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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KCHS 181123
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
723 AM EDT TUE JUN 18 2013

.SYNOPSIS...
-- Changed Discussion --
A COLD FRONT WILL APPROACH FROM THE NORTHWEST TODAY...THEN SLOWLY
PROGRESS THROUGH THE AREA WEDNESDAY AND THURSDAY. HIGH PRESSURE
WILL THEN BUILD FROM THE NORTH INTO THE WEEKEND AND SETTLE OVER
THE ATLANTIC EARLY NEXT WEEK.
-- End Changed Discussion --

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --
IT LOOKS TO BE ANOTHER ACTIVE DAY FOR SHOWERS/TSTMS. MODELS ARE
SIMILAR IN SHOWING ANOTHER POTENT SHORTWAVE TRAVERSING SOUTHEAST
SOUTH CAROLINA AND SOUTHEAST GEORGIA THIS AFTERNOON AS INSOLATION
PEAKS. SOME FILTERED SUNSHINE THIS MORNING WILL ALLOW
TEMPERATURES TO RISE QUICKLY...REACHING THE UPPER 80S TO LOWER 90S
AWAY FROM THE BEACHES BY EARLY AFTERNOON. THE RESULTANT SEA BREEZE
AS WELL AS LINGERING CONVECTIVE OUTFLOWS AND POSSIBLY SOME
DIFFERENTIAL HEATING BOUNDARIES WILL SERVE AS THE PRIMARY FOCI FOR
CONVECTIVE DEVELOPMENT. GENERALLY FOLLOWED THE 4KM WRF/S
CONVECTIVE SOLUTION TO CONSTRUCT HOURLY POPS WHICH MATCHES FAIRLY
WELL WITH THE LATEST H3R. GIVEN THAT...WILL GO WITH A 30-70 POP
REGIME TODAY...WITH THE HIGHEST GRIDDED POPS ALIGNED NORTH OF A
METTER-BEAUFORT-CHARLESTON LINE. LOCALLY HEAVY RAINFALL IS
POSSIBLE WITH PWATS 1.8 TO 2.0 INCHES AND AN ISOLATED SEVERE TSTM
OR TWO CAN NOT BE COMPLETELY RULED OUT...ESPECIALLY WHERE UPDRAFTS
ARE ENHANCED DUE TO MESOSCALE BOUNDARY INTERACTIONS.
-- End Changed Discussion --

&&

.SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY/...
TONIGHT...SHOWER/TSTM ACTIVITY WILL LINGER INTO THE NIGHT AS A
COLD FRONT MEANDERS CLOSER TO THE REGION. THE FRONT LOOKS TO
REMAIN TO THE WEST PRIOR TO SUNRISE...KEEPING THE AREA WELL WITHIN
THE WARM SECTOR. WEAK IMPULSES/VORTICITY LOBES WILL LIKELY KEEP
AT LEAST SCATTERED ACTIVITY GOING FOR MUCH OF THE NIGHT...ALTHOUGH
IDENTIFYING THE AREAS WHERE POCKETS OF CONVECTION WILL OCCUR IS
PROVING DIFFICULT. WILL KEEP CHANCE POPS GOING ALL NIGHT. LOWS
WILL RANGE FROM THE LOWER 70S INLAND TO THE MID 70S AT THE COAST.

WEDNESDAY...THE WAVE OF LOW PRESSURE RIDING ALONG THE COLD FRONT
WILL HAVE SHIFTED OFF THE MID ATLANTIC COASTLINE BY
DAYBREAK...WHILE THE MAIN SHORTWAVE RAPIDLY PROGRESSES TOWARD THE
EAST COAST AND PUSHES THE FRONT INTO THE FORECAST AREA. THE
COMBINATION OF UPPER LEVEL FORCING WITH FRONTAL CONVERGENCE WILL
SUPPORT SOLID THUNDERSTORM CHANCES UP TO 50 PERCENT DURING THE
DAYTIME HOURS...BEFORE THE FRONT SLIPS FARTHER SOUTH/SOUTHEAST AND
PULLS DEEPEST MOISTURE TOWARD THE ALTAMAHA RIVER AFTER SUNSET.
HIGHER RAIN CHANCES WERE CONSIDERED...YET FAIRLY SIGNIFICANT
TIMING DISCREPANCIES REGARDING THE PROGRESSION OF THE FRONT IS
EVIDENT BETWEEN MODELS...LENDING SOME UNCERTAINTY TO COVERAGE
DETAILS. WILL TREND CONVECTIVE POTENTIAL DOWNWARD FROM NORTH TO
SOUTH OVERNIGHT...WHILE STILL MAINTAINING 20 TO 30 PERCENT POPS
THROUGH THE PRE DAWN HOURS ON THURSDAY. INSTABILITY WILL BE
COMPROMISED BY PERSISTENT CLOUD COVER...AND WITH UNIMPRESSIVE WIND
PROFILES...THE MAIN HAZARD FROM THE STRONGEST CONVECTION WILL BE
HEAVY DOWNPOURS DUE TO SLOW STORM MOTION.

THURSDAY AND FRIDAY...THE FRONT IS EXPECTED TO STALL NEAR THE
SOUTHERN BORDER OF THE FORECAST AREA AS IT BECOMES PARALLEL TO THE
FLOW ALOFT LATE IN THE WEEK. SURFACE HIGH PRESSURE WILL BUILD
INTO THE REGION FROM THE NORTH...WITH THE PATTERN EVENTUALLY
TRANSITIONING INTO AN INLAND WEDGE/COASTAL TROUGH TYPE SCENARIO.
EXPECT BEST CONVECTIVE COVERAGE TO BE FOUND ALONG AND SOUTH OF THE
STALLED FRONT DURING THE DAYTIME HOURS...WITH SHOWER/THUNDERSTORM
ACTIVITY SHIFTING MORE TOWARD THE COAST AND OFFSHORE EACH NIGHT
WITHIN COASTAL TROUGH CONVERGENCE.

HIGH TEMPERATURES EACH DAY WILL GENERALLY RANGE FROM THE UPPER 80S
NORTH TO AROUND 90 DEGREES SOUTH...WITH LOCALLY COOLER CONDITIONS
ALONG THE COASTLINE. OVERNIGHT LOWS WILL TREND A FEW DEGREES
COOLER THAN EARLIER IN THE WEEK...RANGING FROM THE UPPER 60S
INLAND TO LOWER 70S COAST.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
A WEAK INLAND WEDGE/COASTAL TROUGH PATTERN WILL PERSIST INTO
SATURDAY...BEFORE THE TROUGH DAMPENS BY SUNDAY AS HIGH PRESSURE
SETTLES OVER THE ATLANTIC. THE FORECAST AREA WILL THEN REMAIN
ALONG THE WESTERN PERIPHERY OF THE ATLANTIC HIGH PRESSURE INTO
EARLY NEXT WEEK. SHOWER/THUNDERSTORM CHANCES WILL RANGE FROM
AROUND 20 TO 30 PERCENT EACH AFTERNOON AND EARLY EVENING...BEFORE
DIMINISHING OVERNIGHT AS MORE TYPICAL FOR EARLY SUMMER. THE
INITIALLY WEAK AND ILL DEFINED UPPER LEVEL PATTERN WILL TRANSITION
INTO BROAD RIDGING ALOFT...SUPPORTING A GRADUAL WARMING TREND
THROUGH THE PERIOD. HIGH TEMPERATURES AROUND 90 DEGREES AWAY FROM
THE COASTLINE SATURDAY AND SUNDAY WILL WARM INTO THE LOWER 90S BY
MONDAY AND TUESDAY.

&&

.AVIATION /11Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --
VFR FOR MOST OF THIS MORNING WITH PROBABILITIES INCREASING FOR
SHOWERS/TSTMS AFFECTING THE TERMINALS LATER THIS MORNING INTO THE
AFTERNOON HOURS. HIGHEST PROBABILITIES FOR IMPACTS LOOK TO OCCUR
17-20Z AT KCHS AND 16-19Z AT KSAV...BUT TIMING ADJUSTMENTS WILL BE
NEEDED AS THE DAY PROGRESSES. CAPPED CONDITIONS AT MVFR FOR NOW...
BUT BRIEF BOUTS OF IFR OR LOWER VSBYS ARE POSSIBLE IN HEAVY
CONVECTIVE RAINS. THE RISK FOR SHOWER/TSTMS WILL LINGER INTO MOST
OF THE NIGHT AS A COLD FRONT APPROACHES FROM THE WEST. ITS UNCLEAR
WHERE EXACTLY ANY LINES OF CONVECTION WILL OCCUR...SO DID NOT
INCLUDE ANY MENTION OF PCPN DURING THE NIGHT TIME HOURS.

EXTENDED AVIATION...PERIODIC FLIGHT RESTRICTIONS TUESDAY THROUGH
THURSDAY IN ASSOCIATION WITH SCATTERED TO NUMEROUS
SHRA/TSRA...MAINLY DURING THE AFTERNOON HOURS.
-- End Changed Discussion --

&&

.MARINE...
TODAY...SOUTHERLY FLOW REGIME WILL REMAIN IN TACT. WINDS WILL
GENERALLY REMAIN 10-15 KT WITH SEAS 2-4 FT NEARSHORE WATERS AND
4-5 FT OFFSHORE WATERS.

TONIGHT...WINDS WILL PICK UP SLIGHTLY AS A COLD FRONT APPROACHES
FROM THE WEST. WINDS LOOK TO PEAK 15-20 KT OVER THE GEORGIA
OFFSHORE WATERS AND THE CHARLESTON COUNTY COASTAL WATERS WITH 15
KT ELSEWHERE OUTSIDE OF THE CHARLESTON HARBOR. SEAS WILL REMAIN
2-4 FT NEARSHORE AND 4-5 FT GEORGIA OFFSHORE WATERS...BUT MAY
FLIRT WITH 6 FT AT TIMES ABOUT 15 NM EAST OF THE CHARLESTON COUNTY
COAST. SITUATION LOOKS TO MARGINAL FOR A SECOND PERIOD SMALL CRAFT
ADVISORY...SO WILL DEFER ANY ADVISORY DECISION TO THE NEXT
FORECAST SHIFT.

WEDNESDAY THROUGH SATURDAY...A COLD FRONT WILL SLIP INTO THE
COASTAL WATERS WEDNESDAY AND LIKELY STALL NEAR THE GEORGIA MARINE
ZONES THURSDAY. SOUTHERLY WINDS EARLY WEDNESDAY WILL THUS BECOME
EAST/NORTHEAST WEDNESDAY NIGHT INTO THURSDAY BEHIND THE DESCENDING
FRONT. A BRIEF SURGE IN NORTHEAST FLOW IS POSSIBLE THURSDAY
AFTERNOON...AS HIGH PRESSURE RAPIDLY BUILDS FROM THE NORTH AND
BRIEFLY TIGHTENS THE GRADIENT. WIND SPEEDS COULD INCREASE TO 15 TO
20 KT OVER PORTIONS OF THE WATERS AT THAT TIME...YET CONDITIONS
WILL REMAIN BELOW SMALL CRAFT ADVISORY CONDITIONS. MODERATE
EAST/NORTHEAST FLOW WILL CONTINUE INTO FRIDAY WITHIN A COASTAL
TROUGH TYPE PATTERN...BEFORE WINDS BECOME LIGHTER ON SATURDAY AS
THE CENTER OF HIGH PRESSURE SHIFTS OFFSHORE.

&&

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

&&

$$

ST/WMS