Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 170350

Area Forecast Discussion
National Weather Service Blacksburg VA
1050 PM EST Tue Jan 16 2018

A cold front will move through the region overnight into
Wednesday morning bringing measurable snow to parts of the
region and very cold temperatures to the entire area. High
pressure will build into the region through the weekend, along
with dry weather and milder temperatures. Another cold front
will cross the area on Monday, bringing a line of moderate to
heavy rain showers, some with very gusty winds.


As of 1030 PM EST Tuesday...

New 00Z/7PM guidance is coming in. Confidence now above 75
percent that areas south and east of Danville will reach warning
criteria (4 inches of snow or more). Per coordination with NWS
Wakefield, a Winter Storm Warning is now in effect for
Casewell, Halifax, Charlotte Counties. Remainder of the forecast
area unchanged. There will be a sharp northwestern edge to the
snow plume. As expected the snow is struggling to make it over
the mountains from the OH/TN valley, the precip essentially
drying up as the arctic front crosses the mountains. Still
anticipating a wave of low pressure to develop along the surface
front over North Carolina. Main impact from this feature will
be over the Piedmont of NC and into southeastern VA...east of
Danville and Lynchburg with a sharp gradient to the northwest
where dryer/colder arctic air will be infiltrating the region
from the northwest. Onset will be in the 3-5AM time frame and
continue into the afternoon Wednesday before ending.

Previous Discussion
As of 815 PM EST Tuesday...

A positive tilted trough draped over Ohio Valley southwest to
the Ozark, will slowly push a cold front over the region tonight
into Wednesday morning. This front will also be slowed by a
series of reflections developing along the front, tracking to
the northeast. The upper level trough will move over the mid
Atlantic region Wednesday afternoon pushing the front and snow
off the coast. Associated with this front will be snow, wind,
and cold temperatures/wind chills.

As the front drifted over West Virginia and western Kentucky
today, snow amounts ranged from 2 to 5 inches. Slightly lesser
amounts (2-4 inches) are expected in our extreme western
counties (Tazewell VA to Greenbrier WV) tonight. Accumulating
snow will taper to flurries during the early morning hours
Wednesday, ending as early as sunrise for our western counties.

As the front moves to the Blue Ridge this evening, jet dynamics
develop south and east of the area overnight. This will create
a precipitation minimum over counties along the Blue Ridge and
immediate foothills, where less than an inch of snow is
expected. Snow is expected to taper to flurries around sunrise,
ending by late morning.

Farther east, Highway 29 corridor and points east, the
expectation is for snow to develop late tonight and linger
longer into the day Wednesday. A wave of low pressure is
forecast to develop along the front vicinity of the NC
Piedmont. Best lift and model dynamics for snow production are
forecast along a CLT-GSO/RAH-RIC line/corridor with the heaviest
of the snow occurring south and east of Danville...between
Danville and Raleigh. At the present time it looks like LYH-MTV
will be the back edge of this moisture plume. A general 1-3
inches of snow is being forecast from Lynchburg-Danville with
our eastern 3 counties (Charlotte-Halifax-Caswell) teetering
with 4. These numbers may need to be adjusted slightly pending
the next round of model ensemble guidance. Not out of the
question that our eastern 3 counties may meet warning criteria
(4 or more inches of snow across more than 50% of the county).
If this turns out to be the case then warnings will be expanded
into parts of southern/eastern VA.

For this forecast package, there were very few changes to any
headlines. Yadkin County was added for the potential for up to 2
inches of snow there and a buffer to the winter storm warnings
farther to the south and east (e.g. the Triad). Advisories in
the far western CWA and eastern CWA for snow remain in place
through Wednesday morning. Unless the forecast changes
overnight, a special weather statement will be issued for
counties bordering the Blue Ridge for possible minor travel
impacts. The map contains a large donut hole with respect to the
Advisory Headlines for a reason. There will be a cooridor (I-81)
right along the Blue Ridge including the Shenandoah, Roanoke
and eastern New River Valleys that get very little snow
accumulation from this event. As a general rule Advisories are
generally not issued until amounts exceed 2-3 inches and
warnings are not issued unless we are anticipating more than 4-5
inches...using those numbers as an average.

A tight pressure gradient develops behind the front, but until
clouds can clear, most of the strongest winds will remain above
3000 ft. As the inversion lowers towards morning across the
mountains, winds will blow 15-25 MPH with gusts up to 35 MPH
through the day. These winds will likely blow snow on to treated
roadways. Wind coupled with very cold temperatures will also
send wind chills values below zero across the higher elevations
to the single digits in the mountain valleys Wednesday morning.

Temperatures overnight will drop below freezing areawide.
Temperatures over the foothills and piedmont counties warmed
into the 40s Tuesday afternoon. Despite the warmer temperatures,
this should not impact the snow accumulation potential as
wetbulb temperatures are well below freezing. With dewpoints in
the teens/20s, readings air temperatures will quickly wetbulb
below 32 degrees once the snow starts later tonight.

Arctic air on the west side of the frontal boundary will enter
the mountains overnight with temperatures dropping into the 10F-
20F range. Cold air will continue to surge in during the day
tomorrow. Mountain temperatures will warm very little with
highs ranging from 15F to 25F. Cold air will make it east of the
Blue Ridge resulting in nearly steady or falling temperatures
for the foothills and piedmont into the 20s. Downsloping winds
and sun in the afternoon should allow temperatures to warm into
the upper 20s to lower 30s Wednesday. Areas with a 2-3 inch snow
pack will be cooler by 3F- 5F.


As of 130 PM EST Tuesday...

At start of Wednesday night, the center of the upper level
low/trough partially responsible for Tuesday night and
Wednesday`s snowfall, will be directly overhead. As its shifts
east overnight, gusty northwest winds will help maintain some
upslope snow showers and flurries over portions of southeast
West Virginia. However, the trajectory will be a little bit more
north than true northwest, so the impacts of the upslope will
not be maximized. Regardless, much drier air is progged to
quickly enter the region thus minimizing what uplsope there will

During the day Thursday, the prevailing flow will back to the
west and the overall synoptic pattern will be a near zonal flow
across the area. This pattern will continue through Friday will
gradually increasing heights/temps as a shortwave ridge starts
to build over the central potions of the nation.

Temperatures will trend milder during this portion of the
forecast with readings averaging some five degrees above normal
by Friday.


As of 1215 PM EST Tuesday...

Heading into the weekend, an upper level trough will begin to
deepen over the Four Corners region and eject into the Central
Plains states, all while upper level ridging builds over our
part of the country. Concurrently, the low level temperature
profile will gradually warm as southwest flow warm air advection
is forecast. Also, moisture will increase across our region,
especially the western sections. The result will be a period of
increasing temperatures, with limited chances of precipitation.
Only the far western sections of the area will have mention of
some isolated showers both Saturday and Sunday afternoon. High
temperatures by Sunday are forecast to range from the mid to
upper 50s across the mountains with upper 50s to around 60
across the Piedmont.

Sunday night through Monday night, the Central Plains trough is
expected to close off, and lift rapidly northeast into and
through the Great Lakes region, and then into southeast Canada.
Its associate surface cold front is progged to progress through
our region Monday afternoon and evening. Anticipate a well
defined line of showers to cross the area during this time
frame, along with the potential for some gusty winds based upon
an associated 40 to 50 kt jet crossing the area both pre- and
post- frontal passage. It may be a scenario very gusty showers
crossing the, with decent cold air advection in the wake of the
system. A mix or change over to snow is expected in the west
Monday night. By Tuesday, the system is expected to east of the
region, with low level winds backing rapidly during the course
of the day, thus shutting off any northwest flow upslope in the
west early in the morning.

Temperatures Monday into Tuesday will trend cooler, but still
average about five to ten degrees above normal for this time of


As of 730 PM EST Tuesday...

A full latitude long wave trof extends from the Great Lakes to
the Gulf of Mexico. Trof continues to dig and strengthen with
cold arctic air covering a large expanse west of the
Appalachians. Arctic front extended along the western slopes of
the Appalachians with a stripe of wintry weather occurring along
and just behind the front with snowfall of 2 to 5 inches
occurring from tn/ky into far western VA and into WV. IFR
conditions was associated with this area of snow.

The arctic front is forecast to cross the mountains overnight
with mvfr to ocnl ifr conditions developing over and east of the
mountains overnight. A wave of low pressure is forecast to
develop along the front over the North Carolina Piedmont early
Wednesday. This will likely result in a stripe of moderate snow
along a CLT-GSO/RAH-RIC line/Corridor associated is IFR/LIFR

Pressure rises behind the front will bring winds of 15-25 kts
wind gusts. Skies will gradually clear from west to east behind
the system later Wednesday. Moderate turbulence is likely along
the Blue Ridge.

Extended Discussion...

Dry air will restore conditions to VFR by Thursday under high
pressure. VFR conditions should persist into the weekend with
warming temperatures. Moisture will return to west Sunday night
into Monday.


As of 545 PM EST Tuesday...

NOAA Weather Radio, WXL60 (Roanoke Transmitter) which
broadcasts at 162.475 MHz is off the air. No estimated back in
service time. Verizon is testing the circuit which normally carries
the signal to the site.


VA...Winter Weather Advisory until 10 AM EST Wednesday for VAZ007-
     Winter Storm Warning until 5 PM EST Wednesday for VAZ058-059.
     Winter Weather Advisory until 3 PM EST Wednesday for VAZ034-
NC...Winter Storm Warning until 5 PM EST Wednesday for NCZ006.
     Winter Weather Advisory until 3 PM EST Wednesday for NCZ004-
WV...Winter Weather Advisory until 10 AM EST Wednesday for


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