418
FXUS62 KGSP 172321
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
721 PM EDT Thu Sep 17 2026

.WHAT HAS CHANGED...
No significant changes to the public forecast.

The aviation discussion was updated to reflect the recent 00Z
TAF issuance.

&&

.KEY MESSAGES...
1. Summer-like weather with hot conditions and afternoon showers
and thunderstorms continue through Monday.
2. Precipitation chances continue Tuesday through Thursday with
temperatures dropping to near or even below normal.

&&

.DISCUSSION...
Key message 1: Summer-like weather with hot conditions and afternoon
showers and thunderstorms continue through Monday.

Isolated mountain convection appears to have concluded for the
evening, but lingering cloud cover is visible on satellite imagery
pushing into the area from the north.  Expect this cloud cover
to gradually push south across the region through the first half
of tonight, nixing our prospects of another crystal-clear night.
No additional rainfall is forecast, however, and clearing is
likely by the predawn hours.  Mountain valley fog and stratus are
expected to develop across the NC mountains overnight...though
perhaps delayed compared to the last few nights by aforementioned
cloud cover.

Otherwise...upper ridge over the area weakens as shortwaves
move across the Mid-Atlantic and an upper low moves west across
Florida. This allows shortwaves to move around the periphery of
the ridge and across our area Friday. With a moist and unstable air
mass in place across the area, expect convection to develop during
the afternoon. An outflow boundary from overnight convection will
move south into the area as well with the potential to help bring
some organization to the convection. Steep low level lapse rates
and the weak organization will lead to the potential for isolated
damaging wet microburst in the stronger storms, especially from
the Blue Ridge south and east across the Piedmont. SPC has this
area in a Marginal risk of severe storms which looks reasonable
given these factors. Highs will be in the low to mid 90s outside
of the mountains and around 90 in the warmer mountain valleys.

A backdoor cold front drops into the area Saturday bringing clouds
and cooler but still above normal temps. There will also be an
increase in deep moisture. With the forcing and moisture, expect
more widespread convection but a lower severe threat. There may
be some spotty heavy rainfall, but the overall flood threat is low.

Temperatures tick back up Sunday and Monday as the backdoor
cold front dissipates and southerly flow returns. This keeps deep
moisture over the area. Quasi-zonal flow will bring some shortwaves
moving over the area as well. This keeps a good chance of convection
across the area both days. Instability is weak though. Therefore
the chance of severe storms is very low. There could be some
heavy rainfall on Monday given the coverage of convection. There
will be a low flood threat especially after a few straight days
with convection.


Key message 2: Precipitation chances continue Tuesday through Thursday
with temperatures dropping to near or even below normal.

Fall may finally be on the way by the middle of next week. A cold
front drops into the area Tuesday, through the area Wednesday, and
south of the area Thursday. The forcing combined with continued deep
moisture keeps a good chance of showers and thunderstorms across the
area Tuesday. Highs will drop to near normal. Guidance agrees on a
cooler and drier airmass moving in behind the front Wednesday and
Thursday. There may be enough lingering moisture to keep some
showers over the area both days, but it looks like coverage should
be lower than the previous few days. There is a signal for the
potential for the high building behind the front to be a Cold Air
Damming high. This would lead to much below normal temps developing.
This is still uncertain as a drier and less cloudy air mass would
keep temps from falling that low. However, do expect at least near
normal temps which will be much cooler than recent conditions.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
At KCLT and elsewhere: Isolated convection has mostly ended across
the NC mountains, with no expectations for it to ramp back up as
we head into sunset.  Hi-res guidance depicts a SCT to BKN deck of
altocu working across the area from the north (with hints of this
debris already pushing into the I-40 corridor as of around 23Z)
through the first half of tonight.  Think this cloud cover may
somewhat delay development of IFR to LIFR fog and stratus in the
mountain valleys tonight, but nonetheless expect restrictions to
develop at KAVL and surrounding locations within the French Broad
and Little Tennessee during the predawn hours, as cloud cover thins.
Mostly light and variable winds still expected overnight.

A north wind will pick up during the day Friday.  Afternoon
convection is expected across the entire area.  Uncertainty remains
on coverage...but it should be at least scattered.  PROB30s were
introduced at all six TAF sites for this activity, which is expected
to initiate over the NC Blue Ridge Escarpment and/or I-40 corridor,
then move south through late evening.  Mid- and low-level cloud
cover may linger into Friday night/Saturday morning even after
showers and storms conclude.

Outlook: Shower and thunderstorm chances should continue each
afternoon through Tuesday.  Mountain valley fog and low stratus
will be possible each morning, and lingering low-level stratocu
may persist everywhere on Saturday morning.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$

MPR/RWH