672
FXUS62 KGSP 281806
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
206 PM EDT Sat Jun 28 2025

.SYNOPSIS...
A typical summer pattern continues through the weekend and into
early next week with seasonable temperatures and daily chances for
afternoon and early evening thunderstorms, especially over the
mountains. A cold front approaches the area on Tuesday with
thunderstorm chances increasing area wide. Drier weather may return
late next week heading into the 4th of July holiday if the front is
able to push south of the area and allow drier air to settle across
the region.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 205 PM EDT Saturday: Convection ongoing across the mountains
and east of I-77 along a differential heating boundary. The air mass
is becoming very unstable with plenty of moisture while DCAPE values
are more subdued than the past few days. Still, there is enough
DCAPE and sfc delta theta-e for a damaging downburst on cells that
can become tall enough to entrain the available mid level dry air.
Little to no bulk shear will limit the chance of any organized
severe storms. PW values remain high with light S to SE steering
flow. This may allow cells to train or become anchored along S to SE
facing slopes, bringing a chance of excessive rainfall and possible
flooding. Latest guidance still shows best coverage across the
mountains but has better coverage than previously expected across
the rest of the area. Still, the western Upstate and NE GA will see
later onset as soundings show a weak cap that needs to be overcome
there. Guidance also suggests convection lingers later into the
evening but still dissipating near or shortly after midnight.

Expect another round of mountain valley fog when convective debris
dissipates. Can`t rule out patchy fog elsewhere. Lows near normal
mountains and a few degrees above normal elsewhere.

Although guidance is showing the air mass won`t be as unstable
Sunday, it will still be moderately unstable. PW values remain high
with even less mid level dry air leading to lower DCAPE and sfc
delta theta-e values. However, forcing will be enough for more
diurnal convection favoring the mountains and foothills with
scattered coverage elsewhere. Severe chance is lower but heavy rain
chance higher given the previously mentioned conditions. Training or
anchoring of cells will be possible once again. Highs will be near
normal across the mountains and a few degrees above normal
elsewhere.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
As of 1221 PM Saturday: The forecast continues tomorrow night with
broad Bermuda ridge extending across the Atlantic and into the
southeast coast. Farther upstream, a northern stream trough will be
swinging across the Canadian Prairies and Northern Plains. The trough
is progged to slide across the Midwest on Monday and across the
Great Lakes into New England on Tuesday. Weak deep-layer southwest
flow will keep a moist sub-tropical airmass entrenched across the
area with PWATs of 1.75-2". A persistence forecast seems likely on
Monday with scattered to numerous diurnally driven thunderstorms
with the greatest rain chances across the mountains. Outflow
boundaries pushing out of the mountains may initiate new scattered
convection mainly along and north of I-85 with generally isolated to
widely scattered coverage farther south/east. The forecast turns
wetter on Tuesday as the previously mentioned trough passes north of
the area and drags a cold front within the trough axis towards the
area. Deep moisture pooling ahead of the boundary along with a
slight uptick in flow/weak forcing will prove sufficient to
instigate numerous to widespread afternoon/early evening storms
across much of the area. Storms may loosely organize into
clusters/linear segments along composite cold pools. As with any
summer convection, a few strong to isolated severe storms cannot be
ruled out with the main threat being wet microbursts. The
environment won`t be overly conducive to damaging winds with poor
lapse rates, DCAPE, surface delta ThetaE and vertical totals - thus
any severe threat should remain fairly isolated.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 1232 PM Saturday: The latest suite of global model guidance is
in fairly good agreement that the frontal boundary will slide into
the area on Wednesday with another day of fairly high coverage of
diurnal thunderstorms. By Thursday, the boundary begins to push
south and east of the area with much lower ThetaE air arriving in
its wake. This would shunt the greatest rain chances south of the
area with a return to a mostly dry forecast. Depending on how far
south the boundary makes it, the forecast may remain dry through the
4th of July holiday weekend. Of course a few isolated showers/storms
can never be ruled out over the mountains even in a post-frontal
airmass. Should the boundary stall over or near the area, however,
the forecast would stay active through the holiday weekend. Current
model trends support the drier forecast, so will keep rain chances
in line with the national model blend with only isolated chances
being advertised.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
At KCLT and elsewhere: Convection ongoing across the mountains and a
differential heating boundary east of KCLT. Guidance still shows the
best coverage across the mountains but an uptick in coverage outside
of the mountains. Therefore, have kept the TEMPO at KAVL and
converted to TEMPOs at KCLT and KHKY. Kept it at PROB30 for the SC
sites but kept them in longer as guidance shows activity continuing
into the evening. Generally SW wind outside of the mountains with NW
at KAVL. Any storm will produce variably gusty winds. Should see
diminishing convective debris clouds overnight with mountain valley
fog developing. In theory, KAVL has a better chance of restrictions
but given the off and on nature of fog there, have gone with MVFR
for now. Cu develops again by noon Sunday with more diurnal
convection. Light SW wind expected for all but KAVL where NNW wind
develops.

Outlook: Daily chances for afternoon and evening showers and
thunderstorms into next week. Fog and/or low stratus possible
each morning in the usual mountain valleys as well as near lakes
and rivers.

&&

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

&&

$$

SYNOPSIS...TW
NEAR TERM...RWH
SHORT TERM...TW
LONG TERM...TW
AVIATION...RWH