608
FXUS62 KGSP 161430
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1030 AM EDT Fri Aug 16 2024

.SYNOPSIS...
High pressure will drift off the coast today, before a cold front
will arrive over the weekend, bringing widespread showers and
thunderstorms.  Drier conditions will return next week alongside
seasonable temperatures through at least Wednesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1025 AM EDT Friday: Low stratus and fog have dissipated with
some MVFR to VFR stratocu crossing the area. Convection, all but a
lone shower moving into the NW Piedmont, has been much slower to
start than previously expected. Expect good heating as the stratocu
scatters out and cumulus develops keeping most areas mostly sunny
for the bulk of the day.

A short wave ridge will move east of the forecast area by the end of
the day, with large scale height falls expected to impact much of
the area along and west of the Appalachians by the end of the
period. Within this pattern, increasing cyclonic flow aloft will
provide for a more favorable scenario for convective development.
Indeed, the bulk of short term guidance depicts scattered/numerous
convective cells moving into and/or developing over the mountains
this afternoon, and likely PoPs appear to be a good bet across much
of this area. Things become a little more complex east of the
mountains, as guidance generally agrees that instability will
diminish from NW->SE across the foothills and Piedmont. The latest
CAMs show scattered convection moving out of the mountains and
across the NC Foothills and Piedmont late afternoon into the
evening, but little over the Upstate or NE GA. Have kept the rather
sharp PoP gradient will be advertise in the official forecast, such
that chances are only 10-20% across out southern tier of counties.
There will be a small risk of severe storms over the mountains,
especially if any loosely organized convection is able to make a run
for the CWA from the TN Valley.

Max temps should be a little warmer than in previous days...placing
them pretty close to...maybe slightly above normal. Convective
coverage and intensity will diminish this evening, with very little
in the way of coverage anticipated after ~mid-evening. However, with
flow aloft becoming increasingly NW, can`t rule out some activity
wandering into the NC mountains late tonight, and token small PoPs
are carried there to account for that. Min temps are expected to be
a degree or two above normal.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 148 AM EDT Friday: A robust longwave trough will deepen over
the Eastern Seaboard over the weekend, producing multiple lobes of
z500 vort energy through the period.  By Saturday afternoon, a
prefrontal trough will develop over the western Carolinas ahead of a
strong cold front advancing across the Ohio Valley.  Within this air
mass, operational guidance depicts a tongue of 1200-2000 J/kg sbCAPE
and some 30kts of 0-6km shear.  Shear vectors will be oriented more
or less perpendicular to the boundary...and a weak dry layer aloft
will support marginal DCAPE values of 800-1000 J/kg...both of which
support a severe threat over heavy rainfall threat despite PWs
exceeding 1.75".  Still, some localized heavy rain issues could
present if storms train over the same areas.  Temperatures should
climb to no more than a category above normal Saturday afternoon.

On Sunday, the 00z suite of deterministic guidance is beginning to
align on a solution in which the frontal boundary has not yet made a
complete passage across the region...and therefore can provide a
point for convective initiation, at least across the eastern zones.
These areas are now forecast to attain diurnal instability max in
excess of 1000 J/kg, once again with non-trivial deep layer shear.
No run-to-run consistency yet, and the broader envelope of ensemble
guidance still depicts scenarios where the severe risk doesn`t pan
out, but the dominant signal is now for a possible outside severe
threat.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 205 AM EDT Friday: Long-range ensembles remain in decent
agreement that the large scale pattern will only slowly shift next
week, with upper troughing staying strong through Tuesday and then
slowly deteriorating through the end of D7.  Monday will feature a
round of diurnal convection as postfrontal air manages to
destabilize over much of the forecast area...although it`s unclear
how much synoptic forcing will be available, so coverage remains in
question.  As NW flow drives ever-drier air into the region on
Tuesday and beyond, and weak low-level CAA upsets already-waning
lapse rates, we can expect drier conditions from Tuesday onward.
Temperatures will be near or slightly below normal through the end
of D7.

&&

.AVIATION /15Z FRIDAY THROUGH TUESDAY/...
At KCLT and elsewhere: Convection is expected to form (or move into)
the NC mountains and foothills during the afternoon...with a tempo
for TSRA warranted at KAVL, and a Prob30 for such at KHKY.
Instability is forecast to weaken toward the Piedmont, so confidence
wanes in terms of convection reaching the rest of the terminals, but
there`s enough of a signal to add a Prob30 for SHRA at the upstate
SC sites and at KCLT. Light/variable or calm winds will become SW at
5-7 kts late this morning/early this afternoon, generally continuing
through the period.

Outlook: A cold front will track over the forecast area this weekend
keeping convection around. Drier conditions return behind the front
early next week. Patchy fog and low stratus will be possible each
morning 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...MPR
NEAR TERM...JDL/RWH
SHORT TERM...MPR
LONG TERM...MPR
AVIATION...JDL/RWH