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000
FXUS62 KGSP 202351
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
751 PM EDT MON MAY 20 2013

.SYNOPSIS...
AN APPROACHING UPPER LEVEL TROUGH WILL CONTINUE TO INFLUENCE THE
REGION FOR MOST OF THIS 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 TUESDAY/...
AS OF 545 PM...THE MAIN CHANGES TO THE FCST WITH THIS UPDATE WERE TO
THE POP TRENDS FOR THIS EVENING. SO FAR...THE MAIN SOURCE OF
CONVECTIVE INITIATION HAS BEEN DIFFERENTIAL HEATING IN THE SW NC
MTNS AND PORTIONS OF THE SC AND GA MTNS. THERE IS SOME SCATTERED
CONVECTION ALSO DEVELOPING ON WRN SIDE OF MID LVL SHEAR AXIS ACRS
CENTRAL NC. SOME OF THIS ACTIVITY MAY BE ABLE TO PROPAGATE SWWD INTO
THE I-77 CORRIDOR...AS THESE AREAS MANAGED TO REACH ABOUT 2000 J/KG
OF CAPE. THE ENVIRONMENT OVER THAT AREA IS STILL LIKE YESTERDAY
(HIGH PWATS/LOWER MICROBURST TREAT). WILL KEEP A CHC POP IN THE
EAST...BUT CUT BACK POP ELSEWHERE. THERE IS ALSO LITTLE INDICATION
THAT WE/LL HAVE MUCH NOCTURNAL CONVECTION...SO POPS WERE TRENDED
LOWER THRU THE OVERNIGHT AS WELL.

AS OF 230 PM EDT... WEAK TROUGH/CYCLONIC SHEAR AXIS ALOFT OVER THE
CENTRAL TO EASTERN PORTION OF THE CWA WILL SEPARATE SLIGHTLY BETTER
CHANCE OF POPS EAST OF MOUNTAINS FROM LOWER CHANCE IN THE FAR WEST.
FLOW ALOFT FAVORS A SOUTHEASTWARD MOVEMENT OF SHOWERS AND
THUNDERSTORMS THIS EVENING FROM SOUTHWEST VIRGINA THROUGH OUR
CENTRAL AND EASTERN COUNTIES. PRECIPITABLE WATER VALUES ARE RATHER
HIGH... NEAR 150 PERCENT OF NORMAL... SO CONVECTION SHOULD BE FAIRLY
EFFICIENT AT PRODUCING SUBSTANTIAL RAINFALL. LATEST SPC MESOANALYSIS
STILL SHOWS WELL-DEFINED AXIS OF DEEP MOISTURE OVER THE EAST...
INCLUDING THE CHARLOTTE METRO AREA. WILL HAVE TO KEEP AN EYE ON
POSSIBILITY OF TRAINING THAT COULD RESULT IN EXCESSIVE RAINFALL.
TROUGH SHIFTS SLOWLY EAST LATE TONIGHT AND TUESDAY LEAVING DEEPEST
MOISTURE IN THE FAR EASTERN PORTION OF THE CWA. AIR MASS DRIES OUT A
BIT ON TUESDAY...BUT EXAMINATION OF AFTERNOON MODEL SOUNDINGS
REVEALS SUFFICIENT CAPE AND ATTAINABLE CONVECTIVE TEMPERATURE SUCH
THAT CHANCE POPS ARE JUSTIFIED.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
AS OF 230 PM MONDAY...LOOKS AS IF NOT MUCH HAS CHANGED WITH REGARDS
TO MODEL GUIDANCE IN THE SHORT TERM.  REMNANTS OF UPPER TROF
RESPONSIBLE FOR THE WEATHER ACROSS THE REGION OVER THE LAST FEW DAYS
WILL FINALLY BEGIN TO PUSH OF THE EAST COAST TUESDAY EVENING.  AN
UPPER LEVEL RIDGE WILL BUILD IN ACROSS THE REGION DURING THE
OVERNIGHT HOURS OF WEDNESDAY MORNING.  MODEL SOUNDINGS CONTINUE TO
INDICATE WEAK CAPPING AND MODERATE INSTABILITY THROUGH THE PROFILE
WEDNESDAY.  EXPECTING CONVECTION TO GET GOING ACROSS THE MOUNTAINS
EARLY ON WEDNESDAY AS MECHANICAL FORCING WILL OVERCOME ANY WEAK
INVERSIONS.  CONVECTIVE ACTIVITY WILL SPREAD SOUTHEAST ACROSS
THE I85 CORRIDOR BY MID TO LATE AFTERNOON AS DIURNAL HEATING
DESTABILIZES THE BOUNDARY LAYER FURTHER.  SHEAR PROFILES LOOK RATHER
WEAK ACROSS NORTHEAST GEORGIA AND THE CAROLINAS DURING THIS
PERIOD SO EXPECTING ANY CONVECTION TO BE SOMEWHAT DISORGANIZED
LEADING TO MORE OF A PULSE/CLUSTER TYPE STORM MODE THREAT.  WITH
THAT...THE MAIN THREATS WITH ANY OF THESE STORMS WILL BE BRIEF HEAVY
RAINFALL AND GUSTY WINDS.  TEMPERATURES ON WEDNESDAY WILL DEPEND
SOMEWHAT ON OVERALL COVERAGE OF SHOWER AND THUNDERSTORM ACTIVITY IN
THE AREA.  HOWEVER...WENT WITH SLIGHTLY ABOVE NORMAL LOWS...AND NEAR
NORMAL HIGHS.

MEANWHILE...DEEP UPPER LEVEL TROF AND ITS ASSOCIATED SURFACE LOW
WILL CONTINUE TO SLOWLY MOVE TO THE EAST ACROSS THE GREAT LAKES
REGION.  A SURFACE COLD FRONT EXTENDING TO THE SOUTHEAST ACROSS THE
MISSISSIPPI RIVER VALLEY WILL CONTINUE ITS EASTWARD PROGRESSION
TOWARDS THE APPALACHIANS.  FORECAST MODELS SEEM TO SHOW SLIGHTLY
WEAKER INSTABILITY ACROSS THE REGION ON THURSDAY...HOWEVER SHEAR
PROFILES LOOK STRONGER AS THE UPPER LEVEL WAVE PASSES BY AND THE
SURFACE COLD FRONT APPROACHES.  AS THE FRONT MOVES INTO THE AREA ON
THURSDAY AFTERNOON...HEIGHTS WILL FALL ALLOWING SHOWERS AND
THUNDERSTORMS TO INITIATE ACROSS THE HIGHER TERRAINS FIRST...THEN
SPREAD TO THE SOUTHEAST ACROSS THE PIEDMONTS OF THE CAROLINAS.  SOME
OF THESE THUNDERSTORMS COULD BE STRONG TO SEVERE AS UPPER LEVEL
SUPPORT COULD ALLOW FOR SOME ORGANIZATION.  THUS...THE MAIN THREATS
ON THURSDAY WILL BE HEAVY RAINFALL...AND THE POTENTIAL FOR DAMAGING
WIND GUSTS AND SMALL HAIL.  OVERALL TEMPERATURES ON THURSDAY WILL BE
SLIGHTLY ABOVE NORMAL.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
AS OF 100 PM MONDAY...THE LARGE SCALE PATTERN IS WELL AGREED UPON
THROUGH THE PERIOD. A STRONG...YET MOISTURE LIMITED S/W WILL CROSS
OVER THE FCST AREA FRI...WHILE A STRONG MEAN RIDGE AXIS DEVELOPS TO
THE WEST AND DOMINATES THE SENSIBLE WEATHER THROUGH MON.

THERE ARE ENOUGH VARYING IDEAS BTW THE OP MODELS WRT THE AIRMASS
CHANGE AND POSSIBILITY OF A BACK DOOR COLD FRONT SUN TO KEEP POPS ON
THE LOW END SUN/MON. BEFORE THAT...FRI SHOULD SEE THE BEST CHANCE FOR
SHOWERS AND DEEPER CONVECTION...BUT THE UPPER S/W WILL BE BATTLING A
H8/H7 LAYER OF CAA AND A DRYING NE/LY SFC FLOW. SO...WILL KEEP POPS
LOW END CHANCE AND MAINLY ACROSS THE HIGHER TERRAIN DUE TO GOOD MECH
LIFT ENHANCEMENT AND LLVL MOISTURE REMAINING RELATIVELY HIGH. MODEL
SOUNDINGS ARE SHOWING SOME WEAK AFTERNOON INSTABILITY AND PROBABLY
ENOUGH TO SPAWN A FEW CONVECTIVE SHOWERS WITH THE DEEP
OMEGA...HOWEVER TSTMS SHOULD BE HARD TO DEVELOP WITHIN A DEEPLY DRY
ATMOS IN PLACE.

THINGS WILL REMAIN DRY THROUGH THE WEEKEND WITH A LOW CONFIDENCE
BACK DOOR COLD FRONT BUILDING IN FROM THE NORTH SUN. THE ECWMF IS
MORE PRONOUNCED WITH THIS FEATURE BUT THE GFS ALSO HAS A LLVL
THETA/E BOUNDARY IN THE AREA WHICH LOOKS TO LINGER INTO MON. THE
MODELS DIVERGE ONCE AGAIN MON WITH THE AMOUNT OF S/W ENERGY ROUNDING
THE UPSTREAM RIDGE...WITH THE GFS MORE DEFINITIVE ON ENOUGH UPPER
SUPPORT TO GENERATE AT LEAST SCT -SHRA AND TSTMS ACROSS THE HIGH
TERRAIN AND ALONG THE AFOREMENTIONED SFC BOUNDARY. THE ECMWF ON THE
OTHERHAND...KEEPS THE BEST ULVL DYNAMICS WELL TO THE NORTH AND THUS
NO GOOD CHANCE OF PRECIP IN THE CWFA. THUS...POPS LATE SUN THROUGH
MON HAVE BEEN MAINTAINED IN THE SLIGHT RANGE AND LIMITED TO MAINLY
THE WRN ZONES. MAX TEMPS WILL BEGIN THE PERIOD RIGHT AROUND
NORMAL...AND PROBABLY ADJ DOWN A COUPLE DEGREES SUN AND MON WITH THE
CP AIRMASS AND WEAK CAD CONFIG.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
AT KCLT...THERE ARE A FEW SHRA/TSRA TRYING TO DEVELOP ACRS THE NC
PIEDMONT THIS EVENING...BUT PROBABLY REMAIN FAIRLY ISOLD. SO NO
MENTION OF TS WILL BE CARRIED IN THE KCLT TAF ATTM. GUIDANCE HAS
BEEN OVERDOING CONVECTION ASSOCIATED WITH MOIST AIR MASS IN
PLACE...AND THIS MAY BE AFFECTING THEIR PROGS ON CIGS/VSBY OVERNIGHT
INTO TUESDAY MORNING. HAVE GONE MORE OPTIMISTIC...GIVEN LACK OF
RAINFALL ACRS THE REGION TODAY. WITH THAT SAID...A LIGHT S/SE LLVL
FLOW COULD BRING BACK VERY MOIST AIR AND SUPPORT STRATUS/FOG
DEVELOPMENT. WILL KEEP SOME IFR CIGS AROUND DAYBREAK. THESE CLOUDS
SHUD SCATTER AND LIFT BACK TO VFR BY LATE MORNING. TUESDAY
AFTN...CONVECTION SHUD BE MAINLY CONFINED TO THE HIGH TERRAIN...WITH
JUST ISOLD CELLS OUT ACRS THE PIEDMONT. SO NO CONVECTION WILL BE
MENTIONED IN THE OUTLOOK PERIOD. WINDS SHUD REMAIN LIGHT OUT OF THE
S OR SW.

ELSEWHERE...CONVECTION IS GENERALLY WANING AS WE APPROACH SUNSET. A
FEW SHRA/TSRA MAY LINGER OVER PORTIONS OF THE NC PIEDMONT. WILL
CARRY A VCTS AT KHKY FOR NEXT COUPLE HOURS. OTHERWISE...SHUD BE
QUIET THIS EVENING. GUIDANCE GENERALLY GOING WITH LESS STRATUS AND
FOG...ESP COMPARED TO LAST NIGHT...AS THERE WAS NOT AS MUCH RAIN
ACRS THE REGION AS EARLIER ANTICIPATED. STILL EXPECT VLY FOG TO
DEVELOP...SO HAVE IFR VSBY/CIGS AT KAVL. RESTRICTIONS ELSEWHERE WILL
BE PATCHY...AND MORE DEPENDENT ON ANY DIRECT HIT BY SHRA...WHICH IS
LOW. SO EXPECTING MAINLY VFR OVERNIGHT. SCATTERED CONVECTION
EXPECTED AGAIN TUESDAY AFTN....ESP IN THE NC MTNS. WILL GO WITH
PROB30 GROUPS FOR TS AT ALL SITES.

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

CONFIDENCE TABLE...

            00-06Z        06-12Z        12-18Z        18-24Z
KCLT       HIGH 100%     MED   76%     HIGH  86%     HIGH 100%
KGSP       HIGH 100%     HIGH  90%     HIGH  97%     HIGH 100%
KAVL       HIGH 100%     HIGH  96%     HIGH 100%     HIGH 100%
KHKY       HIGH 100%     HIGH  91%     HIGH  97%     HIGH 100%
KGMU       HIGH 100%     HIGH  94%     HIGH  96%     HIGH 100%
KAND       HIGH 100%     MED   79%     HIGH  98%     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...ARK/LGL
SHORT TERM...CDG
LONG TERM...SBK
AVIATION...ARK