Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 210559

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1259 AM EST Tue Nov 21 2017

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.


As of 1255 AM EST: The beginning of upglide-induced stratocumulus is
evident on satellite imagery and surface observations over NE GA and
the Upstate The numerical models continue to indicate that
isentropic lift and shallow moisture mainly below 850 mb will arrive
in the upper Savannah River before daybreak then spread northward
across the forecast area through the morning. This is in line with
current observations. 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.


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.


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.


At KCLT and Elsewhere: VFR conditions will continue through much of
the early morning but with lowering VFR stratocumulus moving NE
across the area. The guidance remains mixed, but given upstream
conditions, MVFR cigs arriving from the southwest seem likely
starting around 09Z at KAND and 13Z 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. Conditions will likely deteriorate
overnight as low level moisture remains over the area.

Outlook: Low-level moisture may keep restrictions in the forecast
into early Wednesday morning. 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:




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