Avalanche Forecast

Strong winds Saturday should have easily formed new, firm, wind slabs especially above the rain line. Wind slabs may be hiding under a few inches of soft snow and be more difficult to see than normal. Look for fresh cornices, snow blown off trees, and firm hollow sounding snow to indicate wind slabs are nearby. Due to the strong winds you may find wind slabs further down the slope and in unusual location. Avoid any open slope greater than 35 degrees where you have observed wind blown snow.

At lower elevations and in wind sheltered areas, you will find right-side-up new snow over a newly forming and strengthening crust. This may cause travel conditions to be difficult

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.

It’s been more than a week since we have heard any reports of avalanches on the deep persistent weak layer. That’s a good sign. We think this layer is gaining strength, however we also know that deep persistent layers like this are very difficult to assess and predict. You are most likely to encounter this problem on north and east aspects above 5000 ft where a layer of surface hoar and facets are buried 6-8 ft deep. If you plan on traveling into larger avalanche terrain near and above treeline, you should take time to consider and discuss this low likelihood but high consequence avalanche problem.

Release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer, deep in the snowpack or near the ground. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage. They commonly develop when Persistent Slabs become more deeply buried over time.

Deep Persistent Slabs avalanches can be destructive and deadly events that can take months to stabilize. You can trigger them from well down in the avalanche path, and after dozens of tracks have crossed the slope.

A snowboarder triggered this Deep Persistent Slab near treeline, well down in the path.

Deep, persistent slabs are destructive and deadly events that can take months to stabilize. You can triggered them from well down in the avalanche path, and after dozens of tracks have crossed the slope. Give yourself a wide safety buffer to handle the uncertainty, potentially for the remainder of the season.