Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
459 AM EDT Mon Apr 11 2022

Valid 12Z Mon Apr 11 2022 - 12Z Thu Apr 14 2022

A long duration winter storm, producing significant snow and
strong winds will impact portions of the northwestern to the
north-central U.S. through midweek.

...Pacific Northwest...
Days 1-3...
A compact low will continue to move onshore this morning, bringing
additional moderate to heavy precipitation to portions of
southwestern Washington, western Oregon and Northern California. 
Heavy mountain snows are likely for portions of the Cascades, as
well as the southwestern Oregon and northwestern California
ranges, and the northern Sierra.  Snow levels will drop notably
today behind associated cold front, supporting the potential for
some light accumulations across the lower elevations as unsettled
weather persists.  A series of shortwaves are expected to slide
southeast along the British Columbia coast into the region,
bringing additional rounds of organized precipitation on Tuesday
and Wednesday.  While widespread heavy amounts are not expected,
portions of the southern Cascades and the Northwest California
mountains could see some locally heavy additional amounts.

Northern Rockies through the Northern Plains...
Days 1-3...
Strong dynamic lift associated with the low entering the Pacific
Northwest this morning is expected to translate east into the
northern Rockies today.  Early in the period, a low-to-mid level
warm front ahead of the low, overlapped by left-exit region upper
jet forcing will help to support heavy snows developing across the
southern Idaho into the western Wyoming ranges.  Then by late
today and continuing into the overnight, strong easterly flow
north of a low level center moving from southern Idaho eastward
along the Montana-Wyoming border will help support heavy snow in
the upslope regions of the western to central Montana ranges. WPC
probabilities indicate that by early Tuesday accumulations of 4-8
inches will be common across these areas, with heavier amounts
likely across the higher peaks.

By early Tuesday morning snow will begin to spread east across the
High Plains.  As the upper low continues to move east, a powerful
surface low is forecast to track northeast from the central High
Plains.  Low-to-mid level frontogenesis overlapped by coupled
upper jet forcing will help support heavy snow developing and
spreading east from eastern Montana into North Dakota on Tuesday. 
Models continue to differ on the timing and amplitude of the
system, limiting confidence on the details of the forecast,
however very heavy amounts still appear likely for portions of
eastern Montana and western to central North Dakota.  WPC
probabilities indicate that storm total amounts of 18 inches or
more are likely for portions of western to central North Dakota,
where snow is likely to continue through Wednesday as the system
continues to deepen and move slowly east across the Dakotas.  In
addition to the heavy snow, strong winds will be a concern as
well.  A tight pressure gradient between the deepening low and
high pressure anchored over western Canada is expected to support
strong wind gusts and blizzard conditions for some areas.  By
early Thursday, snowfall is expected to diminish, however strong
winds will likely persist as the low begins to lift north into
Canada.  

For Days 1-3, the probability of 0.10 inch or more of ice is less
than 10 percent.


~~~Key Messages for April 11-14 Blizzard~~~

--A long duration, significant winter storm will bring heavy snow
to the Cascades through Monday, then the northern Intermountain
West through the northern Plains Monday night into Thursday.

--A combination of heavy snow and strong wind gusts are likely to
produce blizzard conditions from the eastern slopes of the
northern Rockies across the northern Plains.

--Heavy snow combined with strong winds has the potential to
produce power outages, tree damage, hazardous to impossible travel
conditions, and impact livestock, especially calves and lambs.

--Prepare now for impactful winter weather and hazardous to
potentially impossible travel conditions.

Pereira