651
FXUS62 KGSP 131041
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
641 AM EDT Sun Jul 13 2025

.SYNOPSIS...
Expect scattered thunderstorms and heavy downpours around the region
each day of the coming week. A few storms could produce damaging
wind gusts, particularly today and Monday. Daily high temperatures
will be several degrees above normal at the beginning of the week
but trend back to around normal Tuesday through Thursday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 640 AM EDT Sunday: Major mountain valley fog and low
stratus underway, but only isolated instances of shallow fog
elsewhere. The forecast remains on track with only minor tweaks
made based on current observations and latest trends.

Only very subtle changes to the synoptic pattern as a ridge over the
Gulf noses further north in to the region, allowing for warmer and
drier air to work into the vertical profiles. Positively-tilted
trough over the central CONUS will gradually work eastward during
the forecast period, dragging an attendant boundary with it. The
actual frontal boundary will remain well northwest of the region.
With more warmer and drier air aloft, expect the atmosphere to be
slightly capped. Factor in a downward trend in PWAT values (1.25"-
1.75") and convective coverage should shrink compared to the past
few days. Still expect isolated convective initiation over the
ridgetops and Blue Ridge Escarpment by the early afternoon and will
shift east into the foothills and Piedmont by outflows and cold pool
organization later into the afternoon and evening. The environment
will still consist of 2000-3000 J/kg SBCAPE and <20 kts of deep
layer shear, but with drier air entrainment within the profiles,
storms that do develop will have a higher chance of becoming strong
to severe compared to Saturday as DCAPE values will uptick to 800-
1200 J/kg, with pockets of higher than 1200 J/kg. Wet microbursts
will be the main threat, which is typical with summertime pulse
convection. Hi-Res guidance have hinted at better convective
coverage along and east of I-77 as a pool of higher PWAT values is
evident and the lee trough shifting further away from the
Appalachians. As a result, chance PoPs (25%-53%) are introduced for
the CLT metro and I-77 corridor, while only slight chance (15%-24%)
to unmentionable PoPs (<14%) for locations south of I-85 in the
Upstate and Upper Savannah regions. With slightly higher heights and
the lack of morning stratus, afternoon highs are forecasted to top
out a few degrees above normal. Heat index values should reach
triple digits in portions of the Piedmont zones, but will remain
below Heat Advisory criteria.

Most of the convection should gradually dissipate after sunset with
the loss of peak diurnal heating. Lingering convective debris,
available low-level moisture, and locations that receive heavy
rainfall will be prone to another round of low stratus and fog
overnight Sunday, especially if the convective debris clears
out early on during the overnight period. Overnight lows will be
similar to tonight with low 70s across the Piedmont and mid to
upper 60s across the mountains and foothills.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
As of 1230 AM Sunday: A weak upper anticyclone will be centered over
the Gulf Coast region Monday, as a weak shortwave passes by to our
north associated with a slowing cold front in the lower Ohio Valley.
Inverted trough meanwhile will drift west invof the Bahamas. The
result is nebulous upper forcing over our area but a broad zone of
low to midlevel convergence centered over central NC/SC/GA and thus
perhaps just to our east and south. Diurnal instability will be the
main driver of showers/storms, with coverage enhanced above climo
on account of the convergence and modestly high PWATs. Model QPF
response has increased slightly in our CWA compared to runs from a
day ago, and notably there appears a better chance of activity to
continue after sunset; peak chances for Monday appear to be near
00z for our southeastern half. Temps look to be at or slightly
above Sunday`s values, but dewpoints could be slightly higher so a
few lower Piedmont spots briefly see heat index exceed 105. Shear
is weak; despite moist profiles, very heavy downpours and water
loading still maintain some wet microburst risk.

As the northern shortwave moves further east the trailing front
seems to finally stall just to our north. Partial thicknesses fall
seemingly as a result of the inverted trough moving westward and
replacing the upper ridge. Temps should trend cooler, back to around
climo, even if the front technically stays to our north. Convergence
still could be enhanced by the inverted trough. The cooler temps
but similar if not higher dewpoints result in lower LCLs. CAPE
and PoPs increase accordingly. Via the convergence zone another
slow nocturnal decline is expected Tue night.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 115 AM Sunday: The inverted trough may have some enhancing
influence Wednesday, but otherwise the dominant feature for the
medium range looks to be the Bermuda High. Wednesday looks like the
"coolest" day as partial thicknesses reach their nadir on most
of the global models, possibly also owing to cloud cover with
convective coverage near the trough axis. A gradual warming trend
then occurs as the Bermuda High retrogrades over the Southeast
Coast. Relatively high afternoon dewpoints will keep LCLs low and
support above-climo PoPs again Thu.

There is some spread among models, and between the GFS and EC
ensemble members, as to how deep the Bermuda ridge ends up over
our region. The next frontal system will pass the Great Lakes
circa Thursday; GFS and GDPS suggest the ridge will hold off that
system from our area until the associated shortwave is reinforced
by a secondary trough digging into the northern Plains and western
Great Lakes late Fri or early Sat. The EC brings the convergence
zone into our area a bit sooner. The upshot of all this is that the
GFS and GDPS solutions feature more typical PoPs (i.e., mainly over
the mountains) whereas the EC maintains enhanced values reflecting
less terrain influence. Given the timing differences confidence
decreases Fri-Sat.

Heat index still could peak at 100 to 105 in the warmer Piedmont
areas Fri-Sat. Slow-moving cells producing heavy rainfall will
remain a daily concern particularly where soils saturate following
repeated rounds of showers/storms over the course of the week.

&&

.AVIATION /12Z SUNDAY THROUGH THURSDAY/...
At KCLT and elsewhere: Stout low stratus and fog across the
mountain valleys but struggling to reach KAVL. Any low stratus or
fog outside of the mountain valleys will be sparse, which is shown
in the latest TAF update. Took out the TEMPO for KAVL and extended
the TEMPO for KHKY through 13Z. Otherwise, fairly quiet through
daybreak for the terminals. VFR conditions will prevail for the
daytime period with isolated to scattered showers and thunderstorms
expected, especially for the North Carolina TAF sites. Included a
PROB30 for TSRA and associated restrictions at all terminals except
KAND, where TSRA chances are the lowest. Light and variable winds
through daybreak, will pick up out of the north-northwest by peak
heating. Another round of low stratus and fog can`t be ruled out
overnight Sunday, especially over the mountain valleys once again.
Winds also go back to light and variable Sunday night.

Outlook: Typical summertime weather is expected into early next
week, with scattered to numerous thunderstorms mainly in the
afternoon/evening and fog and/or low stratus possible each morning.

&&

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

&&

$$

SYNOPSIS...Wimberley
NEAR TERM...CAC
SHORT TERM...Wimberley
LONG TERM...Wimberley
AVIATION...CAC