Area Forecast Discussion
Issued by NWS Greer, SC

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766
FXUS62 KGSP 080757
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
257 AM EST Thu Dec 8 2016

.SYNOPSIS...
Cold high pressure will gradually spread across the region, bringing
the coldest temperatures so far this season. A cold front will
approach the Western Carolinas late Sunday and move through the area
early Monday with high pressure returning in its wake.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 230 AM EST Thursday: Surface low remains in place across the
foothills, along a cold front that will be pushing through the area
today.  The front is very dry, with no precip reaching the ground
anywhere across the area, even looking upstream into KY.  Some of
the guidance wants to break containment and allow some precipitation
to fall across the NC Piedmont later this morning, but overall
chances are extremely low. If any precipitation does fall across the
mountains, for now temperatures except for the highest elevations
remain plenty warm so that no mixed precip is a concern, but will
have to monitor the predawn hours as temperatures reach the
overnight lows (though by then what little moisture there is will be
to the east).

The bigger story is that behind the front, a surface high anchored
over Canada but ridging all the way down into the Southern Plains
and around the base of a shortwave lingering over the Great Lakes
will continue to push an Arctic airmass into the area, with the
coldest air of the season right on our doorstep. For the Piedmont,
temperatures today will be cooler than those yesterday and a few
degrees below seasonal normals, but the mountains will certainly
begin to feel the deep-layer CAA with some areas barely getting
above freezing and really not much improvement from this morning`s
expected lows. Temperatures will plummet this evening after sunset
with almost a 30-degree diurnal range across the Piedmont and
certainly the coldest air of the season. Widespread teens expected
across the mountains with mid 20s at best across the Piedmont. Add
in the strong NW winds behind the front and we have some pretty cold
wind chills to deal with overnight tonight - not enough for a wind
chill advisory but most certainly worth note, especially for
children waiting for the bus Friday morning who will need to be
properly dressed.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 230 AM EST Thursday...Quasi-zonal flow will persist in the
upper levels across the entire CONUS during the short term. At the
surface, a cold high pressure system will gradually shift east from
the Mid-MS Valley to the Mid-Atlantic Coast by 12Z Sunday. Skies
will be mostly clear thru the period, with temps well below normal.
Highs will range from the 20s to mid 30s in the mountains Friday, and
mid 30s to lower 40s Saturday. The Piedmont will see temps in the
40s both days. As for lows, temps will be in the teens in the
mountains Friday night, and 20s Saturday night. In the Piedmont,
lows will be in the 20s both nights.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 250 AM EST Thursday: The first part of the ext range features
more zonal flow than the previous package as the models have slowed
the development of a midwestern h5 s/w. This has the effect of
keeping the deeper moisture west of the NC mtns...esp during the day
Sun while a weak sfc low develops through the OH Valley. Pops were
adj down a bit to lower and mid range chances overnight as the best
moisture flux may not reach the mtn spine zones till 12z. Enuf cold
air will be in place for -snsh or a ra/sn mix across the nrn mtns
with little accums before sfc temps warm above freezing. The GFS
model soundings dropped across Avery Co show little moisture
available while temps are favorable for wintry precip...while the
ECMWF soundings show very dry low levels. There is a strong warm
nose however...and if moisture levels pan out earlier than
fcst/d...areas of -fzra will be possible before daybreak.

There is a general consensus with the eastward progression of the
cold front thru the day Mon...however the guidance has wholly
varying ideas with the amount of available moisture. For now will
expect a low to mid chance pop event over the cwfa with lingering
weak nw flow -snsh overnight. Not sure what to think about Wed with
the models widely differing in their synoptic/hemispheric solns. The
GFS is much more amplified than the ECMWF and quickly induces
cyclogenesis up toward the glakes region while pushing a strong moist
cold front across the area thru 12z...and very cold arctic high
pushing in behind that. The ECMWF on the other hand...has more zonal
flow and a weaker sfc high...while a stationary front remains to our
southeast. Thus...with high uncertainty will keep pops limited to
slight or low-end chances thru the last period....mainly nw flow
-snsh for now. As far as temps...the period begins a couple cats
below normal Sun...rebounds to arnd normal Mon-Wed...then the colder
arctic air pushing in Wed night.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
At KCLT and elsewhere: MVFR and IFR restrictions in place again this
morning and will monitor expansion of restrictions as necessary for
TAF amendments and potential for Dense Fog Advisory. Should see
improvement again after sunrise as dry air filters in. Light SW to W
winds early this morning will shift NW and increase to 10-15kt with
some low-end gusts (higher at KAVL). Should see a mid-level deck
push across the area during the day, but clearing filtering in this
afternoon. NW winds will drop off a little late tonight but
generally remain 5-10kt.

Outlook: Drier and much colder conditions continue through the
weekend. Another front will approach the area Sunday afternoon
bringing a chance of precipitation and restrictions.

Confidence Table...

            08-14Z        14-20Z        20-02Z        02-06Z
KCLT       Med   73%     High  98%     High 100%     High 100%
KGSP       Low   58%     High  98%     High 100%     High 100%
KAVL       Med   70%     High 100%     High 100%     High 100%
KHKY       Med   74%     High 100%     High 100%     High 100%
KGMU       Low   58%     High  98%     High 100%     High 100%
KAND       Low   58%     High  91%     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...SBK
NEAR TERM...TDP
SHORT TERM...ARK
LONG TERM...SBK
AVIATION...TDP



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