FXUS62 KCHS 300140
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
840 PM EST SUN NOV 29 2009
.SYNOPSIS...
HIGH PRESSURE WILL SHIFT OFF THE COAST TODAY THROUGH MONDAY.
A COLD FRONT WILL MOVE INTO THE AREA FROM THE NORTHWEST MONDAY
NIGHT...THEN STALL SOUTH OF THE AREA ON TUESDAY. A GULF LOW
PRESSURE SYSTEM WILL DEVELOP TUESDAY AND TUESDAY NIGHT...THEN
TRACK NORTHEASTWARD ALONG THE APPALACHIANS WEDNESDAY AND
WEDNESDAY NIGHT. A COLD FRONT WILL SWING THROUGH THE AREA
THURSDAY...FOLLOWED BY HIGH PRESSURE FOR THE END OF THE WEEK
THROUGH NEXT WEEKEND.
&&
.NEAR TERM /THROUGH MONDAY/...
TEMPS HAVE FALLEN FAST OVER THE INTERIOR THIS EVENING...WITH CHS
SITTING 6 DEGREES BELOW GUIDANCE AT 00Z. I HAD TO ADJUST DOWN THE
TEMPS THIS EVENING BASED ON THESE TRENDS...BUT WITH HIGH CLOUDS
EXPECTED TO HANG AROUND ALL NIGHT AND AT LEAST LIGHT WINDS...WE
MAY NOT GET A WHOLE LOT COOLER THAN WE ARE NOW. I ADJUSTED THE MIN
TEMPS DOWN 1 DEGREE ACROSS THE BOARD...WHICH MAKES FOR ESSENTIALLY
NO CHANGES IN THE ZONES. I WILL HAVE TO UPDATE THE TABULAR
GUIDANCE PRODUCTS...BUT NO OTHER UPDATES ARE NECESSARY.
&&
.SHORT TERM /MONDAY NIGHT THROUGH 6 PM MONDAY/...
A POTENT NORTHERN STREAM SHORTWAVE MOVING ACROSS THE UPPER
MISSISSIPPI VALLEY WILL DIG ACROSS THE OHIO AND TENNESSEE VALLEYS
MONDAY. ITS ATTENDANT COLD FRONT WILL APPROACH FROM THE NORTHWEST
AND PUSH INTO NORTHWEST PORTIONS OF OUR FORECAST AREA EARLY IN THE
EVENING. THE LACK OF DEEP MOISTURE AHEAD OF THE FRONT PRECLUDES
RAIN CHANCES UNTIL LATE IN THE DAY ACROSS FAR INLAND AREAS AND
THUS WILL LIMIT POPS TO SLIGHT CHANCE...MAINLY WEST OF A LINE FROM
MONCKS CORNER TO RIDGEVILLE TO HAMPTON TO SYLVANIA TO METTER. HIGHS
WILL REACH INTO THE LOWER 70S EXCEPT ALONG THE COAST WHERE
A WEAK RESULTANT SEA BREEZE SHOULD KEEP THE BEACHES A BIT COOLER.
&&
.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
MEDIUM RANGE GUIDANCE IS IN FAIRLY GOOD AGREEMENT WITH OVERALL
SYNOPTIC PATTERN...WITH SOME MINOR TIMING DIFFERENCES NOTED WITH
RESPECT TO A POTENT STORM SYSTEM AFFECTING THE SOUTHEAST UNITED
STATES DURING THE MIDDLE OF THE WORK WEEK.
A COLD FRONT WILL PUSH THROUGH THE REGION MONDAY EVENING...WITH WEAK
HIGH PRESSURE THEN BUILDING BACK INTO THE AREA FOR TUESDAY. WITH
SOME ENTRANCE REGION FORCING FROM A 160+ KT H25 JET OVERSPREADING
THE AREA AND 1000-500 MB CONDENSATION PRESSURE DEFICITS DROPPING
INTO THE 20-30 MB RANGE...FEEL THAT SOME SHOWER ACTIVITY WILL IMPACT
THE FORECAST AREA AND WILL CARRY SLIGHT CHANCE/LOW CHANCE POPS
MONDAY EVENING. RAIN FREE WEATHER IS THEN EXPECTED FOR TUESDAY.
OPERATIONAL GUIDANCE CONTINUES TO SHOW A STORM SYSTEM DEVELOPING IN
THE GULF OF MEXICO TUESDAY AND TUESDAY NIGHT...THEN LIFTING
NORTHEASTWARD GENERALLY NEAR OR ALONG THE APPALACHIANS WEDNESDAY AND
WEDNESDAY NIGHT. TIMING DIFFERENCES ARE NOTED AS EARLY AS TUESDAY
NIGHT...WITH THE NAM SHOWING A DRY NIGHT...THE GFS SHOWING RAINFALL
BREAKING OUT SHORTLY AFTER 00Z WEDNESDAY...AND THE CANADIAN/ECMWF
SOLUTIONS SOMEWHERE IN BETWEEN. GIVEN THE TYPICAL BIAS OF THE GFS IN
EJECTING SOUTHWEST UPPER LOWS TO QUICKLY...EXPECT THAT THE OTHER
MODEL SOLUTIONS HAVE A BETTER HANDLE ON HOW THE PATTERN WILL
EVOLVE...AND WILL TREND THE FORECAST IN THIS DIRECTION WITH THE
AFTERNOON PACKAGE. AS A RESULT...HAVE LOWERED POPS INTO THE SLIGHT
CHANCE/LOW CHANCE RANGE TUESDAY EVENING ACROSS THE SOUTHERN 2/3RDS
OF THE FORECAST AREA...WITH RAIN FREE CONDITIONS ACROSS THE NORTH.
AFTER MIDNIGHT TUESDAY...WILL KEEP POPS IN THE LIKELY RANGE ACROSS
THE FAR SOUTH...WITH SLIGHT CHANCE OR CHANCE POPS ELSEWHERE.
THINGS BECOME MUCH MORE INTERESTING WEDNESDAY AND WEDNESDAY
NIGHT...AS THE FORECAST AREA WARM SECTORS WITH THE POTENT STORM
SYSTEM TRACKING BY TO THE WEST OF THE REGION. HAVE CARRIED LIKELY
POPS THROUGH THIS TIME FRAME...AS RAIN PROBABILITIES APPEAR HIGH BUT
TIMING DIFFERENCES IN THE MODELS PRECLUDE GOING WITH CATEGORICAL
POPS AT THIS TIME. ASIDE FROM RAINFALL POTENTIAL...SEVERE WEATHER
PROBABILITIES APPEAR TO BE A FAIRLY DECENT PROBABILITY AS DEPICTED
BY GUIDANCE AT THIS TIME. THE FORECAST AREA WILL COME UNDER THE
INFLUENCE OF ENTRANCE REGION FORCING FROM A 140+ KNOT H25
JET...STRONG QG FORCING FROM A NEGATIVELY TILTING UPPER LEVEL
TROUGH...MID LEVEL LAPSE RATES DROPPING TO BETWEEN 6.5 AND 7 C/KM
AND H85 WINDS STRENGTHENING TO BETWEEN 70 AND 80 KNOTS LATE
WEDNESDAY AFTERNOON AND WEDNESDAY NIGHT. WITH THE FORECAST AREA
SOLIDLY WARM SECTORED AND SURFACE DEWPOINTS CLIMBING INTO THE MIDDLE
AND UPPER 60S...EXPECT SOME WEAK SURFACE BASED INSTABILITY WILL BE
REALIZED ACROSS THE REGION EVEN DURING THE OVERNIGHT HOURS.
THEREFORE...WILL ADD MENTION OF THE POTENTIAL FOR SEVERE
THUNDERSTORMS INTO THE HAZARDOUS WEATHER OUTLOOK...WITH THE PRIMARY
HAZARDS EXPECTED TO BE DAMAGING STRAIGHT LINE WINDS...MARGINALLY
SEVERE HAIL AND POSSIBLY TORNADOES.
A COLD FRONT WILL PUSH THROUGH THE REGION LATE WEDNESDAY NIGHT OR
EARLY THURSDAY MORNING AS THE STORM SYSTEM CONTINUES TO TRACK
NORTHEASTWARD AND AWAY FROM THE AREA. HIGH PRESSURE WILL THEN BUILD
BACK INTO THE AREA FOR THE END OF THE WORK WEEK AND OVER THE
UPCOMING WEEKEND. WILL KEEP THE FORECAST RAIN FREE THURSDAY THROUGH
SUNDAY.
&&
.AVIATION /02Z MONDAY THROUGH FRIDAY/...
VFR CONDITIONS WILL PREVAIL THROUGH MONDAY AT BOTH CHS AND SAV
TERMINALS. SOUTHWEST WINDS WILL BE LIGHT OVERNIGHT ...THEN
INCREASING TO AROUND 10 KNOTS BY 15Z MONDAY AS A COLD FRONT
APPROACHES THE SOUTHEAST. THERE COULD BE A FEW STRONGER GUSTS AS
WELL. I HAVE GRADUALLY LOWERED THE CEILING BY LATE MONDAY...BUT
STILL SHOW VFR OR BETTER. I THINK MOST OF THE LOWER CIGS/RWS WILL
HOLD OFF UNTIL LATE.
EXTENDED AVIATION OUTLOOK...VFR CONDITIONS ARE EXPECTED THROUGH
TUESDAY NIGHT. MVFR OR LOWER CIGS/VSBYS WILL BE POSSIBLE WEDNESDAY
THROUGH THURSDAY MORNING AS A POTENT STORM SYSTEM MOVES THROUGH THE
AREA.
&&
.MARINE...
TONIGHT...CURRENT FORECAST ON TARGET. WINDS ARE LIGHT AND SEAS ARE
QUITE LOW THIS EVENING...BUT 00Z SOUNDING SHOWED 24 KNOT WINDS AT
1K FEET...SO SOME OF THAT SHOULD MIX DOWN OVERNIGHT AND
INCREASING WIND TREND SHOWN IN THE FORECAST LOOKS REASONABLE.
MONDAY...WINDS WILL INCREASE FURTHER ON MONDAY AS THE GRADIENT
TIGHTENS WITH THE APPROACH OF A COLD FRONT. BOTH WINDS AND SEAS
WILL REMAIN BELOW SMALL CRAFT ADVISORY THRESHOLDS...HOWEVER SPEEDS
AS HIGH AS 15-20 KT CAN BE EXPECTED...WITH THE HIGHEST WINDS AGAIN
FOUND NORTH OF EDISTO BEACH. EXPECT SEAS MAINLY 2-4 FT...ALTHOUGH
SEAS MAY BUILD UP TO 5 FT OVER THE OUTER GA WATERS AND NORTHERN SC
WATERS LATE UNDER THE STRENGTHENING SW FLOW.
MONDAY NIGHT THROUGH FRIDAY...A COLD FRONT WILL TRACK THROUGH THE
WATERS MONDAY NIGHT...WITH HIGH PRESSURE THEN BRIEFLY BUILDING
OVER THE AREA ON TUESDAY. HIGH PRESSURE WILL QUICKLY LOSE ITS GRIP
ON THE MARINE AREA TUESDAY NIGHT AND WEDNESDAY...AS A STORM SYSTEM
DEVELOPS OVER THE GULF OF MEXICO AND TRACKS NORTHEASTWARD WEST OF
THE REGION. A COLD FRONT WILL THEN PUSH THROUGH THE AREA LATE
WEDNESDAY NIGHT OR EARLY THURSDAY MORNING...WITH HIGH PRESSURE
THEN BUILDING IN FOR THE END OF THE WORK WEEK.
COULD SEE SMALL CRAFT CONDITIONS ACROSS PORTIONS OF THE WATERS
MONDAY NIGHT INTO TUESDAY BEHIND THE COLD FRONT. THE BIGGER STORY
WILL BE THE POTENTIAL FOR GALE FORCE WINDS ACROSS ALL WATERS
WEDNESDAY AFTERNOON AND WEDNESDAY NIGHT AS THE POTENT STORM SYSTEM
TRACKS BY TO THE WEST OF THE AREA. GIVEN THE GOOD MODEL AGREEMENT
WITH RESPECT TO WIND SPEEDS...HAVE INCREASED WINDS INTO THE 25 TO 35
KNOT RANGE ACROSS MOST WATERS LATE WEDNESDAY AFTERNOON AND WEDNESDAY
NIGHT. IF GUIDANCE CONTINUES TO SHOW GOOD CONTINUITY KEEPING WINDS
WITHIN THIS RANGE...A GALE WATCH MAY EVENTUALLY BE NEEDED FOR ALL OR
PORTIONS OF THE WATERS. IMPROVING CONDITIONS AREA EXPECTED TO FOLLOW
FOR THURSDAY THROUGH FRIDAY...WITH CONDITIONS EXPECTED TO DROP BELOW
SMALL CRAFT THRESHOLDS THURSDAY NIGHT.
&&
.TIDES/COASTAL FLOODING...
A POTENT STORM SYSTEM WILL DEVELOP IN THE GULF OF MEXICO TUESDAY
NIGHT AND TRACK WEST OF THE REGION WEDNESDAY AND WEDNESDAY NIGHT.
GIVEN ALREADY HIGH PREDICTED ASTRONOMICAL TIDE LEVELS...THE
COMBINATION OF STRONG ONSHORE FLOW AND RAINFALL MAY VERY WELL RESULT
IN TIDAL DEPARTURES SIGNIFICANTLY HIGHER THAN PREDICTED VALUES. THE
GFS EXTRATROPICAL STORM SURGE GUIDANCE SHOWS TIDAL LEVELS REACHING
7.6 FEET IN CHARLESTON HARBOR AND 10.0 FEET AT FORT PULASKI DURING
THE WEDNESDAY MORNING HIGH TIDE. THESE LEVELS WOULD RESULT IN
COASTAL FLOODING CONCERNS ALONG THE SOUTH CAROLINA AND GEORGIA
COASTS WEDNESDAY MORNING...AND COASTAL FLOOD WATCHES OR ADVISORIES
MAY EVENTUALLY BE NEEDED AS DETAILS BECOME MORE CLEAR.
ASTRONOMICAL TIDES ARE EXPECTED TO REMAIN HIGH THURSDAY MORNING AS
WELL...AND COASTAL FLOODING ADVISORIES MAY BE NECESSARY FOR THE
SOUTH CAROLINA AND GEORGIA COAST.
IN ADDITION TO HIGH TIDES AND COASTAL FLOODING...STRONG WINDS OVER
THE ATLANTIC COASTAL WATERS MAY RESULT IN A NEED FOR A HIGH SURF
ADVISORY WITH BREAKERS BUILDING TO BETWEEN 5 AND 7 FEET IN THE SURF
ZONE. THIS COULD ALSO RESULT IN MODERATE TO SIGNIFICANT BEACH
EROSION ALONG THE SOUTH CAROLINA AND GEORGIA COAST.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...NONE.
&&
$$
