000
FXUS62 KGSP 032340
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
640 PM EST WED DEC 3 2008
.SYNOPSIS...
HIGH PRESSURE WILL MOVE OFF THE CAROLINA COAST TONIGHT AS A COLD
FRONT APPROACHES FROM THE NORTHWEST. THE FRONT WILL CROSS OUR
REGION LATE THURSDAY AND THURSDAY NIGHT. A STRONG DISTURBANCE IS
EXPECTED TO PASS NORTH OF THE AREA SATURDAY NIGHT PRODUCING QUITE
BREEZY CONDITIONS. HIGH PRESSURE WILL BE THE DOMINANT WEATHER
FEATURE EARLY NEXT WEEK...UNTIL THE NEXT FRONT REACHES OUR AREA IN
MID WEEK.
&&
.NEAR TERM /THROUGH THURSDAY/...
LATEST RUNS OF THE GFS AND NAM HOLD OFF UNTIL AFTER 12 UTC THU WITH
FRONTAL BAND PCPN IN THE NC MTNS. I/VE FOLLOWED THAT TREND BY
CUTTING BACK POPS LATE TONIGHT AND FRI MORNING OVER THE WEST.
CONDENSATION PRESSURE DEFICITS TUMBLE AFTER 12 UTC ON THE GFS 295K
ISENTROPIC SFC...SO I DO THINK THE POTENTIAL EXISTS FOR AT LEAST
LIGHT PCPN PCPN ALONG THE TN LINE SHORTLY AFTER 12 UTC. THIS RAISES
THE QUESTION OF MIXED PCPN. MODEL SOUNDINGS SHOW A +10 DEG C WARM
NOSE DEVELOPING OVER THE MTNS TNGT UNDER 850 MB. THIS WILL KEEP THE
HIGHER ELEVATIONS ABOVE FREEZING WHILE THE VALLEYS FALL TO A DEGREE
OR TWO BELOW. BY THE TIME THE PCPN PICKS UP IN INTENSITY...EVERYONE
SHOULD HAVE RISEN ABOVE FREEZING AND I HAVE NO MIXED PCPN IN THE
GRIDS.
WHILE STRONG UPPER DIVERGENCE IS SHOWN ON BOTH THE NAM AND GFS EARLY
ON THU AHEAD OF THE APPROACHING SHORT WAVE...BY EARLY AFTERNOON THE
SYNOPTIC FORCING IS MOSTLY GONE AS THE WAVE DAMPENS OUT. A WELL
DEFINED FRONTAL BAND SHOULD STILL MAKE IT A WAYS ACROSS THE NC
MTNS...BUT I DON/T SEE MUCH SURVIVING THE TRIP TO MAKE IT INTO THE
FOOTHILL AND PIEDMONT ZONES WITHOUT ANY DEEP LAYER FORCING TO
OVERCOME LLVL DOWNSLOPE DRYING.
&&
.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
AS OF 145 PM WEDNESDAY...THE COLD FRONT WILL CROSS THE AREA THU
EVENING...WITH SHOWER CHANCES LINGERING ACROSS THE MTNS. THE NAM AND
GFS DIFFER ON THE EXTENT OF PRECIP CHANCES EAST OF THE MTNS...WITH
THE GFS BEING THE WETTER MODEL. BOTH MODELS FEATURE A RATHER STRONG
SW TROUGH PASSING OVER THE HEART OF THE CWFA DURING THE EVENING...
WHICH WOULD ARGUE FOR HEALTHY POPS EVEN EAST OF THE MTNS. HOWEVER...
BOTH MODELS ALSO FEATURE WANING LOW LEVEL CONVERGENCE AS THE FRONT
MOVES EAST OF THE BLUE RIDGE. WEAK SURFACE LOW PRESSURE NEAR THE
GULF COAST WOULD ARGUE FOR ORGANIZED CONVECTION IN THAT AREA...
POSSIBLY INTERRUPTING MOISTURE TRANSPORT INTO THE SOUTHEAST. POPS
WILL THUS BE LIMITED TO 30-40 PERCENT ACROSS THE FOOTHILLS/PIEDMONT
THU EVENING.
THE WEAK GULF COAST LOW WILL TRACK ACROSS SOUTH ALABAMA/FLORIDA
PANHANDLE THU NIGHT/EARLY FRIDAY...SLOWING THE PROGRESS OF THE
FRONT...AND POSSIBLY SPREADING MOISTURE AS FAR NORTH AS THE LOWER
PIEDMONT. WE WILL FEATURE SLIGHT TO LOW CHANCE POPS ACROSS OUR
SOUTHERN ZONES ON FRIDAY.
A RATHER POTENT CLIPPER SYSTEM WILL MOVE ACROSS THE MIDWEST ON
SATURDAY...WITH THE GFS ACTUALLY BRINGING PRECIP TO THE NORTHWEST
PART OF OUR CWFA BY THE END OF THE SAT PERIOD. THIS IS COMPLETELY AT
ODDS WITH THE NAM...AND EVEN THE GFS FEATURES SCANT LOW LEVEL
MOISTURE ACROSS THE AREA. WE WILL LIMIT POPS TO A SLIGHT CHANCE FOR
NOW. PROGGED THERMO PROFILES SUGGEST A RA/SN MIX WILL OCCUR IF
PRECIP DOES DEVELOP.
&&
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
AS OF 3 PM WEDNESDAY...THE EXTENDED PERIOD BEGINS WITH A DEVELOPING
WEAK NWFS EVENT ACROSS THE TN BORDER COUNTIES OF NC. THE AXIS OF AN
H5 TROF WILL SWEEP ACROSS THE SOUTHERN APPALACHIANS BETWEEN 0-12Z
SUN...RESULTING IN VEERING SOUTHWEST TO NORTHWEST WINDS OVER THE
MOUNTAINS. FORECAST GFS SOUNDINGS INDICATE THAT MOISTURE WILL REMAIN
ABUNDANT FROM THE SFC TO 5 KFT 0-9Z SUN. HOWEVER...MOISTURE SHOULD
ERODE FROM SW TO NE AFTER 12Z...RESULTING IN A 6-12HR WINDOW OF
ACCUMULATING SNOW...I WILL FORECAST A 0.5 TO 1 INCH OF ACCUMULATION.
DRY HIGH PRESSURE WILL DOMINATE THE REGION FROM SUNDAY AFTERNOON
THROUGH MONDAY EVENING. TEMPERATURES WILL GENERAL REMAIN A FEW
DEGREES BELOW NORMAL UNDER THE HIGH. BEGINNING MONDAY NIGHT THROUGH
WEDNESDAY...THE FORECAST BECOMES VERY UNCERTAIN WITH A COMPLICATED
PATTERN. I WILL FOLLOW HPC GUIDANCE AND FAVOR A BLEND OF THE ECMWF
AND GFS. BY SUNRISE TUESDAY...A FULL LATITUDE TROF WILL DEVELOP
ACROSS THE CENTRAL CONUS WITH BROAD RIDGING ACROSS THE EAST COAST. A
LOW PRESSURE SYSTEM IS EXPECTED TO DEVELOP OVER THE DEEP SOUTH AND
SPREAD GULF MOISTURE NORTHWARD. RECENT GUIDANCE SUGGEST THAT
MEASURABLE PRECIPITATION WILL REACH THE CWA TUES MORNING AND REMAIN
THROUGH WEDNESDAY. TEMPERATURE GUIDANCE KEEPS TEMPERATURES ABOVE
FREEZING...EXCEPT THE HIGH ELEVATIONS OF NC EARLY TUES. I WILL
FORECAST A MIX OF SNOW/RAIN FOR THE HIGH ELEVATIONS BEFORE NOON
TUES...RESULTING IN LITTLE WINTER ACCUMS. HOWEVER...THIS SYSTEM HAS
THE POTENTIAL FOR A SIGNIFICANT EVENT...ESPECIALLY IF THE TREND OF
THE 12Z GFS CONTINUES.
&&
.AVIATION /00Z THURSDAY THROUGH MONDAY/...
MODELS HAVE KEPT THE TIMING OF THE NEXT COLD FRONT SLOW. THERE WILL
BE SOME CIRRUS OVERNIGHT...BUT DEEP MOISTURE AND PRECIPITATION
REMAIN WEST OF THE AREA UNTIL AFTER 12Z THU. CIGS WILL GRADUALLY
LOWER DURING THE DAY AS THE MOISTURE MOVES IN...HOWEVER LOW VFR CIGS
WILL HOLD OFF UNTIL AFTERNOON. GOOD CONSENSUS ON MVFR CIGS
DEVELOPING AT KAVL BY LATE AFTERNOON. NOT AS MUCH CONSENSUS
ELSEWHERE. THEREFORE...HAVE INCLUDED MVFR CIG AT KAVL...BUT ONLY LOW
VFR ELSEWHERE. THE EXCEPTION IS KCLT...WHERE LOW VFR CIGS SHOULD
HOLD OFF UNTIL EVENING. INCLUDED VCSH WHERE PRECIP CHANCES ARE
BEST...BASICALLY WHERE THE LOW CIGS DEVELOP. VSBY SHOULD REMAIN VFR
UNLESS A HEAVIER SHOWER MOVES OVER THE AIR FIELD. SOUTH TO SOUTHWEST
WINDS CONTINUE ALL AREAS. KAVL WIND BECOMES NORTHWEST DURING THE
AFTERNOON AS THE FRONT MOVES IN.
OUTLOOK...COLD FRONT WILL MOVE ACROSS THE AREA THU NGHT. CIG/VSBY
RESTRICTIONS DO NOT APPEAR AS THOUGH THEY WILL BE WIDESPREAD ALONG
THE FRONT. FAIR WX WITH NO CIG/VSBY RESTRICTIONS FRI. A COLD FRONT
WILL CROSS THE REGION SATURDAY. A FEW SHOWERS WILL BE POSSIBLE AT
KAVL ALONG THE FRONT...AND LOW CIGS WILL BE POSSIBLE THERE BEHIND
THE FRONT INTO SUNDAY.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.
&&
$$
SYNOPSIS...DEO
NEAR TERM...MCAVOY
SHORT TERM...JDL
LONG TERM...NED
AVIATION...MCAVOY/RWH
