775
FXUS62 KGSP 171038
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
638 AM EDT Fri Oct 17 2025

.SYNOPSIS...
Cooler temperatures develop Friday night behind a reinforcing
cold front.  Clouds and temperatures both increase on Saturday
before a stronger cold front arrives Sunday, producing some rain
and possibly some thunder.  Dry and cool conditions return next
week, and linger through the end of the period.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 635 AM EDT Friday: An upper ridge axis associated with a
weakening omega block moves into the area through the period. A
short wave rides up the ridge west and north of the area tonight. At
the surface, the center of high pressure moves across the area this
morning, settling to our southeast by afternoon. Dry conditions will
continue through the period. Mountain valley fog dissipates by mid
morning then returns overnight. Some stratocu will linger across the
Upstate, NE GA, and the southern NC mountains this morning as
convergence downstream of the higher ridges acts on moisture trapped
under a subsidence inversion. These clouds should dissipate by
afternoon as the flow weakens. Expect cirrus associated with the
short wave to increase across the area today then move east
overnight. Highs will be a little above normal, but up to 5 degrees
above normal over the Upper Savannah River valley and the mountains
west of the French Broad. Lows will be a little above normal across
the mountains and near normal elsewhere.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 1243 AM EDT Friday: We begin the period on Saturday, with
modest height falls over the Carolinas, as upper ridging previously
centered over the Eastern Seaboard begins retreating ahead of a
negatively-tilted z500 trough.  For most/all of Saturday, conditions
look quiet; moisture should steadily increase as a prefrontal WAA
regime develops, permitting profiles to moisten from the bottom
up...but this will do little other than to increase cloud cover
and raise dewpoints on Saturday and Saturday night.  As a result,
Saturday`s highs look to land in the upper 70s, maybe even the low
80s across the SC Upstate and the I-77 corridor.  Lows Saturday
night will barely fall below 60...maybe not even, if you`re near
a large body of water.

The real action - well, maybe...don`t get too excited - will
materialize on Sunday.  As the trough enters the Carolinas, it`ll
drive an upper speed max essentially right across GSP`s forecast
area, while at the low-levels a prefrontal LLJ is depicted in most
operational guidance.  Unfortunately for our convective prospects,
that same operational guidance is...not keen on giving us much
instability to work with, depicting some 200 J/kg or less sbCAPE
during the afternoon Sunday.  The limiting factor appears to be
lapse rates, which don`t improve much with the trough and thus
don`t produce an especially deep unstable layer; there are indeed
some members of the latest-avaible LREF cycle that produce as much
as 450 J/kg sbCAPE...but these appear to be high-end outliers, with
even the 75th percentile of ensemble guidance depicting <300 J/kg.
That`s all to say that severe risk looks limited, though nonzero.
In 24 hours, we`ll have an HREF run that extends out far enough
in time to have a better (read: high-res) look at what to expect.
In the meantime...expect some rain, maybe some thunder Sunday
afternoon, and definitely a cooling trend late Sunday into Sunday
night as the actual cold front pushes through and we get an air mass
change.  Highs on Sunday are a little tough to pin down since it`s
not totally clear where the front will be during peak heating...but
lows Sunday night should easily drop into the 40s everywhere,
with some of the higher elevations even seeing lows in the 30s.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 1254 AM EDT Friday: The upper pattern will remain progressive
through the long term period next week...but this won`t really
mean much in terms of getting any much-needed rain.  On Monday,
a broad ~1023mb surface high will settle into the Southeast
beneath low-amplitude upper ridging.  During this time, an
upper low will be gaining some traction over the northern Great
Plains, and this feature will dip into the Ohio Valley by late
Tuesday or early Wednesday (ensembles don`t quite have their
heads around this one yet, so timing remains a question mark).
An attendant cold front will slide through the western Carolinas
by early Wednesday morning, but if our rain/thunder prospects
didn`t look good with the weekend front, they really don`t look
good with this late-period system...with long-range ensembles in
very poor agreement on whether we`ll even get any rain with this
system, or whether we`ll stay dry and just see further cooling.
For now, the NBM isn`t depicting any more than a few hundredths
of an inch of rain along the NC-TN border.  It looks more likely
we`ll just see an influx of cooler air as the next surface high
builds in...which should keep highs in the 60s or low 70s and lows
in the 40s through the end of D7.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
At KCLT and elsewhere: VFR stratocu may briefly go BKN at the SC
sites this morning before dissipating by afternoon. Few or SCT
elsewhere. Mountain valley fog should stay away from KAVL this
morning but a brief restriction can`t be ruled out. Expect cirrus to
spread in through the day then move east overnight. This will keep
the potential for mountain valley fog in play. Again, given recent
trends, will keep out of KAVL for now. Light N to NE wind becomes S
to SW for the afternoon, then light and variable overnight.

Outlook: VFR conditions continue Saturday, except for the potential
for mountain valley fog and/or low stratus in the morning. A cold
front may bring showers and associated restrictions Sunday along
with breezy conditions. Dry conditions return on Monday. A dry cold
front may bring breezy conditions again on Tuesday.

&&

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

&&

$$

SYNOPSIS...MPR
NEAR TERM...RWH
SHORT TERM...MPR
LONG TERM...MPR
AVIATION...RWH