Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
353 PM EST Fri Feb 07 2020

Valid 00Z Sat Feb 08 2020 - 00Z Tue Feb 11 2020

...West of the Continental Divide...

Days 1-3...

Vigorous mid-upper level shortwave crossing Vancouver Island and
the PAC NW this evening will drop slowly south across CA during
day 2, then cut off over far northwest Mexico on day 3. As it does
so, some of the energy will translate eastward via the northern
stream across the northern Great Basin-northern Rockies during day
1 (Sat). Snow levels will drop behind the trough -- resulting in a
fairly widespread swath of high probabilities of 8 or more inches
during day 1 across elevations the WA/OR Cascades above 3kft
(including Olympics), the Blue Mountains in northeast OR, the
northern ID and western-central MT mountains, and northern WY
ranges.

By day 2, the heavier snow (highest 8+ inch probabilities) will be
confined over the lower Wasatch Range in southern UT, along with
the central CO Rockies as the positively-tilted trough nudges
south across CA and the central Great Basin. By day 3, heavy snow
probabilities will translate into the San Juan and Sangre De
Cristo Ranges of southern CO into northern NM.


... Northern Great Plains and into the Upper MS Valley and Upper
Great Lakes...

Days 1-2...

The aforementioned northern stream shortwave energy ejects east
from the northern Rockies Saturday, crossing NE-SD Sat night,
southern MN/WI Sunday and the Great Lakes Sunday night and Monday.
Albeit a fairly compact system, robust deep-layer forcing will
ensue on the heels of a developing w-e oriented 110 kt 250 mb jet
streak, along with an uptick in low-mid layer frontogenesis. As
low-level southerly trajectories ahead of the shortwave begin to
tap western GOMEX moisture, weakening mid-level static stability
will take place along and just north of the 850 mb low track, as
model forecast 700-500 mb theta-e lapse rates drop to near or just
below 0C Sat night and Sun across eastern SD, southern MN/northern
IA, and southern WI. Therefore, continue to expect some mesoscale
enhancement to the snowfall, resulting in narrow bands of locally
higher totals (10+ inches) within a swath of snowfall averaging
6-8 inches. Probabilities of 6 or more inches will be highest
(50%) from southern MN and far northern IA into central-southern
portions of WI.


The probability of ice accumulations of 0.25 inch or greater is
less than 10 percent all 3 days.

Hurley