Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 131406
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
906 AM EST Wed Dec 13 2017

.SYNOPSIS...
Arctic air encompasses the region this morning. Strong
northwest winds will persist early this morning before
diminishing. Another clipper will cross the Great Lakes and Ohio
Valley tonight and early Thursday with another round of elevated
wind speeds, although temperatures will not be as cold.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 905 AM EST Wednesday...Update to cancel the Wind Chill
Advisory and issue a updated forecast refresh. Changes however
were negligible. It is still quite cold out with northwesterly
winds still resulting in lowest wind chills between -3 and 0 at
Bluefield and Hillsville respectively. Sunshine will help boost
temperatures and raise wind chill values further. Should also
see some improvement in road conditions by late morning as
patches of snow and ice melt as the sun heats the pavement.
Aside from accounting from current observations and blending in
with expected near-term trends, forecast looks good.

Previous discussion issued at 330 AM...

Arctic airmass over the region is resulting in temperatures in
the teens. Winds are gradually beginning to diminish, but still
resulting in single and sub-single digit wind chills. Snow
showers across the mountains yesterday and last night have left
a dusting to as much as 2 inches of new accumulation. The
wind has drifted quite a bit of this onto the roads, and with
temperatures in the teens its making for some icy travel per
road treatments not being very effective at these temperatures.

If we can grin and bear it through lunch-time, then we should
see a market improvement for the afternoon. Coldest of the
airmass is already in place with 850 MB Temps of m15 deg C. That
means its all uphill from here, with models indicating warming
throughout the day and 850 mb readings near 0 deg C by the end
of the day. Temperatures at the surface will still struggle to
get much above freezing for high temperatures, but with full
sunshine it will hopefully allow road treatments in the
mountains to be a lot more effective at clearing some of the ice
and snow from the highways. East of the Blue ridge where little
or no snow occurred yesterday, the sun should allow
temperatures to make a run for 40 degrees by mid afternoon.

Another fast moving upper level disturbance (clipper front) can
be seen on the water vapor imagery entering the upper Midwest
this morning. This clipper is forecast to move across the Great
Lakes and Ohio Valley, farther north than the last system.
Greatest pressure rises with this feature are expected to pass
north of our region, never the less, we will get a surge of wind
tonight and early Thursday. Forecast 850mb winds of 50kts may
require need for a wind advisory for parts of our region
tonight, but will allow existing advisories to play out before
issuing any new headlines.

As for potential snow with tonight`s clipper, it looks to be a
lot less compared to Tuesday`s event. Depth of the moisture
profile on Tuesday was all the way up to 8000 ft. Tonight`s
forecast depth is only to 4500 ft which suggests any
accumulation will be confined to the highlands of WV with trace
amounts as far south as the high country of NC. For now will go
with 1-2 inches of new accumulation for NW Greenbrier and mainly
flurries elsewhere.

With the passage of the clipper, the 850 MB temperatures slip
back to about m5 deg C. This suggests a relatively milder night
with lows in the 20s to around 30 (compared to the teens from
last night).

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/...
As of 335 AM EST Wednesday...

Thursday, the pressure gradient behind the departing shortwave
trough will slacken, allowing for decreasing winds throughout the
day. However, conditions early Thursday morning will still be on the
very gusty side.

Thursday into early Friday, the area will transition into a brief
zonal pattern, with building high pressure across the region. This
will yield dry and cooler conditions across the area.

Late Friday afternoon into Friday night, the next Great Lakes upper
level shortwave trough will progress west to east, north of the
region. The tail end of the trough axis will cross the region with
shallow moisture. Increasing northwest flow will once again increase
across the region with isolated upslope snow showers across portions
of southeast West Virginia continuing into and through Friday night.

By Saturday, an upper level shortwave ridge will move into the
region, helping to decrease the winds once again, and bring slightly
milder conditions to the area.

&&

.LONG TERM /SUNDAY THROUGH TUESDAY/...
As of 258 PM EST Tuesday...

High amplitude pattern seen during the past week will finally begin
to flatten this weekend and gradually work into weak upper ridging
across the southeast states early next week. This should basically
act to cut off any added cold air intrusions with more of a Pacific
nature airmass from Sunday through Tuesday. However a leftover wave
across the Gulf states may push far enough north within increasing
warm advection aloft to bring some light precipitation Sunday into
Sunday night before drying returns Monday. However timing of this
system remains iffy with some solutions much slower with rain
lingering into Monday. This would support mainly a rain event with
perhaps some mix at the onset if earlier arrival occurs Sunday
morning. Otherwise running with mainly chance pops Sunday into
Monday morning, then dry Monday afternoon/Tuesday under slightly
higher heights and south of most northern stream energy at this
point.

Good moderation in temperatures to occur through the period as the
cold pool aloft lifts out Saturday followed by decent west/southwest
flow through Tuesday. This supports highs rebounding to near normal
to start and then above normal into Day 7 including some 50s ahead
of the next weak front

&&

.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
As of 700 AM EST Wednesday...

Aviation conditions will improve today as winds subside. Aside
for some sct-bkn strato-cu across the VA/WV highlands this
morning the overall trend is for clear skies for the bulk to the
daylight hours.

Weak high pressure will build across the central Appalachians
today. Another clipper front will cross the area tonight, winds
increasing as strong pressure rises occur across the Great Lakes
and Ohio Valley. Some low level cloud cover will develop after
03Z/10PM with the potential for mountain snow showers and
flurries.

Medium to high confidence in ceilings, visibilities and winds
during the TAF period.

Extended Discussion...

Upper level disturbance (clipper) will move east and away from
the area Thursday. Conditions then trend VFR for the weekend,
with the next chance for sub-VFR being Sunday night into Monday
with a system emanating out of the mid- Mississippi Valley.

&&

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

&&

$$
SYNOPSIS...PM
NEAR TERM...AL/PM
SHORT TERM...DS
LONG TERM...JH
AVIATION...PM


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