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Archived

Avalanche Forecast

Dec 11th, 2018–Dec 12th, 2018
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable

Regions: Cascades - West.

We have received significant snowfall, strong winds, and have a weak snowpack. This is a recipe for avalanches. It is not the time to travel in areas where avalanches can start, nor linger where they can run or stop.

Discussion

Avalanche Summary

In the neighboring zones of Stevens Pass and Mt. Baker, we have reports of both natural and human triggered avalanches from Monday and Tuesday. At least some of these avalanches are failing on a layer of buried surface hoar. There is no clearer sign of unstable snow than recent avalanche activity.

Snowpack Discussion

Regional Synopsis coming soon.

Avalanche Problems

Wind Slabs

Expect recent winds to have significantly moved snow around in the mountains. You will likely find deeply drifted areas, firm hollow wind slabs, and areas stripped by the wind. When you encounter firm surface snow on steep slopes, know that avalanches may break above you.

Even in areas sheltered from the wind, you can still find unstable snow. In some areas, new snow sits atop a weak layer of facets and/or buried surface hoar. If avalanches occur on this layer they may act in surprising ways including remote triggers and wide propagation.

Release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

 

Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..

 

Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.

 

Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Very Likely

Expected Size: 1 - 1