432
FXUS62 KGSP 201857
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
257 PM EDT THU AUG 20 2026
WHAT HAS CHANGED
REVISED INFO ABOUT SEVERE WEATHER POSSIBILITIES TODAY AND
FRIDAY, AND HEAVY RAINFALL POTENTIAL ON FRIDAY.
KEY MESSAGES
1. SCATTERED STRONG THUNDERSTORMS ARE POSSIBLE THIS AFTERNOON
AND 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
AFTERNOON AND 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 /18Z THURSDAY THROUGH TUESDAY/
AT KCLT AND ELSEWHERE: THE WEATHER PATTERN IS SOMEWHAT ILL-DEFINED
ACROSS THE TERMINAL AREA THIS AFTERNOON, SO CONFIDENCE IS
SOMEWHAT LIMITED. A STATIONARY FRONT SOUTHEAST OF THE AREA
SUGGESTS PREDOMINANTLY NW FLOW, THOUGH THERE APPEARS TO BE
A LEE TROUGH OR OTHER WEAK CONVERGENCE ZONE CAUSING SW'LY
WINDS AT TIMES AT ALL SITES EXCEPT KAVL, AT LEAST IN THE FIRST
COUPLE HOURS OF THE PERIOD. THINK KCLT WILL REMAIN ON THE NW
SIDE FOR A TIME BUT SHOULD PREVAIL SW AGAIN AS DEEPER MIXING
IS ESTABLISHED. THE CONVERGENCE WILL HELP DRIVE DEVELOPMENT
OF SCATTERED SHRA/TSRA CLOSER TO THE USUAL DIURNAL PEAK THAN
PREVIOUSLY EXPECTED. PROB30S REMAIN FOR ALL SITES BUT IN MOST CASES
HAVE BEEN SHIFTED EARLIER. GUSTY WINDS ARE POSSIBLE AS A RESULT
OF TSRA PARTICULARLY AT KCLT/KGSP/KGMU/KAVL. CONVECTIVE DEBRIS
SHOULD LINGER TONIGHT AND ASSUMING THAT OCCURS RADIATION FOG WILL
BE LIMITED IN SCOPE. HOWEVER, A COLD FRONT IS EXPECTED TO REACH
THE NW PORTIONS OF THE AREA BY DAYBREAK FRI AND THAT MAY INDUCE
AN MVFR TO IFR STRATUS DECK AT LEAST AFFECTING KHKY, WITH LOWER
CONFIDENCE FOR IMPACTS AT KCLT AND KAVL. WINDS COULD TURN N'LY
AGAIN BEHIND THE FRONT. SHRA/TSRA LIKELY TO DEVELOP FRI AFTERNOON,
CHANCES ALREADY BEING SUFFICIENT TO INCLUDE PROB30 AT KAVL AND KCLT.
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.
JCW
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