075
FXUS62 KGSP 031801
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
201 PM EDT THU SEP 3 2026
WHAT HAS CHANGED
THE RISK FOR SEVERE THUNDERSTORMS ON SATURDAY HAS INCREASED.
THE AVIATION FORECAST WAS UPDATED TO REFLECT THE 18Z TAF ISSUANCE.
KEY MESSAGES
1. HOT AND HUMID CONDITIONS PERSIST THROUGH SATURDAY, WITH
EXPECTED HEAT INDEX VALUES IN THE LOWER 100S MOST PLACES EAST OF
THE MOUNTAINS EACH AFTERNOON. A HEAT ADVISORY REMAINS IN EFFECT
FOR UNION COUNTY NC THIS AFTERNOON.
2. SEVERE THUNDERSTORM RISK WILL INCREASE ON SATURDAY AFTERNOON
AS A STRONG COLD FRONT APPROACHES.
DISCUSSION
KEY MESSAGE 1: HOT AND HUMID CONDITIONS PERSIST THROUGH SATURDAY,
WITH EXPECTED HEAT INDEX VALUES IN THE LOWER 100S MOST PLACES EAST
OF THE MOUNTAINS EACH AFTERNOON. A HEAT ADVISORY REMAINS IN EFFECT
FOR UNION COUNTY NC THIS AFTERNOON.
A TYPICAL HOT SUMMERTIME PATTERN WILL PERSIST THROUGH FRIDAY,
FEATURING A LARGE UPPER ANTICYCLONE INITIALLY CENTERED OVER THE
CAROLINAS THIS AFTERNOON. THE ANTICYCLONE SHOULD STICK AROUND
THROUGH TONIGHT, BUT ON FRIDAY CHANGES WILL BE UNDERWAY AS AN
UPPER LEVEL BLOCKING PATTERN AMPLIFIES OVER NORTH AMERICA. FROM
FRIDAY INTO FRIDAY NIGHT, THE PATTERN CHANGE SHOULD MOVE/RELOCATE
THE ANTICYCLONE TO THE PLAINS, BUT NOT FAST ENOUGH TO PREVENT ONE
MORE POTENTIALLY HOT DAY ON SATURDAY, DEPENDING ON THE TIMING OF
A STRONG COLD FRONT. MORE ON THAT LATER.
FCST HIGH TEMPS FOR FRIDAY LOOK VERY SIMILAR TO TODAY, MEANING
A CONTINUATION OF HIGHS ON THE ORDER OF 10-15 DEGREES ABOVE
NORMAL, WHILE THE DEWPOINT SHOULD REMAIN IN THE UPPER 60S AND
LOWER 70S. THE DEWPOINT IS THE TRICKY PART OF THE FCST AS IT HAS
MIXED OUT LOWER THAN FCST FOR THE PAST FEW DAYS. NO REASON TO
THINK THAT IT WON'T MIX OUT AGAIN ON FRIDAY AFTERNOON, SO SOME
OF THE DRIER RAW MODEL GUIDANCE WAS BLENDED WITH THE NBM TO DROP
THE DEWPOINT DOWN TO PROBABLY MORE REASONABLE LEVELS. THIS HAS THE
EFFECT OF LOWERING THE HEAT INDEX DOWN A FEW DEGREES AND KEEPS IT
BELOW HEAT ADVISORY CRITERIA FOR ALL BUT A FEW SPOTS AROUND METRO
CHARLOTTE. THE GENERAL IDEA HERE IS THAT CONFIDENCE IS LOW AT THIS
TIME THAT WE WOULD NEED AN ADVISORY FOR FRIDAY AFTERNOON. SATURDAY
IS MORE PROBLEMATIC BECAUSE THE TEMPS WILL BE MORE LIKELY TO BE
AFFECTED BY OUTFLOW BOUNDARIES AND THE TIMING OF CONVECTION, BUT
IN THE ABSENCE OF THOSE, THE AIR MASS REMAINS HOT AND CAPABLE OF
MAKING 10 DEGREES ABOVE NORMAL. THE DEWPOINTS SHOULD BE HIGHER,
THOUGH, SO HEAT ADVISORY CRITERIA WOULD BE MORE ATTAINABLE.
AT ANY RATE, TEMPS SHOULD COOL BACK DOWN TO AROUND NORMAL FOR
THE FIRST HALF OF NEXT WEEK AS WE COME UNDER THE INFLUENCE OF
THE CYCLONIC UPPER FLOW AROUND THE UPPER LOW OFF THE CANADIAN
MARITIMES. ALAS, THE BLOCKING PATTERN COMES UNDONE AND PROGRESSIVE
FLOW WILL BRING THE HEAT BACK LATER NEXT WEEK.
KEY MESSAGE 2: SEVERE THUNDERSTORM RISK WILL INCREASE ON SATURDAY
AFTERNOON AS A STRONG COLD FRONT APPROACHES.
DEEP CONVECTION IS EXPECTED TO REMAIN RELATIVELY ISOLATED AND
CONFINED TO THE HIGHER TERRAIN THIS AFTERNOON AND MOST LIKELY AGAIN
FRIDAY AFTERNOON. FOR TODAY, IT WOULD APPEAR THAT JUST ENOUGH OF
A WEAK CAP REMAINS IN PLACE TO KEEP THE CONVECTION SHALLOW, OWING
PROBABLY TO THE LACK OF A GOOD TRIGGER. THE MESOANALYSIS SHOWS
SUFFICIENT BUOYANCY ACROSS THE REGION, WITH ROUGHLY 3000 J/KG OF
MOST-UNSTABLE CAPE TO WORK WITH, AND YET THE RADAR REMAINS FAIRLY
QUIET AND THE HRRR ONLY DEVELOPS A FEW CELLS OVER SOME RIDGETOPS
WHERE UPSLOPE FLOW CONVERGES ENOUGH TO OVERCOME ANY CAPPING. THE
CHANCES OF ANY STRONG STORMS IS VERY LOW, BUT NON-ZERO. FRIDAY LOOKS
SIMILAR TO TODAY WITH PERHAPS A LITTLE STRONGER CAPPING, SO ONCE
AGAIN THE DEEP CONVECTION WILL BE CONFINED MAINLY TO THE MTNS. WILL
ADD A SLIGHT CHANCE TO THE NORTHWEST PIEDMONT IN DEFERENCE TO THE
DAY 2 CONVECTIVE OUTLOOK WHICH BRUSHES THE MARGINAL RISK ACROSS
THAT AREA. THUNDERSTORM CHANCES ARE CERTAINLY MUCH HIGHER FARTHER
TO THE NORTH, BUT THERE IS SOME SMALL CHANCE THAT SOMETHING COULD
ARRIVE LATE IN THE DAY ON AN OUTFLOW BOUNDARY FROM THE CONVECTION
MOVING PAST WELL TO OUR NORTH.
WHICH BRINGS US TO SATURDAY. SEEMS LIKE A LOT OF HEAT WAVES (IF
THAT'S WHAT YOU WANT TO CALL THE LAST SEVERAL DAYS) END WITH A
BANG. THE DAY 3 CONVECTIVE OUTLOOK FROM THE SPC SHOWS A SLIGHT RISK
ACROSS MUCH OF THE FCST AREA, AND THAT IS CERTAINLY WARRANTED. AS
WE COME MORE UNDER THE CYCLONIC INFLUENCE OF THE UPPER LOW OVER
THE CANADIAN MARITIMES, A COLD FRONT SHOULD DROP DOWN FROM THE
NORTHWEST, POSSIBLY WITH IDEAL TIMING DURING PEAK HEATING. THE 15Z
RAP LOOKS COMPELLING AT 18Z SATURDAY, SHOWING AN ENVIRONMENT WITH
UPWARDS OF 3500 J/KG OF MUCAPE AND 20-30 KT OF EFFECTIVE/DEEP
LAYER SHEER TO GO ALONG WITH AN EXCELLENT TRIGGER. CONVECTION
MOVING PAST TO THE NORTH MAY ALSO LEAVE BEHIND AN OLD OUTFLOW
OR CLOUDY/CLEAR BOUNDARY TO BE A FOCUS FOR AFTERNOON STORMS. THE
EVENT REMAINS TANTALIZINGLY JUST OUTSIDE THE WINDOW OF THE CAMS, SO
CONFIDENCE IS KEPT LOW, BUT WE EAGERLY AWAIT LATER RUNS TO PROVIDE
MORE CLARITY. SHOULD BE QUIET AFTER THE FRONT PASSES SATURDAY NIGHT.
AVIATION /18Z THURSDAY THROUGH TUESDAY/
AT KCLT AND ELSEWHERE: VFR THROUGH THIS EVENING WITH SCATTERED HIGH
BASED CU. WIND WILL BE LIGHT AND VARIABLE IN MANY LOCATIONS. IF
THERE IS A PROBLEM, IT WILL BE MTN/VALLEY FOG AND LOW STRATUS AT
KAVL. IT DIDN'T HAPPEN THIS PAST MORNING AND THERE ARE NO GUARANTEES
FOR THE UPCOMING NIGHT, BUT IFR WILL BE INCLUDED AFTER 09Z. APART
FROM THAT, NOT MUCH GOING ON FOR FRIDAY. DIURNAL CONVECTION WILL
DEVELOP OVER THE MTNS, BUT CONFIDENCE IS TOO LOW FOR INCLUDING IN
THE TAF.
OUTLOOK: 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 UNTIL 8 PM EDT THIS EVENING FOR NCZ082.
SC...NONE.
PM
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