143
FXUS62 KGSP 242200
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
600 PM EDT Sat May 24 2025

.SYNOPSIS...
A stationary front draped across the Deep South will keep weather
unsettled and mild across the area through Monday, with several
rounds of scattered showers and isolated thunderstorms expected.
Unseasonably cool temperatures and widespread showers will occur on
Tuesday, as a warm front approaches the area.  Later next week,
a cold front approaches the region, resulting in shower and
thunderstorm chances Wednesday through Friday.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 545 PM: No major changes this update. Deterioriating sfc high
remains over our area, atop which a plume of midlevel moisture is
present, north of a warm front near the FL Panhandle. High based
radar returns are seen over the CWA via that moisture and weak
upglide. A small pocket of sprinkles in N GA set to advect across
the Savannah Valley and into over the next couple of hrs. The
more robust convective activity seen in Alabama and Mississippi
should miss us to the SW, although it is in a weakening state.
Pivotal feature for the next 24 hours will be the deteriorating
high and the warm front.  A shortwave trough now over the MS
Delta region could provide enough lift for more showers late in
the evening and also enhance upglide, so PoPs ramp up mainly over
the S half of the CWA after midnight. Although a rumble of thunder
can`t be ruled out, it`ll be elevated and isolated.

Continued activation of the warm front should allow increasing
precip coverage Sunday morning. By this point, increasingly strong
low-level warming and moisture advection will begin the process
of developing in situ cold-air damming...to be fully realized as
rain sets in during the day and a sfc wedge develops.  Profiles on
Sunday will be even more stable, and any elevated instability that
develops will be weak, owing to a lack of good upper-level dynamics
and resultant weak lapse rates even above the wedge-top inversion.
The one exception might be the So again, while some thunder can`t
be ruled out...it`ll be low impact.  Thus...with HREF PMMs on the
low side, and no convective enhancement to rain rates...expect
little more than run-of-the-mill rainfall.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
As of 300 PM EDT Saturday...

A relatively flat upper-level pattern overnight Monday begins
to amplify modestly ahead of a shortwave ridge building across
the upper Midwest.  A weak shortwave is expected to move through
the mean flow aloft Monday night, bringing us a quick round of
scattered to numerous showers that will likely depart the area by
mid-morning Monday.  Total rainfall with this wave will be light
and insignificant.  A backdoor cold-front will enter the area as
this wave departs Monday morning, as 1028mb high pressure builds
into the Great Lakes region.  Weak northeasterly flow on the east
side of the high pressure center will begin to establish a CAD
regime across the area later Monday which will persist through the
short-term period.  We will begin feel the effects of this cooling
boundary layer on Monday, with high temperatures struggling to
reach 70 across the North Carolina Piedmont.  Scattered showers and
an isolated thunderstorm are forecast along the front, which will
be located in the proximity of the Savannah River later Monday,
but average rainfall amounts are expected to be very light.  As is
typical, the Savannah River Valley and southwestern North Carolina
mountains will remain the warmest ahead of the backdoor front.

CAD will become firmly entrenched across the area overnight
Monday through Tuesday, as the shortwave ridge axis oriented over
the upper Ohio River valley propagates the attendant surface
high over the Northeast.  The high will be in perfect position
for this anomalous late May wedge pattern.  Meanwhile, the next
longwave trough digging into the upper Mississippi River Valley
will finally push the stationary front draped across the Deep South
to the north and east as a warm front.  Isentropic lift over the
front will fuel the development of numerous to widespread showers
across the area on Tuesday, but absent strong large-scale forcing
and instability, amounts are expected to be quite manageable.
The cloud cover and rainfall will reinforce the CAD regime and
suppress high temperatures to 15-20 degrees below normal for this
time of year.  As a result, highs will struggle to get into the
mid-60s across the western Piedmont and South Carolina Upstate.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 235 PM EDT Saturday: Surface high parked just offshore the
Mid-Atlantic Coast keeps an ongoing hybrid CAD event situated
over the CFWA Tuesday. Moist upglide atop the CAD dome will help
to keep it intact and allow for a chilly and dreary day Tuesday,
especially for late May. Model guidance suggest CAD will be
relatively short-lived as the surface high shifts further offshore
and a shortwave trough moves in from the west Tuesday night into
Wednesday. Stalled frontal boundary to the south will induce
cyclogenesis as a cluster of vort energy slides in from the west
and develop a surface low to ride along the boundary, moving the
low across the Deep South and up the Southeast Coast Tuesday into
Wednesday. In this process, the CAD should slowly erode through
surface divergence and allow for better insolation to reach the
ground later in the day Wednesday as the low shifts offshore and
cuts off any source from the aforementioned high to preclude CAD. The
temperature forecast becomes tricky, but anytime there`s an obvious
CAD regime locked in over the area, especially this late in Spring,
temperatures come out ~15-20 degrees below normal for afternoon
highs and near-normal for overnight lows. This is expected Tuesday
and Tuesday night, with slight recovery Wednesday with the likely
CAD erosion.

The pattern remains fairly active through the rest of the forecast
period as a series of shortwaves traverse across the CFWA seemingly
each day going into the upcoming weekend. Without any CAD in
place, profiles should gather up better instability and allow for
daily showers and thunderstorms to remain in the forecast. Can`t
rule out strong to severe storms each day starting on Thursday,
but nothing of note to suggest anything outside of the normal
summertime convective threat. As of now, Friday may be the best
setup for any type of real severe threat as guidance introduce
better shear parameters overlapped with decent instability to help
form more organized convection. There is light at the end of the
tunnel as the synoptic setup sets up a digging upper low sliding
into the northeastern CONUS and Atlantic Canada, allowing for broad
cyclonic flow aloft to settle overhead going into next weekend. The
attendant frontal boundary will finally push into the by D7/D8
as the trough gradually slides east, with signs of a clearing
post-frontal regime after the extended forecast period. Expect
temperatures to be near normal Thursday through the end of the
period, with humid conditions as well.

&&

.AVIATION /22Z SATURDAY THROUGH THURSDAY/...
At KCLT and elsewhere: Still expect VFR conditions to prevail
through most if not all of tonight at all the TAF sites.
Widespread cirrus and scattered to broken mid-level clouds are
already streaming across the forecast area, and by this evening,
expect moisture to begin increasing more steadily.  Hi-res guidance
continues to depict a deteriorating cluster of showers arriving in
the western Upstate, and perhaps parts of the southern NC mountains,
before midnight, and gradually expanding across the Upstate sites
through daybreak.  Fairly consistent signal at this point that
convection will remain south of KCLT and the other NC sites until
after daybreak tomorrow...so PROB30s advertised for SHRA at the
Upstate sites overnight, but held off on any mention at KCLT and
KHKY until after 15z.  A rumble of thunder still cannot be ruled
out, but any thunder will be elevated in nature and its coverage
far too sparse for any inclusion in the TAFs.  Generally expect
a south wind at all the TAF sites, though a period of light ENE
winds at KCLT appears likely overnight.

Outlook: Shower and thunderstorms chances increase into early next
week. The highest coverage is expected Tuesday, with diminishing
coverage expected Wed into Thu. Mainly mountain valley fog and low
stratus are possible each morning early next week, with chances
increasing for all areas toward the middle of the week.

&&

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

&&

$$

SYNOPSIS...JMP
NEAR TERM...MPR/Wimberley
SHORT TERM...JMP
LONG TERM...CAC
AVIATION...MPR