468
FXUS62 KGSP 121046
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
646 AM EDT Sat Jul 12 2025

.SYNOPSIS...
Expect scattered thunderstorms and heavy downpours around the region
each day of the coming week. A few storms this weekend will pose
a risk of damaging wind gusts. The hottest days of the next week
look to be Sunday and Monday, with heat index rising over 100 each
of those days in most of the Piedmont.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 645 AM EDT Saturday: Shallow low stratus deck and fog layer
has developed over portions of the area, especially the major
mountain valleys per usual. Expect the low cloud cover to burn off
over the next few hours as daytime mixing commences. Otherwise, the
forecast remains on track with only minor tweaks made based on
current observations and latest trends.

Wash, rinse, repeat. Weak mid-level shortwave to the west and
weak west-southwesterly flow aloft will allow for some dry air
entrainment in the mid-levels. Relatively similar environment as
Friday with PWAT values between 1.50"-2.00", 2000-3000 J/kg SBCAPE,
and <20 kts of deep layer shear will once again set the stage
for typical summertime diurnal pulse thunderstorms. Convective
initiation will start over the ridgetops across the southern
Appalachians and the Blue Ridge Escarpment during the early
afternoon hours, followed by downstream initiation with the presence
of an inverted ridge on the lee of the Appalachians. Profiles
indicate slightly less drier air to work with in the mid-levels
compared to Friday to go along with decent low-level inverted-v
profiles helping to produce DCAPE values between 600-1000
J/kg. As a result, the threat for wet microbursts are still in
the forecast, but may not be as exacerbated as Friday. Associated
outflow boundaries from any "splats" will help to carry convection
further east into the Piedmont zones later in the afternoon into
the evening hours. A few strong to severe storms are possible,
with the main threat being damaging wind gusts. Slow moving storms
and high rainfall rates will likely lead to a couple instances of
localized flash flooding as well, especially in locations that have
been hit harder compared to others over the past few days. Afternoon
highs should run a couple of ticks higher compared to Friday without
the presence of an obvious low stratus deck. Most of the activity
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 will be
prone to another round of low stratus and fog overnight Saturday,
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 /SUNDAY THROUGH MONDAY NIGHT/...
As of 100 AM Saturday morning: Diurnal instability remains the main
driver for showers/storms Sunday and Monday with only subtle
features affecting convective initiation as one might expect in
July. Broad shortwave will be aligned near the upper Mississippi
River Sunday, surrounding cyclone crossing Canada.  The trough
advances eastward to near the northern Appalachians by Monday
afternoon. Upper anticyclone will remain strong over the Southeast
although it still appears to retrograde slightly over the period;
flow over the top of that feature may be responsible for a decline
in PWATs seen in guidance for our CWA. A zone of enhanced convective
coverage appears to set up east of the Appalachians, arguably from
lee troughing but possibly associated with warm conveyor belt into
the Canadian system. Convection looks somewhat less likely than
Saturday owing to the lower PWATs, but we still feature 60-70% PoP
over the mountains. Only isolated to scattered coverage for most of
our Piedmont, with the convergence zone seeming to set up near the
US 1 corridor and keeping the best chances to our east. Where storms
do form, given higher sfc-midlevel delta-theta-e, they may be more
capable of damaging wind than on Saturday. Shear is weak and pulse
storm mode will be preferred; slow storm motion could translate to
locally excessive rainfall even if rates are limited by the lower
PWATs.

The trough is shown to fill and weaken as it tracks eastward and the
associated DPVA does not look to have much effect this far south, as
if being held off by the Southeast anticyclone. The associated cold
front appears to stall northwest of the CWA. Actual airmass change
thus still looks unlikely at least thru Monday. PoPs remain on par
with Sunday`s, slightly higher than climo. Shear remains weak and
pulse storm threats will remain a concern. PWATs trend higher on some
guidance by Monday afternoon, seemingly as an inverted trough drifts
west from the Atlantic, bringing low-level flow southeasterly and
enhancing moisture flux. We retain a slower than usual decline of
PoPs Monday night, with chances hanging on longest in the eastern
zones--this had once appeared to be the result of the front working
thru the area but now may be more a reflection of the inverted
trough.

Daily max temps will be in the mid 90s for much of the Piedmont and
upper 80s to near 90 in the major mountain valleys. Despite some
afternoon dewpoint mixing, heat index will reach the low 100s and may
locally exceed 105 in a few spots southeast of I-85, although
confidence is low this will be extensive enough for Advisory
issuance.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 130 AM Sat: Unsettled pattern with above-climo PoPs for the
medium range. Tuesday, the stalled front looks to be oriented from
near the New England coast to the southern Appalachians, but may be
reactivated as a cutoff low near the Ozarks drifts north and merges
with a frontal system crossing the northern Plains and Great Lakes.
Accordingly, appreciable drying looks unlikely. The inverted trough
near the Carolina/Georgia coast remains in play through the middle of
the week. As the Bermuda ridge retrogrades, the pattern could return
to a more typical summertime setup for our area with more
climatological PoPs, but the northern-tier frontal system could
enhance precip development just as that occurs. Hence we maintain
mostly 60-70% PoPs each afternoon through Friday with a slower than
usual nocturnal decline each evening. Temps do trend cooler with
lower thicknesses Tue and with more abundant cloud cover each day,
but in reality that only brings daily maxes back to near normal.
Dewpoints are likely to remain elevated during the afternoons and
heat index still could top 100 in warmer Piedmont areas each day.
Slow-moving cells producing heavy rainfall will remain a daily
concern particularly where soils saturate following repeated rounds
of showers/storms.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: An area of low stratus and patchy dense
fog has developed in the mountain valleys and other various portions
of the area. As a result, kept a TEMPO for IFR cigs at KGMU and
KGSP. Any low stratus or fog that develops should dissipate around
13Z-14Z or so. SCT VFR cu will be in store after mid-morning at all
TAF sites, with another round of scattered to numerous showers and
thunderstorms this afternoon and evening. Placed a PROB30 with peak
heating timing and associated restrictions at all TAF sites. Light
west-southwesterly winds expected, with north-northwesterly at KAVL.
Most of this activity should dissipate shortly after sunset, with
lingering VFR convective debris expected through the early overnight
hours. Another round of low stratus and fog will be possible across
the area just before daybreak Sunday.

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