Severe Thunderstorm Warning 122, NWS Charleston, SC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
336 PM EDT WED SEP 4 2013

.SYNOPSIS...
A WEAK FRONT WILL CONTINUE TO DISSIPATE WITHIN A WEAK PRESSURE
PATTERN THROUGH TONIGHT. A DRY FRONT WILL DROP THROUGH THE REGION
THURSDAY NIGHT AND FRIDAY...WITH HIGH PRESSURE BUILDING FROM THE
NORTH FOR THE WEEKEND AND MOST OF NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
ISOLATED SHOWERS AND THUNDERSTORMS HAVE INITIATED BY MID TO LATE
AFTERNOON ALONG AND INLAND OF THE SEABREEZE. THE WEAK FRONT THAT
HAD STALLED OVER THE FORECAST AREA CONTINUES TO DISSIPATE...AS THE
PATTERN AT THE SURFACE AND ALOFT HAS BECOME RATHER WEAK OVER THE
SOUTHERN STATES. THE SEABREEZE WILL MAKE STEADY PROGRESS INLAND
THROUGH THE EVENING HOURS...AND BEING THE MAIN FOCUS FOR
CONVECTION...EXPECT SHOWER/THUNDERSTORM ACTIVITY TO TREND AWAY
FROM THE COAST ACCORDINGLY. HAVE INDICATED SLIGHT CHANCE POPS
THROUGH SUNSET...AS THE SEABREEZE DEPARTS THE AREA AND INSTABILITY
WANES. MESOSCALE BOUNDARY INTERACTIONS COULD SUPPORT ISOLATED
STRONG UPDRAFTS WITHIN CONVECTION AND A BRIEF STRONG TO MARGINALLY
SEVERE STORM...HOWEVER THE OVERALL SEVERE WEATHER THREAT REMAINS
LOW FOR THE NEAR TERM PERIOD.

THE MAIN FORECAST CONCERN OVERNIGHT WILL BE THE COVERAGE AND
DENSITY OF ANY FOG. EXPECT THE MAJORITY OF CLOUD COVER TO
DISSIPATE BEHIND THE SEABREEZE SHORTLY AFTER SUNSET...WITH MOSTLY
CLEAR SKIES AND LIGHT WINDS PREVAILING TONIGHT. NUMERICAL MODEL
GUIDANCE HINTS THAT AT LEAST PATCHY FOG DEVELOPMENT IS POSSIBLE
DURING THE PRE-DAWN HOURS...WITH QUITE A BIT OF DISAGREEMENT
REGARDING THE ACTUAL DENSITY. THE MAIN FACTOR DICTATING FOG
IMPACTS WILL BE THE OCCURRENCE OF RAINFALL THIS AFTERNOON AND
EVENING...AND SINCE RADAR TRENDS ARE JUST NOW BECOMING
EVIDENT...PREFER TO MAINTAIN MENTION OF JUST PATCHY FOG AT THIS
TIME. SUBSEQUENT FORECASTS WILL ASSESS THE NEED FOR CHANGES
ACCORDING TO CONVECTIVE COVERAGE AND OVERALL TRENDS.

LOW TEMPERATURES WILL BE A FEW DEGREES WARMER THAN SEASONAL
NORMALS...RANGING FROM THE MID 70S ALONG THE COAST TO THE LOWER
70S INLAND.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
THE UPPER RIDGE WILL REMAIN ACROSS THE CENTRAL PLAINS STATES
MAINTAINING NW FLOW OVER OUR FORECAST AREA. THIS WILL BE A
PERSISTENT FEATURE FOR THE REST OF THE WEEK AND WEEKEND. A VERY WEAK
SURFACE PRESSURE PATTERN WILL DOMINATE THURSDAY...WHICH WILL ALLOW
THE SEA BREEZE TO MOVE FURTHER INLAND COMPARED TO RECENT DAYS.
THURSDAY NIGHT A WEAK AND DRY COLD FRONT WILL ADVECT IN FROM THE
NORTH...SHIFTING BOUNDARY LAYER WINDS TO NE BY FRIDAY AFTERNOON. THE
PROFILE WILL REMAIN FAIRLY MOIST IN THE LOW LEVELS ON THURSDAY
THOUGH THE WNW FLOW ABOVE 700 MB WILL MAINTAIN A DECENT SUBSIDENCE
CAP. WITH THE ABSENCE OF ANY IMPRESSIVE UPPER LEVEL DYNAMICS AND
LIMITED VERTICAL MOTION...ONLY HAVE AN ISOLATED POP ACROSS SOUTHEAST
GA WHERE THE MOISTURE IS A LITTLE BETTER. HIGHS THURSDAY WILL BE IN
THE LOWER 90S.

ON FRIDAY WE WILL HAVE DRIER AIR MOVING IN FROM THE NORTH REDUCING
THE FOG RISK. HOWEVER AS THE STEERING FLOW VEERS TO THE NORTH...THE
CAP WILL WEAKEN. PREVAILING BOUNDARY LAYER FLOW WILL BE ONSHORE
DURING THE AFTERNOON. THIS COULD TRIGGER ISOLATED SHOWERS AND TSTMS
DURING THE AFTERNOON. THE NORTHERLY FLOW SHOULD LIMIT THE HIGHS OVER
MOST OF THE CWA TO THE UPPER 80S.

SLIGHTLY COOLER AND DRIER HIGH PRESSURE WILL PREVAIL ON SATURDAY.
THE DRIEST CONDITIONS WILL BE ACROSS SOUTHERN SC. A MORE ONSHORE
FLOW COMPONENT IN SOUTHEAST GA WILL KEEP LOW-LEVEL MOISTURE A BIT
HIGHER. WITH ANOTHER DECENT SEA BREEZE PENETRATION AN ISOLATED
CONVECTIVE CELL COULD POP UP IN SOUTHEAST GA. THE COOLER TEMPS WILL
BE MORE NOTICEABLE IN THE MORNING AND HIGHS WILL RANGE FROM MID TO
UPPER 80S WITH SLIGHTLY LOWER DEWPOINTS.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
AS AN UPPER LOW OVER THE PACIFIC NORTHWEST BEGINS TO WEAKEN AND LIFT
NORTHEAST...THE BROAD CENTRAL UNITED STATES RIDGE WILL FINALLY SHIFT
EAST. OUR LONG TERM PERIOD LOOKS RATHER QUIET AS DEEP-LAYERED
RIDGING MAINTAINS RELATIVELY DRY CONDITIONS AND NEAR-NORMAL
TEMPERATURES.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
ISOLATED THUNDERSTORM ACTIVITY THIS AFTERNOON WILL BE FOCUSED
ALONG AND INLAND OF THE SEABREEZE. LIGHT LOW LEVEL FLOW WILL ALLOW
THE SEABREEZE TO PROGRESS THROUGH AND AWAY FROM THE TERMINALS BY
MID AFTERNOON...AND HAVE THUS CONTINUED TO INDICATE WIND
DIRECTIONS VEERING TO SOUTHERLY BY LATE AFTERNOON. LATEST RADAR
TRENDS SUGGEST THAT KSAV HAS THE BEST POTENTIAL TO SEE VICINITY
THUNDERSTORMS...SO HAVE ADDED A VCTS THROUGH 00Z ACCORDINGLY.
OTHERWISE...CONFIDENCE THAT CONVECTION WILL IMPACT THE TAF SITES
IS STILL LOW. WILL CONTINUE TO MONITOR RADAR AND MAKE ADJUSTMENTS
IF NECESSARY.

NUMERICAL MODEL GUIDANCE CONTINUES TO DISAGREE STRONGLY REGARDING
THE POTENTIAL FOR FOG DEVELOPMENT AFTER MIDNIGHT. THE NAM
GUIDANCE REMAINS THE MORE CONSERVATIVE SOLUTION WITH A FEW HOURS
OF MVFR VSBYS...WHILE THE GFS CONTINUES TO SUGGEST IFR OR LOWER
CONDITIONS AT BOTH KCHS AND KSAV. WITH LIGHT WINDS AND CLEARING
SKIES OVERNIGHT...AT LEAST PATCHY FOG IS POSSIBLE. HESITANT TO BE
MORE PESSIMISTIC AT THIS TIME...DUE TO UNCERTAINTY THAT EITHER TAF
SITE WILL RECEIVE RAINFALL TO SUPPORT DENSER FOG. SUBSEQUENT
FORECASTS WILL BE ABLE TO ADDRESS TRENDS AND REFINE FOG POTENTIAL
FURTHER.

EXTENDED AVIATION OUTLOOK...OTHER THAN POSSIBLY A BRIEF PERIOD OF
MVFR VSBYS WITH AFTERNOON SHOWERS...MAINLY VFR CONDITIONS EXPECTED.

&&

.MARINE...
QUIET CONDITIONS EXPECTED THROUGH TONIGHT...WITH THE WEAK
DISSIPATING FRONT IN THE REGION SUPPORTING A VERY LIGHT PRESSURE
GRADIENT ACROSS THE WATERS. SEAS WILL BE GENERALLY 2 FT OR LESS
WITH WINDS 10 KT OR LESS. IT REMAINS POSSIBLE THAT SOME GROUND
FOG OVERNIGHT COULD SPILL INTO THE IMMEDIATE NEARSHORE WATERS AS
WELL AS THE HARBORS...REDUCING VISIBILITIES TEMPORARILY.

A WEAK ONSHORE FLOW WILL EXIST THURSDAY AND THURSDAY NIGHT. WINDS
WILL BECOME NNE LATER FRIDAY AND INCREASE TO 10-15 KT...CONTINUING
THROUGH SATURDAY NIGHT BEHIND A WEAK COLD FRONT. VERY QUIET
CONDITIONS WILL CONTINUE THEREAFTER AS HIGH PRESSURE SETTLES
OVERHEAD.

&&

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

&&

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

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE CHARLESTON SC
320 AM EDT WED SEP 4 2013

AMZ330-350-352-354-374-GAZ087-088-099>101-114>119-137>141-SCZ040-
042>045-047>052-050730-
CHARLESTON HARBOR-
WATERS FROM SOUTH SANTEE RIVER TO EDISTO BEACH SC OUT 20 NM-
WATERS FROM EDISTO BEACH SC TO SAVANNAH GA OUT 20 NM-
WATERS FROM SAVANNAH GA TO ALTAMAHA SOUND GA OUT 20 NM...INCLUDING
GRAYS REEF NATIONAL MARINE SANCTUARY-
WATERS FROM SAVANNAH GA TO ALTAMAHA SOUND GA EXTENDING FROM 20 TO
60 NM-JENKINS-SCREVEN-CANDLER-BULLOCH-EFFINGHAM-TATTNALL-EVANS-
INLAND BRYAN-COASTAL BRYAN-INLAND CHATHAM-COASTAL CHATHAM-LONG-
INLAND LIBERTY-COASTAL LIBERTY-INLAND MCINTOSH-COASTAL MCINTOSH-
ALLENDALE-HAMPTON-INLAND COLLETON-DORCHESTER-INLAND BERKELEY-
INLAND JASPER-BEAUFORT-COASTAL COLLETON-CHARLESTON-COASTAL JASPER-
TIDAL BERKELEY-
320 AM EDT WED SEP 4 2013

THIS HAZARDOUS WEATHER OUTLOOK IS FOR ATLANTIC COASTAL
WATERS...SOUTHEAST GEORGIA AND SOUTHEAST SOUTH CAROLINA.

.DAY ONE...TODAY AND TONIGHT.

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY.

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ASSISTANCE IS NOT ANTICIPATED AT THIS TIME.

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