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000
FXUS62 KCHS 190814
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
414 AM EDT SUN MAY 19 2013

.SYNOPSIS...
AN UPPER LEVEL DISTURBANCE WILL DISSIPATE OVER THE AREA THROUGH TUESDAY.
OTHERWISE ATLANTIC HIGH PRESSURE WILL BE THE DOMINANT WEATHER FEATURE
THROUGH FRIDAY WHEN A COLD FRONT DROPS INTO THE AREA.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
PRE-DAWN...AN 850 MB THERMAL RIDGE EXTENDED N THROUGH THE FORECAST
AREA OVERNIGHT AND CONVECTION WAS STARTING TO REDEVELOP AT IT/S NOSE
ALONG COASTAL CHARLESTON COUNTY AT 4 AM. CLOUDS HAVE BEEN PREVALENT
MANY AREAS ALTHOUGH SOME CLEARING WAS NOTED TO THE S OF I-16 IN
GEORGIA. WE ADDED SOME PATCHY FOG TO THE FORECAST IN SOME OF
GEORGIA ZONES WHERE THE CLOUDS SCATTERED OUT OVERNIGHT. TEMPS
INLAND 65-69 DEGREES...BUT STILL VERY MILD ALONG COASTAL SOUTH
CAROLINA WITH READINGS IN THE LOWER 70S.

TODAY...THE MAIN MID LEVEL DISTURBANCE IS FORECAST TO SAG ESE
INTO THE MOUNTAINS OF NORTH CAROLINA WHILE A BAGGY UPPER TROUGH
TAKES SHAPE OVER OUR FORECAST REGION. UNSETTLED WEATHER CONDITIONS
ARE EXPECTED TO EXPAND IN COVERAGE BY THIS AFTERNOON...ESPECIALLY
ALONG AND W OF INTERSTATE 95. DIURNAL CONVECTION WILL DEVELOP IN A
REGIME MARKED BY DEEP MOISTURE AND LOW LEVEL CONVERGENCE ENHANCED
BY THE LATE SEA BREEZE OSCILLATION. MODELS HAVE COME AROUND TO
INDICATE THE BETTER INSTABILITY WILL DEVELOP ACROSS OUR INLAND
AREAS AND OUR POP SCHEME TRENDED TOWARD LIKELY POPS ALONG AND W OF
I-95 THIS AFTERNOON WITH CHANCE POPS TOWARD THE IMMEDIATE COAST.

SKY COVER IS TRICKY TODAY BUT TRENDS FROM OVERNIGHT SUGGEST THE
BETTER CHANCES FOR ANY SUBSTANTIAL INSOLATION WOULD BE ALONG AND
S OF I-16 IN GEORGIA. MOSTLY CLOUDY CONDITIONS SHOULD BE THE
STORY FOR MOST AREAS. WITH VARIOUS MODELS INDICATING 2500 J/KG OF
SB CAPE OVER CENTRAL/WESTERN AREAS...THERE BE COULD BE ISOLATED
STRONG TO SEVERE TSTMS MAINLY ALONG/W OF I-95 WHERE BOUNDARIES
INTERACT. MID LEVEL INSTABILITY IS MARGINAL WITH WEAK LAPSE RATES
BUT CANNOT RULE OUT SOME POTENTIAL FOR WET MICROBURSTS AND MOSTLY
SMALL HAIL. LOCALLY HEAVY RAINFALL IS ALSO POSSIBLE GIVEN PWATS
BETWEEN 1.5 AND 1.8 INCHES WITHIN A RELATIVELY WEAK STEERING FLOW
REGIME.

WE MADE VERY FEW CHANGES TO MAX TEMPS AND SURFACE WINDS
TODAY...CLOUDS EXPECTED TO KEEP MOST AREAS IN THE MID 80S OR LESS.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY/...
THE MID LEVEL DISTURBANCE TO THE N WILL DRIFT TOWARD THE FOOTHILLS
OF VIRGINIA/NORTH CAROLINA BY LATE TONIGHT. CONVECTIVE RAINS WILL
LINGER THROUGH THE EVENING OVER INLAND AREAS WITH A GRADUAL TREND
TOWARD DECREASING COVERAGE/INTENSITY OF CONVECTION AFTER SUNSET...
ESPECIALLY OVER INLAND SE GEORGIA. IN SOUTH CAROLINA ADJACENT TO THE
MIDLANDS AND PEE DEE REGIONS...WE MAY SEE CONVECTIVE RAINS HANG
ON INTO THE NIGHT. LATE NIGHT SHOWERS/ISOLATED TSTMS ALSO POSSIBLE
ALONG COASTAL SOUTH CAROLINA WHERE SPEED/MOISTURE CONVERGENCE
INCREASE AFTER MIDNIGHT.

A JUICY AIRMASS WILL RESIDE ACROSS THE FORECAST AREA MONDAY INTO
TUESDAY WITH PW VALUES HOVERING AROUND 1.8 INCHES. UPPER SHORTWAVE
ENERGY WILL BE OVER THE AREA ON MONDAY BEFORE DISSIPATING MONDAY
NIGHT AND TUESDAY AS WEAK UPPER RIDGING OCCURS. THE BEST COVERAGE OF
SHOWERS AND TSTMS IS EXPECTED MONDAY WITH DIMINISHING COVERAGE EACH
DAY THEREAFTER. THE INCREASING UPPER HEIGHTS WILL ALSO RESULT IN A
GRADUAL WARMING TREND WITH INLAND HIGHS CLIMBING BACK TO NEAR 90 BY
WEDNESDAY. SOME LOCALLY HEAVY RAINFALL WILL BE POSSIBLE ON MONDAY
GIVEN DECENT INSTABILITY COMBINED WITH THE UPPER FORCING...
UNSEASONABLY HIGH PRECIPITABLE WATER VALUES AND STEERING FLOW LESS
THAN 10 KT.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
SIGNIFICANT MODEL DIFFERENCES APPEAR IN THE LONG TERM...MAINLY
REGARDING THE NEXT UPPER TROUGH THAT SHIFTS INTO THE EASTERN UNITED
STATES LATE IN THE WEEK. WE ARE TRENDING TOWARD THE ECMWF WHICH
MOVES THE UPPER TROUGH AND A COLD FRONT THROUGH THE AREA ON SATURDAY
WITH A DRY AND COOLER CANADIAN HIGH PRESSURE SYSTEM BUILDING IN
THEREAFTER. THUS WE ARE SHOWING DIURNAL...MAINLY SEABREEZE-DRIVEN
POPS THURSDAY AND FRIDAY...THEN DRY OVER THE WEEKEND.

&&

.AVIATION /08Z SUNDAY THROUGH THURSDAY/...
AT KSAV...VFR CONDITIONS OVERNIGHT BUT THERE ARE CHANCES THAT SOME
CLEARING MAY LEAD TO AREAS OF FOG TOWARD DAYBREAK. WE MAINTAINED
A TEMPO FOR MVFR VSBYS IN THE 06Z TAF. WE ALSO INTRODUCED PROBABILITIES
FOR TSTMS 17Z-21Z AS THE SEA BREEZE INTERACTS WITH DEEP MOISTURE
AND MODERATE INSTABILITY.

AT KCHS...WE HAVE INTRODUCED VCSH FOR THE MORNING HOURS NEARING DAYBREAK
UNTIL MIDDAY THEN INTRODUCED PROBABILITIES OF SHOWERS 16Z-20Z AS THE
SEA BREEZE INTERACTS WITH DEEP MOISTURE. INSTABILITY APPEARS WEAKER
THAN AREAS TO THE SW AND S OF THE TERMINAL AND WE HAVE OPTED TO
LEAVE THUNDER OUT EVEN THOUGH TSTMS ARE CERTAINLY POSSIBLE.

EXTENDED AVIATION...THE MAIN CONCERN WILL BE SPORADIC REDUCTIONS IN
CEILINGS AND VISIBILITIES ASSOCIATED WITH SCATTERED SHOWERS AND
THUNDERSTORMS THROUGH THE PERIOD. THE GREATEST CHANCES WILL BE IN
THE AFTERNOON HOURS SUNDAY THROUGH TUESDAY.

&&

.MARINE...
PERSISTENT ATLANTIC HIGH PRESSURE WILL PRODUCE SOUTH TO SOUTHEAST
WINDS AVERAGING LESS THAN 15 KNOTS THROUGH TONIGHT. SEAS THIS MORNING
MAINLY IN THE 2 FT RANGE BUT GRADUALLY EDGING INTO THE 2 TO 4 FEET
RANGE THROUGH TONIGHT. THE 4 FT SEAS SHOULD BE RELEGATED TO OUTER
GEORGIA WATERS SEAWARD FROM GRAYS REEF.

OFFSHORE HIGH PRESSURE WILL PERSIST THROUGH NEXT WEEK...WITH
LOCALLY/BRIEFLY STRONGER ONSHORE WINDS AS HIGH AS 20 KT DUE TO THE
DIURNAL SEA BREEZE CIRCULATION EACH DAY NEXT WEEK. SEAS WILL
AVERAGE 2 TO 4 FEET MUCH OF THE TIME...ALTHOUGH SEAS AS HIGH AS
5-6 FT COULD BEGIN TO IMPINGE UPON WATERS BEYOND 20 NM BY MID TO
LATE WEEK.

&&

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

&&

$$

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