Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 202338

Area Forecast Discussion
National Weather Service Blacksburg VA
738 PM EDT Tue Mar 20 2018

Low pressure will cross the region overnight, and deepen off the
coast of New England as a Nor`easter by Thursday morning. High
pressure briefly returns to the region on Friday. Over the weekend,
anther potential winter weather system will cross our region.


As of 700 PM EDT Tuesday...

Forecast updated to reflect some sleet mixing in with rain in
the southwest, but also lowering temps further north compared to
previous forecast. Warnings/advisories on track, but will re-
evaluate latest high-res models and mesoanalysis to see if
changes are needed to total snowfall amounts and/or headlines.

Previous discussion from mid afternoon...

Not a whole lot has changed regarding the synoptic transition
of the events that are expected tonight into Wednesday. What has
changed is the degree to which warmer air will allow for
rainfall for a slightly longer period of time than originally
anticipated. Also, low level profiles are hinting at the
potential of sleet at the onset of the change from from liquid
to frozen. Both of these factors will place a greater limit on
the amount of forecast snow expected at the lower elevations.
The opposite is true at the higher elevations, especially those
along and north of Route 460. Northern sections of the New River
Valley of southwest Virginia, north into the Alleghany
Highlands, and the higher ridges of southeast West Virginia
will have a slightly higher forecast of snow thanks to those
elevations remaining colder, and a bit more qpf than earlier
offered to generate snowfall. So, while we will keep our
advisories and warnings in place, the range between valley and
ridge top has increased. Some mountain valley locations may only
see around an inch of snow, but its neighboring ridge tops have
values more in the 4 to 8 inch range. The highest snowfall
totals, 8 to 11 inches, are forecast across western sections of
Greenbrier County.

The warning likely will be divided into a northern section where
amounts will be higher, to a southern section where amounts will be
borderline for achieving measured warning criteria, but the
travel concerns with the potential for blowing snow on the
backside of the system would justify a continuation of the
warning for impact. The eastern bordering Winter Weather
Advisory is of a similar status whereby the rain/sleet scenario
will keep snowfall numbers a little lower. However, along the
elevations of western Amherst County, snowfall amounts have
increased enough to justify an average forecast across the
county that just clips the lower end of warning criteria. This
county will be upgraded from an Advisory to a Warning, and
placed in the aforementioned northern warning group.

Winds will be gusty on across the higher terrain of mainly the
Mountain Empire region and southern New River Valley of southwest
Virginia, south into the Northern Mountains of North Carolina. Here
gusts of 35 to 45 mph will be common at the higher peaks
starting late tonight through the day Wednesday. Blowing snow is
expected at these locations by Wednesday morning.

Low temperatures tonight will range form the upper 20s to around
freezing across the mountains to the low to mid 30s across the
Piedmont. On Wednesday, high temperatures will range from the low to
mid 30s across the mountains to the upper 30s to lower 40s across
the Piedmont.


As of 330 PM EST Tuesday...

Wednesday evening the closed upper low is just off the Virginia
coast. Deformation area around upper low crosses through Virginia
through Wednesday evening. Surface and low level winds come around
to the northwest which will kick in upslope on the west side of the
central Appalachians and suppress amounts in the foothills. Little
additional accumulation expected in the piedmont but more snow
adding to totals in the western mountains. Expect much of the
upslope snow showers to end by Thursday morning. Clearing will take
longer but there will be some breaks in the cloud cover by Thursday

Models show a 40 to 50 knot low level jet from the northwest along
the Blue Ridge Wednesday night and Thursday morning. Another low re-
enforces the upper trof over the eastern United States on Friday and
Friday night. Have stayed below guidance for lows on Wednesday night
in areas that will have new snow. Also below guidance for highs on
Thursday where little to no sunshine expected.


As of 140 PM EST Tuesday...

Low pressure tracks from Missouri on Saturday night, across the
Tennessee Valley and Carolinas to the western Atlantic by Sunday
night. Some differences in the guidance how far south this low will
move, which in turn will impact where the winter weather will be on
the northern side of the baroclinic zone. Timing has been
consistent, keeping the best probability of precipitation from
Saturday afternoon into Sunday morning.

Surface high pressure wedges down the east slopes of the
Appalachians Monday and Tuesday. Precipitation over the Tennessee
and Ohio Valley may spill east into the mountains but the
probability remains low. Temperatures will remain below normal
through the period, especially daytime highs.


As of 730 PM EDT Tuesday...

Not a quiet night for aviation as storm system will bring rain
then sleet/snow to the area with low cigs/vsbys. This system
will stick around into Wednesday and overall looking at sub-MVFR
conditions through at least midday Wednesday before winds shift
to the west and northwest which should bring steady precip to an
end with more showery nature though snow showers will persist
into the afternoon along/west of the mountains, with rain/snow
shower mix in the east. Cigs/vsbys anticipated to at least go
MVFR Wed afternoon outside of the WV mountains.

Northwest winds are expected to become gusty in the afternoon
with a few gusts over 30kts not out of the question.

Extended Aviation Discussion...

Wednesday night into the daytime Thursday, the upslope snow
showers will continue to gradually decrease in coverage with
decreasing wind speeds.

Mainly VFR conditions are expected by Thursday night through
Friday night.

Saturday into Sunday, a return to sub-VFR conditions is expected
as our next potential winter weather system crosses the area.


As of 335 PM EDT Monday...

The Mount Jefferson NWR remains off the air. The radio unit
needed to repair the system is expected to arrive on Wednesday.
The earliest this system will again be operational will be
Wednesday afternoon.


VA...Winter Storm Warning from midnight tonight to 8 AM EDT
     Thursday for VAZ007-009>020-022>024-035.
     Winter Weather Advisory from midnight tonight to 8 AM EDT
     Thursday for VAZ032>034-045>047.
NC...Winter Storm Warning from midnight tonight to 8 AM EDT
     Thursday for NCZ001-002-018.
WV...Winter Storm Warning from midnight tonight to 8 AM EDT
     Thursday for WVZ042>044-507-508.


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