FXUS62 KCHS 091156
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
656 AM EST WED DEC 9 2009
.SYNOPSIS...
A COLD FRONT WILL SHIFT ACROSS THE AREA TODAY. SURFACE HIGH PRESSURE
WILL BUILD INTO THE REGION TONIGHT THROUGH FRIDAY. LOW PRESSURE
WILL ADVANCE NORTHEAST NEAR THE SOUTHEAST COAST SATURDAY INTO
SUNDAY...AS A WEDGE OF HIGH PRESSURE PREVAILS INLAND. HIGH
PRESSURE WILL REBUILD OVER THE AREA MONDAY...WITH A COMPLEX STORM
SYSTEM THEN EXPECTED TO IMPACT THE REGION THROUGH TUESDAY.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
THE WARM FRONT HAS LIFTED INTO THE SC MIDLANDS THIS MORNING WITH A
POTENT 50-60 KT LOW-LEVEL JET PUNCHING INTO SOUTHERN SC. STRONG WARM
ADVECTION OVERNIGHT HAS ALLOWED TEMPERATURES TO CLIMB INTO THE UPPER
60S TO AROUND 70 DEGREES WHILE DEWPOINTS HAVE ALSO CLIMBED INTO THE
MIDDLE TO UPPER 60S. THE LOW-LEVEL WARM ADVECTION HAS LIFTED THE
INVERSION TO ABOUT 1500 FT...ALLOWING SOME OF THE STRONGER WINDS
ALOFT TO MIX DOWN. WE HAVE SEEN SUSTAINED WINDS RANGING FROM 10 TO
20 KNOTS FOR THE LAST FEW HOURS AS WELL AS SOME GUSTS APPROACHING 30
KT. CONSIDERING THE FACT THAT THE MIXED LAYER IS LESS THAN 2 KFT
DEEP AND WE HAVE ALREADY BEEN SEEING THESE WIND SPEEDS...WE COULD
SEE SOME PRETTY WINDY CONDITIONS TODAY ONCE ADDITIONAL WARMING
OCCURS.
UPSTREAM SATELLITE IMAGERY INDICATES THE MID AND HIGH LEVEL
CLOUDINESS IS BEGINNING TO ERODE ALTHOUGH A FAIRLY WIDESPREAD
STRATUS DECK REMAINS. THERE IS A DECENT CHANCE THAT SOME BREAKS IN
THE CLOUD COVER THIS MORNING WILL ALLOW TEMPERATURES TO RAPIDLY
CLIMB INTO THE MIDDLE TO UPPER 70S. DUE TO HIGH UNCERTAINTY ON
MANY CLOUD BREAKS...WE PLAN TO CONTINUE WITH GOING HIGHS IN THE
MIDDLE 70S BUT THICKNESSES WOULD SUPPORT HIGHS CLOSE TO 80 SHOULD
MUCH SUNSHINE MAKE IT TO THE SURFACE. 925 MB WINDS PROGGED TO
REMAIN BETWEEN 50 AND 60 KTS THROUGH 18Z BEFORE SLOWLY DECREASING.
MODEL SOUNDINGS SUGGEST SUSTAINED SURFACE WINDS WILL INCREASE TO
18-25 KTS WITH GUSTS EXCEEDING 30 KTS SHORTLY AFTER DAYBREAK
ACROSS MUCH OF SOUTHERN SC AND EXTREME EASTERN GA. ANY UNFORESEEN
SURFACE HEATING WOULD LIKELY INCREASE SUSTAINED WINDS AND GUSTS
FURTHER. ALTHOUGH OUR WINDS COULD FALL JUST SHY OF OUR LOCAL WIND
ADVISORY CRITERIA...THE UNCERTAINTY REGARDING ADDITIONAL SURFACE
HEATING AND THE PLETHORA OF ELEVATED BRIDGES AND OVERPASSES TIPPED
US TOWARD A WIND ADVISORY FOR MUCH OF THE AREA THROUGH 6 PM. AREAS
THAT HAVE SEEN UP TO AN INCH OF RAIN IN THE LAST 24 HOURS MAY ALSO
SEE SOME WEAK TREES FALL IN THESE CONDITIONS.
REGARDING POPS...A PRETTY ROBUST SQUALL LINE WITH EMBEDDED BOWING
LINE SEGMENTS WILL PROGRESS INTO WESTERN PORTIONS OF THE FORECAST
AREA THIS MORNING...WARRANTING INCREASING POPS INTO THE HIGH
CHANCE/LIKELY CATEGORY. CAPES AHEAD OF AND ALONG THIS LINE WILL
REACH 500-1000 J/KG WHILE LIFTED INDICES DROP TO AROUND -2C.
THUNDERSTORMS WILL BE CAPABLE OF MIXING DOWN THE STRONGER WINDS
ALOFT...ESPECIALLY WITHIN ANY BOWING LINE SEGMENTS...RESULTING IN A
DAMAGING WIND THREAT. THE GREATEST POTENTIAL FOR DAMAGING WINDS
APPEARS TO BE ACROSS THE NORTHERN THIRD OF THE FORECAST AREA...WHERE
THE STORM PREDICTION CENTER HAS ISSUED A TORNADO WATCH UNTIL 10 AM.
WHILE THERE IS A VERY ISOLATED TORNADO THREAT...THE GREATEST
DIRECTIONAL WIND SHEAR/HELICITY HAS LIFTED NORTH OF THE AREA WITH
THE WARM FRONT. POPS SHOULD DIMINISH THIS AFTERNOON AS PRECIPITATION
ALONG THE FRONTAL BOUNDARY THINS...LOW-LEVEL WINDS VEER AND FRONTAL
CONVERGENCE DECREASES.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
THE COLD FRONT IS EXPECTED TO PUSH OFF THE COAST BY THIS EVENING
WITH SOME COOLER...DRIER AIR FILTERING IN. THE FRONT MAY STALL
ACROSS FAR SE PORTIONS LATE TONIGHT WITH SOME ISOLATED SHOWERS
PERSISTING. DO NOT EXPECT THE CLOUDS TO CLEAR OUT VERY MUCH EXCEPT
MAYBE FAR INLAND ZONES AS RESIDUAL MOISTURE BELOW 850 MB HUGS THE
COAST. COLD ADVECTION SHOULD DROP TEMPS INTO THE LOWER TO MIDDLE
40S. STRONG COLD ADVECTION CONTINUES ON THURSDAY WITH SOME CLOUDS
REMAINING ACROSS THE SOUTHEASTERN HALF OF THE AREA. HIGHS WILL
ONLY REACH THE UPPER 50S ACROSS THE BOARD.
&&
.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
SURFACE HIGH PRESSURE WILL SETTLE OVER THE TENNESSEE VALLEY THURSDAY
NIGHT...ALLOWING WINDS TO LIGHTEN AND SKIES TO BECOME MAINLY CLEAR
ACROSS THE AREA. THIS WILL PROMOTE GOOD RADIATIONAL COOLING...WITH
THE POTENTIAL FOR FREEZING CONDITIONS TO DEVELOP ACROSS MUCH OF THE
FORECAST AREA AWAY FROM THE IMMEDIATE COAST. PATCHY TO SCATTERED
FROST WILL ALSO BE A CONCERN INLAND OF THE BEACHES. HIGH PRESSURE
WILL SHIFT OVER THE SOUTHERN MID-ATLANTIC AND CAROLINAS ON
FRIDAY...WITH COOL AND DRY CONDITIONS EXPECTED ACROSS THE REGION.
DEEP LAYERED MOISTURE WILL INCREASE FROM THE SOUTH FRIDAY NIGHT AS
ISENTROPIC LIFT STRENGTHENS ACROSS THE AREA AHEAD OF A WARM LIFTING
FROM THE SOUTH. A GOOD CHANCE OF RAIN IS EXPECTED ACROSS THE
NORTHERN THIRD OF THE FORECAST AREA BY LATE FRIDAY NIGHT...WITH RAIN
BECOMING LIKELY FARTHER SOUTH. LOW TEMPERATURES SATURDAY MORNING
WILL BE IN THE MID TO UPPER 30S INLAND. DESPITE THESE COOL
TEMPERATURES...PRECIPITATION TYPE ISSUES ARE NOT ANTICIPATED AT THIS
TIME GIVEN THE STRENGTH OF WARM AIR ADVECTION ALOFT. MODEL SOUNDINGS
DEPICT A VERY SHALLOW COOL LAYER RIGHT AT THE SURFACE...BUT THE
EXTENT OF WARM AIR ALOFT AND RELATIVELY WARM GROUND TEMPERATURES
SHOULD ELIMINATE ANY THREAT FOR FREEZING RAIN AND/OR SLEET WELL
INLAND.
DEEP LAYERED MOISTURE WILL EXPAND OVER THE REMAINDER OF THE FORECAST
AREA ON SATURDAY...WITH RAIN LIKELY EVERYWHERE AS STRONG ISENTROPIC
ASCENT PERSISTS. THE RAIN WILL ALSO ENHANCE THE WEDGE OF HIGH
PRESSURE INLAND...MAKING FOR A VERY COOL DAY IN WHICH GUIDANCE IS
LIKELY TOO WARM. LOW PRESSURE WILL TRACK ALONG AN INVERTED TROUGH
OFF THE SOUTHEAST COAST ON SUNDAY...WITH ENOUGH MOISTURE IN PLACE TO
WARRANT AT LEAST A SLIGHT CHANCE OF RAIN.
HIGH PRESSURE WILL BRING DRY WEATHER AND MORE SEASONABLE
TEMPERATURES BY MONDAY...BUT IN THIS PROGRESSIVE PATTERN ANOTHER
STORM SYSTEM APPEARS POISED TO IMPACT THE AREA BY TUESDAY.
&&
.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
INITIATED BOTH KCHS AND KSAV WITH MVFR CEILINGS ALONG WITH GUSTY
WINDS WHICH WILL PREVAIL THROUGH MAJORITY OF THE DAY...ESPECIALLY
FOR KCHS. THE 12Z KCHS SOUNDING SHOWED 35 TO 50 KNOT WINDS JUST OFF
THE SURFACE WHICH WILL CONTINUE TO MIX DOWN RESULTING IN GUSTS UP TO
30 KNOTS AT TIMES LATER THIS AFTERNOON. AS GUSTS DIMINISH AT THE
SURFACE THIS EVENING...MARGINAL LLWS COULD RESULT BUT WILL EXCLUDE
FROM TAFS AT THIS TIME. THE MAIN CONCERN FOR PRECIP REMAINS ACROSS
KCHS AS A LARGE SQUALL LINE TO THE WEST APPROACHES THE AREA. TIMING
REMAINS QUITE DIFFICULT THUS EXPECT AMENDMENTS AS THE SQUALL LINE
NEARS. YET HAVE INCLUDED A TEMPO GROUP FROM 14Z TO 16Z TO INDICATE
THE THREAT OF MODERATE RAIN WHICH COULD BE HEAVY AT TIMES.
EXTENDED AVIATION OUTLOOK...PERIODS OF IFR OR LOWER CONDITIONS
POSSIBLE FRIDAY NIGHT THROUGH SATURDAY NIGHT...OTHERWISE VFR
CONDITIONS ARE EXPECTED TO PREVAIL.
&&
.MARINE...
SOLID SMALL CRAFT CONDITIONS TO CONTINUE THROUGH TODAY ACROSS ALL
WATERS AS A STRONG 50-60 KT LOW-LEVEL JET CONTINUES OVERHEAD.
STRONGEST WINDS WILL OCCUR OVER THE WARMER WATERS...ESPECIALLY OFF
THE SC COAST AND OFFSHORE GA WATERS. WINDS AND SEAS COME DOWN
QUITE RAPIDLY TONIGHT AND THURSDAY AFTER THE COLD FRONT SWEEPS
THROUGH AND WINDS GO OFFSHORE.
THURSDAY NIGHT THROUGH SUNDAY...A RATHER TIGHT SURFACE PRESSURE
GRADIENT WILL KEEP WINDS ELEVATED THROUGH FRIDAY. SMALL CRAFT
ADVISORY CONDITIONS SHOULD DEVELOP OVER PORTIONS...IF NOT ALL OF THE
COASTAL WATERS...FRIDAY NIGHT INTO SATURDAY AS THE SURFACE PRESSURE
GRADIENT TIGHTENS FURTHER IN RESPONSE TO LOW PRESSURE PASSING OFF
THE SOUTHEAST COAST. ALTHOUGH WINDS WILL BEGIN TO DIMINISH SATURDAY
NIGHT...SEAS WILL REMAIN ELEVATED THROUGH SUNDAY.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...WIND ADVISORY UNTIL 6 PM EST THIS EVENING FOR GAZ087-088-101-
118-119.
SC...WIND ADVISORY UNTIL 6 PM EST THIS EVENING FOR SCZ040-042>045-
047>051.
MARINE...SMALL CRAFT ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR AMZ350-352.
SMALL CRAFT ADVISORY UNTIL 4 PM EST THIS AFTERNOON FOR AMZ354.
SMALL CRAFT ADVISORY UNTIL 7 PM EST THURSDAY FOR AMZ374.
SMALL CRAFT ADVISORY UNTIL 9 PM EST THIS EVENING FOR AMZ330.
&&
$$
