Avalanche Forecast

Small isolated wind slabs have formed on a variety of aspects near and above treeline. You can avoid these avalanches by staying off of steep wind loaded slopes. Use visual clues to assess and avoid wind loaded features.  Snow drifts, fresh cornices, and uneven snow surfaces with cracking can all indicate wind slabs exist on nearby slopes.

Older weak snow still exists in the snowpack. Persistent slab avalanches have been the culprit in several accidents and fatalities over the month. New precipitation may change how these layers react. You can avoid persistent slab avalanches by staying away from large steep open terrain where these large avalanches may occur. 

The new snow is falling on a variety of snow surfaces including firm surface crust, near surface facets, and potentially surface hoar. Be ready to dial back your terrain if you experience any signs of unstable snow such as observing new avalanches, hearing whumphs, or seeing shooting cracks. This is most likely to occur in areas receiving higher snow fall amounts.

Several inches of new snow has fallen around the region in the last 24hrs. Rain on Thursday slowly turned to snow as freezing levels lowered throughout the day. This likely created a favorable bond between the new and old snow surfaces.

Above the rain line, 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.

Moderate winds likely transported new snow forming soft wind slabs near and above treeline. These wind slabs will generally be shallow and isolated to exposed ridgelines and mid-slope terrain features.

Below the most recent snow and crust, several older persistent weak layers continue to be reported. Persistent Slabs in the upper snowpack are easier to trigger, but may be more isolated in their distribution. Persistent Slabs deeper in the snowpack (2/13 or 16 layer) are more widespread, but are harder to trigger. Observations from the Eastern areas of the Cascades have found these layers reactive and they were in involved 3 avalanche fatalities in early March. The exact persistent weak layer depends on your location.

Commonly seen persistent weak layers are:

• Surface hoar and facets buried on 3/8. This layer is typically found 10-16’  below the snow surface near and below treeline. Professionals near Washington Pass have reported that the surface hoar is fairly widespread in that area. The distribution of this layer may be more variable in the Central and Southern zones. 
• 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 2-4 feet 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.

Observations

Central

On Thursday Mission Ridge Ski Patrol reported 4 inches of generally right-side-up storm snow by mid afternoon. 

NWAC professional observer Matt Primomo traveled in the North Fork of the Teanaway River on March 15th. (just north of Cle Elum). The 3/8 buried surface hoar layer was found about 12 inches below the snow surface. It was reactive in some snowpack tests. The 2/5 layer was also found in this area about 3 feet below the snow surface.