859
FXUS62 KGSP 180543
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
143 AM EDT TUE AUG 18 2026
WHAT HAS CHANGED
ADDED DETAILS ABOUT CONVECTION AND LOW-END SEVERE POTENTIAL THE
LATTER HALF OF THE WEEK.
THE AVIATION FORECAST WAS UPDATED TO REFLECT THE RECENT 06Z TAF
ISSUANCE.
KEY MESSAGES
1. HOT AND MUGGY CONDITIONS CONTINUE FOR MOST OF THE WEEK,
BUT SUBSIDE JUST ENOUGH THAT NO HEAT ADVISORY IS NECESSARY FOR
TUESDAY. A PATTERN CHANGE MAY BE IN STORE FOR THIS WEEKEND.
2. FOLLOWING A FEW DAYS OF SUPPRESSED CONVECTION, DIURNAL SHOWERS
AND THUNDERSTORMS RETURN BY THURSDAY AND PERSIST THROUGH THE
WEEKEND. A COLD FRONT MAY FURTHER ENHANCE STORM ACTIVITY OVER
THE WEEKEND.
DISCUSSION
KEY MESSAGE 1: HOT AND MUGGY CONDITIONS CONTINUE FOR MOST OF THE
WEEK, BUT SUBSIDE JUST ENOUGH THAT NO HEAT ADVISORY IS NECESSARY
FOR TUESDAY. A PATTERN CHANGE MAY BE IN STORE FOR THIS WEEKEND.
HEIGHTS HAVE FALLEN SIGNIFICANTLY OVER THE FORECAST AREA FOLLOWING
THE PASSAGE OF A WEAK COLD FRONT AND ASSOCIATED H50 VORT LOBE;
WATER VAPOR IMAGERY AND RECENT RAP ANALYSIS NOW SUGGEST THAT THE
SUBTROPICAL RIDGE IS MORE OF AN ELONGATED ANTICYCLONE, CENTERED
MORE OR LESS OVER THE FOUR CORNERS REGION OF THE US SOUTHWEST,
AND EXTENDING EAST TOWARD THE GULF COAST.
DON'T EXPECT TERRIBLY MUCH CHANGE IN THIS CONFIGURATION THROUGH AT
LEAST WEDNESDAY. THE SUBTROPICAL RIDGE WILL BECOME RE-ESTABLISHED
OVER THE WESTERN ATLANTIC OVER THE NEXT 24 HOURS OR SO, BUT THE
GENERAL WEAKNESS OVER THE SOUTHEAST WILL PERSIST AS A MASSIVE
BOWLING BALL UPPER LOW MEANDERS FROM NORTHERN MANITOBA INTO
THE HUDSON BAY, EJECTING A SERIES OF SHORTWAVES ACROSS THE
MIDWEST AND UPPER MID-ATLANTIC THROUGH THE MIDDLE OF THE WEEK.
THESE DISTURBANCES WON'T IMPACT THE WESTERN CAROLINAS DIRECTLY,
BUT WILL SERVE TO MAINTAIN WEAK TROUGHINESS OVER THE AREA,
KEEPING HEIGHTS CONSTRAINED AND MORE GENERALLY RESULTING IN COOLER
TEMPERATURES THE NEXT TWO OR THREE DAYS THAN WE'VE HAD SINCE LATE
LAST WEEK. NO HEAT ADVISORY WILL BE ISSUED FOR TUESDAY AFTERNOON;
DETERMINISTIC GUIDANCE SUGGESTS SIGNIFICANT DAYTIME MIXING OF
DEWPOINTS, RESULTING IN DRY ENOUGH CONDITIONS IN THE POSTFRONTAL
AIR MASS THAT CONFIDENCE SIMPLY REMAINS TOO LOW ON ANY LOCATIONS
REACHING THE 105-DEGREE HEAT INDEX THRESHOLD TODAY. THE SAME IS
TRUE FOR WEDNESDAY; BY THURSDAY, A RESURGENCE IN MOISTURE COULD
ALLOW A FEW SPOTS SOUTH OF I-85 TO FLIRT WITH ADVISORY CRITERIA
ONCE AGAIN.
BY THE WEEKEND, LONG-RANGE ENSEMBLES ARE STILL IN GOOD AGREEMENT
ON A WEAK COLD FRONTAL PASSAGE FURTHER ERODING THE WARM, MOIST
AIR OVER OUR AREA. SATURDAY AND BEYOND, HIGH TEMPERATURES SHOULD
TREND BACK TOWARD SEASONAL NORMALS AND PROVIDE SOME RELIEF FROM
THE LATE-SUMMER HEAT.
KEY MESSAGE 2: FOLLOWING A FEW DAYS OF SUPPRESSED CONVECTION, DIURNAL
SHOWERS AND THUNDERSTORMS RETURN BY THURSDAY AND PERSIST THROUGH
THE WEEKEND. A COLD FRONT MAY FURTHER ENHANCE STORM ACTIVITY OVER
THE WEEKEND.
A COLD FRONT (WHICH WAS LARGELY RESPONSIBLE FOR MONDAY EVENING'S
SEVERE WEATHER) IS NOW LOCATED SOMEWHERE ALONG OR JUST SOUTH OF
I-85, BASED ON RECENT SURFACE ANALYSIS AND MESOANALYSIS FIELDS.
OVER THE NEXT 12 HOURS IT SHOULD CONTINUE ITS SOUTHEASTWARD TREK,
PLACING THE ENTIRE FORECAST AREA IN A POSTFRONTAL AIR MASS AND
KEEPING CONDITIONS SUPPRESSED THE NEXT FEW DAYS. WEAK CAPPING ATOP
THE PBL SHOULD BE ENOUGH TO PREVENT CONVECTIVE INITIATION TUESDAY
AND WEDNESDAY AFTERNOON...AND INDEED NONE OF THE 00Z SUITE OF HI-RES
GUIDANCE FEATURES ANY SHOWERS OR THUNDERSTORMS THE NEXT TWO DAYS.
BY THURSDAY, ANOTHER WEAK BOUNDARY ASSOCIATED WITH AN H50 SHORTWAVE
CROSSING THE MID-ATLANTIC WILL SETTLE ACROSS THE TENNESSEE VALLEY.
THOUGH GUIDANCE DOESN'T DEPICT AN ACTUAL FRONTAL PASSAGE THROUGH THE
END OF THE WEEK, THE ENVIRONMENT ACROSS THE WESTERN CAROLINAS SHOULD
BECOME MOIST AND UNSTABLE ENOUGH TO SUPPORT A RETURN TO DIURNAL
CONVECTION ON THURSDAY AND FRIDAY. IT'S NOT EVEN ENTIRELY OUT OF
THE QUESTION THAT A DECAYING MCS ORIGINATING ON THE FRONTAL BOUNDARY
COULD SLIDE ACROSS THE AREA, THOUGH THE UPPER PATTERN ISN'T AS
FAVORABLE FOR SUCH A SYSTEM TO MOVE INTO OUR AREA VERSUS LOCATIONS
FARTHER NORTH. REGARDLESS, EVEN IF WE ONLY SEE SEASONALLY-TYPICAL
DIURNAL CONVECTION, PROFILES DEPICT ENOUGH DCAPE TO SUPPORT A
COUPLE OF STRONG TO SEVERE STORMS PRODUCING WET DOWNBURSTS.
BY FRIDAY, AND CERTAINLY BY SATURDAY, THE APPROACHING FRONT AND
STRENGTHENING UPPER FLOW WILL ALLOW DEEP LAYER SHEAR TO INCREASE,
AND WE'LL BEGIN TO SEE THE POTENTIAL FOR MORE ORGANIZED CONVECTION
TO DEVELOP, UNTIL THE FRONT CROSSES THE AREA OVER THE WEEKEND.
AVIATION /06Z TUESDAY THROUGH SATURDAY/
AT KCLT AND ELSEWHERE: A LOW-CONFIDENCE NIGHT LOOMS AHEAD AS
WIDESPREAD CONVECTION DRAWS TO A CLOSE. IT'S NOW DRY BASICALLY
EVERYWHERE WITH WHATEVER LINGERING SHOWERS REMAIN HAVING PASSED
SOUTH OF THE AREA. THERE'S A LOT OF MOISTURE OUT THERE, THOUGH,
WITH VIRTUALLY THE ENTIRE TERMINAL FORECAST AREA HAVING RECEIVED
SOME RAINFALL OVER THE LAST SIX HOURS, WHICH IS A POINT TOWARD AT
LEAST PATCHY FOG DEVELOPMENT; HOWEVER, THICK CONVECTIVE DEBRIS
FROM A SEGMENT OF THE CONVECTIVE LINE THAT MOVED THROUGH NORTH
GEORGIA IS NOW STREAMING INTO THE AREA FROM THE WEST. THESE TWO
COMPETING EFFECTS WILL DETERMINE HOW MUCH, IF ANY, FOG DEVELOPS.
EVEN IF FOG FAILS TO DEVELOP IN MOST PLACES - WHICH SEEMS THE MORE
LIKELY SCENARIO - SOME MOUNTAIN VALLEY STRATUS LOOKS POSSIBLE,
SO WILL NEED TO CLOSELY MONITOR THE MOUNTAIN SITES FOR RESTRICTIONS.
CONDITIONS ARE EXPECTED TO REMAIN DRY AND VFR TOMORROW, WITH LITTLE
TO NO CONVECTIVE ACTIVITY IN THE WAKE OF TONIGHT'S FRONTAL PASSAGE.
WINDS SHOULD FAVOR A N/NW DIRECTION BEHIND THE FRONT, BECOMING
INCREASINGLY N THROUGH THE DAY.
OUTLOOK: ISOLATED SHOWERS AND THUNDERSTORMS MAY DEVELOP ON
WEDNESDAY, MAINLY OVER THE MOUNTAINS, BUT DIURNAL CONVECTION IS LESS
LIKELY TO RETURN UNTIL THURSDAY, WHEN AT LEAST DIURNAL CONVECTION
WILL DEVELOP EACH DAY THROUGH THE WEEKEND. LOW STRATUS AND FOG
WILL BE POSSIBLE EACH MORNING, ESPECIALLY IN THE MOUNTAIN VALLEYS.
GSP WATCHES/WARNINGS/ADVISORIES
GA...NONE.
NC...NONE.
SC...NONE.
MPR
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