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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KGSP 031144
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
644 AM EST Thu Dec 3 2020

.SYNOPSIS...
A moderating high pressure area remains over the area today. A low
pressure system will cross the area Saturday. A return to cool and
generally dry weather is expected next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 645 AM Thursday: Still on track with the current forecast
trend through the near-term. Some morning fog has started showing up
over Lake Hartwell and surrounding lakes. This not expected to spew
out past the bodies of water. High clouds from the west have started
to enter the far western zones, so a slightly faster trend in
bringing in clouds were updated in the grids. Expect the mid- to
upper-level cloud deck to increase through the day. Temperatures
should bottom out into the mid to upper 20s by sunrise for most
locations with very good radiational cooling and light winds.

Otherwise, another pleasant day will be in store for the area
on Thursday as the sfc high axis pushes across SC during the morning
hours which will back low-level winds from a NW-ly to a S-ly
component by the afternoon as the inversion mixes out. A closed
upper low has settled over the Southern Plains recently and will
gradually push eastward, which is our next weather producer.
Shortwave ridging today will allow the area to moderate in
temperatures for Thursday and Thursday night, but quickly slides
across the region with SW-ly flow aloft building in ahead of the
upper low. Mid- to upper-level clouds and moisture advection really
stack the deck Thursday night into Friday. The associated frontal
boundary and precip with the upper low won`t impact the cwa during
the near-term and more information on how everything pans out will
be discussed in the short-term. Highs for Thursday will be in the
50s for most with a couple of spots in the mountains struggling to
get out of the 40s. Lows will be in the 30s to low 40s in the
southern tier. Chance PoPs will be back in the forecast for the SW
facing slopes and Smokies after 06Z Friday.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 245 AM Thursday: Good agreement with the guidance on the short
term, the main difference is the ECMWF remains faster with the
movement of the low pressure system. Therefore, have discounted the
timing of the ECMWF and have gone with a slower solution. An upper
low moves out of the Southern Plains into the MS Valley Friday. The
low moves to the Southern Appalachians Friday night and to the
Delmarva Saturday. Surface low cyclogenesis takes place to our west
with the low moving into the TN valley Friday. The low then moves by
just to our north Friday night bringing a cold front into the area.
Guidance now shows the warm sector air mass moving into at least a
portion of the CWFA from the south with some sbCAPE developing over
or near the I-77 corridor Friday night into early Saturday. With
very strong shear and helicity over the area, any location where
sbCAPE can be tapped would have a chance for high shear/low CAPE
severe convection. As always, the chance of this is low and highly
dependent on where/if any sbCAPE develops. Even with only a low
severe threat, breezy to windy conditions are expected across the
area as the front moves through with a tight pressure gradient and
increasing low level winds.

The quick movement of this system and lack of strong convection
keeps overall QPF on the moderate side, generally less than an inch
outside of the mountains. Across the mountains, 1 to 2 inches are
possible producing a low end isolated flood threat, especially if
there area stronger convective elements and some training. Similar
caveats apply to the flood threat as the severe threat.

As the cyclone becomes increasingly wrapped up as it moves away from
the area, cold advection and lingering moisture from the TN Valley
into the southern Appalachians should result in at least a brief
period of northwest flow snow showers on Saturday, with minor accums
possible across the higher elevations near the TN border. CAA and
NW winds are not especially strong or prolonged, so for now, it
looks to be a minor event at the highest elevations.

Highs will be near normal Friday then fall to around 5 degrees below
normal for Saturday across the mountains but remain near normal
elsewhere. Lows 5 to 10 degrees above normal Friday night fall to
around 5 degrees below normal Saturday night.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 320 AM Thursday: A complex/split upper air flow pattern will
persist through the medium range, with troughing generally
predominant over the East. As such, temps are forecast to be a
little below normal until Wednesday when heights rise as the trough
axis moves east bringing temps back to normal. There is agreement
that an upper low/clipper type system crosses the area in the Monday
to Tuesday time frame. In fact the trough digs far enough south that
some precip breaks containment into the Piedmont and foothills. In
collaboration with neighboring offices, we have introduced slight
chance PoP for the mountains and CLT metro area. There is
disagreement on QPF and thermal profiles, but should this happen, a
rain/snow mix would be possible. A dry forecast is expected for the
periods before and after this system.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
At KCLT and elsewhere: VFR conditions will be in store through the
TAF period. Light winds area variable for now with the exception of
KAVL that still holds a NW-ly component. As the inversion mixes out
in the morning winds will back to a SW to S-ly component by
lunchtime for most sites. Fog isn`t likely across any of the TAF
sites, but mountain valleys and lakes will likely receive some kind
of reduction in vsby due to isolated fog development. Sfc high will
be in control for half of the TAF period, but mid- to upper-level
clouds have already started to roll in and will continue to increase
into the nighttime period as the sfc high pushes offshore.
Restrictions of any kind are not expected until late Thursday night
into Friday.

Outlook: VFR conditions will prevail until the next system
approaches the area late tonight into Friday. VFR conditions should
prevail once again over the weekend.

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 100%     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

&&

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

&&

$$
SYNOPSIS...RWH
NEAR TERM...CAC
SHORT TERM...RWH
LONG TERM...RWH
AVIATION...CAC