Avalanche Forecast

Avalanche danger will slowly decrease Saturday as new wind slabs begin to gain strength. Even though the hazard is decreasing, you may still trigger a wind slab on steep slopes near ridgeline. You are more likely to trigger a wind slab on convex rollovers, steep unsupported slopes, or below fresh cornices. You can use visual clues to identify and avoid wind loaded slopes greater than 35 degrees. Snow drifts, cornices, and firm snow surfaces with cracking all indicate that nearby slopes received wind deposited snow.

Observations continue to show older weak snow in the snowpack. It can be difficult to identify exactly which slopes have persistent weak layers and which ones do not. Persistent slab avalanches have been the culprit in several accidents and fatalities over the month. New precipitation may change how these layers react. While snowpack tests can provide useful information about buried weak layers, they are not a decision making tool. You can avoid persistent slab avalanches by staying away from large steep open terrain where these large avalanches may occur.

The strong March sun can quickly change conditions on slopes receiving direct sunshine. If the sun comes out, expect small loose wet avalanches, rollerballs, and pinwheels. Be ready to move off of and avoid steep sunny slopes during periods of intense sunshine.

Approximately 8-10” of snow has fallen in the Washington Pass area since Wednesday evening. Winds during the storm transported snow forming new wind slabs on lees slopes and cross-loaded features near and above treeline. The new snow fell on a variety of old snow surfaces. On sunny aspects, firm melt-freeze crusts have formed during the recent clear weather. In shaded locations, near surface facets and surface hoar were observed earlier in the week. This may form a new buried weak layer within the snowpack.

At lower elevations rain slowly turned to snow as freezing levels lowered throughout the day. This likely created a favorable bond between the new and old snow surfaces.

Below the most recent snow and crust, several older persistent weak layers continue to be found. While there have not been any new avalanches reported on these layers, snowpack tests continue to demonstrate that avalanches can occur. Persistent weak layers were responsible for 3 avalanche fatalities in the past month. The exact persistent weak layer depends on your location.

Commonly seen persistent weak layers are:

• Surface hoar and facets were buried on 3/8. This layer is typically found 18-24” (45-60cm) below the snow surface on shaded aspects near and below treeline.
• A more widespread persistent weak layer is found just above a firm crust layer buried on 2/5. This layer of weak sugary facets (2/13 or 16) can be found 3-5 feet (90-150cm) below the snow surface. Professionals near Washington Pass and the north end of the East Cascades have reported that this layer most problematic below treeline.
• Other shallow and very weak areas of snowpack may be found further east of the crest or in areas with less snow.

North

On Wednesday NCH found surface hoar and near surface facets present on shaded slopes. The 3/8 buried surface hoar was reported as 10-14 inches below the snow surface.