588
FXUS62 KGSP 170557
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
157 AM EDT Thu Jul 17 2025

.SYNOPSIS...
Daily thunderstorm chances continue through the week and into the
weekend. A few storms could produce damaging wind gusts and
localized flash flooding. The pattern favors a potential MCS track
for the start of next week. Hot and humid conditions stick around
through most of the forecast period.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1235 AM Thu: 594+ dam ridge at 500mb will nose into the area
from the Atlantic with the Bermuda High. North of the ridge, low
pressure passing across the Great Lakes and associated shortwave
results in relatively fast but quasi-zonal flow across the OH
Valley and Mid-Atlantic coast. A prefrontal trough, possibly
warm conveyor belt into the northern system, is driving a band of
convection from the lower TN Valley to PA, currently west of the
NC mountains. Modest SW`ly flow continues over the CWA. Early this
morning isolated or widely scattered showers will continue in the
Savannah River Valley and into the higher terrain of SW NC. Both
that activity, and the upstream convection in TN, should diminish
nocturnally although similar to yesterday morning, capping is weak
enough aloft that with low LCLs and moist profiles it`s hard to
rule out redevelopment near the south-facing Blue Ridge Escarpment
any time this morning.

The Great Lakes system will move into the St Lawrence Valley
today. Shift of the 700mb moisture axis across the southern
Appalachians, and hints of a weak vort axis at 500mb in western
NC, suggest convective coverage will be enhanced over the
NC mountains/foothills after diurnal instability develops. A
subsidence inversion is not seen on most prog soundings. Shear
remains weak that organization is questionable; DCAPE would appear
to be lacking owing to the deep moisture and PWATs remaining near
2 inches. Slight westerly steering flow should allow some of the
mountain cells to propagate into the Piedmont, so healthy PoPs will
be carried in that area as well as over the mountains. Isolated
or widely scattered convection is possible elsewhere. Main threat
probably will be locally heavy rainfall given the marginal DCAPE and
delta-theta-e values. Higher thicknesses should support slightly
higher temps; heat index again will top out near 100 in parts of
the lower Piedmont.

Convection should wane diurnally but with SW`ly low-level jet
appearing to maintain a mixed layer aloft thru the evening, we can
probably expect a few showers or storms to regenerate for a time
after sunset as has happened the past couple of days. Otherwise
another generally uneventful but seasonably muggy night.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 125 AM EDT Thursday: Bermuda ridge will be in the process
of retrograding from the Southeast Coast to the Southern Plains
through the forecast period. Steady southwesterly flow at the
surface will help to elevate dewpoints with very warm thicknesses
(=>594 dm) in place and in turn, support continued hot and humid
conditions both Friday and Saturday afternoons. As a result,
heat indices will flirt with Advisory criteria each afternoon,
especially in the Charlotte metro and Lower Piedmont. The Bermuda
ridge is expected to extend from the Southern Plains to being just
offshore the Southeast Coast. This will keep the typical summertime
pattern in place with convective initiation across the ridgetops
during the afternoon through differential heating. The trend will
be for diurnally driven convection with orographic initiation and
being outflow driven to break containment from the higher elevations
into the foothills and Piedmont.A developing baroclinic zone on the
northward extent of the ridge will be draped just to the north of
the CFWA and could favor a potential MCS track, mainly across the
northern portions of the CFWA, but can`t rule out an MCS making a
run across the entire area starting Saturday afternoon, with the
"Ring of Fire" becoming more established by Sunday into the first
half of the extended. In this case, highest PoPs will reside in
the mountains (50-75%) and lower the further south and east from
the mountains (25-50%). Temperatures will run a category or so
above normal Friday through the weekend.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 145 AM EDT Thursday: Weakness in the eastern extent of the
upper anticyclone over the southeastern CONUS in response to a deep
closed upper low located southeast of the Hudson Bay will begin
to really set the stage for a MCS track across the area Sunday
into the early part of next week. The flow aloft will gradually
turn northwesterly and support multiple MCS runs at the CFWA,
especially Sunday through Tuesday. The convective elements will
be in place and could create a scenario for an elevated risk of
straight-line damaging wind gusts across a larger area in comparison
to typical summertime pulse convection with each MCS run. The
latest deterministic models suggest the "Ring of Fire" could become
realized across the CFWA, especially across the mountains. This
potentially throws a monkey wrench into the current temperature
forecast as well due to the uncertainty in timing with MCSs and
lingering convective debris. We will definitely need to continue
monitoring this development as we get closer in time. Otherwise,
hot and humid conditions remain in place through the middle part of
next week and temperatures stay a few ticks above normal. It may
be worth mentioning that trends are drier for next Wednesday and
Thursday once the "Ring of Fire" pattern breaks down, but that`s
always a dangerous assumption during the Dog Days of Summer.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
At KCLT and elsewhere: As has occurred for the past two mornings,
convection redeveloped after sunset on moist SW upslope flow
near KAVL and the SC sites. KAVL has already seen some precip and
restrictions can`t be completely ruled out, although if higher cloud
decks remain that should mitigate the threat somewhat. The SW flow
and moist vertical profiles support low LCLs and the possibility
of spotty MVFR level clouds developing before daybreak and not
mixing up to VFR level until mid to late morning, so all sites get
a FEW-SCT mention thereof. PROB30 chances for TSRA this afternoon
with VCSH mentioned at KAVL after 00z given consistency of the
moist SW flow regime. Winds mainly breezy and SW`ly with a few
gusts of 15-20 kt possible this aftn. Not yet seeing a signal for
low clouds at KCLT Fri morning, but otherwise any cigs probably
would not be until after 06z.

Outlook: Thunderstorm chances each afternoon/evening. Low stratus
or fog are possible each morning in mountain/river valleys.

&&

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

&&

$$

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