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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KGSP 051150
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
650 AM EST Sat Dec 5 2020

.SYNOPSIS...
In the wake of a cold front, light snow and brisk winds will
continue this morning in the North Carolina mountains near the
Tennessee border. Another fast-moving system could bring light
precipitation to the region Monday, and possibly another round of
light snow for the mountains. Seasonably cool and dry weather is
otherwise expected through Friday.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
As of 630 AM Saturday...We`re currently seeing some light RADAR
returns over the NC/TN border, especially along northern Swain
and Haywood Counties. Still anticipate sub-Advisory level snow
accumulations, however some isolated areas across the Smokies
and TN spine could receive up to 3 or 4 inches before the snow
tapers off later this morning. Wind gusts up to roughly 40 mph
will continue over the higher terrain as well this morning, with
the strongest gusts above 4000ft or so. They will gradually taper
off thru the aftn as the pressure gradient weakens overhead.

Otherwise, the upper trof axis will continue to lift NE and off
the Atlantic Coast today/tonight. This will result in a brief, nearly
zonal upper pattern towards the end of the period early Sunday before
the next round of upper-lvl energy approaches the fcst area from the
north and west. At the sfc, the low pressure system will continue to
move northward and up the Atlantic/New England Coast as broad high
pressure spreads back over the region in its wake. This will make for
a sunny and breezy Saturday for most of the CWFA with temps outside
the mtns, near normal, if not a couple degrees below. Highs across the
higher terrain will be 1 to 2 categories below normal. Clouds and light
NW-flow snow showers will linger over the higher terrain and especially
along the NC/TN border thru late morning. Any accumulations should
remain below Advisory criteria, with the exception of a few isolated
spots along the NC/TN border. As we move into the aftn, guidance has
bndy layer moisture diminishing across the higher terrain and precip
ending.
-- End Changed Discussion --

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 200 AM Sat: Near-normal temps and near zero PoPs are expected
Sunday as weak high pressure remains over the region. The upper flow
will begin to turn cyclonic ahead of a shortwave crossing the middle
Ohio Valley. This wave is embedded in a deep eastern CONUS trough;
additional shortwaves are positioned upstream and will rotate closer
to the CWA by Monday. Still some disagreement among the major models
on how they will phase. The NAM, ECMWF, and Canadian GDPS all phase
the first wave with the southernmost one, resulting in enough forcing
for light precip over a portion of the CWA early Monday; the unphased
GFS depiction is dry for us at that time. The cooling should occur
from the top down, and the wetter models also depict warmer temps.
Thus it appears likely most of the area still will be warm enough to
advertise rain, except in the higher elevations.

Cold advection will continue through Monday, although most of the
guidance depicts a lull in dynamic lift. Thus, precip chances will
diminish for a time, except in the NW Flow upslope areas, as a fair
amount of low-level moisture will persist as winds turn NW. Temps
will remain cool enough across some of the mountains to expect
accumulating snow to continue thru the day. Cloud cover and CAA will
keep max temps considerably below normal. The final shortwave looks
like it will have cut off by the time it crosses the southern
Appalachians Monday afternoon or evening; precip chances increase
again across the area again as a result, and temp profiles will
become increasingly supportive of wintry precip across the lower
elevations as time goes on. The challenge is to determine whether the
upper low will be associated with enough moisture to carry precip
downstream of the mountains, and in that case, if it will be deep
enough for ice crystallization. For our Piedmont, it still looks more
likely than not that the answer to one of those questions will be
"no," although the GFS and ECMWF are both pretty close. The GFS has
better moisture but the ECMWF has cooler wet-bulb profiles. Most
likely, however, it looks most likely precip will end in the Piedmont
before temps cool enough Monday evening. Min temps Tue morning will
dip into the 20s at most locations, several degrees below normal.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 240 AM Sat: One more trailing shortwave is progged to traverse
the area Tuesday as upper trough shifts offshore, but without any
moisture to speak of. A broad ridge will replace these features,
bringing dry wx and moderating temps to the South Wednesday thru
Friday. Maxes will be a couple categories above normal Thu and Fri,
in the upper 50s and lower 60s for the mtn valleys and Piedmont. One
or more shortwaves will reach the Plains by the end of the work week;
GFS and ECMWF both depict cyclogenesis such that a cold front
approaches the area Friday night. The CMC GDPS instead shows the sfc
low crossing the Great Lakes. Given this disagreement, and this
development being very close to the end of the period, precip chances
are being kept below the mentionable threshold thru 12z Sat.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
At KCLT and elsewhere: Expect VFR conditions to prevail thru the
12z taf period. Skies remain mostly clear early this morning as the
sfc low lifts farther NE and away from our area. KAVL remains the
only exception, where they continue to see MVFR cigs just under
3000ft in the moist, NWLY flow. KAVL should scatter out by the late
morning to early aftn at the latest. In addition, they will continue
to see gusts in the 20 to 25kt range thru the morning with gusts
tapering off by the aftn. Otherwise, winds will remain out of the
W to NW thru the period with speeds weakening this evening as the
pressure gradient relaxes. Most sites will likely go light and
vrb overnight with patchy fog possible, especially over the mtn
valleys.

Outlook: VFR conditions expected for most of the weekend. Moisture
will return Sunday night with cig restrictions likely on Monday as
another low pressure system lifts out of the Gulf and up the Atlantic
Coast.

Confidence Table...

            11-17Z        17-23Z        23-05Z        05-06Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High  89%     High 100%     High 100%     High 100%
KHKY       High 100%     High 100%     High 100%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High 100%     High 100%

The percentage reflects the number of guidance members agreeing
with the scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables are available at
the following link:

www.weather.gov/gsp/aviation
-- End Changed Discussion --

&&

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

&&

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