776
FXUS62 KGSP 251100
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
700 AM EDT SAT JUL 25 2026
WHAT HAS CHANGED
UPDATED AVIATION DISCUSSION FOR 12Z TAF SET.
KEY MESSAGES
1. POTENTIAL FOR AT LEAST LOCALIZED EXCESSIVE RAINFALL CONTINUES
TODAY NEAR A STALLED FRONT. ON SUNDAY THE PATTERN CHANGES SUCH
THAT THE HEAVY RAIN POTENTIAL DECREASES, BUT THE POTENTIAL FOR
STRONG TO SEVERE THUNDERSTORMS INCREASES AND COULD BE A DAILY
CONCERN THROUGH WEDNESDAY.
DISCUSSION
KEY MESSAGE 1: POTENTIAL FOR AT LEAST LOCALIZED EXCESSIVE RAINFALL
CONTINUES TODAY NEAR A STALLED FRONT. ON SUNDAY THE PATTERN CHANGES
SUCH THAT THE HEAVY RAIN POTENTIAL DECREASES, BUT THE POTENTIAL
FOR STRONG TO SEVERE THUNDERSTORMS INCREASES AND COULD BE A DAILY
CONCERN THROUGH WEDNESDAY.
WE ARE STILL FEELING THE EFFECTS OF A WEDGELIKE PATTERN, IN WHICH
A MOIST FRONTAL BOUNDARY IS BASICALLY STALLED SOUTH OF THE CWA. LOW
STRATUS REMAINS ON THE COOL SIDE OF THE FRONT, WITH PATCHY DRIZZLE
AND OCCASIONAL LIGHT SHOWERS EVIDENT FROM SURFACE OBS, EVEN THOUGH
RADAR RETURNS ARE WEAK. WATER-VAPOR IMAGERY SHOWS A SHARP SHORTWAVE
AXIS JUST SOUTH OF THE OHIO RIVER AS OF EARLY SAT MORNING; WEAK
VORT RIPPLES ARE EVIDENT AHEAD OF IT ACROSS THE SOUTHERN APPS AND
VICINITY. WHILE FLOW OVER THE FRONTAL BOUNDARY APPEARS QUITE WEAK,
THERE IS ENOUGH UPGLIDE AND SLIGHT ELEVATED INSTABILITY OF A FEW
HUNDRED J/KG, TO EXPLAIN THE FEW SHOWERS WHICH HAVE FORMED AT TIMES
OVER OR WEST OF THE CWA. CAMS HAVE NOT BEEN TERRIBLY CONSISTENT
SO CONFIDENCE IS LIMITED IN THEM, BUT GENERALLY HAVE SHOWN AN
UPTICK IN QPF RESPONSE IN THE PREDAWN HOURS, SO WE RETAIN DECENT
POPS EARLY THIS MORNING--MAINLY JUST SHOWERS WITH ONLY AN OUTSIDE
CHANCE OF A THUNDERSTORM.
THE MAIN SHORTWAVE AXIS WILL SWING SOUTHEASTWARD TODAY,
AND IS ON TRACK TO PASS THE NW HALF OF OUR CWA PRIOR TO PEAK
HEATING. THAT SHOULD TURN MIDLEVEL FLOW MORE NW'LY AND PROMOTE
SOME DRYING/SCATTERING OF THE CLOUD DECK, THOUGH IT APPEARS LIKELY
TO TAKE LONGER THAN ORIGINALLY ANTICIPATED. THE DELAYED CLEARING
AND WARMING, PLUS THE LESS THAN IDEAL TIMING OF THE BETTER FORCING
ASSOCIATED WITH THE WAVE, SUGGESTS THE EXPECTED RETURN OF DIURNALLY
DRIVEN SHOWERS/STORMS INTO QUESTION, IN PARTICULAR BECAUSE SBCAPE
IS LOWER THAN IS TYPICAL FOR THIS TIME OF YEAR. WE RETAIN NO BETTER
THAN ABOUT 30% POPS THIS AFTERNOON, FOR THE IDEA OF CELLS FIRING
OVER THE ESCARPMENT AND PROPAGATING EAST INTO THE PIEDMONT. PWATS
BEGIN A GRADUAL DOWNWARD TREND WITH THE DRYING ALOFT, BUT REMAIN
HIGHER THAN NORMAL AND ANY CELLS THAT FORM WILL HAVE POTENTIAL FOR
TORRENTIAL RAINFALL RATES. THE THREAT OF FLASH FLOODING IS ARGUABLY
EVEN LOWER THAN FRIDAY WITH THE STEERING FLOW LESS PERPENDICULAR
TO THE FRONT. THE DRYING TREND WILL CONTINUE TONIGHT INTO EARLY
SUNDAY, AS THE FRONT PUSHES FARTHER SOUTH.
THIS NORTHWEST FLOW PATTERN, AS PREVIOUSLY NOTED, WILL FEATURE A
DEEP EAST COAST UPPER TROUGH AND SPRAWLING UPPER ANTICYCLONE OVER
THE SOUTHERN ROCKIES AND PLAINS. MULTIPLE WEAK DISTURBANCES LOOK TO
ROTATE THROUGH THE TROUGH BETWEEN SATURDAY NIGHT AND TUESDAY NIGHT,
POSSIBLY EVEN WEDNESDAY. BY SUNDAY OVER OUR AREA, THERMODYNAMIC
PROFILES LOOK MORE TYPICAL FOR SUMMER, WITH DEEPER MIXING AND DRIER
AIR IN THE MID TO UPPER LEVELS AND MODELED SBCAPE VALUES CLOSER
TO WHAT IS USUALLY SHOWN FOR JULY AFTERNOONS. TEMPERATURES ALSO
RETURN TO NEAR NORMAL. WHAT IS UNUSUAL IS THE 0-6KM BULK SHEAR,
WHICH IS GREATER THAN 30 KT OVER MOST OF THE AREA SUNDAY AND REMAINS
SO THROUGH TUESDAY. THE RIDGE-TROUGH PATTERN WILL FEATURE A NW-SE
ORIENTED THERMAL GRADIENT FROM THE UPPER MIDWEST TO THE SOUTH
ATLANTIC COAST, WITH VERY HOT, HUMID, UNSTABLE CONDITIONS IN THE
OHIO VALLEY. COUPLED WITH THE REPEATED SHORTWAVES, WE VERY WELL
MAY BE IN THE TRACK OF AT LEAST ONE MCS EXITING THE GREAT LAKES OR
OHIO VALLEY SUNDAY THROUGH WEDNESDAY. MODELS SHOW ENOUGH SPREAD ON
THE SHORTWAVE TIMING/POSITIONING THAT CONFIDENCE REMAINS LOW AS TO
WHEN WE MIGHT EXPERIENCE THE RESULTANT SEVERE/HYDRO THREATS OF AN
MCS. THERE IS ALSO THE POTENTIAL FOR THE MCS TO FIZZLE OVERNIGHT
BEFORE REACHING THE AREA, BUT LEAVE BEHIND A COLD POOL THAT COULD
CAUSE A TEMP/SKY FORECAST TO BUST. PER THE DAY 4-8 OUTLOOK FROM
FRIDAY MORNING, SPC HAS ALREADY HIGHLIGHTED PART OF THE CWA IN A 15%
CONTOUR FOR TUE AND TUE NIGHT (EQUIVALENT TO SLIGHT RISK) AND THERE
WOULD STILL APPEAR TO BE MODEL SUPPORT FOR OUR INCLUSION ON THIS
MORNING'S DAY 3 OUTLOOK. TUESDAY ALSO LOOKS TO BE THE WARMEST DAY OF
THE PERIOD AND THE DAY WHEN HEAT INDEX IS MOST LIKELY TO EXCEED 100,
BUT THERE IS BUST POTENTIAL DUE TO A COLD POOL OF COURSE. GIVEN THE
DIFFERENCES IN TIMING THE EMBEDDED SHORTWAVES AND IN PARTICULAR THE
FINAL VORT LOBE ROTATING THROUGH CIRCA WEDNESDAY ACCOMPANIED BY A
COLD FRONT, IT LOOKS LIKELY SOME THREAT WILL CONTINUE INTO THAT DAY,
WITH A RETURN TO NEAR-NORMAL TEMPS AT LEAST BRIEFLY THURSDAY-FRIDAY.
AVIATION /12Z SATURDAY THROUGH WEDNESDAY/
AT KCLT AND ELSEWHERE: STRATUS DECK VARYING BETWEEN LIFR AND MVFR
ACROSS THE TERMINAL AREA AT ISSUANCE TIME. AREAS OF DZ AND PATCHY
SHRA ARE GENERALLY CAUSING BRIEF IMPROVEMENT WHEN OCCURRING, BUT
WITH A FEW EMBEDDED HEAVIER SHRA CAUSING IFR VSBY ALSO. TEMPOS
HANDLE THESE AS WELL AS REFLECT THE PORTION OF THE TAF PERIOD WITH
THE GREATEST PRECIP CHANCES. COVERAGE OF SHRA IS EXPECTED TO REMAIN
SIMILAR OR EVEN INCREASE THRU 13-15Z BEFORE BEGINNING TO TAPER OFF
FROM NW TO SE. CIGS SHOULD BEGIN TO IMPROVE 14-16Z, WITH WINDS
TURNING NW ALOFT AND HELPING TO ADVECT IN DRIER AIR. SFC WINDS
WILL BE MAINLY NW TO START BUT WITH WEAK FORCING AND COMPETING
INFLUENCES DIRECTION MAY BE HARD TO PIN DOWN AND SPEED LIGHT,
SO PERIODS OF VRB ARE WARRANTED. CAN'T RULE OUT SOME ISOLATED
SHRA OR EVEN A FEW TSRA THIS AFTERNOON AND EARLY EVENING, BUT THE
CHANCE NOW APPEARS LOWER THAN ONCE EXPECTED AND PROB30S ARE NO
LONGER INCLUDED EXCEPT AT KGSP/KGMU WHICH WOULD BE MOST LIKELY
TO CATCH ANY ACTIVITY FORMING OVER THE HIGHER TERRAIN NEAR THE
NC/SC BORDER. A SMALL CHANCE OF PRECIP DOES EXIST TONIGHT, AS
ENSUING NW FLOW REGIME COULD BRING IN SOME SHOWERS FROM WEST OF
THE APPALACHIANS. VCSH INCLUDED AT THE SC SITES. SFC MOISTURE WILL
REMAIN ABUNDANT AND SKIES SHOULD BE CLEAR OF HIGHER DECKS SO SOME
POTENTIAL FOR RADIATION FOG/STRATUS EXISTS. WITH LOW CONFIDENCE DID
NOT HIT RESTRICTIONS VERY HARD IN THE CURRENT SET OF TAFS SAT NIGHT.
OUTLOOK: DRYING IS EXPECTED FOR SUNDAY AND MONDAY, WITH CONVECTION
AND ASSOCIATED RESTRICTIONS LOOKING ISOLATED. POTENTIAL FOR DECAYING
THUNDERSTORMS TO MOVE INTO THE AREA BRINGING REMNANT AREAS OF
RESTRICTIONS MON, HOWEVER. STRONG THUNDERSTORMS COULD DEVELOP
TUESDAY. LOW STRATUS AND/OR FOG WILL BE POSSIBLE EACH MORNING
IN THE MTN VALLEYS AND AT ANY LOCATIONS THAT RECEIVE APPRECIABLE
RAINFALL THE PREVIOUS DAY/EVENING.
GSP WATCHES/WARNINGS/ADVISORIES
GA...NONE.
NC...NONE.
SC...NONE.
JCW
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