Avalanche Forecast

Issued: Dec 29th, 2018 10:00AM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Wind Slabs.

Northwest Avalanche Center NWAC, Northwest Avalanche Center

Wind-driven snow will be the story Sunday. Stay off steep wind loaded terrain because there’s a good chance you’ll trigger a dangerous wind slab avalanche. Expect winds to build sensitive wind slabs even below treeline.  

Summary

Snowpack Discussion

Updated Regional Synopsis coming Sunday 12/30

Problems

Wind Slabs

An icon showing Wind Slabs

Westerly winds will move snow around at all elevations. Stay off steep wind loaded terrain because there’s a good chance you’ll trigger a dangerous wind slab avalanche Sunday. Avoid traversing onto a wind loaded slope where a hard slab avalanche may break above you. If you find less wind affected snow below treeline (where the conditions are likely better), give the new storm snow time to settle by avoiding steep unsupported slopes. Near and above treeline, a freezing rain crust formed Saturday may make backcountry travel difficult in wind-scoured areas.  

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

Likely

Expected Size

1 - 1

Valid until: Dec 30th, 2018 10:00AM