Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 220343
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1043 PM EST Tue Nov 21 2017

.SYNOPSIS...
Moist southerly flow in the lower atmosphere will bring some small
chances for rain or drizzle until a weak cold front crosses our area
tonight.  A passing area of low pressure to our south may bring some
precipitation to the Midlands and Southern Upstate on Thanksgiving
Day. However, from Friday through early next week, dry high pressure
will dominate our weather.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
As of 1040 PM Tuesday...Light northeastward moving rain showers
along the I-77 corridor continue on an overall eastward track
tonight, as latest radar imagery depicts the heavier
precipitation now just south of the forecast area. Have adjusted
PoPs with the latest forecast update to account for a slightly
sped up decreasing trend, as am expecting activity to move out
of the area within the next few hours.

Upper trough across the Great Lakes continues to gradually
propagate eastward tonight as it`s associated cold front,
currently moving through the TN Valley, will push through the
area overnight. With lingering clouds, do not expect much of a
temperature drop overnight, as have kept with low to mid 40`s
for much of the area, and slightly cooler across the mountains.
Anticipate areas of fog to develop late overnight into the early
morning hours with light winds and low level moisture in place.
After daybreak, any fog development will begin to disperse as
dry air infiltrates into the area from high pressure building in
from the west. This feature along with a sfc low moving just
offshore up the Carolina coast, increased pressure gradient
across the area will aid in increased northerly winds (up to 10
kts) on Wednesday, with higher gusts from gap winds possible.
High temperatures will climb into the low to mid 60`s in the
afternoon hours, as the mountains remain a bit cooler in the
upper 40`s to 50`s.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
As of 230 PM Tuesday: A split 500 mb trough will phase into a deeper
longwave over the Appalachians on Thanksgiving, allowing a cool and
dry high pressure to settle in from the NW. As the trough phases,
weak cyclogenesis is expected over the eastern Gulf. The low will
slowly cross the FL Peninsula Thursday thru Friday. The 12z GFS is
still the only model that throws a shallow layer of moisture up into
the southern edge of the CWFA. It keeps a small area of light QPF
just south of Greenwood/Abbeville counties, and even then, the
forecast soundings look too dry for measurable rain. So I will go
with a dry fcst for Thanksgiving. There may be some stratocu across
NE GA and the Upstate, at least thru the morning, but otherwise, it
should be mostly sunny. Temps will be about 10 degrees below normal
on Thanksgiving, then rebound to about 3-5 degrees below normal on
Friday.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
As of 100 PM EST Tue: The medium range fcst period kicks off on
Friday night amidst broad eastern CONUS troffing with a northern
stream wave digging across the upper Midwest, while ridging prevails
out west.  At the surface, the wave that we have been watching
evolve in the guidance for a few days now continues to track
offshore, and therefore yielding no sig impacts across northeast
GA and the western Carolinas.  Weakening high pressure across the
region will allow for a brief period of wly/swly backed surface
flow into/through Saturday before the aforementioned northern
stream wave and surface cold front move into the region in the
evening/overnight hours.  There remains some discontinuity with
regard to any frontal precip as the GFS favors enough upper support
tied to the wave to produce a quick burst of rain, possibly snow
at the highest elevations, while the ECMWF remains dry.  As such,
both of these guidance sources favor no residual nwfs behind the
front among the cold advection.  Therefore, will leave the fcst
dry through this time frame.  Moving along, caa will prevail on
Sunday as deep layer high pressure settles across much of the
southern Appalachians leading to dry conditions and below normal
temperatures into Tuesday.    At that point, the upper ridge begins
to shift east taking the surface component along with it, leading to
sly veered flow and thus waa.  This is all ahead of a late period
front moving across the Mississippi River valley into Wednesday,
which shouldn`t yield any affects on the cwfa through periods end.

&&

.AVIATION /04Z WEDNESDAY THROUGH SUNDAY/...
At KCLT and Elsewhere: Latest radar imagery continues to depict
light showers moving across eastern portions of the forecast area,
thus have kept with VCSH/-SHRA for KCLT over the next couple of
hours. Overall, expect VFR cigs/vsbys to prevail through this
evening as conditions will gradually deteriorate to MVFR/IFR
(varying in severity) at all TAF sites as a cold front begins to
push through the area from the west. Cigs will continue to lower and
areas of fog develop late overnight into the early morning hours,
with conditions improving to VFR after daybreak on Wednesday. Winds
will become northwesterly, increasing to 4 to 8 kts towards the end
of the period, with the exception of KHKY AOB 10 kts, with gusts up
to 18 kts possible with gap winds.

Outlook: Expect VFR through the forecast period as dry/cool
conditions prevail.

Confidence Table...

            03-09Z        09-15Z        15-21Z        21-00Z
KCLT       Med   70%     Med   79%     High 100%     High 100%
KGSP       Med   60%     High  95%     High 100%     High 100%
KAVL       High  86%     High  95%     High 100%     High 100%
KHKY       Med   78%     High  81%     High 100%     High 100%
KGMU       Low   49%     High  96%     High 100%     High 100%
KAND       Low   37%     Low   57%     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 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...SGL
SHORT TERM...ARK
LONG TERM...CDG
AVIATION...TDP



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