High Country Snow for the Northwest

By Alex Sosnowski, Expert Senior Meteorologist

November 30,2012; 7:45PM,EST

A series of storms into early next week will bring tremendous high country snow and the risk of avalanches to the West.
Yards of snow will fall on the northern Sierra Nevada, and feet of snow will accumulate in the Cascades.
Snow levels will vary during the siege of storms and will dip to pass levels at times, especially over the northern Cascades.
At elevations above 7,500 feet in the northern Sierra Nevada, the storms are likely to bring between 6 and 10 feet of snow with blizzard conditions at times. Similar conditions are in store for Mount Shasta.

High winds, even below snow levels, could cause some high-profile vehicles to roll over.

Conditions may get much worse than this over some of the passes in the Cascades this weekend. (Photos.com image)

Through the weekend and into early next week, from 2 to 4 feet of snow is forecast to fall over the high country in the Cascades of Washington and Oregon, as well as the Bitterroots of Idaho and Montana.
Wintry Travel
For a brief time, snow will fall down to the high spots on I-80 at Donner Pass, where a half a foot to a foot of wet snow can fall through Friday night. Over the weekend, snow levels will rise above pass level in the northern Sierra Nevada.

Farther north, rounds of snow will end up being more of a problem for travelers.
Initially, through the first part of Saturday, accumulating snow will be above most passes in the Cascades of Washington and Oregon. Snow levels during this period will generally be above 4,000 feet.
However, over the balance of the weekend, snow levels will lower in the Northwest as the air turns a bit colder. This will bring accumulating snow to many passes Sunday into next week.

The storms and their snow through much of next week will avoid the Arizona Rim Country, the Wasatch and central and southern Rockies.

in the northern Sierra Nevada, snow levels will rise significantly Saturday into Sunday, before falling back early next week. As a result, a rapid meltdown of the snow at high elevations is possible for a time and will add to the risk of flooding and other problems.

Avalanche Danger
The series of storms with their high country snow will raise the risk of avalanches.
Feet and yards of snow accumulating in rapid fashion, combined with locally high winds and fluctuating temperatures, will make the slopes very unstable.

While avalanches are more common in the late winter and spring, they can occur in situations like this during the late autumn and early winter.

There is a possibility of significant snow slides especially over the weekend into next week.
By then the weight of the snow will be tremendous and any surge of warmth next week can cause the snow on the slopes to give way.