Cleveland, South Carolina Weather Forecast Discussion

246
FXUS62 KGSP 231053
AFDGSP
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
653 AM EDT Tue Sep 23 2025
.SYNOPSIS...
Scattered showers and thunderstorms, mainly over the mountains,
through Wednesday. A cold front reaches the area with more showers
and thunderstorms possible by Friday. Temperatures remain above
normal ahead of the front before cooling into the weekend with drier
weather.
&&
.NEAR TERM /THROUGH TONIGHT/...
As of 645 AM Tue: Shortwave moving thru the middle Ohio Valley
is driving bands of showers and embedded storms across eastern
KY/TN, but steering flow should keep activity mostly skirting
by to our northwest. ML/MU CAPE is considerably higher in that
area than it is in our mountains; small revised PoPs near the TN
border will persist this morning for the possibility of showers
advecting in. The more vigorous activity farther west in TN looks
to be associated with a warm front, which will weaken diurnally
and such activity should diminish and remain to our west anyway.
RAP, as well as larger scale models, depict the main vort max
associated with the shortwave passing the mountains by late morning,
which could help explain the limited QPF/convective response from
CAMs today. However, some less distinct vort maxes will trail the
main wave, and notably the 12km NAM seems to latch onto a loosely
organized line forming in TN with an apparent MCV, which reaches the
northern mountains 15-18z. Other CAMs reflect more typical diurnal
mountain initiation although they favor the northern mountains,
possibly a nod to forcing from a remnant MCV like feature. Lapse
rates do marginally improve today via the cooler air aloft brought
by the shortwave, so a chance range PoP is forecast for most of the
mountains. Models continue to show a few spotty cells moving off
the northern Escarpment and into the NW NC Piedmont; did proceed
with slight increases in PoP in that area with this update. Surface
temperatures trend 2-4 degrees warmer today across the board.
Heights fall slightly in the mid-MS and lower OH Valleys tonight
as next shortwave moves into the central Plains. Convection is
expected to wane more easily tonight in East TN without the boost
from a shortwave as seen this morning. WAA will persist there,
however, and into some of our mountains for that matter, so small
PoPs are again forecast near the TN border for the possibility of
stray convective initiation tonight or early Wed. Mountain valley
fog likely to return once again.
&&
.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
As of 120 AM EDT Tuesday: Picking up on Wednesday, an upper low
across the Midwest sticks around and slowly moves NE. Meanwhile,
guidance has a positively tilted trough elongated over the central
CONUS that amplifies through Thursday night. Ahead of a cold front
approaching toward the end of the period, more widespread showers
and thunderstorms are expected. Looking at the parameters, short
term model soundings show some instability with 20-25kt bulk shear.
The one caveat is the positive tilt to the trough, which could keep
the lid on more severe weather as the better forcing shifts well
north of the CWA. At this time, the Storm Prediction Center keeps
the area in a general thunder pattern. As with any short or long
term forecast, this could change, but the confidence is increasing
that any widespread severe is becoming less likely. As the front
nears, expect PoP chances to ramp up Wednesday through the end of
the period, with categorical (76%-80%) across the mountains and
eventually 60-75% elsewhere on Thursday into Thursday night. As far
as QPF response, the probability of receiving more than 1 inch of
rainfall is 15-20%. This is mainly for the far western NC mountains
as the chance decreases rapidly east of the mountains. This could
change, but as of now, model guidance is not depicting too much
concern for rainfall totals. Will continue to monitor. As for
temperatures, expect above normal temps ahead of the front with
relief to follow.
&&
.LONG TERM /FRIDAY THROUGH MONDAY/...
As of 125 AM EDT Tuesday: By Friday, the cold front continues to
push toward the CWA, bringing showers and thunderstorms. Aloft, long
term guidance suggests the upper low weakens and gets reabsorbed
into the general flow, keeping the better DPVA far to the north of
the CWA. At this time, the front looks to cross the area Friday and
into Friday night, ushering in drier air by the start of the
weekend. Timing for the front is still not exactly certain this far
out. Friday, at this time, looks to have PoPs ramping down with
chance (55-60%) for the majority of the area and dipping to slight
chance (30-40%) by Saturday. Winds turn northerly for the remainder
of the extended period, reinforcing the drier air from the north.
After Saturday, model guidance gets sketchy. At the surface, the GFS
wants to keep a persistent area of high pressure that eventually
slides eastward toward the coast suppressing the majority of rain
chances. Once the front comes through, temperatures are trending to
be much cooler and more conducive for Fall.
&&
.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
At KCLT and elsewhere: Debris clouds from convection in TN have
so far kept valley fog/stratus brief and MVFR near KAVL. Not out
of the question restrictions will return thru 13z or so. Diurnal
cu will break out at 040-060 late morning to midday, a bit higher
than previously expected. Winds remain largely SSW to SW for the
day. Mountain convection has been persistent enough in CAM output
near KAVL to now warrant including PROB30 in addition to VCSH this
aftn. Can`t completely rule out a cell near KHKY as well but chance
is low enough not to mention there. Winds turn light again tonight;
mountain valley fog probably will return in some form after 06z
Wed with less storm coverage in TN, and thus higher cloud decks
looking less of a factor overnight.
Outlook: Mountain shower and thunderstorm chances return again Wed,
then fog and stratus possible in valleys Wed night. Better chances
for restrictions with a front Thursday and Thursday night. Low
confidence as to flight conds Fri-Sat with guidance split between
dry high pressure and an upper low producing showers and promoting
moist onshore flow.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.
&&
$$
SYNOPSIS...CP
NEAR TERM...Wimberley
SHORT TERM...CP
LONG TERM...CP
AVIATION...Wimberley

NWS GSP Office Area Forecast Discussion