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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KGSP 021809
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
109 PM EST Wed Dec 2 2020

.SYNOPSIS...
A moderating high pressure area will be in control of our weather
through Thursday. A low pressure system will cross the area this
weekend. Generally fair weather expected next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
As of 1 PM EST Wednesday: Quiet weather continues with clear skies
and temperatures recovering nicely under full sun. A relaxing
surface pressure gradient is allowing winds across the mountains to
gradually drop off. The forecast is tracking well with updates this
package focused on aviation interests.

Otherwise sfc high and shortwave ridging begin to move into the area
today and slightly moderates the overall airmass. The departing
trough will continue to produce gusty winds, mainly across the
mountains as the backside of it continues to move over the area this
morning. As the sfc high slides across the Southeast and over our
region during the day, expect a shift in the winds to mainly support
a west to southwesterly component. Downsloping winds will be in
store with this wind shift and dry air continues to filter in
through the mid-and upper-levels. With a slight breeze and the
amount of dry air aloft, expect min RH values to dip below 20%,
which can lead to some form of fire concerns, but shouldn`t rise to
the occasion with the recent rain and mountain snow. There will be
an uptick in max temperatures today as we return closer to normal
for this time of the year due to increasing heights, but still
remaining ~5 degrees below normal for most locations. Lows tonight
will into the 20s across the cwa with a few spots slightly warmer,
hovering near the freezing mark through the overnight hours.
-- End Changed Discussion --

&&

.SHORT TERM /THURSDAY/...
As of 240 AM Wednesday: Guidance coming into better agreement
regarding the weather system affecting our area Friday and Saturday
although some differences remain. Before then, Thursday will be dry
as high pressure slides off shore. Highs will be near to slightly
above normal.

Change begins Thursday night as an upper low over the southern
Plains begins moving east as some flavor of phasing with a northern
stream short wave diving into the Great Lakes. The ECMWF shows
greater phasing as the low opens up and quickly moves across the
area as it is absorbed into the developing East Coast trough. The
GFS keeps the low closed making it the dominant system and slowly
moving it across our area. A surface low moves to near the Mobile
area by Friday morning with an inverted trough to the north. Low
level flow turns southerly with increasing low level moisture and
isentropic lift. The guidance has generally slowed keeping most of
the precip to the west Thursday night, then spreading precip over
the area Friday. Forecast soundings show a warm nose developing
which would mean precip would be rain, but could be a brief period
of freezing rain if temps were cold enough across portions of the
mountains. For now, there doesn`t appear to be a significant chance
of wintry precip Thursday night/Friday morning.

The surface low takes on more of a Miller B look as the low moves
north along the inverted trough and strengthens Friday and Friday
night. This spreads showers across the area. The ECMWF is faster
showing a mainly dry Saturday as the low and associated cold front
move east. The GFS is slower with showers ending Saturday morning.
Both show the potential for heavy rainfall. The GFS also shows some
muCAPE developing as the cold front moves through along with strong
shear and helicity. Of course, there are still questions regarding
these features, so flooding and severe potential remains uncertain.

Both models also show a moist NW flow with CAA developing behind the
departing system suggesting a period of NW flow snow. The GFS is
more bullish than the ECMWF, so amounts are uncertain as well.

Highs remain nearly steady Friday and Saturday. Lows will be above
normal Thursday and Friday nights, then fall below normal Saturday
night.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
As of 310 AM Wednesday: Forecast for the long term rather tame
compared to the short term. A series of upper lows and short waves
drop through the long wave trough over the eastern CONUS. Guidance
differs on timing and track of these systems. The do agree that any
cyclogenesis associated with these systems will generally be
somewhere off shore well away from our CWFA. There is potential for
some moisture to brush the mountains with elevation rain snow
sometime during this period. However, timing and amounts differ
completely. Therefore, have continued with a dry forecast for now.
Windy to breezy conditions may also develop from time to time. Temps
will remain nearly steady up to 5 degrees below normal through the
period.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
-- Changed Discussion --
At KCLT and elsewhere: VFR through the period, with the pesky cloud
deck that lingered along the TN border and northern tier through the
overnight hours has almost fully dissipated and should quickly
scour out after sunrise. WNW winds expected generally through the
morning period, with some low-end gusts still possible, especially
at KAVL. Could see some wind components backing more to WSW
especially across the Piedmont this afternoon, but by then wind
speeds should be 5kt or below.

Outlook: VFR conditions will prevail until the next system
approaches the area late Thursday into Friday.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       Low   50%     Low   50%     Low   50%     Low   50%
KGSP       Low   50%     Low   50%     Low   50%     Low   50%
KAVL       Low   50%     Low   50%     Low   50%     Low   50%
KHKY       Low   50%     Low   50%     Low   50%     Low   50%
KGMU       Low   50%     Low   50%     Low   50%     Low   50%
KAND       Low   50%     Low   50%     Low   50%     Low   50%

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...RWH
NEAR TERM...CAC/Munroe
SHORT TERM...RWH
LONG TERM...RWH
AVIATION...Munroe