111
FXUS62 KGSP 030533
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
133 AM EDT THU SEP 3 2026
WHAT HAS CHANGED
LOWERED DEWPOINTS ON THURSDAY AND FRIDAY BASED ON THE LAST TWO DAYS'
VERIFICATION. HEAT INDEX FORECAST HAS COME DOWN UP TO 2 DEGREES
IN SOME LOCATIONS AS A RESULT, BUT STILL EXPECTING WIDESPREAD
100-105 DEGREE HEAT INDEX VALUES BOTH AFTERNOONS.
THE AVIATION FORECAST WAS UPDATED TO REFLECT THE RECENT 06Z TAF
ISSUANCE.
KEY MESSAGES
1. HOT AND HUMID CONDITIONS PERSIST THROUGH SATURDAY AFTERNOON,
WITH HEAT INDEX VALUES IN THE LOWER 100S EAST OF THE MOUNTAINS. A
HEAT ADVISORY IS IN EFFECT FOR PORTIONS OF THE I-77 CORRIDOR FOR
THURSDAY AFTERNOON. A COOLING TREND ARRIVES SUNDAY.
2. DIURNAL CONVECTION REMAINS MOSTLY CONFINED TO THE MOUNTAINS ON
THURSDAY AND FRIDAY, BEFORE A COLD FRONT DRIVES MORE WIDESPREAD
SHOWERS AND STORMS ON SATURDAY.
DISCUSSION
KEY MESSAGE 1: HOT AND HUMID CONDITIONS PERSIST THROUGH SATURDAY
AFTERNOON, WITH HEAT INDEX VALUES IN THE LOWER 100S EAST OF THE
MOUNTAINS. A HEAT ADVISORY IS IN EFFECT FOR PORTIONS OF THE I-77
CORRIDOR FOR THURSDAY AFTERNOON. A COOLING TREND ARRIVES SUNDAY.
A BROAD 595DM UPPER ANTICYCLONE REMAINS DRAPED ACROSS THE SOUTHEAST,
EXTENDING FROM THE OZARK PLATEAU, ACROSS THE TENNESSEE VALLEY, AND
INTO THE CAROLINAS. THE RESULTING SUPPRESSED PATTERN HAS KEPT US
MOSTLY DRY, WITH CLEAR CONDITIONS TONIGHT AND NO RETURNS ON RADAR.
THE UPPER PATTERN IS PROGGED TO REMAIN MOSTLY UNCHANGED FOR THE NEXT
TWO DAYS, WITH ANTICYCLONIC FLOW REMAINING CENTERED RIGHT OVER US,
AND RESULTANT WEAK SUBSIDENCE AND MOSTLY DRY CONDITIONS. WEAK BUT
MOIST SOUTHERLY SURFACE FLOW LOOKS TO PERSIST THROUGH FRIDAY,
DRIVEN BY A BERMUDA HIGH-LIKE FEATURE OVER THE WESTERN ATLANTIC.
THE RESULT STILL LOOKS LIKE ABOVE-NORMAL TEMPERATURES AND UNBEARABLE
HUMIDITY ON THURSDAY, FRIDAY, AND SATURDAY AFTERNOONS. HEAT INDEX
VALUES ARE EXPECTED TO CLIMB INTO AT LEAST THE LOW 100S EAST OF
THE MOUNTAINS EACH AFTERNOON. FOR THURSDAY, A HEAT ADVISORY IS IN
EFFECT FROM 11 AM UNTIL 8 PM FOR UNION COUNTY, NC; SURROUNDING ZONES
WILL COME CLOSE TO, BUT NOT QUITE REACH, HEAT ADVISORY CRITERIA.
THE BIG QUESTION MARK REMAINS AFTERNOON DEWPOINT MIXING. FORECAST
PROFILES FROM THE GFS AS WELL AS THE 00Z HREF MEMBERSHIP DEPICT
A DEEP MIXED LAYER (TOPPING OUT AS HIGH AS 700MB, WITH ONLY
A WEAK PBL- TOP INVERSION, ON THURSDAY AND FRIDAY) SUPPORTIVE
OF SIGNIFICANT AFTERNOON DEWPOINT DROPS. THE LAST TWO DAYS,
THIS HAS INTERFERED SIGNIFICANTLY WITH THE DEWPOINT FORECAST,
WITH AFTERNOON DEWPOINTS UNDERCUTTING MOST OF THE GUIDANCE BY 1-3
DEGREES AND RESULTING IN COOLER (ALBEIT STILL DANGEROUSLY HOT)
HEAT INDEX VALUES FOR MOST OF THE FORECAST AREA. AS A CONSEQUENCE,
CONFIDENCE IS LIMITED ON THE EXACT HEAT INDEX FORECAST...AND IT MAY
BE MORE APT TO SAY THAT HEAT INDEX VALUES WILL DIFFER SIGNIFICANTLY
FROM LOCATION TO LOCATION DUE TO LOCALIZED VARIATIONS IN MIXING.
THE THINKING FOR SATURDAY IS SIMILAR, BUT CONFIDENCE IS LOWER.
BY SUNDAY, ENSEMBLES AND GLOBAL DETERMINISTIC MODELS ARE IN
EXCELLENT AGREEMENT THAT AS THE SUBTROPICAL RIDGE BECOMES MORE
AND MORE "SQUISHED" BY SUCCESSIVE SHORTWAVES TRACKING OUT OF THE
GREAT LAKES AND ACROSS THE MID-ATLANTIC, A SURFACE FRONT WILL BE
DRIVEN ACROSS THE CAROLINAS, USHERING IN A SOMEWHAT COOLER AND
DRIER AIR MASS. STILL THINK, THEREFORE, THAT TEMPERATURES WILL
RETURN TO NEAR- NORMAL FOR MONDAY AND TUESDAY. ENSEMBLES BEGIN
TO DIVERGE WILDLY BY THE MIDDLE OF THE WEEK, WITH SOME 00Z LREF
MEMBERS DEPICTING CONTINUED TROUGHING OVER THE EASTERN CONUS AND
A BUILDING RIDGE OVER THE ROCKIES AND GREAT PLAINS...AND OTHERS
DEPICTING THE SUBTROPICAL RIDGE BECOMING RE-ESTABLISHED OVER THE
SOUTHEAST. CONFIDENCE, THEREFORE, IS VIRTUALLY NONEXISTENT FOR
THE FORECAST AT THIS POINT IN TIME.
KEY MESSAGE 2: DIURNAL CONVECTION REMAINS MOSTLY CONFINED TO THE
MOUNTAINS ON THURSDAY AND FRIDAY, BEFORE A COLD FRONT DRIVES MORE
WIDESPREAD SHOWERS AND STORMS ON SATURDAY.
STILL THINK THAT BROAD SUBTROPICAL RIDGING WILL KEEP CONVECTION
SUPPRESSED TODAY, WITH GFS AND 00Z HREF PROFILES STILL FEATURING
A WEAK CAP THAT SHOULD, IN THE ABSENCE OF ANY SYNOPTIC FORCING
TO SPEAK OF, BE ENOUGH TO KEEP CONVECTION AT BAY EAST OF THE
MOUNTAINS. HAVING SAID THAT, THE 00Z SUITE OF HI-RES MODELS
IS IN GOOD AGREEMENT THAT SCATTERED SHOWERS, AND PERHAPS A FEW
THUNDERSTORMS, WILL INITIATE OVER THE RIDGETOPS THIS AFTERNOON,
WITHIN AN ENVIRONMENT DEVOID OF ANY SHEAR BUT WITH 1000-1500 J/KG
SBCAPE. A FEW OF THE CAMS (MOST NOTABLY THE NAMNEST AND SEVERAL
MEMBERS OF THE 00Z REFS) DEPICT CONVECTION BREAKING CONTAINMENT AND
RIDING OUTFLOWS INTO THE WESTERN UPSTATE THROUGH THE EVENING HOURS.
GENERALLY THINK THIS IS A LOW-PROBABILITY SCENARIO GIVEN HOW HIGH
LFCS WILL BE, BUT SHOULD IT OCCUR, CELLS WOULD HAVE A NARROW WINDOW
TO TAP INTO A MORE UNSTABLE ENVIRONMENT OVER THE UPSTATE, FEATURING
CLOSER TO 2000 J/KG SBCAPE AND SUFFICIENT DCAPE TO SUPPORT A STRAY
STRONG THUNDERSTORM OR TWO.
FLOW WILL BEGIN TO IMPROVE A TAD ON FRIDAY, WITH THE CAMS WHICH
EXTEND OUT THAT FAR AGAIN DEPICTING A SMALL CHANCE OF A FEW CELLS
ESCAPING THE MOUNTAINS, BUT WITH THE SAME LIMITING FACTORS AS
THURSDAY IN THE FORM OF HIGH LFCS, WEAK CAPPING, AND POOR MID-LEVEL
LAPSE RATES. NONETHELESS, THERE'S A HIGHLY-CONDITIONAL SCENARIO
IN WHICH A SHORTWAVE GRAZING THE I-40 CORRIDOR FRIDAY AFTERNOON
COULD CONTRIBUTE JUST ENOUGH FLOW ALOFT THAT IF THE CAP BREAKS AND
PERMITS CONVECTIVE INITIATION, AND THE UPPER FLOW BECOMES STRONG
ENOUGH WHILE CONVECTION IS ACTIVE, THAT AN ISOLATED STRONG TO
SEVERE STORM COULD PRODUCE DAMAGING WINDS OVER THE FAR NORTHEASTERN
PORTION OF OUR FORECAST AREA.
CONDITIONS WON'T REALLY BECOME MORE FAVORABLE FOR CONVECTION
OVER THE LOW TERRAIN UNTIL SATURDAY, WHEN UPPER SHORTAVES ROLLING
THROUGH THE SUBTROPICAL RIDGE START TO ERODE CAPPING AND STEEPEN
LAPSE RATES. AT THE SAME TIME, A COLD FRONT WILL SETTLE INTO THE
LOWER MID-ATLANTIC, POSSIBLY ARRIVING IN THE CAROLINAS BY EARLY
SATURDAY AFTERNOON AND PROVIDING A BETTER TRIGGERING MECHANISM FOR
SHOWERS AND STORMS, AS WELL AS A MORE FAVORABLE PARAMETER SPACE
FOR CONVECTIVE ACTIVITY. ENSEMBLES FEATURE ANYWHERE FROM 1500 TO
UPWARDS OF 2000 J/KG SBCAPE, A RESPECTABLE 20-25KTS OF DEEP-LAYER
SHEAR, AND DCAPE ON THE ORDER OF 1200-1500 J/KG WITH PWS > 1.8". ALL
THIS COULD BE SUPPORTIVE OF SOME SEMI-ORGANIZED SEGMENTS, AS WELL AS
WET MICROBURSTS. HOWEVER, CONFIDENCE REMAINS LIMITED, AND ALTHOUGH
IT LOOKS LIKE SEVERAL FAVORABLE INGREDIENTS WILL BE IN PLACE FOR
A NON-ZERO SEVERE THREAT...THERE'S STILL ROOM FOR THINGS TO CHANGE.
AVIATION /06Z THURSDAY THROUGH MONDAY/
AT KCLT AND ELSEWHERE: PREDOMINANTLY VFR CONDITIONS ON TAP ONCE
AGAIN FOR THE 06Z TAF PERIOD, WITH ANOTHER ROUND OF VALLEY FOG AND
LOW STRATUS IN STORE FOR THE NC MOUNTAINS. GUIDANCE IS LOOKING
A LITTLE LESS AGGRESSIVE WITH RESTRICTIONS TONIGHT THAN PREVIOUS
NIGHTS, SO HEDGED ON ONLY MVFR TO HIGH-END IFR RESTRICTIONS AT AVL.
WHATEVER RESTRICTIONS DEVELOP SHOULD SCATTER OUT AFTER DAYBREAK,
GIVING WAY TO A VFR DAY.
HI-RES MODELS KEEP CONVECTION CONFINED TO THE MOUNTAINS ONCE AGAIN
THURSDAY, ALBEIT WITH SOMEWHAT BETTER COVERAGE THAN WE'VE HAD MOST
OF THIS WEEK. FELT COVERAGE WAS INCREASED ENOUGH TO INCLUDE A
VCSH AT AVL FOR A FEW HOURS DURING THE AFTERNOON AND EARLY EVENING,
BUT OTHERWISE NO PRECIP MENTION FOR THE 06Z TAFS. DRY AND MOSTLY
VFR CONDITIONS ARE EXPECTED TO CONTINUE INTO THURSDAY NIGHT.
OUTLOOK: DIURNAL CONVECTION, MOSTLY CONFINED TO THE MOUNTAINS,
RETURNS ON FRIDAY. MORE WIDESPREAD SHOWERS AND STORMS ARE EXPECTED
ON SATURDAY AS A COLD FRONT CROSSES THE AREA. SUPPRESSED WEATHER
RETURNS SUNDAY AND BEYOND.
GSP WATCHES/WARNINGS/ADVISORIES
GA...NONE.
NC...HEAT ADVISORY FROM 11 AM THIS MORNING TO 8 PM EDT THIS EVENING
FOR NCZ082.
SC...NONE.
MPR
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