FXUS62 KCHS 232358
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
658 PM EST WED DEC 23 2009
.SYNOPSIS...
A HIGH PRESSURE WEDGE WILL STRENGTHEN INLAND THROUGH THURSDAY. A
COMPLEX STORM SYSTEM WILL IMPACT THE REGION THURSDAY NIGHT THROUGH
FRIDAY. HIGH PRESSURE WILL BUILD INTO THE REGION THIS WEEKEND AND
REMAIN THE DOMINANT WEATHER FEATURE THROUGH THE MIDDLE OF NEXT
WEEK.
&&
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
CLOUD COVER WILL FURTHER INCREASE OVERNIGHT...A COMBINATION OF
ONGOING HIGH CLOUDINESS WITH POSSIBLE LOW CLOUD DEVELOPMENT
BENEATH THE NOCTURNAL INVERSION. LOW TEMPERATURE GRADIENT WILL
REFLECT THE WEDGE PATTERN IN PLACE. COOLEST TEMPERATURES IN THE
UPPER 30S WILL BE ACROSS INLAND SOUTH CAROLINA...AND WARMEST
TEMPERATURES EXPECTED IN SOUTHEAST GEORGIA FURTHEST AWAY FROM THE
AXIS OF THE INLAND SURFACE RIDGE. DRY CONDITIONS WILL CONTINUE
TONIGHT.
&&
.SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
STRONG STORM SYSTEM DEVELOPING OVER THE SOUTHERN PLAINS WILL SHIFT
NORTHEAST INTO THE MISSISSIPPI VALLEY ON THURSDAY. TIMING DIFFERENCES
CONTINUE BETWEEN THE MODELS REGARDING THE LIFTING WARM FRONT AND
EROSION OF THE INLAND WEDGE DURING THE DAY. GFS HAS CONSISTENTLY
BEEN FASTER WITH THE WARM FRONT...WHILE NAM HOLDS ON TO THE WEDGE
PATTERN. AS A RESULT...SENSIBLE WEATHER DIFFERENCES FOR THURSDAY
ABOUND. PREFER TO REMAIN CONSERVATIVE IN THE TIMING OF THE WARM
FRONT AND LEAN TOWARD THE SLOWER NAM...WITH CURRENT THINKING BEING
THAT THE WEDGE WILL BE MORE RELUCTANT TO SHIFT.
AS A RESULT...HAVE DELAYED RAIN CHANCES OVER LAND UNTIL LATER
THURSDAY...KEEPING MOST PRECIPITATION CONFINED WITH THE BEST
MOISTURE CONVERGENCE ALONG THE COASTAL FRONT OFFSHORE.
ORIENTATION OF THE FRONT AND ASSOCIATED TROUGH COULD ALLOW SHOWERS
TO PUSH LOCALLY ONSHORE OF COASTAL COUNTIES DURING THE LATE
AFTERNOON HOURS...MAINLY THE CHARLESTON COUNTY COASTLINE. HAVE THUS
ALLOWED SLIGHT CHANCE POPS TO TOUCH THE SOUTH CAROLINA SHORE AFTER
18Z.
THE PRESSURE GRADIENT WITHIN THE INLAND SURFACE WEDGE WILL
TIGHTEN AS THE STRONG LOW SYSTEM PUSHES NORTH AND EAST. DESPITE
THICK CLOUD COVER DURING THE DAY...HIGH TEMPERATURES ON THURSDAY
WILL REACH THE LOWER TO MID 60S ACROSS MUCH OF THE FORECAST
AREA...A RESULT OF THE AMPLIFYING UPPER RIDGE AHEAD OF THE STORM
SYSTEM TO THE WEST.
&&
.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
PRETTY GOOD MODEL AGREEMENT THROUGH THE PERIOD...LEADING TO SLIGHTLY
HIGHER THAN NORMAL FORECAST CONFIDENCE...ALTHOUGH THERE ARE STILL
SOME DIFFERENCES WITH THE SYSTEM THU NIGHT THROUGH FRI NIGHT AND
ANOTHER SYSTEM FOR THE MIDDLE OF NEXT WEEK.
MODELS...INCLUDING THE SHORT RANGE ENSEMBLE /SREF/...SEEM TO HAVE
COME MORE INTO AGREEMENT REGARDING THE TIMING OF THE COASTAL
TROUGH/WARM FRONT PUSHING INLAND LATE THU NIGHT...ALTHOUGH THE
GFS/ECMWF REMAIN A BIT QUICKER. THIS PREFERRED SLOWER SOLUTION WILL
LIKELY KEEP INSTABILITY MINIMAL THROUGH THU NIGHT...ESPECIALLY OVER
LAND...BUT LOOKS DECENT ENOUGH FRI SO HAVE ADDED IN A SLIGHT CHANCE
OF TSTMS OVER LAND. TEMPERATURES THU NIGHT SHOULD RISE THROUGH THE
NIGHT...ESPECIALLY ALONG THE COAST...LEADING TO EARLY LOWS. HIGHS
FRI SHOULD PUSH INTO THE MID/UPPER 60S...WITH SOME LOWER 70S
POSSIBLE ACROSS SE GA.
A WEAK WAVE OF LOW PRESSURE FORMING JUST INLAND ALONG AN APPROACHING
COLD FRONT WILL MOVE NORTH AND EAST OF THE AREA FRI ALLOWING A
TRAILING COLD FRONT TO PUSH THROUGH LATE FRI. THUS...WILL HAVE POPS
INCREASING FROM THE SOUTHWEST THU NIGHT...THEN DIMINISHING FROM
SOUTHWEST TO NORTHEAST THROUGH THE DAY FRI. PRECIPITABLE WATER
VALUES ARE FORECAST TO INCREASE TO AROUND 1.5 INCHES FRI AND WE
COULD SEE 1 TO 2 INCHES OF RAIN...WITH LOCALLY HIGHER
AMOUNTS...WHICH IS SIMILAR TO WHAT HPC IS THINKING. SINCE 1-HR AND
3-HR FLASH FLOOD GUIDANCE IS AROUND 2.5-3.0 AND 3.0 TO 3.5
INCHES...RESPECTIVELY...DO NOT ANTICIPATE SIGNIFICANT FLOODING
ISSUES. HOWEVER...WE COULD POSSIBLY SEE SOME FLOODING ISSUES ALONG
THE SC COAST AROUND THE EARLY MORNING FRI HIGH TIDE...ESPECIALLY IF
HEAVY RAIN IS FALLING AT THAT TIME.
COLDER AND DRIER HIGH PRESSURE IS THEN EXPECTED TO MOVE OVER THE
AREA FOR THE WEEKEND...THEN PERSIST THROUGH AT LEAST TUE. ANOTHER
GULF LOW PRESSURE SYSTEM MAY BEGIN TO AFFECT THE AREA WED BUT WILL
MAINTAIN A DRY FORECAST ATTM DUE TO THE UNCERTAINTY THIS FAR OUT.
TEMPERATURES SHOULD REMAIN AT OR ABOVE NORMAL THROUGH FRI NIGHT...
THEN RETURN BACK TO NEAR OR BELOW NORMAL SAT THROUGH WED.
FREEZING TEMPERATURES ARE POSSIBLE BEGINNING SAT NIGHT WELL
INLAND...BECOMING MORE WIDESPREAD SUN NIGHT THROUGH TUE NIGHT...
ALTHOUGH PROBABLY NOT ENOUGH TO END THE GROWING SEASON ACROSS THE
ENTIRE FORECAST AREA.
&&
.AVIATION /00Z THURSDAY THROUGH MONDAY/...
MAIN CONCERN WILL BE THE DEVELOPMENT OF MVFR CIGS/VSBYS AT THE
SAV TERMINAL BY 14Z THURSDAY AS LOW CLOUDS PROGRESS FROM SOUTHWEST
TO NORTHEAST ALONG A DEVELOPING WARM FRONT. THERE IS POTENTIAL
FOR MVFR CIGS BRIEFLY BETWEEN 09Z TO 14Z AT SAV TONIGHT...BUT
CONFIDENCE REMAINS TOO LOW TO INCLUDE IN TAF. THE CHS TERMINAL IS
LIKELY TO SEE MVFR CIGS/VSBYS BY 00Z FRIDAY...BUT LOW CONFIDENCE
REMAINS IN TIMING OF EVENT NEAR THE END OF THE 00Z TAF
PERIOD...THUS HAVE OPTED TO KEEP OUT OF CURRENT TAF.
HIGH CLOUDS WILL CONTINUE TO DOMINATE SKY COVER OVERNIGHT. CLOUD
COVER IN COMBINATION WITH 15 KT LOW LVL WINDS SUGGEST LOW FOG
POTENTIAL OVERNIGHT. CLOUD COVER WILL INCREASE BY DAYBREAK
FRIDAY AS MOISTURE INCREASES OVER THE SOUTHEAST. LOW LVL WINDS
WILL INCREASE DURING THE AFTERNOON HOURS THURSDAY...LEADING TO GUSTS
UP TO 18 KTS AT BOTH TERMINALS. CLOUD COVER HOWEVER WILL LIKELY
LIMIT THE POTENTIAL OF HIGHER WIND GUSTS DURING THE AFTERNOON.
EXPECT CIGS TO CONTINUE LOWERING AT BOTH TERMINALS THROUGH 00Z
FRIDAY.
EXTENDED AVIATION OUTLOOK...PERIODS OF MVFR/IFR LIKELY IN RAIN
THURSDAY NIGHT THROUGH FRIDAY...POSSIBLY INTO FRIDAY NIGHT AT
KCHS. MAINLY VFR SATURDAY THROUGH EARLY NEXT WEEK.
&&
.MARINE...
NORTHEAST WINDS GENERALLY 10 TO 15 KT PREVAIL ACROSS THE MARINE
ZONES UNDER AN INLAND WEDGE PATTERN. WINDS AND SEAS WILL INCREASE
TONIGHT AND THURSDAY...AS THE GRADIENT TIGHTENS BETWEEN THE WEDGE
AND A COASTAL TROUGH OFFSHORE. MODELS ARE IN GOOD AGREEMENT THAT
SMALL CRAFT ADVISORY CONDITIONS WILL DEVELOP ACROSS MOST MARINE
ZONES THURSDAY AFTERNOON...WITH NORTHERN WATERS EXPERIENCING THE
EARLIEST AND STRONG SURGE CLOSEST TO THE TIGHTEST PINCHING OF THE
GRADIENT. HAVE RAISED AN ADVISORY FOR ALL WATERS EXCEPT THE
NEARSHORE GEORGIA ZONES...WHERE TIMING IS STILL UNCERTAIN.
THURSDAY NIGHT THROUGH MONDAY...A HIGH PRES WEDGE WILL PERSIST
INLAND THU NIGHT AS A COASTAL TROUGH OF LOW PRES/WARM FRONT TRIES TO
PUSH TOWARD THE COAST LATE. SMALL CRAFT ADVISORY WINDS/SEAS APPEAR
LIKELY THU NIGHT FOR ALL WATERS...AND EVEN A PERIOD OF GALES CANNOT
BE RULED OUT. WINDS AND SEAS WILL DIMINISH FRI AS THE TROUGH PUSHES
INLAND AND THE PRES GRAD RELAXES...BUT SEAS SHOULD REMAIN AOA 6 FT ACROSS
ALL WATERS EXCEPT POSSIBLY THE GA WATERS WITHIN 20 NM. A COLD FRONT
WILL CROSS THE WATERS EARLY FRI NIGHT...AND WITH THE LACK OF STRONG
COLD AIR ADVECTION/LOW-LEVEL WINDS...EXPECT IMPROVING MARINE
CONDITIONS THROUGH THE NIGHT. ALL NEARSHORE ADVISORIES SHOULD BE
DROPPED BY DAYBREAK SAT WITH THE WATERS BEYOND 20 NM SEEING ADVISORY
CONDITIONS END BY AFTERNOON. EARLY NEXT WEEK...ANOTHER SURGE OF W/NW
WINDS COULD AGAIN SUPPORT SMALL CRAFT ADVISORY CONDITIONS ESPECIALLY
BEYOND 20 NM.
&&
.TIDES/COASTAL FLOODING...
STRONG ONSHORE WINDS COULD PRODUCE HIGH SURF...ELEVATED TIDES...
SHALLOW COASTAL FLOODING AND BEACH EROSION THURSDAY NIGHT INTO
FRIDAY. THE BEST CHANCE OF SHALLOW COASTAL FLOODING APPEARS TO BE
EARLY MORNING FRIDAY WHEN THE TIDE LEVEL MAY APPROACH THE ADVISORY
CRITERIA OF 7.0 FEET MEAN LOWER LOW WATER IN CHS HARBOR...ESPECIALLY
IF THIS IS COINCIDENT WITH HEAVY RAINFALL.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 10 AM THURSDAY TO 1 PM EST FRIDAY
FOR AMZ330.
SMALL CRAFT ADVISORY FROM 1 PM THURSDAY TO 9 PM EST FRIDAY FOR
AMZ352.
SMALL CRAFT ADVISORY FROM 10 AM THURSDAY TO 5 AM EST SATURDAY
FOR AMZ350.
SMALL CRAFT ADVISORY FROM 10 AM THURSDAY TO NOON EST SATURDAY
FOR AMZ374.
&&
$$
