Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 210235
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
935 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 930 PM EST: The beginning of upglide-induced stratocumulus is
evident on satellite imagery and surface observations over southeast
Georgia late this evening. The numerical models continue to indicate
that isentropic lift and shallow moisture mainly below 850 mb will
arrive in the upper Savannah River area late tonight and then spread
northward across the forecast area through Tuesday. It still appears
that the combination of thickening cirrus aloft and scattered lower
stratocumulus late should keep temperatures from crashing in
southwest sections - with above freezing temps likely when any light
precip starts early Tuesday. Will feature mainly very light rain and
drizzle as the predominant precipitation character with anything
that falls given the shallow nature of the moisture.

The continued isentropic lift, and weak upslope into the
southern/eastern mountain escarpments, will permit chance PoPs for
measurable precipitation in most areas at some point on Tuesday.
Anticipate a rather dreary day, with plenty of clouds and
temperatures struggling into the 50s in most areas. QPF will be very
light throughout.

&&

.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 Piedment. 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
Piedment 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 /03Z TUESDAY THROUGH SATURDAY/...
At KCLT and Elsewhere: VFR conditions will continue through much of
the overnight hours, with mainly cirrus early but lowering VFR
stratocumulus developing from the southwest the closer we get to
daybreak. The guidance remains mixed, but MVFR cigs arriving from
the southwest seem likely starting around 09Z to 11Z at KAND and
arriving 14Z to 16Z at KCLT. Light southerly flow will likely adjust
to east-northeast once any light precipitation, likely very light
rain or drizzle, begins falling from the lowering cloud bases. MVFR
conditions could well get locked in through late Tuesday as upglide
slowly wanes.

Outlook: Low-level moisture may keep restrictions and perhaps light
rain or drizzle in the forecast into Tuesday night. Otherwise,
dry/cool conditions should return through 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...HG
SHORT TERM...SW/Wimberley
LONG TERM...CDG
AVIATION...HG



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