Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 182326
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
626 PM EST Thu Jan 18 2018

.SYNOPSIS...
Dry high pressure will build over the region on Friday before
gradually moving offshore over the weekend. Temperatures will
rapidly increase to above normal values. Another cold front arriving
from the west will bring precipitation to the Carolinas and
northeast Georgia early next week, with drying following through mid-
week.

&&

.NEAR TERM /THROUGH FRIDAY/...
As of 625 PM EST: Based on the last of the visible satellite
depiction of existing snow cover, the current duration and extent of
above-freezing temperatures, and reports of road conditions, the
current Winter Weather Advisory for black ice still looks well
placed over much of western North Carolina for areas of black ice
tonight through Friday morning. The Special Weather Statement for
the rest of the forecast area also looks well placed as those areas
will still experience patchy black ice through Friday morning.

Otherwise, water vapor imagery shows the departing closed low off
the east coast moving away over the offshore waters, while another
closed low pressure system develops in the southern stream over
Texas. Shallow ridging is developing in between across the
southeast, with drier surface high pressure over the region, and an
embedded mountain lee trough. Good radiating conditions tonight will
produce plenty of teens and 20s min temps despite some dewpoint
recovery.

The closed southern tier system will move across the lower MS River
Valley through Friday, with the surface lee trough and dry profiles
persisting over our area. A warming westerly, downslope flow will
set up and maxes will rebound above normal in most locations by
tomorrow afternoon to complete the melting of any lingering snowpack.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
As of 220 PM Thursday: The upper pattern will be characterized by
rising heights (on the mean) over the eastern Conus.  However, a
compact upper low will briefly disrupt the building long wave ridge
along the East Coast early in the weekend, which passes by just
south of our forecast area. Limited moisture will result in nothing
noteworthy for our area on the sensible weather front. Meanwhile, a
deepening cyclone in the lee of the Rockies will instigate warm
frontal activation across the TN Valley over the weekend, with
attendant broad warm advection regime and associated moisture
possibly impacting the southern Appalachians over the weekend.
However, there should be little impetus for precip production as far
east as our forecast area, so pops will be omitted from the
forecast.

Otherwise, the period will be marked by a continuation of the
warming trend, as temps are expected to return to above-normal
levels by the end of the weekend. One interesting note regarding the
increasing warmth (as well as moisture) is the NAM`s depiction of
widespread dense fog and low stratus across the area Sunday morning
(and actually continuing through much of the day Sunday). This
appears to be a consequence of the NAM holding on to widespread snow
cover, and a resultant advection fog event. This seems highly
dubious, as good melting conditions tomorrow and Saturday should get
rid of much of the snow cover across the area, so the NAM and it`s
anomalously cool Sunday temps has been largely ignored.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 200 PM Thu: Warm temperatures will persist into Monday thanks
to ridging over the Southeast coast. The primary impact weather
for the early portion of the medium range period is associated
with a cold front, associated with a well developed cyclone moving
across the Upper Midwest, which will sweep across the South Monday
and early Tuesday. Global models continue to time the front across
our CWFA Monday night, and essentially zero sfc-based instability
(and only a tiny amount that is elevated). A modestly strong LLJ
will precede the front and thus shear parameters will be too strong
to ignore. Even minor SBCAPE will be enough to generate a localized
severe wind threat, and with above-normal temperatures expected a
trend toward a daytime fropa would be a significant development. The
LLJ may also produce robust upslope precip along the south-facing
Escarpment; this signal is currently reflected most in the EC QPF,
which features nearly an inch in that area Monday evening.

Guidance continues to depict temps cooling enough on the back side
of the front for a changeover to snow in the mountains should precip
be able to linger there, but that continues to look relatively
low-impact. Temperatures overall will cool back to near normal by
midweek. While guidance consensus suggests we remain dry through
the end of the forecast period, there is one potential development
to watch. Another shortwave is progged to move into the Southern
states late Wednesday. The GFS and Canadian GDPS depict this as
inducing a frontal wave near the Gulf Coast and/or bringing some
dynamic lift of its own. They disagree on the finer details,
but such developments could warrant a PoP at some point.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
At KCLT and Elsewhere: VFR conditions will continue through the
period. Winds will be light from the WSW to SW across the foothill
and piedmont sites, as a lee trough persists through the period,
with continued NNW flow at KAVL. Expect clear skies through the
period, although some cirrus may move in from the west late in the
period.

Outlook: Dry/VFR conditions are expected to continue through the
weekend, with moisture returning ahead of a strong cold front early
next week.

Confidence Table...

            23-05Z        05-11Z        11-17Z        17-18Z
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 100%
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:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...Winter Weather Advisory until noon EST Friday for NCZ033-
     035>037-048>050-053-056-057-065-068>072-082-501>510.
SC...None.

&&

$$
SYNOPSIS...HG
NEAR TERM...HG/RWH
SHORT TERM...JDL
LONG TERM...Wimberley
AVIATION...RWH



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