FXUS62 KGSP 280819
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
319 AM EST FRI DEC 28 2007

.SYNOPSIS...
HIGH PRESSURE WILL PERSIST ACROSS THE MID ATLANTIC STATES THROUGH 
MID DAY FRIDAY IN ADVANCE OF AN APPROACHING COLD FRONT. THIS FRONT 
WILL CROSS THE FORECAST AREA EARLY SATURDAY WITH AN AREA OF HIGH 
PRESSURE BUILDING IN THROUGH THE WEEKEND. ANOTHER SYSTEM WILL AFFECT 
THE CAROLINAS SUNDAY THROUGH MONDAY MORNING...BEFORE COLDER CANADIAN 
HIGH PRESSURE SETTLES ACROSS THE AREA TUESDAY THROUGH THE END OF THE 
WORK WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
THE MAIN FORECAST CHALLENGE FOR TODAY IS THUNDERSTORM POTENTIAL AND 
WINDS IN THE MTNS...AS A COLD FRONT APPROACHES FROM THE WEST. SHORT 
RANGE GUIDANCE SHOWS THE POTENTIAL FOR SOME SPRINKLES MAINLY ACROSS 
THE PIEDMONT THIS MORNING...AS ISENTROPIC LIFT STRENGTHENS. THE 
STRONGEST OMEGA LOOKS TO BE DURING THE AFTN...WITH ENOUGH MOISTURE 
FOR WIDESPREAD COVERAGE (PWATS WELL OVER AN INCH). INSTABILITY IS 
VERY WEAK (250 J/KG CAPE AT MOST ACROSS SOUTHWESTERN COUNTIES). 
SHEAR WILL BE DECENT...HOWEVER...AS 850MB JET IS PROGGED TO BE 50-60 
KT OUT OF THE SOUTHWEST. THIS LLVL JET ADDS THE POTENTIAL FOR WIND 
ADVISORY CRITERIA GUSTS ESPECIALLY ABOVE 3500 FT. SO I DID NOT MAKE 
ANY CHANGES TO INHERITED WIND ADVISORY. WITH REGARDS TO SEVERE WX 
POTENTIAL...IT LOOKS QUITE REMOTE...AS THE MAIN VORT MAX IS EXPECTED 
TO TRACK WELL NORTH OF THE AREA. SPC HAS KEPT THE SLIGHT RISK TO OUR 
WEST IN THE DAY1 OUTLOOK. TEMPERATURES SHOULD REACH THE 50S AT ALL 
AREAS BY EARLY EVENING...DESPITE CLOUDY SKIES DUE TO STRONG WAA 
FLOW. MOST OF THE RAIN IS EXPECTED TO OCCUR OUT AHEAD OF THE COLD 
FRONT THROUGH THIS EVENING.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/...
AS OF 300 AM FRIDAY...A BUSY SHORT RANGE WITH TWO SYSTEMS TO DEAL 
WITH. THE FIRST SYSTEM WILL BE MOVING THROUGH THIS EVENING. THE 
MODELS ARE IN FAIRLY GOOD AGREEMENT WITH THE TIMING OF THE FRONT AND 
CATEGORICAL POP LOOKS LIKE A GOOD BET OVER THE MTNS AND FOOTHILLS. 
HAVE KEPT THUNDER IN THE EVENING BUT LACK OF UPPER FORCING SUGGESTS 
THAT IT WILL NOT BE ANYTHING MORE THAN SCATTERED. MODELS SHOW A 
STRONG LOW LEVEL JET ON THE ORDER OF 50 TO 60KTS...BUT SIMILAR TO 
OTHER WARM ADVECTION FLOWS...THINK THE STRONG WINDS WILL NOT MAKE IT 
BELOW THE TALLEST RIDGETOPS. SIMILAR TO LAST EVENT...THINK AN 
ADVISORY SHOULD HANDLE THE POTENTIAL APPROPRIATELY...SO NO CHANGES 
THERE. TEMPS ARE A GUIDANCE BLEND.

SATURDAY SHOULD HAVE A LOW CHANCE OVER THE FAR EAST TO ACCOUNT FOR 
LEFTOVERS...BUT OTHERWISE THERE SHOULD BE SOME CLEARING AND A BREAK 
IN THE ACTION DURING THE AFTERNOON AND INTO THE EVENING. NUDGED THE 
MAX TEMP TOWARD THE GRIDDED MOS FIGURING THAT MET GUIDANCE WAS TOO 
HIGH WITH THE POTENTIAL FOR HIGH CLOUDS AND A LATE START ACROSS THE 
PIEDMONT.

THINGS SHOULD GO STEADILY DOWNHILL AGAIN SATURDAY NIGHT AS A WAVE 
TAKES SHAPE ALONG THE FRONT OVER THE NW/NRN GULFMEX. STRENGTHENING 
ISENTROPIC UPGLIDE THROUGH MID LEVELS SHOULD FORCE THE DEVELOPMENT 
OF LIGHT PRECIP FROM S TO N AFTER MIDNIGHT...BUT INITIALLY DRY LOW 
LEVELS WILL EVAPORATE A LOT OF THIS BEFORE IT REACHES THE GROUND. 
HAVE KEPT THE MEASURABLE PRECIP TO THE S OF I-40 BY THE END OF THE 
NIGHTTIME PERIOD. CHANCES RAMP UP QUICKLY IN THE MORNING WITH 
LIKELY/CATEGORICAL POPS IN THE AFTERNOON...WHICH SEEMS REASONABLE AS 
THE SURFACE LOW PASSES AND UPPER FORCING IS MAXIMIZED. THERE COULD 
BE SOME PRECIP TYPE ISSUES EARLY IN THE MORNING ON SUNDAY OVER THE 
NRN MOUNTAINS IF WET BULB EFFECTS ARE TAKEN INTO ACCOUNT. THE TOP 
DOWN METHOD SUGGESTS THE POTENTIAL FOR SOME SLEET MIXED IN ACROSS 
THAT AREA...SO IT WILL BE INCLUDED WITH THE RAIN. BY NOON... PRECIP 
TYPE SHOULD BE RAIN ACROSS THE ENTIRE FORECAST AREA. KEPT HIGH TEMP 
ON THE COOL SIDE SIMILAR TO THE MAV GIVEN THE HIGH POP.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
AS OF 315 AM FRIDAY...THE MAIN FEATURE OF THE MEDIUM RANGE FORECAST 
IS THE POTENTIAL FOR A BLOCKBUSTER NORTHWEST FLOW SNOWFALL EVENT DURING 
THE MIDDLE OF NEXT WEEK. OVERALL...00Z/28 RUNS OF THE GFS AND ECMWF 
ARE IN GOOD AGREEMENT ON THE SYNOPTIC PATTERN EVOLUTION FROM MONDAY 
THROUGH FRIDAY. THE TROUGH AFFECTING THE REGION SUNDAY NIGHT QUICKLY 
PUSHES OFF THE EAST COAST...TAKING WITH IT THE SURFACE CYCLONE. RAIN 
CHANCES DRY UP QUICKLY SUNDAY NIGHT INTO EARLY MONDAY AS BEST LIFT 
AND MOISTURE EXIT STAGE RIGHT. DO CARRY SOME LINGERING CHANCE 
POPS...MAINLY IN THE EAST IN THE 00-06Z TIME FRAME MONDAY.

THE MOST INTERESTING PORTION OF THE FORECAST TAKES SHAPE TUESDAY 
THROUGH THURSDAY. THE MOST RECENT MODELS RUNS PORTRAY ALL OF THE 
INGREDIENTS FOR A HIGH IMPACT NORTHWEST FLOW SNOWFALL EVENT. A 
CLIPPER TYPE LOW DEVELOPS AND MOVES EASTWARD ACROSS THE GREAT LAKES 
ON TUESDAY...PUSHING A WEAK COLD FRONT THROUGH THE FORECAST AREA. 
BEHIND IT...H85 TEMPS BEGIN FALLING BELOW 0C AFTER 12Z TUESDAY. GFS 
SHOWS H85 TEMPS GETTING AS LOW AS -18C BY 06Z THURSDAY ACROSS THE NC 
MOUNTAINS. LOW LEVEL MOISTURE IMPINGES ON WESTERN CAROLINAS ON 
TUESDAY AND REMAINS IN PLACE THROUGH THURSDAY MORNING. LOW LEVEL NW 
WINDS AND MOISTURE MAXIMIZE WEDNESDAY AND WEDNESDAY NIGHT...MAKING 
THIS THE PRIME PERIOD FOR SNOWFALL. CROSS SECTIONS TAKEN FROM OFF 
THE TIP OF LAKE MICHIGAN TO THE NC MOUNTAINS SHOW THE TOP OF THE 
MOIST LAYER REACHING -30C WEDNESDAY AFTERNOON...WHICH IS WELL INTO 
THE DENDRITIC CRYSTAL GROWTH LAYER. MODEL SOUNDINGS ALONG THE 
TENNESSEE BORDER ALSO SHOW 25-50 J/KG OF CAPE ON WEDNESDAY WHICH 
WOULD SUPPORT CONVECTIVE NATURE OF SNOW SHOWERS AND SOME BURSTS OF 
HEAVY SNOW. ALSO...ORIENTATION OF ISOBARS CREATES A BACKWARD 
TRAJECTORY POTENTIAL THAT WOULD BE CONDUCIVE FOR A GREAT LAKES 
INFLUENCE AND ENHANCEMENT OF SNOWFALL ACROSS THE AREA. I HAVENT EVEN 
MENTIONED THE COLD AIR YET...WHICH IS VERY IMPRESSIVE. IF YOU HAD TO 
MAKE A LIST OF THE INGREDIENTS FOR A BIG NORTHWEST FLOW SNOW 
EVENT...THE CURRENT MODEL RUNS PORTRAY THEM ALL.

LOW LEVEL MOISTURE RETREATS NORTHEASTWARD ON THURSDAY AS A STRONG 
SURFACE HIGH BUILDS IN FROM THE WEST. HIGHEST POPS ARE IN PLACE 
WEDNESDAY AND WEDNESDAY NIGHT. CURRENTLY...THIS EVENT LOOKS AS 
THOUGH IT IS EASILY CAPABLE OF PRODUCING WARNING CRITERIA SNOWFALL 
ACROSS MUCH OF THE NC MOUNTAINS.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
SFC HIGH PRESSURE IS BUILDING OFF THE MID ATLANTIC COAST...WHILE LOW 
PRESSURE ALOFT APPROACHES THE AREA FROM THE WEST. THE RESULT IS 
MOIST UPGLIDE ACROSS THE REGION...WITH LOWERING CIGS AND POSSIBLY 
SOME VSBY RESTRICTIONS. PRECIP WILL DEVELOP BY MIDDAY FRIDAY...WITH 
GENERALLY IFR CIGS AND/OR VSBY THROUGH THE REST OF THE TAF PERIOD. 
WINDS WILL VEER TO SOUTHEASTERLY...THEN SOUTHWESTERLY DURING THE DAY.

AVIATION OUTLOOK...LOW CEILINGS AND LIGHT TO MODERATE RAINFALL 
SHOULD CONTINUE INTO LATE FRI NIGHT. A COLD FRONT WILL SWEEP ACROSS 
THE AREA BETWEEN 6Z-15Z SAT. AFTER 15Z SAT...UNLIMITED CEILING AND 
VIS SHOULD REMAIN ACROSS THE WESTERN CAROLINAS UNTIL LATE SUN 
AFTERNOON. SUN EVENING AND NIGHT...LOW CEILINGS AND WIDESPREAD RAIN 
SHOULD DEVELOP ACROSS THE CWA. CONDITIONS SHOULD IMPROVE EARLY MON 
MORNING. GUSTY NORTHWEST WINDS WILL ARRIVE TUESDAY...AND MOUNTAINS 
SNOW SHOWERS AND ASSOCIATED RESTRICTIONS MAY VISIT KAVL.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...WIND ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR GAZ010.
NC...WIND ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR NCZ033-048>053-
     058-059-062>065.
SC...NONE.

&&

$$
SYNOPSIS...BSH
NEAR TERM...ARK
SHORT TERM...PM
LONG TERM...BSH
AVIATION...ARK