Startex, South Carolina Weather Forecast Discussion

128
FXUS62 KGSP 231742
AFDGSP
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
142 PM EDT Tue Sep 23 2025
.SYNOPSIS...
There will be scattered showers and thunderstorms, mainly over the
mountains, through Wednesday. A cold front reaches the area with
greater coverage of showers and thunderstorms Thursday and Friday.
Temperatures remain above normal ahead of the front before cooling a
few degrees over the weekend with drier weather.
&&
.NEAR TERM /THROUGH WEDNESDAY/...
As of 1245 PM Tuesday: Been watching an area of showers with
embedded thunderstorms over the TN Valley region all morning long
forced by an approaching short wave, but it just can`t seem to
get past a wall near I-75, thus we are no closer to seeing rain
in western NC than we were at daybreak. Perhaps this is due to
the main forcing at upper levels being pushed more southeast than
east. At any rate, the new guidance for the afternoon has come in
with less coverage and more of a concentration near the TN border,
though confidence there is only marginally suggestive of keeping
a chance of showers/storms. At least we are seeing some better cu
buildup over the higher ridges. We have about 1000 J/kg of sfc-based
CAPE to work with, so a few showers should manage to grow. East
of the mtns, it is looking less and less possible that anything
will make it much past the Escarpment, and probably the northern
foothills if it does. At this hour, much of the western Piedmont
and Upstate are essentially stable. Perhaps this is a remnant of
the old inverted ridge. Either way, precip chances will be kept
out of those locations.
For tonight, after the short wave passes, the flow aloft will
be nearly flat as an upper anticylone remains stretched out to
our S and two upper low centers over the central High Plains
and Upper Great Lakes essentially keep a very positively tilted
upper ridge axis to our N. There shouldn`t be anything to keep
forcing convection much past sunset, so expect a quiet night. An
increase in moisture and cloud cover might keep the valley fog at
bay again across the mtns, as it did this past morning. Low temps
are expected to be seasonally mild and roughly five degrees above
normal. Not much change is expected for Wednesday as the high
Plains upper low pivots eastward to the Ozarks and mid-MS Valley
regions. This will back the flow aloft around to something more SW
during the day, which should essentially keep shower activity stuck
over the higher terrain. Looks like the warmest day yet, though,
with high temps on the order of ten degrees above normal. Nowhere
near a record, though.
&&
.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
As of 105 PM EDT Tuesday: An upper low spins over the Great Lakes on
Thursday then opens and moves off the New England coast Friday. A
trough stretches southwest of the low across the OH and lower MS
River valleys. A strong short wave dives into this trough and closes
off into an upper low over the Mid-South. This low moves into the
Middle TN Valley on Friday. Our area will be in SW flow ahead of
these systems with short waves moving through the flow and across
the area. At the surface, broad SW flow will be in place ahead of a
cold front that moves into the area late in the day. There will be
enough forcing and moisture for categorical PoP over the mountains,
with likely PoP spreading eastward into the evening. The question is
how much heating can take place. If heating is limited, instability
will be as well limiting any severe storm potential. If decent
heating can take place, then moderate instability would be possible.
This combined with 30 to 40 kts of shear would lead to the potential
for some severe storms with damaging winds the main threat. SPC
currently has our area in a Marginal risk which matches these
parameters. Right now, it appears that rainfall amounts will be in
the "much needed" category, mainly an inch or less for all but
portions of the mountains near the TN border. As the front crosses
the area Friday, moisture and forcing remain elevated but
instability will be weak. Thunderstorms are expected but the severe
potential will be much lower. Rainfall again generally less than an
inch. Highs are expected to be near normal for all but the I-77
corridor and south of I-85 in the Upstate and NE GA where they will
be around 5 degrees above normal. All areas will be near to slightly
below normal on Friday. Lows will be above normal both days.
&&
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
As of 125 PM EDT Tuesday: The TN Valley upper low slowly moves into
the Carolinas by Sunday. The low then retrogrades to the Lower MS
Valley by Tuesday as an anti-cyclone builds over the top of it
across the Midwest, with the pattern taking on the look of a Rex
Block. Friday`s cold front stalls along the Carolina coast Saturday
through Monday with a series of low pressure waves moving northward
along it. The front then moves offshore Tuesday. There looks to be
enough moisture rotating around the developing easterly flow from
the low pressure waves and high pressure building in from the north,
for mainly scattered diurnal convection Saturday through Monday.
Precip chances then drop to slight chance on Tuesday as drier air
begins working in. Moderate QPF is possible Saturday with lighter
amounts through the rest of the period. Highs start out a few
degrees below normal Saturday then remain around normal through the
end of the period. Lows start out slightly above normal then remain
around normal through the end of the period.
&&
.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
At KCLT and elsewhere: Seeing some enhanced cu developing over
the ridgetops and a few showers should pop up in the next hour
or two. Meanwhile, the persistent area of showers and storms to
the west continues to struggle to make it any farther east than
the TN-NC border. Guidance is not keen on much coverage away
from the TN border, so KAVL was cut back to only a VCTS. Thus,
all terminals are VFR thru the evening. Wind should stay light
S to SW. Tonight, with more mid/high clouds moving overhead, mtn
valley fog/low stratus don`t look like as good a bet as the last
several days. Thus, KAVL was dialed back to a prevailing MVFR and
temporary IFR after 10Z given that trend. After the restrictions
burn off around mid-morning, all terminals should be VFR again
with only sct stratocu and a light SW wind. Precip chances happen
too late at KAVL to include.
Outlook: Mountain shower and thunderstorm chances return again
Wed afternoon, then fog and stratus possible in valleys Wed
night. Better chances for restrictions with a front Thursday and
Thursday night. Low confidence as to flight conds Fri-Sat with
guidance split between dry high pressure and an upper low producing
showers and promoting moist onshore flow.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.
&&
$$
SYNOPSIS...DEO
NEAR TERM...PM
SHORT TERM...RWH
LONG TERM...RWH
AVIATION...PM

NWS GSP Office Area Forecast Discussion