Avalanche Forecast

While you can trigger wind slab avalanches at all elevations, they could be big enough to bury or kill you near and above treeline. You’re most likely to trigger avalanches on slopes that are steeper than 35 degrees on the leeward (down wind) side of ridges. The combination of cold temperatures, light snow, and gusty wind has drifted snow very efficiently and into unique areas. Expect wind drifts in open areas below treeline, and cross-loading on slopes well below ridges. Take note of how the distribution of wind slabs will change as you move through terrain. Wind slab avalanches could step down into buried weak layers and result in a very dangerous avalanche.

Watch for signs that you can trigger a wind slab avalanche, such as; Actively blowing snow, cornices hanging over a slope at the top of a ridge, wind sculpted features or thick lens-like pillows, especially smooth snow cover, and deeper snow compared to the opposite side of the ridge. The best way to manage the risk of being caught in a wind slab avalanches is to:

Avoid leeward, wind-loaded start zones and cross-loaded features low on slopes

Steer around wind features as well as convexities, where slopes roll steeper

Stop and re-group in safer areas, well out from under and away from wind-loaded avalanche terrain.

The current snow and wind-loading is adding stress to weak layers of snow well below the surface. This storm may be enough to re-awaken these old buried weak layers. If you see obvious signs of avalanche danger, like recent avalanches, collapsing, or cracks breaking through the snow, avoid all slopes 35 degrees and steeper. Persistent slab avalanches are dangerous and difficult to predict. In 2017/18 these deadly avalanches were the cause of every avalanche fatality that occurred in the Cascades.

There are two weak layers to watch for:

1) A layer of surface hoar that formed around Christmas is buried 1 to 2 feet below the surface. This layer is mainly a concern above 6,000ft. Around the New Year, observers reported avalanches on this layer on Northerly through Southeasterly aspects. These avalanches were surprising in how widely they broke across the slopes. 

2) Weak facets near the ground are a concern in the east end of the zone. Observer at Mission Ridge and above Mazama have reported this snowpack structure. If you trigger an avalanche on this layer it could be over 4 feet deep. Use caution where stiff slabs sit over weak snowpack less than 5 feet deep and on steep, unsupported slopes on the eastern edge of the range.