584
FXUS62 KGSP 161800
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
200 PM EDT Wed Jul 16 2025

.SYNOPSIS...
Daily thunderstorm chances continue through the week and into the
weekend. A few storms could produce damaging wind gusts and
localized flash flooding. Hot and humid conditions stick around
through most of the forecast period.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 155 PM Wed: The region is situated along the western side of
the Bermuda high. The ridge axis that extends westward from
this anticyclone is tilted to the south with height, resulting
in weak wind profiles that are southerly near the surface and
veering out of the southwest in the low to mid levels and west-
southwest in the mid to upper levels.

The flow is currently light (under 15 kt) throughout the
troposphere, but the low-levels are forecast to strengthen to
15-20 kt by late this afternoon and peak at 25-30 kt tonight into
Thursday morning. Development of this low-level jet is in response
to a deepening low over the Great Lakes and its attendant cold
front extending southwestward along the Ohio Valley. This will
cause the pressure/geopotential height gradient to tighten on the
western periphery of the Bermuda ridge and upstream trough.

A moist air mass remains across the eastern seaboard with PWATs
around 1.9 inch according to the latest CIRA Total Blended
Precipitable Water (PWAT) imagery - this is around 25-35 percent
above climo for mid summer. The CIRA Advected Layered Precipitable
Water (ALPW) animation reveals modest moisture advection occurring
at all levels of the troposphere just to our south and east as
the return flow around the ridge taps into some of the tropical
moisture from the disturbance near the FL Panhandle. PWATs may
peak to near 2 inches later this afternoon as this moisture plume
reaches the Upstate.

Convective initiation had occurred a bit earlier than usual (mid to
late morning) owing to plenty of boundary-layer moisture, low LCLs
heights and easily attainable convective temperatures in the mid
80s. However, large-scale subsidence underneath the ridge should
limit the propensity (intensity, organization and to a lesser
extent the coverage) of showers and storms today as convective
updrafts have to overcome a capping inversion between 700-600 mb,
especially without the presence of deeper lift. Nonetheless, the
environment will be supportive of wet microbursts (surface-600 mb
theta-e differences of 20C) and locally heavy rainfall producers
(weak steering flow aloft, deep-warm cloud layer, and high-moisture
content) this afternoon and evening storms.

While convection should follow a diurnal trend and diminish
after sunset, there is a potential for a few showers and storms
to continue or develop through the night, especially along
southward- facing slopes in the NC mountains and along the Blue
Ridge Escarpment where upslope flow in concert with the low-level
jet will support it.

Coverage of showers and storms on Thursday should be a tick higher
than today in the mountain zones with a pre-frontal trough becoming
better defined over the central and southern Appalachians during
the afternoon. Hourly PoPs closely follow NBM guidance for Thursday
which seemed reasonable with chances ranging from 20-30 percent
across the Piedmont to 60-70 percent across the northern mountains.

The perpetual summer heat and humidity will continue. Heat indices
reach the 96-100F range in the Foothills and 99-103F range this
afternoon. Forecast peak heat indices for Thursday are 2-3 degrees
higher than today.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
As of 110 PM EDT Wednesday: Picking up on Thursday night, the
overall pattern remains relatively unchanged. The southeast is
locked into the typical summertime pattern with the Bermuda high
continuing to churn over the Atlantic and maintaining a steady
stream of moisture advection on its western fringe. expect daily
diurnally driven convection during the afternoons and evenings. The
mountains, as usual, have the higher chances (60-80%) and east
anywhere from 25-50%. Without much steering flow aloft, these pop-up
showers and thunderstorms are likely to move very slowly, causing
localized flooding risks. As for the temperatures, hot and humid
conditions continue. Surface winds become more easterly, providing a
steady moisture fetch from the Atlantic, raising dewpoints in parts
of the Upstate SC and NC Piedmont. This is also evident in the PWAT
guidance, nudging it over the 2.00 inch mark. All in all, these
factors could have a direct impact on heat index values well into
the triple digits. At this time, HI values of 100-104 are the most
likely, but there are a few areas with scattered 105+ possible each
day, especially in the more urban areas. Will continue to monitor.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
As of 120 AM EDT Wednesday: Cut and paste for the extended period as
the typical July pattern continues. Guidance keeps that Bermuda high
off the coastline and broad flow in place for the foreseeable
future. Looking into the weekend and next week, the general flow
starts to develop a weak trough in the upper NW CONUS, creating a
response downstream of height increases. Long term guidance starts
to build in a moderate ridge over the southeast, at least at the
500mb heights. Surface high pressure remains in tact with daily pop-
up convection over the mountains and east. Moisture stays put with
the more easterly surface winds persisting. Guidance also continues
to increase the PWATs with some areas, especially in the NC
Piedmont, seeping into the 2.00-2.10 inch range. This correlates to
even higher dewpoints and thus, pushes heat index values into the
triple digits. Monday at this point has the potential to be the
hottest with HI values over 105 in multiple areas. Heat Advisory
criteria will continue to be monitored. There is a hint of a surface
high off to the north toward the end of the period that could bring
in slightly cooler-ish temps with NE surface winds. But, this is
almost a week out and temps are still on track to remain hot
regardless.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
At KCLT and elsewhere: Scattered showers and isolated thunderstorms
have developed early this afternoon across the area.  This activity
so far has mainly been focused over the SC-NC Piedmont and another
in the western and northern NC mountains. Using current obs
(radar and satellite) and CAMs, the risk for showers and storms
is highest at CLT for the next couple of hours where a TEMPO was
added for the first few hours of the TAF. The bulk of this activity
may split the other TAF sites, but there is still an isolated risk
for a pop-up shower or storm in the vicinity through sunset. S-SW
winds will increase to around 10 kt through the remainder of the
afternoon with a few gusts between 15-18 kt possible through sunset.
Not expecting significant restrictions from fog or stratus tonight
except briefly at KAVL toward sunrise. Another round of showers and
storms are expected to develop during the late morning and early
afternoon Thursday. The highest coverage will be in the mountains.

Outlook: Thunderstorm chances each afternoon/evening. Low stratus
or fog are possible each morning in mountain/river valleys.

&&

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

&&

$$

SYNOPSIS...CP
NEAR TERM...JRK
SHORT TERM...CP
LONG TERM...CP
AVIATION...JRK