000
FXUS62 KGSP 210750
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
350 AM EDT TUE MAY 21 2013

.SYNOPSIS...
AN APPROACHING UPPER LEVEL TROUGH WILL CONTINUE TO INFLUENCE THE
REGION FOR MOST OF THE WEEK. SOUTHERLY FLOW WILL KEEP THE AREA IN A
MOIST AND GENERALLY UNSETTLED AIRMASS WITH STORM CHANCES EACH
AFTERNOON. RAIN CHANCES DIMINISH AFTER A COLD FRONT CROSSES THROUGH
BY THE END OF THE WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AT 300 AM EST TUESDAY...A WEAK BUT PERSISTENT UPPER LOW WILL DRIFT
NORTHEAST AND AWAY FROM OUR AREA TODAY AND TONIGHT...WHILE AN UPPER
RIDGE AXIS CROSSES THE SOUTHERN APPALACHIANS...AND AN UPPER TROUGH
MOVES FROM THE PLAINS TO THE MS RIVER VALLEY. MODEL TIME HEIGHTS
SHOW LINGERING MOISTURE IN THE WAKE OF THE DEPARTING TROUGH...BUT
WITH DIMINISHED UPPER FORCING...PRECIPITATION WILL BE DRIVEN BY
DIURNAL HEATING. INSTABILITY IN EXCESS OF 1000 J/KG WILL SUPPORT
THUNDERSTORM FORMATION THIS AFTERNOON IF A WEAK LOW LEVEL CAP CAN BE
OVERCOME. DRY AIR ALOFT AND BENEATH CLOUD BASES WILL SUPPORT
EVAPORATIVE COOLING AND DOWNDRAFT PRODUCTION. SHEAR WILL DECREASE
THROUGH THE DAY...LIMITING STORM ORGANIZATION. A WEAKENING STEERING
FLOW WILL MEAN SLOW MOVING THUNDERSTORMS MAY PRODUCE LOCALLY HEAVY
RAINFALL. CONVECTION WILL LINGER INTO THE EVENING BEFORE THE LOW
LEVELS STABILIZE. TEMPERATURES WILL RUN SEVERAL CATEGORIES ABOVE
NORMAL UNDER THE UPPER RIDGE.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 245 AM TUESDAY...SHORT WAVES ROTATING AROUND AN UPPER TROF
MOVE INTO THE AREA WED AND WED NITE. THE UPPER TROF THEN SHARPENS
AND MOVES INTO THE AREA THU NITE. AT THE SFC...A WEAK RIDGE
EXTENDING FROM THE ATLANTIC IS OVER THE AREA WED MORN. THE RIDGE
WEAKENS AS A COLD FRONT APPROACHES FROM THE WEST. THIS WILL ALLOW
SLY FLOW TO DEVELOP BRINGING MOISTURE BACK INTO THE AREA.
INSTABILITY DEVELOPS...BUT REMAINS WEAK. HOWEVER...FORCING WILL
INCREASE AS THE SHORT WAVES MOVE IN. BEST PRECIP CHC REMAINS OVER
THE MTNS AND DIMINISHES SOUTH OF I-85. GIVEN THE FORCING AND WEAK
BUT INCREASING SHEAR...ISOLATED SVR STORMS CANNOT BE RULED OUT. AS
THE SHORT WAVES MOVE EAST AND ATMOS STABILIZES OVERNIGHT...PRECIP
CHC DIMINISHES WITH CHC POP MTNS AND SLIGHT CHC ELSEWHERE. COLD
FRONT JUMPS INTO THE DEVELOPING LEE TROF ON THU. THIS BRINGS BEST
FORCING TO THE NRN AND ERN CWFA...WHERE HIGHEST POP WILL BE FCST.
PRECIP CHC RETREATS TO THE MTNS OVERNIGHT WITH LINGERING MOISTURE
AND NWLY UPSLOPE FLOW. HIGHS WILL BE A LITTLE ABOVE NORMAL EACH DAY.
LOWS AROUND 5 DEGREES ABOVE NORMAL WED NITE DROP TO NEAR NORMAL THU
NITE IN THE COOLER AIR MASS MOVING IN BEHIND THE FRONT.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
AS OF 345 AM TUESDAY...THE CWFA REMAINS IN NWLY FLOW ALOFT AS A TROF
SLOWLY MOVES OUT OVER THE ATLANTIC AND AN UPPER RIDGE MOVES EAST
ACROSS THE CENTRAL CONUS. SHORT WAVE ENERGY THEN MOVES ACROSS THE
AREA BY EARLY NEXT WEEK AS THE FLOW BECOMES MORE ZONAL. AT THE
SFC...DRY HIGH PRESSURE SETTLES IN FROM THE NW FOR FRI AND SAT. A
WEAK WARM FRONT DEVELOPS TO OUR WEST ON SUN AND MOVES TOWARD THE
AREA THRU MON. THE GFS AND ECMWF DISAGREE ON THE AMOUNT OF MOISTURE
AND LIFT THAT DEVELOP AS THE FRONT MOVES EAST. HOWEVER...THEY DO
AGREE THAT PRECIP MAY DEVELOP FOR SUN NITE AND MON. HAVE SLIGHT CHC
POP FOR NOW. HOWEVER...THE BIGGER STORY IS THAT THE AIR MASS MOVING
IN WITH THE HIGH IS QUITE COOL. IN FACT...HIGHS WILL BE AROUND 5
DEGREES BELOW NORMAL FRI AND SAT...RISING TO A COUPLE OF DEGREES
BELOW NORMAL SUN AND MON. LOWS WILL BE AROUND 5 DEGREES BELOW NORMAL
FRI AND SAT NITES...RISING TO NEAR NORMAL SUN NITE.

&&

.AVIATION /08Z TUESDAY THROUGH SATURDAY/...
AT KCLT...NO PRECIPITATION WILL BE CARRIED OVERNIGHT AS HEATING HAS
ABATED AND THE ATMOSPHERE HAS STABILIZED. A BLEND OF MODEL GUIDANCE
SUPPORTS ONLY LOW VFR VSBY IN FOG TOWARD DAWN...DESPITE MOIST LOW
LEVELS. CONFIDENCE ON CIGS IS QUITE LOW DUE TO MODEL VARIANCE.
CLOUDS HEIGHTS WILL GENERALLY BE BASED ON CURRENT OBSERVATIONS...
WITH A DAYBREAK DIP TO MVFR...WHICH IS SUPPORTED BY THE MIDDLE OF
THE ROAD MET GUIDANCE. INSTABILITY WILL SUPPORT ROBUST CONVECTION ON
TUESDAY...MAINLY IN THE AFTERNOON...BUT COVERAGE WILL BE RATHER
LIMITED AS UPPER LEVEL SUPPORT DRIFTS TO THE EAST. LIGHT SOUTH WINDS
WILL PERSIST.

ELSEWHERE...RADAR TRENDS SUPPORT LEAVING PRECIPITATION OUT OF THE
TAFS OVERNIGHT IN A STABILIZING ATMOSPHERE. A GUIDANCE BLEND
SUPPORTS A DAYBREAK IFR CIG AT KAVL...LOW VFR AT KGSP...AND MVFR AT
ALL OTHER SITES. CONFIDENCE IS LOW ON CIGS...ESPECIALLY AT
DAYBREAK...AS MODEL GUIDANCE VARIES CONSIDERABLY...AND THERE IS
STILL SOME DOUBT CLOUD COVERAGE WILL INCREASE ENOUGH BY DAWN IN THE
WAKE OF A DEPARTING UPPER SYSTEM. MVFR CIGS WILL BE CARRIED TOWARD
DAYBREAK AT KGMU...KGSP AND KHKY...WHICH IS SUPPORTED BY LESS
EXTREME MET GUIDANCE. ALTHOUGH CONVECTIVE COVERAGE WILL BE LIMITED
TUESDAY AS UPPER FORCING DEPARTS TO THE EAST...INSTABILITY WILL
SUPPORT VIGOROUS UPDRAFTS. LIGHT SOUTH WINDS ARE EXPECTED.

OUTLOOK... CEILING AND VISIBILITY RESTRICTIONS IN SCATTERED SHOWERS
AND THUNDERSTORMS AGAIN WEDNESDAY AND THURSDAY AFTN/EVE. GENERALLY
VFR WEATHER FRIDAY AND SATURDAY.

CONFIDENCE TABLE...

            08-14Z        14-20Z        20-02Z        02-08Z
KCLT       LOW   57%     HIGH  90%     HIGH 100%     HIGH 100%
KGSP       MED   64%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       LOW   51%     LOW   59%     LOW   58%     MED   62%
KHKY       MED   74%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       MED   77%     HIGH  97%     HIGH 100%     HIGH 100%
KAND       MED   74%     HIGH  97%     HIGH 100%     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...RWH
NEAR TERM...JAT
SHORT TERM...RWH
LONG TERM...RWH
AVIATION...JAT