237
FXUS62 KGSP 030629
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
229 AM EDT SAT OCT 3 2026
WHAT HAS CHANGED
TEMPERATURES HAVE TRENDED SLIGHTLY DOWNWARD FOR TODAY AND
THUNDERSTORM CHANCES INCREASED. THE OVERALL RAINFALL AMOUNTS FOR
THE EVENT HAVE TRENDED DOWNWARD.
UPDATED THE AVIATION DISCUSSION FOR THE 06Z TAF ISSUANCE.
KEY MESSAGES
1. SHOWERS AND THUNDERSTORMS WILL BECOME NUMEROUS THIS AFTERNOON
AND EVENING ALONG AND AHEAD OF A FRONT DROPPING DOWN FROM THE
NORTH, FOLLOWED BY WIDESPREAD RAIN OVERNIGHT AND AGAIN SUNDAY
AFTERNOON AND EVENING. THE COMBINATION OF EVENTS WILL RAISE THE
THREAT FOR EXCESSIVE RAINFALL THAT COULD RESULT IN SOME LOCALIZED
FLOODING THROUGH SUNDAY NIGHT.
2. DRY FROM MONDAY AFTERNOON ONWARD. COOL TEMPERATURES RETURN
FOR THE MIDDLE OF NEXT WEEK, FOLLOWED BY A STEADY WARMUP LATE IN
THE WEEK.
DISCUSSION
KEY MESSAGE 1: SHOWERS AND THUNDERSTORMS WILL BECOME NUMEROUS THIS
AFTERNOON AND EVENING ALONG AND AHEAD OF A FRONT DROPPING DOWN FROM
THE NORTH, FOLLOWED BY WIDESPREAD RAIN OVERNIGHT AND AGAIN SUNDAY
AFTERNOON AND EVENING. THE COMBINATION OF EVENTS WILL RAISE THE
THREAT FOR EXCESSIVE RAINFALL THAT COULD RESULT IN SOME LOCALIZED
FLOODING THROUGH SUNDAY NIGHT.
A COMPLEX RAINFALL SCENARIO IS EXPECTED TO DEVELOP ACROSS THE
FORECAST AREA THROUGH THE WEEKEND WITH SEVERAL FACTORS TO CONSIDER,
THE COMBINATION OF WHICH COULD BECOME FAVORABLE FOR EXCESSIVE RAIN
AND INCREASED FLOODING RISK. FORTUNATELY, WE BEGIN THE EVENT ON
A RECENT DRY STREAK.
THE INITIAL, MORE CONVECTIVE, PHASE SHOULD DEVELOP THIS AFTERNOON AS
A COLD FRONT CURRENTLY LAID OUT ACROSS THE TN VALLEY/MID-ATLANTIC
GETS DRIVEN SOUTHWARD IN BACK-DOOR FASHION BY A SFC HIGH MOVING
EAST FROM THE GREAT LAKES TO NEW ENGLAND TODAY. THE FRONT WILL
PROBABLY NOT REACH THE FCST AREA UNTIL THE AFTERNOON, SUCH THAT
AT LEAST THE SOUTHERN HALF OF THE FORECAST AREA SHOULD BE ABLE TO
WARM UP INTO THE LOWER 80S AND DESTABILIZE WITH UP TO 1500 J/KG
OF SFC-BASED CAPE IN A WARM ADVECTION FLOW. BY AFTERNOON, THE
BACK DOOR FRONT WILL IMPINGE UPON THIS LIGHT SW LOW LEVEL FLOW AND
SHOULD TRIGGER NUMEROUS SHOWERS AND THUNDERSTORMS. HEAVY RAIN LOOKS
LIKE THE BIGGEST THREAT FROM THIS INITIAL ROUND OF ACTIVITY AS THE
WARM ADVECTION FLOW LIFTS A REMNANT PLUME OF DEEPER SUB-TROPICAL
MOISTURE NORTHWARD INTO THE UPSTATE/PIEDMONT. PRECIPITABLE
WATER SHOULD RISE ABOVE 2 INCHES IN THIS PLUME, UP NEAR THE
CLIMATOLOGICAL MAXIMUM. THE CONCERN IS THAT THE OPPOSING NE FLOW
BEHIND THE BACKDOOR FRONT AND THE SW FLOW AT 850 MB COULD RESULT
IN AN EFFECTIVE SLOW STORM MOVEMENT AT SOME POINT THIS EVENING IN
SOME LOCATION, PROBABLY EAST OF THE MTNS. THE 00Z HREF SHOWS SOME
6-HR RAINFALL POTENTIAL ABOVE 2 INCHES. THIS MIGHT NOT BE ENOUGH
TO CAUSE FLOODING OUTSIDE OF URBAN AREAS, BUT IT COULD SET THE
STAGE FOR FLOODING IN THE SECOND ROUND. HOWEVER, IF THE FRONTAL
BOUNDARY SHOULD STALL, FLOOD PROBLEMS WILL RAMP UP OVERNIGHT. THE
THREAT FOR SEVERE STORMS THROUGH SATURDAY NIGHT APPEARS RELATIVELY
LOW OWING TO POOR LAPSE RATES.
BEHIND THE FRONT, A COLD AIR DAMMING WEDGE WILL SET UP EAST OF
THE BLUE RIDGE AND WILL PERSIST THROUGH SUNDAY WITH TEMPERATURES
REMAINING IN THE UPPER 60S TO LOWER 70S. MOST OF THE CAMS SUGGEST
SOMETHING OF A LULL IN THE ACTION SUNDAY MORNING BEFORE DEEPER
AND BETTER FORCING ARRIVE AHEAD OF A SHEARING SHORT WAVE MOVING
IN FROM THE WEST IN THE AFTERNOON. THIS SECOND PHASE WILL BE
MORE DYNAMICALLY FORCED AND WILL HAVE THE POTENTIAL TO PRODUCE
ANOTHER INCH OR TWO OF RAIN IN SOME SPOTS. LOCATIONS THAT GET HEAVY
RAIN IN BOTH PHASES COULD SEE FLOODING ISSUES. THAT BEING SAID,
THERE IS TOO MUCH UNCERTAINTY REGARDING WHAT LOCATIONS HAVE THE
BEST POTENTIAL, AND THE OVERALL QPF HAS TRENDED DOWNWARD ON THIS
FORECAST CYCLE. THUS, A FLOOD WATCH WAS NOT ENTERTAINED.
KEY MESSAGE 2: DRY FROM MONDAY AFTERNOON ONWARD. COOL TEMPERATURES
RETURN FOR THE MIDDLE OF NEXT WEEK, FOLLOWED BY A STEADY WARMUP
LATE IN THE WEEK.
THE MAIN SHORT WAVE AXIS SHOULD MOVE EAST ACROSS THE FORECAST
AREA EARLY IN THE DAY ON MONDAY, AFTER WHICH THE SUPPORT FOR
ANY LINGERING PRECIP IS QUICKLY SWEPT EASTWARD AND THE REMAINING
WEDGE SHOULD DRAIN AWAY. THE IDEA IS THAT WE WOULD HAVE A WINDOW
OF OPPORTUNITY BEFORE THE COOLER AIR ASSOCIATED WITH THE SFC
HIGH OVER THE UPPER MIDWEST/GREAT LAKES SPILLS THIS FAR SOUTH,
ALLOWING TEMPS TO REBOUND NICELY BACK TO NORMAL WITH SKY SLOWLY
CLEARING. THE MODEL GUIDANCE THAT HAS SOME PRECIP RESPONSE INTO
THE AFTERNOON OVER THE FCST AREA APPEARS TO BE OVERDONE.
FROM MONDAY NIGHT ONWARD, HIGH PRESSURE WILL STAY IN CONTROL
OF OUR WEATHER WITH THE UPPER PATTERN SLOWLY TRANSITIONING TO
QUASI-ZONAL FLOW. THE FIRST HIGH PRESSURE AIR MASS WILL BRING
SEASONALLY COOL TEMPERATURES ON THE ORDER OF 5-10 DEGREES BELOW
NORMAL WITH MOSTLY CLEAR SKY FOR TUESDAY AND WEDNESDAY AS IT MOVES
PAST TO OUR NORTH. TEMPS HAVE CREPT UP EVER SO SLIGHTLY AGAIN IN
THIS MODEL CYCLE, MEANING THAT ONLY ELEVATIONS ABOVE 6000 FEET
STAND MUCH OF A CHANCE OF SEEING TEMPERATURES GETTING DOWN INTO
30S ON TUESDAY NIGHT. A CHUNK OF THAT FIRST HIGH WILL BREAK OFF
AND LINGER OVER THE SOUTHERN APPALACHIANS THURSDAY AND FRIDAY,
WITH THE AIR MASS MODIFYING BACK TO NORMAL TEMPERATURES. SHOULD
BE MORE SPECTACULAR AUTUMN WEATHER. A DRY COLD FRONT MAY BRING IN
A REINFORCING HIGH FOR NEXT WEEKEND.
AVIATION /06Z SATURDAY THROUGH WEDNESDAY/
AT KCLT AND ELSEWHERE: INCREASING MOISTURE AHEAD OF APPROACHING
FRONTAL BOUNDARY IS EXPECTED TO ENHANCE THE PROBABILITY FOR
RESTRICTIONS IN LOW CLOUDS AND/OR FOG LATER THIS MORNING ACROSS
THE TERMINAL FORECAST AREA. MOST SITES HAVE AT LEAST A TEMPO
FOR RESTRICTIONS...MOSTLY IFR OR LOW MVFR CIGS...ALTHOUGH LIFR
CONDITIONS ARE TEMPO/D AT KAVL AND KHKY. CAN'T RULE OUT LIFR AT THE
OTHER TERMINALS AS WELL, BUT THIS APPEARS TO BE UNLIKELY. SHOWERS
AND THUNDERSTORMS ARE EXPECTED TO DEVELOP THIS AFTERNOON AS THE
ATMOSPHERE DESTABILIZES AHEAD OF THE FRONT...WHICH IS FORECAST TO
SAG GRADUALLY SOUTH ACROSS THE AREA THROUGHOUT THE AFTERNOON AND
EVENING. PROB30S FOR TSRA ARE CARRIED AT ALL SITES AT SOME POINT
THIS AFTERNOON, FOLLOWED BY CATEGORICAL -SHRA/VCTS FROM MID/LATE
AFTERNOON INTO THE EVENING.
GENERAL LIGHT S/SW WINDS OR LIGHT/VARIABLE WINDS ARE EXPECTED THIS
MORNING. WINDS WILL TURN TO THE NE AT 5-10 KTS BEHIND THE FRONT,
BUT TIMING THIS TRANSITION WILL BE TRICKY DUE TO UNCERTAINTY ON
THE SPEED OF THE FRONT. SHOWER AND TS COVERAGE WILL DIMINISH BY THE
OVERNIGHT HOURS...ALTHOUGH SOME DEGREE OF SHRA COVERAGE IS LIKELY
TO CONTINUE. THE LARGER CONCERN TONIGHT INTO EARLY SUNDAY WILL
BE THE EXPECTATION OF LOW CLOUDS DEVELOPING IN ASSOCIATION WITH
COLD AIR DAMMING DEVELOPING NORTH OF THE FRONTAL BOUNDARY...AND
IFR/LIFR CIGS ARE LIKELY AT MOST SITES BY 06Z SUNDAY.
OUTLOOK: WIDESPREAD SHRA, COLD AIR DAMMING, AND ASSOCIATED
WIDESPREAD, PERSISTENT FLIGHT RESTRICTIONS ARE EXPECTED ACROSS
THE AREA ON SUNDAY. IMPROVEMENT TO VFR IS EXPECTED BY MONDAY,
AND WILL PERSIST WELL INTO NEXT WEEK.
GSP WATCHES/WARNINGS/ADVISORIES
GA...NONE.
NC...NONE.
SC...NONE.
JDL/PM
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