342
FXUS62 KGSP 031049
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
649 AM EDT Wed Sep 3 2025

.SYNOPSIS...
High pressure moves offshore today as a weak upper-level system
move across the area. This will bring a round of mountain and
foothill showers and storms this afternoon and evening. A weak
cold front approaches from the northwest on Thursday and may bring
another round of showers and storms to the area. Temperatures
remain at or below seasonal normals through Thursday. A warming
trend returns Friday into the weekend ahead of another advancing
cold front. Rain chances return this weekend and may linger into
early next week depending on whether the front fully clears the
area or stalls across the region.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 645 AM EDT Wednesday: A quick update to the PoPs this morning
to reflect greater coverage of showers than previously anticipated
thanks to a stout upper-level impulse. The latest CAMs also trending
a little more bullish with some convection breaking containment
from the mountains this aftn into early evening, in line with the
MOS, warranting some mentionable PoPs into the northern Upstate
and all of the NC foothills.

Later this morning, the impulse will cross the CWFA and take the mid
clouds/energy with it. We will actually have pronounced deep-layer
DNVA behind the wave during the peak heating hours. But despite
that, Forecast soundings show tall, skinny CAPE developing across
the mountains, and enough low-level moisture will persist to support
scattered convection. Steering flow will push the activity east
into the NC foothills and NW Piedmont.  But much less instability
there should cause most of the activity to dissipate. The 00z HRRR
is rather aggressive with convection reaching the I-77 corridor by
early evening. This seems to be an outlier, so no deviations from
the NBM were made. Whatever does develop, it is not expected to
be severe, given lack of forcing and relatively low DCAPE. Highs
will once again be similar to the previous day, a few degrees
below normal.

Tonight, strong shortwave energy will deepen the longwave trough
over the Midwest. A cold front will push into the OH Valley from
the NW, with increasing SWLY flow ahead of the front across the
TN Valley and the Southern Appalachians. Nearly all the guidance
has some amount of showers development overnight across northern
GA/eastern TN that may work into our western zones before daybreak
Thursday. There is not as much mid-level cloudiness in the guidance
as we`ve seen the last couple nights, but perhaps more low clouds in
the increasing SWLY WAA flow, may limit mountain valley fog again.
Lows will be near normal in the mountains and slightly below normal
in the Piedmont.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 1159 PM Tuesday: Guidance is in good agreement that broad
troughing will encompass must of the CONUS east of the Rockies as a
parent closed upper low spins just north of the Great Lakes over
southern Ontario. Several shortwave troughs will dive across the
Great Plains and into the Midwest/Ohio Valley with the lead trough
sliding across the Ohio Valley on Thursday. This will drag an
attendant surface cold front into western Kentucky and southern
Ohio. The western Carolinas and northeast Georgia will remain on the
southern flank of the upper trough with the strongest forcing for
ascent displaced well north of the area towards the central
Appalachians and Mid-Atlantic. H5 heights will be rather high in the
578-580 dam range with height tendencies neutral at best. As such,
the 00z suite of CAM guidance is in good agreement that a band of
more organized pre-frontal convection will propagate across eastern
Kentucky into western Virginia and portions of West Virginia. A
broken band of scattered convection will be possible across east
Tennessee with some of this activity making a run at the mountains
late Thursday afternoon into the early evening hours. Here,
parameter space will be characterized by 30-40kts of deep-layer
vertical wind shear and modest instability with around 2000 J/kg of
surface-based instability. A couple strong storms with locally gusty
winds will be possible and an isolated severe storm cannot be
completely discounted. However, a dearth of forcing will generally
preclude greater coverage and severity with convection struggling to
make it east of the mountains. By Friday, the lead shortwave trough
will quickly pull away from the area as it lifts into New England
with broad zonal flow becoming established in the base of the mean
trough across much of the region. This will in turn stall the cold
front northwest of the area, which combined with rising heights will
support a notable warming trend. Afternoon highs are forecast to be
above average for the first time in quite a while with upper 80s to
near 90 common east of the mountains.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 1225 AM Wednesday: Heading into the weekend, the closed upper
low is generally expected to meander east across Ontario with two
more in a series of shortwave troughs diving through the Northern
Plains and into the Midwest and Ohio Valley. Once again, the
majority of associated upper forcing will remain displaced well
north of the area, however a large sprawling surface high spilling
into the Great Plains will finally push the stalled cold front into
the area. Forecast confidence quickly wanes at this point as
guidance rapidly diverges with regards to the evolution of the
surface and upper patterns. Several members of guidance push the
front through the area on Saturday with dry conditions to close the
weekend into early next week. On the other hand, other pieces of
guidance stall the front across or in the vicinity of the area with
multiple days of active weather along the boundary continuing into
the start of next week. The one agreement amongst guidance, however,
is for the aforementioned surface high to translate into New England
with a CAD surface pressure pattern developing early next week.
Another warm day is expected ahead of the front on Saturday before
the presence of precip and/or the development of CAD brings
temperatures back down to below seasonal averages.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
At KCLT: Plenty of mid clouds have spread over the terminal forecast
area this morning, but should thin out somewhat by midday, leaving a
lower-based cu field for the rest of the day. More shower coverage
than expected across the mountains, and it looks to continue thru
the day. So have bumped up the SHRA in the KAVL TAF, with a PROB30
for TSRA this afternoon. Guidance is not in very good agreement on
how much convection will be able to track east off the mountains
late aftn thru early evening. The trend seems to be for increased
chances in the NC foothills and northern Upstate. So have added
some VCSH to KGSP/KGMU with potential showers mainly north of
those sites in the 20z-00z time frame. Confidence remains too low
for any mention at KCLT at this time, with the HRRR backing off
activity around CLT compared to previous runs. Convection should
dissipate late evening, but another round of showers may develop in
the NC mountains late tonight, as a cold front approaches from the
northwest. Less mid clouds expected tonight, but some stratocu may
linger, and limit mountain valley fog forming. Winds will be light,
toggling to SW in the 16-18z time frame east of the mountains,
but could be variable around convection.

Outlook: At least sct aftn/evening convection will be possible
across the higher terrain on Thursday with chances diminishing
again on Friday. Nocturnal fog and/or low stratus will also be
possible overnight and into the morning, especially in the favored
mtn valleys.

&&

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

&&

$$

SYNOPSIS...TW
NEAR TERM...ARK
SHORT TERM...TW
LONG TERM...TW
AVIATION...ARK