FXUS62 KCHS 251150
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
650 AM EST FRI DEC 25 2009
.SYNOPSIS...
A HIGH PRES WEDGE WILL CONTINUE TO BREAK DOWN THIS MORNING AS A
COMPLEX STORM SYSTEM IMPACTS THE REGION. A COLD FRONT WILL PUSH
SOUTH AND EAST OF THE REGION TONIGHT. WEAK HIGH PRES WILL THEN
BUILD INTO THE SOUTHEAST SATURDAY INTO SUNDAY. WEAK LOW PRES WILL
PASS JUST OFF THE SOUTHEAST COAST SUNDAY NIGHT...THEN STRONGER
HIGH PRES WILL EXPAND INTO THE REGION MONDAY THROUGH WEDNESDAY.
LOW PRESSURE COULD IMPACT THE REGION THURSDAY.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A STRONG COLD SEASON WARM FRONT WAS LIFTING N FROM NORTHERN SCREVEN
AND JENKINS COUNTIES IN SOUTHEAST GEORGIA TO NEAR JAMESTOWN IN
SOUTH CAROLINA. A TORNADO WATCH REMAINS IN EFFECT FOR OUR ENTIRE
FORECAST AREA AS WIND FIELDS REMAIN STRONG AND VEER WITH HEIGHT.
INSTABILITY ON THE LOW END FOR NOW...BUT THIS STORM SYSTEM HAS
HAD A DISTINCT HISTORY OF PRODUCING SEVERE WEATHER AND MODELS
STILL HINT FOR A WINDOW OF DAMAGING WINDS AND ISOLATED TORNADOES
INTO EARLY AFTERNOON.
THIS MORNING...DYNAMIC FORCING AHEAD OF AN APPROACHING SHORT WAVE
AND DRY SLOT WILL SPREAD RAINS INTO OUR REGION WITH A THIN BAND
OF LOW-TOPPED CONVECTION CONTINUING TO SPREAD E AND NE INTO AREAS
TO THE W OF I-95 BY MID MORNING. NOT MUCH LIGHTNING ACTIVITY LEFT
WITH OVERALL INSTABILITY AND LAPSE RATES AHEAD OF THIS FEATURE
ON THE WEAK SIDE CURRENTLY. THE WRF/SREF ENSEMBLES SHOW A SLOT
OF INCREASING INSTABILITY THROUGH OUR FORECAST AREA AFTER DAWN.
CERTAINLY WIND FIELDS ARE MOST IMPRESSIVE AND DEEP MOISTURE
CONVERGENCE IS ALREADY RAMPING UP OVER THE AREA. WIDESPREAD
RAINFALL DEVELOPING WITH THE DEEP LAYERED MOISTURE AND BROAD OMEGA
ACROSS THE REGION APPEARS TO BE A LIMITING FACTOR FOR SEVERE
WEATHER TODAY. LOCALLY STRONG AND GUSTY WINDS WILL ACCOMPANY ANY
STRONGLY FORCED CONVECTION THROUGH OUR ZONES TODAY AT THE VERY
LEAST.
WE ARE IN SOLID AGREEMENT WITH THE SPC ASSESSMENT THIS MORNING ON
THE DAY ONE OUTLOOK WITH A SLIGHT RISK OVER OUR FORECAST AREA BUT
UNTIL TRENDS BECOME MORE FOCUSED LATER THIS MORNING...WE HAVE
OPTED TO LEAVE SEVERE WORDING FROM OUR ZONE FORECAST ALTHOUGH
POTENTIAL FOR BOTH DAMAGING WIND GUSTS AND ISOLATED TORNADOES WILL
BE DISCUSSED IN OUR HAZARDOUS WEATHER OUTLOOK.
WE BELIEVE THE OVERALL PROGRESSION OF THE SYSTEM WILL KEEP RAINFALL
TOTALS DOWN BUT MANY AREAS COULD STILL SEE 1-2 INCHES OF RAIN
TODAY GIVEN THE DYNAMICS...LOW LEVEL CONVERGENCE AND HIGH PWATS.
WINDS WILL BE AN ISSUE ALONG COASTAL SOUTH CAROLINA TODAY AND WE
HAVE OPTED TO CONTINUE A WIND ADVISORY ALONG COASTAL CHARLESTON
COUNTY WHERE MODELS SHOW POTENTIAL FOR 25 TO 35 MPH ONSHORE FLOW
DEVELOPING THIS MORNING.
RAIN IS EXPECTED TO END THIS AFTERNOON TO THE W OF I-95 AND SKIES
CLEARING BY LATE DAY. TEMPERATURES VERY TRICKY WITH COMPLEX SYNOPTIC
SITUATION TO INITIALIZE THIS MORNING...WE THINK HIGHS AT LEAST IN
THE LOWER 70S IN THE WARM SECTOR ARE A GOOD BET THIS AFTERNOON AND
WE EVEN RAISED HIGHS A COUPLE DEGREES WELL INLAND AS GUIDANCE TRENDS
TOWARD A MORE ROBUST WARM SECTOR.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
0Z GUIDANCE AGREES THAT DEEP LAYER MOISTURE WILL HAVE EXITED THE
REGION TO THE E/NE BY EARLY THIS EVENING...THUS LOWERED ALL POPS
OVER LAND TO LESS THAN 15 PERCENT AND REMOVED ANY MENTION OF
PRECIPITATION OVER LAND THIS EVENING. OTHERWISE...THE COLD FRONT
WILL PUSH OFFSHORE THIS EVENING...AND COLD ADVECTION WILL PUSH
TEMPERATURES INTO THE LOWER TO MID 30S INLAND/LOWER TO MID 40S AT
THE COAST BY DAYBREAK SATURDAY.
SATURDAY...WEAK HIGH PRESSURE WILL BUILD OVER THE REGION FROM THE
W/SW. DOWNSLOPE FLOW SHOULD ALLOW TEMPERATURES TO RECOVER TO NEAR
NORMAL...AROUND 60F AT MOST LOCATIONS. HOWEVER...HIGH CLOUDS
STREAMING INTO THE REGION FROM THE SW WILL LIMIT INSOLATION.
&&
.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
WE HAVE BEEN CONCERNED THAT ANY WAVE EMBEDDED WITHIN THE MOIST
SUBTROPICAL JET TO OUR SOUTH COULD AMPLIFY AND SPREAD MOISTURE/
MOISTURE/PRECIPITATION ACROSS THE SOUTHEAST LATE THIS WEEKEND.
INDEED...0Z GUIDANCE DEPICTS A WEAK WAVE EJECTING NE WITH ENHANCED
MOISTURE BLOSSOMING NE ACROSS THE REGION SUNDAY. TIMING REMAINS
UNCERTAIN...WHILE LOW LEVEL DRY AIR PROVIDED BY HIGH PRESSURE AND A
WEAK/PROGRESSIVE WAVE COULD ENSURE THAT MOST/ALL MEASURABLE
PRECIPITATION REMAINS JUST S/E OF THE REGION. HOWEVER...GUIDANCE
TRENDS JUSTIFY SLIGHT CHANCE POPS SUNDAY INTO SUNDAY EVENING...AND
WOULD NOT BE SURPRISED IF HIGHER POPS AND TIMING ADJUSTMENTS ARE
REQUIRED WITHIN SUBSEQUENT FORECASTS.
ALSO OF NOTE...IF ASCENT/DEEP LAYER MOISTURE SPREAD INTO THE REGION
EARLIER THAN EXPECTED LATE SATURDAY NIGHT/EARLY SUNDAY MORNING...LOW
LEVEL DRY AIR/ASSOCIATED LOW LEVEL WET BULB TEMPS BELOW 0C COULD
SUPPORT A BIT OF SLEET AT THE ONSET OF PRECIPITATION. HOWEVER...THE
ODDS FOR ICE PELLETS REMAINS MUCH TOO LOW TO INCLUDE A MENTION
WITHIN THIS FORECAST...AND ANY SLEET WOULD NOT ACCUMULATE ANYWAY.
LATER SUNDAY NIGHT INTO WEDNESDAY...HIGH PRESSURE SHOULD STRENGTHEN
AND EXPAND OVER THE REGION...ENSURING A PERIOD OF RAIN-FREE
CONDITIONS AND BELOW NORMAL TEMPERATURES. EVENTUALLY...THE MOISTURE
LADEN SUBTROPICAL JET WILL BUCKLE AND ANOTHER WAVE OR SERIES OF
WAVES WILL EMERGE FROM THE GULF OF MEXICO TO BRING RAIN TO THE
SOUTHEAST. THIS FORECAST INDICATES SLIGHT CHANCE POPS WEDNESDAY
NIGHT AND CHANCE POPS THURSDAY. HOWEVER...OVERRUNNING
MOISTURE/PRECIPITATION COULD SURGE INTO THE REGION EARLIER THAN
EXPECTED...AND SIGNIFICANTLY HIGHER POPS WILL EVENTUALLY BE REQUIRED
ONCE EVENT TIMING COMES INTO FOCUS.
&&
.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
AT KCHS...LIGHT SHOWERS THROUGH MID MORNING WITH PERIODIC MVFR CIGS
THEN GREATER PROBABILITIES OF HEAVY SHOWERS AND POTENTIAL CB INTO
MID AFTERNOON BEFORE RAIN QUICKLY EXITS OFF TO THE NE IN THE LATE
AFTERNOON. IFR CONDITIONS WILL BE SHORT LIVED TODAY...MAINLY
ASSOCIATED WITH POCKETS OF HEAVY RAIN.
MODELS SHOW MVFR CIGS FILLING BACK IN BEHIND THE LINE OF
CONVECTION IN THE EARLY AFTERNOON AND THEY MAY LINGER UNTIL THIS
EVENING. CLEARING TONIGHT WITH VFR CONDITIONS. STRONG WINDS FROM
THE SE THIS MORNING...WE MAINTAINED PREVAILING SPEEDS NEAR 20 KT
WITH GUSTS NEARING 30 KT AT TIME. WINDS SHOULD BEGIN TO SUBSIDE
AFTER EARLY AFTERNOON.
AT KSAV...RAINS ARE QUICKLY MOVING IN FROM THE SSW AT INITIALIZATION
TIME. CIGS HAVE BEEN SLOW TO DETERIORATE THIS MORNING BUT PLENTY
OF MVFR CIGS ARE LIFTING OUT OF THE GEORGIA SWAMP REGION INTO
UPPER COASTAL GEORGIA. WINDS WERE GUSTY THIS MORNING BUT PREVAILING
GUSTS SHOULD NOT CONTINUE TOO LONG PAST MIDDAY AS THE FRONT SWEEPS
TOWARD THE SAVANNAH RIVER REGION. MVFR CIGS ARE POSSIBLE MID TO
LATE AFTERNOON BUT RAINFALL WILL BE ON THE WANE. MAINLY VFR
CONDITIONS EXPECTED TONIGHT AFTER 00Z/26.
VFR TONIGHT THROUGH SATURDAY NIGHT. BRIEF MVFR POSSIBLE IN RAIN
SUNDAY INTO SUNDAY NIGHT. VFR THEREAFTER.
&&
.MARINE...
AS A STRONG WARM FRONT SHIFTS INLAND TODAY...ONSHORE WINDS WILL
CONTINUE TO BLOW AT GALE FORCE WELL OFF THE COAST WITH GUSTS TO
GALE FORCE AT TIMES OFF THE CHARLESTON COUNTY COAST AND PERHAPS
WELL OFF THE GEORGIA COAST THIS MORNING. MIXING PROFILES ARE NOT
IMPRESSIVE WITH MID 50S SEA SURFACE TEMPERATURES BUT THE STRENGTH
OF THE WIND FIELDS SUGGEST A CONTINUATION OF THE GALES IN PARTS OF
OUR MARINE AREA THIS MORNING. SEAS WERE CONTINUING TO BUILD THIS
MORNING WITH RECENT REPORTS OF 13 FT SEAS AT 41004 AND 7 FT AT
GRAYS REEF.
THE STRONG ONSHORE PUSH WILL EASE N OF THE CHARLESTON COUNTY LATE
TODAY BUT SEAS INITIALLY WILL BE A BIT SLOW TO SUBSIDE. OVER OUR
GEORGIA NEAR SHORE WATERS...THE ARRIVAL OF THE WIND SHIFT WILL
BE A BIT SOONER AND LOW LEVEL WINDS JUST A BIT LESS ROBUST.
SMALL CRAFT ADVISORIES CONTINUE OVER WATERS ADJACENT TO OUR GALES
TODAY.
IN THE WAKE OF COLD FROPA THIS EVENING...A SURGE OF W/NW WINDS/COLD
ADVECTION WILL MAINTAIN ELEVATED WINDS/SEAS ACROSS COASTAL WATERS.
SMALL CRAFT ADVISORY CONDITIONS SHOULD PERSIST MOST AREAS THIS
EVENING...THEN WINDS WILL GRADUALLY DIMINISH AND SEAS WILL GRADUALLY
SUBSIDE FROM S/SW TO N/NE OVERNIGHT. SEAS ARE EXPECTED TO SUBSIDE
BELOW 6 FT ACROSS AMZ350 BY EARLY SATURDAY MORNING AND ACROSS THE
OUTER GA WATERS BY SATURDAY AFTERNOON.
WINDS/SEAS SHOULD THEN REMAIN BELOW SMALL CRAFT ADVISORY LEVELS
THROUGH SUNDAY. THEN...A WAVE OF LOW PRESSURE WILL PASS JUST S/E OF
THE WATERS SUNDAY NIGHT. IN THE WAKE OF THIS WAVE...ANOTHER SURGE
OF COLD ADVECTION WILL SUPPORT INCREASING WINDS/BUILDING SEAS...AND
SMALL CRAFT ADVISORY CONDITIONS COULD DEVELOP LATE SUNDAY NIGHT
THROUGH MONDAY NIGHT ESPECIALLY BEYOND 20 NM. THEN...CONDITIONS
SHOULD IMPROVE SOMEWHAT AS HIGH PRESSURE EXPANDS OVER THE COASTAL
WATERS TUESDAY AND WEDNESDAY.
&&
.TIDES/COASTAL FLOODING...
HIGH TIDE AT CHARLESTON OVERNIGHT FELL JUST SHORE OF SHALLOW COASTAL
FLOODING ADVISORY CRITERIA. THE STRONG ONSHORE WINDS WILL HOLD PLENTY
OF WATER IN AT LOW TIDE THIS MORNING BUT THE NEXT HIGH TIDE CYCLE ALSO
APPEARS TO FALL SHORT OF ADVISORY CRITERIA. A HIGH SURF ADVISORY
WILL CONTINUE FOR THE SOUTH CAROLINA COAST FOR BREAKERS OF 5-6 FT
DEVELOPING IN THE SURF ZONE. THE WAVE SENSOR AT THE END OF THE FOLLY
BEACH PIER WAS ALREADY OVER 5 FT THIS MORNING.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...LAKE WIND ADVISORY UNTIL 5 PM EST THIS AFTERNOON FOR SCZ045.
HIGH SURF ADVISORY UNTIL 5 PM EST THIS AFTERNOON FOR
SCZ048>051.
WIND ADVISORY UNTIL 11 AM EST THIS MORNING FOR SCZ049-050.
MARINE...SMALL CRAFT ADVISORY UNTIL 9 PM EST THIS EVENING FOR AMZ352.
GALE WARNING UNTIL 5 PM EST THIS AFTERNOON FOR AMZ350-374.
SMALL CRAFT ADVISORY UNTIL 5 PM EST THIS AFTERNOON FOR AMZ330-
354.
&&
$$
