000
FXUS62 KGSP 230248
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1048 PM EDT WED MAY 22 2013

.SYNOPSIS...
AN APPROACHING UPPER LEVEL TROUGH WILL CONTINUE TO INFLUENCE THE
REGION THROUGH THURSDAY. A COLD FRONT MOVES THROUGH THE AREA
THURSDAY NIGHT...BEFORE A COOLER AND DRIER AIRMASS SETTLES IN FOR
THE WEEKEND AND MODIFIES THROUGH THE EARLY PART OF NEXT WEEK.

&&

.NEAR TERM /THROUGH THURSDAY/...
AS OF 1045 PM...BROKEN MULTICELL LINE OF THUNDERSTORMS CONTINUES TO
MOVE TO THE EAST NORTHEAST ACROSS THE UPSTATE IN ASSOCIATION WITH
CONVERGENCE NEAR FRONTAL BOUNDARY. ELSEWHERE...DISCRETE PULSE
SHOWERS AND THUNDERSTORMS WERE PRESENT ACROSS PORTIONS OF THE NORTH
CAROLINA FOOTHILLS/PIEDMONT.  THE MAIN THREATS WITH ANY OF THESE
THUNDERSTORMS ARE BRIEF HEAVY RAINFALL...LARGE HAIL...DAMAGING
WINDS...AND FREQUENT CLOUD TO GROUND LIGHTNING.  AS FOR THE
FCST...THE ACTIVITY CURRENTLY EXTENDING ACROSS THE WESTERN CWFA
SHOULD MOVE EASTWARD ACROSS THE CWFA GRADUALLY DIMINISHING IN
INTENSITY AS INSTABILITY WANES. GENERALLY CHANGED POPS TO REFLECT
THIS WAVE OF ACTIVITY BEING FOLLOWED BY MUCH LOWER POPS IN SCHC TO
LOW CHC RANGE DUE TO CONTINUED PRESENCE OF UPSTREAM ACTIVITY.
ADJUSTED TEMPERATURE TRENDS FURTHER BY LOWERING TEMPS ACROSS THE
NORTH CAROLINA PIEDMONT DUE TO OUTFLOW BOUNDARIES FROM EARLIER
CONVECTION SPREADING ACROSS THIS REGION.

REMAINDER OF PREVIOUS DISCUSSION...

AS OF 800 PM...TOUCHED UP EVENING TEMP TRENDS...WHICH HAVE BEEN
IMPACTED GREATLY BY THUNDERSTORMS AND THEIR COOL OUTFLOW. RADAR
INDICATES SEVERAL BOUNDARIES SPREADING ACROSS THE PIEDMONT...WHERE
TEMPS REMAIN IN THE MID TO UPPER 70S. THINK THESE WILL BE IMPACTED
BY BOTH DIURNAL COOLING AS WELL AS THE OUTFLOW. LAMP TEMPS SEEM TO
REFLECT THE CURRENT SITUATION FAIRLY WELL AND THESE ARE IN DECENT
AGREEMENT WITH LATE EVENING TEMPS...SO NO CHANGES MADE OTHER THAN TO
UPDATE FIRST FEW HRS.

AS OF MID AFTERNOON...A BROKEN BAND OF SHOWERS AND THUNDERSTORMS WAS
LOCATED JUST EAST OF THE BLUE RIDGE IN NC FROM I-40 NEWD...WITH
OTHER STORMS POPPING UP ACROSS THE HIGHER TERRAIN AIDED BY
DIFFERENTIAL HEATING. EXPECT THE STORMS TO BECOME MORE NUMEROUS
ACROSS THE MTNS THROUGH LATE AFTERNOON...WITH THAT CONVECTION MOVING
EAST OVER THE FOOTHILLS AND PIEDMONT INTO THE EVENING. POP HAS BEEN
ADJUSTED ACCORDINGLY. SOME OF THESE STORMS WILL PRODUCE LARGE HAIL
AND DAMAGING WIND GUSTS. HIGH TEMPS STILL LOOK OKAY.

FOR TONIGHT...THE CONVECTION ALLOWING MODELS SUGGEST THAT ANOTHER
ROUND OF STORMS WILL FIRE TO THE WEST AND THEN MOVE EAST INTO THE
FCST AREA IN THE EARLY EVENING. THE HRRR AND 4KM WRF PAINT A SIMILAR
PICTURE WITH NUMEROUS STORMS OVER THE WESTERN HALF OF THE FCST AREA
THROUGH MID TO LATE EVENING. A SHORT WAVE MOVING AROUND THE UPPER
TROF...COMBINED WITH SOME UPPER DIVERGENCE...SHOULD PROVIDE THE
NECESSARY SUPPORT FOR THIS CONVECTION TO THRIVE. WITH THAT IN
MIND...THE POP WAS RAISED TO LIKELY OVER THE WESTERN HALF. AFTER
SOME LOSS OF HEATING...THE STORMS SHOULD BECOME A BIT LESS NUMEROUS
OVER THE NC PIEDMONT. AT THAT POINT...THE POP WAS KEPT BELOW 50 PCT
ONLY BECAUSE OF SOME UNCERTAINTY GIVEN BY THE CONVECTION HAVING NOT
YET DEVELOPED AS OF 18Z. MIN TEMPS SHOULD REMAIN MILD.

THE COLD FRONT WILL MOVE IN FROM THE WEST ON THURSDAY...MOST LIKELY
OVER THE MTNS IN THE MORNING AND THEN MOVING OUT OVER THE FOOTHILLS
IN THE AFTERNOON. NEW CONVECTION SHOULD DEVELOP ALONG THE FRONT
MAINLY OVER THE PIEDMONT IN THE AFTERNOON. THIS IS TRICKY BECAUSE OF
THE LIKELIHOOD OF WIDESPREAD DEBRIS CLOUDINESS INTO THE EARLY
AFTERNOON THAT WOULD LIMIT CONVECTION. THINK THE MTNS STAND A CHANCE
BECAUSE OF THE FRONT EARLY IN THE DAY. THE UPSTATE AND NE GEORGIA
HAS THE LEAST FAVORABLE ENVIRONMENT...SO A 20 PCT POP WAS KEPT. THE
PIEDMONT HAS A BETTER CHANCE AHEAD OF THE FRONT SO A LIKELY POP WAS
CARRIED OVER THE EASTERN ZONES FOR A TIME. SEVERE STORMS ARE
POSSIBLE...BUT MORE LIKELY TO THE EAST OF I-77. HIGH TEMPS WILL BE
A FEW DEGREES COOLER.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
AS OF 230 PM WEDNESDAY...A SURFACE COLD FRONT SHOULD BE LOCATED NEAR
THE EDGE OF OUR WESTERN NORTH CAROLINA PIEDMONT EARLY THURSDAY
EVENING. THIS LINES UP WELL WITH THE SHORT TERM SUITE OF MODELS...
AND LINES UP WITH WITH AN AXIS OF DPVA WHICH SHOULD BE CROSSING THAT
REGION LATE IN THE DAY/EARLY EVENING. CONVECTIVE ALLOWING MODELS
ALSO DEPICT THIS TREND AND IS SUPPORTED BY INSTABILITY LINGERING
ACROSS THAT AREA. AS A RESULT WE WILL HAVE A CORRIDOR OF LOWER
CHANCE POPS IN OUR EASTERN FORECAST AREA (FA) UNTIL AROUND DARK OR
SO.

A SECOND AREA OF PRECIPITATION FOR THURSDAY NIGHT WILL BE IN THE NC
MOUNTAINS WHERE ANOTHER LOBE OF ENERGY...EMBEDDED IN A SHARPENING H5
TROF...CROSSES THE AREA. WE WILL CARRY CHANCE POPS IN THE NC
MOUNTAINS THURSDAY NIGHT AND FRIDAY MORNING...IN A CONTINUALLY
DEEPENING FORCED UPPER AIR PATTERN. ALTHOUGH THE SHARPENING TROF
CROSSES ALL OF OUR REGION FRIDAY...THE ATMOSPHERE LOOKS TO DRY FOR
ANY PRECIPITATION.

MEANWHILE THE H85 ISALLOBARIC PATTERN WAS INDICATING SIGNIFICANT
CROSS CONTOURS OF THERMAL STRUCTURE AND HEIGHTS FRIDAY. THIS
SUGGESTS AT LEAST SIGNIFICANT COLD AIR ADVECTION (ESPECIALLY JUST
ABOVE THE SURFACE) AND MIXING DOWN. WE HAVE FOLLOWED BUFKIT
INFORMATION FOR WIND GUSTS FRIDAY...AND IN ALL LIKELIHOOD WE WILL
NEED SOME TYPE OF WIND HEADLINE FRIDAY FOR PART OF OUR FAA...
PARTICULARLY IN THE AFTERNOON.

HIGH PRESSURE WILL EDGE TOWARD THE REGION FRIDAY NIGHT...WHICH WILL
BRING A COOL/COLD NIGHT AROUND THE AREA. SOME MOUNTAIN LOCATIONS TO
DIP INTO THE 30S...BUT BELIEVE ENOUGH MIXING SHOULD PREVENT FROST
DUE TO THE LINGERING GRADIENT OF HIGH PRESSURE OFF TO THE NORTHWEST
AND LOW PRESSURE MOVING UP THE EASTERN SEABOARD. HOWEVER WE WILL
HAVE TO MONITOR TRENDS.

HIGH PRESSURE TO HOLD SWAY SATURDAY WITH A PLEASANT DAY ON
TAP.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
AS OF 225 PM WEDNESDAY...RATHER GOOD AGREEMENT IS HAD IN THE UPPER
LEVEL OMEGA PATTERN OVER THE EXT RANGE. THE 12Z GFS IS A BIT OF AN
OUTLIER AND SHARPENS THE EAST COAST TROF AND SUBSEQUENT DEEP NW/LY
FLOW GRADIENT MORESO THAN THE OTHER OP MODELS...BUT NOT ENOUGH FOR A
SIGFNT LLVL RESPONSE. AT THE SFC...THERE ARE MAJOR DIFFERENCES
EVOLVING WITH THE SYNOPTIC PATTERN...THUS A LESS THAN AVG
CONFIDENCE IS HAD AS THE EXT RANGE PROGRESSES.

HIGH PRESSURE CONTINUES TO BUILD IN FROM THE NORTH SUN AND KEEPS
THINGS DRY. HIGH TEMPS WILL BE A LITTLE BELOW NORMAL WITH A
REINFORCING CP AIRMASS MIXING IN. THE LLVL FLOW BECOMES DEFINED
SW/LY MON AS THE ATL HIGH NUDGES IN. THIS WILL ALSO ENABLE A WARM
FRONT OR STATIONARY TO PERHAPS IMPINGE UPON THE REGION MON NIGHT
INTO TUE. THERE IS LOW CONFIDENCE IN THIS FEATURE...HOWEVER...AS THE
GFS KEEPS ANY FRONTOGENESIS WELL TO THE NORTH OF THE REGION WITH A
WEAK TROF BUILDING INTO THE SFC SE RIDGE...WHILE THE ECMWF HAS THE
WARM FRONT STALLING OUT ACROSS THE CWFA DURING THE DAY TUE INTO WED.
RIGHT NOW...POPS HAVE BEEN CONTINUED IN THE LOW END CHANCE RANGE MON
THROUGH TUE...AND A DRIER HPC BLEND WAS MAINTAINED FOR WED.
SOUNDINGS SHOW VERY LITTLE SBCAPE DEVELOPING MON AS THE UPPER FLOW
KEEPS A SUBSIDENCE INVERSION IN PLACE...HOWEVER A RELATIVE WEAKENING
ALOFT TUE SHOULD ENABLE THE DEVELOPMENT OF SOME ENHANCE CONVECTION
AND TSTMS. MAX TEMPS WILL WARM EACH DAY MON THROUGH THE PERIOD TO A
LITTLE ABOVE NORMAL IN GOOD SW/LY FLOW AND INSOLATION.

&&

.AVIATION /03Z THURSDAY THROUGH MONDAY/...
AT KCLT...PREVAILING VFR THIS EVENING BUT THERE REMAINS THE
POSSIBILITY OF RESTRICTIONS FROM THUNDERSTORMS. STABILIZING OUTFLOW
FROM UPSTREAM TS MAY PUT A STOP TO CONVECTION BUT ITS LEADING EDGE
COULD BE THE FOCUS FOR NEW DEVELOPMENT FOR A TIME TONIGHT. INCLUDED
A TEMPO THRU 04Z FOR MVFR TSRA...BUT WILL CLOSELY WATCH TRENDS OVER
NEXT COUPLE OF HOURS AND MAY BE ABLE TO REMOVE IT. PROFILES BECOME
INCREASINGLY MOIST OVERNIGHT AHEAD OF FRONTAL BOUNDARY. PER MODEL RH
FIELDS EXPECT A LOWERING TO SOLID MVFR LATE...WITH SUFFICIENT
ELEVATED INSTABILITY TO WARRANT ANOTHER TEMPO FOR TSRA. LULL IN
ACTIVITY EXPECTED NEAR DAYBREAK WITH LOW MVFR PERSISTING UNTIL
MIXING GETS UNDERWAY MID MORNING. DECENT THUNDER CHANCES AGAIN WITH
DIURNAL HEATING WARRANTING -TSRA BUT VFR.

ELSEWHERE...CONVECTION CONTINUES THIS EVENING ACROSS MAINLY THE
MTNS/FOOTHILLS. MUCH OF THE PIEDMONT WILL BE STABILIZED BY TS
OUTFLOW WITH UPSTREAM ACTIVITY LIKELY TO DIMINISH TOO QUICKLY WITH
LOSS OF HEATING TO HAVE EFFECTS. OVERNIGHT FROPA WILL BRING BACK TS
OR SHRA CHANCES. HANDLED THIS WITH VCTS OR TEMPOS AS APPROPRIATE.
PLENTY OF MOISTURE TO THINK RESTRICTIVE CIGS WILL DEVELOP BEHIND THE
FRONT AND PERSIST THRU DAYBREAK. DIURNAL CU WILL QUICKLY GROW IN
UNSTABLE ATMOSPHERE BY LATE MORNING. CU BASES EXPECTED TO BE WELL
WITHIN VFR TERRITORY...WITH SOME LOW TS CHANCES ALSO THROUGH PEAK
HEATING.

OUTLOOK...RESTRICTIONS POSSIBLE WITH LINGERING MOISTURE OVERNIGHT
THU NIGHT AND FRI MORNING. GENERALLY VFR WEATHER FRIDAY AND SATURDAY.

CONFIDENCE TABLE...

            02-08Z        08-14Z        14-20Z        20-02Z
KCLT       MED   60%     HIGH  86%     HIGH  80%     HIGH 100%
KGSP       LOW   58%     MED   72%     HIGH  82%     HIGH 100%
KAVL       MED   71%     HIGH  97%     HIGH  98%     HIGH 100%
KHKY       LOW   45%     MED   77%     HIGH  91%     HIGH 100%
KGMU       LOW   58%     MED   73%     HIGH 100%     HIGH 100%
KAND       MED   65%     MED   76%     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...SBK
NEAR TERM...CDG/PM/WIMBERLEY
SHORT TERM...TS
LONG TERM...SBK
AVIATION...CDG/WIMBERLEY