492
FXUS62 KGSP 181855
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
255 PM EDT Fri Sep 18 2026

.WHAT HAS CHANGED...
Minor changes to precip chances this weekend and temperatures
during the middle of next week.

&&

.KEY MESSAGES...
1. A cold front dropping down slowly from the north may trigger
a few severe thunderstorms during the afternoon and evening,
and again over the western half of the forecast area on Saturday
afternoon and evening. Otherwise, this afternoon should be the
last really hot day for the next week.
2. A shift in the upper pattern will finally bring some cool
weather right on schedule for the start of autumn.

&&

.DISCUSSION...
Key message 1: A cold front dropping down slowly from the north
may trigger a few severe thunderstorms during the afternoon and
evening, and again over the western half of the forecast area on
Saturday afternoon and evening. Otherwise, this afternoon should
be the last really hot day for the next week.

One last hot summer afternoon courtesy of a lingering upper
ridge, meanwhile a cold front should approaching slowly from the
north. Before showers and thunderstorms fire later this afternoon,
temps will reach well into the 90s outside the mtns with heat
index climbing into the lower 100s over much of the Piedmont and
Upstate. However, the extent of heat index getting close to 105
remains small and short-lived.A Heat Advisory is not planned, but
take the usual heat-related precautions just the same one last time
(hopefully) for the season, which ends in a few days anyway.

About those storms...radar/satellite imagery shows scattered to
numerous showers and storms developing to the south of an old
outflow boundary from early morning storms over eastern KY and
southern WV. Most of the CAMs redevelop convection and drop it
southward over the western Piedmont through the afternoon, though
the timing varies by several hours amongst the ensemble members. The
earlier members appear to be on the right track. The environment is
expected to maintain a sfc-based CAPE of 2000-2500 J/kg, but with
generally weak shear of 20kt or less. At face value that doesn`t
seem to support much severity, but the potential organization
along an outflow makes the Marginal Risk on the SPC Day 1 Outlook
warranted, particularly with the dCAPE being above 800 J/kg. The
I-77 corridor might have the best chance for severe storms because
of having the best chance for cold pool organization. Damaging
wind gusts will be the main threat.

The cold front should be located somewhere draped across the
forecast area on Saturday, making the temp fcst tricky with a
gradient between lingering heat and lower-90s over the Lakelands
(potentially) and a cooler northeasterly flow and low/mid 80s
over the NW Piedmont. More storms are likely to develop in the
afternoon along/ahead of this boundary as it continues to ooze
south and southwest through Saturday evening. The Day 2 Outlook
shows another Marginal Risk for the western zones and the convective
environment might be better than today. People with outdoor plans
over the mountains, northeast GA, and the western Upstate should
keep an eye out storms.

The rest of the weekend and into Monday still look unsettled with
better coverage of showers and storms. We will no longer have the
suppressive influence of the upper ridge and moisture will increase
with a weak upper low over the northeast Gulf. By this time, what
small threat for severe weather will switch to excessive rain given
the deeper moisture. A marginal risk is noted on the excessive
rainfall outlooks starting Monday. Temps will fall back to normal.


Key message 2: A shift in the upper pattern will finally bring some
cool weather right on schedule for the start of autumn.

Forecast uncertainty increases once we get into the first half of
next week and the upper pattern becomes blocky, particularly over
eastern North America. It might not look especially coherent,
but it also doesn`t look much like summer any longer, which is
appropriate given the date. The operational models indicate a rex
block pattern over the Great Lakes and Ontario starting on Tuesday
and continuing into Wednesday, before evolving into the more typical
omega pattern by the end of the week. If this pattern develops as
shown, a corresponding cold frontal passage Tuesday night or early
Wednesday would usher in the first cool air mass right on schedule
for the start of autumn, with temps dropping to 5-10 degrees on the
cool side of normal for a change on Wednesday. The change would be
remarkable. Either way, Wednesday looks cool with extensive cloud
cover and precip chances. For the rest of the week, we woud remain
in the cool side of the pattern with a slow modification of the air
mass. Drier air would limit precip chances to the higher terrain.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: Prevailing VFR through this evening, but
with a chance of thunderstorms across most of the forecast area at
some point later this afternoon and early this evening. The CAM
guidance has been all over the clock with the timing of onset,
so a compromise was selected, followed by a four hour window for
restrictions. Confidence is highest over the western Piedmont of NC,
closer to the trigger which is an outflow from old convection to
the north, so KHKY and KCLT got the TEMPO and other terminals were
kept at a PROB30. A boundary will move into the area late tonight,
and the easterly flow behind the boundary will bring a good chance
for a low cloud ceiling restriction developing in the pre-dawn
hours at least over the NC terminals, and fog over the mtns. By
that time, wind should come around more northeasterly. Confidence
is low in precip, other than afternoon showers and storms again,
but beyond the valid time for all but KCLT.

Outlook: Shower and thunderstorm chances continue each afternoon
through Tuesday. Mountain valley fog and low stratus possible
each morning.

&&

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

&&

$$

PM