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614
FXUS62 KGSP 220556
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
156 AM EDT Sun Sep 22 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 TODAY/...
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As of 150 am EDT: Another round of mountain valley fog and low
stratus is expected this morning, although overall coverage and
temporal extent may be limited by areas of mid-level clouds wafting
over the forecast area. Some fog is also likely outside the
mountains in some of the major river valleys, especially across the
foothills. Lows will be 5 to 10 degrees above normal. Otherwise, an
upper ridge remains over the area through the period with increasing
thickness values. Warming mid levels should limit instability, but
it should be sufficient to allow for spotty diurnal convective
development, especially across western areas. Highs will be around
10 degrees above normal.
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&&

.SHORT TERM /TONIGHT THROUGH TUESDAY/...
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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.
-- End Changed Discussion --

&&

.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 /06Z SUNDAY THROUGH THURSDAY/...
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At KCLT and elsewhere: Potential morning low stratus and/or fog will
again be the main concern for this forecast period, as low level
moisture remains more than adequate for restrictions. Based upon
observational trends, restrictions are forecast to be confined to
the usual suspects: KAVL and KHKY, where at least tempo IFR
conditions are expected after daybreak. Certainly can`t rule out
restrictions at other sites, but it`s unlikely. Otherwise, periods
of mid-level clouds are expected this morning, followed by
development of spotty diurnal convection this afternoon/evening,
especially across the western half of the area. Coverage is
generally expected to be isolated and therefore not worthy of a TAF
mention. Generally light/variable winds early this morning are
expected to gradually turn the dial from NW=>NE=>E/SE from late
morning through the evening, while speeds will mostly remain 5 kts
or less.

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.
-- End Changed Discussion --

&&

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

&&

$$

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