Area Forecast Discussion
Issued by NWS Greer, SC

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113
FXUS62 KGSP 100345
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1045 PM EST Sat Dec 9 2017

.SYNOPSIS...
An upper level low will bring a period of snow across the North
Carolina mountains tonight. Below normal temperatures and dry
conditions will return Sunday and persist through the middle of next
week.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 1030 PM EST Saturday: Increased pops across the mountains to
account for NW flow snow showers making it all the way to Asheville.
So far none really breaking containment. Updated QPF and snow totals
accordingly. Temperatures not dropping as quickly as forecast but
should catch up by sunrise, so just adjusted hourly trends but not
overnight lows. Will refresh products, but overall no significant
changes.

Otherwise, clouds and snow showers return to the NC mountains late
this afternoon and continue through the night as low level moisture
moves in on strengthening NW flow. A short wave crosses the area
along with some upper divergence to enhance the lift created by the
NW flow. The moisture and lift are short lived however, keeping the
snow limited to a relatively short duration. This will keep new
snowfall totals low generally under 2 inches. Cannot rule out some 2
inch amounts above 5000 feet. Winds also increase and become very
gusty but h85 winds remain below 50 knots. This should also keep any
advisory level wind gusts limited to above 5000 feet. Outside of the
mountains, skies clear and winds pick up with some low end gusts
possible. May see some stronger gusts downwind of the mountain gaps
as usual in this type of flow. Can`t rule out some clouds breaking
containment and spreading across the foothills and piedmont from
time to time. Will be a very cold night with lows in the teens
across the mountains and low to mid 20s elsewhere. Despite the wind
and cold, wind chill values also remain above advisory levels or all
but areas above 5000 feet. Will however issue a Winter Weather
Advisory for black ice in the areas where there was significant
snowfall. Will bracket that with an SPS for black ice in the
counties where the county average did not reach significant
accumulation levels.

Mountain snow showers taper off quickly Sunday morning as the
moisture lifts out and NW flow slowly diminishes. Should be sunny to
mostly sunny elsewhere. Highs will be around 15 degrees below
normal.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
As of 200 PM Sat: Conditions still look to be settled Sunday night
into Monday morning. Heights will rise slightly over the Southeast,
even as the eastern half of the CONUS remains under a mean upper
trough. Min temps Monday morning thus are expected to be perhaps a
category warmer than the previous night. Sunshine Monday will permit
further airmass modification and bring temps back up to near normal.

In general, the remainder of the period will be characterized by
an amplifying upper pattern as strong shortwaves and attendant sfc
lows rotate through the aforementioned trough. Monday night, a cold
front associated with one of these lows pushes through the area,
with the shortwave following close behind. While these features
will have little moisture to work with, winds veer in their wake and
eventually sufficiently moist conditions develop in the low levels
to expect another round of northwest flow snowfall. Chances ramp up
in the early morning hours Tuesday along the Tenn border, peaking
Tuesday when moisture is most abundant. However, winds remain strong
and upslope overnight into early Wednesday; the snow finally looks
to taper off by about daybreak. Strong CAA should result in mins
dropping back into the teens over most of the mountains and lower
to mid 20s in the Upstate and GA Lakelands. Sub-zero wind chills
(advisory level) most likely will result in the high elevations;
wind gusts may also reach advisory criteria in spots.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 245 PM EST Saturday: A deep upper level trough of low pressure
will remain anchored across the eastern CONUS through the latter
half of the upcoming work week. A subtle shift to a temporary west
to northwest flow aloft, could materialize next Saturday.

Meanwhile the weather looks quiet Wednesday as a surface bubble of
high pressure shifts across our forecast area (FA).

However, a sharpening trough, with another shot of energy, will be
crossing our area late Thursday into Friday. The system will also be
accompanied by a surface wind shift line, which will act as a
frontal convergent area. We have brought chance POPS into the
western NC mountains and foothills, far northeast Georgia and the
mountains of upstate South Carolina. We have kept POPS in the chance
or slight chance range this far out. Outside the aforementioned
areas we have kept things dry.

Otherwise we have a dry forecast into early next weekend. At that
time we note considerable differences on timing and location, for
inclement weather to return, between the GFS and European. The
differences crop-up just beyond this forecast period, therefore we
will have Saturday dry, and watch closely those periods beyond.

In the temperature department, a shot of colder air will filter into
the area Wednesday. This will be followed by some moderation
Thursday, then a subtle cooling trend late in the upcoming work
week. It appears when we average everything out in the temperature
department, we still remain below normal.

&&

.AVIATION /04Z SUNDAY THROUGH THURSDAY/...
At KCLT and elsewhere: Clouds have finally cleared out of the
KCLT area, so trends are now on track. Have reduced to FEW instead
of SCT for the 04z AMD, but otherwise no changes, with VFR
conditions prevailing everywhere through the rest of the period.
Cannot rule out brief MVFR at KAVL with the northwest flow that
might briefly spill up the valley. WSW winds expected between 5-10kt
for all but KAVL, where NW will prevail. Low-end gusts possible
through the overnight hours especially KAVL and the upstate TAFs.

Outlook: Dry conditions expected at all sites into early next week.

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:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...Winter Weather Advisory until 10 AM EST Sunday for GAZ010-017.
NC...Winter Weather Advisory until 10 AM EST Sunday for NCZ033-
     035>037-048>053-056>059-062>065-068-069-501>510.
SC...Winter Weather Advisory until 10 AM EST Sunday for SCZ001>003.

&&

$$
SYNOPSIS...SBK
NEAR TERM...RWH/TDP
SHORT TERM...Wimberley
LONG TERM...TS
AVIATION...TDP



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