652
FXUS62 KGSP 021831
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
231 PM EDT Fri Oct 2 2026

.WHAT HAS CHANGED...
Timing of rain onset for tomorrow`s showers and storms was refined,
and the temperature forecast was updated based on the latest round
of hi-res guidance`s handling of a backdoor cold front and cold-air
damming development.

Rainfall totals were updated for this weekend`s system.

The aviation forecast was updated to reflect the recent 18Z TAF
issuance.

&&

.KEY MESSAGES...
1. Quiescent weather continues today and tonight, with little
more than a token shower or two west of I-26 expected this evening.
2. Widespread rainfall is expected on Saturday and Sunday,
potentially causing localized flooding in a few spots. Confidence
remains limited in details.
3. Dry and cool conditions persist most of next week. Temperatures
will steadily warm back up through Friday.

&&

.DISCUSSION...
Key message 1: Quiescent weather continues today and tonight, with
little more than a token shower or two west of I-26 expected
this evening.

Broad high pressure off the Atlantic coast continues to drive
light S/SW flow over most of the forecast area today, while aloft,
a low- amplitude shortwave trough remains trapped over the Ozarks.
The bulk of better moisture transport appears to be confined to
the TX/LA Gulf coast, north into the Ozark Plateau and western
Tennessee Valley...but some steady increase in moisture over
our area continues nonetheless.  Make no mistake...dewpoints are
currently in the mid- to upper-60s across most of the area, and
with a shrinking low-level dry slot, many locations along the I-85
corridor and south may see dewpoints hit 70 degrees this afternoon.

Hi-res guidance continues to key on the potential for some isolated
showers, perhaps even a rumble of thunder, across the upper Savannah
River Valley and into the Smokies/Balsams.  These zones may wind
up realizing several hundred joules of surface-based instability
during peak heating this afternoon...a far cry from the environment
needed for any strong updrafts, but enough to support some weak
convection should ridgetop triggering get a cell or two going.


Key message 2: Widespread rainfall is expected on Saturday and
Sunday, potentially causing localized flooding in a few spots.
Confidence remains limited in details.

Increasingly active conditions are forecast to develop over the
weekend as a dynamic upper system arrives.  Deterministic guidance
depicts the remnants of a shortwave trough, initially impressive
over the Great Plains and Midwest, becoming smeared across the Ohio
Valley and steering a surface cold front to our western doorstep
by early Saturday.  A backdoor cold front will begin to settle down
the Virginia Piedmont by mid- to early-afternoon, but for our part,
we seem likely to remain within a warm sector-like environment
for most of Saturday.  Most of the CAMs feature initiation of
showers by noon or so on Saturday, within a plume of 500-900 J/kg
sbCAPE, based on the spread of the latest-available REFS ensemble.
Though a stray strong to severe storm can`t be entirely ruled
out...the thinking remains that absent much good deep-layer shear,
more than a few generic thunderstorms will struggle to develop.

Saturday evening and into the overnight, the environment will
change dramatically as the backdoor cold front settles south across
the area.  Within just a few hours, forecast soundings depict the
onset of a cold-air damming wedge concurrent with strong surface CAA
behind the front.  As a consequence, the potential for surface-based
convection will diminish, although some weakly-enhanced convective
rain rates may persist, by virtue of elevated instability above the
wedge layer.  Rain, though, seems increasingly likely to continue
through the night and into at least the first half of Sunday, as a
second and more well-defined shortwave crosses the Ohio Valley and
incites stronger moist upglide over the wedge.  This should have
the added effect of further reduce Sunday`s temperatures...keeping
them two to three categories below normal for most of the area.

The jury is still out, then, on exactly how any heavy rainfall
threat will pan out.  The case seems very limited initially. Through
Saturday night, the most impressive signal for heavy rainfall comes
in the 2" or greater PWs developing mainly south of I-85...which,
to wit, is above the 95th percentile of historical data for this
time of year; paired with even weak updrafts, this could result in
impressive rain rates.  However, upper flow should be sufficient to
keep showers and storms moving, so limited residence time should
keep widespread hydro issues at bay.  The notable exception is
locations which receive heavier showers early in the day in the
warm- sector portion of the event, and then get a second round of
rain as the backdoor front arrives in the evening.  Recent runs of
the HREF and REFS all feature an axis of higher QPF consistent with
this thinking, but vary wildly in terms of where that axis sets up.

The forecast becomes murkier after 12Z Sunday. Few of the CAMs
extend out that far, but the deterministic guidance supports
improving synoptic forcing as the second shortwave crosses the
area through Sunday night.  In response to the shortwave, the
surface front will finally push east across the area; long-range
ensembles remain split on how quickly this will take place, though
the 12Z suite of guidance seems to have trended toward a slower
evolution, and a later end to rainfall.  More generally, think the
threat of heavy rain on Sunday will hinge on how much rain certain
areas receive on Saturday/Saturday night and whether/how long any
convective rates persist into Sunday.  Continued rainfall on Sunday
may result in a more of a cumulative, slow-burn flood threat for
some locations.  Confidence remains limited, but should begin to
improve over the next 12 to 18 hours as models hopefully develop
a consensus on the first half of the event, and as more of the
hi-res guidance begins to capture the latter half of the event.


Key message 3: Dry and cool conditions persist most of next week.
Temperatures will steadily warm back up through Friday.

Lingering cold air damming should begin to drain on Monday as flow
aloft slackens.  Dry and cool cP air will settle into the Carolinas
behind a cold front, and that air mass will largely sit and modify
through most of the week.  It should be another dry and unperturbed
week...an afternoon breeze on Tuesday, followed by cool temperatures
each day, steadily warming back to around normal by Thursday or
Friday as the air mass modifies.  The latest forecast has trended
a tad warmer for Tuesday night and Wednesday morning...but could
still see isolated spots across the high terrain of the northern
Blue Ridge approach freezing before dawn.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: VFR on tap for the bulk of the 18Z TAF
period, with mainly thin cirrus and a mid-level cu field developing
this afternoon and evening across the terminal forecast area.
SW winds expected to persist this afternoon and evening, with most
sites going light and variable overnight tonight.  Thickening cirrus
tonight as better moisture moves in, and guidance increasingly
keying on the development of a FEW/SCT mid-level cloud deck
above 8 kft, after midnight...mostly altocu based on forecast
soundings. Low confidence on the fog/stratus forecast at KAVL
on Saturday morning; no restrictions developed this morning, and
although moisture may be marginally better Saturday morning...cloud
cover will also be considerably thicker.  The statistical guidance
continues to feature IFR fog and low stratus at all the mountain
terminals...but this forecaster is skeptical, and only included
MVFR restrictions at KAVL in a TEMPO.

Otherwise...isolated showers and perhaps a rumble of thunder
could develop as early as 15-16Z Saturday.  Winds should remain
out of the SW initially (except in the immediate vicinity of any
stronger shower or storm, where they could be gusty and erratic),
but quickly toggle to the NE as a backdoor cold front moves from
the I-40 corridor south and west across the area Saturday evening.
Concurrently, coverage of SHRA and embedded TS will increase, and
restrictions will develop as a cold-air damming sets up for the
latter portions of the TAF period and beyond.  This only really
falls within the 18Z TAF at CLT...but will become an issue for
future iterations of the other TAFs.

Outlook: Widespread SHRA and associated flight restrictions are
expected across the area on Saturday night and the first part
of Sunday.  Improvement to VFR is expected by Monday, and will
persist well into next week.

&&

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

&&

$$

MPR