267
FXUS62 KGSP 131800
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
200 PM EDT Tue Aug 13 2024

.SYNOPSIS...
Dry high pressure gradually builds in from the north through
Thursday, pushing a stalled front further south of the area. The
high will drift east off the East Coast Friday, as a cold front
approaches from the west over the weekend. The front will bring a
return of better chances of shower and thunderstorms through Sunday,
then lower chances early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...

...Key Messages...

1) Isolated Strong to Severe Storms Possible this Afternoon and
Early Evening, mainly across the Upstate and northeast Georgia

2) Heavy rain and localized flooding possible in a few locations
over the Upstate and northeast Georgia

3) Cooler Temperatures over the foothills and western Piedmont of NC

As of 130 PM EDT Tuesday: A few more changes for the afternoon,
as radar and satellite imagery suggest an almost-weak-wedgelike
scenario for the rest of the daylight hours. One boundary lies
across the lower Piedmont/Lakelands, where mesoanalysis indicates
pooled moisture has allowed for sfc-based CAPE on the order of
1500-2500 J/kg. The dCAPE is also modest in that same area in
northeast Georgia, with values almost high enough to support strong
downdrafts and outflows. Thus, a non-zero severe thunderstorm
threat, with damaging wind gusts the main concern. Another
boundary was noted in the satellite imagery, slowly sagging south
across the northern part of the Upstate. Along and south of this
boundary, we might have an outside chance at some heavy rain
and localized flooding, as we retain a very moist air mass that
has precipitable water approaching two inches. The orientation
of the boundary looks favorable for storms to move/train W-to-E,
thus the small threat.  We`ll keep our eyes on that. As for temps,
a large area of rain-cooled air covered by low stratus/stratocu has
temps trapped well down into the 70s over NC east of the mtns. So,
it looks like it is time to cut back on the high temp forecast as
the trends suggest the clouds will not thin quick enough to save
the high temp forecast.

Otherwise, upper troughing will remain over the Carolinas through
the near term while periodic shortwaves track over the region
from the northwest. Meanwhile at the sfc, the southern periphery
of surface high pressure centered over the Great Lakes region
will extend into the Carolinas while a front stalls over the
Southeast. This will lead to a more convectively active day compared
to yesterday. Although deep layer shear will range from 35-45 kts,
lapse rates look relatively poor and the sfc-based CAPE might make
it to around 1500 J/kg during peak heating. Damaging wind gusts
will be the main concern with any severe storms that develop. The
excessive rainfall threat will remain isolated with higher shear
values in place allowing for faster storm motion. However, flash
flood guidance continues to be on the low side (mainly across the
eastern two-thirds of the CWA) due to the rainfall from Debby
last week and the recent rainfall over the weekend. Convection
should gradually end from west to east this evening, with drier
conditions moving in tonight. Lows tonight will end up near climo
to a few degrees above climo. Patchy fog may develop across the
NC mountains and Foothills overnight into daybreak Wednesday.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
As of 145 AM EDT Tuesday: The short term looks fairly quiet, as the
axis of a deep upper trough will swing east off the East Coast,
and upper ridging builds in from the Lower Mississippi Valley
Wednesday thru Thursday. At the sfc, dry air will filter in from
the north, limiting instability. A light easterly or southeasterly
low-level flow may be enough to force a few isolated showers and
perhaps a garden-variety tstm or two Wednesday and Thursday aftns
in the mountains, but otherwise, it should be partly cloudy with
temps slightly below normal. Highs in the mountain valleys and
Piedmont will be mainly in the low to mid 80s and lows in the mid
to upper 60s.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
As of 230 AM Tuesday...The medium range guidance is in good
agreement on a vigorous shortwave diving thru the western Great
Lakes Friday, carving out a fairly deep upper trough across the
Ohio Valley Saturday, then persisting as a long wave trough across
the eastern CONUS into early next week. An associated low pressure
system will bring a cold front into the Ohio Valley and possibly
crossing the forecast area over the weekend. The front is expected
to stall out roughly across the Midlands or Coastal Plain Sunday or
Monday. Overall, the front will have limited moisture to work with,
but should support scattered to numerous showers and thunderstorms
in the NC mountains with help of NWLY upslope flow Friday and
Saturday. Downsloping east of the mountains may limit coverage,
but support a return of near-normal to slightly above-normal
temps. Drier air filters in behind the front Sunday into Monday,
lowering PoPs and bringing temps down a couple degrees.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
At KCLT and elsewhere: An almost-wedgelike configuration is observed
in the satellite imagery, with a large area of low cloudiness
covering most of the foothills and northwest Piedmont. Thus, KCLT
and KHKY will be in-and-out of a low cloud MVFR ceiling through the
afternoon (mostly IN), with a light northeast wind. The Upstate
terminals will also have some low clouds developing through the
afternoon, but will remain mostly OUT of the restriction. Precip
probs are looking less and less based on the recent output
of the CAMs, so we will amend by watching radar trends. Thus,
KCLT and the Upstate terminals get a TEMPO for shower activity
and associated restrictions, but the others don`t. Most of the
lowest cloud deck will finally mix out late in the day, leading to
a period of VFR in the evening and early overnight. Wind should
go light/variable. Tricky forecast overnight. Previous guidance
suggested prevailing VFR, but the last model run before issuance
made a major change to widespread IFR/LIFR restrictions at most
terminals in the pre-dawn hours. Rather than jump on the big change,
preferred to wait to see some consistency over the next few runs
before adding it in. Be on the lookout for changes, though. Wind
should come back up from the ENE in the morning owing to high
pressure to our N. We could easily pop up a low cloud ceiling
restriction with minimal heating, but this was left out for the
time being.

Outlook: Expect mostly diurnal isolated to scattered diurnal
convection through Thursday. Coverage of convection increases Friday
into Saturday as a cold front approaches out of the west. Patchy fog
and low stratus will be possible each night in the mountain valleys
and in any locations that received heavy rainfall the day prior.

&&

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

&&

$$

SYNOPSIS...DEO
NEAR TERM...AR/PM
SHORT TERM...ARK
LONG TERM...ARK
AVIATION...AR/PM