837
FXUS62 KGSP 141326
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
926 AM EDT Wed May 14 2025

.SYNOPSIS...
Low pressure will move slowly northeast across the Ohio River
Valley to the Mid-Atlantic through tonight. This will result in
one more day of scattered to numerous showers and thunderstorms
across our region. Drier high pressure moves over our area Thursday,
followed by a weak cold front late Friday or Saturday. Above normal
temperatures will continue through the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 923 AM Wednesday: An early morning cluster of convection has
weakened as it continues to lift northeast across the I-77 corridor.
Here, showers will continue for another hour or two before all
precipitation shifts out of the area. The ongoing forecast captures
this well and no significant changes were needed. Morning low clouds
will also lift and scatter by early afternoon with a warm and humid
day as temperatures climb into the mid 70s to low 80s.

The aforementioned low pressure system is expected to continue
its northeastward trek today while the upper low opens up into
a negatively tilted wave over the Upper Ohio Valley/Mid-Atlantic
regions. The passage of the mid/upper trof axis is expected this
morning, and that will carry one batch of shower activity away to
the E/NE while weakening in the middle part of the day. Thereafter,
the CAMs suggest the bulk of the afternoon will be relatively
quiet, which makes some sense as the environment won`t be quite
so favorable in the wake of the upper wave. However, there is
good indications that we should be able to destabilize thru the
afternoon to the tune of 1500-2000 J/kg of sfc-based CAPE mainly
outside the mtns. Then, things might get interesting. Guidance
suggests that late in the afternoon into the evening the deep
layer shear across northeast GA into the western Upstate will climb
into the 30-40 kt range, which should be a sufficient to allow for
supercell thunderstorms. That is, if we manage to develop storms
at all. Note the 00Z CAMs are not particularly interested in
making anything more than widely scattered storms. That suggests
our severe weather potential is very conditional upon developing
enough of a storm to acquire supercell characteristics. If that can
happen, the Marginal Risk on the new Day 1 makes sense for wind
and hail. Something to keep an eye on. Otherwise, temps will be
back to normal. The convection might not exactly diminish in the
way we might normally expect, as there are indications that the
stronger NW flow might continue to organize storms upstream and
drive them southeastward into the early morning hours in a loosely
organized band that translates eastward over western NC. That
is still somewhat sketchy but also worth keeping track. The fcst
doesn`t really indicate that for the moment, so don`t be surprised
by a big increase in precip probs late tonight if the model trend
holds. Lows tonight will be mild once again.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY/...
As of 300 AM Wednesday: Relatively quieter weather expected Thursday
and Friday, as an upper ridge builds into the Southeast. The
ridging, combined with an elevated mixed layer (EML) in the profiles
will work to largely cap the atmosphere of deep convection. The
exception will be mainly in the northern NC mountains, which may
see some diurnal mountaintop activity Thursday aftn, which should
be sub-severe. Friday looks basically completely capped thru the
day, with NAM soundings showing over 100 J/kg of CINH with over
4000 J/kg of sbCAPE. The GFS has less CINH, but also a lot less
CAPE. Not surprisingly, the deterministic guidance has little to
no QPF response across the CWFA either day. Temps will continue a
warming trend, with highs about 5-8 deg above normal Thu and 8-12
deg above normal Friday.

There is still some hint that an organized cluster of storms or
a full-blown MCS may form and track into the OH/TN Valley late
Friday. It seems the models are trending a little slower with this
activity, with it not reaching the TN/NC border until after 06z
Sat. At that time of day, there may not be enough instability to
sustain the activity thru the mountains. However, depending on
the timing, they could be slow enough to either cross the area
during the day Saturday, or at least lay out an outflow boundary
that triggers storms in the CWFA Saturday. All that to say, the
PoP forecast for Friday night thru Saturday is a low confidence
forecast. Plenty of bulk shear will be in place, thanks to a passing
trough to our north. So severe storms may be possible. The new Day
3 Convective Outlook has a slight risk to our west, with a marginal
just to the TN/NC border. Temps will continue to be about 10 deg
above normal Saturday.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
As of 330 AM Wednesday...An upper trough will pass by to our north,
briefly flattening the Southeastern ridge. A weak cold front will
slip thru the area on Saturday, which depending on the timing,
may bring a round of showers and storms. But not all the guidance
agrees on that, with the GFS in particular, rather dry. In any case,
Sunday looks largely dry as high pres noses in from the north and
the frontal boundary stalls out just to our southwest. The medium
range guidance is not in great agreement on how far south the front
gets shunted, and may start to lift back into the area as early as
Sunday night. Despite the front`s close proximity, early next week
doesn`t look too active, as we will be in a NWLY flow regime with
a building upper ridge axis over the MS Valley. Temps are expected
to be slightly cooler than Friday and Saturday`s forecast highs,
but still above normal.

&&

.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
At KCLT and elsewhere: The main concern to start with is the blob of
showers moving east of KGSP and on track to reach KCLT by 12Z. For
the most part, the rain was falling out of high-based cloud deck,
but was intense enough to lower the vis to the MVFR range. The
restriction will be handled with a TEMPO. Otherwise, morning low
clouds should lift by mid morning. In the wake of shower activity,
guidance suggests the development of an MVFR cloud deck that
will persist thru the morning, reinforced by new convection that
develops with minimal daytime heating. Thereafter, it`s a matter
of when the next round of thunderstorms develops. A consensus has
formed that our next batch of storms will not be until after 20Z
or so. Either way, there should be a long break between the early
morning activity and the later day activity, during which the low
cloud ceiling should scatter out. Eventually, after the evening
activity dies off or moves northeast, VFR will return. Wind should
stay S to SW thru the period. What is less certain is the coverage
of convection late tonight, so this was left out altogether.

Outlook: In general, a summertime pattern is expected through
the end of the week with diurnally driven convective storms each
day. In addition, fog and low stratus will be possible each morning,
primarily in the mtn valleys and in areas that receive appreciable
rainfall the previous day.

&&

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

&&

$$

SYNOPSIS...ARK
NEAR TERM...PM/TW
SHORT TERM...ARK
LONG TERM...ARK
AVIATION...PM