Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 181407

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
907 AM EST Thu Jan 18 2018

High pressure will overspread the region and drift offshore by early
Saturday, with temperatures increasing to above average through the
weekend. Another cold front will bring precipitation to the
Carolinas early next week.


As of 900 AM EST: The first round of wind chill advisories have
expired and the last set for the northern mountains will likely go
away at 10 am (although the higher ridges should keep values below
minus 5 well into the afternoon.) Black ice issues continue to be
assessed and some combination of advisories and statements for black
ice will likely be needed again tonight.

The current forecast was updated mainly for temperature trends, with
a colder start and slightly slower recovery through mid-morning, but
with afternoon highs still looking on track to provide some melting.
Dewpoints were dried out slightly with the wind shift to west-
southwest perhaps delayed until the afternoon east of the mountains.

Otherwise, the upper low will continue to move away to the east and
be replaced by short wave ridging aloft through tonight. This will
allow high pressure to continue building in from the W and SW today.
The pressure gradient will continue to relax and permit the wind to
diminish, which should in turn alleviate the wind chill concern over
the most of the mtns. Temps will fall well below freezing again
tonight with excellent radiational cooling potential, no doubt
requiring another product to deal with another round of black ice.
Prefer to see how much melting we get through mid afternoon once we
get the sun involved.


As of 230 AM EST Thursday: The short term forecast looks quiet, as
an upper ridge builds over the eastern states in an amplifying
pattern. There is an interesting southern stream compact low that
lifts thru the building ridge, but has little moisture to work with.
The models are still in disagreement on exactly how the low will
track and eventually get sheared out. The GFS is the fastest and
keeps a closed low the longest. It brings some mid and high clouds
thru the area on Saturday, but otherwise, no sensible wx impacts.
The NAM and ECMWF are slower lifting the low out and keep it south
of the area near the Gulf Coast. So other than perhaps a little
increasing clouds on Saturday, it should be mostly clear thru the
period. Temps will be on a warming trends, as the ridge builds.
Highs near normal Friday, and a couple categories warmer on
Saturday. Lows slightly below normal Friday night, but a couple
categories warmer Saturday night.


As of 200 AM EST: The area will be under the influence of surface
high pressure and an upper ridge to start the medium range Sunday
morning, with relatively warm and dry conditions persisting through
Sunday and into early Monday morning. The next system will approach
the area Monday afternoon and evening, with a strong upper and
surface low propagating across the Great Lakes. Pre-frontal moisture
ahead of a cold front trailing the surface low will increase on
Monday, with the QG-induced lift from the upper low inducing QPF
response in our forecast area Monday some time around 18Z. The
system looks quite dynamic in global models and produces shear
profiles that would be quite conducive to organized severe weather
if the instability were not severely limited by the "wet noodle"
soundings at all sites in our CWA. The bulk of the precip and the
best forcing associated with the front will likely arrive overnight
Monday through early Tuesday morning, a timeframe that should also
prevent any diurnally-enhanced instability. Model agreement on the
lack of instability above 100 J/kg is striking, though this could
change if the timing of the front changes. The remains slight
disagreement in the 00Z model suite over when the precip will come to
an end Tuesday, though all global models have clearing with drier
air arriving by Tuesday afternoon. As some cold air arrives behind
the front in the NC mountains Tuesday morning, expect a transition
to rain/snow mix of briefly all snow in the higher terrain of NC.
All other locations will receive liquid precip for the duration of
the event.

The balance of the medium range remains quiet, with a dry
continental airmass moving into the area as a surface high over the
OH River Valley expands towards the northeast. Unusually warm
temperatures ahead of the front will moderate back towards average
by the end of the next work week.


At KCLT and Elsewhere: VFR conditions will continue through the
period. Wind will be light W to NW to start. KAVL will have
occasional gusts for the first several hours, but the gustiness
should diminish by late morning. A lee trof is expected to develop
during the middle of the day, which should bring the wind direction
around to the WSW east of the mtns. Wind will go light/variable at
sunset. Expect sky to remain essentially clear through the period.

Outlook: Dry/VFR condition are expected to continue through the
week and into the weekend.

Confidence Table...

            14-20Z        20-02Z        02-08Z        08-12Z
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:


GA...Winter Weather Advisory until noon EST today for GAZ017-018-
     Winter Weather Advisory until 2 PM EST this afternoon for
NC...Winter Weather Advisory until 1 PM EST this afternoon for
     Winter Weather Advisory until 2 PM EST this afternoon for
     Wind Chill Advisory until 10 AM EST this morning for NCZ033-
SC...Winter Weather Advisory until 1 PM EST this afternoon for
     Winter Weather Advisory until noon EST today for SCZ001>007-


LONG TERM...Carroll/Wimberley
AVIATION...HG/PM is the U.S. government's official web portal to all federal, state and local government web resources and services.