148
FXUS62 KGSP 181033
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
633 AM EDT THU SEP 18 2025
SYNOPSIS
WEAK HIGH PRESSURE REMAINS OVER THE SOUTHEAST THROUGH FRIDAY KEEPING
MOSTLY DRY CONDITIONS AROUND TODAY BUT SHOWER AND THUNDERSTORM
CHANCES RETURN ACROSS THE MOUNTAINS FRIDAY AFTERNOON. A BACKDOOR
COLD FRONT STALLS ACROSS THE REGION THIS WEEKEND INTO EARLY NEXT
WEEK, POTENTIALLY BRINGING BETTER CHANCES FOR SHOWERS AND
THUNDERSTORMS. THE WARMING TREND CONTINUES THROUGH FRIDAY BEFORE A
COOLING TREND DEVELOPS THIS WEEKEND INTO EARLY NEXT WEEK.
NEAR TERM /THROUGH TONIGHT/
AS OF 630 AM EDT WEDNESDAY: MOUNTAIN VALLEY FOG, AND PATCHY FOG
ELSEWHERE, WILL DISSIPATE BY MID MORNING. PERIODS OF ALTOCU/STRATOCU
WILL LINGER THIS MORNING AS WELL.
IN THE WAKE OF THE DEPARTING COASTAL SYSTEM, A WEAK BAGGY TROUGH
WILL REMAIN OVER THE AREA THROUGH THE PERIOD. SOME WEAK SHORT WAVE
ENERGY WILL MOVE THROUGH THE TROUGH AND ACROSS THE AREA. WEAK
INSTABILITY IS EXPECTED TO DEVELOP AGAIN OVER THE MOUNTAINS WEST OF
THE FRENCH BROAD INTO THE NE GA MOUNTAINS. THIS AND SOME LINGERING
LOW LEVEL MOISTURE WILL LEAD TO ISOLATED DIURNAL CONVECTION OVER
THIS AREA. EXPECT MAINLY CUMULUS ELSEWHERE. HIGHS WILL BE A FEW
DEGREES ABOVE NORMAL.
CONVECTION SHOULD DROP OFF QUICKLY THIS EVENING WITH LOSS OF
HEATING. SKIES WILL CLEAR WITH ANOTHER ROUND OF MOUNTAIN VALLEY FOG
AND PATCHY FOG ELSEWHERE. LOWS WILL BE NEAR NORMAL ACROSS THE
MOUNTAINS AND A FEW DEGREES ABOVE NORMAL ELSEWHERE.
SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/
AS OF 130 AM EDT THURSDAY...
KEY MESSAGES:
1) TRENDING WETTER THROUGH THE SHORT TERM, ESPECIALLY ON SATURDAY
2) FRIDAY WILL BE THE WARMEST DAY OF THE WEEK
3) COOLING TREND STARTS SATURDAY BUT ABOVE NORMAL TEMPS CONTINUE
WEAK AND BRIEF UPPER RIDGING DEVELOPS OVER THE REGION ON FRIDAY
WHILE WEAK SFC HIGH PRESSURE REMAINS OVER THE SOUTHEAST. THIS WILL
ALLOW FRIDAY TO BE THE WARMEST DAY OF THE WEEK WITH HIGHS EXPECTED
TO RUN 6-8 DEGREES ABOVE NORMAL. AFTERNOON TEMPS ON FRIDAY WILL
CLIMB INTO THE MID TO UPPER 80S EAST OF THE MOUNTAINS, WITH SOME
ISOLATED LOCATIONS POSSIBLY REACHING 90 DEGREES. MOSTLY DRY
CONDITIONS ARE EXPECTED AGAIN EAST OF THE MOUNTAINS BUT THE 00Z CAMS
SHOW ISOLATED CONVECTION DEVELOPING IN THE MOUNTAINS FRIDAY. SINCE
THE LATEST NBM CAME IN MOSTLY DRY, OPTED TO ADD SLIGHT CHANCE POPS
ACROSS THE MOUNTAINS FRIDAY AFTERNOON AND EARLY EVENING. ALSO ADDED
SOME SLIGHT CHANCE THUNDER AS WELL AS THE 00Z CAMS HAVE SOME
INSTABILITY DEVELOPING DURING PEAK HEATING. IF CAM TRENDS REGARDING
CONVECTION CONTINUE, SHOWER AND THUNDERSTORM CHANCES MAY NEED TO BE
INCREASED IN FUTURE UPDATES. LOWS FRIDAY NIGHT WILL RUN ~5-7 DEGREES
ABOVE NORMAL.
A BACKDOOR COLD FRONT APPROACHES OUT OF THE NORTH FRIDAY NIGHT,
PUSHING ACROSS THE FORECAST AREA EARLY SATURDAY MORNING BEFORE
STALLING OVER THE CAROLINAS THE REST OF THE PERIOD. 00Z GLOBAL
MODELS, AS WELL AS THE NBM, ARE TRENDING WETTER FOR SATURDAY. THE
LATEST RUN OF THE NBM CAME IN WITH CHANCE POPS AND CHANCE THUNDER
FOR SATURDAY AFTERNOON AND EVENING WHICH APPEARS TO LINES UP WELL
WITH THE LATEST MODEL TRENDS. HIGHS ON SATURDAY WILL BE SLIGHTLY
COOLER BUT ARE STILL ON TRACK TO BE ~4-6 DEGREES ABOVE NORMAL. IF
SHOWER AND THUNDERSTORM CHANCES CONTINUE TRENDING UPWARD, THIS MAY
LEAD TO EVEN COOLER HIGHS. FOR NOW, HIGHS ARE FORECAST TO REACH INTO
THE MID 80S EAST OF THE MOUNTAINS. LOWS SATURDAY NIGHT WILL BE
SLIGHTLY COOLER BUT STILL ~4-6 DEGREES ABOVE NORMAL.
LONG TERM /SUNDAY THROUGH WEDNESDAY/
AS OF 200 AM EDT THURSDAY...
KEY MESSAGES:
1) CONFIDENCE REMAINS BELOW NORMAL REGARDING PRECIP CHANCES TUESDAY
INTO WEDNESDAY
2) COOLER TEMPERATURES RETURN BUT REMAIN A FEW DEGREES ABOVE NORMAL
3) NBM BACKING OFF ON THE BREEZY WIND POTENTIAL EAST OF THE
MOUNTAINS ON SUNDAY
THE AFOREMENTIONED BACKDOOR COLD FRONT REMAINS STALLED OVER THE
CAROLINAS THROUGH MONDAY BEFORE PUSHING SOUTH OF THE WESTERN
CAROLINAS TUESDAY, STALLING OVER THE COASTAL CAROLINAS THROUGH THE
END OF THE PERIOD. MEANWHILE, THE SOUTHWESTERN PERIPHERY OF SFC HIGH
PRESSURE WILL EXTEND OVER THE SOUTHEAST ON SUNDAY, LINGERING THROUGH
EARLY NEXT WEEK. HOWEVER, THE SFC RIDGE WILL GRADUALLY WEAKEN EARLY
NEXT WEEK.
00Z GLOBAL MODEL GUIDANCE SOURCES GENERALLY AGREE THAT MOSTLY DRY
CONDITIONS MAY RETURN EAST OF THE MOUNTAINS SUNDAY INTO MONDAY WHEN
THE SFC RIDGE IS THE STRONGEST. HOWEVER, GUIDANCE SHOWS THE
POTENTIAL FOR MOUNTAIN CONVECTION TO DEVELOP DURING PEAK HEATING
EACH AFTERNOON. SINCE THE LATEST NBM ONLY HAS SPOTTY SLIGHT CHANCE
POPS IN PLACE ACROSS THE MOUNTAINS EACH AFTERNOON, POPS MAY NEED TO
BE INCREASED IN FUTURE UPDATES IF THE MOUNTAIN CONVECTION TREND
HOLDS. THE NBM IS ALSO BACKING OFF ON THE BREEZY WIND POTENTIAL
SOMEWHAT EAST OF THE MOUNTAINS. WINDS WILL STILL REMAIN ELEVATED BUT
GUSTS NOW APPEAR TO REMAIN BELOW 15 MPH FOR MOST AREAS EAST OF THE
MOUNTAINS. COOLER HIGHS ARE EXPECTED SUNDAY AND MONDAY BUT AFTERNOON
TEMPS ARE STILL EXPECTED TO RUN A FEW DEGREES ABOVE NORMAL. LOWS
EACH NIGHT WILL REMAIN ~5-7 DEGREES ABOVE NORMAL.
MODEL GUIDANCE DIVERGES REGARDING BOTH THE UPPER AND LOW LEVEL
PATTERN TUESDAY INTO WEDNESDAY. HOWEVER, 00Z GUIDANCE SOURCES
GENERALLY AGREES THAT THE POTENTIAL FOR CONVECTION WILL GRADUALLY
INCREASE TUESDAY INTO WEDNESDAY AS THE SFC RIDGE WEAKENS. WITH
CONFIDENCE REMAINING LOW, NBM CAPPING POPS TO CHANCE APPEARS
REASONABLE FOR NOW. HIGHS INCREASE SLIGHTLY ON TUESDAY, WITH SIMILAR
VALUES EXPECTED ON WEDNESDAY. AFTERNOON TEMPS EACH DAY WILL RUN ~5
DEGREES ABOVE NORMAL. LOWS EACH NIGHT WILL END UP ~7-9 DEGREES ABOVE
NORMAL.
AVIATION /12Z THURSDAY THROUGH MONDAY/
AT KCLT AND ELSEWHERE: MOUNTAIN VALLEY FOG HAS DEVELOPED BUT HASN'T
MADE IT TO KAVL. MVFR FOG NEAR KHKY AS WELL. WILL BY AN ISSUANCE
TIME DECISION ON WHETHER ANY RESTRICTIONS ARE NEEDED THERE.
OTHERWISE, PERIODS OF ALTOCU THIS MORNING BECOMES CUMULUS BY
AFTERNOON. ISOLATED DIURNAL CONVECTION IS POSSIBLE SW OF KAVL BUT
CHANCE AT THE TAF SITE IS TOO LOW FOR A TAF MENTION. LIGHT AND
VARIABLE WINDS THIS MORNING BECOME LIGHT W TO SW BY AFTERNOON THEN
LIGHT AND VARIABLE AGAIN THIS EVENING. MORE MOUNTAIN VALLEY FOG IS
EXPECTED OVERNIGHT.
OUTLOOK: CHANCE OF ISOLATED TO SCATTERED DIURNAL CONVECTION IS
INCREASING ON FRIDAY AND SATURDAY THEN DIMINISHES SUNDAY AND MONDAY.
MOUNTAIN VALLEY FOG WILL REMAIN POSSIBLE EACH MORNING WHEREVER
CLOUDS DO NOT INHIBIT NOCTURNAL RADIATION.
GSP WATCHES/WARNINGS/ADVISORIES
GA...NONE.
NC...NONE.
SC...NONE.
SYNOPSIS...AR
NEAR TERM...RWH
SHORT TERM...AR
LONG TERM...AR
AVIATION...RWH
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