Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 130351

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1051 PM EST Tue Dec 12 2017

Northwest flow moisture will dissipate over the mountains tonight,
with dry high pressure building over the region through mid-week. A
cold front will cross the area from the northwest Wednesday night
through Thursday before high pressure sets up through much of the
weekend. Low pressure and moisture are expected to return from the
west by early next week.


As of 1030 PM EST Tuesday: Temperature trends look good this
evening. Clouds have lifted north of the mountains so any light snow
showers should be over. Will leave the advisory in place to cover
any black ice issues that may develop, especially with temperatures
so low, but will refresh wording. No other changes at this time.

Otherwise, with a recently passed strong, dry cold front, northwest
winds will continue to increase across the area this afternoon as
strong CAA builds in. Expect increased winds to persist across the
NC mountains overnight into Wednesday morning. These increased winds
along with temperatures dropping into the lower teens to single
digits across the NC mountains will allow for wind chills to drop to
around 5 degrees above zero to minus 10 degrees below zero in
locations, mainly above 3500 ft near the TN border. Elsewhere,
overnight low temperatures will drop into the low to mid 20`s, with
wind chills in the mid to upper teens.

As sfc high pressure becomes situated to our south and clouds
decrease during the morning hours, expect a quiet yet cold day on
Wednesday. With northwest winds around 10 mph (slightly higher
across the NC mountains), afternoon high temperatures will climb
into the low to upper 40`s across the Upstate and Piedmont, where
colder temperatures in the 30`s will persist across the mountains.


As of 230 PM EDT Tuesday:  The short term fcst kicks off on
Wednesday evening as a Clipper wave slides across the southern Great
Lakes pulling a dry reinforcing cold front southward into the OH/TN
valleys by daybreak Thursday.  Guidance has trended slightly wetter
with this fropa, mainly focusing any moisture along western slopes
of the Appalachians where H85 flow remains veered nwly.  With that,
will continue the current low end pops across the central/northern
TN line mtn zones, with thermal profiles supportive of a few light
snow showers amidst gusty winds.  H85 flow looks to weaken into the
evening hours therefore any residual upslope snow showers should
wrap up quickly leading to a dry forecast to round out the period
as the front sweeps through the rest of the fcst area.

Meanwhile, another northern stream upper wave will dive through the
Rockies with deep layer flow across northeast GA and the western
Carolinas backing wly then swly overnight into Friday morning.
However, dry high pressure sliding east across the central
Appalachians will setup over/near the Delmarva by midday Friday
yielding weak cold advective nely flow in lee of the mountains.
Despite the intrusion of the weak front, temperatures across
the region on Thursday will be slightly warmer than recent days,
especially for the foothills/piedmont given ample downsloping and
thus modest insolation, not to mention possible backed swly sfc
flow thanks to lee troffing.  Temperatures will be cooler on Friday
as the aforementioned northern high edges southward into the region.


As of 220 PM EST Tuesday: the extended fcst picks up at 00z on
Saturday with the upper trof axis moving over the fcst area and
then rapidly lifting NE of the region over the next 12 to 24 hrs.
As we move into Sunday, the pattern flattens out as upper ridging
builds over the Greater Antilles. As we move into Monday, upper
ridging persists over the southeast as an embedded southern stream
H5 trof digs down across the Southern Rockies and moves eastward.
The ECMWF continues to be more progressive with this system and
brings it to our doorstep by Monday afternoon, while the other
long-range models are about 18 to 24 hrs slower. Either way, the
trof axis should be passing over the fcst area by the end of the
period on Tues. At the sfc, the pattern will remain dynamic thru
the period with quite a bit of uncertainty remaining wrt the pattern
evolution. On Sat, drying high pressure will slide in behind a departing
coastal low. The high is not expected to hang around for too long,
as it will shift NE and move off the Atlantic Coast on Sunday.
Beyond this point, the synoptic pattern becomes unclear as each
model has a different scenario wrt exactly where and when the
next sfc low will spin up to our west. They generally agree that
the later part of Sunday thru early Monday could be fairly wet
with some drying after that, however overall fcst confidence for
days 6 and 7 remains low at this time.


At KCLT and Elsewhere: Adjusted the winds just slightly to keep
them a tad more NW rather than WNW, but no other changes to the CLT
TAF for the 04z AMD. VFR through the period. SCT low VFR Cu still
possible for another few hours at KAVL, but otherwise just some
passing high clouds especially Wed afternoon. NW winds will continue
to be gusty this evening, but will subside somewhat overnight,
dropping to between 5-10kt just about everywhere (but will remain
highest at KAVL). Winds back to the SW by sunrise, and some low-end
gusts possible in the afternoon everywhere.

Outlook: Potential continues for flight restrictions Thursday night
into Friday, especially at KAVL, with a system approaching from the
west. Otherwise expect VFR.

Confidence Table...

            15-21Z        21-03Z        03-09Z        09-12Z
KCLT       High  81%     High  82%     Med   68%     Low   56%
KGSP       Med   70%     Med   75%     High  83%     Med   64%
KAVL       High  94%     High  85%     Med   70%     High  87%
KHKY       High 100%     High  83%     Med   66%     High 100%
KGMU       Med   76%     High  86%     High  85%     Med   63%
KAND       Med   76%     Med   65%     High  90%     Med   61%

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:


NC...Winter Weather Advisory until 7 AM EST Wednesday for NCZ033-
     Wind Advisory until 7 AM EST Wednesday for NCZ033-048>052-058-
     Wind Chill Advisory until 7 AM EST Wednesday for NCZ033-


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