FXUS61 KRNK 181043

Area Forecast Discussion
National Weather Service Blacksburg VA
543 AM EST Fri Jan 18 2019

Weak high pressure will briefly build across the area from the
Ohio Valley today. A storm system moving out of the Rockies
will move east, impacting our region Saturday and Saturday night
with a period of rain. An arctic front will merge with this
system to promote heavy snow farther north from Pennsylvania
into New England. In the wake of this storm, much colder air
will arrive across our region Sunday, associated with strong
northwest winds.


As of 500 AM EST Friday...

The upper level disturbance which brought yesterday's wintry
precipitation has moved east and off the Mid-Atlantic Coast. A
weak surface trough trails this disturbance and will pass across
the forecast area this morning, bringing a shift in wind
direction to the northwest for the afternoon, and hopefully a
bit of clearing for parts of the CWA. Low level moisture
profiles still suggest the western CWA will remain overcast with
abundant low level moisture pinned against the west side of the
Appalachians. East of the mountains, the forecast will
entertain at least some partial clearing, although not confident
we will be able to completely scour the boundary layer before
mixing subsides at the end of the day.

With today's cloud cover in the west, still looking at some
higher elevation drizzle and fog. Can't rule out some patchy
freezing drizzle early this morning until temperatures can
squeak above 32. MOS suggests some really warm temperatures
today (40s/50s), too warm in my opinion given cloud cover and
new snow cover, so will skew the forecast to the cooler side of
guidance. Still think southside VA into the piedmont of NC will
have a chance to test 50, but 30s in the mountains and 40s for
the foothills may be all that can be mustered due to the
abundant cloud cover and the white heat sink which covers the

Not to be overly preoccupied with today's winter weather clean
up (a nuisance at most), will have to turn our attention to a
storm system emanating from the Rockies. This potent storm
brought blizzard conditions to the Sierra Nevada (snowfall in
feet) and will trek across the center part of the country today
on a path that will rendezvous with the Eastern U.S. this
weekend. Until then, enjoy our one day of respite, and grease
the skids for a roller coaster ride with respect to temperature
this weekend.


As of 435 AM EST Friday...

A strong low pressure system will move across the Tennessee Valley
Saturday then track northeast along the western side of the
Appalachian Mountains in the evening. Pockets of freezing rain are
possible Saturday morning across mountain valleys north of Highway
460, but for the most, rain will be the main p-type/threat Saturday
afternoon and evening. With approximately a half of an inch of
liquid remaining on the ground from the previous sleet/snow storm
and yesterday's snow, coupled with an inch or more of rain from this
low pressure system brings an increasing concern for areal and river
flooding Saturday into Sunday.

After midnight, a secondary surface low forms east of the Blue
Ridge. A relative dry slot is expected over the mountains while
moderate to heavy rain moves east of the piedmont during the early
morning hours. An Arctic front will cross over the area Sunday
morning bring with it a sudden drop in temperatures which may result
in a rapid freeze and strong northwest winds, as well as low wind
chills. Advisory level winds are possible from the North Carolina
High Country to the Roanoke Valley into Sunday evening. Temperatures
will likely top-out in the upper 20s Sunday morning across the
mountains, then drop into the lower 20s through the afternoon. East
of the Blue Ridge may also see their high temperatures for the day
during the morning hours, ranging in the low to mid 40s, dropping
into the 30s in the afternoon. Temperatures will continue to fall
Sunday night with readings from the single digits across the
mountains to the teens east of the Blue Ridge. Winds will weaken
some Sunday night, but will remain high enough to produce below zero
wind chill values across the mountains to single digits east of the
Blue Ridge Monday morning.

Accumulating snow across the mountains is also possible Sunday and
Sunday night. Unlike a typical frontal passage where northwest flow
brings several inches of snow to western slopes, winds behind
Sunday's front will be out of the north-northwest. With less
moisture influence from the Great Lakes, snowfall amounts will range
from 1 to 4 inches along the western slopes, with western Greenbrier
at the high-end of the range.


As of 155 PM EST Thursday...

Brief period of ridging at 500 MB Tuesday then second strong 500 MB
short wave comes onshore on the west coast as the upper pattern
evolves into a deep upper trough covering much of the continental
United States for Wednesday and Thursday.

850MB temperatures forecast to range from -22 across southwest
Virginia and southeast West Virginia to -14 in northern North
Carolina on Monday morning. Pressure gradient weakens on Monday and
Monday night and by Tuesday axis of high pressure will be over
Virginia and North Carolina. So the wind will gradually diminish
this time frame.

Cold air retreats north Tuesday as low level winds come around to
the southwest ahead of the next low pressure system. Timing on
the ECMWF and other guidance bring the next cold front and
associated precipitation through the Mid Atlantic region and
Carolinas on Wednesday or Thursday.


As of 1155 PM EST Thursday...

Sub-MVFR is likely through the morning across most of the area,
with precip becoming limited to the BLF/LWB area with patchy
light rain/snow/drizzle and fz drizzle. Visibilities with
limited wind and low level moisture should be at least MVFR to
IFR with possible LIFR or lower in the BLF area.

Improving conditions will develop east of the Blue Ridge after
daybreak but low cigs and some light precipitation/drizzle will
continue west of the Ridge, and confidence is at least moderate
to high that bkn/ovc sub-VFR cigs will remain into the evening,
though am allowing BCB to rise to VFR after 21z, though
confidence is low given lack of mixing.

High confidence on poor flying conditions this morning, with
trends toward lower confidence beyond 18z Friday for
improvements in cigs.

Extended Aviation Discussion...

Not really seeing much clearing in the mountains late Friday

A more significant cold front will arrive by Saturday night-
Sunday. Confidence increases for more widespread IFR/MVFR
ceilings and rain showers throughout the remainder of this
upcoming weekend. Northwest winds will also be very strong
behind a passing cold front Sunday into Sunday night before
diminishing Monday into Tuesday as widespread VFR returns under
high pressure.




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