Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 171138

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
638 AM EST Fri Nov 17 2017

Dry high pressure will linger atop the region today.  A strong
cold front will cross the area Saturday night followed by dry and
cooler weather Monday and Tuesday.


As of 630 AM Fri: Skies continue to be virtually clear under the
influence of dry high pressure centered over Ohio. While light winds
overnight kept the boundary layer relatively warm and mixed in most
of the area, a few outlying areas are experiencing nearly saturated
sfc conditions with temps near or below freezing. Shallow freezing
fog, particularly in depressions in the landscape, will occur for
the next hour or two in these areas and could result in slippery
frost. Otherwise full sunshine is expected today, as the high
begins to migrate across our area and eventually to the Carolina
coast. This will bring winds around to the south. Based on the
best performing guidance of late, max temps should reach the
lower 60s over the SC/GA zones, reaching 60 in the mountain
valleys and portions of the NC Piedmont also.

Tonight, upper height trends begin to reverse as a sharp and dynamic
trough swings into the Mississippi Valley. Shallow moist isentropic
upglide develops over the southern half of the CWFA, resulting in
expanding cloud cover (in addition to upper level cloudiness blowing
in downstream of that trough). It appears too shallow to expect
a mentionable chance of any precip, even against the south-facing
Escarpment. Mins will be 1-2 categories warmer than this morning.


As of 235 AM Friday: A strong short wave trough approaches the area
Saturday then crosses the area Saturday night. This pushes a cold
front quickly across the area Saturday night. Moisture increases
across the area in the southwesterly flow. Although the best forcing
moves north, there is enough forcing for showers to develop across
the mountains late on Saturday, then spread across the area Saturday
night as the front moves through. H85 winds increase ahead of and
behind the front creating quite a bit of shear. Instability will be
minimal however keeping the threat of thunderstorms quite low. The
winds are strong enough that a wind advisory or even a high wind
warning may be needed across the NC mountains. Breezy to windy
conditions will develop elsewhere. Even with the quick movement of
this system, moisture will be high enough for moderate to possibly
heavy precip to develop across the mountains with the front. That
said, excessive rainfall is not expected. Light to possibly moderate
QPF expected elsewhere. Precip ends quickly outside of the mountains
late Saturday night, but lingers across the mountains.

Lingering low level moisture, strong NW flow, and CAA will keep NW
flow precip across the TN border counties. There`s even a trailing
short wave moving through. Expect the rain to change to snow above
3500 feet, but many valleys will stay all rain. Precip tapers off
quickly Sunday but clouds linger across the TN border counties.
Clearing skies and dry conditions expected elsewhere. Windy to
breezy conditions expected across the area. Clouds diminish across
the TN border Sunday night with mostly clear skies expected all
areas through Monday. Winds diminish for all but the highest

Temps above normal Saturday ahead of the front fall to around 10
degrees below normal for Sunday and Monday.


As of 200 AM EST Friday: The medium range begins Monday night with
the area under the influence of upper shortwave ridging and surface
high pressure. A shortwave trough will swing towards the southern
Appalachians Tuesday, with the surface high centered near the Outer
Banks providing a brief period of moist southeasterly flow. Guidance
is now hinting that the upper support and shallow moisture plume may
align Tuesday afternoon and evening to provide some QPF response, so
pops were increased just to slight chance to account for this. Dry
air will filter in Wednesday before the next upper shortwave dives
towards the Gulf of Mexico and eventually cuts off. Guidance has
been inconsistent on the handling of this low, though confidence is
increasing that the low will track to the south of our area,
confining QPF response mainly to Florida and Georgia through Friday.
Guidance again diverges on the handling of the same Gulf low and QPF
response in our area after next Friday. Temperatures will remain
near or slightly below average through the period.


At KCLT and Elsewhere: VFR at all TAF sites. High pressure presently
over the Ohio Valley will translate across the area today, setting
up over the Carolina coast tonight. This will lead to more or
less continually veering winds: light SE winds at all sites by
mid-afternoon, eventually reaching SW tonight. The only clouds that
will be seen today will be occasional cirrus passing through within
relatively fast and northwesterly upper level flow. This evening, as
a potent upper trough approaches from the west, thicker alto/cirrus
clouds will form high-based cigs. Low-level warm upglide will also
develop over portions of GA/SC, too shallow for any precip but
producing FEW-SCT low VFR to MVFR level clouds near daybreak. Low
cigs currently are not expected but model trends bear watching.

Outlook: Potential for MVFR/IFR due to increased cloud cover/low
cigs and increasing rain chances Saturday with a cold front pushing
thru Saturday night.  Otherwise expect VFR.

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:




NEAR TERM...Wimberley
LONG TERM...Carroll
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