FXUS62 KGSP 242304
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
604 PM EST THU DEC 24 2009

.SYNOPSIS...
HIGH PRESSURE WILL WEAKEN AND MOVE EAST OF THE AREA THROUGH THE 
OVERNIGHT...BEFORE A STRONG COLD FRONT PUSHES ACROSS THE CAROLINAS 
AND NORTHEAST GEORGIA CHRISTMAS DAY. HIGH PRESSURE WILL BUILD BACK 
OVER THE REGION SATURDAY AND SLOWLY MOVE EAST THROUGH NEXT TUESDAY.

&&

.NEAR TERM /THROUGH FRIDAY/...
DRAMATIC INCREASE IN LLVL WAA FLOW/FRONTOGENESIS...FOLLOWED BY A SLUG
OF DEEPER FORCING...INDICATED BY AN INCREASE IN MID/UPPER LVL 
Q-VECTOR CONVERGENCE...WILL RESULT IN PRECIPITATION BECOMING 
WIDESPREAD REGIONWIDE TONIGHT. CATEGORICAL PCPN CVRG CHRISTMAS 
MORNING TO DWINDLE BY THE AFTERNOON AS LATEST OP MODEL SOLUTIONS... 
ALTHOUGH SOME TIMING DIFFERENCES REMAIN...PROG DRY SLOT TO 
OVERSPREAD THE REGION FROM THE SW.

STILL EXPECTING DAMMING HIPRES TO DEVELOP AND REMAIN ORIENTED IN 
FAVORABLE POSITION TO ADVECT SUB-FREEZING SFC WET BULB TEMPS SWWD
ALONG THE NC LEE SLOPES TONIGHT. ALTHOUGH THE SREF P-TYPE PLUME 
DIAGRAMS OVER THE PAST FOUR RUNS HAVE BEEN TRENDING TOWARD 
PROGRESSIVELY LESS ICE ACCRETION FOR ASHEVILLE/HICKORY/BOONE... 
WARNINGS AND ADVISORIES ARE ALREADY IN PLACE THRU NOON TOMORROW AND 
WILL SIMPLY NUDGE ACCUMS DOWNWARD TOWARD...FCSTG A MARGINAL WARNING 
ACCRETION FOR THE LEE SLOPES BEFORE WARM RAIN PROCESSES AND OVERALL 
DIMINISHMENT OF PCPN WINS OUT.

PLUME OF UNSEASONABLY HIGH PWAT VALUES...1.00 TO 1.25 INCHES...
REMAIN PROGGED TO OVERSPREAD THE CWFA LATER TONIGHT. AIDED BY
THE AFOREMENTIONED DEEP FORCING AND STOUT UPSLOPE FLOW...A PERIOD OF 
HEAVY RAIN IS PROBABLE. THE CONSENSUS RAINFALL TOTALS ARE 2 TO 2.5
INCHES ALONG AND JUST EAST OF THE BLUE RIDGE. HIGH RUNOFF WILL 
CERTAINLY OCCUR...PERHAPS EVEN AT AN EXCESSIVE LVL...ESPECIALLY
WHERE MTN SNOWMELT OCCURS. GIVEN SPEED OF SYSTEM AND THE CHANCE FOR
SOME INTERRUPTION OF MOISTURE TRANSPORT DUE TO ANTICIPATED DEEP 
CONVECTION TO OUR S/SE...WILL HOLD OFF ON AN AREAL FLOOD WATCH
BUT MENTION HEAVY RAIN IN THE FCST. IT IS A LITTLE MORE PROBABLE
THAT AREAS ALONG THE UPPER FRENCH BROAD WILL EXPERIENCE LARGER
STEM FLOOD FLOWS AND A FLOOD WATCH HAS ALREADY BEEN ISSUED FOR THIS 
AREA.

THE TIMING AND MAGNITUDE OF STOUT 65-70 KT SSELY 85H JET REMAINS ON 
TRACK...TO LIFT NE ACRS THE CWFA TONIGHT/FRIDAY MORNING. CURRENT
PLACEMENT OF MTN WIND ADVISORY STILL LOOKS GOOD ALTHOUGH HAVE
EXPANDED THREAT EASTWARD INTO THE UPSTATE AND GEORGIA PIEDMONT
WHERE GUSTS TO 35 MPH HAVE THE POSSIBILITY OF REACHING THE SFC.
WHILE WERE TALKING ABOUT WIND CONCERNS...THERE IS ALSO THE 
POSSIBILITY OF LATE NIGHT/EARLY MORNING GRAVITY WAVE DEVELOPMENT 
ACRS THE PIEDMONT...AS WITHIN STABLE AIR JUST N/NW OF WEDGE FRONT AS 
NOSE OF UPPER JET STREAK IS PROGGED TO ROTATE IN FROM THE
SW...ENCROACHING UPON INFLECTION POINT OF MID-LVL TROUGH.

ALSO ON FRIDAY MORNING...AS WEDGE BNDRY RETREATS INTO THE PIEDMONT
AND TRIPLE POINT LOW MOVES NE ALONG IT...PLUME OF NEAR IF NOT
SFC BASED INSTABILITY WILL BEND NWWD INTO THE FAR SE CWFA. WITHIN 
THE EXPECTED STRONG/DEEP SHEAR ENVIRONMENT...SHALLOW CONVECTION IS 
POSSIBLE...PERHAPS RESULTING IN LOCALIZED DAMAGING WIND GUSTS.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
AS OF 200 PM THU...AN INTENSE UPPER LOW WILL PARK OVER THE WESTERN 
GREAT LAKES STATES FRI NGHT AND SAT. OUR AREA WILL BE UNDER A STRONG 
SOUTHWESTERLY UPPER LEVEL FLOW...THOUGH THE AIRMASS WILL BE QUITE 
DRY OVERALL. THE NAM SOUNDINGS AND TIME/HEIGHTS STILL HAVE AMPLE 
LLVL HUMIDITY OVER THE REGION FRI NIGHT...ESPECIALLY OVER THE NC 
FOOTHILLS AND PIEDMONT. HYDROLAPSES ARE FAVORABLE FOR FOG 
FORMATION...WHICH MAKES SENSE AS THE DEEP LAYER FLOW ONLY HAS A VERY 
WEAK DOWNSLOPE COMPONENT...AND WE SHOULD HOLD ONE TO A DEEP MOIST 
LAYER UP IN THOSE ZONES. I THINK WE/LL SEE FOG IN THESE AREAS AND 
I/VE ADDED IT TO THE GRIDS. A BIT OF A GAP WIND FLOW DOWN THE FRENCH 
BROAD VALLEY SHOULD KEEP THE FOG FROM FORMING THERE OVERNIGHT.

BY SUNDAY THE UPPER LOW WILL WILL BEGIN TO BE PICKED BACK UP BY THE 
WESTERLIES...DIVING BRIEFLY TO THE SOUTH BEFORE LIFTING OFF TO THE 
NORTH. AS THIS HAPPENS...SOME UPPER DIVERGENCE DEVELOPS OVER THE SRN 
PART OF THE FA ON THE GFS AS A SHORT WAVE SHOOTS ACROSS THE REGION.  
THE ECMWF SUPPRESSES THIS SRN STREAM ENERGY AND IS DRY OVER THE 
REGION. THE NAM IS ALSO DRY...AND THE SREF POPS ARE ONLY ON THE 
ORDER OF 15 TO 20 PERCENT. I HAVE KEPT SLIGHT CHANCE POPS ALONG THE 
TN LINE...BUT EVEN THAT LOOKS A LITTLE HIGH. THICKNESSES WOULD 
SUPPORT A RAIN/SNOW MIX.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
AS OF 230 PM THURSDAY...LOOKS LIKE WE ARE STILL UP FOR A BRIEF NW 
FLOW SNOW SHOWER EVENT SUNDAY NIGHT AND MONDAY MORNING. THE MODELS 
ARE IN A BIT BETTER AGREEMENT IN THAT THEY SWING THE UPPER TROF AXIS 
ACROSS THE REGION DURING THIS TIME FRAME. THIS WILL FINALLY BRING 
THE FLOW AT 850MB AROUND TO THE NW SUNDAY NIGHT AND PUSH THE 
REMAINING LOW LEVEL MOISTURE UP THE WEST SIDE OF THE MTNS. THE 
MOISTURE IS NOT PARTICULARLY DEEP BUT THE AIR MASS WILL BE COLD 
ENOUGH TO SUPPORT SNOW SHOWERS. KEPT A CHANCE POP ALONG THE TN 
BORDER OVERNIGHT AND INTO THE MORNING OVER THE NORTHERN MTNS...AND 
THIS SHOULD END IN THE AFTERNOON. RIGHT NOW IT LOOKS LIKE A MINIMAL 
EVENT. TEMPS WERE GENERALLY KEPT NEAR A GUIDANCE BLEND.

MONDAY NIGHT AND TUESDAY ARE THE QUIET PERIODS AS HIGH PRESSURE 
MOVES ACROSS THE REGION...WHILE THE NEXT SRN STREAM SYSTEM TAKES 
SHAPE OVER THE WRN GULF. THE MODEL TREND HAS BEEN TO DELAY THE ONSET 
OF MOISTURE RETURN...SO OPTED TO KEEP TUESDAY NIGHT DRY.

CONFIDENCE IS LOW ABOUT THE EVOLUTION OF THE NEXT SYSTEM...ALTHO AT 
LEAST THE MODELS AGREE THAT SOMETHING WILL TRY TO DEVELOP IN THE SRN 
STREAM DURING THE MIDDLE PART OF THE WEEK. THE FORECAST GENERALLY 
FOLLOWS CLOSER TO THE ECMWF AND HPC LOW POSITION BECAUSE OF BETTER 
CONTINUITY. THE FORECAST WILL SHOW A CHANCE OF PRECIPITATION 
SPREADING ACROSS THE REGION WEDNESDAY AND CONTINUING WEDNESDAY NIGHT 
AND THURSDAY. PARTIAL THICKNESSES ARE SUCH THAT WE WOULD SEE A MIX 
OF PRECIP TYPES. HOWEVER...I WOULD CAUTION YOU TO NOT PUT TOO MUCH 
STOCK INTO ANY POTENTIAL WINTER WEATHER EVENT BECAUSE SIGNIFICANT 
CHANGES ARE LIKELY. JUST FILE IT AWAY FOR NOW THAT WE COULD HAVE A 
PROBLEM AROUND NEW YEARS EVE.

&&

.AVIATION /23Z THURSDAY THROUGH TUESDAY/...
AT KCLT AND ELSEWHERE...MVFR CIGS ENCROACHING FROM THE S AND W WILL 
CONTINUE TO LOWER THIS EVE WITH INCRSNG CHC RAIN AND IFR CIGS 
EXPECTED AFTER MIDNIGHT. WINDS WILL ALSO INCRS FROM THE ENE...SE AT 
KAVL...AND BECOME GUSTY AFTER MIDNIGHT. ONCE PRECIP BECOMES STEADY 
VSBY SHOULD LOWER TO IFR...DESPITE WINDS. CHC -FZRA AT KAVL AND KHKY 
OVERNIGHT SO INCLUDED IT THERE...BECMG -RA AFTER 15Z. SHOULD SEE 
SLOW IMPROVEMENT THRU THE AFTN.

OUTLOOK...VFR CONDITIONS EXPECTED SAT THROUGH TUE. A WEAK COLD FRONT 
WILL APPROACH THE AREA WED AND POSSIBLY LOWER CIGS TO MVFR ACROSS 
MOST TAF SITES THROUGHOUT THE DAY. HIGH PRESSURE AND DRIER AIR WILL 
MOVE IN QUICKLY WED NIGHT RETURNING FLIGHT CATS TO VFR FOR THU.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...LAKE WIND ADVISORY UNTIL NOON EST FRIDAY FOR GAZ018-026-028-
     029.
     WIND ADVISORY UNTIL NOON EST FRIDAY FOR GAZ010-017.
NC...ICE STORM WARNING UNTIL NOON EST FRIDAY FOR NCZ033-035-049-050-
     501>506.
     WIND ADVISORY UNTIL NOON EST FRIDAY FOR NCZ048-051-052-058-059-
     062-063.
     FREEZING RAIN ADVISORY UNTIL NOON EST FRIDAY FOR NCZ036-053-
     056-064-065-068-507>510.
SC...LAKE WIND ADVISORY UNTIL NOON EST FRIDAY FOR SCZ001>014-019.

&&

$$
SYNOPSIS...SBK
NEAR TERM...CSH
SHORT TERM...MCAVOY
LONG TERM...PM
AVIATION...RB