Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 201046

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
646 AM EDT Tue Mar 20 2018

A complex low pressure system will cross the region from the west
today. Colder air will spill southward into the region behind the
system, with mountain snow showers returning tonight, and scattered
snow showers possibly extending east of the mountains early
Wednesday. Drier high pressure will briefly return over the area on
Thursday, but with another moist low arriving from the west for the


As of 640 AM: A Dense Fog Advisory has been posted throughout the
region as dry air aloft moves in atop the saturated boundary layer,
with model condensation pressure deficits showing values less than 5
mb this morning through 14Z. Slow improvement is expected through
late morning.

Otherwise, conditions should be fairly dry around the region through
the early afternoon hours until showers redevelop from the west
under the approaching upper trough axis this afternoon and evening.
Some embedded thunder, and possibly small hail toward evening, are
expected with the afternoon convection as lapse rates steepen aloft.

The closed upper low will move from the central Appalachians tonight
to the Delmarva coast through Wednesday. The complicated surface low
pressure system will continue to occlude overhead, with steadily
cooling temperatures from the high terrain down toward the lower
valleys this evening through the overnight. Snow levels will crash
quickly across the mountains from the west tonight and then cold air
will continue to spill southward west of the low through Wednesday
as northwest upslope flow moisture becomes rather robust and winds
increase. The Winter Storm Watch was migrated to a Warning for all
but Jackson County, and an Advisory tier has been added for the rest
of the NC mountains except Transylvania and Henderson for now. Will
feature these counties, along with Rabun GA, in the HWO since an
advisory could be needed at some point. In addition, moisture
breaking containment east of the mountains, along mainly the I-40
corridor but possibly into Charlotte, could produce some snow
showers early Wednesday. It appears too early for an Advisory there.
Will also wrap advisory level wind gusts into the mountain products.


As of 350 AM Tuesday: The northwest upslope flow moisture into the
southern Appalachians will steadily taper off by daybreak Thursday,
but winds in the cold advection will remain quite strong through
most of the night and yield some advisory level gusts. Otherwise,
deep layer northwest flow will continue through Thursday, with drier
surface high pressure briefly setting up through Thursday night.
Another slug of moisture will arrive back into the region from the
northwest Thursday night through Friday, warranting mainly mountain
showers. Temperatures will remain a below climo through the period.


As of 400 AM Tuesday: A flat upper ridge will persist over the
southeast U.S. Saturday through Monday. However, a warm front will
reactivate from the western Carolinas to the upper Midwest. In the
resulting upglide, northern tier temperatures will be interestingly
chilly over the weekend. A rain/snow mix mention will be featured
mainly north of I-40 for primarily Saturday, and then just along the
Blue Ridge for early Sunday. Cool, wedge-like temperatures will be
possible with a fropa on Monday.


At KCLT: Visibilities have been relatively slow to fall compared to
the rest of the region this morning, but the thicker mid/high clouds
are moving east and the mid-level drying atop the low level moisture
should permit VLIFR visibility to fill in quickly from the west.
LIFR cigs and fog will then be slow to lift to VFR through late
morning or early afternoon. Another round of scattered showers, with
perhaps isolated thunderstorms, is expected this afternoon and
evening under the passing upper trough. Expect SW to WSW winds
through the day, becoming northerly tonight with restrictions
returning behind the departing low pressure.

Elsewhere: VLIFR to LIFR fog has become widespread acorss the
mountains and foothills and these conditions should persist until
roughly 14Z. Expect some lifting through MVFR to perhaps lower VFR
by early afternoon. Additional showers will redevelop from the west
with the appraoching trough, but confidence is currently too low to
advertise thunderstorms. Expect mainly SW to WSW winds east of the
mountains, but with more variables wind directions at KAVL and KHKY.
Winds will turn NW to N throughout tonight, with gusts developing
over the high terrain. Mountain snow showers may start to mix in
near KAVL overnight.

Outlook: Colder air wrapping around the exiting system will bring
snow to the mountains through at least Wednesday, and potentially
mixed precip to KHKY and KCLT Wednesday morning, with rain showers
expected elsewhere. MVFR/IFR is anticipated, with VFR returning
gradually Wednesday night through Thursday. Another moist system
will arrive from the west this weekend.

Confidence Table...

            10-16Z        16-22Z        22-04Z        04-06Z
KCLT       Med   71%     High  86%     High  83%     High  93%
KGSP       Low   54%     High  97%     High 100%     High 100%
KAVL       Med   73%     High 100%     High  97%     Med   73%
KHKY       Med   65%     High  83%     High  84%     Med   66%
KGMU       Med   66%     High 100%     High 100%     High 100%
KAND       Med   65%     High  94%     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...Dense Fog Advisory until 10 AM EDT this morning for GAZ010-017-
NC...Winter Weather Advisory from 8 PM this evening to 8 AM EDT
     Thursday for NCZ053-059-062-063-501-503-505.
     Dense Fog Advisory until 10 AM EDT this morning for NCZ033-
     Winter Storm Warning from 8 PM this evening to 8 AM EDT
     Thursday for NCZ033-048>052-058.
SC...Dense Fog Advisory until 10 AM EDT this morning for SCZ001>014-


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