346 
FXUS62 KGSP 250016
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
816 PM EDT Wed Sep 24 2025

.SYNOPSIS...
An unsettled pattern emerges ahead of a cold front and upper 
trough with multiple rounds of showers and thunderstorms into the 
weekend. Temperatures remain warm through Thursday before cooling 
to near seasonable normal high temperatures into early next week.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 800 PM EDT Wednesday: Cloud cover continues to gradually 
increase from the west and some scattered showers continue lifting 
NE across the NC Piedmont. Seeing a line of showers and 
thunderstorms approaching out of eastern TN and northern Georgia 
this evening as well. Confidence is low on how well this line will 
hold together as it pushes off the mountains later this evening into 
tonight. A dearth of instability during the nocturnal minimum should 
preclude any severe weather threat, but a strong storm with locally 
gusty winds cannot be discounted should more organized structures 
remain.

By Thursday, a positive tilt upper trough will gradually shift east 
with a belt of enhanced flow and upper divergence translating across 
the Appalachians. At the same time, the piece of energy in the base 
of the trough is forecast to break off and begin evolving into a 
closed upper low in the vicinity of the Lower Mississippi Valley. At 
least some degree of shower activity will likely be ongoing across 
the mountains with considerable cloudiness as well. CAM guidance 
depicts redevelopment of convection during the afternoon across 
portions of the area, but coverage and location remain somewhat 
uncertain. Extent of cloud cover and lingering showers from 
overnight activity will play a significant role in the evolution of 
mesoscale details for the afternoon. One such scenario is that a 
differential heating boundary materializes east of the morning cloud 
cover and serves as the location for later convective initiation. 
Guidance is also mixed on coverage with some CAM members depicting 
mainly scattered storms. Depending on could cover, upwards of 2000 
J/kg of surface-based instability will be present with 30-40kts of 
deep-layer vertical wind shear. This will be sufficient for a couple 
isolated severe storms with a threat for locally damaging winds. 
Positive tilt of the trough and respective shear vector orientation 
isn't overly favorable for widespread organized convection and in 
fact, should convective coverage become greater than expected there 
would be a tendency for storms to become undercut by composite cold 
pools.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
As of 1250 PM EDT Wednesday: The center of an upper low moves from 
the Mid-South at the start of the period eastward into the Southern 
Appalachians by the end of the period. At the surface, a cold front 
moves into the area from the west Friday and stalls along the coast 
by Saturday while a series of weak low pressure centers moves north 
along the front. The deepest moisture and strongest forcing, along 
with better instability, occurs on Friday as the front is moving 
through. The precipitation will be more convective in nature, but the 
severe chance will be lower than Thursday as the instability is 
weak. Some mid level drying takes place on Saturday, but low level 
moisture remains high with the low level flow turning more 
northeasterly. Precip chances actually increase on Saturday with 
better upper divergence ahead of the upper low, but thunder chances 
are lower with weaker instability. Widespread heavy rainfall is 
unlikely either day, but moderate QPF is expected. Isolated, brief 
heavy rainfall will be possible in any storm, but the overall flood 
threat is low. That said, any location where storms train over the 
same area could lead to spots of nuisance flooding. Highs near 
normal Friday drop below normal for Saturday. Lows above normal each 
morning.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
As of 125 PM EDT Wednesday: The upper low remains in place on Sunday 
before retrograding into Middle TN on Monday. It then opens up and 
moves to the SC coast by way of GA Tuesday. The low moves east 
Wednesday as a ridge builds into the OH Valley from the Desert SW. 
At the surface, the front remains stalled over or near the Carolina 
coast with waves of low pressure moving north along the front. High 
pressure builds into the area from the north. These features keep a 
moist E to NE low level flow across the area through the period, 
although it does weaken on Wed as the front finally begins moving 
east. The result is scattered showers for most of the area Sunday 
and Monday with diminishing chances Tuesday and Wednesday. QPF is 
generally light through the period which is good given the prolonged 
nature of the precip chances. This keeps the flood threat very low 
while helping the drought conditions across the area. Also, for now, 
the 12Z GFS and its ensemble mean show one consolidated tropical 
system but keep it well off shore. The Canadian and 00Z ECMWF show 
two systems with one making a glancing blow to the Carolina coast. 
As always, this could change so keep up to date with the latest 
forecast. Highs remain near to slightly below normal until Wednesday 
when they fall to around 5 degrees below normal. Lows will be 
slightly above normal until Wednesday when they fall a few degrees 
below normal.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
At KCLT and elsewhere: Active through the 00Z TAF period as a cold 
front approaches out of the west. The front will remain west of the 
terminals through the TAF period so winds will remain S/SW. Showers 
and thunderstorms are steadily approaching out of the west ahead of 
the front as of 00Z. How well this line holds together east of the 
mountains will be the main forecast challenge through the TAF 
period. Thus, went with PROB30s for SHRA east of the mountains this 
evening into late tonight, with the exception of KCLT as this 
terminal should remain dry. Confidence is higher that KAVL will see 
SHRA so went with a combination of prevailing SHRA and 
PROB30s/TEMPOs overnight into Wednesday morning. Confidence on 
prevailing SHRA from 13Z-16Z is very low as guidance is not in 
agreement on whether KAVL will see periodic rain or brief drying at 
times during the morning hours. Confidence on the formation of 
mountain valley fog remains low as increasing cloud cover and rain 
should keep dense fog at bay. However, vsbys will lower in 
association with rain overnight so have this account for in the 
PROB30s/TEMPOs. Cigs will gradually lower late tonight into early 
Thursday morning dropping mostly to MVFR levels, although IFR cannot 
be entirely ruled out. There will be little improvement throughout 
the day tomorrow regarding cigs but guidance shows KCLT having the 
best chance to see VFR cigs return late tomorrow afternoon into 
tomorrow evening. Models are in better agreement regarding TSRA 
chances tomorrow afternoon/early evening so went with PROB30s across 
the terminals. Winds will go light to calm and VRB this evening into 
tonight, increasing again throughout the day tomorrow. Speeds will 
range from 5-10 kts with low-end intermittent wind gusts expected to 
develop again, mainly at KCLT, KGSP, and KGMU.

Outlook: Shower and thunderstorm chances, as well as associated 
restrictions, continue for all terminals into the weekend thanks to 
the cold front. Mountain valley fog and low stratus are possible 
each morning but could be limited somewhat by both cloud cover and 
rain.

&&

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

&&

$$

SYNOPSIS...DEO
NEAR TERM...AR/TW
SHORT TERM...RWH
LONG TERM...RWH
AVIATION...AR