724
FXUS62 KGSP 250655
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
255 AM EDT SAT JUL 25 2026
WHAT HAS CHANGED
SHIFTED FOCUS OF THE DISCUSSION TOWARD THE SUNDAY TO
WEDNESDAY PERIOD WHEN PERIODIC CHANCES FOR SEVERE WEATHER AND HEAVY
RAINFALL MAY DEVELOP.
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 /06Z SATURDAY THROUGH WEDNESDAY/
AT KCLT AND ELSEWHERE: CHALLENGING TAF FORECAST WITH CONTINUING
IFR TO LIFR STRATUS ACROSS THE AREA THIS MORNING NORTH OF A STALLED
FRONT, AND POTENTIAL FOR OCCASIONAL -DZ OR -SHRA TO EITHER IMPROVE
OR WORSEN RESTRICTIONS. IT LOOKS GENERALLY LIKELY THAT VSBY WILL
REMAIN MVFR OR VFR WHEN PRECIP IS VERY LIGHT, STRATUS SHOULD REMAIN
AT IFR TO LIFR UNTIL 12-15Z. HOWEVER, CONDITIONS APPEAR FAVORABLE
FOR A FEW SHRA--AND PERHAPS A STRAY TSRA-- TO DEVELOP OVER THE AREA
BEGINNING IN THE PREDAWN HOURS. TEMPO OR PROB30 GROUPS ARE INCLUDED
AT ALL SITES IN THIS EARLY MORNING TIMEFRAME FOR THAT ACTIVITY TO
SCATTER THE LOWER CIGS AND/OR CAUSE BRIEFLY LOWER VSBY. A LULL IN
PRECIP POTENTIAL IS EXPECTED DURING THE LATE MORNING TO MIDDAY AND
SLIGHT DRYING SHOULD OCCUR ALOFT WHICH WILL PROMOTE THE STRATUS
TO CONTINUE TO LIFT OR MIX OUT. MOST SITES SHOULD RISE TO LOW MVFR
THROUGH THAT PROCESS WITH CLOUDS GOING BKN OR SCT AND BASES RISING
TO FL030 OR ABOVE DURING THE AFTERNOON. CAN'T RULE OUT DIURNALLY
DRIVEN DEVELOPMENT OF SHRA AT KCLT/KGSP/KGMU DURING THE AFTERNOON
WHICH WARRANTED PROB30S THERE, BUT ELSEWHERE THE MORE ISOLATED
COVERAGE WARRANTED ONLY VCSH. SOME REDEVELOPMENT OF RESTRICTIONS
APPEARS LIKELY AFTER 06Z SUN BUT CONFIDENCE IS LOW; WILL BE MORE
CONFIDENT AFTER SEEING HOW PRECIP EVOLVES THIS MORNING AND HOW
MODELS CHANGE FOR THIS AFTERNOON'S POTENTIAL CONVECTION. WINDS
WILL BE LIGHT THRU THE PERIOD BUT SHOULD FAVOR NORTHERLY EXCEPT
AT KAND TODAY, WHICH WILL BE MORE WESTERLY.
OUTLOOK: DRYING IS EXPECTED FOR SUNDAY AND MONDAY, WITH CONVECTION
AND ASSOCIATED RESTRICTIONS LOOKING LESS LIKELY. 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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