951
FXUS62 KGSP 211834
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
234 PM EDT Tue Jul 21 2026

.WHAT HAS CHANGED...
Forecast rainfall totals and the threat for isolated flash flooding
are increasing for the period from late Wed through Thu.

&&

.KEY MESSAGES...
1. Very active convective weather is expected, mainly from
Wednesday through the end of the week, as a frontal boundary moves
into the area and stalls. Isolated severe storms are possible
this evening and again tomorrow, with an escalating risk of heavy
rainfall and flash flooding expected from late tomorrow through
at least Thursday.
2. A return to typical late July weather is expected next week.

&&

.DISCUSSION...
Key message 1: Very active convective weather is expected, mainly
from Wednesday through the end of the week, as a frontal boundary
moves into the area and stalls. Isolated severe storms are possible
this evening and again tomorrow, with an escalating risk of heavy
rainfall and flash flooding expected from late tomorrow through
at least Thursday.

Isolated convection is beginning to develop within a moderately
unstable air mass (sbCAPE ~2500 J/kg) across the northern NC
mountains this afternoon. Regionally, the best parameter space (by
far) is forecast to remain across the Ohio Valley and Mid-Atlantic
this afternoon/evening, and this is where the greatest severe
storm risk is expected. However, a couple of isolated severe storms
remain possible across our far north. Convective coverage will be
spotty-at-most outside of the northern tier through the afternoon.

The remnants of organized convection may move into the forecast
area from the NW at some point during the overnight/early Wed
morning, but the severe storm potential appears minimal in the
absence of organizing shear values, weak instability, and with
this convection becoming increasingly displaced from large scale
forcing. The leading edge of a frontal zone is forecast to move into
the forecast area during Wed afternoon, and scattered-to-numerous
convective coverage is forecast within a moderately unstable air
mass along/ahead of the front Wed, with 50-70 PoPs warranted across
the NW half of the area, with mainly 20-40% across the southeast
half. Accelerating mid-level flow associated with multiple rounds
of height falls will result in increased deep layer shear of 25-30
kts, so another threat for isolated severe storms will exist Wed
afternoon/evening.

The increasingly slower-moving frontal zone is forecast to settle
over the forecast area overnight Wed/early Thu, possibly even
stalling somewhere over the area. Meanwhile, precipitable water
values are forecast to surge to 2" (or more) over the area within
deep SW flow, and forecast soundings depict very deep warm cloud
depths of over 12 kft, along with notable instability lingering
well past the typical diurnal cycle. With mean cloud-bearing
winds of 20 kts or more expected, cell movement will be swift
(for mid-summer, anyway.) However, the mean flow will be oriented
almost perfectly parallel to the boundary...creating the threat
for training, highly efficient rainfall-producing cells. This
threat is confirmed by some extreme localized rainfall totals in
convection-allowing models. It is very possible that a Flood Watch
for flash flooding will eventually be issued for Wed night/early
Thu, but there is too much uncertainty about the eventual position
of the boundary to entertain any headlines at the current time.

The boundary is forecast will most likely remain over, or near our
area through at least Thursday, but a slowly-developing inverted
ridge associated with 1020+ surface high pressure building into
the northeast Conus will try to nudge the boundary south of
the CWA. Thus, more stable air will gradually filter into the
area with time. The potential for heavy rainfall and isolated
flash flooding will nevertheless continue into Thursday, as the
potential for training, highly efficient rain showers and storms
will continue. This threat should gradually relent toward week`s end
as the boundary settles farther south. After a day of near-normal
heat on Wed, max temperatures are forecast to cool to well-below
normal levels Thu through Sat under the influence of cooling
easterly flow, anomalously low heights, and widespread cloud cover.


Key message 2: A return to typical late July weather is expected
next week.

The global models largely agree that deep-layer drying will
occur across the region by Sunday, thus bringing an end to the
period of relatively cool and very active convective weather
that is anticipated late this week. Forecast temps return to
near-normal Sunday, then slightly above climo early in the new work
week. Convection is still in the forecast each day Sunday-Tuesday,
but PoPs are mainly in the 20-30% range and timing of said PoPs
is largely tied to the diurnal heating cycle.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
At KCLT and elsewhere: VFR conditions are forecast to prevail
through this forecast period. Some isolated convection is
anticipated across the mountains and northern portions of the
Terminal Forecast Area this afternoon/evening, but coverage is
expected to be insufficient for a TAF mention at this time. Gusty
SW winds are expected at most sites through the afternoon, with
winds remaining elevated...possibly with occasional Piedmont gusts
during the overnight. Convective chances are expected to ramp up
early during the daylight hours Wed, as a frontal boundary and/or
remnant convective activity approaches from the north. Prob30s
for TSRA are included at KAVL and KHKY at some point beginning in
the morning, while chances are expected to mostly hold off until
after 18Z at the other TAF sites.

Outlook: Very active convective weather is expected from Wed
afternoon through the end of the week as the front stalls in or
near the area. Convection is likely to linger well past the normal
afternoon/evening time frame for at least Wed/Thu night. Low
stratus and/or fog will be possible each morning, especially in
the mtn valleys.

&&

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

&&

$$

JDL