Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 082349
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
649 PM EST Thu Dec 8 2016

.SYNOPSIS...
A strong push of cold air will overtake the region tonight behind
the passage of an arctic front. This cold airmass will stick around
through Saturday before beginning to moderate ahead of a cold front
that will approach late Sunday Night.

&&

.NEAR TERM /THROUGH FRIDAY/...
As of 632 PM EST Thursday...

Surface winds will continue to pick up as pressure rises increase
through the evening as strong high pressure builds in from the
west. As such dewpoints on northwest flow have dried a bit more
lee of the Appalachians, so have overall lowered dewpoints toward
single digits to lower teens along and either side of the Blue
Ridge. The lower clouds and snow showers have not formed as far
south as of 6pm, models still showing very low threat but will
keep the mention overnight. Will be issuing a Special Wx Statement
to cover the very cold wind chills late tonight into Friday
morning. Though not sinking below advisory level wind chills,
which is -5F, this arctic push of air will be a wake up call to
those who have been used to normal and above normal temperatures
the past few weeks.

Previous afternoon discussion...

An Arctic front will continue to move east across the region this
afternoon into tonight. CAA and low level forcing from increasing
northwesterly upslope wind flow will provide the opportunity for
mountain snow flurries and snow showers tonight into Friday. Some
light accumulation of snow is possible for the West Virginia
Highlands with 1 to 2 inches of snow possible for northwestern
Greenbrier County, northwest of Lewisburg. Elsewhere only trace
amounts expected, with no accumulation east of the Blue Ridge were
downslope flow and drying will result in clear skies tonight.

Strong cold air advection and blustery conditions will be in full
swing tonight, 850 mb temperatures falling to -6 to -12C. Low
temperatures tonight will vary from the teens in the highest
elevations to the mid 20s in the Piedmont. Wind chills will range
from the teens east of the Blue Ridge to the single digits west of
the Blue Ridge, and sub-single digits (zero to around 5 below)
for elevations above 3500 feet. Will keep mention of cold wind
chills in HWO, and issue an SPS later and closer to time window.
Because the coverage is limited SPS planned in lieu of a Wind
Chill Advisory.

On Friday, clouds and mountains snow flurries and snow showers
will linger into late morning then taper off in the afternoon.
Any additional snow accumulations will be less than an inch.
Meanwhile, plenty of sunshine will prevail east of the mountains.
High temperatures Friday will range from the around 20 degrees in
Northwest mountains of western Greenbrier County to the upper 30s to
near 40 degrees in the Piedmont.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
As of 320 PM EST Thursday...

Friday night into early Saturday, the region will still be situated
under a region of northwest flow. Speeds will gradually decrease
after sunrise Saturday as the center of high pressure builds over
the region. Some lingering light snow showers and flurries will
continue across western Greenbrier County, WV Friday evening and
decrease in coverage through the night. Temperatures will continue
to trend lower as the Arctic airmass continues to make progress into
the area. Low temperatures will range from the teens across the
mountains to around 20 into the lower 20s across the Piedmont. Wind
speeds will be weaker than those expected tonight, so despite the
lower temperatures, wind chills will not be quite as low Friday
night compared to tonight.

High pressure will allow for roughly 24 hours of precipitation-free
conditions late Friday night through Saturday night. By sunday,
southwesterly flow will be increasing across the area as the axis of
the high shifts east, and our next weather system will be
approaching from the west and southwest.

Models are trending slower with associated precipitation within the
warm sector of the approaching low. Have decreased precipitation
chances on Sunday to only a slight chance across the western half of
the region. Low level thermal profiles at this point are
questionable regarding specific details.  While we cannot rule out a
mix of precipitation type possibilities, will opt for a simple snow
versus rain forecast Sunday afternoon. This will hold true as well
Sunday night as precipitation chances increase with the system
drawing closer to the area.

Temperature will trend cooler through Saturday and then start to
rebound on Sunday. As a whole, temperatures will average a few
degrees below normal during this portion of the forecast.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 320 PM EST Thursday...

Low pressure passes east through the Great Lakes region towards New
England Monday into Monday night. Its associated cold front is
forecast to progress through our region either Monday afternoon or
evening. Look for temperatures to warm enough on Monday for any
wintry precipitation transition to all rain by the time of the
frontal passage.

Monday night into early Tuesday, colder air will race into the area
on gusty northwest winds. Look for a transition to snow showers
across the mountains during the overnight.

No sooner does this system exit our region do we turn our eyes
southwest again with the approach of yet another potentially wintry
system starting either late  in the day Tuesday or late Tuesday
night. There are notable differences on timing, storm path,
precipitation coverage and amount between the GFS and ECMWF. Given
the differences, our forecast will favor more of a persistence
forecast with the model blend.

A wintry mix will again be possible during this onset window of
opportunity. However, for now given the uncertainties, a snow versus
rain forecast is more practical. By Wednesday afternoon, the
associated trough axis, regardless of model, is expected to be east
of the area and we switch again to a gusty northwest flow regime.
Our precipitation will transition to rain or snow showers, with the
best coverage of snow showers across the mountains, winding down
Wednesday night.

Thursday looks to be drier with less cloud cover.

Temperatures during this portion of the forecast will start the
period around ten degrees above normal, and cool to reading around
normal by the end of the period.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
As of 627 PM EST Thursday...

There will be some cirrostratus out east this evening then appears
lower cigs will work into the BLF/LWB area by 04z, reaching BCB by
06z. Should be mainly VFR aside from some MVFR cigs at BLF/LWB.
Will keep snow showers in late tonight more like flurries in the
west. Will also keep sustained winds around 8-14 from the wnw with
gusts to 16-25kts, higher in the ROA/BCB area and BLF at times
through most of the taf period.

As drier air moves in Friday will see stratocu in the west scatter
out and/or lift to VFR.

Extended aviation discussion...

Winds should quickly fade by Saturday as high pressure builds
overhead making for overall VFR conditions this weekend. Next
weather system to follow will be a cold front, models suggesting a
Sunday Night arrival which will be bringing some sub-VFR
conditions at times, and possibly wintry mix in the mountains. The
cold front enters Monday with continued threat of showers and
sub-VFR at times, then somewhat of a break Monday night, with
possibly more precip Tuesday. Attm seems an active enough pattern
Sunday night-Tuesday to keep an eye on for flying plans.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.

&&

$$
SYNOPSIS...PM
NEAR TERM...KK/WP
SHORT TERM...DS
LONG TERM...DS
AVIATION...KK/WP


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