Avalanche Forecast
Regions: Stevens Pass.
Happy new year! If traveling to upper elevations use caution where deep wind drifts exist over open slopes. In adjacent zones, people have been able to trigger avalanches on a layer of buried surface hoar near and above treeline. This should give us pause, and reason to avoid these types of features.
Discussion
Snow and Avalanche Discussion:
The storm that ended on the 30th past storm brought about 17†inches of new snow with 3.3†of water equivalent to Stevens Pass. It rained up to at least 5200ft during the storm, then a cold front with strong winds blew through as the snow accumulated. We are left with fresh, cold snow over a refreezing wet snow crust, and some deep wind drifts. On the 30th, ski area snow safety teams were able to trigger wind slabs big enough to injure, bury, or kill a person with control work. Numerous human triggered avalanches have been reported in adjacent zones. These appear to be failing on a layer of buried surface hoar from Christmas. In the East Central Zone, observers remotely triggered slides 18" deep on Northeast to Southeast aspects above 6,000ft. One of these was triggered from 200ft away.
Snowpack Discussion
Coming soon.
Avalanche Problems
Wind Slabs
Moderate to strong winds have created stiffer slabs at upper elevations and in wind-exposed terrain that could break widely. I wouldn't trust these slabs, especially near and above treeline. On the eastern edge of the zone, above 5,500ft, a layer of buried surface hoar may have survived the storm. If so, it may be fairly easy to trigger avalanches up to two deep. These slides could wrap widely around terrain features. Use extra caution in places where the wind typically creates firmer slabs. Use low angle slopes for travel and stick to the ridges. Have a look at the situation in the East Central Forecast Zone. Below treeline, where the rain crust is thick and no wind slabs exist, the avalanche danger is generally low.
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: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1