Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 191931

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
231 PM EST Fri Jan 19 2018

Cool high pressure will gradually move offshore this weekend giving
way to a warming southerly flow of air. A cold front arriving from
the west will bring precipitation to the region early next week,
with drying following through mid-week.


As of 220 PM EST: An SPS for black ice will be issued for the
western piedmont of NC and the northern NC foothills tonight into
Saturday morning. Visible satellite imagery still shows some
lingering snow cover in this area and temperatures expected to dip
well into the 20s overnight.

Otherwise, a weak but dry upper trough axis will approach from the
west through the evening, while the southern part of the upstream
split flow pattern continues to close off over eastern Texas and
western Louisiana. Then, the 500 mb closed system will slowly
migrate across the Deep South tonight through Saturday. Any deeper
layer moisture should remain shunted to our southwest through the
period, however 950 to 850 mb moisture in westerly upslope flow
could return to the NC mountains late tonight through Saturday. The
latest NAM and SREF are spitting out some light QPF along the
western mountains overnight through Saturday. This is troublesome
because if it occurs early enough, western mountain temps will still
be below freezing. However, the GFS and ECMWF remain dry, and the
SREF has onset a touch later, so will confine any daybreak PoPs to
slight chance of freezing rain or drizzle, at worst. Maxes should
rebound nicely into the 50s most everywhere Saturday afternoon, with
upper 40s along the mountain ridge tops.


As of 230 PM EST Friday:  The short term fcst period kicks
off on Saturday night amidst a weak H5 low moving atop the I10
corridor with shortwave ridging to the west over the MS delta
and a deepening trof further west atop the Rockies.  At the
surface, weak high pressure across the southern Appalachians
will be slowly meandering eastward while cyclogenesis occurs
over the plains beneath the aforementioned Rocky Mountain trof.
Pattern evolution into/through Sunday will highlighted by the
southeast ridge sliding over the western Atlantic allowing for
persistent southerly waa across the southeast states while the
Plains cyclone deepens further beneath a now closed upper low, all
setting up a nice zone of baroclynicity along the MS river valley.

A cold front associated with this system, will march east
into/through the MS valley on Monday morning while gradual waa
improves surface dewpoints eastward across northeast GA and the
Carolinas.  Guidance has converged nicely with regard to timing
of this frontal intrusion into the NC high terrain and northeast
GA by late day Monday, with perhaps some upsloping of moisture
amidst modest sly H850/H925 flow along the southern Blue Ridge a few
hours earlier.  From that point guidance favors an evening/overnight
fropa across the remainder of the fcst area, fortunately limiting
potential instability amidst a rather dynamically robust system.
That being said, higher elevations across the region could see some
impacts from high winds given the strength of the sly llj overnight
into Tuesday morning.  Thus the fcst will remain dry with above
normal temperatures favored through midday Monday.  At that point
pops will gradually ramp up from the southwest with high likely
pops favored regionwide at some point through the overnight hours.
Pops will taper sharply from the west toward daybreak Tuesday with
only slight chances included along/east of I77 as well as along
the TN line where a brief round of nwfs showers cannot be ruled out.


As of 215 PM Fri: The frontal precip is expected to depart the
area Tuesday morning; the already small chances for upslope precip
along the Tenn border look to taper off by midday given relatively
backed winds and diminishing moisture. Continental high pressure
will move into the Southeast behind the front, and should more or
less remain over the area through the rest of the work week. 850mb
heights rise steadily into late Friday per GFS/EC consensus. This
seems to offset the cold advection occurring within the high,
keeping temperatures at or slightly above normal. Pattern change
is supported by the GFS, EC, and Canadian by next weekend, as the
ridge sets up east of the area and we enter the warm sector of a
deep Midwest low; precip chances remain too low to mention until
after the end of the fcst period.


At KCLT and Elsewhere: Most terminals will see little more than
slowly increasing high clouds through the period. The main
exceptions will be increasing W to NW upslope moisture into the
western mountains, and spotty low clouds and fog in the northwest NC
piedmont where the melting snow is making for a somewhat moist near-
surface layer. Current indications are that stratocumulus ceilings
in the western mountains will generally stay down-valley from KAVL,
and that lower restrictions will not affect the airfield at KCLT.
Conditions will need to be closely monitored at these two sites
overnight. Otherwise, expect dry and VFR conditions through the
period, with light SW winds east of the mountains and light NW flow
at KAVL. Some low end gusts will be possible at KAVL from time to
time late today and again with mixing on Saturday.

Outlook: Dry/VFR conditions are expected to continue through the
late weekend. Moisture will return along and ahead of an approaching
cold front Monday into Tuesday, with associated restrictions
possible. Dry weather returns by the middle of next week.

Confidence Table...

            19-01Z        01-07Z        07-13Z        13-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High 100%     High  95%
KHKY       High 100%     High 100%     High 100%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     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:




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