921
FXUS62 KGSP 151327
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
927 AM EDT Thu May 15 2025

.SYNOPSIS...
Warm high pressure settles over our area today through Friday. A
cold front will approach from the northwest and may bring a line
of showers and storms into the NC mountains late Friday night
into early Saturday. The front will push through to our south and
stall over the weekend, ushering in slightly cooler, but still
above-normal temperatures into early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 924 AM Thursday: Latest satellite observations depict
continued erosion of locally dense fog along and north of the I-40
corridor from Marion to Mocksville. The area of dense fog will
shrink as the edges mix out with daytime heating with all fog
expected to be gone within the next hour or so. Otherwise, the
remainder of the forecast remains on track and no substantial
changes were needed.

Now that we finally have the old mid/upper trof well to our
northeast today, we should enjoy an amplifying upper ridge
building in from the west with sfc high pressure building up from
the south. The main story will most likely be warmer temps...some
five degrees warmer than yesterday...and feeling summerlike because
of all the humidity that will be in the air from evaporation off
the wet ground we have in most places. Most of the region will be
effectively capped off from deep convection this afternoon/evening,
including northeast GA/Upstate SC/central and southern mtns
of NC. In theory, that would also include the rest of the fcst
area, but there looks like some sneaky potential to break the
cap along/N of I-40 into the NW Piedmont as it will probably be
weaker there. Certainly that potential is much greater farther to
the northeast into the RNK/RAH fcst areas, and the plan is for
the building ridge to nudge the cap farther north and keep the
storms out of the GSP forecast area, but we will have to keep an
eye out for it. The potential will certainly wane with the loss of
heating, and after sunset we will keep an eye out to the west. As
the upper ridge axis moves overhead late tonight, there will be
an avenue by which upstream convection could reach the mtns after
midnight. However, the CAMS for the most part kill it off before
reaching the mtns and leave us only with some scattered remnant
showers. Overnight low temps will be warm.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 330 PM Wednesday, key messages:

1. Friday still looks largely capped, but some guidance hints at
one or two storms developing in the northern part of the CWA in
what is a very concerning environment for severe weather.

2. Organized convection will likely develop in the lower OH or TN
valleys Friday, and could track into or across the Appalachians
at some point between Friday evening and Saturday morning.

3. Muggy Friday with temperatures about 10 above normal.  A little
cooler and less humid Saturday but still above normal.

Height falls aloft expected from the Mid-MS Valley to the Carolinas,
as a potent upper low tracks east across the Great Lakes. The
associated sfc low will be occluded, but with an active cold
front extending south across the Midwest. Forecast soundings show a
pronounced elevated mixed layer (EML) atop the forecast area Friday,
with steep lapse rates resulting 3000+ J/kg of sbCAPE by early
aftn. There will also be 0-6km shear 50-60 kt. This is concerning
for any convection that can break the capping inversion caused
by the EML. Some of the CAMs now go thru 00z Sat, and show a few
isolated supercells popping along/near the Blue Ridge escarpment
roughly along or north of I-40 in the aftn. These depicted cells
manage to track east across the Northwest NC Piedmont. If this
happens, these storms could produce very large hail and damaging
wind gusts. With that said, a lot of guidance still keeps our
entire CWA capped. Will introduce some slight chc to low-end chc
PoPs along/north of I-40. The other story Friday will be the muggy
conditions. Despite dewpts mixing out into the 60s, highs in the
upper 80s to around 90 will feel more like the low to mid 90s across
most of the Piedmont. Highs overall about 8-12 deg above normal.

Friday night, the NAMnest and High-Res FV3 go thru this period
and show strong convection upstream of the forecast area going
upscale and entering the NC mountains as a pretty solid line of
convection before 12z Saturday. The activity will likely be on
a weakening trend. But the environment may support damaging wind
gusts as the line first enters the mountains from TN. The new Day
2 SPC convective outlook only has a marginal risk right along the
border. But I wouldn`t be surprise if later outlooks bring the
marginal or even slight further east into the area. The convection
still only has a 20-30% chance of surviving across the mountains
to the Piedmont per latest consensus PoPs. This is mainly due to
lingering CIN from the EML, and the early morning hour minimum in
MUCAPE. Even if the line completely falls apart, an outflow/wind
shift looks to push thru the southeast edge of the forecast area
by early Saturday aftn. If for some reason the line is slower,
it could tap into some diurnal instability before completely
exiting the forecast area. With the uncertainty in the timing of
the potential line of convection, will keep PoPs in the slight chc
to low-end chc range east of the mountains Saturday. The new Day
3 convective outlook has the entire CWA in a marginal risk, with
a slight risk just to our east. The passing cold front will also
result in deeper mixing and breezy conditions Saturday aftn. Temps
will remain around 10 deg above normal, with downslope flow helping
offset any cooling from the front.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 300 AM Thursday...An upper ridge will amplify across the
lower and mid-MS Valley Sunday thru Tuesday, with the axis drifting
east to the OH/TN Valley, then crossing to our east Wednesday. A
sfc front will stall out across the Southeast, oriented roughly
from the Central Plains east to the I-20 corridor of AL/GA. The
latest guidance still suggests it will be far enough south to
allow Sunday to be a dry day. But from there, the front begins to
activate as a warm front and nudge northward. This may place the
forecast area within an MCS track for Monday and/or Tuesday. But
the deterministic guidance does not show strong instability over
the area. So any convection that tracks toward us may struggle to
maintain intensity. The best chances will be in the NC mountains,
with a west-northwesterly downslope flow largely capping the
atmosphere east of the mountains. A deep and well-organized low
pressure system may form in the Midwest Wednesday, and bring a
chance of showers and storms to the forecast area. The environment
may even support a severe weather threat. Temps will be slightly
above normal thru the medium range.

&&

.AVIATION /14Z THURSDAY THROUGH MONDAY/...
At KCLT and elsewhere: VLIFR vis has developed around KHKY early
this morning so that is our trouble spot. Now that the sun is up,
the vis should improve by 9 am or thereabouts. Otherwise, fog
restrictions are noted around metro Charlotte but not at KCLT,
and given their greater dewpt depression, think KCLT will stay
VFR and out of the fog. Once that`s out of the way, today looks
relatively quiet as the old upper low/trof has finally moved away
and a warm layer aloft keeps a lid on the deep convection. Wind
will come up from the SW and could be occasionally gusty in the
afternoon. We should lose the gusts and any low clouds at dusk,
after which we watch the radar for upstream convection making a
run at the mtns early Friday morning.

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