139
FXUS62 KGSP 220140
AFDGSP

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

.SYNOPSIS...
High pressure will linger across the region through the weekend
keeping above normal temperatures around. A more moist airmass
arrives early this week, lingering through at least mid-week.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 935 PM EDT: Main change was the removal of thunder chances
through the evening hours. Otherwise, the forecast remains on track.
Seeing dry conditions return this evening, but a few isolated
showers may redevelop along the shortwave in the NC Piedmont through
the next several hours. Thus, have maintained the isolated
convection mention across portions of the NC Piedmont this evening
into the overnight hours. Should be another round of mountain valley
fog with patchy fog elsewhere. Lows will be 5 to 10 degrees above
normal.

An 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 /02Z SUNDAY THROUGH THURSDAY/...
At KCLT and elsewhere: VFR (outside of mountain valley fog/low
stratus daybreak Sunday) through the 00Z TAF forecast period. Mostly
clear skies are in place with a FEW to SCT VFR cirrus streaming over
the terminals as of 0130Z. Cirrus will continue to stream over the
terminals through the overnight hours. KAVL and KHKY may see LIFR to
IFR fog and/or low stratus develop around daybreak so have TEMPOs at
both sites to account for this potential. Fog and low stratus should
mix out by 13Z-14Z. Winds east of the mountains will generally be
S/SW this evening into tonight before gradually turning N/NE on
Sunday. Winds at KAVL will start out WSW before toggling WNW
overnight into Sunday. Another cu field may develop Sunday
afternoon/early evening.

Outlook: A weak cold front will slowly approach from the west early
next week before tracking over the area on Thursday. This front will
keep diurnal shower and thunderstorm chances around through at least
the middle of next week. Mountain valley fog/low stratus may develop
each morning around daybreak.

&&

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

&&

$$

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