Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 120014

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
714 PM EST Mon Dec 11 2017

High pressure will weaken before a strong cold front crosses the
area overnight. Dry high pressure will build back in Wednesday with
temperatures dropping below normal. A slow warming trend begins late
in the week.


As of 700 PM EST Monday: Temperatures are running pretty much on
track this evening, so most of the updates are for aviation-related
parameters. New guidance is ticking slightly up on winds across the
mountains, so will reflect that when the NPW is updated.

Otherwise, as conditions remain quiet, temperatures will dip into
the mid 30`s overnight, with the upper 20`s/low 30`s across the
northern foothills into the NC mountains. Expect clouds to increase
tonight ahead of the next approaching system, a shortwave/clipper
system, well defined by latest water vapor imagery. As this system
continues to progress eastward across the Ohio Valley this afternoon
and through tonight, it`s associated dry cold front will push west
to east, making it`s way through the mountains late overnight into
the early morning hours on Tuesday.

Behind the front, low-level moisture along the TN/NC border and a
return to northwest flow will bring snow showers to the NC mountains
on Tuesday. New snow accumulations of 1 to 2 inches are possible
right along the TN/NC border, as noted in the Winter Weather
Advisory. Increased CAA will also bring increased northwest winds
across the entire area, with sustained winds 10 to 15 kts and higher
gusts to near 20 kts across the Upstate and Piedmont. Into the
mountains, higher winds are expected thus warranting a wind advisory
for portions of the NC mountain counties, some for areas above 3500
ft. Aside from the mountains, conditions will remain quiet
weather wise on Tuesday, as lingering clouds begin to decrease into
the evening hours. Expect high temperatures in the upper 40`s to
lower 50`s across the area on Tuesday, with the exception of 30`s
across the mountains.


As of 245 PM EDT Monday: The short term fcst period kicks off on
Tuesday night amidst broad troffing across the eastern CONUS aiding
prominent northwest flow into the southern Appalachians.  With that,
llv moisture sufficient for snow showers will remain in place along
the spine of the Appalachians at fcst initialization.  Thus the near
term winter weather advisories as well as wind advisories will carry
over until Wednesday morning given gusty winds and snow totals in
the 2-3" range.  In addition, these potent winds combined with the
caa regime will lead to wind chills below zero across much of the
high terrain, yet reaching advisory criteria across the northern
mountains, as well as locales above 3500ft southward.  Therefore a
wind chill advisory for Tuesday night has also been issued that will
run through 7AM Wednesday for wind chills less than minus 5 degrees.

Beyond that, the forecast dries out yet remains cold with
temperatures below normal levels through Wednesday.  Meanwhile
another weak clipper system sliding through/into the OH valley will
pass north of the fcst area Wednesday night into Thursday likely
with little fanfare across northeast GA and the western Carolinas.
Lastly, the pattern looks to shift on Thursday as upper/mid lvl flow
backs swly thanks to the ejection of the persistent longwave trof.
This pattern shift will lead to some gradual warming yielding
temperatures that will approach normal by the end of the period.


As of 225 PM EST Monday: the extended fcst picks up at 00z on
Friday with another round of impressive upper-lvl energy diving
southward on the on the backside of the persistent eastern CONUS
upper trof. The trof axis is expected to pass over the fcst area
by late Fri/early Sat and then rapidly lift NE of the region over
the next 12 to 24 hrs. The pattern then flattens out as we move into
Sunday. From this point onward, the extended models diverge a fair
amount wrt the synoptic pattern. The ECMWF deepens another upper
trof to our west and brings it to our area by late Sun/early Mon
while the latest 12z GFS and Canadian are about 12 to 24 hrs slower
with the trof. At the sfc, the pattern will remain dynamic thru
the period with a fair amount of uncertainty wrt the pattern
evolution. We do expect a coastal low to spin up on Friday just
off the NC Coast and become a strong Nor`easter over the next 24
hrs or so. Dry high pressure will slide in behind the low for
Sat and then move offshore by early Sun. Another low will spin up
to our west on Sun and bring another cold front to our doorstep
by late Sun/early Mon.


At KCLT and Elsewhere: VFR through the period with the possible
exception of brief MVFR tomorrow at KAVL with NW flow moisture
crossing the mountains. Expect low VFR stratocu/Cu to develop around
midday Tuesday for all sites. Cannot totally rule out brief -SHSN at
KAVL, but chances not high enough to include in TAF at this time.
Bigger impact will be the winds. Light SW winds to start the period
will increase Tuesday morning and veer out of the WNW by around 14-
15z. Gusts will pick up especially KAVL and KAND, where g25kt or
higher will be possible. As winds pick up aloft, before the stronger
winds reach the surface, some brief LLWS will be possible overnight
for KAVL; have included this from 03-08z.

Outlook: Restrictions may be possible Thursday night into Friday,
especially at KAVL, with a system approaching from the west.
Otherwise expect dry and cool, VFR conditions.

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 from 4 AM Tuesday to 7 AM EST
     Wednesday for NCZ033-048>052.
     Wind Advisory from 4 AM Tuesday to 7 AM EST Wednesday for
     Wind Chill Advisory from 10 PM Tuesday to 7 AM EST Wednesday
     for NCZ033-048>052-059.


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