60S UNDER THICK INSULATING
CLOUD COVER. UNSEASONABLY WARM TEMPERATURES WILL CONTINUE THROUGH
MONDAY AFTERNOON...AS DAYTIME HIGHS REACH THE UPPER 70S AWAY FROM THE
COAST WITHIN BREEZY AND WARM SOUTH/SOUTHWEST FLOW. A COLD FRONT
WILL BE GRADUALLY MOVING TOWARD THE EAST COAST...DOWNSTREAM OF A
LONG WAVE UPPER TROUGH EXTENDING FROM SOUTHERN CANADA INTO THE
SOUTHERN PLAINS STATES. NUMERICAL MODEL SOLUTIONS SUGGEST SOME
DEGREE OF PRE-FRONTAL PRECIPITATION DEVELOPING ACROSS THE MID
ATLANTIC AND SOUTHEAST STATES MONDAY AFTERNOON...AND WILL MAINTAIN
A SOLID CHANCE FOR SHOWERS ACCORDINGLY. CONSIDERING ANOTHER WARM
DAY...WILL ALSO INCLUDE MENTION OF A SLIGHT CHANCE FOR THUNDER.
SEVERE POTENTIAL LOOKS LOWER ON MONDAY DUE TO LESS IMPRESSIVE WIND
FIELDS.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
THE COLD FRONT IS EXPECTED TO MOVE THROUGH THE REGION MONDAY
NIGHT...THEN LINGER JUST OFF THE COAST INTO THE MIDDLE OF NEXT
WEEK WHILE THE AXIS OF THE UPPER TROUGH REMAINS JUST TO THE WEST.
SCATTERED SHOWERS COULD CONTINUE TO AFFECT PORTIONS OF THE
FORECAST AREA AS A RESULT...AND WILL THUS MAINTAIN A CHANCE OF
RAIN THROUGH TUESDAY AFTERNOON. THE AXIS OF THE UPPER TROUGH WILL
FINALLY SWEEP TOWARD THE COAST WEDNESDAY...PUSHING THE OFFSHORE
SYSTEM FARTHER AWAY AND ALLOWING DRIER HIGH PRESSURE TO BUILD IN
FROM THE WEST. A COOLING TREND IS EXPECTED THROUGH THE
WEEK...INITIALLY DRIVEN BY PASSAGE OF THE COLD FRONT...THEN
REINFORCED BY THE PROGRESSION OF THE TROUGH AXIS MID WEEK. HIGH
TEMPERATURES WILL REACH THE LOW TO MID 60S TUESDAY
AFTERNOON...BEFORE BECOMING SUPPRESSED IN THE UPPER 50S TO LOWER
60S FOR THE REMAINDER OF THE WEEK. LOW TEMPERATURES WILL FALL INTO
THE MID TO UPPER 30S FOR WEDNESDAY AND THURSDAY NIGHTS.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
VFR MOST...IF NOT ALL...OF THE PERIOD. THE RISK FOR STRATUS WILL
INCREASE AFTER 10Z AS ISENTROPIC ASCENT INCREASES OVER THE
AREA...ESPECIALLY AT KSAV. HOWEVER...CHANCES REMAIN TOO LOW TO
MENTION AT THIS TIME.

EXTENDED AVIATION OUTLOOK...MVFR CEILINGS POSSIBLE BEGINNING LATE
SATURDAY AT KSAV...BUT MORE LIKELY SATURDAY NIGHT INTO SUNDAY
NIGHT AT KSAV/KCHS...AS A WARM FRONT AND DEEP MOISTURE LIFT NORTH
THROUGH THE AREA. VISIBILITY WILL ALSO BE RESTRICTED AT TIMES
WITHIN MODERATE TO HEAVY RAINFALL. BREEZY CONDITIONS POSSIBLE SUNDAY
AND MONDAY.

&&

.MARINE...
TODAY...OFFSHORE WINDS WILL GRADUALLY COME AROUND TO THE NORTH AND
NORTHEAST AS HIGH PRESSURE BEGINS TO WEDGE SOUTH ACROSS THE
SOUTHEAST STATES. WINDS WILL REMAIN RATHER GUSTY OVER THE COASTAL
WATERS WITH WINDS 15-20 KT...EXCEPT 15 KT OVER THE GEORGIA
NEARSHORE WATERS. SEAS WILL BUILD THROUGH THE DAY AS THE FLOW
TURNS FROM OFFSHORE TO THE NORTHEAST...RANGING FROM 2-4 FT
NEARSHORE WATERS AND 4-5 FT OFFSHORE WATERS THIS AFTERNOON.

TONIGHT...WINDS AND SEAS WILL CONTINUE TO BUILD TONIGHT AS THE
PRESSURE GRADIENT BETWEEN INLAND HIGH PRESSURE AND A WEAK COASTAL
TIGHTENS. THE WORST CONDITIONS LOOK TO BE CONFINED TO THE CENTRAL
AND SOUTHERN WATERS TONIGHT MODEL PROGS SHOW THE TIGHTEST GRADIENT
SETTING UP WITH WINDS INCREASING TO 20-25 KT. THE CHARLESTON
COUNTY WATERS LOOK TO REMAIN IN THE 15-20 KT RANGE...ALTHOUGH IT
WILL REMAIN QUITE GUSTY. SEAS WILL BUILD IN THE FAVORABLE
NORTHEAST FETCH...REACHING 4-5 FT CHARLESTON COUNTY WATERS...4-6
FT OVER THE NEARSHORE WATERS FROM EDISTO BEACH TO THE ALTAMAHA
SOUND WITH 5-7 FT OVER THE GEORGIA OFFSHORE WATERS PER OUTPUT FROM
THE LATEST SWAN. BASED ON THIS...SMALL CRAFT ADVISORIES WILL BE
ISSUED FOR ALL WATERS WITH THE EXCEPTION OF THE CHARLESTON HARBOR
AND THE CHARLESTON COUNTY WATERS FOR TONIGHT.

SATURDAY THROUGH TUESDAY...HIGH PRESSURE TO THE NORTH WILL MOVE
OFFSHORE SATURDAY. A WARM FRONT WILL THEN LIFT NORTH THROUGH THE
AREA SUNDAY...BEFORE A COLD FRONT PUSHES TOWARD THE COAST MONDAY
NIGHT INTO TUESDAY. MARINE CONDITIONS WILL DETERIORATE SATURDAY
THROUGH MONDAY...AS THE PRESSURE GRADIENT TIGHTENS AND SOUTHERLY
FLOW STRENGTHENS. SMALL CRAFT ADVISORIES WILL BE ONGOING FOR THE
WATERS SOUTH OF EDISTO ON SATURDAY...WITH POSSIBLE EXPANSIONS AND
EXTENSIONS POSSIBLE INTO SUNDAY AND MONDAY. CONDITIONS SHOULD DROP
BELOW ADVISORY LEVELS FOR ALL WATERS TUESDAY AS THE PRESSURE
GRADIENT WEAKENS.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 11 AM EST
     SATURDAY FOR AMZ352-354.
     SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 5 AM EST
     TUESDAY FOR AMZ374.

&&

$$

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






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