Area Forecast Discussion
Issued by NWS Greer, SC

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327
FXUS62 KGSP 171818
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
218 PM EDT Sun Aug 17 2025

.SYNOPSIS...
Rain chances through Tuesday are mainly confined to the
mountains. Hot and humid weather starts the week, but temperatures
trend cooler Tuesday, ending up near normal through Thursday. Rain
chances increase at the end of the week with temperatures a few
degrees below normal.

&&

.NEAR TERM /THROUGH MONDAY/...
As of 1245 PM Sunday: The deep convection appears to be a bit
delayed compared to the last few days, but satellite imagery
shows enhanced ridgetop cu, so a few showers should pop up
momentarily. The environment has 2000-3000 J/kg of sfc-based CAPE,
though that should drop a little bit into peak heating as the
dewpoints mix out a little bit. Still think the model blend is
undercooked with the possible extent of the deep convection today,
even more so after seeing the 12Z CAMs on the HREF page, so precip
probs were bumped up closer to climo across the mtns/foothills for
the afternoon. The area S of I-85 could see an isolated shower or
storm as well. The mid-levels are much drier today compared to the
past few weeks, so it might be tough for anything to really get
going because it will have to overcome the dry air entrainment,
but if it can, there`ll be enough dCAPE to allow for some strong
downdrafts and sfc wind gusts. Temp/dewpt trends appear to be
in decent shape, so no changes to the high temp fcst. The shower
activity should diminish with sunset.

Another quiet night is planned as the axis of a mid/upper
ridge extending from the anticyclone over the Plains shifts
northward. After we get rid of whatever convective debris clouds
we have floating around, we should be able to cool off enough
for another round of mtn valley low stratus and fog. Meanwhile, a
weak remnant cold front/outflow boundary will probably be hanging
out to our north overnight. That boundary may help out Monday to
increase the precip chances and coverage through the afternoon as
it settles down across the region, as the convective environment
looks otherwise nearly identical to today. The CAMs indicate
better coverage in the afternoon, so precip chances might end up
on the higher side of climo. Monday will probably be the warmest
day of the week with temps topping out a few degrees above normal,
but the heat index should stay just under advisory criteria.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
As of 200 PM EDT Sunday: Highs on Tuesday are expected to be
about 6-8 degrees lower than Monday, or slightly below-normal,
as transient high pressure moves off the New England coast and
weak, deep-layer NEly flow advects a modified maritime airmass
off the Atlantic.  This will support increasing PoPs area wide,
with high-end chance to likely PoPs currently progged across the
mountains Tuesday afternoon under weak upslope flow.  Instability
looks to be quite anemic for August as profiles look fairly warm,
resulting in poor lapse rates and SBCAPE values below 1000 J/kg.
Parcels may also have to contend with an inversion between
750-800mb; therefore, strong/severe storms are not a concern.
Despite very weak steering flow, limited instability will make
it difficult to realize the entirety of the 1.7-1.9" PW values
across the area and the excessive rainfall threat also appears to
be quite marginal.

By Wednesday morning, the forecast area will be sandwiched between
Hurricane Erin well off the Carolina coastline and an approaching
weak cold front over the Tennessee Valley.  The front is expected
to enter the mountains by Wednesday afternoon and should provide
enough low-level convergence to justify PoPs similar to Tuesday
across the mountains and foothills.  However, lapse rates are even
shallower than Tuesday given increasing temperatures throughout
the mid- and low-levels with a persistent low-level inversion
to further suppress instability.  Therefore, away from the front
across the Piedmont, PoPs decrease to slight chance.  PWs are also
lower given a subsident column on the fringes of Erin`s influence,
as evident by forecasted mid-levels drying.  As such, Wednesday
looks to be even less threatening in terms of a strong storm and
hydro threat.  Temperatures will be similar to Tuesday as the area
is still under the influence of a weak NEly flow, though decreased
cloud cover given the drier column supports highs perhaps a degree
or two warmer, or near normal for mid-August.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 200 PM EDT Sunday: General troughiness will dominate the
upper-level pattern over the southern Appalachians through the end
of the work week as Hurricane Erin thankfully recurves out into
the Atlantic and a sprawling anticyclone keeps the western US hot.
The weakness aloft will keep the area unsettled ahead of a potent
shortwave trough dropping into the upper Midwest by Friday.  A weak
warm front may also be draped across central GA into SC Thursday,
and guidance is suggesting isentropic lift north of the front will
work to enhance coverage of showers and storms.  Therefore, chance
(Piedmont) to likely (mountains) PoPs are forecasted on Thursday and
will continue into Friday within low-level southerly flow.  Unlike
earlier in the week, the column is a bit cooler.  The resultant
steeper lapse-rates will increase instability which may drive
more impressive rainfall rates within a persistently moist column.
Therefore, the better strong storm/excessive rainfall threat will
likely occur later in the work week.  The other main story will be
high temperatures, as the mostly cloudy skies and higher convective
coverage will suppress the diurnal range.  Expect highs to be a
couple of degrees below normal on Thursday and potentially 5-7
degrees below normal for Friday.

Heading into the weekend, shortwave propagation and amplification
around a deep upper-level low near James Bay will develop a
longwave trough over the eastern ConUS as an attendant cold front
approaches the area later Saturday from the northwest.  This pattern
supports a continued relatively cool and unsettled forecast for
the weekend with numerous to widespread showers and storms likely.
A continued excessive rainfall threat is likely through the end of
the period, especially given the near-term antecedent conditions.
Expect highs to be 7-9 degrees below normal on Saturday, with some
modest warming on Sunday if the timing of the next FroPa is indeed
post-daytime heating as the NBM suggests.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
At KCLT and elsewhere: Widely scattered showers and storms have
developed due to differential heating over the higher terrain early
this afternoon. Will include a PROB30 for thunderstorms over the
mtns and the Upstate based on radar trends and CAM output. The
storms should diminish at sunset. Any flight restrictions at those
places will be kept in the PROB group. Otherwise, prevailing
VFR. Meanwhile, at KCLT, there could be an occasional bkn VFR
ceiling through the afternoon. Wind will be light and variable
across the region, but will favor a northerly direction more than
anything else. After sunset, another quiet night with cirrus and
a light/variable wind. Expect another round of mtn valley low
stratus and fog, so KAVL gets the prevailing VFR/temporary IFR
around daybreak. Otherwise, the day should be very similar to
today. Will hold off with any mention of showers/storms for now.

Outlook: Afternoon showers and thunderstorms with associated
restrictions are expected mainly across the mtns Mon-Wed. Chances
currently fcst at all terminals Thu.  Morning fog and low stratus
are also possible, especially across the mountain valleys each day.

&&

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

&&

$$

SYNOPSIS...DEO
NEAR TERM...PM
SHORT TERM...JMP
LONG TERM...JMP
AVIATION...PM