000
FXUS62 KCHS 241150
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
650 AM EST TUE NOV 24 2009

.SYNOPSIS...
A WEDGE OF HIGH PRES OVER THE INLAND CAROLINAS WILL SLOWLY WEAKEN
THROUGH TONIGHT. AN AREA OF LOW PRES WILL LIFT NE...WELL OFF THE
COAST OF THE SOUTHEAST UNITED STATES WED AND WED NIGHT. A DRY COLD
FRONT WILL MOVE THROUGH THE AREA THU...WITH HIGH PRES THEN BUILDING
INTO THE REGION. ANOTHER STORM SYSTEM MAY APPROACH THE REGION
EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
SURFACE HIGH PRES OVER THE SE STATES THIS MORNING. A WARM
SUBSIDENCE LAYER ALOFT WITH A COOL AND MOIST AIR MASS KEEPING A
WEDGED LOW LEVEL ATMOSPHERE IN PLACE. THE MAIN BAROCLINIC AXIS
EXTENDS FROM THE N CENTRAL GULF OF MEXICO ENE TO THE GULF OF
MEXICO AND WARM AIR ADVECTION CLOUDS ALOFT SHOULD CONTINUE TO
STREAM OVER OUR THE SE HALF OF OUR FORECAST AREA TODAY AS UPPER
FLOW WAITS UNTIL LATER TODAY TO BACK MORE SHARPLY. OUR MAIN
FORECAST PROBLEMS TODAY ARE FOG POTENTIAL AROUND SUNRISE AND
EROSION OF STRATUS TODAY FROM BOTH A TEMPORAL AND SPACIAL
STANDPOINT.

VSBYS HAVE ACTUALLY INCREASED OVERNIGHT IN MANY AREAS AS DRIZZLE
HAS ABATED AND LAYERED CLOUDS OVER THE STRATUS DECK HAS CAUSED
AT LEAST A TEMPORARY LIFTING TREND IN CLOUD BASES. GIVEN THE COMPLEX
WARM AND MOIST AIR ADVECTION PROCESSES GOING ON ABOVE THE WEDGE...
WE THINK MOST AREAS WILL AVOID DENSE FOG PROBLEMS THIS MORNING WITH
AREAS OF FOG AND CONTINUED PATCHY DRIZZLE AT TIMES. WE WILL INITIALIZE
ZONES WITH AREAS OF FOG AND MONITOR TRENDS THROUGH MID MORNING.

LOW CLOUDS UNDER THE WEDGE INVERSION SHOULD PERSIST BUT THERE APPEARS
TO BE A CHANCE THAT SOME AREAS EVEN SCATTER OUT LOWER CLOUDS AT
TIMES THIS AFTERNOON IN SE GEORGIA AND COASTAL SOUTH CAROLINA.
EVEN IF THIS DOES LOCALLY OCCUR...LAYERED CLOUDS IN THE MID AND
HIGH LEVELS KEEP ANY REAL BREAKS FROM OCCURRING. OVERALL...WEDGE
AIR MASS AND SLOW IMPROVEMENT WITH HIGHS A BIT BELOW GUIDANCE AND
STILL BELOW CLIMO VALUES.

&&

.SHORT TERM / WEDNESDAY THROUGH 6 AM WEDNESDAY/...
A SOUTHERN STREAM STORM SYSTEM IS EXPECTED TO LIFT ENE FROM THE
GULF OF MEXICO TOWARD THE NW QUARTER OF FLORIDA BY DAWN ON WED. WE
WILL KEEP PLENTY OF CLOUDS AROUND TONIGHT WITH LOWS MAINLY 50-55
DEGREES AND ONLY PATCHY FOG ANTICIPATED. THE TIMING OF THE N FRINGE
OF THE PRECIPITATION SHIELD IS HANDLED DIFFERENTLY BY VARIOUS
MODEL SUITES ON THE 00Z RUN. LIGHT NON-CONVECTIVE RAINS MAY RUN
OUT AHEAD OF MODEL TIMING AFTER MIDNIGHT BUT ANY MEASURABLE
AMOUNTS SHOULD BE CONFINED TO NEAR-COASTAL AREAS OF SOUTHERN SOUTH
CAROLINA LATE. WE DID EXTEND SLIGHT CHANCES A BIT FURTHER N LATE
IN THE TONIGHT PERIOD. S OF SAVANNAH...THERE CERTAINLY LOOKS LIKE
A CHANCE OF SHOWERS DEVELOPING PRIOR TO SUNRISE.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
MEDIUM RANGE GUIDANCE IS IN GOOD AGREEMENT THROUGHOUT THE EXTENDED 
PERIODS THIS MORNING. THE ONE EXCEPTION REVOLVES AROUND THE HANDLING 
OF A WAVE OF LOW PRESSURE AND THE AMOUNT OF OVERRUNNING MOISTURE 
THAT WILL ADVECT INTO THE SOUTH CAROLINA AND GEORGIA LOW COUNTRY ON 
WEDNESDAY. GUIDANCE SUGGESTS THAT DEEP MOISTURE WILL TRANSLATE OVER 
THE FORECAST AREA WEDNESDAY...BUT DISAGREE ON STRENGTH OF THE 
OVERRUNNING PRECIPITATION THAT MAY DEVELOP. THE NAM AND CANADIAN 
MODELS KEEP THE FORECAST AREA VIRTUALLY RAIN FREE...WITH THE GFS 
SHOWING BETWEEN 0.50 AND 1.00 INCHES OF RAIN SLIDING ACROSS THE 
REGION. THE ECMWF APPEARS TO BE A GOOD COMPROMISE BETWEEN THE TWO 
EXTREMES...AND WILL GENERALLY FOLLOW THIS SOLUTION FOR THE WEDNESDAY 
FORECAST. THEREFORE...HAVE INCREASED POPS INTO THE CHANCE RANGE 
ACROSS THE EASTERN HALF OF THE FORECAST AREA...WITH SLIGHT CHANCE 
POPS ACROSS WESTERN AREAS WHERE THE MOISTURE WON/T BE QUITE AS DEEP.

GUIDANCE HAS COME INTO GOOD AGREEMENT SHIFTING THE DEEP MOISTURE 
NORTHEAST AND OUT OF THE FORECAST AREA WEDNESDAY EVENING...SO WILL 
REMOVE POPS FROM THE FORECAST HERE. A MOISTURE STARVED COLD FRONT 
WILL MOVE THROUGH THE REGION THURSDAY...FOLLOWED BY COLD HIGH 
PRESSURE BUILDING BACK INTO THE REGION FOR THE TAIL END OF THE WORK 
WEEK AND OVER THE UPCOMING WEEKEND. BIGGEST FORECAST CONCERN IN THE 
THURSDAY THROUGH SUNDAY TIME FRAME REVOLVES AROUND OVERNIGHT LOW 
TEMPERATURES FRIDAY NIGHT AND SATURDAY NIGHT WITH THE COLDEST AIR 
MASS OF THE SEASON SETTLING INTO THE AREA. PROBABILITIES FOR 
FROST/FREEZE CONDITIONS CONTINUE TO LOOK FAIRLY GOOD...SO WILL 
CONTINUE TO MENTION THIS IN THE HAZARDOUS WEATHER OUTLOOK.

HIGH PRESSURE WILL SLIDE EASTWARD INTO THE ATLANTIC SUNDAY NIGHT AND 
MONDAY...ALLOWING RETURN FLOW TO SET UP ACROSS THE FORECAST AREA. 
GUIDANCE SHOWS DEEP MOISTURE QUICKLY INCREASING FROM WEST TO EAST 
ACROSS THE FORECAST AREA MONDAY DUE TO THE STRONG UPPER LEVEL JET 
PUSHING ACROSS THE SOUTHERN UNITED STATES FROM THE PACIFIC. WILL 
KEEP THE FORECAST RAIN FREE SUNDAY NIGHT AND INTRODUCE SLIGHT CHANCE 
POPS FOR MONDAY.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
KCHS...AT TAF RELEASE TIME...LIGHT DRIZZLE FALLING WITH STRATUS
CIGS A BIT RAGGED AT 500 FT AND VSBY AROUND 5SM. WINDS ON THIS
MORNINGS SOUNDING WERE VERY LIGHT AND WITH STRATUS AND DRIZZLE
BLANKETING THE LOW COUNTRY... ANOTHER DAY OF VERY SLOW
IMPROVEMENTS IS EXPECTED. MODELS A BIT UNREALISTIC IN FORECAST
SOUNDINGS BY MIDDAY WITH LOW LEVEL TEMPS TOO WARM AND NOT ENOUGH
RESPECT TO ONGOING WEDGE SITUATION. WE STILL REMAINED PERSISTENCE
IN ALLOWING CIGS GOING MVFR DURING THE AFTERNOON BUT UNABLE TO BUY
INTO LOWER CLOUDS SCATTERING OUT. TONIGHT...WE INTRODUCED LOW-END
MVFR CIGS WITH THE WEAK WEDGE PERSISTING. WOULD NOT BE SURPRISED
TO SEE IFR CIGS AGAIN TONIGHT. A LOT DEPENDS ON WHAT TRANSPIRES
WITH THE LOW CLOUD FIELDS THIS AFTERNOON.

KSAV...SIMILAR TO KCHS BUT INITIAL CONDITIONS CURRENTLY LOW END
MVFR. IFR CIGS SURROUNDING THE SAVANNAH AIRPORT ON ALL SIDES 
INCLUDING KSVN. TRICKY FORECAST GIVEN THE LACK OF STABLE CIGS
AND VSBYS OVERNIGHT BUT WE PLAYED TODAY ON THE PESSIMISTIC SIDE
WITH IFR CIGS LIFTING TO MVFR THIS AFTERNOON. TONIGHT...STRATUS
POSSIBLE AGAIN BUT CONFIDENCE LOW. SLIGHT CHANCE OF LIGHT RAIN
TOWARD SUNRISE ON WED. THESE POSSIBILITIES WILL BE INVESTIGATED
ON LATER TAF RELEASES TODAY.

EXTENDED AVIATION OUTLOOK...MVFR/IFR CIGS ARE LIKELY WED INTO WED
EVENING. OCNL MVFR OR IFR VSBYS POSSIBLE AS WELL. VFR CONDITIONS
ARE EXPECTED LATE WED NIGHT THROUGH SAT.

&&

.MARINE...
COOL NEAR SHORE WATERS SHOULD ANCHOR A LIGHT N TO NE FLOW THROUGH
TONIGHT...ESPECIALLY WITH THE WEDGE HIGH NOT LIKELY SHIFT MUCH.
THERE IS A SOLID 2 FT SWELL WATER OFF THE COAST AND THIS ALSO
WILL REMAIN FAIRLY CONSISTENT. THUS WITH THE LIGHT GRADIENT...
SPEEDS WILL MAINLY BE BELOW 15 KT AND SEAS 2-3 FT THROUGH
TONIGHT.

A WAVE OF LOW PRESSURE WILL PASS BY WELL TO THE EAST OF THE COASTAL 
WATERS WEDNESDAY AND WEDNESDAY NIGHT. A COLD FRONT WILL MOVE THROUGH 
THE WATERS THURSDAY AFTERNOON...WITH HIGH PRESSURE THEN BUILDING 
BACK INTO THE REGION THROUGH SATURDAY. 

WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT LEVELS 
THROUGH THURSDAY. EXPECT A PRETTY DECENT SURGE IN STRONG COLD AIR 
ADVECTION THURSDAY NIGHT...AND SMALL CRAFT ADVISORIES APPEAR LIKELY 
FOR ALL WATERS INCLUDING CHARLESTON HARBOR. SMALL CRAFT CONDITIONS 
LOOK TO LINGER INTO FRIDAY...WITH WINDS AND SEAS THEN SUBSIDING 
BELOW SMALL CRAFT THRESHOLDS AS HIGH PRESSURE BUILD IN FOR THE 
WEEKEND.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...NONE.

&&

$$