Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 041501
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1101 AM EDT FRI SEP 4 2015

.SYNOPSIS...
A WEAK PRESSURE PATTERN WILL PERSIST ACROSS THE REGION THROUGH
TONIGHT. A WEAK COLD FRONT WILL DROP INTO THE AREA SATURDAY AND
STALL THROUGH TUESDAY BEFORE DISSIPATING. ATLANTIC HIGH PRESSURE
WILL REBUILD FOR THE MIDDLE AND LATTER PART OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
LATE THIS MORNING...CLEAR SKIES PREVAIL WITH A VERY WEAK PRESSURE
PATTERN IN PLACE. ALOFT...THE PATTERN IS A BIT COMPLEX WITH A WEST
TO EAST ORIENTED TROUGH AXIS ACROSS THE FORECAST AREA EXTENDING
OUT OVER THE ATLANTIC. THIS VERY WEAKLY FORCED ENVIRONMENT WILL
REMAIN THROUGH THE EVENING AND DIURNAL CONVECTION CHANCES WILL BE
DRIVEN BY THE SEA BREEZE AND DIFFERENTIAL HEATING BOUNDARIES ALONG
SOME CLOUDS ACROSS SOUTHEAST GEORGIA. THE MODELS...ESPECIALLY THE
HI-RES MODELS SEEM TO BE FAVORING SOUTHEAST GEORGIA WHERE THOSE
HEATING BOUNDARIES WILL RESIDE. THERE IS A BIT OF SUBSIDENCE NOTED
IN SOUNDINGS...AND THAT WILL KEEP INITIATION FROM STARTING UNTIL
CLOSER TO THE MID AFTERNOON. POPS HAVE BEEN ADJUSTED TO LIMIT THE
CHANCE POPS TO SOUTHEAST GEORGIA WITH SLIGHT CHANCES ELSEWHERE.
THE SEVERE THREAT IS LOW...THOUGH A COUPLE OF STRONG STORMS CAN/T
BE RULED OUT FOR SOUTHEAST GEORGIA WHERE BETTER INSTABILITY AND
LAPSE RATES WILL BE. IT WILL BE A WARM AFTERNOON WITH MANY
LOCATIONS ALREADY REACHING THE UPPER 80S. FORECAST HIGHS ARE IN
THE LOW TO MID 90S...WHICH WOULD BE ABOUT 6-8 DEGREES ABOVE
NORMAL.

TONIGHT...HIGH PRES BUILDING INTO THE MID ATLC REGION FROM THE NE
WILL EDGE A BACKDOOR FRONT CLOSER OVERNIGHT. MODEL SOUNDINGS
INDICATE SOME RESIDUAL ELEVATED INSTABILITY BUT BY THE TIME A WEAK
MID LEVEL SHORT WAVE ARRIVES FROM THE NORTH LATE...WE THINK RAIN
CHANCES ARE FAIRLY SLIM OVERALL. AFTER 2 AM...THERE COULD BE ISOLATED
SHOWERS OR TSTMS SLIDING SOUTH FROM THE MIDLANDS OR PEE DEE OF
SOUTH CAROLINA. WE MAINTAINED SOME LOW-END POPS LATER TONIGHT.
THERE ALSO BE SOME PATCHY FOG AGAIN INLAND FROM U.S. 17 BUT NOT
ENOUGH EVIDENCE AS YET TO ADD TO THE FORECAST/GRIDDED PRODUCTS.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY/...
A POSITIVELY TILTED UPPER TROUGH ACROSS THE WESTERN ATLANTIC WILL
RETROGRADE ON SATURDAY AND EVENTUALLY CLOSE OFF OVER THE SOUTHEAST
UNITED STATES. AT THE SURFACE...BROAD HIGH PRESSURE OFF THE NEW
ENGLAND COAST WILL BUILD SOUTH BEHIND A COLD FRONT THAT PUSHES INTO
THE AREA SATURDAY. THE DEEPEST MOISTURE ON SATURDAY WILL BE ACROSS
SOUTHEAST GA WHILE SOME DRIER AIR FILTERS INTO SOUTHERN SC.
CONVERGENCE WILL BE GREATEST ALONG AND SOUTH OF THE COLD FRONT AS IT
PROGRESSES SOUTH DURING THE DAY...THOUGH AN AFTERNOON SEA BREEZE MAY
ALSO PROVIDE SOME LIFT. INSTABILITY WILL BE MARGINAL THOUGH AMPLE TO
SUPPORT THUNDERSTORMS WHEREVER CONVECTION DEVELOPS. WE SHOW THE
HIGHEST POPS ACROSS SW ZONES WITH LOWER VALUES FARTHER NORTH WHERE
MOISTURE WILL BE LOWER. HIGHS WILL RANGE FROM UPPER 80S NORTH TO
LOWER 90S SOUTH. SATURDAY NIGHT THE BEST CONVECTIVE POTENTIAL WILL
SHIFT OUT OVER THE COASTAL WATERS WITH MAINLY DRY CONDITIONS OVER
LAND.

ON SUNDAY THE MEAN TROPOSPHERIC FLOW BECOMES MORE ENE WHICH WILL
BRING INCREASING MOISTURE INTO THE AREA. BY AFTERNOON THE PWATS
RECOVER INTO THE 1.9-2.0" RANGE. UPPER HEIGHT FALLS AS THE UPPER LOW
RETROGRADES...IN CONCERT WITH INCREASING LOW-LEVEL MOISTURE AND A
STRONGER SEA BREEZE...ALL POINT TOWARD BETTER COVERAGE OF SHOWERS
AND TSTMS ESPECIALLY DURING THE AFTERNOON. DECREASING LOW-LEVEL
THICKNESSES WILL ALSO KEEP TEMPS IN THE MID TO UPPER 80S IN MOST
LOCATIONS.

A SIMILAR PATTERN CONTINUES INTO MONDAY AS THE UPPER LOW SHIFTS JUST
WEST OF THE AREA AND LOW-LEVEL FLOW IS OFF THE ATLANTIC. WITH MID-
LEVEL LAPSE RATES REMAINING CLOSE TO 6 C/KM AND AMPLE MOISTURE IN
PLACE...PRETTY GOOD COVERAGE OF SHOWERS AND TSTMS IS AGAIN EXPECTED
WITH HIGHS IN THE MID 80S.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
THE CLOSED UPPER LOW OVER THE SOUTHEAST UNITED STATES WILL GRADUALLY
WEAKEN THOUGH A BROAD UPPER TROUGH WILL LIKELY PERSIST FOR MUCH OF
THE PERIOD. BERMUDA HIGH PRESSURE WILL SETTLE IN...BRINGING A RETURN
TO SOUTHERLY FLOW OVER THE AREA AND SLIGHTLY ABOVE NORMAL
TEMPERATURES. PRECIPITATION WILL FOLLOW A TYPICAL SUMMER REGIME WITH
SCATTERED CONVECTION DURING THE DAY OVER LAND AREAS AND ISOLATED TO
SCATTERED STORMS OVER THE WATERS AT NIGHT.

&&

.AVIATION /15Z FRIDAY THROUGH TUESDAY/...
VFR CONDITIONS ARE EXPECTED AT BOTH THE KCHS AND KSAV TERMINALS
THROUGH 12Z SATURDAY. HOWEVER...THERE IS A SLIGHT CHANCE OF LATE
AFTERNOON OR EVENING SHOWERS OR TSTMS AT BOTH TERMINALS WITH THE
SEA BREEZE THE MAIN MECHANISM FOR CONVECTIVE DEVELOPMENT.
OVERNIGHT...CANNOT RULE OUT AN ISOLATED SHOWER OR TSTM...
ESPECIALLY AROUND KCHS JUST AHEAD OF A BACKDOOR COLD FRONT.

EXTENDED AVIATION OUTLOOK...LOW TO MODERATE POTENTIAL FOR PERIODIC
FLIGHT RESTRICTIONS IN MAINLY DAYTIME SHOWERS/TSTMS. POSSIBLE LOW
STRATUS AROUND DAYBREAK SUN AND MON AT KCHS.

&&

.MARINE...
THROUGH TONIGHT A LAZY PRESSURE PATTERN WILL PREVAIL...ALLOWING A
WEAK AFTERNOON SEA BREEZE TO KICK IN AS WINDS CLOCK AROUND FROM
WEST/NW IN THE MORNING TO EAST/SE IN THE AFTERNOON. SEAS 1 OR 2
FT. A WEAK COLD FRONT WILL MOVE TOWARD THE WATERS AFTER MIDNIGHT
WITH WINDS REMAINING LIGHT AND SEAS STILL IN THE 1-2 FT RANGE.
THERE COULD BE A BIT OF A WEAK NE SURGE NORTH OF THE CHARLESTON
PILOT BUOY LATE BUT WE ARE THINKING SPEEDS BELOW 15 KT TOWARD
DAYBREAK OFF THE SANTEE RIVER ENTRANCE.

HIGH PRESSURE BUILDING SOUTH BEHIND A COLD FRONT SATURDAY WILL ALLOW
NE WINDS OF 10-15 KT TO SETUP OVER THE WATERS WITH SLIGHTLY BUILDING
SEAS. THE NE FLOW CONTINUES THROUGH MONDAY WITH MAINLY DAYTIME
COASTAL ENHANCEMENTS WITH THE SEA BREEZE. NEXT TUESDAY THROUGH LATE
WEEK...AS ATLANTIC HIGH PRESSURE REBUILDS THE FLOW WILL BECOME
SOUTHERLY. THIS WILL YIELD A TYPICAL WARM SEASON PATTERN WITH
DAYTIME SEA BREEZE CIRCULATIONS AT THE COAST AND NOCTURNAL JETTING
OVER THE OFFSHORE WATERS.

WATERSPOUTS...LIGHT WIND FIELDS AND SUFFICIENT ATMOSPHERIC
CONDITIONS MAY SUPPORT A RISK FOR WATERSPOUTS THIS MORNING AND
AGAIN SATURDAY MORNING ALONG ANY CONVERGENCE LINES THAT DEVELOP.

&&

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

&&

$$

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



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