Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
1201 PM EST Friday Feb 12 2016
an upper level disturbance will pass just south of the region this
afternoon bringing periods of light snow or snow showers
especially across the mountains. A surge of Arctic air follows
this system overnight resulting in very windy conditions and
bitterly cold temperatures...along with some added snow showers
for the far western slopes of the Appalachians into Saturday. By
Monday another winter storm system will begin to affect the region
with the potential for snow and mixed precipitation through the
first part of next week.
Near term /through tonight/...
as of 945 am EST Friday...
Column continuing to slowly moisten as axis of isentropic lift
spills east ahead of the strong upper shortwave seen on water
vapor passing to the south. Latest short term guidance continues
to vary on just how far east any of these bands will make it with
some primarily confined to the western slopes...while others
including the WRF-arw and to some degree the hrrr spill light
snow east to the Blue Ridge and points east. Although this looks
overdone...period of backing aloft may be enough to help push
light snow farther east than typical downsloping would allow
espcly with the upstream trailing channeled vorticity axis seen back
in Kentucky. Thus bumped up amounts a bit across the far SW per current
trajectory of snow to the west and heading out east of the Blue
Ridge for at least a coating. Appears least amount of snow may
occur over the north as the Transfer of energy from the mountains
to the coastal ducks farther south through the afternoon. Still
going headlines on track for an inch or so today out west and
combined upslope overnight so no changes there other than to tweak
amounts. Also made some slight upward adjusts to temperatures mainly east
where could surge up as a few breaks develop ahead of any precipitation
that attempts to head east of the ridges. Think most ptype even
out there to be snow given coldness aloft so running with mostly
Will need to take a look at the winds overnight into Saturday
morning behind the passing Arctic front as could see warning
criteria SW but will await 12z guidance before updating.
Previous discussion as of 400 am EST Friday...
The main weather players for our region today and tonight will be an
upper level short wave bringing some light snow to the far western
portion of the area before a strong cold front moves through and sets
off another round of upslope snow showers west of the Blue Ridge.
Believe the mountain Empire region will see an inch or less of snow
before the upslope really kicks in and provides additional accumulations
along the far western slopes through tonight. The air moving in behind
the front is quite cold indeed and will create some very steep low level
lapse rates and even a bit of cape...which may bring US another chance
for a period of thundersnow early tonight. Mesoscale models also indicate
a decent upstream contribution to the moisture from the Great Lakes.
Believe these factors will combine to generate snow accumulations
generally in the 2 to 4 inch range for the western slopes with some
locally higher amounts possible so will issue an advisory for this area
from this afternoon through tonight.
Low level winds will also start to increase tonight and good momentum
Transfer in the boundary layer will allow for quite a bit of wind
overnight with gusts over 40 miles per hour expected especially over the higher
terrain. This will combine with temperatures west of the Blue Ridge
falling into the single digits to generate wind chill values of 5 to 15
below zero...with readings to 25 below for western Greenbrier County in
West Virginia. Winds will gradually subside on Saturday but the
combination of wind and very cold temperatures will continue to
generate very low wind chill values through Sunday morning. A Wind
Chill Advisory will be issued for the area along and west of the Blue
Ridge from tonight through Sunday morning with a wind chill warning for
western Greenbrier. Conditions east of the ridge will not be quite as
severe as lows tonight reach the 15 to 20 degree range with wind chill
values into the single digits.
Short term /Saturday through Monday night/...
as of 430 am EST Friday...
Coldest air of the season still slated to be spreading into the
region for Saturday...with temperatures bottoming out Sunday
morning. The models have backed off the intensity of the cold air
mass just slightly with each succeeding run...now stopping around
-22c across the far northern portion of the County Warning Area. Similar events
the past two years have seen readings closer to -25/-26c...so feel
confident that morning low temperatures Sunday morning will fall a
couple of degrees shy of what we saw the last couple of years with
similar Arctic outbreaks. Also...snow cover is limited east of
the Alleghany front and the mountains of SW Virginia/northwest NC...so that
will also not help drive temperatures to The Levels we saw around
this time last year. Nonetheless...it will be bitterly cold and
very windy...prompting a continuation of the wind chill advisories
west of the Blue Ridge and the warning for western Greenbrier.
Winds will begin to diminish late in the day and Saturday
night...but with temperatures falling into the single digits and
near 0 to -5f at the higher elevations...the advisories/warnings
are warranted to continue into Sunday morning as it will take very
little for wind chills to meet criteria with temperatures that low.
Upslope snow showers should be winding down Saturday morning
fairly quickly as the very dry Arctic air mass spreads into the
region. Will keep slight chance to low chance probability of precipitation for snow
showers going through mid-day...then end them...albeit some
flurries could continue into the afternoon as Arctic cold-
advection squeaks out any remaining moisture. Winds will be
strong and gusty throughout the day...but likely drop below
advisory criteria in the west during the afternoon...although that
is lumped into the west-southwest.
The Arctic high settles over the region Sunday morning with...as
noted above...bitterly cold temperatures...but winds trending
toward calm. By afternoon...the Arctic high has already shifted
toward the Virginia/Maryland coast with return flow evident especially in
southwest Virginia. A northern stream short wave quickly moves toward
the region by Sunday afternoon...with increasing moisture from top
down. The antecedent air mass will clearly be very dry and cold
and not sure how quickly the air mass will saturate to allow
generated precipitation aloft to reach the ground. Indications are
that this should begin to take place after sunset in the west and
closer to midnight in the east. Thus...will leave the daytime
hours of Sunday dry with probability of precipitation below 15 percent. All precipitation
Sunday night will be snow across the entire County Warning Area as the soundings
remain below freezing at all levels.
As we move into Monday...the situation becomes increasingly
complicated. The northern stream short wave will move northeast of
the region early Monday...while a stronger southern stream short
wave deepens into the mid-south. Deep surface low pressure will
then develop in response to this second southern stream short wave
across the mid-south...moving toward the eastern Tennessee Valley by
Monday evening. All of the models have taken a slight west jog
with the surface low pressure...resulting in the potential for
warmer air from the south and southeast to encroach on the region.
Nonetheless...the antecedent air mass will be very cold and models
often advertise a warmup too quickly with this type of situation.
A warm front will lie across the region Monday night...then begin
to lift northward early Tuesday. This is when the p-type issues will
begin with a transition from snow to sleet to freezing rain and
perhaps even rain in parts of the Piedmont. This entire period
will eventually have to be handled by top-down or similar p-type
procedures...but given it is still out in the day 4 and beyond
period....will stick with a rain/snow mixture for now. Although
snow/sleet/ice amounts still highly in question...it still appears
quite certain that winter storm criteria will likely be met across
much of the County Warning Area in the Sun night through early Tuesday time
frame...with still the potential for significant snowfall
accumulations in the western mountains. Thus...will continue to
highlight this potential in the severe weather potential statement. A Winter Storm Watch for this
period will likely need to follow on the heels of the current
winter weather advisories.
Long term /Tuesday through Thursday/...
as of 100 PM EST Thursday...
A deepening surface low...remaining mostly inland...will track
across the County Warning Area Tuesday...moving toward the northern middle-Atlantic by
evening. Significant winter weather will likely continue for much
of the County Warning Area...but potentially transitioning to rain across the
Piedmont. BUFKIT shows considerable vertical motion in the snow
growth zone early Tuesday...so there could be a burst of heavy
snow/sleet before the dry slot spreads into the region from the
southwest and shuts off the heavier precipitation...which should
occur by midday Tuesday. By evening...colder air begins to filter
back into the western areas and upslope snow showers commence once
In the wake of the strong synoptic system Tuesday...another
clipper is evident in continued northwest flow aloft. Overall
warming of any significance looks limited during this period.
Although previous runs of the GFS showed substantial warming
during this time frame...that is not evident today. Mexmos keeps
western areas mostly at or below freezing through midweek...with
only limited warming during the later half of the week. The
clipper Tuesday night/Wed...could bring additional minor snow
accumulations to the western parts of the County Warning Area before moving
northeast of the region. Outside of upslope snow showers...that
should be the last of any synoptic-scale induced precipitation for
Aviation /18z Friday through Wednesday/...
as of 1150 am EST Friday...
Lower ceilings and associated light snow bands will continue to head
east crossing the Blue Ridge by early afternoon. This will result
in periods of MVFR/IFR over the western sites and brief MVFR
espcly around kdan by middle afternoon. Once the winds turn more
northwest should see conditions improve over the east and return
to VFR by early evening if not sooner.
However for kbcb/kblf/klwb the northwesterly winds will be upslope and
this will keep snow showers at these locations with MVFR/IFR
ceilings/visibilities into this evening at kbcb...continuing overnight at
kblf/klwb. Behind the front all sites will see significant wind
gusts as a well mixed boundary layer allows for efficient momentum
Transfer of increasing low level flow. Expect g40-45kt at kroa
with gusts at or above 35kt for kbcb/kblf overnight.
A gradual return to VFR appears likely on Saturday although
kblf/klwb likely to keep MVFR in snow showers around until late in
the day. Winds will remain strong on Saturday with gusts to 30-40
kts likely until high pressure builds in during the afternoon.
The next low pressure system will arrive on Sunday night.
Confidence is high that poor flying weather will take place during
Monday and Tuesday. This system will likely bring wintry
precipitation to much of the area...but further updates from the
longer range models may impact the details on precipitation type
and storm track. Another weak clipper area of low pressure may
keep MVFR conditions across the mountains Tuesday night into
Wednesday with mainly VFR east of the Blue Ridge.
coldest air of the season arrives this weekend. Several record low
maximum temperatures and low temperatures are possible. Below are the
current records for Saturday 2/13 and Sunday 2/14.
site mint year Lomax year
kblf 4 1988 19 1988
kdan 11 1955 32 1981
klyh 5 1979 9 1899
kroa 8 1917 18 1914
krnk -4 1969 14 1955
site mint year Lomax year
kblf 5 1971 16 1960
kdan 15 1986 32 1986
klyh 4 1899 24 1905
kroa 10 1943 26 1986
krnk -2 1969 24 1986
Virginia...Wind Chill Advisory from 11 PM this evening to 10 am EST
Sunday for vaz007-009>020-022>024-032>035.
Winter Weather Advisory until 7 am EST Saturday for vaz007-009-
NC...Wind Chill Advisory from 11 PM this evening to 10 am EST
Sunday for ncz001-002-018.
Winter Weather Advisory until 7 am EST Saturday for ncz001-018.
WV...Wind Chill Advisory from 11 PM this evening to 10 am EST
Sunday for wvz042>044-507.
Winter Weather Advisory until 7 am EST Saturday for wvz042-043-
Wind chill warning from 11 PM this evening to 10 am EST Sunday