797
FXUS62 KGSP 212339
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
739 PM EDT Thu Aug 21 2025

.SYNOPSIS...
Chances for mainly afternoon and evening showers and thunderstorms
increase into the weekend. Temperatures will be a few degrees below
normal Friday into the weekend. Temperatures warm up briefly Monday
ahead of a cold front before cooler and drier conditions develop
behind the front the rest of the workweek.

&&

.NEAR TERM /THROUGH FRIDAY/...
As of 712 PM EDT Thursday...

Key Messages:

1) Locally Heavy Rainfall/Isolated Flash Flooding Threat Continues

2) Patchy Fog and/or Low Status Will Develop Again Overnight into
Early Friday Morning

Forecast has proceeded mostly according to plan this evening, with
decent shower and thunderstorm coverage over the Upstate ahead of a
weak boundary advancing across the area.  Over the I-77 corridor,
coverage turned out to be less than expected...which ultimately
makes sense as the boundary is hard to find there on recent surface
charts.  Upper forcing remains nebulous...but generally looks like
weak troughing over the forecast area...with more pronounced dry
air behind it, draped across the eastern Tennessee Valley on water
vapor imagery.

Otherwise...18Z CAMs still depict some potential for ongoing
convection over the VA Piedmont to develop a weak MCV...and prompt
a second round of overnight convection, tapping into lingering
elevated instability across the I-77 corridor, and perhaps even
the northeastern SC Upstate through daybreak Friday.  Lows tonight
will end up ~4-8 degrees above normal thanks to lingering cloud
cover and precip. Patchy fog and/or low stratus will develop again
overnight into daybreak Friday across the entire forecast area
thanks to low-level moisture in place.

Scattered convection should be ongoing across portions of
the forecast area Friday morning...though confidence remains
limited on where.  Low stratus will remain in place all day with
little improvement expected for most locations. However, the
NC Piedmont/Foothills may see stratus lift Friday afternoon but
confidence is low. Patchy fog may linger through the morning hours
before lifting during the early afternoon hours. Otherwise, the SW
periphery of the aforementioned sfc high pressure will nudge into
the GSP CWA on Friday while the frontal boundary sinks south towards
Florida. The sfc high may act to suppress convective chances across
portions of the CWA Friday afternoon and evening. However, how far
south and west the sfc ridge is able to build is the main forecast
challenge. For now, it appears that the NC Piedmont/Foothills and
the eastern SC Upstate have the best potential to stay mostly dry
Friday afternoon and evening. NBM PoPs reflect this trend and have
even gone lower on PoPs across the eastern SC Upstate and the NC
Piedmont/Foothills and higher on PoPs elsewhere. Thus, shower and
thunderstorm chances should be highest across the mountains, NE
GA, and the western SC Upstate. Per the 12Z global and high-res
guidance, instability also looks the best across the mountains,
NE GA, and the western SC Upstate with SBCAPE values ranging from
1,000 to 1,800+ J/kg and DCAPE values possibly reaching 1,000 J/kg
(there is low confidence on DCAPE actually reaching 1,000 J/kg
as the latest NBM is trending cooler for Friday). Although the
severe threat will remain low thanks to weak deep layer shear
(only 10-15 kts), a few strong, sub-severe severe storms remain
possible across areas with the best instability. Temps Friday
afternoon will be noticeably cooler behind the front compared to
today and yesterday, ending up 4-7 degrees below normal for most
locations. Highs will struggle to reach into the upper 70s to
lower 80s across the mountain valleys and east of the mountains
thanks to mostly cloudy skies. Highs across the higher elevations
will be slightly cooler, ranging from the mid 60s to mid 70s.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
As of 1245 PM Thu: The center of a surface high moves off the Mid-
Atlantic coast Saturday. A wave of low pressure moves east along a
stalled frontal boundary to our south. This sets up a moist
southeasterly low level flow across the area and keeps PW values
from 1.5 to 2 inches across the area. Instability remains weak but
the forcing will lead to numerous to widespread convective coverage
for the mountains into the western Upstate and NE GA. Lesser
coverage expected over the I-77 corridor. Heavy rainfall and
isolated flooding could be an issue given the slow moving storms
and upslope flow. Lows will be near normal and highs around 5
degrees below normal.

The wave of low pressure rides up the Carolina coast Sunday as a
cold front moves into the area late in the day. This brings and end
the southeasterly low level flow and allows some drying to take
place. PW values drop into the 1.25 to 1.75 range. Instability
remains weak, but forcing will be enough for widespread convection
over the mountains, dropping to numerous coverage over the foothills
and scattered coverage into the Piedmont. There is still some heavy
rain threat with slow moving storms, but overall chances should be
lower. Lows will be near normal with highs ranging from near normal
to 5 degrees below normal.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 115 PM Thu: The Sunday cold front moves east of the area
Monday bringing an end to the bringing a drier air mass and and end
to the multiple recent days of convection. High pressure builds in
from the west through the period, settling over to the area on
Thursday. The cooler air is delayed until Tuesday, so Monday`s highs
will only be a few degrees below normal. Highs drop to around 10
degrees below normal for Wednesday and Thursday. Lows drop to around
10 degrees below normal by then as well. Much lower dew points also
move in bringing an end to the muggy conditions. Afternoon dew
points will be in the 50s with some 40s over the higher elevations.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
At KCLT and elsewhere: Shower activity has mostly wrapped up
for the evening as a cold front sags south across the terminal
forecast area.  No more than VCSH advertised through midnight...but
for the wee hours of the morning, included PROB30s for some
sites, especially KCLT and KHKY, for a potential second round of
overnight SHRA developing before dawn.  Expect widespread MVFR
to IFR ceilings across the region overnight, and only very slow
improvement into the day tomorrow.  SHRA / -TS may continue into
the first part of Friday, but coverage and intensity look to be
considerably hampered by lingering low ceilings and patchy fog.
Model guidance is all over the place with tomorrow`s showers...so
absent much confidence on how things will develop/evolve, mostly
handled tomorrow`s convection with VCSH.  Meanwhile...when each TAF
site will return to VFR conditions tomorrow, remains a difficult
question to answer.  Generally expect improvement by late afternoon
as drier air builds into the area from the north...bringing an
end to both flight restrictions and precipitation.

Outlook: Shower and thunderstorm chances along with associated
flight restrictions will linger through the weekend.  Drier
conditions will return next week.  Fog and low stratus will be
possible each morning.

&&

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

&&

$$

SYNOPSIS...AR
NEAR TERM...AR/MPR
SHORT TERM...RWH
LONG TERM...RWH
AVIATION...MPR