259
FXUS62 KGSP 231519
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1119 AM EDT Sun Jun 23 2024

.SYNOPSIS...
Hot temperatures will linger through next week, with humidity
increasing east of the mountains starting Wednesday. A cold front
will track across the area overnight tonight into daybreak Monday
bringing a weak line of showers and isolated thunderstorms to the
area. Drier conditions return the rest of the day Monday, lingering
into the first half of Wednesday. Another cold front will push
across the area Wednesday night into Thursday, potentially bringing
better shower and thunderstorm chances to the area mid to late week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1045 AM Sunday: Satellite imagery shows a band of higher-level
clouds moving over the mtns/foothills...messing with the low cloud
development...but that should only be a temporary delay. The SPC
mesoanalysis shows that sfc-based CAPE has reached 1000-1500 J/kg
as of late morning...not terribly impressive but not nothing and
we are uncapped at the moment...but there remains some indications
that we should mix out a bit in the afternoon and keep the buoyancy
modest. Meanwhile, we lack a trigger other than differential
heating. The HRRR and some other CAMs are not interested in
developing convection this afternoon across the region, while the
latest NAM Nest looks overdone with its depiction of a line of
showers/storms east of the mtns this afternoon. Think the latter
model is overly-optimistic (as usual) with its dewpoints and thus
its amount of CAPE. So, the precip probs will not be changed much
from their currently low slight chances mainly over NC thru early
evening, and we still prefer to ramp up the precip probs in the
tonight period as some forcing arrives in the form of a short wave
vort lobe that drops in from the WNW. Note the sfc reflection of
this appears not to be the band of showers moving southeast from the
OH River at this hour. The guidance weakens this feature somewhat
thru afternoon, and develops a new band of broken showers/storms
that comes over the mtns after dark. For the high temps today,
think the fcst is in good shape, so no changes and no Heat Advisory.

Otherwise...between an upper anticyclone centered over Texas,
and an upper low off the Carolina/Georgia coast, we remain in
a relatively neutral pattern without much forcing, but also
with less suppression. A few runs of the CAMs depict convective
activity continuing to propagate east after 00Z, by which time
height falls may work their magic; PoPs thus continue and in some
cases increase then. The trough also will bring a weak cold front
across the Appalachians overnight, which will bring the best overall
chance of the period for the NC mountains and GA/SC Piedmont, but
still no better than scattered coverage. Low clouds will develop
along the front in the NC mountains but should begin to diminish
by morning; high level clouds will be seen over the Piedmont.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
Key Messages:

1) Humidity has Trended Down Monday into Tuesday

2) Mostly Dry Conditions are now Expected Monday into Tuesday

As of 230 AM EDT Sunday...The last few forecast cycles it was
looking like most areas along the I-77 corridor and in the Upper
Savannah River Valley would flirt with Heat Advisory criteria,
especially on Monday afternoon, but that is no longer the case.
Guidance has just started depicting much lower dew points (and thus
lower humidity) filtering into the region behind a departing cold
front to kick-off the workweek. While there`s still the potential
for portions of northeast Georgia and the far western SC Upstate to
still see heat indices climb into the lower 100s Monday afternoon,
it`s looking less likely that these areas will flirt with Heat
Advisory Criteria (which starts at a heat index of 105 degrees).
Heat indices on Tuesday are expected to be lower than Monday`s,
generally remaining below 100 degrees. All things considered, this
is a good trend to have. The downside to this drier airmass is that
precipitation chances have lowered quite significantly. Mostly dry
conditions are now expected on Monday thanks to guidance showing a
much faster FROPA (front should be south of the area by daybreak
Monday). However, a few isolated showers, or perhaps even a
thunderstorm, may be able to eke out behind the front on Monday but
there`s low confidence on this due to the dry air behind the front.
Dry high pressure will filter into the region throughout Monday,
lingering through Tuesday night leading to dry weather across the
board. High temperatures are still expected to climb into the lower
to mid 90s each afternoon east of the mountains, remaining around 5-
8 degrees above climo. Lows each night should end up around 2-5
degrees above climo.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Key Messages:

1) Humidity Increases East of the Mountains Starting Wednesday and
May Linger through the Remainder of the Long Term

2) Another Cold Front Tracks Across the Area Overnight Wednesday
into Thursday, Potentially Bringing Better Coverage of Showers and
Thunderstorms

3) Shower and Thunderstorm Chances May Linger through Rest of the
Long Term but Confidence is Low

As of 300 AM EDT Sunday...A cold front will track out of the Midwest
throughout Wednesday before tracking across the western Carolinas
overnight Wednesday into Thursday. Dry conditions are expected to
continue through at least the first half of Wednesday before shower
and thunderstorm chances return the second half of Wednesday ahead
of the main FROPA. Capped PoPs chance (below 50%) area-wide
Wednesday into Thursday as global models are still not in agreement
regarding the coverage or timing of convection. Humidity will
increase on Wednesday ahead of the front, allowing heat indices to
climb into the upper 90s and lower 100s east of the mountains. The I-
77 corridor and the Upper Savannah River Valley should see the
highest heat indices on Wednesday, with a isolated areas potentially
flirting with Heat Advisory Criteria (which starts at a heat index of
105 degrees). However, most locations should remain below Heat
Advisory Criteria on Wednesday. Temps on Wednesday should climb into
the mid 90s east of the mountains and the lower 90s in the mountain
valleys. This should lead to Highs around 8-10 degrees above climo
Wednesday afternoon. However, highs could end up a few degrees lower
depending on the timing of convection Wednesday afternoon. Lows
Wednesday night will end up around 6-9 degrees above climo thanks to
increasing cloud cover and convective chances. Highs on Thursday
should end up a few degrees cooler, but are still expected to reach
into the lower to mid 90s east of the mountains. Humidity looks to
linger on Thursday (for now) despite the FROPA. Thus, heat indices
may once again climb into the upper 90s/lower 100s across portions
of the I-77 corridor and the Upper Savannah River Valley. Lows
Thursday night should remain around 6-9 degrees above climo.

The cold front will stall along the Carolina Coast Friday into
Saturday while a sfc high tracks north of the Carolinas. Global
guidance continues to show some lingering convection Friday into
Saturday so went with low-end chance PoPs (35% or less) area-wide
the second half of the long term. Highs should rebound into the
lower to mid 90s east of the mountains both days, remaining around 5-
7 degrees above climo. Humidity may linger heading into the weekend
as well, so heat indices may climb back into the upper 90s/lower
100s each afternoon, mainly across portions of the I-77 corridor and
the Upper Savannah River Valley. Lows each night should remain
around 6-9 degrees above climo.

&&

.AVIATION /15Z SUNDAY THROUGH THURSDAY/...
At KCLT and elsewhere: Breezy SW winds today in general. Weak
low-level convergence has produced some VFR stratocu in spots,
with low MVFR to IFR cigs creeping north from the SC Midlands
within maritime air. TEMPO at KCLT retained for these lower
clouds. Some instability will develop again today with profiles
similar in nature to the previous two days; again forcing will
be very weak and profiles dry aloft, so expect no better than
very isolated coverage of SHRA this aftn. Felt this warranted
VCSH at KCLT and KHKY begining in late aftn. Weak cold front
will reach the mountains this evening and could instigate a few
SHRA in that area tonight. Hence a late VCSH is also assigned to
KAVL. The front should promote slight drying tonight, suggesting
less threat of daybreak fog/stratus in the Piedmont. However
KAVL may see occasional MVFR cigs via upslope clouds or debris
following any showers. and support veering winds, such that KAVL
flips to NW in the middle of the night and KCLT by around 12z Mon.
VFR cu will develop diurnally late Mon morning.

Outlook: Drying trend now expected to continue Mon-Tue with little
to no diurnal convection those afternoons. Summertime humidity
returns Wed-Thu with SHRA/TSRA chances also returning.

&&

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

&&

$$

SYNOPSIS...AR
NEAR TERM...PM/Wimberley
SHORT TERM...AR
LONG TERM...AR
AVIATION...Wimberley