Simpsonville, South Carolina 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

078
FXUS62 KGSP 260721
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
321 AM EDT Sun Jul 26 2026

.WHAT HAS CHANGED...
No major changes to overall thinking.

&&

.KEY MESSAGES...
1. The severe threat remains low through Monday before increasing
ahead of a cold front Tuesday afternoon and evening, possibly
lingering into Wednesday. A warming trend is expected through
Tuesday, with slightly cooler highs and lower humidity Wednesday
into next weekend.

&&

.DISCUSSION...
Key message 1: The severe threat remains low through Monday before
increasing ahead of a cold front Tuesday afternoon and evening,
possibly lingering into Wednesday. A warming trend is expected
through Tuesday, with slightly cooler highs and lower humidity
Wednesday into next weekend.

Surface front looks to be oriented NW-SE across the CWA early this
morning, extending upstream into the lower Ohio Valley. Aloft,
a full-latitude trough is in place over the Eastern Seaboard and
Great Lakes, with a deep, broad upper anticyclone situated over
the Rockies/Plains. This pattern will leave us in a persistent NW
flow regime aloft through the first half of the week, and multiple
subtle embedded shortwaves or ripples of vorticity are expected to
dive through the trough and over the southern Appalachian region,
potentially enhancing the development of convection, some of which
may be nondiurnal in nature.

Today and Monday, forcing is rather ill-defined overall; drier air
will gradually filter into the area and should push the frontal
zone southward. Ridgetop convergence, and/or a lee trough at the
surface, potentially will fire a few storms this afternoon even if
the shortwaves aloft aren`t a factor, so we retain 20-40% PoPs over
much of the area downstream of the Blue Ridge Escarpment. 0-6km
shear will be high for this time of year, 30-40 kt, with 0-3km
shear 15-25 kt. Any storms that do fire may form into clusters,
and if so they could pose a risk of damaging wind. The 00z NAM
develops convection over the area after sunset which could be
partially due to one of the embedded ripples aloft, but confidence
is low on where that might happen if at all. The continued drying
leaves behind dry and slightly capped profiles in place for Monday,
which results in only 10-20% PoPs at best. Shear parameters will be
similar but the severe threat during the afternoon would appear to
be lower on account of lower instability. A few models have been
hinting at a possible MCV or cold pool arriving Monday night from
an upstream MCS, but even if that were to occur it would appear
unlikely to survive over the Appalachians with the unfavorable
thermodynamic profiles. SPC does hint at the possibility of an MCS
reaching the far northern or western portions of the CWA before
falling apart, by including those areas in a marginal risk on Day
2. Currently can`t advocate for any more of the CWA being included
than those areas.

A better defined shortwave will rotate into the trough on Tuesday
and will bring a cold front southward toward our area. Assuming we
are not still stabilized by a cold pool or debris cloudiness from
Monday night, our MCS potential still looks greatest late Tuesday
into Tuesday night: WAA ahead of the front should promote warmer
daytime temps and deeper mixing which should overcome the cap,
so we will see instability return to values more typical of a
hot July afternoon, still with favorable shear and sfc-midlevel
delta-theta-e values suggesting easy cold pool formation ahead of
the front. Timing of the front suggests convective/severe threat
could be greatest after peak heating, well into Tuesday night
particularly in the southern CWA. Confidence is still limited partly
due to not knowing how any cold pool from Monday night come into
play. Day 3 outlook is not out as of this writing, but based on
yesterday`s Day 4, we are likely to be included in a marginal or
slight risk for Tue/Tue night. Temps Tuesday will be the warmest
of the week, mostly in the lower to mid 90s across the Piedmont;
heat index is likely to exceed 100 and may reach 105 in the urban
areas in the I-85 corridor or southeast.

Temps trend back to near or slightly below normal Wed-Sat in the
wake of the front, but perhaps of more interest humidity should
be much lower with dewpoints falling into the lower 60s each
afternoon. The ridge-trough pattern across the CONUS does not
break down, however. The front will stall north of the Gulf Coast
and potentially will be reactivated by the next shortwave or low
diving past the anticyclone. A few diurnal showers/storms appear
possible by Friday with chance PoPs for all areas on Saturday with
the activating front.

&&

.AVIATION /07Z SUNDAY THROUGH THURSDAY/...
At KCLT and elsewhere: Broad area of low VFR to MVFR stratus extends
along a stalled front over the Carolinas early this morning. A
few SHRA/TSRA will be possible beneath this cloud deck. Northwest
downslope flow over the Appalachians has led to some breaks in the
deck at times; thinking is that where the stratus scatters, with
light winds and lack of higher cloud decks areas of LIFR stratus
and/or fog could form. Confidence is limited on where this may occur
so TEMPOs were used near daybreak for that possibility and/or for
vsby restrictions in precip. Restrictive cigs are expected to linger
through late morning before scattering. With warmer temperatures
returning spotty development of diurnal SHRA/TSRA this afternoon
warranted inclusion of a PROB30 at all sites except KAVL, which
only receives a VCSH due to storms being more likely to form to
the east or southeast and propagate away from the terminal. Low
confidence for timing/placement of restrictions tonight/early Mon
though sfc will remain moist and cloud cover expected to be SCT
at best. Will be evaluating that more closely for 12z issuance.

Outlook: Only isolated TSRA expected Monday
afternoon/evening. Strong to severe thunderstorms, as well as,
breezy SW winds are possible Tuesday afternoon/evening ahead of
a cold front. The severe storm threat could linger into early
Wednesday, but confidence is low at this time. Low stratus and/or
fog will be possible each morning, mainly in the mtn valleys.

&&

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

&&

$$

JCW