700
FXUS62 KGSP 220017
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
817 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.

In the absence of any good upper forcing, convection has remained
isolated and unimpressive this evening.  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 to 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 /00Z WEDNESDAY THROUGH SUNDAY/...
At KCLT and elsewhere: Still expecting VFR for the bulk of the 00Z
TAF period.  As expected, isolated convection developed over the
northern Blue Ridge this afternoon, as well as some unanticipated
showers over the I-77 corridor, and most recently, the Savannah
River Valley...but no impacts to the TAF sites are expected,
with all activity so far remaining widely scattered at best and
struggling to maintain its integrity.  A dry overnight period is
expected, with some mid- and high-level cloud cover.  It`s not out
of the question that high-end MVFR ceilings may briefly develop
at KAVL after midnight, but guidance favors low-end VFR ceilings.

Hi-res models have slowed considerably with respect to a line
of showers and thunderstorms arriving in the area Wednesday.
While a few forecast ensembles still depict showers developing over
the I-40 corridor as early as 15Z, the model consensus now keeps
upstream convection at bay until at least 18Z.  At least somewhat
organized convection should then cross the terminal forecast
area from northwest to southeast through late Wednesday evening.
Showers and thunderstorms may persist past the end of the 00Z TAF
window...even at CLT, where precipitation could remain after 06Z
Thursday.  Some flight restrictions are of course likely to develop
wherever convection does; both TSRA and associated restrictions
are now handled with VCSH and PROB30s where appropriate.

Outlook: Active forecast to continue with potential for convection
through the end of the week, as a cold front stalls in or near
the terminal forecast area.  Convection may persist well into the
overnight again on Thursday night.  Low stratus and/or fog will
be possible each morning, especially in the mountain valleys and
locations which receive especially heavy rainfall.

&&

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

&&

$$

JDL/MPR