047
FXUS62 KGSP 212152
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
552 PM EDT Sat Sep 21 2024

.SYNOPSIS...
High pressure will linger across the region through the weekend,
with balmy temperatures today and tomorrow.  A more moist airmass
will arrive early this week, lingering through at least mid-week.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 550 PM: Made some minor tweaks to PoPs and thunder chances
through the early evening hours based on the latest KGSP radar
loops. Otherwise, no major changes were needed this update.

Despite an upper ridge extending from an anticyclone over Texas
settling over the area, a weak short wave has led to enough forcing
to allow for some isolated showers to develop, mainly over western
NC. With instability and shear lingering through evening hours,
isolated convection should continue. Have retained the isolated
convection near and along the Blue Ridge given the upstream
convective activity. This feature moves across the NC Piedmont this
evening into the overnight bringing the potential for isolated
convection there. Should be another round of mountain valley fog
with patchy fog elsewhere. Lows will be 5 to 10 degrees above normal.

The upper ridge remains over the area Sunday with increasing
thickness values. Warming mid levels should limit instability and
put a lid on convection. Have a dry forecast for now. Highs will be
around 10 degrees above normal.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
As of 140 PM EDT Saturday: No major changes to the short term
forecast this afternoon.  Ensembles are coming into somewhat better
agreement that on Monday, the z500 ridge axis over the Carolinas
will be nudged east of the forecast area, permitting a steady
increase in upper-level moisture streaming into the area from the
west.  On Tuesday, it`ll become further suppressed, as a lobe of
shortwave energy translates up the Ohio Valley and over the
ridge. This`ll also have the effect of driving a weak cold front
across Tennessee and northern Alabama. The bulk of guidance
depicts this feature stalling west of the Appalachians by
Tuesday evening, which will keep the Carolinas locked into a
warmer, moisture air mass.

So, expect lots of cloud cover through the period.  High
temperatures will be in the mid to upper 80s in most locations both
afternoons, and on Monday, a few spots across the lower Savannah
River Valley may even hit 90.  This would be a little on the high
side of model consensus, but given the setup, it`s not unreasonable.
Models also depict scattered shower coverage both afternoons,
and a plume of afternoon instability to the tune of 1000 J/kg
sbCAPE...enough to support some embedded thunder, at the very least.
Forecast profiles aren`t especially impressive in terms of shear,
lapse rates, or overall updraft strength on Monday...so severe risk
doesn`t look especially notable.  By Tuesday, there`s considerably
more disagreement among long-range ensembles in terms of features
like dry air aloft, the location of the frontal circulation,
and mid-level lapse rates, so for now suffice to say there`s a
potential for some thunder, with details on the nature of that
thunder hopefully becoming clearer with future model cycles.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 155 PM EDT Saturday: By Wednesday, even the new 12z suite of
operational guidance begins to diverge on important synoptic
forecast details.  Like yesterday, ensemble guidance basically falls
into two camps: first, those depicting a weaker trough passage that
leaves a stronger ridge in place over the Atlantic coast, and
second, those depicting a stronger trough that nearly or completely
scours out the remnant upper ridge on Wednesday and early Thursday.
The first solution, with a stronger ridge, remains the dominant one,
and would drive a cold front through the region by Thursday,
ushering in drier weather on the whole as we move into the end of
the medium range.  The second solution, which also develops an upper
low over the Ozarks and central Great Plains, would result in no
frontal passage an instead a strong mid-level moisture return over
the Deep South, resulting in rainier conditions late next week.

Of note is the development of a tropical system over the Gulf in
most guidance towards the end of the medium range.  Should the first
solution above play out, remnants of this system could impact the
Carolinas toward the end of D7 and beyond; the second solution`s
deep upper low would potentially steer any remnant low away from the
Carolinas or absorb it entirely.  Confidence in the overall track
and timing of this system, as well as any potential impacts, remains
very low at this point.

&&

.AVIATION /22Z SATURDAY THROUGH THURSDAY/...
At KCLT and elsewhere: Low VFR Cu, along with cirrus, will remain
over the area this afternoon. Isolated convection is expected this
afternoon and evening, but coverage will again be too sparse to
warrant a TAF mention at any site. A generally light SW wind becomes
calm to light and variable overnight. Expect fog and low stratus
again in the mountain valleys with patchy coverage elsewhere. Have
MVFR TEMPO IFR Vsby/LIFR cigs again at the most likely locations of
KAVL and KHKY. This should dissipate before mid morning with some
low VFR Cu again developing. Light W to NW wind on Sunday.

Outlook: A weak frontal system approaches the area and stalls over
or near the area through Thursday bringing the potential for diurnal
convection. Daybreak restrictions could recur each morning
especially in mountain valleys.

&&

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

&&

$$

SYNOPSIS...MPR
NEAR TERM...AR/RWH
SHORT TERM...MPR
LONG TERM...MPR
AVIATION...RWH