000
FXUS62 KGSP 211425
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1025 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/...
1430 UTC UPDATE...THE FOG HAS LIFTED ACROSS THE NC MTN VALLEYS AND
THE LOW CIGS ARE IN THE PROCESS OF BREAKING UP ACROSS THE ERN
PIEDMONT ATTM. SKY COVER WAS ADJ ACCORDINGLY WITH GOOD CLEARING IN
WEAK DOWNSLOPE FLOW. MAX TEMPS WERE BUMPED UP A DEGREE OR TWO MOST
AREAS BASED ON A LLVL THICKNESS BLEND. STILL ANTICIPATE SCT
CONVECTION ACROSS THE MTNS THIS AFTERNOON IN ISENT/MECH LIFT ALIGNED
WITH STEEP MLVL LAPSE RATES...AND HIGH CAPE/LOW SHEAR PULSE STORMS
ACROSS THE NON/MTNS. ALONG WITH GOOD HAIL PRODUCERS...THESE STORMS
WILL ALSO CREATE A HIGH WIND THREAT WITH INCREASING DCAPE THROUGH
THE AFTERNOON.

1015 UTC UPDATE...VISIBILITY WAS UPDATED FROM OBSERVATIONS...PLACING
PATCHES OF DENSE FOG IN SOME LOCATIONS. AS THE DENSE FOG AREAS ARE
SCATTERED ABOUT...NO DENSE FOG ADVISORY IS PLANNED AT THIS TIME.

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 /15Z TUESDAY THROUGH SATURDAY/...
1430 UTC UPDATE FOR KCLT...MAINTAINED AN IFR CIG / TEMPO MVFR AT THE
TERMINAL THROUGH 16Z WITH PERSISTENT CLOUDINESS ALIGNED IN A WEAK
SFC TROF. THUNDER CHANCES LOOK TO BE MORE SCTTERED THIS AFTERNOON
AND WILL CONSIDER REMOVING PREVAILING THUNDER FOR THE 18Z TAFS.

AT KCLT...A BRIEF MVFR CIG OR VSBY RESTRICTION WILL BE POSSIBLE
EARLY THIS MORNING IN A MOIST AIR MASS. OTHERWISE...LOW VFR CLOUDS
WILL PERSIST FOR MUCH OF THE DAY...WITH MIDDAY BREAKS POSSIBLE.
INSTABILITY WILL BE SUPPORTIVE OF CONVECTION TODAY...MAINLY IN THE
AFTERNOON. LIGHT SSW WINDS WILL PERSIST. BLENDED GUIDANCE DOE NOT
SUPPORT WEDNESDAY MORNING RESTRICTIONS...BUT IF PRECIPITATION FALLS
AT THE FIELD TODAY...FOG AND STRATUS WOULD BE MORE LIKELY LATE
TONIGHT.

ELSEWHERE...RESTRICTIONS AT KAVL WILL LINGER INTO MID MORNING.
FOOTHILLS SITES MAY EXPERIENCE BRIEF RESTRICTIONS AS WELL BEFORE
HEATING TAKES PLACE THIS MORNING. CONVECTION WILL BE SUPPORTED BY
INSTABILITY THIS AFTER NOON AND EVENING...PERHAPS EVEN BY LATE
MORNING IN THE MOUNTAINS. LIGHT WINDS WILL FAVOR THE SSW. GUIDANCE
SUPPORTS MVFR FOG AT KAVL EARLY WEDNESDAY MORNING...WITH LOW VFR AT
KHKY AND KAND. ANY SITES THAT RECEIVE RAIN THIS AFTERNOON OR EVENING
WOULD BE VULNERABLE TO LOWER RESTRICTIONS.

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

CONFIDENCE TABLE...

            14-20Z        20-02Z        02-08Z        08-14Z
KCLT       HIGH  92%     HIGH 100%     HIGH 100%     HIGH  85%
KGSP       HIGH  98%     HIGH 100%     HIGH 100%     HIGH  85%
KAVL       HIGH  90%     HIGH 100%     HIGH  88%     HIGH  83%
KHKY       HIGH  97%     HIGH 100%     HIGH 100%     HIGH  80%
KGMU       HIGH  96%     HIGH 100%     HIGH 100%     HIGH  81%
KAND       HIGH  95%     HIGH 100%     HIGH 100%     HIGH  98%

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/SBK
SHORT TERM...RWH
LONG TERM...RWH
AVIATION...JAT/SBK