Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
651 PM EST Monday Feb 8 2016
a strong cyclone in the upper levels of the atmosphere will sink
south across the Great Lakes and into the Ohio Valley this evening.
The area of low pressure will cutoff and remain nearly stationary
for the next three days. The coldest of the air will not arrive
until Tuesday. Weak upper level impulses will move across the
mountains during the week resulting in a prolonged snow shower
event especially over the mountains through midweek.
Near term /until 6 am Tuesday morning/...
as of 615 PM EST Monday...
Focus is on transition of rain to snow in the west...but overall
radar coverage is more scattered than categorical in terms of
probability of precipitation. Will follow close to the 22z hrrr and 18z local WRF as it
slides a narrow band of snow across the New River valley into the
Shenandoah Valley and Blue Ridge north of Carroll County Virginia through
evening. There is some good reflectivity signatures and with
colder air aloft we have had some thundersnow reports. Some areas
could see a good 1-2 inches of snow in a 1 hour period and an Special Weather Statement
will cover this through the next couple of hours.
Once this mesolow along the front over SW Virginia moves east
expect a drier period but upslope kicks in.
Previous discussion from early afternoon...
today's precipitation did not start until late in the
morning...which allowed temperatures to peak in the upper 30s to
lowers 40s west of the Blue Ridge to the upper 40s to lower 50s
east. Warm air advection ahead of a cold front brought some snow
to higher elevations and white rain to the valleys this afternoon.
This precipitation lowered temperatures across the mountains
during the afternoon by 5f or so. Because the warm boundary is so
shallow...snow was able to make it to the ground even...though
temperatures were above freezing.
The first cold front...located across the Ohio and Tennessee
valleys...will move across the mountains early this evening...then
across the Piedmont by midnight. This front may be a few hours
slower to clear the area...as a surface reflection develops along
the front tracking across the Piedmont this evening. Precipitation
with the front will remain light with snow or white rain across
the mountains and a cold rain in the east. A second cold front
with Arctic air will approach the area early Tuesday morning.
Precipitation ahead and behind this front will be all snow with
accumulations primarily along western slopes. Western slopes of
Greenbrier and Summers County could see 2-3 inches this afternoon
into tonight. Western slopes from the Bluefield-Richlands area to
the Grayson Highlands and northwest North Carolina high County
could have 1-2 inches...possible 3-4 inches above 4000 feet.
For headlines...we will continue the Winter Weather Advisory for
the first front through 6pm this evening for our western counties.
We will allow this advisory to expire. We will then upgrade the
current Winter Storm Watch to a Winter Storm Warning for western
slopes of Greenbrier County south into Summers and Mercer County.
Other counties in the watch will be changed to a Winter Weather
Advisory from the Alleghany Highlands to the mountain Empire and
northwest North Carolina high County. At this time...no other
counties will have headlines to included the New River and Roanoke
valleys...who may see some snow tonight into Tuesday with only
Short term /6 am Tuesday morning through Thursday night/...
as of 330 PM EST Monday...
Deep upper low over the Ohio Valley Tuesday and Wednesday. Short
wave over the forecast area Tuesday morning along with much colder
temperatures aloft...in the range of -30 to -36 will provide some
lift and relative instability. This should extend snow showers
well east of the Blue Ridge on Tuesday...especially north of
Roanoke. 850 mb temperatures will continue to drop...reaching -18
to -20 by 12z/7am Thursday. Models are similar in overall synoptic
pattern but subtle differences show up in speed and location of
short waved embedded in the large upper trough.
Enough cold air coming in that western slope locations and areas
with snow showers will have steady or even slightly falling
temperatures during the day Wednesday. Expecting snow to liquid
ratios of 25:1 by Wednesday night. Enough dry air and downsloping
on Wednesday and Thursday to have some clearing east of the Blue
Long term /Friday through Monday/...
as of 250 PM EST Monday...
Eastern upper trough gets re-enforced Friday night and
Saturday...then trough axis moves of the coast on Sunday. Both the
European model (ecmwf) and GFS bring a clipper across the central United States
Monday then into the middle Atlantic region by Tuesday. Wpc suggested
the track off the European model (ecmwf) may be too far south.
Some 850 mb warm air advection and low level convergence along
the leading edge of the next surge of Arctic air. Best lift looks
to be on Friday with some upper diffluence. Snow should be more
widespread than just upslope. Then gusty winds and very low wind
chill values on Friday night through Saturday night with northwest
850 mb winds approaching 50 knots. Wind chills will again be in
advisory criteria...between -5 to -19 in the mountains on Saturday
A roughly 1045 mb surface high will build into the area Friday
night and Saturday. This feature will be centered over the middle
Atlantic region Monday morning. Winds will diminish enough with
the approach of this high...and with the associated dry air...to
end upslope snow showers in the mountains Sunday.
Aviation /00z Tuesday through Saturday/...
as of 645 PM EST Monday...
Narrow band of heavier snow will move across bcb/roa between
00z-01z...and also lwb. There will be some IFR or lower visibilities with
this but short lived. Overall look for MVFR ceilings/visibilities at most taf
sites through this period...exception being blf where upslope will
provide some IFR ceilings. A stronger upper vorticity moving across SW Virginia
toward 12z expected to bring an enhancement in snow showers at
blf/lwb reaching bcb by 13z. How far east this gets is debatable
but will leave roa/lyh/Dan VFR once northwest flow kicks in.
This enhancement of snow showers 12-16z will likely result in IFR
at times blf with MVFR at lwb/bcb...but cannot rule out IFR with
Sub-VFR should become more confined to the mountains and western
slopes Tuesday night into midweek with prolonged MVFR/IFR
conditions at kblf/klwb in snow showers through at least Wednesday
night as Arctic air arrives. Potential also for periods of MVFR at
kbcb/kroa as impulses rotate across the mountains and bands of
snow develop during the overnight hours. Accumulating snow is
likely in the mountains west of the Blue Ridge. Flurries may also
occur as far east as the Piedmont where intervals of VFR to MVFR
ceilings could also occur.
Conditions should briefly return to mainly VFR Thursday/Thursday
night as weak high pressure builds in and moisture decreases.
Another system moving across the south may bring sub VFR
conditions with wintry precipitation Friday into Friday night. Another
Arctic front crosses by Sat morning with gusty winds and upslope
snow showers with sub VFR in the mountains
Virginia...Winter Weather Advisory until 7 am EST Thursday for vaz007-
NC...Winter Weather Advisory until 7 am EST Thursday for ncz001-018.
WV...Winter Weather Advisory until 7 am EST Thursday for wvz042>044-
Winter Storm Warning until 7 am EST Thursday for wvz043-508.
short term...air mass
long term...air mass