SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/... As of 420 AM EDT Friday...
There is moderate chance of another impactful winter storm to affect
a large part of the western half of the RNK CWA Saturday
into the early morning hours of Sunday. Light to moderate snowfall amounts
are also expected across eastern areas during the weekend.
Significant accumulations of snow are likely along/west of the Blue Ridge.
Models continue to key on a strong short wave embedded within the back
side/base of a persistent northeastern U.S. trough. This short wave will
track quickly from the Northern Plains southeast into the central/southern
Appalachians today through Saturday. This is a part of the same system that
brought heavy rainfall to southern California yesterday. Strong dynamics
will combined with PWATS of 0.7 to 1.0 to bring general qpf to the region
of 0.25 to 0.75 inch. With 850mb temperatures largely at or below 0C, most
of this precipitation will fall in the form of snow. Model soundings show
most if not all of the atmospheric column, except perhaps in some warmer
areas right near or at the surface, below 0C throughout the duration of the event.
With an average 10/1 ratio for the rain to snow ratio, this potentially
could bring 2-8 inches of snow to much of the CWA. The main thing that changed
from yesterday`s forecast for this event is not so much the amounts,
but more the exact track of the storm system and where the heaviest snow
will likely fall. Given the tight, compact nature of this Alberta Clipper type system,
significant variations in snow amounts will occur over a short distance.
Yesterday the model consensus track was from central WV through west central
VA then toward north central/northeast NC. Latest models, including even
now the 06Z NAM, have shifted the track about 100 miles further southwest,
now through the New River Valley and more northwest NC then north central NC.
As a result, the heaviest snow has shifted from yesterday`s thinking closer
to the I64 corridor and the Greenbrier Valley into the southern Shenandoah Valley
more now to the New River Valley and the mountains of southwest VA and northwest NC.
Again, there will be a sharp gradient in snow amounts from potentially 8+ inches in
the core of the heaviest snowfall, to less than 1 inch across the eastern
and northeastern parts of the CWA. Following a conference all with WPC
and neighboring offices, have decided to leave the Winter Storm Watch in place for
the original set of counties and added, because of the new projected track
of the storm system, Grayson, Ashe, and Watauga counties. Confidence is still
not high enough to upgrade to a third period warning or issue any advisories,
although most likely both will be coming with the afternoon forecast package.
Time of year, time of day, and relatively warm ground temperatures will have
a significant impact on how much snow accumulates, when, and where.
Across the Piedmont of VA/NC, much of this may translate to a "white rain".
Once the storm system moves out of the area Sunday, a high amplitude yet
progressive ridge will progress from the central U.S. into the eastern U.S.
reaching the forecast area by Wednesday. In advance of this ridge, northwest
flow aloft bringing cold air from Canada and the northeast will remain in place
with much below normal temperatures and mostly dry conditions.
Temperatures will run around 15-20 degrees below normal through Monday with high
in the 30s mountains to 40s Piedmont and lows in the 20s mountains to the 30s Piedmont.
