Severe Thunderstorm Warning 69, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
247 PM EDT Thu May 8 2025

.SYNOPSIS...
A cold front crosses the area Friday and stalls over the Southeast
this weekend into early next week, keeping unsettled weather around
through then. The front and associated low pressure system finally
clears the area Thursday.

&&

.NEAR TERM /THROUGH FRIDAY/...
As of 245 PM EDT Thursday: Elongated upper trough and associated
height falls stretch from the eastern Atlantic Canada through
the Great Lakes and into the Ozarks. This is helping to send an
attendant cold front towards the region, with the best forcing
encroaching the CFWA and should exist over the area later this
afternoon and evening. Deep layer shear of 30-40 kts are present,
especially over the North Carolina zones being closer in vicinity
to the better forcing and frontal zone. MLCAPE of 1000-2000+
J/kg is currently in place as well. Low-level southwesterly flow
has allowed for a decent WAA regime out of the Gulf with PWAT
values between 1.00'-1.25". Model guidance continue to agree that
ridgetop convergence will set the stage for convective initiation
after 19Z. Discrete cells will develop with robust supercell
features. Steep and drier low/mid-level lapse rates and lower than
normal freezing level (~10,000') suggest the onset threat will be
large hail, with isolated convection capable of producing hail of 2"
or greater and downbursts (DCAPE 600-800 J/kg), mainly across the
North Carolina mountains/foothills. As the activity pushes east,
CAMs continue to show upscale growth and the development of a cold
pool late afternoon into the evening across the North Carolina
Piedmont and northern Upstate to help aid in storm initiation
downstream from the original starting point. Storm mode becomes
more linear and allows for the hail threat to diminish, but upticks
the damaging wind threat as the convection pushes further east.

CAMs also depict another area of interest across the Upstate and
northeast Georgia as the convection from Tennessee and northern
portions of the Deep South grow upscale and make a run at the
southern half of the CFWA, where the environment may be left
untapped. Storm mode would be more linear in this case and look
for the threat to be mainly damaging winds. In both cases when the
storm mode shifts more linear, hodographs become a little more
deeper as the LLJ (15-25 kts) is better established later this
evening. In this case, a tornado or two can't be ruled out, but
the lack of low-level shear will make full tornadogenesis difficult.

The cold front to the northwest of the area will struggle to reach
the CFWA until Friday afternoon as the upper-level pattern amplifies
with the trough developing a closed upper low and slows down the
frontal boundary advancement. As a result, lingering convection
will be possible overnight as model guidance struggle to fully
get rid of elevated CAPE and overall forcing. Convective debris
will likely linger through much of the nighttime period, but if
some clearing can get going expect areas of fog and possibly low
stratus to settle in just before daybreak.

The now closed upper low will intensify and set up shop over the
Mid-Atlantic by Friday as the front gradually enters the CFWA from
the northwest by late morning to early afternoon Friday. Another
round of convection is expected ahead of the front during peak
heating Friday. CAMs are not as excited with this potential,
but still show an environment conducive for multi-cellular to
supercellular storm mode as 25-35 kts of shear and 1000-2000 J/kg
of MLCAPE develop. The overall forcing isn't the best, however,
inverted-v profiles and dry mid-level indicate damaging winds will
be the main threat, but large hail can't be ruled out. Coverage
will be more isolated compared to today, but the severe threat will
persist nonetheless as the cold front moves across the area during
peak heating Friday. Afternoon highs will end up a few degrees above
normal ahead of the front, but cooler than normal for locations
behind the front (mainly across the mountains) during peak heating.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
As of 200 PM EDT Thursday: Any left over convection will quickly
dissipate with loss of heating Friday evening as drier and cooler
high pressure builds in from the north and the frontal boundary
moves south of the area. Lows now look to drop to near or 5 degrees
below normal.

Guidance continues to trend drier for Saturday as the drier air mass
and surface high penetrate farther into the Southeast. Even with
those expectations, there may be some showers over the Lakelands
into the Upper Savannah River Valley as moisture may try to lift
north over the stalled frontal boundary. Even if that occurs, any
precip will be very light. Despite the cooler air mass, the lack of
precip will allow temps to warm more than previously expected as no
real cold air damming develops. Highs will still be around 5 degrees
below normal.

This drier trend continues into Sunday with precip slower to move
back north as the moist low level flow and isentropic lift take
longer to develop in response to the developing upper low and
associated surface low near the Gulf Coast remaining farther south
and west of the area. Still have a chance of showers moving into NE
GA and the Upstate by afternoon with slight chance over NC. But
again, any precip would be light. The lack of precip keeps the CAD
from forming and allowing temps to warm more than previously
expected. Didn't go full on with the model blend given the
uncertainty, but highs end up around 5 degrees below normal but
could be warmer if the precip remains slow to develop.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 230 PM EDT Thursday: Widespread precip does begin moving back
into the area Sunday night as the stacked low pressure system begins
moving north and a stronger, moist low level southerly flow and
isentropic lift develop. This does help the hybrid cold air damming
to set in by Monday and holding on through Monday night as precip
continues. The CAD erodes Tuesday as the high moves well off shore
cutting off support for the CAD and the stacked lows move north and
east. Widespread precip remains over the area though with the
strong, moist southerly flow and isentropic lift. The lows only
slowly move northeast on Wednesday keeping moisture and precip over
the area through the day. The lows finally move northeast of the
area on Thursday, but some lingering NW flow showers may continue.

There is a threat of moderate to heavy rainfall with this system.
The guidance has poor run to run consistency of QPF however. In
fact, overall precip will likely be on the lower side of guidance
given the now drier short term. Still, some excessive rainfall and
minor flooding can't be ruled out. There will be some thunderstorms
once the CAD erodes, but chance of severe storms looks quite low for
now.

Highs will be around 10 degrees below normal Monday in the CAD, then
slowly warming to near normal by Wed and above normal by Thursday.

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
At KCLT and elsewhere: Diurnal cu with very low VFR cigs continue
to roam the sky in anticipation of a SHRA/TSRA developing after 19Z
in the mountains and pushing east across the rest of the area by
00Z, maybe a little after. Placed a TEMPO group at all TAF sites
to forecast the best timing for TSRA and associated restrictions
at each terminal. Strong winds (=> 30 kts) and large hail (=>
1") are possible through the afternoon and evening. Expect the
coverage in SHRA/TSRA to dwindle around 06Z or so. Model guidance
still hint at restrictions forming overnight through mid-morning
with IFR/MVFR cigs/vsby. There are uncertainties for the overall
extent of restrictions, but with the potential for heavy rainfall,
ground fog could become an issue to go along with low stratus. Most
vsby/cig restrictions should scatter around mid to late Friday
morning. Winds continue out of the west to southwest this afternoon,
while likely becoming variable with any thunderstorm that passes
by. Winds should toggle more west to northwesterly on Friday as
another round of SHRA/TSRA and associated restrictions are possible
just after the end of the 18Z TAF update.

Outlook: An unsettled pattern will linger into early next week
keeping chances for showers and thunderstorms around as well as
associated restrictions.

&&

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

&&

SYNOPSIS...RWH
NEAR TERM...CAC
SHORT TERM...RWH
LONG TERM...RWH
AVIATION...CAC

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