Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
229 AM EDT Sat May 17 2025

.SYNOPSIS...
A cold front will push a line of strong to severe storms across the
area early to mid-morning, with dry conditions returning from west
to east late this morning into early this afternoon. The front will
stall in the vicinity of the area through early next week, keeping
the relatively active pattern around. Warm and above normal temperatures
will stick around through early next week before cooler and below
normal temperatures return mid to late week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Key Messages:

1) A line of strong-to-severe thunderstorms is expected to impact
the mountains in the next few hours, with the threat decreasing
eastward.

2) Daytime temperatures above normal today.

As of 145 AM EST Saturday: Synoptically, the ridge continues to
flatten allowing for shower and thunderstorm chances through the
early morning hours. Out west, a potent line of storms has congealed
across central TN/KY and is moving eastward. As the line approaches
the TN/NC border, damaging winds and heavy rainfall are the main
concerns that are expected to weaken crossing the mountains. Taking
a look at the environment, modeled soundings ahead of the line shows
strong shear (50-60kts) with modest instability both at the surface
and aloft. S/SE surface winds do help to increase the SRH into the
200-225 range, allowing for the possibility of an isolated TOR
threat as the line first reaches the CWA and into the mountains.
Though low to begin with, the TOR risk is still there, but should
weaken as it crosses eastward. One concern for this line to stay
together is the speed of the line and the CAP in place across most
of the area. Given the slower speed, this could allow the cap to
erode more ahead of the line and keep a more balanced line. Though
some weakening is likely to occur, redevelopment east of the
mountains near daybreak is possible, but with damaging winds as the
main threat. The Storm Prediction Center continues the Slight risk
across most of the mountain areas through 7AM. Current projections
for this line of storms reaching the TN/NC border between 3AM-4AM.
If it holds together, it could reach the GSP and Charlotte areas
after 6AM.

Once the line continues to fall apart and moves eastward this
morning, the remainder of the forecast period is relatively quiet.
Gusty winds throughout most of the CWA today behind the exiting
line, but should start to diminish after sunset. Expect very warm
daytime highs today with temps approaching the high 80s and
overnight lows in the 60s.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 130 AM Saturday...

Key Messages:

1) Shower and Thunderstorm Chances Return Sunday Across the Western
Zones with Better Coverage Expected on Monday

2) Severe Weather Potential will be Low on Tuesday but Chances
Increase Slightly on Monday

3) Warm and Above Normal Temperatures Stick Around

Upper-level flow will start out quasi-zonal the first half of Sunday
before weak upper ridging builds across the Southeast Sunday evening
into Monday night. At the sfc, a stationary front will stall over
the forecast area throughout the short term. This front combined
with embedded shortwaves tracking over the CWA each day will keep
unsettled weather around through the period. Highs each afternoon
will end up ~4-6 degrees above normal with lows each night ending up
~8-10 degrees above normal.

Both high-res and global model guidance generally agree that the
western half of the CWA will have the best chance to see showers and
thunderstorms on Sunday. With activity expected to remain scattered
at best, capped PoPs to chance (15% to 30%) across the western
zones. With a few hundred J/kg of SBCAPE developing Sunday
afternoon/early evening across the western zones and 40-50 kts of
deep layer shear in place, isolated strong to severe storms are
possible. However, confidence on the severe threat for Sunday is low
as CAMs depict the strongest activity tracking across the Deep South
rather than the NE GA and the western Carolinas.

Global model guidance continues to show better coverage of showers
and thunderstorms, as well as better instability, on Monday. Thus,
have likely (60%) PoPs across the mountains with chance PoPs (20% to
50%) elsewhere. Also have most locations seeing the potential for
scattered thunderstorms during the afternoon/early evening hours.
With 40-50 kts of deep layer shear and SBCAPE ranging from 1,000-
1,500 J/kg during peak heating on Monday, a few strong to severe
storms are possible.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 200 AM Saturday...

Key Messages:

1) Shower and Thunderstorm Chances Continue through the Long Term
with the Best Coverage Currently Expected on Wednesday

2) Strong to Severe Storms are Possible on Both Tuesday and Wednesday

3) Above Normal Temperatures Linger through Tuesday Night Before
Cooler and Below Normal Temperatures Return Mid to Late Week

Upper ridging remains in place over the Southeast through Tuesday
night before an upper low tracks eastward out of the Midwest into
the Northeast Wednesday into Friday. At the sfc, the aforementioned
front in the short term will remain stalled over the CWA on Tuesday
before a sfc low pressure system tracks east across the Lower
Midwest/OH Valley on Wednesday and across the Northeast Thursday
into Friday. Thus, unsettled weather will continue through at least
Thursday before drier conditions return for most locations on
Friday. Warm and above normal temperatures will continue through
Tuesday night before cooler and near normal temperatures develop
Wednesday into Wednesday night. Even cooler and below normal
temperatures return Thursday into Friday behind the low pressure
system.

Coverage of showers and thunderstorms will gradually increase
through Wednesday ahead of the low pressure system so have likely
PoPs (60%) across the mountains and chance PoPs elsewhere on Tuesday
(20% to 50%) and likely to categorical PoPs (60% to 70%) on
Wednesday. Strong to severe storms will be possible again on both
Tuesday and Wednesday. However, the severe potential looks better on
Tuesday thanks to 40-50 kts of deep layer shear remaining in place
as well as 1,500-2,000 J/kg of SBCAPE developing during peak
heating. Although deep layer shear will increase to 50-60 kts on
Wednesday, SBCAPE will be slightly lower, ranging from 1,000-1,500
J/kg, and may only develop east of the NC mountains. Thus,
confidence on strong to severe storms on Wednesday is lower compared
to Tuesday.

The sfc low will lift northeast of the CWA Wednesday night into
Friday allowing a more stable airmass to filter into the region so
thunder is not expected on Thursday or Friday. Model guidance is
still not in agreement regarding when moisture will push east of the
forecast area. The latest GFS shows dry conditions developing from
west to east Wednesday night into daybreak Thursday while the latest
ECMWF shows precip lingering across mainly the northern half of the
area on Thursday. Thus, capped PoPs to chance (25% to 50%) across
the northern zones and slight chance (15% to 20%) across the
southern zones Thursday. Some NW flow rain showers may linger over
the NC mountains Thursday night into Friday so maintained chance
PoPs (30% or lower) across these zones for now.

&&

.AVIATION /07Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: VFR conditions are expected across all
terminals outside of a few hours of TSRA. A line of TSRA approaches
and eventually crosses all sites this morning before 13z. For this,
a TEMPO at all terminals with the mountain zones arriving earlier.
KAVL by 07z and KCLT after 10z. Expect VRB winds and brief vsby
restrictions with the storms. These storms should be out of the area
later this morning, leaving gusty winds in its wake. Winds stay W/SW
everywhere expect at KAVL where brief WNW winds arrive before
turning SW. Expect 15-25kt gusts at all sites through the TAF period
expect at KCLT where winds diminish late tonight.

Outlook: Thunderstorm chances return Sunday and continue through the
middle of next week. Early morning fog/low stratus possible in the
mountain valleys and locations where rain fell the previous
afternoon/evening.

&&

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

&&

SYNOPSIS...AR
NEAR TERM...CP
SHORT TERM...AR
LONG TERM...AR
AVIATION...CP

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