243
FXUS62 KGSP 291810
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
210 PM EDT Tue Sep 29 2026

.WHAT HAS CHANGED...
Revised information on potential heavy rain this weekend, and
separated that event into its own Key Message.

&&

.KEY MESSAGES...
1. Dry weather through Thursday with temperatures trending
gradually warmer through late week.
2. Rain is likely this weekend with a slow-moving frontal
system. The rain could be heavy at times, particularly Saturday
night. Temperatures trend slightly cooler Saturday, and much
cooler Sunday, with dry weather probably returning by Monday.

&&

.DISCUSSION...
Key message 1: Dry weather through Thursday with temperatures trending
gradually warmer through late week.

A weak area of high pressure will remain centered over the East
Coast through Wednesday morning, upstream of a coastal low moving
out of New England. The surface high centers offshore and heights
rise over our region through Wednesday, basically returning to
a pattern influenced by the Bermuda High. Light southerly return
flow will bring temperatures warmer for Wednesday, a trend that
continues Thursday. Dewpoints trend higher each afternoon as well,
and mountain/river valley fog may become more common through
Friday morning. However, subsidence should preclude development
of showers/storms through Thursday night.


Key message 2: Rain is likely this weekend with a slow-moving frontal
system. The rain could be heavy at times, particularly Saturday
night. Temperatures trend slightly cooler Saturday, and much cooler
Sunday, with dry weather probably returning by Monday.

Return flow continues Friday, providing warm and moist southerly
flow across the Gulf Coast states, and north to TN and western
NC. Meanwhile cooling occurs in the midlevels ahead of a broad
shortwave moving near the US-Canada border. Accordingly the
subsidence inversion erodes on prog soundings, and diurnal
convection again becomes plausible Friday in the Savannah River
Valley and/or SW NC mountains, though synoptic forcing remains
rather weak. Nevertheless a return of 15-25% PoPs is warranted
in those locations. That shortwave will be accompanied by a cold
front at the leading edge of a cooler, continental airmass. 500mb
flow turns quasi-zonal briefly as the shortwave swings into the
Maritime provinces, which should lead the cold front to pivot
across the lower OH Valley and Mid-Atlantic, just to our north. The
southerly flow regime continues into Saturday, extending eastward
into our CWA, while forcing amplifies further as another shortwave
moves into the mid-MS valley and we enter the right entrance
region of a jet streak. Warm advection develops overhead, and the
aforementioned surface high ridges down the Eastern Seaboard, such
that the ingredients likely come together for widespread precip
by afternoon, and for hybrid CAD to develop. PWATs trend steadily
higher through Saturday, rising at or above 2 inches in portions of
the CWA by the end of the day, and likely rise at least slightly
more Saturday night (peaking 2 to 3 SD above climo). Perhaps
of no surprise, vertical profiles are very moist, so thunder is
likely to be isolated at best, though even with weak MUCAPE there
still could be a convective component to rainfall. If all of these
elements sufficiently overlap, we could be looking at a significant
rainfall event between Saturday afternoon and Sunday afternoon.

Precip appears most likely to taper off late Sunday as the second
shortwave axis pushes east of the area, turning low-level flow to
the northwest, diminishing moisture and promoting erosion of the
CAD. Some guidance members depict a sfc low forming over coastal
NC or VA, where the shortwave interacts with the front. That leads
to spread in how rapidly the drying occurs, so small PoPs linger
into Monday. Otherwise, we are likely to be under the influence of
another, stronger continental airmass with dry/sunny skies Monday.

Models differ as to whether CAD onset occurs in time for Saturday to
be as sharply cooler as one might expect with CAD, so confidence is
low on Saturday`s max temps, but it appears safe to say it will be
at least marginally cooler than Friday, owing to cloud cover. The
GFS for example suggests a 15-20 degree drop in maxes from Fri to
Sat. By Sunday CAD should have set in and we should see max temps
well below normal, possibly in the 60s over much of the area. If
precip ends and CAD erodes Sunday night, Monday`s maxes may rise
back to near normal under downsloping, before mins and maxes trend
below normal Monday night into Tuesday.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
At KCLT and elsewhere: Largely VRB winds this afternoon/evening with
weak high pressure centered north of the terminal area, though KAVL
and KAND are more likely to remain S to SE. FEW-SCT cumulus at low
VFR level. With little change in the pattern and dewpoints mixing
out a bit more than forecast this afternoon, think radiation fog
will remain confined to the valleys similar to how fog played out
Tue morning, when KAVL remained VFR. Thus, no mention of fog made
at KAVL. By Wednesday afternoon the high pressure should drift
off the East Coast and winds will favor S to SW around the area,
though not likely setting up there until around 18z, so that shift
is only reflected at KCLT. More diurnal cumulus developing Wed.

Outlook: Dry, VFR conditions should persist thru Thursday. Moisture
will begin to increase across the area on Friday, with a chance of
showers by Friday afternoon over the mountains and more widespread
showers across the area on Saturday. Mountain valley fog/low
stratus remains possible each morning.

&&

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

&&

$$

JCW