FXUS62 KGSP 040820
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
320 AM EST FRI DEC 4 2009

.SYNOPSIS...
HIGH PRESSURE WILL LINGER OVER THE AREA THROUGH FRIDAY AFTERNOON. 
ANOTHER LOW PRESSURE SYSTEM WILL THEN MOVE TOWARDS THE CAROLINAS 
FROM THE GULF OF MEXICO LATE FRIDAY AND THROUGH THE DAY ON 
SATURDAY. BEHIND THIS SYSTEM...HIGH PRESSURE WILL REBUILD OVER THE 
REGION AND REMAIN IN PLACE UNTIL EARLY NEXT WEEK. A DEEP LOW WILL 
THEN DEVELOP OVER THE CENTRAL PLAINS AND APPROACH THE FORECAST AREA 
BY THE MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
A SHORT WAVE CURRENTLY DIVING ACROSS SW NEW MEXICO WILL ROUND THE 
BASE OF THE CENTRAL CONUS LONG WAVE TROF...AND MOVE ACROSS THE SRN 
APPALACHIANS ON SATURDAY. THE LONG WAVE WILL BEGIN TO DEAMPLIFY 
DURING THIS TIME AND SRN STREAM WAVE WILL ACTUALLY BECOME SHARPER IN 
THE INCREASINGLY ZONAL FLOW. THIS WILL RESULT IN A FAIRLY NICE AREA 
OF FORCING LATE TONIGHT AS THE WAVE APPROACHES. THE GFS IS THE 
FASTEST AND WEAKEST WITH THE WAVE...WHILE THE NAM IS THE SLOWEST AND 
STRONGEST. OVER THE PAST SEVERAL RUNS ALL THE NUMERICAL MODELS HAVE 
BEEN TRENDING LOWER WITH THEIR QPF. 

I DIDN/T MAKE MANY CHANGES...BUT I DID LOWER THE QPF AND SNOW 
AMOUNTS A LITTLE...WHICH IS CONSISTENT WITH THE DIMINISHING MODEL 
QPF/S. ALSO...USING A MODEL CONSENSUS...THE BULK OF THE PCPN DOESN/T 
START UNTIL RIGHT AROUND 12 UTC...THOUGH I DIDN/T WANT TO BACK AWAY 
TOO MUCH OWNING TO THE FASTER SOLUTION OF THE GFS. THE NAM HAS 
FAIRLY IMPRESSIVE H8-H7 FRONTOGENESIS OVER THE NC ZONES EARLY 
SATURDAY...AND GOOD DEEP LAYER Q-VECTOR CONVERGENCE AS WELL. SO 
WHILE THE TREND IS FOR THE QPF TO BE LOWER...IF THE MORE AGGRESSIVE 
NAM/S QG FORCING WERE TO MATERIALIZE...HIGHER PCPN AMOUNTS ARE STILL 
POSSIBLE. 

ONCE PCPN BEGINS...IT WILL TAKE A WHILE FOR IT TO CHANGE OVER TO 
SNOW IN THE VALLEYS. THE WATCH IS ALREADY ELEVATION DEPENDENT OVER 
THE SW MTNS...AND I DON/T SEE ANYTHING TO CHANGE THAT...AT LEAST 
THROUGH TONIGHT. ELEVATIONS BELOW ABOUT 2500 FEET SHOULD BE ALL RAIN 
UNTIL RIGHT AROUND SUNRISE.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY/...
AS OF 245 AM FRIDAY...STILL EXPECTING MODERATELY FORCED PASSAGE OF 
RATHER FAST MOVING L/WV AXIS SATURDAY. THERE CONTINUES TO EXIST 
RATHER MINOR DIFFERENCES AMONG THE MODELS IN TROUGH PASSAGE TIMING
AND STRENGTH...BUT WILL FAVOR THE LESS DEEP SREF/ECMWF/GFS...ALTHOUGH
WILL SLOW UP THE GFS TIMING. AT ANY RATE...BEST FORCING IS SLATED
FOR 12-18 UTC SATURDAY AND WILL RAMP CVRG UP TO CATEGORICAL FOR THAT
PERIOD AND PROGRESSIVELY WIND POPS DOWN IN THE AFTERNOON. 

NOTHING TOO TERRIBLY SURPRISING WAS NOTED IN THE MODEL THERMAL 
PROFILES...ADVISING LITTLE CHANCE OF SNOW OUTSIDE OF THE MOUNTAINS 
SATURDAY MORNING WITH FREEZING LEVELS ABOVE 3000 FEET...ALTHOUGH 
WILL PLAN ON SPREADING AT LEAST A MIX INTO THE FTHLS AS COLDER WRAPS 
EASTWARD DURING THE TAIL HALF OF THE EVENT. 

WHAT IS MOST DISCONCERTING...WITH THE EXCEPTION OF THE OUTLIER 
NAM...IS MODEL LIQUID EQUIV QPF ACRS THE BOARD TOPS OUT AROUND 
0.20"...AND EVEN THE NEW 03 UTC SREF CONTINUES IT/S DOWNWARD TREND 
OVER THE PAST FIVE RUNS...NOW FCSTG ONLY A 0.10" LIQUID EQUIV STORM 
TOTAL. CERTAINLY THERE IS LITTLE CONFIDENCE AT THIS JUNCTURE FOR ANY 
UPGRADE TO GOING WATCH...AS IT IS LOOKING LIKE EVEN THE HIGH COUNTRY 
MAY STRUGGLE TO GET 3 INCHES...OUR 12 HR CRITERIA FOR A WARNING. 
BEST COURSE OF ACTION IS TO KEEP WATCH GOING AS IS AND LET NEXT 
SHIFT REEVALUATE WHETHER DOWNGRADE TO ADVISORY IS NEEDED...OR 
PERHAPS EEK OUT A MARGINAL HIGH ELEVATION WARNING.

QUICK INFLUX OF DEEP DRYING ON TRACK FOR SATURDAY NIGHT AS SFC HI 
PRESSURE BUILDS ATOP THE REGION. IT IS DEBATABLE WHETHER THERE
WILL BE ENOUGH PCPN FOR NOTABLE BLACK ICE DEVELOPMENT...BUT WILL 
CONTINUE TO ADDRESS THE THREAT IN THE HWO AS TEMPS FALL INTO THE 20S 
OVERNIGHT. SUNSHINE ACCOMPANIED BY CONTINUED COOL CONDITIONS REMAIN 
SLATED FOR SUNDAY BEFORE THE FAST MOVING AND WEAK FRONTAL PASSAGE ON 
MONDAY...WHERE SCATTERED SHOWERS...PERHAPS MIXED WITH SNOW IN
THE MTNS WILL BE POSSIBLE.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
AS OF 2 AM FRIDAY...THE MEDIUM RANGE FCST BEGINS AT 00Z ON TUESDAY 
WITH THE MODELS IN REASONABLE AGREEMENT WITH THE LARGE SCALE 
SYNOPTIC PATTERN. THE FIRST PORTION OF THE PERIOD WILL BE 
CHARACTERIZED BY PREDOMINATELY ZONAL MID AND UPPR LVL FLOW OVER MUCH 
OF THE EASTERN CONUS. A DEEP UPPER TROUGH DEVELOPS OVER THE WESTERN 
STATES AND TRANSLATES EASTWARD DURING THE MIDDLE OF THE WEEK. MODELS 
HAVE THE H5 TROUGH MOVING OVER THE CWA BY LATE WED/EARLY THURS WITH 
THE 00Z GFS BEING A BIT SLOWER AND MORE AMPLIFIED THAN THE 00Z 
ECMWF. AT THE SFC...AN IMPRESSIVE EXTRA-TROPICAL CYCLONE IS 
GENERATED OVER THE SW CONUS EARLY IN THE PERIOD AND STEADILY DEEPENS 
AS IT MOVES OVER THE SOUTHERN PLAINS AND MISS RIVER VALLEY. THIS LOW 
SHOULD PASS TO OUR NW AS THE NEWER MODEL RUNS HAVE PUSHED THE 
OVERALL TRACK FARTHER TO THE NW. I EXPECT WIDESPREAD PRECIP OVER THE 
CAROLINAS LATE TUES THROUGH WED WITH THE POSSIBILITY OF SOME 
LIGHT/PATCHY WINTRY MIX EARLY TUES...HOWEVER I KEPT JUST A SLIGHT 
CHANCE IN THE POP GRID DURING THIS TIME. ANY LIGHT PRECIP SHOULD 
TRANSITION TO LIQUID QUICKLY DURING THE DAY ON TUESDAY. DRIER AIR 
WILL PUSH BACK INTO THE REGION ON THURSDAY AS A SFC RIDGE BUILDS 
BACK OVER THE SE AND LINGERS THRU DAY 7.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
KCLT...HKY...KAND AND KGMU...WINDS WILL BE LIGHT OUT OF THE N TO NNE 
OVERNIGHT AND A LITTLE STRONGER OUT OF THE NE DURING THE DAY. HIGH 
CLOUDS WILL GRADUALLY INCREASE...AND AT SOME POINT A SCT TO BKN DECK 
SHOULD FORM UP AROUND 5KFT. THE TIMING OF THIS DECK VARIES QUITE A 
BIT BETWEEN MODELS. I/VE STARTED SCT050 AT 15 UTC AND RUN IT THROUGH 
THE REST OF THE PERIOD...BUT THERE IS A GOOD CHANCE THAT AT SOME 
POINT IT WILL BECOME BKN.  

KAVL...NNW WINDS WILL KEEP AN MVFR DECK OVER THE AIRFIELD THE REST 
OF THE NIGHT. THE WINDS WEAKEN AFTER SUNRISE...AT WHICH TIME THE LOW 
CLOUDS SHOULD RETREAT TO THE TN LINE. VFR CIGS WILL DEVELOP AGAIN  
DURING THE AFTN. WINDS WILL BE OUT OF THE N THIS MORNING...BECOMING 
VARIABLE IN THE AFTN. 

FOR KGSP...WINDS SHOULD REMAIN VERY LIGHT OVERNIGHT WITH A GRADUAL 
SHIFT TO THE NE AND A SLIGHT INCREASE IN INTENSITY IN THE 4-6KT 
RANGE THROUGH FRI. MOSTLY CLEAR SKIES WILL GIVE WAY TO HIGH CLOUDS 
BY MORNING WITH SCT VFR LOW TO MID CLOUDS DEVELOPING BY FRI 
AFTERNOON. 

OUTLOOK...MOISTURE AND LIFT WILL INCREASE RAPIDLY TONIGHT AND 
SATURDAY WITH RESTRICTIONS DEVELOPING. SOME SNOW COULD DEVELOP AND 
AFFECT KAVL LATE TNGT-SAT MRNG...WITH CHC RAIN OTHER TAF SITES. 
CONDITIONS SHOULD IMPROVE QUICKLY SAT NIGHT INTO SUN AS DRY HIGH 
PRESSURE BUILDS IN. VFR LIKELY MON-TUE.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...WINTER STORM WATCH FROM LATE TONIGHT THROUGH SATURDAY EVENING 
     FOR NCZ033-048>053-059.
SC...NONE.

&&

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