FXUS62 KCHS 252217
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
517 PM EST FRI DEC 25 2009
.SYNOPSIS...
A LOW PRESSURE SYSTEM WILL MOVE INTO EASTERN NORTH CAROLINA
TONIGHT...DRAGGING A COLD FRONT THROUGH THE AREA. COLD HIGH
PRESSURE WILL BUILD IN THROUGH MUCH OF NEXT WEEK.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
THE SHORTWAVE ENERGY ROTATING AROUND THE SOUTHEASTERN PERIPHERY OF
THE POWERFUL UPPER LOW HAS MOVED NORTHEAST OF THE AREA THIS
AFTERNOON. AN ASSOCIATED SURFACE LOW MOVING INTO THE NC COASTAL
PLAIN IS DRAGGING A COLD FRONT THROUGH THE FORECAST AREA.
PRECIPITATION HAS BECOME RATHER SPARSE AHEAD OF THE FRONT...
CURRENTLY EXTENDING FROM FLORENCE SC TO SAVANNAH GA. THE FRONT
SHOULD BE SHIFTING OFF THE SC COAST BY EARLY THIS EVENING WITH
DRIER AIR FILTERING IN BEHIND. PRECIPITATION SHOULD COME TO AN END
IN MOST LOCATIONS BY DUSK.
PARTIAL CLEARING OVERNIGHT AND WEAK COLD ADVECTION SHOULD ALLOW
TEMPS TO DROP INTO THE MIDDLE 30S INLAND WITH LOWER 40S ALONG THE
COAST.
THE STRONGEST WINDS HAVE NOW SHIFTED EAST OF THE FORECAST AREA AS
THE LOW PUSHES INTO EASTERN NC. WINDS HAVE DROPPED OFF
SUBSTANTIALLY DURING THE LAST TWO TO THREE HOURS. WE PLAN TO DROP
THE WIND ADVISORY FOR CHARLESTON AND COASTAL COLLETON...AS WELL AS
THE LAKE WIND ADVISORY. WE EXTENDED THE HIGH SURF ADVISORY FOR
COASTAL SC UNTIL MIDNIGHT DUE TO RESIDUAL HIGH SEAS MAKING THEIR
WAY TO SHORE. THE FOLLY BEACH WAVE SENSOR HAS SHOWN 5-7 FT
BREAKERS SINCE 3 AM. SHOULD SEE RAPID DECREASE IN BREAKERS EARLY
THIS EVENING AS WINDS BECOME SOLIDLY OFFSHORE.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
COLD HIGH PRESSURE WILL MAINTAIN DRY CONDITIONS ON SATURDAY WITH
HIGHS IN THE MID TO UPPER 50S. MOST OF THE LOW AND MID CLOUDS
SHOULD BE CLEARED OUT BY MORNING HOWEVER A 140 KT JET STREAK
MOVING ACROSS THE AREA SHOULD BRING IN A FAIRLY EXTENSIVE CIRRUS
VEIL BY MID-MORNING.
&&
.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
A DEEP UPPER TROF WILL START THE PERIOD OVER THE GREAT LAKE
STATES...WITH STRONG UPPER ZONAL FLOW OVER THE SE U.S. AND GULF OF
MEXICO. THE UPPER LOW WILL MOVE OFF THE NEW ENGLAND COAST BY LATE
MONDAY/EARLY TUESDAY...ALLOWING FOR A LOW AMPLITUDE UPPER RIDGE TO
DEVELOP OVER THE SE U.S. TUESDAY THROUGH EARLY WEDNESDAY. IN
GENERAL...A BROAD/FULL LATITUDE UPPER TROF BEGINS TO CARVE OUT OVER
THE CENTRAL U.S. BY THURSDAY AND INTO FRIDAY WITH SW UPPER FLOW OVER
THE SE U.S.. THE MAIN DIFFICULTY WITH THIS FORECAST WILL BE TRYING
TO TIME UPPER IMPULSES THAT APPEAR TO MOVE RAPIDLY FROM
MEXICO...EASTWARD TOWARD THE NE GULF AND SE U.S. WITHIN A STRONG
SUBTROPICAL FLOW. MODELS HISTORICALLY HAVE TROUBLE WITH FEATURES
ACROSS THIS REGION DUE TO SPARSE OBSERVATIONAL DATA. THE FIRST WEAK
IMPULSE LOOKS LIKE IT COULD AFFECT THE AREA ON SUNDAY. LATEST RUNS
OF ALL MODELS APPEAR TO BE BACKING OFF ON THE STRENGTH AND NORTHWARD
EXTENT OF DEEP LAYER MOISTURE WITH THIS FEATURE. IN RESPONSE TO THIS
TREND...HAVE TRIMMED BACK POPS TO SLIGHT CHC FOR JUST THE S 1/3 OF
THE AREA. BEHIND THIS FEATURE...A MODERATELY STRONG SFC RIDGE
/1033MB/ BUILDS FROM THE WEST...USHERING IN COLDER AND DRIER AIR FOR
MONDAY AND TUESDAY. HIGHS BOTH DAYS ONLY IN THE 50S. HAVE KEPT LOWS
JUST ABOVE FREEZING MOST AREAS EXCEPT WELL INLAND FOR MONDAY
MORNING. TUESDAY MORNING LOOKS TO BE THE COLDEST AT THIS TIME.
MODELS STILL SHOWING THAT UPPER 20S ARE POSSIBLE AS FAR EAST AS CHS
AND SAV. ANOTHER COLD NIGHT TUESDAY NIGHT/WEDNESDAY...DESPITE THE
SFC RIDGE STARTING TO SHIFT OFFSHORE. HAVE KEPT MINS IN THE UPPER
20S TO LOWER 30S MOST AREA EXCEPT IMMEDIATE COAST.
WEDNESDAY THROUGH FRIDAY...CONFIDENCE IN THE MODEL FORECASTS FOR
THIS PERIOD IS QUITE LOW. IN GENERAL...THE MODELS SHOW AN
INCREASE IN DEEP LAYER MOISTURE AS ANOTHER SOUTHERN STREAM WAVE
MOVES ENE ACROSS THE GULF OF MEXICO. IT SEEMS NEARLY IMPOSSIBLE AT
THIS POINT TO PIN POINT THE EXACT TIMING AND STRENGTH OF THIS
POTENTIAL SYSTEM. HAVE NUDGED POPS UP A TAD...BUT KEPT THE TREND OF
THE PREVIOUS FORECAST WITH SLIGHT CHANCE POPS LATER WEDNESDAY AND
WEDNESDAY NIGHT...THEN LOW END CHANCE POPS FOR THURSDAY THROUGH
FRIDAY. GIVEN THE MODELS SHOW THE MAIN UPPER ENERGY AND SFC WAVE
REMAINING SOUTH OF THE REGION...KEPT OUT MENTION OF ANY CONVECTIVE
PRECIP. TEMPS ARE EXPECTED TO REMAIN BELOW NORMAL WITH HIGHS IN THE
LOWER TO MID 50S AND LOWS IN THE MID TO UPPER 30S.
&&
.AVIATION /22Z FRIDAY THROUGH WEDNESDAY/...
HAVE INITIATED THE 18Z TAF PERIOD WITH MVFR CEILINGS AND GUSTY WINDS
FOR BOTH KCHS AND KSAV AS LOW PRESSURE AFFECTS THE AREA. BELIEVE
RAIN CHANCES FOR KSAV HAVE ENDED THIS AFTERNOON.
HOWEVER...INCLUDED A BRIEF TEMPO GROUP OF RA FROM 20Z-22Z FOR KCHS
AS A LINE OF RAIN APPROACHES THE TERMINAL. COULD POTENTIALLY SEE
CONDITIONS LOWER THAN MVFR DUE TO HEAVY RAIN...THUS AMENDMENTS MAY
BE NEEDED THIS AFTERNOON. EXPECT MAINLY DRY CONDITIONS AFTER THE
LINE PASSES FOR KCHS. AS GUSTS DIMINISH LATER THIS
AFTERNOON...EXPECT WINDS JUST OFF THE SURFACE TO DIMINISH.
OVERNIGHT WINDS WILL CONTINUE TO DECREASE AT BOTH SITES WITH NO
LLWS ISSUES. MODEL SOUNDINGS SHOW PLENTY OF LINGERING LOW LEVEL
MOISTURE OVERNIGHT BUT EXPECT CEILINGS TO REMAIN VFR. THE NAM
SHOWS POTENTIAL FOR SOME IFR OR LOWER CEILINGS EARLY SATURDAY
MORNING. HOWEVER THIS APPEARS TO BE THE OUTLIER...THEREFORE WILL
PRECLUDE MENTION.
EXTENDED AVIATION OUTLOOK...GENERALLY VFR CONDITIONS EXPECTED
SUNDAY THROUGH TUESDAY. NEXT CHANCE FOR SUB-VFR CONDITIONS WILL
BE WEDNESDAY AS ANOTHER POTENTIAL SYSTEM MOVES WELL TO THE SOUTH
OF THE REGION. CONFIDENCE IN THE TIMING AND STRENGTH OF THIS
FEATURE IS VERY LOW.
&&
.MARINE...
WINDS CONTINUE TO CRANK OVER THE OFFSHORE SC WATERS PER THE
OCCASIONAL GALE FORCE GUSTS AT BUOY 41004. HOWEVER THE STRONGEST
WINDS HAVE SHIFTED EAST OF THE WATERS WITH THE SURFACE LOW AND AS
A COLD FRONT PUSHES THROUGH THE WATERS LATER THIS EVENING WINDS
WILL BECOME WEST AND DECREASE SUBSTANTIALLY. SEE NO JUSTIFICATION
FOR MAINTAINING THE GALE WARNINGS FOR THE CHARLESTON SC NEARSHORE
WATERS AND THE GA OFFSHORE WATERS...NOR FOR MAINTAINING THE SCA IN
CHARLESTON HARBOR. BUT WE WILL CARRY THE SCA FOR ALL OTHER
WATERS...THROUGH MIDNIGHT IN SOME AREAS AND VARYING PORTIONS OF
SATURDAY FOR THE REMAINDER. GREATLY IMPROVING CONDITIONS WILL
CONTINUE THROUGH SATURDAY AFTERNOON AS THE GRADIENT DECREASES.
NO HIGHLIGHTS EXPECTED THROUGH EARLY MONDAY WITH HIGH PRESSURE
SITTING OVER THE REGION. BY LATER MONDAY...STRONGER HIGH PRESSURE
WILL BUILD FROM THE WEST...WITH STRONGER COLD ADVECTION OVER THE
ATLANTIC WATERS. THIS WILL HELP TO INCREASE WINDS TO AT LEAST LOW
END SCA LEVELS OVER THE GA OFFSHORE WATERS LATER MONDAY AND MONDAY
NIGHT. THE WINDS AND SEAS WILL DECREASE AGAIN TUESDAY AS HIGH
PRESSURE BUILDS BACK OVER THE AREA. HIGH PRESSURE WILL WEAKEN AND
MOVE EAST OF THE AREA ON WEDNESDAY AS ANOTHER WEAK AREA OF LOW
PRESSURE TRIES TO MOVE TOWARD THE REGION FROM THE GULF OF MEXICO.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...HIGH SURF ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR SCZ048>051.
MARINE...SMALL CRAFT ADVISORY UNTIL 5 AM EST SATURDAY FOR AMZ352.
SMALL CRAFT ADVISORY UNTIL NOON EST SATURDAY FOR AMZ350.
SMALL CRAFT ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR AMZ354.
SMALL CRAFT ADVISORY UNTIL 5 PM EST SATURDAY FOR AMZ374.
&&
$$
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