Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 201906
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
206 PM EST Mon Nov 20 2017

.SYNOPSIS...
Cool high pressure moves off the Carolina coast tonight as a weak
cold front approaches from the northwest.  This front crosses the
area Tuesday night and Wednesday. Low pressure will develop over the
Gulf on Thanksgiving Day then cross Florida and up the Atlantic
seaboard through Friday. Another strong cold front will arrive
over the weekend.

&&

.NEAR TERM /THROUGH TUESDAY/...
As of 130 PM EST Monday: Dry high pressure will continue to dominate
the area today, but a shortwave trough digging down the MS Valley
will continue to push the high offshore this afternoon and tonight.
Another fast shortwave diving down out of the northern Rockies
tonight will phase with the MS Valley wave, resulting in a high-
amplitude trough pushing toward the Appalachians by the end of the
period. The approaching front will be mainly dry on the southern
end, with most of the dynamics remaining well to the north, but we
will be dealing with increasing low-level moisture coming in from
the Atlantic and eastern Gulf around the western periphery of the
Atlantic high.

Isentropic upglide increases across extreme western zones after
midnight, and with orographic lift added to this, expect to see
increasing clouds and chances for light rain as we push toward
sunrise. The clouds will luckily keep temperatures above freezing in
areas where moisture will be on the increase, but cannot totally
rule out some very light freezing drizzle across the southern
mountains as the precip starts. Temperatures tonight should be
several (8-10) degrees warmer than they were this morning, but
definitely some bust potential there if clouds come in earlier (or
later) than expected.

Moisture is very shallow and limited to about 850mb and below, with
pretty dry airmass above it, so most precip will be in the form of
light rain or perhaps even drizzle. Pops were still generally held
to low chances and below, but wouldn`t be surprised to see the need
for increase pops (but with continued very low QPF). Clouds and
moisture/rain will keep temperatures down again tomorrow, 5-8
degrees below normal.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
As of 130 PM Mon: Northwest mid level flow will be in place through
the period. This will lead to mainly dry conditions with just a few
mainly mountain showers exiting the region Tuesday night. Strong
high pressure will build south across the Ohio and Tennessee Valleys
while low pressure will form over Florida. The forecast area will be
in between these features with the strong high slowly bridging the
mountains on Wednesday and Thanksgiving day.

Wednesday will be the warmer day of this period with temperatures
reaching into the upper 50s to lower 60s in the Piedmont.
Expect cooler conditions in the mountains especially the western
mountains as colder air slowly pushes into the region. Thursday
will be cooler in all areas with highs reaching into the lower
to middle 50s in the Piedmont and 40s to lower 50s in the
mountains.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
As of 200 PM EST Monday:  The medium range fcst period kicks off
on Thursday night amidst an amplified upper pattern highlighted
by troffing across the east and broad ridging out west.  At the
surface, weak high pressure will be in place across northeast
GA and the Carolinas as cyclogenesis occurs in the GOM beneath a
southern stream shortwave impulse and the broader overall trof.
Guidance seems to be converging on the on a solution which favors
a slower ejecting GOM surface low, which is turn allows for
arrival of the next approaching northern stream wave on Friday.
Therefore, it looks that the previous non mentionable pops were
the right call then, and now, as the arriving northern stream
wave picks up the coastal wave.   In the meantime, the weak high
across the cwfa will slowly slide east allowing for a brief window
of wly/swly veered sfc flow ahead of the next trof/front that is
set to arrive Saturday night.  With that front, strong caa looks
favored amidst deep nwly flow bringing yet another cold Canadian
airmass into the eastern sector of the CONUS.  Guidance favors
said nwly flow banking against the high terrain Sunday with some
Great Lakes moisture fetching possible.  Therefore we could be
looking at our first potential advisory level mtn snowfall of the
season, however confidence is rather low at this point given the
time range.  Elsewhere, expecting dry/cold conditions to round of
the period with temperatures possibly falling nearly 2 categories
below normal levels.

&&

.AVIATION /19Z MONDAY THROUGH SATURDAY/...
At KCLT and Elsewhere: VFR this afternoon and tonight with light S
winds, occasionally VRB. Cirrus will increase from the W and thicken
through the period, then low-level moisture will increase from the
S/SW overnight. Expect low VFR cigs to filter into the Upstate
around or just before sunrise, with MVFR shortly thereafter, as well
as PROB30 for -RA/SHRA. For KCLT/KHKY, MVFR should overspread the
area by around 15z. For now, KAVL forecast remains low VFR.

Outlook: Low level moisture may keep restrictions and perhaps -RA
through Tuesday night. Otherwise, dry/cool conditions should persist
into late week.

Confidence Table...

            17-23Z        23-05Z        05-11Z        11-12Z
KCLT       High  87%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High  94%     High 100%     High 100%     High 100%
KHKY       High 100%     High 100%     High 100%     Low   58%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High  94%     High 100%     High 100%     High  83%

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

www.weather.gov/gsp/aviation

&&

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

&&

$$
SYNOPSIS...DEO
NEAR TERM...TDP
SHORT TERM...SCW
LONG TERM...CDG
AVIATION...TDP



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