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FXUS62 KGSP 192310
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
710 PM EDT Tue Aug 19 2025

.SYNOPSIS...
The chance of afternoon and evening showers and thunderstorms
slowly increases into the weekend. Temperatures start out near
normal then fall below normal for the weekend. Cooler and drier
conditions develop early next week after a cold front crosses our
region.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
As of 2:15 PM EDT Tuesday: A 1027 mb surface high was centered over
Quebec-New England. A cold- air damming (CAD) setup is evident in
the U-shape MSLP pattern and northeasterly winds on the eastern
side of the Appalachians. Low clouds have limited diurnal heating
across most of the region which has helped to curb the erosion of
the shallow CAD wedge so far today. Visible satellite imagery shows
clouds mixing out farther upstream across southern VA and central
NC, so expect breaks of sunshine to develop across the Piedmont in
the mid afternoon and eventually Foothills during the mid to late
afternoon. Hourly temperatures were modified to show a delayed,
but sharp rise once that occurs. The one exception to this is the
NC mountains where breaks have already occurred.

A few showers and thunderstorms have already developed early
this afternoon in the mountains along a differential heating
boundary (on the western flank of the low clouds) near the NC-TN
border. While coverage of showers and storms in the mountains are
generally expected to be scattered, this boundary will provide
an additional focus for convection over the central and southern
mountains of NC, and in the northeast GA mountains through early
this evening. The greatest coverage of showers (likely PoPs) and
storms are forecast to reside near this boundary, especially where
easterly flow provides orographic lift.

There are favorable ingredients in place for locally heavy rainfall
for the western NC and NE GA m,mountains, including very weak
steering flow under a weakness in the mid-level ridge and high
precipitable water (PWATs around 130-150 percent of climo for
the Southern Appalachians). CIRA Advected Layered PWAT (ALPW)
shows the source of locally higher PWATs across the southwestern
half of the CWA are from (1) the low-level (1000-850 mb layer)
marine air advecting inland and (2) mid-level (700-500 mb layer)
moisture in connection with a shortwave trough that is drifting
westward along the SC-NC border. This setup will produce storms
that are slow moving or even stationary (especially ones that are
tied to the terrain) and efficient rainfall producers (3 inch per
hour rates).  While the signal for an organized heavy rainfall
event isn`t particularly robust in the CAMs, the 12Z HREF 10 km
neighborhood probabilities of QPF > 2 inches are 30-40 percent
in the Smokies, Unicoi, and Nantahala Mountains. The max ensemble
(99th percentile) QPF from the HREF supports a worst-case scenario
of 3-5", but those amounts would be extremely isolated.

Unlike last night, showers and storms should generally wane
after sunset. The deeper moisture and forcing associated with the
aforementioned shortwave trough should sink to our south overnight,
which will make it unfavorable for more than a few showers to
persist overnight.

Expect stratus and mountain-valley fog to redevelop late tonight. As
we saw today, the low clouds tend to hold on longer into the
day than guidance indicates. However, the CAD wedge is expected
to erode by morning, it is likely that breaks in the clouds
on Wednesday develop earlier than today, especially across the
Piedmont where increasing subsidence on the periphery of Hurricane
Erin`s circulation arrives. Highs around 90F are forecast for the
NC Piedmont, NE GA, and the Upstate. Showers and storms will once
again be favored over the mountains during peak afternoon heating,
but coverage will likely be a bit lower than today.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
As of 1250 PM Tue: Erin moves away from the coast Thursday as weak
short wave energy drops across the area in the developing northerly
flow between Erin and a ridge centered over the 4 Corners region. A
ridge axis emanating from the western ridge briefly moves in on
Friday. Despite the fact that a weak surface front will have crossed
the area, moisture returns across the area Thursday and Friday
bringing a increase in PW values and instability. This brings a
return to scattered to numerous showers and thunderstorms both days
with coverage favoring the mountains on Thursday and locations west
of the I-77 corridor on Friday. A moist low level east to southeast
flow keeps the potential for scattered convection to continue
through Thursday night, outside of the usual diurnal time frame.
With the increase in PW and low level flow, storms may be slow
moving with the potential for anchoring or training cells. Should
this occur, heavy rainfall and flooding would be possible. Highs
Thursday will be near normal then drop to 5 to 10 degrees below
normal Friday. Lows will remain steady near normal.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
As of 120 PM Tue: The moist east to southeast low level flow remains
over the area Saturday as a wave of low pressure moves east along
the stalled frontal boundary (the front that moved through in the
Short Term) to our south. Convective coverage on Saturday will be
similar to Friday with good PW values and instability remaining in
place. Heavy rainfall and flood potential will also be similar to
Friday. Highs will be around 10 degrees below normal with lows near
normal.

The moist low level flow abates on Sunday as the wave of low
pressure and stalled front move south and east of the area, but a
cold front moving in from the NW keeps scattered to low end numerous
convection across the area Sunday. PW values drop limiting the heavy
rain potential. Highs around 5 degrees below normal with lows
slightly below normal.

Dry high pressure moves in for Monday and Tuesday bringing an end to
the wet conditions. Highs around 5 degrees below normal Monday drop
to around 10 degrees below normal for Tuesday. Lows up to 5 degrees
below normal Monday morning drop to 5 to 10 degrees below normal
Tuesday morning.

&&

.AVIATION /23Z TUESDAY THROUGH SUNDAY/...
At KCLT and elsewhere: Low stratus has finally scattered across much
of the area with only a few isolated observations of MVFR ceilings
remaining. A welcome return to VFR will persist through the rest of
the evening before things head downhill again tonight. Another batch
of low stratus is expected to develop with MVFR to IFR ceilings
common across the area. A few instances of LIFR ceilings cannot be
completely ruled out either. Patchy fog will also be possible at any
given terminal with the greatest confidence at KAVL where dense fog
could materialize. Fog may also make an appearance at KHKY. As with
today, morning stratus is once again expected to be slow to scatter
and lift with at least MVFR ceilings forecast to persist through
much of the morning with an eventual return to VFR by the afternoon.
Mountain afternoon thunderstorms look like a good bet with temporary
restrictions possible at KAVL. Coverage outside of the mountains is
less confident, but a chance for late afternoon/early evening storms
cannot be discounted at KHKY as well as the Upstate terminals
(KAND/KGMU/KGSP). Winds will be light through the period and mainly
out of the northwest, but variable at times.

Outlook: Widespread afternoon/early evening thunderstorms are likely
across the entire forecast area Thursday and Friday. Morning fog and
low stratus are also possible, especially in the mountain valleys
each day.

&&

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

&&

$$

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