950
FXUS62 KGSP 151024
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
624 AM EDT Mon Sep 15 2025

.SYNOPSIS...
High pressure over the region today weakens as a low pressure system
moves north along the North Carolina coast Tuesday and along the
Virginia coast Wednesday. High pressure returns and remains in place
through the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 620 AM EDT Monday...

Key Messages:

1) Slightly Cooler Today, Especially in the North Carolina Foothills
and Piedmont, Thanks to Cloud Cover

2) Spotty Showers Develop this Afternoon into Tonight, Mainly Across
the Mountains

3) Breezy Winds Expected Along I-77 this Afternoon and Early Evening

4) Patchy Mountain Valley Fog and Low Stratus Possible Again
Overnight into Daybreak Tuesday but Confidence is Low

A closed upper low meanders over the Carolinas through the near
term. Meanwhile, sfc high pressure gradually weakens as a coastal
low slowly lifts NNW towards the North Carolina Outer Banks. This
will allow rain chances to return this afternoon into tonight,
mainly across the mountains.

Dry conditions will continue area-wide through this morning.
Mountain valley fog and low stratus developed overnight and will
linger the next hour or so before lifting as daytime mixing
develops. Most of the mountain valleys have seen patchy fog but
locally dense fog developed at times in the Little TN Valley.
Morning lows are running a few degrees above normal this morning
thanks to scattered to broken cloud cover.

The 06Z CAMs are coming into better agreement regarding the coverage
of convection this afternoon and evening. The 06Z HRRR still depicts
slightly better coverage of showers compared to the 06Z NAMNest but
both CAMs show the potential for some shower activity to break
containment of the mountains this evening into tonight, sinking
southward into the South Carolina Upstate and northeast Georgia.
Thus, it appears that confidence on spotty showers will be highest
across the mountains and lower across northeast Georgia and the
South Carolina Upstate this afternoon and evening. The 06Z CAMs are
backing off on the spotty shower potential for the North Carolina
Piedmont overnight into daybreak Tuesday. Opted to remove any
thunder mention the NBM had through the near term as instability
does not look all that impressive, especially with scattered to
broken cloud cover remaining overhead. Cloud cover will allow for
slightly cooler highs this afternoon for most locations but
especially across the North Carolina Foothills and Piedmont. Highs
across these locations will only reach into the lower 80s. Breezy
winds (15-20 mph) will develop this afternoon and early evening
along/near I-77 in association with the coastal low lifting NNW.
Gusts should diminish around 00Z.

Lows tonight will remain a few degrees above normal thanks to
lingering cloud cover. Patchy mountain valley fog and low stratus
could develop overnight into daybreak Monday but confidence is low.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
As of 105 AM EDT Monday: Guidance in good agreement regarding the
Carolina coastal low during this period. Unfortunately, the result
is little in the way of some much needed rainfall for the area. The
low, while moving onshore across NC, remains much closer to the
coast than some earlier model runs were suggesting. This keeps the
deeper moisture and better forcing to our east. There will be enough
moisture and forcing on the developing easterly flow for scattered
showers Tuesday over the NC Piedmont and northern foothills, quickly
dropping off to no precip for most of the Upstate and NE GA. There
will be a chance of diurnal thunderstorms across the mountains,
including the Upstate and NE GA mountains, where some weak
instability can develop. Overall the QPF will be light, but some
brief, heavy rainfall is possible in any storms. The low north into
Virginia on Wednesday taking the deeper moisture and forcing with
it. This brings an end to precip chances for all but the NC
mountains where some lingering moisture and weak instability could
lead to isolated diurnal convection. The clouds and scattered
showers Tuesday will keep highs around 10 degrees below normal for
the NC Piedmont and northern foothills. Highs around 5 degrees below
normal expected elsewhere. Highs rise to within a few degrees below
normal Wednesday. Lows a few degrees below normal.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 145 AM EDT Monday: 00Z operational guidance is trending drier
for the medium rage. A short wave ridge slowly builds into the area
through Saturday. The ridge axis moves to the east on Sunday as
trough moves into the MS River valley. At the surface, weak high
pressure over the area Thursday and Friday is reinforced by high
pressure moving out of Canada into New England Saturday and Sunday.
There is a weak back door cold front associated with the reinforcing
high, however it remains dry and/or dissipates as it moves into the
area. The ridge of high pressure becomes squeezed by the end of the
period from the cold front associated with the trough to the west
and low pressure forming off shore along a baroclinic boundary but
remains strong enough to keep moisture and precip at bay. This 00Z
ECMWF has come in drier than the 12Z run trending toward the GFS and
Canadian. It does keep some precip over the area, especially the
mountains. Given the uncertainty have followed the guidance blend
which is weighted toward the older guidance with chance PoP over the
mountains and slight chance elsewhere Saturday and Sunday.
Obviously, confidence is low in this solution given the trends in
the guidance. Highs rise back to a few degrees above normal by
Friday then a few degrees below normal by Sunday. Lows near to
slightly above normal through the period.

&&

.AVIATION /12Z MONDAY THROUGH FRIDAY/...
At KCLT and elsewhere: VFR through the 12Z TAF period outside of
mountain valley fog and low stratus this morning and again tomorrow
morning. SCT to BKN cirrus hang around through the TAF period. Thus,
restrictions across the mountain valleys each morning are not
expected to be as bad as the last few mornings. Maintained a TEMPO
at KAVL for IFR restrictions through daybreak as the terminal could
still see fog and stratus develop through sunrise. Per usual,
mountain valley fog and low stratus will lift shortly after daybreak
each day. Winds at KAVL will generally remain calm through daybreak,
although winds may pick up out of the NNW briefly around sunrise.
Winds east of the mountains will also generally be calm through
daybreak, but could go light N/NNE at times. Winds at KAVL will
gradually turn SE/ESE later this morning before going calm to light
and VRB again this evening into tonight. Winds east of the mountains
will turn more NE after daybreak before toggling back N/NNE tonight.
Wind speeds will range from ~4-8 kts today. However, slightly
stronger winds will develop this afternoon/early evening at KCLT.
KCLT will see wind speeds from 7-10 kts and gusts from 15-18 kts,
with gusts diminishing ~00Z. Spotty showers should develop this
afternoon, lingering into tonight (mainly across the mountains).
Confidence on whether showers will track directly over any of the
terminals remains low so maintained dry TAFs for now. SCT cumulus
may develop this afternoon/early evening, especially where any
showers develop.

Outlook: Mountain valley fog and low stratus remain possible each
morning but could be limited somewhat by lingering cloud cover
through mid-week. Rain chances will stick around through mid-week
with periodic MVFR restrictions possible at times. Drier conditions
should return by Friday.

&&

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

&&

$$

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