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000
FXUS62 KCHS 211752
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
152 PM EDT TUE MAY 21 2013

.SYNOPSIS...
ATLANTIC HIGH PRESSURE WILL PREVAIL THROUGH THURSDAY. A COLD FRONT
WILL DROP THROUGH THE AREA ON FRIDAY WITH DRY HIGH PRESSURE BUILDING
IN NEXT WEEKEND INTO EARLY NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
SCATTERED SHOWERS AND THUNDERSTORMS CONTINUE TO IMPACT THE
CHARLESTON TRI COUNTY REGION BY EARLY AFTERNOON...WHILE ISOLATED
TO SCATTERED CONVECTION HAS ALSO INITIATED ALONG AND INLAND OF THE
SEABREEZE FARTHER SOUTH. HAVE UPDATED FORECAST TO INCLUDE LATEST
RADAR TRENDS...INDICATING HIGHEST COVERAGE OF THUNDERSTORMS ACROSS
MUCH OF THE SOUTH CAROLINA ZONES AND GENERALLY WEST OF INTERSTATE
95 IN SOUTHEAST GEORGIA.

LATEST STORM PREDICTION CENTER MESOANALYSIS SHOWS INSTABILITY
MAXIMIZED TO THE WEST...WEAKENING CLOSER TO THE COASTLINE. AS A
RESULT...THE MAIN HAZARD ASSOCIATED WITH AFTERNOON CONVECTION HAS
BEEN HEAVY AND PERSISTENT DOWNPOURS. UPPER AIR SOUNDINGS INDICATE
LITTLE WIND IN THE LOW TO MID LEVELS...ALLOWING STORM MOTIONS TO
BE QUITE SLOW WITHIN A HIGH PRECIPITABLE WATER ENVIRONMENT. THE
POTENTIAL FOR LOCALIZED FLOODING WITHIN SLOW MOVING THUNDERSTORMS
WILL LINGER THROUGH THE AFTERNOON INTO THE EARLY EVENING...WHEN
THE MAJORITY OF THE CONVECTION WILL PUSH INLAND WITH THE SEABREEZE
AND DISSIPATE WITH WANING HEATING/INSTABILITY. ALTHOUGH THE SEVERE
THREAT LOOKS MARGINAL OVERALL DUE TO RATHER WEAK WIND FIELDS AND
BEST LAPSE RATES CONFINED WEST OF THE AREA...WILL CONTINUE TO
MONITOR THE SOUTHWEST ZONES...WHERE MORNING INSOLATION ALLOWED
FOR IMPROVED INSTABILITY. HOWEVER...IT WILL LIKELY TAKE BOUNDARY
INTERACTIONS TO SUPPORT ANY ISOLATED SEVERE STORM DEVELOPMENT.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY/...
INLAND CONVECTIVE RAIN WILL BE ENDING EARLY IN THE EVENING...AS
THE SEA BREEZE PUSHES WELL INLAND AND CONVERGENCE DIMINISHES. NO
CHANGES TO THE FORECAST TONIGHT...WITH CLOUDS GRADUALLY THINNING
AND LOW TEMPERATURES RANGING FROM 65 TO 70 DEGREES. MAY NEED TO
EVENTUALLY ADD SOME PATCHY FOG TO THE FORECAST AGAIN
TONIGHT...DEPENDENT ON TRENDS WITH CLOUD DISSIPATION.

A FAIRLY SIMILAR PATTERN WILL PERSIST WEDNESDAY INTO THURSDAY WITH
BROAD UPPER TROUGHING AND ATLANTIC HIGH PRESSURE. SOUTHERLY
LOW-LEVEL FLOW WILL MAINTAIN A FAIRLY MOIST ATMOSPHERE AND HELP PUSH
A SEABREEZE INLAND EACH DAY. THE UPPER TROUGHING WILL CREATE A
SOMEWHAT MORE FAVORABLE ENVIRONMENT FOR CONVECTION TO DEVELOP...
PRIMARILY DRIVEN BY THE SEABREEZE AND BOUNDARY INTERACTIONS. WE KEPT
POPS IN THE 20-30 PERCENT RANGE BOTH DAYS.

THE MODELS ARE NOW QUITE A BIT FASTER AND IN BETTER AGREEMENT
REGARDING A COLD FRONT PUSHING THROUGH FRIDAY MORNING. WE REMOVED
POPS ON FRIDAY AND SHOW DEWPOINTS DROPPING INTO THE UPPER 50S TO
AROUND 60 DURING THE AFTERNOON.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
THERE IS GOOD MODEL AGREEMENT THAT DRY CANADIAN HIGH PRESSURE WILL
EXPAND SOUTHEAST INTO THE FORECAST AREA OVER THE WEEKEND THEN SHIFT
OFFSHORE. DEWPOINTS LOOK TO DROP INTO THE LOWER 50S SATURDAY AND
SUNDAY...WHICH COMBINED WITH HIGHS IN THE LOWER 80S WILL RESULT IN
PLEASANT SPRING WEATHER. OVERNIGHT LOWS WILL PROBABLY DROP INTO THE
UPPER 50S IN SPOTS. LOW-LEVEL MOISTURE INCREASES EARLY NEXT WEEK AS
THE SURFACE HIGH SHIFTS OFFSHORE...BUT WE DID NOT SEE ANY STRONG
SYNOPTIC SCALE FEATURES TO WARRANT ADDING PRECIP.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
SHOWERS AND THUNDERSTORMS WILL CONTINUE TO DEVELOP NEAR THE
TERMINALS THROUGH THE AFTERNOON...WITH REDUCED VSBYS AND CIGS
LIKELY WITHIN HEAVIER RAINFALL. AMENDMENTS WILL LIKELY BE NEEDED
TO ACCOUNT FOR RADAR TRENDS DURING THE NEXT SEVERAL HOURS...WITH
MOST THUNDERSTORM ACTIVITY DIMINISHING AFTER SUNSET. GIVEN PRIOR
RAINFALL AND LIGHT WINDS...MVFR OR LOWER CIGS/VSBYS WILL BE
POSSIBLE OVERNIGHT. HOWEVER...DUE TO LOW CONFIDENCE IN TIMING AND
DURATION...HAVE OPTED TO NOT INCLUDE MENTION IN THE TAFS AT THIS
TIME AND ALLOW SUBSEQUENT ISSUANCES TO ADDRESS THIS POTENTIAL.

EXTENDED AVIATION...SPORADIC REDUCTIONS IN CEILINGS/VSBYS MAINLY IN
AFTERNOON/EVENING SHOWERS OR STORMS THROUGH THURSDAY.

&&

.MARINE...
THROUGH TONIGHT...THE STEADY STATE SYNOPTIC PATTERN CONTINUES UNABATED.
THE OFFSHORE RIDGE OF HIGH PRESSURE EXTENDS WEST ACROSS THE
COASTAL WATERS...GENERATING SOUTHEAST AND SOUTH WINDS LESS THAN 15
KT AND SEAS IN THE 2-4 FT RANGE...HIGHEST OVER OUTER GEORGIA
WATERS BEYOND 20 NM.

HIGH PRESSURE WILL SIT OVER THE WESTERN ATLANTIC UNTIL FRIDAY WHEN A
CANADIAN HIGH DROPS SOUTHEAST. WE MAY SEE A BRIEF PERIOD OF SMALL
CRAFT ADVISORY CONDITIONS FRIDAY NIGHT INTO SATURDAY AS THE GRADIENT
TIGHTENS AND COLD ADVECTION MIXES SOME DECENT WINDS TO THE SURFACE.

&&

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

&&

$$

NEAR TERM...WMS
SHORT TERM...JRL
LONG TERM...JRL
AVIATION...ECT
MARINE...WMS/JRL