635
FXUS62 KGSP 210002
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
802 PM EDT THU AUG 20 2026
WHAT HAS CHANGED
THE AVIATION FORECAST WAS UPDATED FOR THE 00Z TAF ISSUANCE.
KEY MESSAGES
1. SCATTERED STRONG THUNDERSTORMS ARE POSSIBLE THIS EVENING. THERE
IS SOME POTENTIAL FOR A FEW OF THE STORMS TO PRODUCE DAMAGING
WIND GUSTS. MORE WIDESPREAD COVERAGE OF SHOWERS AND THUNDERSTORMS
IS EXPECTED FRIDAY AFTERNOON, WITH A THREAT OF LOCALLY HEAVY
RAINFALL. DRIER WEATHER RETURNS SUNDAY THOUGH THE PATTERN WILL
BECOME SOMEWHAT FAVORABLE FOR STORMS TO REACH THE AREA FROM THE
NORTHWEST EARLY NEXT WEEK.
DISCUSSION
KEY MESSAGE 1: SCATTERED STRONG THUNDERSTORMS ARE POSSIBLE THIS
EVENING. THERE IS SOME POTENTIAL FOR A FEW OF THE STORMS TO PRODUCE
DAMAGING WIND GUSTS. MORE WIDESPREAD COVERAGE OF SHOWERS AND
THUNDERSTORMS IS EXPECTED FRIDAY AFTERNOON, WITH A THREAT OF LOCALLY
HEAVY RAINFALL. DRIER WEATHER RETURNS SUNDAY THOUGH THE PATTERN WILL
BECOME SOMEWHAT FAVORABLE FOR STORMS TO REACH THE AREA FROM THE
NORTHWEST EARLY NEXT WEEK.
A STATIONARY FRONT IS PRESENT ACROSS THE LOWER PIEDMONT FROM
VIRGINIA TO EASTERN GEORGIA, SEEMINGLY JUST EAST OF OUR CWA AS
OF EARLY AFTERNOON. A WEAK LEE TROUGH IS PROVIDING SOME DEGREE
OF LOW LEVEL CONVERGENCE OVER THE CWA. AN ELEVATED MIXED LAYER
OVERHEAD SEEMS TO HAVE CAPPED OFF CONVECTIVE DEVELOPMENT SO
FAR. DIURNAL MIXING IS EXPECTED TO HELP ERODE THE ASSOCIATED
INVERSION, AND A WEAK VORT AXIS LOOKS TO MOVE THROUGH THE LONGER
TROUGH CENTERED TO OUR NORTH LATER THIS AFTERNOON. HENCE, SOME
DEVELOPMENT OF SHOWERS/STORMS STILL IS EXPECTED. THE 12Z CAMS CAME
INTO CONSENSUS THAT THESE ELEMENTS WOULD COME TOGETHER NEAR PEAK
HEATING, SUPPORTING THE IDEA THAT STORMS WOULD FIRE EARLIER THAN
PREVIOUSLY THOUGHT (WHEN THE MAIN DRIVER FOR CONVECTION WAS AN
MCV OR COLD POOL ARRIVING FROM UPSTREAM). RECENT HRRR RUNS HAVE
HOWEVER TRENDED BACK TOWARD LATER ONSET, SO CONFIDENCE ON TIMING
REMAINS RELATIVELY LOW. WITH THE PATTERN BEING ILL-DEFINED OVERALL
POPS HAVE BEEN KEPT LARGELY 20-50% THIS EVENING. THERE APPEARS
ADEQUATE DCAPE TO SUPPORT MARGINALLY SEVERE WINDS FROM ANY CELLS
THAT DO DEVELOP, AND WITH 0-6KM SHEAR ON THE ORDER OF 20 KT ALONG
WITH THE POTENTIALLY LINEAR FORCING OF THE CONVERGENCE AXIS,
CAN'T RULE OUT THAT STORMS WILL ORGANIZE LOOSELY INTO CLUSTERS
POSING A SOMEWHAT BROADER-SCALE WIND THREAT THAN WE WOULD SEE
WITH PULSE CONVECTION. SPC UPDATED THE DAY 1 OUTLOOK TO INCLUDE
A SLIGHT RISK FOR A PORTION OF OUR PIEDMONT ZONES, POSSIBLY A
NOD TO THE AFOREMENTIONED MODEL CONSENSUS. THE THREAT DOES NOT
LOOK PARTICULARLY HIGHER THAN IT HAD THIS MORNING WHEN WE WERE IN
THE MARGINAL RISK, BUT ONE COULD ARGUE GREATER COVERAGE OF STORMS
TRANSLATES TO GREATER LIKELIHOOD OF SEVERE WEATHER. THE SETUP FOR
ORGANIZED/SEVERE WEATHER DOES STILL LOOK BETTER TO OUR NORTHEAST AND
SOUTHWEST. WITH POTENTIAL COLD POOLS OR OUTFLOW BOUNDARIES ENTERING
OUR CWA FROM ADJACENT AREAS, INCREASINGLY CYCLONIC FLOW ALOFT
OVERNIGHT AS WELL AS THE STRONGER COLD FRONT APPROACHING FROM THE
NORTHWEST, CAN'T SAY THE THREAT OF OVERNIGHT SHOWERS/STORMS IS NIL.
A SECOND VORT LOBE OVER THE OZARKS AS OF EARLY THU AFTERNOON
WILL PROGRESS THROUGH THE SHORTWAVE AND BY FRIDAY APPEARS
TO PHASE WITH ANOTHER VORT LOBE NEARER THE GREAT LAKES. THESE
TOGETHER LEAD TO THE TROUGH SHARPENING SLIGHTLY. AS NOTED ABOVE,
A BETTER DEFINED COLD FRONT SHOULD MOVE THRU THE LOWER OH/TN
VALLEYS OVERNIGHT, ENDING UP SOMEWHERE ACROSS THE CAROLINAS BY
FRI AFTERNOON. MOISTURE POOLING INVOF THE FRONT WILL LEAD TO HIGH
PWATS OVER 2 INCHES ACROSS MUCH OF OUR AREA; WARM-CLOUD LAYERS
ARE VERY DEEP AND MBE VECTORS ARE LARGELY SHORT DUE TO E TO SE
SFC FLOW AND WESTERLY FLOW ALOFT. THESE ALONE SUGGEST A THREAT OF
LOCALLY HEAVY RAINFALL. THERE ARE HINTS AT A SURFACE LOW DEVELOPING
ALONG THE FRONT DUE TO THE INTERACTION WITH THE SHORTWAVE WHICH
COULD ADDITIONALLY FOCUS CONVECTIVE DEVELOPMENT. WRF/NAM FAMILY
MODELS FEATURE VERY HIGH SBCAPE FRIDAY AFTERNOON AND EVENING ON
THE WARM SIDE OF THE FRONT, NEAR OUR SOUTHEASTERN BORDER. HREF
AND REFS PMMS FEATURE BULLSEYES OF 3"+ QPF IN 6 HOURS OR LESS,
PARTICULARLY NEAR AND EAST OF CHARLOTTE. HOWEVER, MODELS VARY
IN THE PATTERN OF CONVECTION WHICH LIMITS CONFIDENCE ON WHERE
THE PEAK THREAT IS, AND MAY ARTIFICIALLY INFLATE THE PMMS. RIGHT
NOW IT APPEARS THE GREATER CONCERN FOR EXCESSIVE RAINFALL WILL BE
JUST TO OUR EAST. NEVERTHELESS SOME CONSIDERATION TO A SHORT-FUSED
FLOOD WATCH MAY BE GIVEN TONIGHT IF THE INGREDIENTS LOOK TO COME
TOGETHER FARTHER WEST. ASIDE FROM THE HEAVY RAIN THREAT, DEEP LAYER
SHEAR AGAIN WILL BE SUFFICIENT THAT STORMS MAY ORGANIZE AND POSE
A DAMAGING WIND THREAT AGAIN, THOUGH COLD POOL FORMATION MAY BE
SOMEWHAT INHIBITED BY THE ABUNDANT MOISTURE.
WHILE THE TROUGH-Y UPPER PATTERN PERSISTS OVER THE AREA INTO
SATURDAY, SYNOPTIC MODELS ARE IN AGREEMENT THAT THE AXIS SHIFTS
EAST JUST ENOUGH TO ALLOW DRIER AIR TO WORK INTO THE WESTERN CWA
FRIDAY NIGHT; THE FRONT WILL SLOWLY DRIFT SOUTH AND EAST. NOT
TOTALLY CONFIDENT WE WILL BE FULLY STABLE ON SATURDAY, WITH MODELS
SUGGESTING THE FRONT MAY NOT TRULY CLEAR THE AREA AND STILL WITH
SOUPY DEWPOINTS AND SBCAPE OF 1500-2000 J/KG POSSIBLE IN THE LOWER
PIEDMONT. BY SUNDAY WE LOOK TO BE IN A NORTHWEST FLOW PATTERN. WHILE
WE WILL BE INITIALLY STABLE, THE AIRMASS WILL MODIFY TO OUR WEST
AND WE APPEAR NOT TO BE OUT OF THE WOODS FOR MCS(S) TO MAKE A RUN
AT THE AREA SOMETIME EARLY NEXT WEEK.
AVIATION /00Z FRIDAY THROUGH TUESDAY/
AT KCLT AND ELSEWHERE: ISOLATED SHOWERS AND THUNDERSTORMS ARE
EXPECTED TO DEVELOP THIS EVENING, MAINLY ALONG THE BLUE RIDGE
ESCARPMENT AND BACK OVER IN EASTERN TENNESSEE. GUIDANCE IS ALL
OVER THE PLACE AS FAR AS OVERALL COVERAGE, BUT HAS CONSISTENTLY
SHOWN ACTIVITY MOVING INTO WESTERN NORTH CAROLINA. KEPT A PROB30
FOR TSRA AND ASSOCIATED RESTRICTIONS AT KCLT/KAVL/KHKY, WHILE
TAKING THE PREVIOUS PROB30 OUT AT THE UPSTATE TAF SITES. LINGERING
CLOUD DEBRIS IS EXPECTED THROUGH A GOOD PORTION OF THE OVERNIGHT
PERIOD. LIGHT AND VARIABLE WINDS OVERNIGHT, PICKING UP OUT OF THE
SE LATE FRIDAY MORNING. THERE IS SOME SPECULATION OF SOME MORNING
STRATUS NEAR KCLT/KAVL/KHKY AROUND DAYBREAK FRIDAY, BUT CONFIDENCE
WASN'T HIGH ENOUGH FOR A PREVAILING BKN/OVC IFR/MVFR CIG MENTION AT
THIS TIME. A COLD FRONT WILL MOVE INTO THE AREA LATER ON FRIDAY,
WITH WINDS TURNING THE DIAL BEHIND THE FRONT WITH A NORTHERLY
COMPONENT. MORE SCATTERED SHOWERS AND THUNDERSTORMS ARE LIKELY
FRIDAY AFTERNOON, SO PLACED A PROB30 FOR TSRA AND ASSOCIATED
RESTRICTIONS AT ALL TAF SITES.
OUTLOOK: AFTERNOON SHRA/TSRA MAY RETURN SATURDAY. BY SUNDAY, A
DRIER PATTERN SHOULD ARRIVE AND LAST THROUGH THE FIRST HALF OF
NEXT WEEK, POSSIBLY KEEPING SHRA/TSRA TO A MINIMUM THOSE DAYS.
MOUNTAIN VALLEY FOG AND LOW STRATUS WILL BE POSSIBLE EACH MORNING.
GSP WATCHES/WARNINGS/ADVISORIES
GA...NONE.
NC...NONE.
SC...NONE.
CAC/JCW
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