FXUS62 KGSP 050743
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
243 AM EST SAT DEC 5 2009

.SYNOPSIS...
AN AREA OF LOW PRESSURE WILL MOVE NORTHEAST ALONG THE CAROLINA COAST 
TODAY.  EXPECT THIS LOW TO PULL AWAY FROM OUR REGION TONIGHT AND 
SUNDAY AS HIGH PRESSURE CONTROLS OUR WEATHER INTO MONDAY.  A FAST 
MOVING COLD FRONT WILL PUSH ACROSS THE REGION LATE MONDAY.  A STRONG 
LOW WILL DEVELOP OVER THE PLAINS STATES AND MOVE NORTHEAST TO THE 
GREAT LAKES ON WEDNESDAY AS THE ASSOCIATED COLD FRONT APPROACHES THE 
CAROLINAS AND GEORGIA FROM THE WEST.

&&

.NEAR TERM /THROUGH TONIGHT/...
THE TIMING AND EVOLUTION OF THE MTN SNOW EVENT STILL LOOKS TO BE ON 
TRACK. REGIONAL SATELLITE IMAGES SHOW A BAROCLINIC LEAF STRETCHING 
ACROSS ERN MS/AL/NW GA AND CNTRL TN ATTM. ON THE SOUTH AND EAST PART 
OF THE THIS AREA OF COOLER CLOUD TOPS...A FAIRLY LARGE AREA OF LIGHT 
TO MODERATE SNOW WAS FALLING OVER NRN AND CENTRAL MS. PCPN WAS ALSO 
BEGINNING TO DEVELOP OVER NW GA AND THE SW NC MTNS...THOUGH WE HAVE 
YET TO VERIFY WHAT TYPE OF PCPN THAT IS. 

SO FAR THE GFS IS DOING A GOOD JOB WITH THE THIS SYSTEM...AND 
THAT/S THE MODEL I/M PRIMARILY USING FOR THIS FORECAST. DEEP LAYER 
Q-VECTOR CONVERGENCE BECOMES MORE ORGANIZED THROUGH 12 UTC OVER THE 
WESTERN CAROLINAS AND NE GA IN ASSOCIATION WITH THE APPROACHING 
SHORT WAVE. WHILE IT/S STARTING TO MOVE NORTH OF THE REGION BY 18 
UTC...THE FORCING STILL LOOKS GOOD ACROSS THE CENTRAL AND NRN NC 
MTNS AND FOOTHILLS. AS THE PREVIOUS SHIFT MENTIONED...THE H8 LOW 
CENTER WILL CROSS SOUTH SE OF THE MTNS BETWEEN 12 AND 18 UTC...WHICH 
IS WHEN I EXPECT THE BEST FORCING AND HEAVIEST SNOW TO OCCUR. A DRY 
SLOT WILL WRAP THROUGH NE GA...THE UPSTATE AND THE SRN NC
PIEDMONT. THESE AREAS WILL BE TOO WARM FOR SNOW ANYWAY...BUT THEY
MAY SEE LITTLE IN THE WAY RAIN EITHER.

THE LATEST LAPS SOUNDINGS SHOW THE SNOW LEVEL TO BE AROUND 4000 
FEET...BUT THIS WILL FALL QUICKLY AS THE PCPN BEGINS...AND THE SNOW 
SHOULD REACH THE VALLEY FLOORS AROUND 12 UTC IF NOT SOONER. THE NAM 
AND SREF QPF IS STILL ON THE LOW SIDE WHILE THE GFS IS HIGHER. OWING 
TO THE GOOD FORCING OVER THE MTNS...AND THE PLUME OF UPSTREAM 
MOISTURE AND PRECIPITATION THAT IS ALREADY IN PLACE...I THINK THE 
HIGHER QPF MAKES SENSE. THIS KEEPS US QUITE CLOSE TO THE PREVIOUS 
SHIFT/S SNOWFALL NUMBERS WITH 1 TO 2 INCHES OVER THE HIGHER 
ELEVATIONS OF THE SRN MTNS...WITH 3 TO 5 INCHES LIKELY OVER THE NRN 
MTNS...AND SIMILAR AMOUNTS AT THE HIGHER ELEVATIONS OF THE CENTRAL 
MTNS.

I/VE LOWERED MIN TEMPS TONIGHT A COUPLE DEGREES...BLENDING IN THE 
COOP MOS. AS WE HAVE BEEN ADVERTISING...THIS WILL RESULT IN AREAS OF 
BLACK ICE LATER TONIGHT...PARTICULARLY OVER THE MTNS AND WRN 
FOOTHILLS.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY/...
AS OF 215 AM SATURDAY...SFC HIPRES TO BUILD COASTWARD THRU 
SUNDAY...AS SUNSHINE GETS INCREASINGLY FILTERED BY HIGH CLOUDS 
ADVECTING EASTWARD WITHIN THE FAST WSW FLOW ALOFT. WILL PLAN ON 
BLENDING INHERITED MAX TEMPS WITH THE COOLER MET NUMBERS...FOR HIGHS
ABOUT 2-4 DEG F BELOW CLIMO. EXPECTING AN INCREASE IN WAA FLOW
ABOVE THE SFC SUNDAY NIGHT IN ADVANCE OF FAST MOVING WEAK FRONTAL 
SYSTEM. WILL FAVOR NAM/SREF RESPONSE IN LIMITING SMALL SHOWER
CHANCES CLOSER TO THE FRONTAL ZONE WELL WEST OF THE MTNS AND
NEAR COASTAL FRONT. HENCE...SENSIBLE WX WILL BE LIMITED TO
A CONTINUED INCREASE IN CLOUDS WITH LITTLE CHANGE TO INHERITED
MIN TEMPS...WHICH ESSENTIALLY SUPPORT A MOS BLEND.

A WEAK FRONTAL PASSAGE REMAINS SLATED FOR MONDAY WITH THE BETTER
FORCING AND DEEPER RH MOISTURE ORIENTED ACRS THE MTNS...A PER
LATEST NAM/SREF. SCATTERED MTN SHOWERS...POSSIBLY IN THE FORM
OF A LIGHT WINTRY MIX DURING THE MORNING ARE PROBABLE...WITH
JUST ISOLATED ACTIVITY IN THE PIEDMONT. EVEN THE COOLER MET
NUMBERS WARRANT AN UPWARD NUDGE TO MAX TEMPS TO AROUND CLIMO.

WITH DECENT AGREEMENT AMONG THE 00 UTC GFS AND ECMWF MODEL MASS 
FIELDS...CONFIDENCE INCREASING THAT STRENGTHENING WAA PATTERN WILL 
RESULT IN STRATIFORM PCPN OVERSPREADING THE CWFA TUESDAY ATOP OF 
DAMMING SFC HIPRES AND HAVE RAISED POP ACCORDINGLY. WILL CONTINUE
TO ADVERTISE A DEGREE OF LIGHT WINTRY MIX...MAINLY ACRS THE MTNS 
DURING THE ONSET OF PCPN.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
AS OF 210 AM SATURDAY...THE MEDIUM RANGE MODELS ARE IN GOOD 
AGREEMENT IN TAKING THE MILLER B SYSTEM NORTHEAST WITH THE HIGHEST 
AMOUNT OF MOISTURE OVER OUR FORECAST AREA TUESDAY NIGHT.  MOISTURE 
GRADUALLY DECREASES OVER THE FOOTHILLS AND PIEDMONT DURING THE DAY 
WEDNESDAY LEAVING JUST THE NC MOUNTAINS WITH NORTHWEST FLOW SNOW 
WEDNESDAY NIGHT.  THE GFS MAINTAINS THE NORTHWEST FLOW LONGER BUT 
DECREASES THE MOISTURE.  THE ECMWF DROPS THE NORTHWEST FLOW EARLIER 
BUT MAINTAINS THE MOISTURE INTO EARLY THURSDAY.  ANYWAY...MADE SMALL 
ADJUSTMENTS TO THE POPS AND SNOW GRIDS DURING THE WEDNESDAY NIGHT TO 
EARLY THURSDAY PERIOD.  AFTER HIGH PRESSURE CONTROLS THE WEATHER 
THURSDAY INTO FRIDAY...THE NEXT SYSTEM MOVES IN FROM THE WEST 
SPREADING MOISTURE IN FRIDAY NIGHT.  I DRASTICALLY DECREASED POPS IN 
THIS PERIOD ACCORDING TO MODELS AND TO BRING US IN AGREEMENT WITH 
THE NEIGHBORS.  LITTLE CHANGE IN TEMPERATURES AS THEY WILL BE WITHIN 
A FEW DEGREES OF NORMAL.

&&

.AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
KCLT AND ELSEWHERE...MVFR CIGS AND LIGHT RAIN HAVE BEEN A LITTLE 
SLOWER TO DEVELOP THAN EXPECTED...BUT THESE CONDITIONS SHOULD 
DEVELOP BY 0900 UTC AT ALL SITES. CIGS SHOULD LOWER MOST QUICKLY 
FROM THE EAST...WHICH MEANS THAT KCLT WILL GO DOWN A LITTLE MORE 
QUICKLY THAN SITES TO THE WEST. ALL THE MODEL GUIDANCE HAS IFR CIGS 
DEVELOPING BY AROUND 12 UTC...AND I/VE KEPT THE PREVIOUS SHIFT/S 
TIMING IN THAT REGARD. WINDS WILL BE N TO NE THIS MORNING...BUT WILL 
TURN OUT OF THE W TO NW IN THE AFTERNOON AS LOW PRESSURE DEEPENS OFF 
THE COAST. AFTER THE WINDS SHIFT...CIGS AND VSBYS SHOULD IMPROVE A 
FEW HOURS LATER. AT KAVL LIGHT RAIN SHOULD CHANGE OVER TO RAIN BY 
AROUND SUNRISE AND CONTINUE INTO THE AFTERNOON HOURS. WINDS WILL 
BECOME GUSTY AT KAVL THIS AFTERNOON AS WELL.

OUTLOOK...CONDITIONS WILL IMPROVE QUICKLY THIS EVENING AS THE LOW 
PRES SYSTEM PULLS AWAY TO THE NE. FREEZING TEMPERATURES WILL LEAD TO 
BLACK ICE CONDITIONS ON RUNWAYS SUNDAY MORNING. DRY WEATHER IS 
EXPECTED SUNDAY. A WEAK FRONT WILL PASS MONDAY. DRY HIGH PRESSURE IS 
THEN EXPECTED AGAIN TUESDAY BEFORE OUR NEXT MAJOR SYSTEM MOVES IN 
FROM THE W TUE NIGHT-WED.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...WINTER WEATHER ADVISORY UNTIL 8 PM EST THIS EVENING FOR NCZ051-
     053-058-059-062>065-501-503-505.
     WINTER STORM WARNING UNTIL 8 PM EST THIS EVENING FOR NCZ033-
     048>053-059-501-503-505.
SC...NONE.

&&

$$
SYNOPSIS...DEO
NEAR TERM...MCAVOY
SHORT TERM...CSH
LONG TERM...DEO/JDL
AVIATION...MCAVOY