FXUS62 KGSP 152339
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
639 PM EST TUE DEC 15 2009
.SYNOPSIS...
STRONG HIGH PRESSURE WILL BUILD IN FROM THE WEST TODAY...THEN
GRADUALLY WEAKEN AND MOVE EAST OF THE AREA BY FRIDAY. LOW PRESSURE
WILL DEVELOP ACROSS THE GULF OF MEXICO LATE IN THE WEEK AND MOVE UP
THE ATLANTIC COASTLINE OVER THE WEEKEND.
&&
.NEAR TERM /THROUGH WEDNESDAY/...
A COLD FRONT WILL WORK ITS WAY ACROSS THE REGION THIS
EVENING...FINALLY PUSHING THE LOW CLOUDS OUT OF THE FORECAST AREA.
YOU MAY NOT NOTICE...HOWEVER...AS A DENSE CI OVERCAST WILL PERSIST
THROUGH THE LATE EVENING HOURS. IT MAY LAST LONGER THAN
THAT...THOUGH THE MOIST LAYER BECOMES A LITTLE SHALLOWER ON MODEL
SOUNDINGS...SO I/LL DECREASE CLOUD COVER. THIS ALSO LINES UP BETTER
WITH NEIGHBORING OFFICES. LLVL MOISTURE DOES NOT LOOK VERY DEEP
ALONG THE WESTERN SLOPES OF THE MTNS. I KEPT THE SLIGHT CHANCE
RAIN/SNOW POPS THROUGH MIDNIGHT ALONG THE TN LINE...BUT PCPN SHOULD
BE OF LITTLE CONSEQUENCE.
THE LAV GUIDANCE IS SHOWING WIND GUSTS UP TO 29 KTS FOR SEVERAL
HOURS STARTING AT MID-EVENING AT ASHEVILLE. WITH A STRONG ARCTIC
HIGH MOVING ACROSS THE MTNS...THE PRESSURE GRADIENT WILL SUPPORT
GUSTS AT LEAST THIS HIGH. GAP WIND EFFECTS DOWN THE FRENCH BROAD
VALLEY MAY RESULT IN EVEN HIGHER GUSTS. THIS IS A SUFFICIENT AMOUNT
OF WIND FOR A LAKE WIND ADVISORY ACROSS THE CENTRAL AND NORTHERN
MTNS...AS WELL AS THE EASTERN SLOPES OF THE NC ESCAPEMENT.
HIGH PRESSURE WILL CONTINUE TO BUILD INTO THE REGION ON WED. UNDER
MOSTLY SUNNY SKIES...MAX TEMPS WILL RUN A FEW DEGREES BELOW
NORMAL...PARTICULARLY OVER THE NC ZONES.
&&
.SHORT TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
AS OF 235 PM TUESDAY...BEGINNING OF SHORT TERM WEATHER EXPECTED TO
BE RATHER TRANQUIL AS A SPRAWLING AREA OF HIGH PRESSURE FROM THE
GREAT LAKES INTO THE TN VALLEY MAINTAINS CONTROL OF THE WEATHER WED
NIGHT THROUGH PROBABLY THU NIGHT. CONDITIONS WILL BE GENERALLY CLEAR
WITH SEASONAL TEMPS DURING THAT TIME PERIOD...WITH INCREASING
CLOUDINSS LATE THU NIGHT. THINGS QUICKLY BECOME MORE INTERESTING AND
COMPLICATED LATE IN THE WEEK AS CYCLOGENESIS COMMENCES IN THE
WESTERN GOM ON THU IN RESPONSE TO DIGGING UPPER TROUGH OVER THE
MIDSECTION OF THE COUNTRY. THIS LOW TRACKS EASTWARD AND WILL
PROBABLY MOVE ACROSS NORTHERN FLORIDA ON FRI AND THEN TO SOMEWHERE
OFF THE SC COAST BY 12Z SAT. ALL MODELS AGREE ON THE CYCLOGENESIS IN
THE GULF AND THE EASTWARD MOVEMENT OF THE LOW...BUT FOR OUR AREA THE
DETAILS ON HOW THE LOW WILL ULTIMATELY INPACT THE WESTERN CAROLINAS
AND NE GA IS STILL RATHER HAZY. THE 12Z GFS SOLUTION IS QUITE
BULLISH ON QPF AND COLD ENOUGH FOR FROZEN PRECIP ACROSS MOST THE
AREA. HOWEVER...THIS SOLUTION IS IN DOUBT AS UPPER TROUGH NEVER
REALLY TAKES ON A NEG TILT AND OTHER MODEL SOLUTIONS FOR THE AREA
NOT AS COLD. THE 12Z ECM HAS THE HEAVIEST PRECIP GENERALLY S OF I-85
AND 12Z GEM EVEN FARTHER S. SO TAKING A MODEL BLEND WOULD FAVOR
HIGHEST POPS/QPF ACROSS NE GA/THE PIEDMONT OF SC WITH LIGHTER QPF
EXTENDING NORTH INTO WESTERN NC. IN REGARD TO WEATHER TYPE...A BLEND
OF GFS/ECM THICKNESS FIELDS AND UTILIZING THE TOP DOWN METHOD WOULD
FAVOR A WINTERY MIX EARLY ON FRI OVER NE GA...SOUTHERN UPSTATE...BUT
ALL RAIN ACROSS THE UPSTATE IN THE AFTERNOON. A WINTERY MIX THEN
RETURNS FRI NIGHT INTO SAT. AT THIS POINT...CAN'T RULE OUT SOME
ACCUMULATING SNOW...BUT RIGHT NOW IT LOOKS TOO PROBLEMATIC TO BE
DEFINITIVE IN ANY WAY. HAVE COOLED MAX TEMPS CONSIDERABLY BELOW GUID
ON FRI/SAT IN DEFERENCE OT CLOUDS AND PRECIP.
&&
.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
AS OF 200 PM TUESDAY...THE EXT RANGE BEGINS WITH THE INTRODUCTION OF
MORE MODEL SPREAD AND UNCERTAINTY. THE 12Z GFS AND 12Z GEM BECOME
MORE AGREEABLE WITH THE UPPER PATTERN...WHILE THE 00Z ECMWF LOOKS
MORE AND MORE LIKE THE OUTLIER. WRAP AROUND MOISTURE STILL LOOKS
GOOD...BUT NOT AS PROLONGED AS THE ECMWF TAKES IT WITH ITS STRONG
POLAR VORTEX CROSSING OVER THE MIDWEST AND OH VALLEYS LATE SUN
THROUGH WED. THE EASTWARD SHIFTING UVLV RIDGE DEPICTED BY THE GEM
AND THE GFS IS GOING TO BE GIVEN MORE CREDENCE IN THIS FCST
PACKAGE...WHICH THEREFORE ACCOUNTS FOR A LOW END WRAP AROUND
EVENT...FOLLOWED BY ANOTHER BROAD ARCTIC HIGH DEVELOPING ACROSS THE
MID/ATL AND SE REGION BEGINNING SUN AFTERNOON.
SO...POPS WILL BE ADJUSTED UP TO LOW END CHANCE ACROSS THE NC MTNS
SAT NIGHT...LOWERING TO SLIGHT CHANCE AFTER 12Z AS LLVL MOISTURE IS
QUICK TO DIMINISH. THE EXPECTED P/TYPE WILL BE ALL -SNSH...EXCEPT
FOR -SHRA ACROSS THE DOWNSLOPING AREAS EAST OF THE NRN FOOTHILLS.
QPF IS STILL NOT CERTAIN...BUT THE OVERALL PROGRESSIVE PATTEN MAKES
THE CASE FOR ADDITIONAL SN ACCUM ON THE LOW END ...MOST LIKELY
AROUND AN INCH OR LESS ACROSS THE HIGHER ELEVATIONS.
THE OP MODELS DO AGREE ON A SIGNIFICANT LOWERING AND MAINTENENCE OF
THE LLVL THICKNESSES REGARDLESS OF THE ARCTIC HIGH PLACEMENT THROUGH
THE EXT. THIS GIVES DECENT CONFIDENCE IN ADVERTISING MAX TEMPS
SUN/MON ABOUT 10 DEGREES BELOW CLIMO EVEN WITH THE INCREASED
INSOLATION ANTICIPATED. RETURN SSW/LY FLOW IS MOST LIKELY TO DEVELOP
BY NEW DAY 7...WHICH SHOULD ALLOW MAX TEMPS TO REACH A COUPLE
DEGREES BELOW NORMAL.
&&
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
KCLT...VFR THRU THE PERIOD WITH OVC ALTO/CIRROSTRATUS DECK IN THE
15000-20000 FT RANGE...EVENTUALLY CLEARING LATE TNGT. WINDS WILL
REMAIN OUT OF THE NNW THIS EVENING...SHIFTING TO NNE LATER TONIGHT
AND FALLING UNDER 10 KTS.
KAVL...GUSTY NNWLY WND THIS EVENING POSSIBLY GUSTING OVR 30 KTS AT
TIMES...THEN GRADUALLY DIMINISHING TO ARND 10 KTS BY DAYBREAK WED.
OBSERVATIONS ACRS ERN TN SHOW MVFR CIGS WITHIN NWLY FLOW. SOME OF
THIS CLOUDINESS MAY REACH THE TERMINAL...BUT ANY MVFR CIGS SHUD BE
BRIEF.
ELSEWHERE...VFR THRU THE PERIOD WITH NLY/NWLY WND GENERALLY ARND 10
KTS...GRADUALLY SHIFTING TO NELY AND DECREASING.
OUTLOOK...UNRESTRICTED CIG/VSBY WED-THU IN DRIER AIRMASS. A WEAK
SYSTEM APPROACHES FROM THE W FRI...POSSIBLY BRINGING LOWER CIG/VSBY
AND SCT RAIN OR SNOW SHOWERS LATER FRI AND SAT.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...LAKE WIND ADVISORY UNTIL 6 AM EST WEDNESDAY FOR NCZ033-048>050-
053-064-065-501-503-505-507-509.
SC...NONE.
&&
$$
SYNOPSIS...SBK
NEAR TERM...MCAVOY
SHORT TERM...LG
LONG TERM...SBK
AVIATION...ARK/MCAVOY
