000
FXUS62 KGSP 211801
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
201 PM EDT TUE MAY 21 2013

.SYNOPSIS...
AN APPROACHING UPPER LEVEL TROUGH WILL CONTINUE TO INFLUENCE THE
REGION THROUGH MIDWEEK. SOUTHERLY FLOW WILL KEEP THE AREA WARM AND
GENERALLY UNSETTLED WITH STORM CHANCES EACH AFTERNOON. A COOLER AND
DRIER AIRMASS SETTLES IN FOR THE WEEKEND AFTER A COLD FRONT MOVES
THROUGH THURSDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
1730 UTC UPDATE...ONLY MINOR CHANGES NEEDED TO THE GOING FCST. TEMPS
AND TD/S ARE RIGHT ON TRACK AND THE MAXT LOOKS GOOD. VIS SATELLITE
INDICATES PULSE STORMS DEVELOPING ACROSS THE MTNS AS STEEPER LAPSE
RATES MOVE IN AND COMBINES WITH MECH LIFT. ACROSS THE ERN
ZONES...THERE IS A NOTABLE LINE OF ISOL PULSE STORMS ALIGNED WITH A
VORT BNDRY REMNANT OF A PREVIOUS S/W. GOOD CAPE HAS DEVELOPED AND
DCAPE IS NOW BTW 800-900 J/KG ACROSS THE MOST OF NON/MTNS. EXPECT A
GENERAL INCREASE IN COVERAGE WITH SLOW MOVING PULSE SEVERE POSSIBLE
OVER THE NEXT COUPLE OF HOURS.

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 /18Z TUESDAY THROUGH SUNDAY/...
AT KCLT...EXPECT LOW VFR CIGS THIS AFTERNOON WITH PERIODIC PULSE
CONVECTION DEVELOPING WITHIN THE TAF ZONE BY 21Z AND PERSISTING
THROUGH 01Z. DEBRIS CLOUDS OVERNIGHT WILL LOWER...SIMILAR TO THIS
MORNING...AND SHUD HELP CREATE MVFR CIGS BY DAYBREAK. ALSO
ANTICIPATE MVFR VSBY AFT 07Z THROUGH 13Z.

ELSEWHERE...VFR CONDS...BUT RESTRICTIVE CONVECTION WILL BECOME MORE
WIDESPREAD THIS AFTERNOON...THUS ALL TAF SITES WERE GIVEN A TEMPO
TSRA THROUGH MID EVENING. A MOIST ATMOS WILL PERSIST OVERNIGHT WITH
DEBRIS CLOUDS LOWERING AND ANTICIPATE MVFR CIGS NON/MTNS AND IFR
CIGS/VSBY AT KAVL DEVELOPING A FEW HRS BEFORE DAYBREAK.

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

CONFIDENCE TABLE...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       HIGH 100%     HIGH 100%     MED   70%     HIGH  80%
KGSP       HIGH 100%     HIGH 100%     HIGH  90%     HIGH  91%
KAVL       HIGH 100%     HIGH  80%     LOW   41%     MED   73%
KHKY       HIGH 100%     HIGH 100%     HIGH  91%     HIGH  94%
KGMU       HIGH 100%     HIGH 100%     HIGH  80%     HIGH  84%
KAND       HIGH 100%     HIGH 100%     HIGH  91%     HIGH  95%

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...SBK