870
FXUS62 KGSP 172327
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
727 PM EDT Tue Jun 17 2025

.SYNOPSIS...
Hot and humid with daily chances for mainly afternoon and
evening showers and thunderstorms through Thursday. A weak cold
front pushes across the area early Friday, bringing a reduction in
rain chances lasting through the weekend. Although humidity looks
lower this weekend, temperatures trend hotter through the beginning
of next week.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
As of 530 PM EDT Tuesday: A few showers and thunderstorms on radar,
but nothing severe at this time. Still expecting an increase in
storm activity in the western zones later this evening.

Meanwhile, PWAT values between 1.75"-2.00" and 2000-3000 J/kg SBCAPE
is prime for heavy rainfall and deep layer shear of 20-30 kts
supports multi-cellular convection this evening. A weak mid/upper-
level trough over the Deep South and TN/OH Valley will provide
slightly better forcing for ascent allowing for better coverage.
Widespread convective coverage over the Deep South will shift
eastward and may survive at least to the Upper Savannah Valley by
sunset. In this typical Summertime regime, can`t rule out an
excessive rainfall threat, but an uptick in 850-300mb mean winds
suggest that convection will ingest a fast enough storm motion to
preclude any hydro threat. Slightly more drier air in the mid-levels
in current profiles support an isolated damaging wind threat as well
with the strongest storms. With the expected dissipation overnight,
lingering convective debris and muggy conditions will prevail. This
could lead to the development of low stratus and fog once again,
especially near bodies of water and where the concentrated areas of
heavy rainfall. Overnight lows will run a category or so above
normal.

Mid/upper-level trough will gradually shift east with pre-frontal
energy entering the CFWA during peak heating Wednesday. Weak
anticyclone offshore the Southeast Coast will nudge into the region
and allow for slightly higher heights (1-2 dm) to build into
the region from the southeast. This will provide more drier air
in the mid-levels and could cap some of the convective coverage,
mainly east of the mountains. However, vort energy traversing over
the NC mountains/foothills with 20-30 kts of deep layer shear and
1500-2500 J/kg SBCAPE support another round of diurnal convection
with isolated strong to severe storms possible. Inverted-V
soundings suggests that DCAPE could end up higher compared to
today and increase the overall microburst threat. Either way,
gusts will pickup during peak heating Wednesday as the boundary
layer deepens and momentum transfer increases. Afternoon highs
will rise be a few ticks above normal for most locations.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
As of 100 PM Tue, key messages:

1. Enhanced convergence ahead of a cold front, as well as
strengthening winds aloft, should enhance shower/storm coverage
Thursday afternoon and evening and pose a damaging wind threat.

2. Behind the front, somewhat cooler in the northern CWA Friday, but
still seasonably warm throughout. Lower humidity.

3. Only isolated shower/storm coverage Friday afternoon.


Subtle height falls will begin early Thursday morning in advance of a
well defined upper trough, the axis of which will pass the CWA
Thursday night or early Friday. Cold front associated with the trough
looks to reach East TN by late afternoon Thursday. Deep layer
southwest flow should continue in the low to midlevels through the
day over our CWA. Moisture pooling preceding the front/trough however
is shown to bring PWATs back up a bit following their dip on
Wednesday. There is some spread in diurnal instability, notably the
GFS which may be depicting a stabilizing impact of outflows from the
previous day. Most sources depict CAPE at least as high as what they
depict for Wednesday, which makes sense. The presence of the trough
looks to result in increased shear, likely exceeding 25 kt over
basically the whole CWA and more than 30 kt in our north. This
increases the potential for storm organization. Marginal DCAPE and
sfc-midlevel delta-theta-e lapses are progged, promoting cold pool
development. No big surprise that the RRFS and 3km NAM depict
convective initiation early in the afternoon over the mountains,
growing upscale into semi-linear clusters which advancing east and
southeast thru the evening. PoPs reflect such timing. SPC featured
the NE CWA in a Slight Risk on the Day 3 outlook with Marginal in
other areas. Hot and humid again with heat index in the upper 90s in
areas southeast of I-85.  Cold outflow from the storms may
effectively move the front through the area, but if not the front
itself should cross Thu night.

Weak continental high pressure will spread into the area behind the
front. Drier air over the area Friday will bring dewpoints several
degrees lower compared to Thursday. Lower PWATs and less favorable
lapse rates aloft suggest much lower convective coverage. Isolated CI
is still possible in the over the mountains and lower Piedmont.
Temps will fall back slightly but remain above normal across our
northern tier, but similar if not slightly warmer in the southern
zones, compared to Thursday.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
As of 145 PM Tue, key messages:

1. Diurnal convective chances will remain lower than climatology
Saturday, but coverage will increase gradually each day thereafter.

2. Temperatures will trend warmer Saturday through Monday, a few
degrees above normal. Heat index may reach 100 in some areas Sunday
and Monday.

No significant change to thinking for the forecast over the weekend
into early next week. Sfc high from Friday will migrate to the East
Coast and upper anticyclone will develop over the inland East.
Ensembles suggest PWATs will remain around if not below climo. Lapse
rates are unsurprisingly not very good. Only isolated convection
thus is forecast over the ridgetops over the weekend, and also in
our far south where moisture remains best. Profiles are not as dry
aloft Monday so chance range PoPs return to the mountains then.
Followed previous cycle`s choice of going a bit below NBM for
dewpoints in the afternoons assuming some of the drier air aloft
will mix down. Temps still look to increase a bit each day as the
airmass modifies; despite the adjustment to dewpoints heat index
still rises to near 100 over a portion of our lower Piedmont Sunday
afternoon and over most areas near and southeast of I-85 on Monday.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
At KCLT and elsewhere: VFR conditions to start the TAF period with
TSRA expected to continue for a few hours. Keeping the TEMPOs at all
sites through 02z and expect it to decrease afterwards. A few low-
end gusts are possible with the storms and will keep it prevailing
at KHKY for now. Overnight, there still could be VCSH or VCTS, but
confidence is too low to prevail at this time. Low stratus doesn`t
look to be as widespread in the mountains by sunrise, though will
keep some MVFR restrictions in for now. May adjust later. For
tomorrow, TSRA coverage is not expected to be as widespread, so a
PROB30 for most sites. KCLT doesn`t look as favorable for TSRA at
this time. Low end gusts could pick up after daybreak at sites east
of the mountains. Winds also remain SW through the period.

Outlook: Showers and thunderstorms are expected each
afternoon/evening through Thursday. Drier conditions return behind a
cold front Friday into Saturday. Fog and/or low stratus will be
possible each morning.

&&

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

&&

$$

SYNOPSIS...DEO
NEAR TERM...CAC/CP
SHORT TERM...Wimberley
LONG TERM...Wimberley
AVIATION...CP