Avalanche Forecast

Issued: Dec 11th, 2018 10:00AM

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

Northwest Avalanche Center NWAC, Northwest Avalanche Center

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.

Summary

Discussion

Avalanche Summary

Poor visibility and stormy weather has limited observations in the Paradise and Crystal areas. We have received reports of buried surface hoar and/or facets in sheltered areas of the Crystal backcountry. Even though we have limited information about the current snowpack and recent avalanches, what we do know is quite clear. We have received significant new snow, strong winds, and have a weak snowpack. Expect avalanches, especially at higher elevations.

Snowpack Discussion

Regional Synopsis coming soon. 

Problems

Wind Slabs

An icon showing Wind Slabs

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

Valid until: Dec 12th, 2018 10:00AM