FXUS62 KGSP 142355
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
655 PM EST MON DEC 14 2009
.SYNOPSIS...
A COLD FRONT WILL MOVE EAST OF THE FORECAST AREA BY TUESDAY
AFTERNOON AS HIGH PRESSURE BEGINS TO BUILD IN FROM THE WEST. THIS
HIGH WILL THEN WEAKEN AND SLOWLY MOVE EASTWARD TOWARD THE MID
ATLANTIC THROUGH THE END OF THE WEEK.
&&
.NEAR TERM /THROUGH TUESDAY/...
WHILE MOST OF THE MTNS AND WESTERN NC FOOTHILLS ARE CLEAR ATTM...LOW
CLOUDS AND FOG PERSIST ACROSS THE PIEDMONT AND THE NC FOOTHILLS
SOUTH OF THE SOUTH MOUNTAINS...AS WELL AS THE NORTHEAST PART OF THE
UPSTATE. THE FOG IS THICK ENOUGH RIGHT AROUND THE CHARLOTTE METRO
AREA THAT I/M ENTERTAINING THOUGHTS OF REISSUING A DENSE FOG
ADVISORY. HOWEVER...NOW THAT A LITTLE SOUTHERLY FLOW HAS
DEVELOPED...THERE SHOULD BE ENOUGH MIXING TO KEEP THE FOG IN CHECK
FOR A FEW MORE HOURS. I DO ANTICIPATE THAT MOST OF THE AREA WILL
NEED AN ADVISORY LATER THIS EVENING. THE LLVL FLOW INCREASES TONIGHT
AS A NRN STREAM TROUGH BEGINS TO DIG ACROSS THE UPPER MID-WEST. THAT
COULD KEEP US A LITTLE MORE MIXED...BUT IT/S HARD TO IGNORE ALL THE
GUIDANCE WHICH HAS PRETTY MUCH EVERY SITE IN THE FA WITH DENSE FOG
OVERNIGHT.
WIDESPREAD SHOWER AND THUNDERSTORM ACTIVITY HAS DEVELOPED OVER THE
DEEP SOUTH IN RESPONSE TO THE INCREASING SLY FLOW. HOWEVER...THE NAM
MU CAPE BYPASSES ALL BUT THE EXTREME SRN PART OF THE FA TONIGHT AND
IS SOUTH OF THE ENTIRE FA TOMORROW. THIS MATCHES SPC/S DAY 1 AND 2
CONVECTIVE OUTLOOKS...AND I/M NOT CARRYING THUNDER IN ANY OF THE
ZONES. SHOWER ACTIVITY WILL INCREASE OVER NE GA AND SRN UPSTATE THIS
EVENING AND LAST MOST OF THE NIGHT...BUT THERE SHOULD BE A FAIRLY
TIGHT N-S ORIENTED PCPN GRADIENT OWING TO THE LOW AMPLITUDE OF THE
SYSTEM AND THE STABLE AND DRY MID LEVEL AIR IN PLACE OVER THE REGION.
THAT NRN STREAM TROUGH WILL SEND A COLD FRONT THROUGH THE FA ON TUE.
THE BEST COLD ADVECTION WILL LAG THE FRONT...AND WITH NORTHWESTERLY
DOWNSLOPE FLOW DEVELOPING...MAX TEMPS WILL RISE INTO THE M60S IN
MANY AREAS. TEMPS WOULD BE EVEN WARMER...BUT THERE WILL BE A DENSE
CI SHIELD TOMORROW IN THE ENTRANCE REGION OF A STRONG UPPER JET.
&&
.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
AS OF 230 PM MONDAY...OVERALL BIG PICTURE WEATHER PATTERN SHOWS HIGH
PRESSURE IN MO/IA TUESDAY EVENING BUILDING INTO THE WESTERN OHIO VLY
BY WEDNESDAY MORNING. JET STRUCTURE IN FAST FLOW ALOFT STILL ALIGNED
ACROSS OUR FORECAST AREA (FA) FOR PART OF TUESDAY NIGHT. TIME HEIGHT
CROSS SECTIONS CONTINUE TO SHOW LAYER OF HIGHER RH (IN THE HIGHER
LEVELS) FOR THE 1ST HALF OF THE NIGHT...GRADUALLY THINNING AS THE
NIGHT WEARS ON.
MEANWHILE EARLY TUESDAY EVENING NWLY UPSLOPE FLOW...IN A SEMI-MOIST
COLD AIR ADVECTION (CAA) PATTERN ALOFT... SHOULD YIELD A SHALLOW
COLUMN OF MOISTURE FROM 1000-850 MB UNTIL AROUND 06Z WED IN THE NC
MOUNTAINS. SOUNDINGS AND CROSS SECTIONS SHOW THIS NICELY...AS A
RESULT WE WILL HOLD ONTO SLGT CHANCE OF EVENING RAIN AND SNOW
SHOWERS THOSE LOCATIONS. THE THRUST OF CAA SHOULD ALSO YIELD GUSTY
WINDS TUESDAY EVENING IN THE NC MOUNTAINS. BASED ON SOUNDINGS HAVE
CAPPED GUSTS OFF IN THE 25 TO 30 KNOT RANGE FOR NOW.
OTHERWISE A SPRAWLING AREA OF HIGH PRESSURE WILL HOLD SWAY FROM THE
GREAT LAKES TO THE TN VALLEY AND CAROLINA/S WEDNESDAY AND THURSDAY...
WITH FAIR WX CONDITIONS ON TAP.
WE HAVE EDGED TEMPS BACK UP A FEW DEGREES NORTH AND EAST SECTIONS OF
OUR FA THURSDAY WITH ABUNDANT SUNSHINE AND THERMAL PROFILES MODIFYING.
&&
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
AS OF 230 PM MONDAY...THERE IS STILL VERY LITTLE TO HANG YOUR HAT ON
IN THE MEDIUM RANGE. THE ECMWF...GFS...AND GEM CONTINUE TO DIFFER
WITH REGARD TO THE TIMING...TRACK...AND EVOLUTION OF FEATURES SO THE
OVERALL FORECAST REMAINS FAIRLY LOW CONFIDENCE. I HAVE GENERALLY
FOLLOWED THE 12Z GFS FOR THE DETAILS OF THE FORECAST THOUGH IT IS
FASTER THAN THE OTHER AVAILABLE SOLUTIONS. THURSDAY NIGHT AND
FRIDAY...MID AND UPPER LEVEL FLOW WILL TURN FROM QUASI ZONAL TO SOME
DEGREE OF CYCLONIC AS A DEEP UPPER LOW ROTATES OVER EASTERN CANADA.
THIS SHOULD GENERALLY BE THE TREND THROUGH EARLY NEXT WEEK AS THE
MID AND UPPER LEVEL FLOW STRENGTHENS ON THE SOUTHERN PERIPHERY OF
THIS POLAR VORTEX AND THE OCCASIONAL VORT MAX MOVES SOUTHEASTWARD
ACROSS THE FA. AT THE SURFACE...MODEL SOLUTIONS CONTINUE TO TAKE THE
LOW OVER THE GULF OF MEXICO DUE EASTWARD ACROSS FLORIDA THROUGH
FRIDAY NIGHT...KEEPING ITS ASSOCIATED PRECIP SHIELD SOUTH AND EAST
OF THE WESTERN CAROLINAS. BEYOND THAT IT LOOKS LIKE A PROLONGED
PERIOD OF WESTERLY TO NORTHWESTERLY FLOW WITH PERIODS OF INCREASED
LOW LEVEL MOISTURE AND CAA BEGINNING IN THE SATURDAY NIGHT TIME
PERIOD. CANADIAN SURFACE HIGH MOVES INTO THE PLAINS EARLY MONDAY AND
SLOWLY BUILDS IN UNDER THE UPPER CONFLUENCE ON THE WEST SIDE OF THE
CLOSED UPPER LOW OVER THE GREAT LAKES. THOUGH THE UPSLOPE FLOW
DOESN/T LOOK GREAT AND MOISTURE COMES AND GOES...WILL CARRY SLIGHT
CHANCE POPS FAVORING THE MOUNTAINS SATURDAY NIGHT THROUGH SUNDAY
NIGHT. IF THERE IS SOMETHING THE MODELS DO SOMEWHAT AGREE ON IT IS
FALLING TEMPS THROUGH THE PERIOD. AT LEAST WEAK CAA WILL BE ONGOING
THROUGH MOST OF THE PERIOD AND LOW LEVEL THICKNESSES CONTINUOUSLY
FALL INTO THE 1260S BY MONDAY MORNING. TEMPS START OUT NEAR NORMAL
ON FRIDAY AND FALL TO A COUPLE OF CATEGORIES BELOW NORMAL BY MONDAY.
&&
.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
KCLT...ANOTHER ROUGH NIGHT FOR AVIATION...AS DENSE FOG IS QUITE
LIKELY AGAIN OVRNGT. WILL KEEP A TEMPO FOR LANDING MINIMUMS (1/2
MILE AND 200 FT)...THOUGH THE CIGS ARE 100 FEET. FOG AND STRATUS
SHOULD BEGIN TO LIFT BY LATE TUESDAY MORNING...AS A COLD FRONT
CROSSES THE NC PIEDMONT.
ELSEWHERE...KAVL REMAINS CLEAR THIS EVENING WITH A DOWN-VALLEY
WIND...WHILE STRATUS AND FOG APPEAR TO BE ADVECTING FROM THE
SOUTHWEST ACRS THE UPSTATE. IFR CONDITIONS ALREADY AT ALL SITES EAST
OF THE MTNS...WHILE KAVL WILL LIKELY GO IFR IN STRATUS AND POSSIBLY
FOG LATER TONIGHT. KHKY NEVER CLEARED OUT...AND VLIFR CONDITIONS ARE
EXPECTED THRU THE NIGHT. CONDITIONS WILL SLOWLY IMPROVE TUE MORNING
BEHIND A COLD FRONT...AND WILL LIKELY BE VFR BY MID AFTN.
OUTLOOK...UNRESTRICTED CIGS AND VSBYS ARE EXPECTED WED THROUGH FRI
IN THE DRY AIRMASS BEHIND A COLD FRONT. A WEAK SYSTEM APPROACHES
FROM THE W SAT...POSSIBLY BRINGING MVFR CIGS AND SOME RAIN OR SNOW
SHOWERS TO THE MTNS.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.
&&
$$
SYNOPSIS...BSH
NEAR TERM...MCAVOY
SHORT TERM...TS
LONG TERM...BSH
AVIATION...ARK/MCAVOY
