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000
FXUS62 KGSP 201039
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
639 AM EDT MON MAY 20 2013

.SYNOPSIS...
A WEAK UPPER LEVEL TROUGH WILL REMAIN OVER THE REGION THROUGH
TUESDAY. THE FORECAST AREA WILL REMAIN IN A MOIST AND RATHER
UNSTABLE AIRMASS...BEFORE A COLD FRONT CROSSES THROUGH LATE IN THE
WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
1030 UTC UPDATE...POPS WERE REDUCED ALONG THE INTERSTATE 77 CORRIDOR
PER RADAR TRENDS...AND RAISED IN THE NORTHERN NC MOUNTAINS.

AT 300 AM EST MONDAY...AN UPPER LOW OVER THE CENTRAL APPALACHIANS
WILL DRIFT SLOWLY EAST TODAY AND TONIGHT...WHILE AN ASSOCIATED
TROUGH MOVES FROM THE FOOTHILLS TO THE PIEDMONT OF OUR AREA. THIS
WILL RESULT IN THE BEST COVERAGE OF POPS SHIFTING EAST WITH
TIME...BUT WILL ALSO RESULT IN BETTER AFTERNOON INSTABILITY
DEVELOPING ACROSS THE AREA AS THICKER AND GREATER CLOUD COVER SHIFTS
EAST. MORNING FOG AND STRATUS WILL BE SLOW TO ERODE IN THE MOIST AIR
MASS OVER OUR AREA...BUT THE MODELS SHOW DRIER AIR MOVING IN FROM
THE WEST THIS MORNING...WHICH SHOULD ALLOW FOR EROSION OF
RESTRICTIONS BY MIDDAY. MODEL SOUNDING SUGGEST A VERY WEAK LOW LEVEL
CAP WILL BE PRESENT TODAY...BUT THE CAP IS SO WEAK THAT CHANCE POPS
WILL BE CARRIED ACROSS THE AREA. WITH DRY ALOFT FOR EVAPORATIVE
COOLING...AND INCREASING WIND SHEAR INCREASING...THE POSSIBILITY OF
SEVERE THUNDERSTORMS WILL EXIST...MAINLY THIS AFTERNOON AND EVENING.
LIGHT SOUTHERLY FLOW INTO THE BLUE RIDGE WILL PROVIDE AN UPSLOPE
COMPONENT AND ENHANCE PRECIPITATION THERE. HIGH TEMPERATURES TODAY
WILL BE RANGE FROM ABOVE NORMAL IN THE MOUNTAINS TODAY AS AN UPPER
RIDGE ADVANCES...TO NEAR NORMAL IN THE FOOTHILLS...AND A BIT BELOW
NORMAL IN THE PIEDMONT NEAREST THE UPPER TROUGH AXIS. MINIMUM
TEMPERATURES WILL BE ABOVE NORMAL AS HEIGHTS RISE ALOFT.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
AS OF 330 AM MONDAY...GUIDANCE NOW SHOWS ENERGY FROM THE UPPER TROF
CURRENTLY OVER THE AREA REMAINING IN PLACE FOR TUE EVEN AS AN UPPER
RIDGE TRIES TO BUILD. WHILE THE FORCING WILL NOT BE THAT STRONG...
THERE IS NOW A LACK OF A SUBSIDENCE INVERSION. MODERATE INSTABILITY
DEVELOPS DURING THE AFTERNOON. THIS SHUD LEAD TO ANOTHER DAY OF SCT
CONVECTION...WITH SLIGHTLY BETTER CHC OVER THE MTNS AND WRN CWFA
WHERE INSTABILITY IS BETTER. CONVECTION WILL LINGER A LITTLE LONGER
OVER THE MTNS TUE NITE...BUT IT SHUD STILL BE MAINLY DIURNAL IN
NATURE. HIGHS WILL BE 5 TO 10 DEGREES ABOVE NORMAL AND LOWS AROUND 5
DEGREES ABOVE.

ANY ATTEMPT AT RIDGING ENDS WED AS A TROF ROTATING AROUND ANOTHER
UPPER LOW MOVES INTO THE AREA. ALTHOUGH INSTABILITY WILL NOT BE AS
STRONG...FORCING WILL BE MUCH BETTER. THEREFORE...EXPECT NUMEROUS
COVERAGE OF CONVECTION OVER THE MTNS AND HIGH SCT ELSEWHERE BY
AFTERNOON. CONVECTION STILL LOOKS TO BE MAINLY DIURNAL AS THE TROF
AND FORCING MOVE EAST OF THE AREA OVERNIGHT. ALTHOUGH INSTABILITY
WILL BE LESS...SHEAR AND FORCING WILL BE HIGHER...SO ISOLATED SVR
STORMS ARE POSSIBLE. HIGHS WILL BE A FEW DEGREES LOWER...WHILE LOWS
WILL BE NEARLY STEADY.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
AS OF 400 AM MONDAY...GFS AND ECMWF IN GOOD AGREEMENT ON AN UPPER
TROF MOVING INTO THE AREA THU AND ACROSS THE AREA FRI. THIS LEADS TO
SCT MAINLY DIURNAL CONVECTION EACH DAY. HIGHS THU ABOUT 5 DEGREES
ABOVE NORMAL AND NEAR TO SLIGHTLY ABOVE NORMAL FRI. LOWS ABOUT 5
DEGREES ABOVE NORMAL THU NITE AND NEAR NORMAL FRI NITE.

WEAK RIDGING BUILDS IN SAT WITH SHORT WAVES MOVING BY JUST NORTH OF
THE AREA SUN. AT THE SFC...THE GFS SHOWS DRY HIGH PRESSURE SAT AND
SUN. THE PREV ECWMF WAS WET FOR THE WEEKEND. HOWEVER...THE LATEST
RUN SHOWS A MAINLY DRY BACK DOOR COLD FRONT MOVING IN ON SUN.
THEREFORE...HAVE GONE WITH A DRY FCST BOTH DAYS. HIGHS AND LOWS WILL
BE NEAR NORMAL BOTH DAYS.

&&

.AVIATION /12Z MONDAY THROUGH FRIDAY/...
AT KCLT...SHOWER ACTIVITY HAS MOVED EAST OF THE FIELD...BUT
RESTRICTIONS WILL LINGER INTO MID MORNING UNTIL HEATING CAUSES THE
CIG TO RISE AND FOG TO ERODE. KCLT WILL BE CLOSE TO THE UPPER TROUGH
AXIS...AND CLOUDS COVER WILL LIKELY KEEP A LOW VFR CIG THROUGH THE
DAY. GREATER INSTABILITY TODAY WILL SUPPORT SCATTERED CONVECTION
THIS AFTERNOON INTO THIS EVENING. LIGHT SOUTH WINDS WILL PREVAIL.
MODEL GUIDANCE IS NOT SUPPORTIVE OF RESTRICTIONS EARLY TUESDAY
MORNING...BUT IF THE FIELD EXPERIENCES HEAVY RAINFALL FROM A
THUNDERSTORM...RESTRICTIONS WOULD BE MORE LIKELY.

ELSEWHERE...RESTRICTION WILL ARE EXPECTED TO LIFT AROUND MID MORNING
AS HEATING OCCURS UNDER AN APPROACHING UPPER RIDGE. LOW VFR CIGS WIL
PERSIST INTO THE AFTERNOON...AFTER WHICH MODEL DATA SUPPORTS
LESSENING CLOUD COVER AT LOW LEVELS. ALTHOUGH PRECIPITATION COVER
SHOULD BE LESS AS AN UPPER TROUGH DEPARTS TO THE EAST...INSTABILITY
WILL BE GREATER...AND BE MORE SUPPORTIVE OF THUNDERSTORMS THIS
AFTERNOON AND EARLY EVENING. LIGHT SOUTH WINDS WILL PERSIST IN THE
FOOTHILLS. WINDS WILL INITIALLY BE LIGHT NW IN THE MOUNTAINS...
BECOMING SOUTHERLY BY AFTERNOON. MODEL GUIDANCE SUPPORTS MVFR FOG AT
KAVL AND KAND EARLY TUESDAY MORNING...WITH LOW VFR VSBY AT OTHER
SITES.

OUTLOOK...SCATTERED SHOWERS AND THUNDERSTORMS...AND ASSOCIATED
RESTRICTIONS...ARE EXPECTED TO CONTINUE DURING THE WEEK...BUT SHOULD
BECOME MORE FOCUSED DURING THE AFTERNOON AND EVENING.

CONFIDENCE TABLE...

            10-16Z        16-22Z        22-04Z        04-10Z
KCLT       HIGH  90%     HIGH  94%     HIGH 100%     HIGH  90%
KGSP       HIGH  91%     HIGH  97%     HIGH 100%     HIGH  93%
KAVL       HIGH  88%     HIGH 100%     HIGH 100%     HIGH  84%
KHKY       HIGH  90%     HIGH  98%     HIGH 100%     HIGH  87%
KGMU       HIGH  85%     HIGH  95%     HIGH 100%     HIGH  97%
KAND       HIGH  92%     HIGH  97%     HIGH 100%     HIGH  91%

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...DENSE FOG ADVISORY UNTIL 10 AM EDT THIS MORNING FOR GAZ018-026-
     028.
NC...NONE.
SC...DENSE FOG ADVISORY UNTIL 10 AM EDT THIS MORNING FOR SCZ004>007-
     010.

&&

$$
SYNOPSIS...RWH
NEAR TERM...JAT
SHORT TERM...RWH
LONG TERM...RWH
AVIATION...JAT