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000
FXUS62 KGSP 231837
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
237 PM EDT THU MAY 23 2013

.SYNOPSIS...
AN UPPER LEVEL TROUGH WILL SWING THROUGH THE REGION TOMORROW...
BRINGING COOLER AND DRIER CONDITIONS FOR THE WEEKEND. TEMPERATURES
WILL MODERATE BY THE BEGINNING OF NEXT WEEK... WITH A CHANCE OF
AFTERNOON SHOWERS AND THUNDERSTORMS EACH DAY CONCENTRATED OVER THE
MOUNTAINS.

&&

.NEAR TERM /THROUGH FRIDAY/...
AS OF MID AFTERNOON...A FEW SHOWERS HAVE POPPED UP QUICKLY NEAR THE
BLUE RIDGE. THESE SHOULD BE DRIVEN EASTWARD OVER THE FOOTHILLS AND
WESTERN PIEDMONT THROUGH LATE AFTERNOON. SATELLITE IMAGERY SHOWS
SOME ENHANCED CU OVER THE RIDGETOPS...SO ADDITIONAL DEVELOPMENT IS
POSSIBLE. THE CURRENT POP FCST...WITH THE HIGHEST VALUES E OF
I-77... STILL LOOKS OKAY. CANNOT RULE OUT ONE OR TWO SEVERE CELLS
GIVEN SUFFICIENT CAPE ON THE LATEST LAPS ANALYSIS AND SOME DCAPE AS
WELL...BUT NEITHER IS AS GOOD AS YESTERDAY. NE GEORGIA AND THE
UPSTATE WILL HAVE THE LEAST CHANCE OF PRECIP BECAUSE OF A LACK OF
TRIGGER.

THE CONVECTION WILL BE SHUNTED EAST BY THE VEERING FLOW AHEAD OF THE
MAIN COLD FRONT...WHICH IS EXPECTED TO CROSS THE FCST AREA THIS
EVENING AS A SHORT WAVE ROUNDS THE BOTTOM OF THE UPPER TROF AND
SWINGS IT EASTWARD...CARRYING MOST OF THE CLOUDS AND SHOWERS WITH
IT. EXPECT SOME LINGERING SHOWER CHANCE ON THE TN BORDER THROUGH
FRIDAY MORNING WITH MOISTURE BEING FORCED UPWARD BY THE INCREASING
NW FLOW.

ON FRIDAY...IT LOOKS LIKE A BREEZY DAY WITH A DECENT PRESSURE
GRADIENT AS HIGH PRESSURE BUILDS IN FROM THE NW. AN EVEN MORE
DYNAMIC SHORT WAVE WILL ROUND THE BASE OF THE TROF AND CARRY THE
TROF AXIS FARTHER EAST DURING THE DAY...BUT THIS WAVE HAS NO
MOISTURE TO WORK WITH THIS FAR SOUTH. MIXING WILL BE RELATIVELY
SHALLOW BECAUSE OF A STRONG INVERSION...WHICH WILL PREVENT THE
TAPPING OF THE MUCH STRONGER WINDS AROUND 850 MB. THUS WE SHOULD
AVOID ANY WIND ADVISORY ISSUES. HIGH TEMPS WILL BE A FEW CATEGORIES
COOLER THAN TODAY.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
AS OF 210 PM THURSDAY...A STRONG UPPER LOW WILL MOVE UP THE EAST
COAST FRIDAY NIGHT AS AN UPPER RIDGE BUILDS OVER THE CENTRAL PART OF
THE COUNTRY. THIS WILL ALLOW A COOL NW FLOW TO CONTINUE ACROSS THE
SOUTHERN APPALACHIANS THROUGH THE WEEKEND.  AT THE SURFACE...A RIDGE
OF HIGH PRESSURE WITH CANADIAN ORIGIN IS FORECAST TO EXTEND FROM THE
GREAT LAKES SOUTHWARD TO FLORIDA FRIDAY NIGHT. THE HIGH WILL CONTROL
THE WEATHER THROUGH SATURDAY PRODUCING GENERALLY CLEAR AND
SEASONALLY COOL WEATHER. IN FACT...SOME SHELTERED MOUNTAIN VALLEYS
COULD SEE SOME SOME SCATTERED FROST FRI NIGHT PARTICULARLY IN THE
LITTLE TN VALLEY.

ON SUNDAY...AN UPPER IMPULSE IN THE NW FLOW ALOFT WILL CROSS THE
AREA ALONG WITH A WEAK BACKDOOR SURFACE FRONT. LOW LEVEL MOISTURE
WILL BE LACKING...BUT MODEL TIME HEIGHTS SHOW MID AND UPPER LEVEL
MOISTURE INCREASING WHICH MEANS AN INCREASE IN CLOUD COVER FOR SAT
NIGHT INTO SUNDAY. MODEL QPF RESPONSE IS QUITE MINIMAL ON SUNDAY AND
ANYTHING THAT DOES FALL WOULD PROBABLY BE JUST A FEW SPRINKLES OVER
THE MOUNTAINS.

USED A MODEL BLEND FOR TEMPS WHICH ADVERTISES WELL BELOW AVERAGE
TEMPERATURES FOR THE ENTIRE WEEKEND. MIN TEMPS FRI NIGHT WILL FALL
INTO THE UPPER 30S OVER MANY MOUNTAIN LOCATIONS WITH 40S COMMON
ELSEWHERE. MAX TEMPS WILL BE IN THE 70S...EXCEPT MID 60S TO AROUND
70 MOUNTAIN VALLEYS.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
AS OF 145 PM THURSDAY...THE 06Z/12Z GFS AND 00Z ECMWF ARE NOW SOMEWHAT
AT ODDS IN REGARD TO THE UPPER LEVEL FLOW PATTERN. THE MAIN
DIFFERENCE IS THAT THE GFS IS QUICKER MOVING THE ANOMOLOUSLY STRONG
UPPER LOW THROUGH NEW ENGLAND AND OUT OF THE PICTURE. THIS ALLOWS
THE FLOW TO DEAMPLIFY OVER THE SE BY MONDAY WITH AN UPPER RIDGE
BUILDING OVER THE REGION BY MIDWEEK. THE ECM ON THE OTHER HAND KEEPS
THE SE U.S. IN A NW FLOW REGIME TO THE EAST OF AN UPPER HIGH IT
HOLDS STATIONARY OVER THE LOWER MISSISSIPPI VALLEY. THIS ALLOWS WEAK
IMPULSES TO TRANSLATE ACROSS THE REGION IN THE NW FLOW MAKING FOR A
RATHER UNSETTLED PERIOD UNTIL LATE WEEK WHEN THE ECM FINALLY BUILDS
THE RIDGE TO THE EAST. THE LATEST GFS ENSEMBLE SUPPORTS THE GFS
OPERATIONAL RUNS.

WPC HAS FAVORED THE ECM IN ITS MEDIUM RANGE. HOWEVER...I HAVE HEDGED
THE FORECAST TOWARD A BLEND OF OUR GSP OFFICIAL/GFS/ECM WHICH WOULD
PUT A DIURNAL HARMONIC TO THE FORECAST FAVORING SCATTERED AFTERNOON
CONVECTION MAINLY OVER THE MOUNTAINS. THE EXCEPTION IS MON AFTERNOON
WHEN SOME SCATTERED SHOWERS/THUNDERSTORMS MAY ALSO OCCUR OVER THE NC
FOOTHILLS/PIEDMONT AS THE BACKDOOR FRONT THAT SLIPPED THROUGH THE
AREA ON SUN RETURNS NORTH AS A WARM FRONT. TEMPS WILL BEGIN THE
PERIOD A LITTLE BELOW CLIMO...THEN WARM TO ABOUT A CATEGORY ABOVE
CLIMO BY THE END OF THE WEEK. IF THE GFS SOLUTION VERIFIES...MAX
TEMPS WOULD BE ABOUT A CATEGORY HIGHER EACH DAY.

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
AT KCLT...MVFR CIG RESTRICTION SHOULD NOT LAST MORE THAN ONE OR TWO
HOURS AS THE BOUNDARY LAYER WARMS AND DEEPENS...LIFTING ANY CLOUD
BASES UP IN TO THE 035 TO 050 RANGE. THINK THAT AT LEAST A TEMPORARY
LOW CLOUD VFR CEILING WILL CONTINUE THROUGH THE AFTERNOON GIVEN
SUFFICIENT MOISTURE IN THE BOUNDARY LAYER. HAVE HELD ONTO A TWO HOUR
WINDOW OF THUNDERSTORMS PER THE 4KM WRF MODEL IN THE 21Z TO 23Z TIME
RANGE...BUT CONFIDENCE IS DROPPING. THE FRONT SHOULD FINALLY CROSS
THE REGION DURING THE MIDDLE PART OF THE EVENING WHICH WILL CLEAR
OUT THE LOW CLOUDS AND SHIFT THE WIND FROM SW TO NW...BY 04Z AT THE
LATEST. CONDITIONS SHOULD BE VFR FROM THAT POINT ONWARD. ON
FRIDAY...ONCE THE WINDS COME UP DURING MID MORNING...EXPECT FREQUENT
GUSTS FROM THE NW.

ELSEWHERE...SIMILAR CHANCES FOR MVFR CEILING UNTIL 20Z OR SO WHEN
THE BOUNDARY LAYER LIFTS THE CLOUD BASES ABOVE 030. OTHERWISE...
LESS OF A CHANCE FOR CONVECTIVE ACTIVITY. ONLY KHKY WARRANTS A
VICINITY THUNDERSTORM FOR THE TIME BEING. EXPECT VFR CONDITIONS
AFTER FRONTAL PASSAGE...WHICH SHOULD BE LATE AFTERNOON TO EARLY
EVENING. SOME UPSLOPE SHOWERS COULD OCCUR ALONG THE TN BORDER...BUT
THIS IS NOT EXPECTED TO AFFECT KAVL. WINDS SHOULD BE STRONG AND
GUSTY FROM THE NW ON FRIDAY.

OUTLOOK...VFR THROUGH THE PERIOD.

CONFIDENCE TABLE...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       HIGH  85%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     MED   79%     HIGH  81%     HIGH  95%
KHKY       HIGH  89%     HIGH 100%     HIGH  83%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     HIGH 100%     HIGH  94%     HIGH 100%

THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING
WITH THE SCHEDULED TAF ISSUANCE FLIGHT RULE CATEGORY. COMPLETE
HOURLY EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES AND ENSEMBLE
FORECASTS ARE AVAILABLE AT THE FOLLOWING LINK: (MUST BE LOWER CASE)

WWW.WEATHER.GOV/GSP/AVIATION_TABLES

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.

&&

$$
SYNOPSIS...LEV
NEAR TERM...PM
SHORT TERM...LG
LONG TERM...LG
AVIATION...PM