FXUS62 KCHS 271036
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
535 AM EST FRI NOV 27 2009
...FROST AND FREEZE CONDITIONS LIKELY TONIGHT AWAY FROM THE
COAST...
.SYNOPSIS...
HIGH PRESSURE WILL EXTEND CROSS THE REGION THROUGH THE WEEKEND. A
COLD FRONT WILL CROSS THE AREA MONDAY NIGHT AND TUESDAY...THEN A
GULF LOW PRESSURE SYSTEM WILL AFFECT THE SOUTHEAST WEDNESDAY AND
THURSDAY.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
WATER VAPOR IMAGERY SHOWS THE BASE OF THE LONGWAVE TROUGH HAS
PIVOTED OFFSHORE AND IS POISED TO MOVE OFF THE NORTH CAROLINA
COAST OVER THE NEXT FEW HOURS. SUNNY SKIES WILL PREVAIL TODAY
AS A BROAD CORRIDOR OF EXTENSIVE MID-LEVEL DRY EXTENDING FROM
THE CAROLINAS WEST ACROSS THE DEEP SOUTH AND INTO OKLAHOMA WILL
REMAIN IN PLACE. FULL SUN LOW-LEVEL THICKNESSES PROGS AND MODEL
BUFR SOUNDINGS SUPPORT HIGHS IN THE MID TO UPPER 50S...COOLEST
ACROSS THE NORTH AND FAR WEST INTERIOR. WINDS WILL REMAIN RATHER
GUSTY THIS MORNING AS COLD AIR ADVECTION ALOFT SLOWLY WEAKENS.
GUSTS COULD APPROACH 20-25 MPH AT TIMES.
LAKE WINDS...OBSERVATIONS FROM PINEVILLE AND SHORT STAY INDICATE
WINDS OVER THE OPEN WATERS OF LAKE MOULTRIE REMAIN ELEVATED AND
VERY NEAR LAKE WIND ADVISORY CRITERIA. FORECAST SOUNDINGS SUGGEST
WINDS WITHIN THE MIXED LAYER WILL REMAIN HIGH ENOUGH TO SUPPORT
WIND SPEEDS NEAR ADVISORY THRESHOLDS THROUGH MID MORNING...AFTER
WHICH WINDS WILL BEGIN TO DIMINISH. WILL KEEP THE LAKE WIND
ADVISORY IN PLACE THROUGH ITS 11 AM EXPIRATION TIME.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
THE MAIN CONCERN FOR TONIGHT IS THE POTENTIAL FOR A FROST/FREEZE
EVENT FOR MUCH OF SOUTHEAST SOUTH CAROLINA AND SOUTHEAST GEORGIA.
HIGH PRESSURE CENTERED OVER THE LOWER MISSISSIPPI VALLEY THIS
MORNING WILL BUILD EAST TODAY AND FORECAST TO BE POSITIONED ACROSS
THE WESTERN FLORIDA PANHANDLE BY SUNRISE SATURDAY. MODELS SHOW A
MODEST GRADIENT IN PLACE THIS EVENING...THEN SLOWLY RELAXING AFTER
MIDNIGHT AS THE CENTER OF THE HIGH APPROACHES. GUIDANCE IS IN GOOD
AGREEMENT IN DROPPING WINDS BELOW 5 MPH AWAY FROM THE COAST BY
MIDNIGHT AND WITH CLEAR SKIES IN PLACE...DECENT RADIATIONAL
CONDITIONS SHOULD ENSUE. WILL FAVOR THE COOLER SIDE OF THE 27/00Z
GUIDANCE PACKAGES TO CONSTRUCT LOWS TONIGHT WITH LOWS RANGING
FROM THE LOWER 30S INLAND WITH LOWER 40S ALONG THE BEACHES.
IT APPEARS THE RISK FOR FREEZING TEMPERATURES WILL BE GREATEST
ROUGHLY ALONG AND NORTH OF A SCARBORO-SYLVANIA-CROCKETVILLE-
RIDGEVILLE-JAMESTOWN LINE AND A FREEZE WARNING WILL BE POSTED FOR
THESE AREAS AWAY FROM LAKE MOULTRIE. THERE IS SOME CONCERN THAT
FREEZING TEMPERATURES MAY DROP AS FAR SOUTH AS A METTER-STATESBORO-
SPRINGFIELD-RIDGELAND LINE GIVEN THE ORIENTATION OF THE SURFACE
HIGH TO THE SOUTHWEST...BUT OUR CONFIDENCE IS NOT HIGH ENOUGH ATTM
TO JUSTIFY A FREEZE WARNING FOR THESE AREAS...SO A FREEZE WATCH
WILL BE ISSUED INSTEAD. FREEZING TEMPERATURES APPEAR UNLIKELY
ELSEWHERE ACROSS THE FORECAST AREA ALTHOUGH MID 30S AWAY FROM THE
COAST WILL SUPPORT SCATTERED FROST FORMATION AS FAR EAST AS
HIGHWAY 17 IN COASTAL SOUTH CAROLINA AND INTERSTATE 95 IN COASTAL
GEORGIA. WILL ISSUE A FROST ADVISORY FOR THE REMAINING ZONES
OUTSIDE OF THE FREEZE WARNING/WATCH AREAS WITH THE EXCEPTION OF
THE GEORGIA COASTAL ZONES AND INLAND MCINTOSH COUNTY WHERE ONLY
PATCHY FROST IS EXPECTED. SHOULD SEE FREEZE DURATIONS OF 3-5 HOURS
IN THE FREEZE WARNING AREA...WHICH SHOULD BE SUFFICIENT ENOUGH TO
END THE 2009 GROWING SEASON. THANKS FFC/CAE/JAX AND ILM FOR THE
COORDINATION.
SATURDAY...DRY AND BELOW NORMAL CONDITIONS WILL PERSIST INTO
SATURDAY AS HIGH PRESSURE HIGH PRESSURE BUILDS EAST. LOW-LEVEL
THICKNESSES SUPPORT HIGHS IN THE LWR-MID 60S WHICH LOOKS
REASONABLE. CIRRUS WILL BE ON THE INCREASE THROUGHOUT THE DAY AS A
SOUTHERN STREAM SHORT WAVE SKIRTS EAST ALONG THE NORTHERN GULF
COAST. THE CIRRUS LOOKS TO REMAIN THIN ENOUGH TO KEEP SKIES SUNNY
TO MOSTLY SUNNY.
&&
.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
SURFACE HIGH PRESSURE AND ZONAL UPPER LEVEL FLOW WILL REMAIN IN
CONTROL OF THE PATTERN SATURDAY NIGHT INTO MONDAY. DECENT
RADIATIONAL COOLING SATURDAY NIGHT UNDER MOSTLY CLEAR SKIES AND
LIGHT WINDS WILL ALLOW LOW TEMPERATURES TO FALL INTO THE MID TO
UPPER 30S INLAND...SUGGESTING SOME FROST POTENTIAL AWAY FROM THE
COAST. DAYTIME HIGH TEMPERATURES BOTH SUNDAY AND MONDAY WILL RISE
SEVERAL DEGREES ABOVE SEASONAL NORMALS WITHIN WARM SOUTHWEST
FLOW.
A COLD FRONT WILL APPROACH THE FORECAST AREA FROM THE WEST MONDAY
AND TUESDAY...AS SHORTWAVE ENERGY SHIFTS FROM THE OHIO VALLEY INTO
THE MID ATLANTIC STATES. THE TIMING BETWEEN MEDIUM RANGE OF
ASSOCIATED PRECIPITATION IS CLOSE ENOUGH TO BLEND SOLUTIONS AND
INDICATE RAIN CHANCES INCREASING FROM WEST TO EAST MONDAY
EVENING...PERSISTING INTO TUESDAY AS THE COLD FRONT MOVES INTO THE
ATLANTIC. TEMPERATURES WILL BE COOLER BEHIND THE FRONT TUESDAY
THROUGH AT LEAST MID WEEK...WITH DAYTIME HIGH TEMPERATURES IN THE
60S.
MODELS DEPICT A SOUTHERN STREAM SHORTWAVE MOVING ACROSS THE GULF
COAST STATES WEDNESDAY...ASSISTING IN THE RAPID DEVELOPMENT OF
SURFACE LOW PRESSURE OVER THE GULF OF MEXICO. 00Z ECMWF HAS MORE
SIGNIFICANT TIMING DIFFERENCES WITH THE 00Z GFS IN TRACKING THE
LOW SYSTEM NORTHEAST WEDNESDAY INTO THURSDAY. ECMWF SOLUTION
INDICATES ANOTHER WAVE OF LOW PRESSURE DEVELOPING ALONG THE
LINGERING BOUNDARY OFF THE SOUTH CAROLINA AND GEORGIA
COASTLINE...WITH A GENERALLY SLOWER PROGRESSION OF THE STORM
SYSTEM FROM THE GULF INTO THE MID ATLANTIC STATES.
DESPITE THESE MODEL DISCREPANCIES...GENERALLY THE BEST CHANCE OF
RAIN THROUGH THE EXTENDED PERIOD APPEARS TO BE TUESDAY NIGHT INTO
WEDNESDAY AFTERNOON. HAVE THUS INDICATED POPS IN THE 40 PERCENT
RANGE DURING THIS PERIOD.
&&
.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
VFR CONDITIONS WILL PREVAIL AT KCHS AND KSAV THROUGH FRIDAY
EVENING. WINDS MAY GUST AS HIGH AS 20 KT AFTER SUNRISE.
EXTENDED AVIATION OUTLOOK...VFR CONDITIONS THROUGH MONDAY. MVFR
OR LOWER CEILINGS AND/OR VISIBILITIES POSSIBLE MONDAY NIGHT INTO
TUESDAY AS A COLD FRONT AFFECTS THE AREA.
&&
.MARINE...
MARINE OBSERVATIONS SUGGEST WINDS HAVE DIMINISHED BELOW GALE FORCE
OVER THE GEORGIA OFFSHORE WATERS...THUS THE GALE WARNING WILL BE
ALLOWED TO EXPIRE AT 6 AM. A SMALL CRAFT ADVISORY WILL BE ISSUED
IN ITS PLACE...EFFECTIVE UNTIL 5 AM SATURDAY MORNING.
ELSEWHERE BOTH WINDS AND SEAS REMAIN SOLIDLY WITHIN SMALL CRAFT
ADVISORY THRESHOLDS. WINDS WILL DIMINISH AFTER SUNRISE AS HIGH
PRESSURE OVER THE LOWER MISSISSIPPI VALLEY BUILDS SLOWLY EAST.
WILL KEEP FLAGS IN PLACE FOR ALL NEARSHORE WATERS INCLUDING THE
CHARLESTON HARBOR THROUGH 11 AM. WITH GUSTY WINDS EXPECTED TO
PERSIST OVER LAND INTO THE EARLY AFTERNOON HOURS THERE IS A
POSSIBILITY THE SMALL CRAFT ADVISORY FOR THE HARBOR MAY NEED TO BE
EXTENDED BY SEVERAL HOURS. WILL LET THE DAY SHIFT MAKE THAT CALL.
ALTHOUGH WINDS ARE EXPECTED TO DROP BELOW ADVISORY LEVELS ACROSS
THE NEARSHORE WATERS THIS MORNING...WINDS ARE EXPECTED TO REMAIN
SOLIDLY 15-20 KT THROUGH TONIGHT WITH 20-25 KT OVER THE GEORGIA
OFFSHORE WATERS. EXPECT SEAS 2-3 FT NEAR THE IMMEDIATE COAST WITH
SEAS AS HIGH AS 6-9 FT BEYOND 20 NM.
SATURDAY NIGHT THROUGH TUESDAY...SOUTHWEST WINDS WILL PREVAIL
ACROSS THE WATERS THROUGH MONDAY...BEFORE A COLD FRONT CROSSES THE
AREA BY EARLY TUESDAY. AS THE FRONT DROPS TO THE SOUTHEAST OF THE
MARINE ZONES ON TUESDAY...COOLER AIR ALOFT WILL ALLOW FOR A BRIEF
SURGE IN NORTH WINDS. A GULF OF MEXICO STORM SYSTEM IS THEN
EXPECTED TO LIFT NORTHEAST THROUGH THE AREA MIDWEEK...WHICH COULD
CONTINUE UNSETTLED CONDITIONS OVER THE COASTAL WATERS. MARINE
ADVISORIES COULD BE POSSIBLE EARLY TO MID WEEK.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...FREEZE WATCH FROM LATE TONIGHT THROUGH SATURDAY MORNING FOR
GAZ099>101.
FROST ADVISORY FROM MIDNIGHT TONIGHT TO 9 AM EST SATURDAY FOR
GAZ114>116-118-137-138.
FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM EST SATURDAY FOR
GAZ087-088.
SC...FREEZE WATCH FROM LATE TONIGHT THROUGH SATURDAY MORNING FOR
SCZ047.
FROST ADVISORY FROM MIDNIGHT TONIGHT TO 9 AM EST SATURDAY FOR
SCZ048>051.
FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM EST SATURDAY FOR
SCZ040-042>045.
LAKE WIND ADVISORY UNTIL 11 AM EST THIS MORNING FOR SCZ045.
MARINE...SMALL CRAFT ADVISORY UNTIL 11 AM EST THIS MORNING FOR AMZ330-
350-352-354.
SMALL CRAFT ADVISORY UNTIL 5 AM EST SATURDAY FOR AMZ374.
&&
$$
