936
FXUS62 KGSP 092334
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
634 PM EST Sat Nov 9 2024

.SYNOPSIS...
Dry high pressure will persist today before a cold front brings rain
and cooler temperatures back to the area Sunday afternoon into
Monday.  Dry high pressure will return Tuesday and Wednesday, before
another cold front arrives toward the end of next week.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 630 PM Saturday: Quiet weather will continue thru this
evening, as sfc high pressure ridges down from the northeast
in what is essentially a dry cold air damming wedge at this
point. Increasing stratocu can be seen on the nighttime RGB product,
but it take a while for moisture to deepen within a southerly
upglide flow across the forecast area. Some tweaks to the sky
cover and PoPs were made for the aviation forecast. But overall,
changes were minor.

Over the next 12 hours or so, a transition will take place
toward a more productive hybrid cold air damming wedge as the
weakening parent high gets pushed off the Mid-Atlantic coast
by the progressive nrn stream ridge. The southerly flow will
gradually increase tonight with isentropic lift commencing in the
early morning hours, altho the moisture takes a few more hours
to arrive. But, arrive it should, by daybreak or so with clouds
and light precip developing first in the southerly upslope areas
of the Blue Ridge Escarpment, and then expanding outward from
there during the morning as the isentropic lift improves. The
CAMs indicate more shower activity than previous model runs,
so the precip chances were bumped up and expanded mainly east
of the mountains into the afternoon. Still in the chance range,
but trending upward, and suspect that more people will get some
light rain than not. Meanwhile, the approach of a cold front from
the west will increase the rain chances over the western side of
the mtns in the afternoon. This fcst trend also supports more
cloudiness, which is more likely to lock in the hybrid wedge,
and keep temps below normal. Thus, the high temp was also nudged
downward a bit for Sunday afternoon.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
As of 1232 PM EDT Saturday: CAD should begin to erode on Monday.
Model soundings depict a shallow wedge still in place early Monday
morning, but by Monday afternoon/evening, deep mixing should start
to erode the wedge from the bottom up.  It`ll be a one-two punch,
too, as potent, if short-lived, low-level CAA arrives with a cold
front digging across the Tennessee Valley. This should effectively
end CAD and allow high pressure to begin building in from the north
on Tuesday.  This will lead to a period of drying, though the center
of the high will be migrated eastward quickly enough that by Tuesday
evening, it`ll already be pushing out of the Ohio Valley and into
the Adirondacks.

So, this will play out as increasing shower activity through Monday
morning , leading up to the arrival of the actual frontal
circulation Monday afternoon.  Rain chances will then diminish
Monday night as the boundary pushes eastward.  Given the depth of
mixing, it`s still not out of the question that we could see a stray
surface-based thunderstorm...but even the most aggressive models
depict a weak residual cap, severely limiting the strength of any
such cell.  Drying is then expected through the remainder of the
period, with mostly clear skies expected Tuesday.  The front will do
little to moderate temperatures, which will be in the low- to mid-
70s both afternoons.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 116 PM EDT Saturday: As surface high pressure continues to
work its way east under a progressive upper pattern, we`ll gradually
revert to a northeast-flow CAD-like pattern on Tuesday and
Wednesday.  Profiles look to remain dry enough, however, and
isentropic ascent weak enough, to preclude the usual dreary weather
associated with established cold-air damming.  Instead, expect
enough afternoon mixing for scattered cloud cover only. Temperatures
will climb into the 70s on Tuesday, but by Wednesday, the intrusion
of cooler air from the northeast will result in afternoon highs in
the mid 60s.

Wednesday night or early Thursday, a cold front is still expected to
make tracks across the area.  This will result in a brief period of
showers from Wednesday night through the first half of the day
Thursday.  Synoptic forcing will be modest at best, and with a weak
frontal circulation given how far removed the parent low will be.
Behind the front, robust high pressure will build in from the
central U.S.  This will somewhat decrease temperatures, but the
effect will be more noticeable at night - with Thursday and Friday
night`s lows falling into the 40s or even upper 30s in some spots -
than during the day, when solar heating and weak downslope flow
could offset any CAA-induced cooling.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
At KCLT and elsewhere: Conditions will start out VFR with expanding
4000-6000 ft stratocu, but deteriorate late tonight in the Upstate
and expand north across western NC during the day Sunday, as
moisture increases atop a wedge of high pressure. Cold air damming
will likely strengthen, as scattered light precip breaks out and
causes cigs to lower to MVFR, then IFR by the end of the 00z TAF
period. With the wedge in place, winds will favor a NE direction
(SSE at KAVL), but will be light.

Outlook: A wedge regime will persist until a cold front passes
early Monday. Dry and mostly VFR weather expected Tue-Wed. Moisture
begins to return from the southwest on Thursday.

&&

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

&&

$$

SYNOPSIS...MPR
NEAR TERM...ARK/PM
SHORT TERM...MPR
LONG TERM...MPR
AVIATION...ARK