Severe Thunderstorm Warning 129, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
239 PM EDT Fri Jul 10 2026

.WHAT HAS CHANGED...
No major changes to overall forecast thinking. Temperatures could
trend cooler Saturday if decaying thunderstorms move over the
area in the morning as some models depict. Confidence on forecast
timing and trends Sunday-Tuesday has diminished slightly due to
a new trend in how a low pressure system may evolve.

&&

.KEY MESSAGES...
1. An active period of convective weather will continue into at
least Monday, with showers and thunderstorms still most likely
in the afternoons and evening, but also being possible at other
times each day, especially Sunday night. A few strong or severe
thunderstorms and isolated flash flooding are possible each day
through Monday.
2. Another hot day today, before a cooling trend sets in over
the weekend, with below normal temperatures forecast early next
week. If you have outdoor activity planned through Saturday,
make sure to stay hydrated and take frequent breaks to cool off
and avoid heat-related stress.

&&

.DISCUSSION...
Key message 1: An active period of convective weather will continue
into at least Monday, with showers and thunderstorms still most
likely in the afternoons and evening, but also being possible at
other times each day, especially Sunday night. A few strong or
severe thunderstorms and isolated flash flooding are possible each
day through Monday.

Broadly cyclonic upper-level flow is already in place across the
eastern US and will amplify over the weekend as ridge builds over
the Rockies and Plains. A well defined shortwave now over the
central Plains will advect southeastward tonight into Saturday
and possibly even partially cut off into an closed upper low over
KY/TN by Sunday.  This pattern, and abundant subtropical moisture
intially over our area, are expected to result in a period of
active weather lasting into Monday, with potential for heavy rain
and thunderstorms not necessarily on the diurnal trend typically
seen this time of year.

Convective complexes which developed Thursday night in the mid-MS
and lower OH valleys created weak upper disturbances or MCVs which
should advect toward NC this afternoon and evening. Seasonably
unstable conditions over our CWA should develop this afternoon,
with slightly more low-level shear than normal due to the westerly
flow aloft.  These conditions combined with the MCVs could result
in some loosely organized clusters of storms producing a damaging
wind threat this afternoon and early evening.

Last night's MCSs also left behind a cold pool which, in the face
of southwesterly flow around the Bermuda ridge, should effectively
place a warm front in place over KY/TN through tonight, and could
provide a focus for overnight covective development upstream. Cold
pool boundaries could remain from earlier convection in our CWA
as well.  As a result we will maintain 60-80% PoPs near the NC/TN
border tonight and at least a 15-30% PoPs east of the mountains
into the very early morning hours. A number of CAM runs also
develop another MCS this evening somewhere over the lower Ohio
Valley and the warm front would provide a route for such an MCS to
make a run at the Appalachians near daybreak Saturday. Thus such
development would appear to have more implications tomorrow, with
potential for a cold pool to stabilize parts of the area and/or
promote initiation of a new round of diurnal storms.

The amplifying trough will be associated with an east-west oriented
cold front, which should progress southward along the East Coast
in backdoor fashion and potentially will induce drier and cooler
weather circa Monday or Tuesday. While this still appears possible,
confidence has decreased somewhat on the cooling/drying due to
some guidance depicting the cutoff low developing to our west,
which suggests the front will stall near or north of the CWA. A
period of easterly low-level flow still is expected to develop
Sunday near the front, supplying Atlantic moisture, while the cloud
layer flow is likely to remain westerly. 60-90% PoPs are forecast
over most of the area then into Monday. Slow-moving or training
convection remains possible along the front and thus this still
looks like a period of greater concern for flash flood potential.
The upper low could however turn the mean flow more southerly,
which might result in the threat being more localized. PoPs do not
start to trend downward until Monday night, doing so from north
to south. The potential for a lingering upper low west of the
area hinders confidence Tuesday and beyond, but otherwise heights
should rise over the area as the upper ridge expands eastward,
and we would expect a return to more typical mountain-focused
convection each day.

Key message 2: Another hot day today, before a cooling trend sets
in over the weekend, with below normal temperatures forecast early
next week. If you have outdoor activity planned through Saturday,
make sure to stay hydrated and take frequent breaks to cool off
and avoid heat-related stress.

Temperatures are running above normal this afternoon with dewpoints
in the upper 60s to near 70 for the most part, resulting in heat
index reaching the low 100s in many spots. An isolated occurrence
of heat index over 105 is possible.

Outflows or cold pools associated with convection could offer
some relief for the heat this afternoon. There remains potential
for convective activity in the TN Valley late tonight or Saturday
morning, which could bring additional cold pools and/or a high
altitude cloud shield over the area. Based on partial thickness
values, heat potential is similar Saturday compared to today, though
enough models depict the cooling effects of convection impacting
temperatures Saturday that NBM values trend a little cooler and back
to about normal in most locations. Heat index accordingly will be
more comfortably below advisory criteria. A moist/cloudy pattern
is even more likely Sunday, but there is also the potential for
some cooler air to arrive with the backdoor cold front, so temps
trend slightly lower that day also. Temperatures are expected to
top out below normal Monday and Tuesday, with Monday still looking
like the coolest day with highs near 10 degrees below normal.

As noted, there is some uncertainty into the overall trend due to
the potential for a cutoff low to impede the progress of the upper
ridge from the central into eastern CONUS toward the middle of next
week, but the consensus remains that heights will trend upward
and the cooler post-frontal airmass will quickly modify. As such
temps trend back to normal Wed and even slightly above normal Thu.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: TEMPOs very early in the period at all sites
(except PROB30 at KAVL) with loosely organized clusters of SHRA/TSRA
scattered around the region. Lower MVFR vsby is mentioned but there
is potential for brief IFR. Some of the existing small clusters
could grow upscale into a larger line which would be associated with
more widespread or longer duration aviation impacts, so monitor for
AMDs. A shortwave trough remains over KY/TN and will drift eastward
into and across the terminal area later this afternoon/evening,
so there is potential for a second round of convection, except
perhaps where the first round consumes the available energy for
storms. This warranted a PROB30 this evening at all sites except
KAVL. SHRA appear more likely in this second round, except at KAND
which is nearest the track of a developing line of TSRA moving into
GA as of 1830z. Gusts of 25+ kt possible with any thunderstorms
this afternoon/evening. Aside from TS impacts, VFR is expected
through evening. Cannot rule out restrictive cigs/vsby forming
tonight where heavy rain falls in the late aftn or evening. Not yet
confident enough to make any mention of convection on Saturday,
except KAVL, which is most likely to see precip due to decaying
convection moving out of TN in the morning, prompting PROB30.

Outlook: Greater than normal coverage of SHRA/TSRA continues for
all terminals Saturday into Monday as multiple rounds of storms
move towards and across the area. Drier conditions should develop
Tuesday into Wednesday. Low stratus and/or fog will be possible
each morning in the mountain valleys and in locations that see
appreciable rainfall the previous afternoon/evening.

&&

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

&&

JCW