000
FXUS62 KGSP 251030
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
630 AM EDT Mon Sep 25 2023

.SYNOPSIS...
Dry high pressure will remain over the western Carolinas and
northeast Georgia today. Moisture will return atop another high
pressure center ridging down from the north Tuesday into Wednesday,
with cloudy, damp, and cool conditions lingering through late in
the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 6:25 AM EDT Monday...Winds remain light to calm across the
fcst area, however any substantial mtn valley fog/low stratus has
been hesitant to develop until the past hour or so. This is largely
due to the increased high cloud cover that has been streaming across
much of the CWA since last night. Any lingering fog/low stratus
should dissipate by late morning as daytime heating increases.

Otherwise, we`ll remain under a somewhat progressive upper pattern
thru the near-term period. A closed upper low will drift southward
and remain just west of the Great Lakes as numerous lobes of upper
shortwave energy pass just to our north and eventually move off the
Atlantic Coast. At the sfc, weak high pressure will continue to nudge
into the fcst area from the north as what`s left of TC Ophelia will
eventually dissipate just off the mid-Atlantic Coast. This pattern
should keep us dry and warm today as WSW 850 mb flow persists,
allowing high temps to climb back into the low to mid 80s across
the lower terrain this afternoon. I do have some slight chance PoPs
over our northern-most zones beginning later this evening as more
moist, NELY low-level flow begins to set up over our area and a
broad area of weak low-level convergence sets up as well. Any QPF
that does materialize thru early Tuesday should be minimal at best.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
As of 306 am EDT Monday: Not much change to the overall plan for
the middle part of the week, although some of the details keep
coming in and out of focus, mostly in terms of precip coverage. A
complex upper blocking pattern over northeastern North America
on Tuesday will conspire to allow sfc high pressure centered well
to our north over the middle of Quebec to ridge all the way down
the east side of the Appalachians. Some of this will be courtesy
of light precip falling into the ridge over the nrn Mid-Atlantic
reinforcing the shallow cool stable air over PA/MD/nrn VA on
Tuesday, and some of this appears to be a sfc ridge in response
to low pressure lingering off the Mid-Atlantic Coast and a sfc
reflection of the upper low over the Midwest/OH Valley. Either
way, model guidance continues to show a relatively cool, stable,
shallow air mass oozing south/southwest into our region early on
Tuesday. A combination of weak isentropic lift and easterly upslope
flow should eventually force the production of light rain over
the foothills/mtns by late in the day. Ahead of the wedge-front,
we could get sufficient instability to support a few thunderstorms
in the afternoon. Temps will be tricky and dependent on how early
we cloud up and develop the light rain, but are likely to remain
below normal over at least the NC part of the fcst area. Precip
probs maximize late Tuesday night and Wednesday, thus Wednesday
looks the most likely to feel wedge-like. Kept the precip probs
in the likely range over the mtns with a chance elsewhere...which
is a small undercut of the guidance.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 205 am EDT Monday: The mid/upper pattern continues to
look blocky through the medium range, with one block over the
Northeast/Eastern Canada on Thursday quickly giving way to a new
Omega block by the weekend that covers most of the CONUS. Through
it all, sfc high pressure will ridge down from the north to mostly
control our weather. Still a low-confidence forecast during the
latter half of the work week because of model differences with the
amount/degree of mostly low level forcing, with the ECMWF being
the most aggressive Thursday and Friday. The mountains will stand a
decent chance of rain because of the upslope forcing, but the fcst
will continue to undercut the guidance over the Piedmont. Those
two days have the best opportunity to remain wedge-like with cooler
temps assuming some light precip develops at some point. Once we get
to the weekend, though, confidence improves with the model agreement
that a new Omega block forms with the upper ridge axis/anticyclone
to our west that provides renewed and better support to a parent
high to our north. By that time, the scenario will no longer
be wedge-like, but more like just an inverted ridge. Any precip
would be well to our east and hopefully offshore. Consequently,
we lose the precip chances and gain some temps closer to normal,
but still a bit on the cool side.

&&

.AVIATION /12Z MONDAY THROUGH FRIDAY/...
At KCLT and elsewhere: Expect dry, VFR conditions and light winds
to continue thru most of the 12z taf period. Towards the end of
the period early Tuesday, lower cigs begin to spread over the NC
terminals from the north as more moist, NLY flow sets up. The SC
terminals are not expected to be impacted by the lower cigs until
after 12z Tuesday. Otherwise, a fair wx cumulus deck is expected
to develop by the early afternoon with periods of sct to bkn cirrus.
Winds should continue to favor a N/NE direction thru the morning,
although many sites may remain vrb/calm. Much like yesterday,
winds are expected to toggle to SWLY during the afternoon and
then switch back to NELY towards the end of the taf period early
Tuesday.

Outlook: A cold-air damming pattern is expected to develop by mid-
week, increasing the potential for precipitation and restrictions.
Mtn valley fog and low stratus will be possible each morning around
daybreak.

&&

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

&&

$$
SYNOPSIS...PM
NEAR TERM...JPT
SHORT TERM...PM
LONG TERM...PM
AVIATION...JPT