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000
FXUS62 KCHS 221927
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
327 PM EDT WED MAY 22 2013

.SYNOPSIS...
ATLANTIC HIGH PRESSURE WILL PREVAIL THROUGH THURSDAY. A COLD
FRONT WILL MOVE ACROSS THE AREA THURSDAY NIGHT...WITH HIGH
PRESSURE BUILDING OVER THE REGION THROUGH EARLY NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
ONGOING SCATTERED CONVECTION ALONG THE SEABREEZE WILL GRADUALLY
SHIFT INLAND THROUGH THE REMAINDER OF THE AFTERNOON HOURS...THEN
STEADILY DIMINISH IN COVERAGE AS THE MARGINAL INSTABILITY THIS
AFTERNOON FURTHER DECREASES WITH SUNSET. HAVE THUS INDICATED 20 TO
30 PERCENT RAIN CHANCES DECREASING FROM EAST TO WEST TOWARD THE
EVENING HOURS. LATEST MESOANALYSIS REVEALS RATHER UNIMPRESSIVE
INSTABILITY THIS AFTERNOON...AND WHEN CONSIDERING WEAK LAPSE
RATES AND VERTICAL WIND PROFILES...SEVERE THUNDERSTORM POTENTIAL
IS LOW THROUGH THIS EVENING.

THE SOUTHEAST STATES WILL BECOME LOCATED ALONG THE PERIPHERY OF A
BROAD UPPER TROUGH STRETCHING FROM THE GREAT LAKES REGION INTO THE
LOWER MISSISSIPPI VALLEY TONIGHT. SOUTH/SOUTHEAST FLOW AROUND
PERSISTENT ATLANTIC SURFACE HIGH PRESSURE WILL CONTINUE TO
SUPPORT DECENT LOW LEVEL MOISTURE OVERNIGHT. BEST INSTABILITY AND
CONVERGENCE WILL SHIFT INTO THE COASTAL WATERS AFTER
MIDNIGHT...AND NUMERICAL MODEL SOLUTIONS SUGGEST ISOLATED SHOWERS
COULD DEVELOP IN THE MARINE ZONES DURING THE EARLY MORNING HOURS.
CONSIDERING AN ONSHORE COMPONENT TO THE SURFACE FLOW...THERE
REMAINS A SLIGHT CHANCE THAT SHOWERS COULD SHIFT LOCALLY ONSHORE
MAINLY ALONG THE CHARLESTON COUNTY COASTLINE. A COLD FRONT WILL
ALSO BE APPROACHING FROM THE WEST...AND A PRE FRONTAL TROUGH
FEATURE WILL ENHANCE MOISTURE/CONVERGENCE DOWNSTREAM...PERHAPS
SUPPORTING THE INTRUSION OF SHOWERS INTO FAR INLAND ZONES JUST
BEFORE SUNRISE. HAVE THUS PINNED THE FORECAST AREA BETWEEN SLIGHT
CHANCE POPS TO THE WEST AND SLIGHT CHANCES ALONG THE NORTHERN
COAST BY DAYBREAK. OVERALL HOWEVER...THE MAJORITY OF THE AREA WILL
REMAIN DRY OVERNIGHT. TEMPERATURES WILL FALL INTO THE MID TO UPPER
60S.

ALTHOUGH PATCHY FOG DEVELOPMENT IS POSSIBLE AFTER MIDNIGHT...MODEL
GUIDANCE REMAINS RATHER CONSERVATIVE IN DEPICTING ANY REDUCED
VISIBILITIES. CONSIDERING SOME UNCERTAINTY IN THE POTENTIAL FOR
CLOUD COVER TO RETURN OVERNIGHT...AS WELL AS LESS RAIN COVERAGE
TODAY...PREFER TO KEEP FOG OUT OF THE FORECAST AT THIS TIME.
SUBSEQUENT FORECAST SHIFTS WILL BE ABLE TO REASSESS TRENDS WITH
THE EVENING UPDATE.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY/...
A SURFACE PRESSURE TROF WILL MOVE INTO THE CWA ON THURSDAY...WITH
MOIST SOUTHERLY WINDS AHEAD OF IT AND SOMEWHAT DRIER WESTERLY WINDS
BEHIND IT. THE TROF SHOULD BE ROUGHLY ALONG INTERSTATE 95 BY EARLY
AFTERNOON...AND AREAS ALONG AND EAST OF THE BOUNDARY WILL HAVE A
CHANCE OF SHOWERS AND THUNDERSTORMS AS DAYTIME HEATING CREATES SOME
SURFACE INSTABILITY AND CONVERGENCE. FURTHER WEST...ESPECIALLY OVER
OUR INTERIOR GEORGIA COUNTIES...THE ATMOSPHERE WILL BE DRIER AND
MORE STABLE...SO THERE WILL ONLY BE A SLIGHT CHANCE OF SHOWERS.
SKIES SHOULD AVERAGE OUT PARTLY CLOUDY...ALTHOUGH THERE WILL BE A
PERIOD OF MOSTLY CLOUDY SKIES TO THE EAST OF THE BOUNDARY DURING A
PORTION OF THE AFTERNOON.

THURSDAY NIGHT...THE INITIAL COOL FRONT PUSHES THROUGH THE
AREA...MOVING THE CHANCES FOR RAIN MOSTLY OFFSHORE...ALTHOUGH I
CANNOT RULE OUT A SLIGHT CHANCE OVER THE TRI COUNTY AREA AS THERE
MAY BE ENOUGH REMNANT MOISTURE WITH THE FRONT TO PROMOTE SOME
SHOWERS.

FRIDAY...THE WINDS WILL BE NORTHWEST BEHIND THE FRONT IN THE
MORNING...PROMOTING SOME DOWNSLOPE LOW LEVEL FLOW AND HEATING.
HOWEVER...DRIER AIR MOVING IN SHOULD PREVENT ANY RAIN...OR MUCH IN
THE WAY OF CLOUDS FOR THAT MATTER. A SECONDARY COLD FRONT WILL MOVE
THROUGH LATER IN THE DAY...CAUSING THE WINDS TO VEER TO NORTH AND
INCREASE AS COLD ADVECTION PICKS UP. FRIDAY NIGHT WILL BE MUCH
COOLER THAN THE PREVIOUS FEW.

SATURDAY...TEMPS WILL BEGIN WELL BELOW NORMAL AS MODIFIED AIR POURS
IN TO THE AREA...BUT THIS TIME OF YEAR THAT MEANS TEMPS MAINLY IN
THE 50S. PLENTY OF SUNSHINE WILL ALLOW AFTERNOON MAX TEMPS TO REACH
TO 80 OR ABOVE...BUT DEWPOINTS WILL DROP INTO THE 40S AWAY FROM THE
COAST.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
MEDIUM RANGE GUIDANCE IS IN GOOD OVERALL AGREEMENT THROUGH THE LONG
TERM PERIOD. THE MID AND UPPER LEVEL PATTERN WILL FEATURE A NEARLY
ZONAL FLOW OVER THE REGION LATE IN THE WEEKEND INTO EARLY NEXT
WEEK...WITH A RIDGE THEN BUILDING TOWARD THE MIDDLE OF NEXT WEEK. AT
THE SURFACE...HIGH PRESSURE WILL PASS NORTH OF THE AREA LATE IN THE
WEEKEND...THEN SETTLE OVER THE WESTERN ATLANTIC THROUGH THE MIDDLE
OF NEXT WEEK.

RAIN-FREE CONDITIONS ARE EXPECTED TO PERSIST INTO EARLY NEXT
WEEK...THEN INCREASING MOISTURE COULD ALLOW FOR SOME MAINLY DIURNAL
ISOLATED CONVECTION ALONG AND AHEAD OF THE SEA BREEZE TUESDAY AND
WEDNESDAY. TEMPERATURES WILL BE SLIGHTLY BELOW NORMAL SUNDAY...THEN
RETURN TO NEAR OR SLIGHTLY ABOVE NORMAL NEXT WEEK.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
VFR IS EXPECTED TO PREVAIL THROUGH THE AFTERNOON. SOME ISOLATED
SHOWERS COULD IMPACT MAINLY KSAV DURING THE FIRST FEW HOURS OF
THE VALID TAF PERIOD...WITH BRIEF PERIODS OF REDUCED VSBYS/CIGS
WITHIN HEAVIER RAINFALL. ACTIVITY WILL DIMINISH AFTER SUNSET. LATE
TONIGHT...RESTRICTIONS WILL BE POSSIBLE ONCE AGAIN DUE TO FOG
AND/OR STRATUS GIVEN SMALL SURFACE T/TD SPREADS...LIGHT
WINDS...AND MODEL SOUNDINGS INDICATING DECENT LOW LEVEL MOISTURE.
DUE TO LOW CONFIDENCE HAVE DECIDED TO KEEP VFR FOR NOW...BUT
SHOWED THE GENERAL DOWNWARD TREND IN THE TAF. AFTER SUNRISE...VFR
SHOULD RETURN. SHOWERS/THUNDERSTORMS WILL BE POSSIBLE IN THE
MORNING.

EXTENDED AVIATION...THERE COULD BE A BRIEF PERIOD OF MVFR/IFR IN
CONVECTION THURSDAY AFTERNOON...BUT VFR CONDITIONS ARE EXPECTED
OTHERWISE...CONTINUING INTO THE WEEKEND. THE WINDS COULD GET A BIT
GUSTY FRIDAY AFTERNOON BEHIND THE SECONDARY FRONT.

&&

.MARINE...
MARINE CONDITIONS WILL BE FAIRLY BENIGN THROUGH TONIGHT...AS THE
AREA REMAINS ON THE WESTERN PERIPHERY OF ATLANTIC HIGH PRESSURE.
EXPECT A GENERAL SOUTHERLY FLOW TO PREVAIL...WITH WIND SPEEDS
BELOW 15 KT.

THURSDAY THROUGH MONDAY...ATLANTIC HIGH PRESSURE WILL DOMINATE
WITH SOUTHERLY FLOW UNTIL A COLD FRONT PUSHES OFFSHORE EARLY
FRIDAY. A NORTHERLY SURGE IS EXPECTED TO DEVELOP IN WAKE OF THE
FRONT FRIDAY NIGHT INTO EARLY SATURDAY AND COULD RESULT IN SMALL
CRAFT ADVISORY CONDITIONS. CONDITIONS WILL THEN IMPROVE LATER IN
THE WEEKEND INTO EARLY NEXT WEEK WITH WINDS/SEAS EXPECTED TO
REMAIN BELOW SMALL CRAFT ADVISORY THRESHOLDS.

&&

.TIDES/COASTAL FLOODING...
HIGH ASTRONOMICAL TIDES AND FAVORABLE NORTH/NORTHEAST WINDS COULD
LEAD TO MINOR SALTWATER INUNDATION NEAR THE COAST DURING THE HIGH
TIDE FRIDAY AND SATURDAY EVENING. BY THE TIME OF THE HIGH TIDE
SUNDAY EVENING AND MONDAY EVENING...WINDS WILL NOT BE AS
CONDUCIVE...YET MINOR SALTWATER FLOODING WILL STILL BE POSSIBLE.

&&

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

&&

$$

NEAR TERM...WMS
SHORT TERM...FWA
LONG TERM...JAQ
AVIATION...ECT
MARINE...FWA/WMS
TIDES/COASTAL FLOODING...