370
FXUS62 KGSP 171054
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
654 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 645 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, and/or warm
conveyor belt into the northern system, was evident as a band
of nocturnal showers/storms in VA and East TN. That activity
has fizzled nocturnally but the forcing will shift over the NC
mountains later this morning. Modest SW`ly flow continues over
the CWA and has allowed some patchy low clouds to develop; these
should scatter out by 9 AM.

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 that prefrontal feature will be in position by midday
to enhance convective coverage over the NC mountains/foothills as
diurnal instability develops. A subsidence inversion is not seen
on most prog soundings. Shear remains weak and organization thus
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. WPC ERO
areas extend into the northern CWA accordingly. SPC Day 1 outlook
features MRGL along our northern border; think severe threat is
indeed very marginal and secondary to heavy rain threat. 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 /12Z THURSDAY THROUGH MONDAY/...
At KCLT and elsewhere: S to SW flow in moist regime has allowed
some areas of MVFR to IFR cigs to form around the region, focused
mainly near KCLT/KHKY and south of the Blue Ridge Escarpment near
KGSP/KGMU. Satellite trends suggest these clouds will be transient
and so restrictions are kept in TEMPO. Low LCLs otherwise indicate
potential for diurnal cu to form at MVFR level in the first
couple hours of the TAF, 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 at KCLT as given in previous
TAF. KHKY/KAVL have been boosted to TEMPO given higher confidence
on impacts, with surrounding VCSH for smaller chances of convection
earlier/later. Any TS will be capable of torrential rainfall and
potential for brief low MVFR to IFR vsby. Winds mainly breezy and
SW`ly with a few gusts of 15-20 kt possible this aftn. Slightly
more veered winds tonight in low levels suggest lesser threat of
overnight restrictions or at daybreak Fri, though MVFR reasonable
mention at KAVL. KHKY/KCLT could see restrictions if heavy rainfall
falls today.

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