FXUS62 KGSP 050834

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
334 AM EST Tue Dec 5 2023

Another reinforcing cold front will cross our region this evening
with a brief increase in moisture tonight and early tomorrow over
the North Carolina mountains, permitting some light rain or snow
near the Tennessee border.  Dry high pressure will then allow
temperatures to warm up through late in the week, before active
weather returns for the weekend as a cold front approaches from
the northwest.


As of 312 AM...Satellite imagery continues to show some shallow
moisture/low cloudiness banked up against the mtns on the TN side by
a light WNW flow, but cloud top temps have been gradually warming
and radar was quiet, so it appears unlikely that any additional
precip will fall. Can`t rule out some rime icing in the upslope
areas though. Also won`t rule out some valley fog in the Little
TN valley through daybreak. Low temps should be right around normal.

Today looks fairly quiet across the region as a short wave ridge
moves overhead this morning supporting weak high pressure, but
that breaks down readily thru the day as the next short wave
trof drops down into the larger upper trof over the Midwest/OH
Valley. The short wave will make steady eastward progress this
afternoon and will push a cold front toward the mtns late in the
day, but guidance is consistent with keeping precip to our west
thru sunset. Most of the fcst area will see plenty of sun today
but temps will be much closer to normal thanks to lowering heights
and thickness this afternoon.

The short wave is expected to dig the mid/upper trof deeper over the
western Carolinas as it moves overhead tonight. The wave will drive
a cold front east across the fcst area this evening, and although
the sfc temps behind the front initially aren`t expected to be much
cooler than this morning, temps aloft will be cooler. In the wake
of the front, a slug of moisture will be pushed up the west side of
the mtns by a strengthening NW flow that will force the development
of precip beginning in the middle part of the evening and spreading
east across most of the mtns by the favorable passage of the short
wave. The snow level should come down to roughly 3000 to 3500 feet
in the late evening. The moist layer extends up into the dendritic
snow growth zone after 03Z on the west side of the mtns, and that
deeper moisture persists until around daybreak Wednesday, suggesting
the potential for some good snow production at high elevations close
to the TN border after midnight tonight. The trend over the last
few model runs has been an upward creep in coverage and amounts,
altho even with that said, elevations below 3500 feet are likely
to only get a trace or maybe something less than an inch, and the
elevations above 3500 feet away from the peaks in the Smokies
barely reach into what would be considered for an Advisory. Be
that as it may, because this is the first real potential snow of
the season and we have that upward trend, we will issue a Winter
Weather Advisory for elevations above 3500 feet in the zones that
border TN, and all of Avery County, beginning late this evening.


As of 234 AM EST Tuesday: Generally quiet conditions are expected
midweek with the Carolinas between systems.  Some lingering NW flow
snow showers will likely continue through the day on Wednesday,
but with more moisture now expected to be squeezed out before
daybreak, anything more than the occasional flurry is unlikely
to continue past the afternoon hours.  Wednesday will be chilly,
with CAA preventing temperatures from escaping the low 50s even
well east of the mountains, and breezy NW winds persisting for
much of the day.

Winds will diminish sharply Wednesday night and Thursday as the
center of a surface high slides into the Tennessee Valley...and lows
will be allowed to fall into the 20s as excellent radiative cooling
conditions set in.  Highs on Thursday will remain below-normal,
though winds will pick up out of the SW, and weak WAA will maintain
above-freezing low temperatures Thursday night.


As of 302 AM EST Tuesday: Clarity is improving on the progression
of the next synoptic disturbance to affect the Carolinas...which
will arrive in the form of a robust 500mb trough crossing the Great
Plains lateweek and emerging in the Southeast by Saturday night
or Sunday.  The latest 00z CMC has toggled back to looking more
like the 00z ECMWF in depicting a less progressive pattern and
resulting in overall higher QPF.  These solutions fail to bring
the trough east of the CWA before Sunday afternoon, resulting in
more rainfall and permitting the development of some afternoon
instability.  As the base of a potent 500mb speed max slides across
the area Sunday, this forecast mode would potentially result in a
convective risk Sunday afternoon.  Out of the 100 or so members in
all three global ensemble systems, however, only about a quarter
support this solution...while others depict solutions where either
the trough pushes through too quickly (like the deterministic GFS)
or where the more potent synoptic forcing gets shunted north of
the CWA and mid-level lapse rates wind up far too weak for any
instability to develop.  So, this is a long-winded way of saying
we still don`t know for sure, but some convection and possibly
even an isolated severe storm aren`t out of the question.

On Sunday night, some guidance depicts a period of NW flow snow.
Right now, even the most aggressive ensemble members depict strong
enough postfrontal CAA to rapidly clear out lingering low-level
moisture...keeping the duration of any snow showers, and therefore
any accumulations, limited.  In any case...following the passage of
this feature and its associated surface reflection...temperatures
will fall and dry high pressure will build in from the west,
setting the stage for clear and chilly weather early next week.


At KCLT and elsewhere: VFR at all terminals thru the forecast
period. Locations outside the mtns will be clear through the day
followed by an increase in mid/high clouds this evening ahead of
another upper wave. Wind will go all around the dial through the
next 24 hours, favoring N thru early morning, then northeast late
morning early afternoon as the sfc high moves away, then SW mid
afternoon and early evening as we get on the backside and the next
system approaches from the west. Over the mtns, some light precip
may reach the western slopes along the TN border from sunset onward,
but it appears unlikely it would reach KAVL until after midnight,
if at all.

Outlook: Dry conditions and VFR are expected thru most of the
week, as a series of moisture-starved waves cross the area. May
see breezy NWLY winds Wednesday.


NC...Winter Weather Advisory from 10 PM this evening to 4 PM EST
     Wednesday for NCZ033-048>052-058.



NWS GSP Office Area Forecast Discussion