FXUS62 KCHS 100543
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1243 AM EST THU DEC 10 2009
.SYNOPSIS...
A COLD FRONT WILL SLOWLY SHIFT OFFSHORE TONIGHT. SURFACE HIGH
PRESSURE WILL BUILD INTO THE REGION THURSDAY INTO FRIDAY. UNSETTLED
WEATHER WILL THEN RETURN TO THE SOUTHEAST STATES FRIDAY NIGHT AND
CONTINUE THROUGH THE MIDDLE OF NEXT WEEK...AS A SERIES OF QUICK
MOVING STORM SYSTEMS AFFECTS THE AREA.
&&
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
COLD FRONT MOVING INTO OUR WESTERNMOST ZONES PRIOR TO MIDNIGHT
WILL SHIFT SE INTO THE ATLANTIC BY 1-2 AM. VERY WARM SW FLOW AHEAD
OF THE FRONT WILL HOLD TEMPS UP WELL INTO THE 60S...BUT A DRAMATIC
DROP IN TEMPS WILL OCCUR IN WAKE OF THE FRONT THROUGH THE NIGHT.
AN INDICATION OF THIS IS SHOWN BY AN 11 DEGREE DROP IN TEMPS
BEHIND THE FRONT AT KMCN SINCE SUNSET. EVEN COOLER AIR IS FOUND
JUST EAST OF THE APPALACHIANS WHERE SUB-50 DEGREE AIR IS BEGINNING
TO PENETRATES AS OF LATE THIS EVENING. AS THE COOLER AIR WORKS ITS
WAY INTO OUR CWFA THROUGH THE NIGHT...READINGS BY MORNING WILL BE
DOWN INTO THE LOWER AND MIDDLE 40S FAR INLAND AND INTO THE UPPER
40S AND LOWER 50S CLOSER TO THE COAST. THIS IS ABOUT 20-30 DEGREES
LOWER THAN TEMPS WERE EARLIER.
THE COMBINATION OF VERY WEAK SHORT WAVES MOVING EASTWARD WITHIN HE
FAST MOVING FLOW ALOFT AND ISENTROPIC LIFT IN WAKE OF THE COLD
FRONT WILL LEAD TO ANOTHER ROUND OF WET WEATHER FOR THE EASTERN
THIRD OF HALF OF THE FORECAST AREA AFTER MIDNIGHT. THE GREATEST
PROBABILITIES WILL OCCUR OVER SE GA....WHERE CHANCE TO LIKELY POPS
WILL OCCUR. CHANCE POPS WILL BE FORECAST OVER COASTAL SC...WHILE
THE NW HALF OF THE REGION WILL HAVE SLIGHT CHANCE PROBABILITIES
OVERNIGHT. RAINFALL AMOUNTS WILL BE MAINLY LESS THAN 1/4
INCH...BUT A FEW HOURS OF STEADY RAINS WILL REDEVELOP.
&&
.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM FRIDAY/...
THE COLD FRONT WILL PUSH OFFSHORE EARLY THURSDAY...WITH COOLER AND
DRIER AIR SHIFTING INTO THE REGION. LINGERING DEEP MOISTURE COULD
REMAIN ALONG THE COASTLINE DURING THE MORNING...AND HAVE
MAINTAINED SHOWER CHANCES IN THE 20 PERCENT TO LOWER 30 PERCENT
RANGE THURSDAY MORNING FOR THE EASTERN HALF OF THE FORECAST
AREA...BEST CHANCES CLOSEST TO THE COAST. STRONG COLD ADVECTION
BEHIND THE FRONT WILL SUPPRESS MAX TEMPERATURES IN THE MID 50S
DESPITE GRADUALLY CLEARING SKIES. AFTER THE MORNING HOURS...EXPECT
RAIN FREE CONDITIONS TO PREVAIL ON THURSDAY.
&&
.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
MEDIUM RANGE GUIDANCE IS IN DECENT AGREEMENT WITH OVERALL SYNOPTIC
FEATURES THROUGH THE EXTENDED PERIODS THIS AFTERNOON...BUT GIVEN THE
VERY PROGRESSIVE WEST-EAST FLOW ACROSS THE UNITED STATES CONFIDENCE
IS BELOW NORMAL.
HIGH PRESSURE IS EXPECTED TO BRIEFLY BUILD BACK INTO THE REGION
THURSDAY NIGHT AND FRIDAY RESULTING IN RAIN FREE WEATHER ACROSS THE
AREA. STILL A BIT OF UNCERTAINTY REGARDING THE AMOUNT OF HIGH CLOUD
THAT WILL BE PRESENT ACROSS THE FORECAST AREA THURSDAY NIGHT...SO
WILL HOLD OFF ON A FREEZE WATCH FOR NOW AND CONTINUE THE SCATTERED
FROST MENTION IN THE GRIDS.
GUIDANCE IS THEN IN GOOD AGREEMENT SHOWING A COASTAL TROUGH
AND DEVELOPING AREA OF LOW PRESSURE OFF THE GEORGIA AND CAROLINA
COAST OVER THE WEEKEND...WITH INCREASING MOISTURE/ISENTROPIC ASCENT
ACROSS THE FORECAST AREA. WILL NEED TO WATCH ONSET OF RAINFALL
FRIDAY NIGHT AND EARLY SATURDAY GIVEN SURFACE HIGH PRESSURE WEDGING
IN PLACE...AS THERE IS SOME POTENTIAL FOR FREEZING RAIN ACROSS FAR
INTERIOR PORTIONS OF THE FORECAST AREA. GIVEN WARM GROUND
TEMPERATURES AND MARGINAL WET BULB TEMPERATURES...WILL KEEP ALL
PRECIP MENTION IN THE FORM OF RAIN AT THIS TIME. OTHERWISE HAVE
INCREASED POPS SATURDAY THROUGH SUNDAY...WITH HIGHEST RAIN
PROBABILITIES EXPECTED SATURDAY AND SATURDAY NIGHT.
THE COASTAL TROUGH OR AREA OF LOW PRESSURE OFF THE SOUTHEAST COAST
IS EXPECTED TO LIFT NORTHEAST AND AWAY FROM THE REGION SUNDAY NIGHT
AND MONDAY...ALLOWING FOR WEAK HIGH PRESSURE TO BUILD BACK INTO THE
AREA. WILL KEEP THE FORECAST RAIN FREE FOR NOW...BUT NOT TOO EXCITED
ABOUT A WHOLE BUNCH OF CLEARING GIVEN LIGHT GRADIENT IN PLACE...WITH
THE INLAND WEDGE POSSIBLY HOLDING THROUGH THE PERIOD.
GUIDANCE DIFFERS A BIT ON HANDLING OF THE NEXT SYSTEM APPROACHING
THE SOUTHEAST STATES...BUT GENERALLY SHOWS A SHORTWAVE TROUGH
AMPLIFYING AS IT TRACKS OVER THE SOUTHERN PLAINS AND LOWER
MISSISSIPPI VALLEY. THIS SHOULD RESULT IN GULF MOISTURE GETTING
PULLED NORTHWARD IN ADVANCE OF THE STRENGTHENING FEATURE...WITH SOME
SURFACE BOUNDARY LIFTING NORTHWARD TOWARD THE FORECAST AREA. FOR NOW
GIVEN THE HIGH DEGREE OF UNCERTAINTY THIS FAR OUT...WILL CARRY
CHANCE/SLIGHT CHANCE POPS MONDAY NIGHT THROUGH WEDNESDAY.
&&
.AVIATION /06Z THURSDAY THROUGH MONDAY/...
MUCH DRIER AIR IS CURRENTLY FILTERING INTO BOTH TAF SITES BEHIND A
COLD FRONT WITH CEILINGS LIFTING ACCORDINGLY. SOME LIGHT
PRECIPITATION ALONG THE FRONTAL BOUNDARY WILL PROBABLY AFFECT SAV
FOR A FEW HOURS WITH CEILINGS RESTRICTED INTO THE MVFR CATEGORY
OCCASIONALLY. FOR THE MOST PART ALL LOW CLOUDS AND PRECIP SHOULD
BE PUSHING OFF TO THE EAST BY 09Z WITH VFR CONDITIONS FOR THE
REMAINDER OF THE PERIOD.
EXTENDED AVIATION OUTLOOK...PERIODS OF IFR OR LOWER CONDITIONS
POSSIBLE FRIDAY NIGHT THROUGH MONDAY.
&&
.MARINE...
COLD FRONT IS EXPECTED TO REACH THE NEAR SHORE WATERS
06-07Z...CLEARING THE MARINE ZONES BY 10-11Z THURSDAY. BUT DESPITE
THE DEVELOPING COLD AIR ADVECTION IN WAKE OF THE FRONT...WINDS
AND SEAS WILL REMAIN BELOW SCA CRITERIA FOR ALL BUT AMZ350 AND
AMZ374. WINDS WILL REACH AS HIGH AS 20 OR 25 KT THROUGH THE
NIGHT...WITH SEAS UP TO 4 TO 6 FT WITHIN 20 NM OF THE COAST...BUT
AS HIGH AS 7 FT ACROSS THE OUTER GA WATERS. EVEN CHARLESTON HARBOR
WILL EXPERIENCE 1 TO 2 FOOT WAVES.
ADDITIONALLY...WE HAVE SEEN REPORTS FROM COASTAL AREAS OF
VISIBILITIES DOWN TO 3-5 MILES AND THAT ALONG WITH LOW STRATUS
DECKS UNDER 1K FT HAS RESULTED IN THE MENTION OF PATCHY FOG ACROSS
OUR SC WATERS. WITH THE PASSAGE OF THE COLD FRONT OVERNIGHT
HOWEVER...ANY REDUCTION IN VISIBILITY WILL COME TO AN END.
WEAKENING COLD AIR ADVECTION AND THE OFFSHORE FETCH ON THURSDAY
WILL ALLOW FOR ONLY SCA CONDITIONS ACROSS AMZ374.
THURSDAY NIGHT THROUGH MONDAY...HIGH PRESSURE WILL BUILD BACK INTO
THE REGION THURSDAY NIGHT AND FRIDAY...BEFORE COASTAL TROUGHING
BEGINS TO SET UP OFF THE SOUTHERN SOUTH CAROLINA AND SOUTHEAST
GEORGIA COAST FRIDAY NIGHT THROUGH SUNDAY. HIGH PRESSURE IS THEN
EXPECTED TO BUILD BACK INTO THE REGION SUNDAY NIGHT AND MONDAY.
EXPECT A RATHER TIGHT PRESSURE GRADIENT TO DEVELOP DUE TO INLAND
HIGH PRESSURE AND COASTAL TROUGHING OFF THE SOUTHEAST COAST FRIDAY
NIGHT THROUGH SUNDAY...AND SMALL CRAFT ADVISORIES MAY EVENTUALLY BE
NEEDED FOR PORTIONS OF THE WATERS. OTHERWISE...WINDS AND SEAS SHOULD
REMAIN BELOW SMALL CRAFT THRESHOLDS.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 7 PM EST THIS EVENING FOR AMZ374.
SMALL CRAFT ADVISORY UNTIL 5 AM EST EARLY THIS MORNING FOR
AMZ350.
&&
$$
