Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 021149
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
649 AM 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/...
As of 645 AM EST Wednesday: most of grids are right on track with
the original trend. Widespread 20s across the board with some
readings in the 10s over parts of the mountains to start off the
day. Abundant insolation will increase temperatures fairly quick
through the morning hours, while mostly sunny skies prevail through
the rest of the day.

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.

&&

.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 TUESDAY/...
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 /12Z WEDNESDAY THROUGH SUNDAY/...
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...

            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



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