FXUS62 KGSP 150506
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1206 AM EST TUE DEC 15 2009
.SYNOPSIS...
STRONG HIGH PRESSURE WILL BUILD IN FROM THE MISSISSIPPI VALLEY
TODAY...THEN GRADUALLY WEAKEN INTO THE SECOND HALF OF THE WEEK. LOW
PRESSURE WILL DEVELOP OVER THE GULF LATE IN THE WEEK AND CROSS
FLORIDA IN THE WEEKEND.
&&
.NEAR TERM /THROUGH TODAY/...
AS OF 10 PM...A WEAK SHORTWAVE WAS ANALYZED ON THE RUC INVOF NRN AL
WITHIN FAST WEST-SOUTHWESTERLY UPPER LEVEL FLOW. THE RUC ALSO SHOWS
SOME 0-3 KM MUCAPE ACRS GA (WHERE EVEN A STRAY LIGHTNING STRIKE OR
TWO WAS OBSERVED IN THE LAST HOUR). THIS AREA OF ELEVATED INSTBY IS
PROGGED BY THE RUC TO MOVE INTO OUR GA COUNTIES AND ACRS MOST OF THE
UPSTATE IN THE 06Z-09Z TIME FRAME. SO I EXPECT SCATTERED SHWRS TO
MOVE INTO THIS AREA WITH PERHAPS A RUMBLE OF THUNDER HERE AND THERE.
I DON/T THINK THUNDER COVERAGE OR INTENSITY WILL BE ENUF TO WARRANT
A MENTION IN THE FCST WITH THIS UPDATE.
THE MAIN STORY FOR TONIGHT IS THE FOG...AS BL NEVER HAD A CHC TO
REALLY DRY OUT THIS AFTN AND WIDESPREAD FOG HAS DEVELOPED ACRS MOST
OF THE PIEDMONT. A COLD FRONT IS FAST APPROACHING THE FA FROM THE
WEST...ALLOWING FOR A LITTLE MIXING...AND ONCE THE SHWRS MOVE INTO
THE SOUTHERN THIRD OF THE FA...VSBYS WILL LIKELY INCR AS PRECIP
FURTHER MIXES THE BL (THIS WAS OBSERVED ACRS CENTRAL GA WHERE DENSE
FOG OCCURRED EARLIER THIS EVENING). I HAVE PLACED AN SPS FOR PATCHY
DENSE FOG ACRS ALL PIEDMONT ZONES...AS SEVERAL METARS HAVE REPORTED
1/4SM VSBY FROM TIME TO TIME THIS EVENING. AS FAR AS HOW LOW VSBYS
CAN GET TOWARD DAYBREAK IS UNCERTAIN FOR THE AFOREMENTIONED
REASONS...BUT A DENSE FOG ADVISORY ISSUANCE FOR SOME PORTION OF THE
PIEDMONT LATER TONIGHT IS STILL POSSIBLE.
TEMPERATURES WERE ONLY SLIGHTLY TWEAKED TO MATCH LATEST OBS.
A 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 /TONIGHT 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 /05Z TUESDAY THROUGH SATURDAY/...
KCLT AND ELSEWHERE...DENSE FOG AGAIN OVERNIGHT. FOG/STRATUS SHOULD
BEGIN TO LIFT BY LATE MRNG AS A COLD FRONT CROSSES THE AREA...BECMG
VFR LATER THIS AFTN WITH BETTER NW DOWNSLOPE WINDS BEHIND FRONT. LOW
CLOUDS WILL LINGER AT KAVL IN MOIST NW UPSLOPE FLOW.
OUTLOOK...UNRESTRICTED CIG/VSBY EXPECTED WED-FRI IN DRY AIRMASS
BEHIND COLD FRONT. A WEAK SYSTEM APPROACHES FROM THE W SAT...
POSSIBLY BRINGING LOWER CIG/VSBY AND SCT RAIN OR SNOW SHOWERS TO THE
MTNS.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.
&&
$$
SYNOPSIS...BSH
NEAR TERM...ARK/MCAVOY
SHORT TERM...TS
LONG TERM...BSH
AVIATION...RB
