Avalanche Forecast

Sunday night: Cloudy, 5-10 cm of snow, moderate west wind, alpine temperature -12 C.

Monday: Mostly cloudy, scattered flurries with 2-5 cm of accumulation, light west wind, alpine high temperature -7 C. 

Tuesday: Cloudy, 15-25 cm of snow overnight and throughout the day, light southwest wind, alpine high temperature -4 C.

Wednesday: Cloudy, 10-15 cm of snow, light southwest wind, alpine high temperature -5 C.

Numerous natural and human-triggered wind slabs were reported on leeward features on Saturday. These avalanches ranged from 10-50 cm deep and were small to large (size 1-2.5). Check out this MIN report from Reudi's on Saturday for a helpful illustration of this problem.

Additional reports of large (size 2-2.5) avalanches breaking on the late December surface hoar continued on all aspects and elevations from natural, human, and explosive triggers. Several of these avalanches were triggered remotely.

Explosive control work and other large triggers have produced large and very large (size 2-3.5) deep persistent slab avalanches on all aspects in alpine terrain. Characteristics common to these avalanches include wide propagation and full depth avalanches scouring away the snowpack to ground.

The most recent snow has been redistributed by strong southwest winds in exposed areas, loading lee features with stiffer, more reactive slabs. 

A total of 40-70 cm of snow has fallen over the past week burying a weak layer of feathery surface hoar and a hard melt-freeze crust on sun-exposed aspects. This layer has demonstrated reactivity past its due date as a storm slab interface, and it continues to produce large avalanches across aspects and elevations.

The base of the snowpack in the Purcells is much weaker than in an average season, and there are deeper weak layers down 70 to 180 cm. This weakness is widespread across all aspects and elevations, and it consists of crust, facets and depth hoar. Recent snowfalls in the past two weeks have overloaded these deeply buried weak layers resulting in very large and destructive avalanches. It is possible that easier-to-trigger wind slab avalanches could step down to these deeper, persistent layers or that the weak layers could be human-triggered in areas where the snowpack is thin, rocky, or variable. 

• Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
• Be alert to conditions that change with elevation and wind exposure.
• Remote triggering is a concern, watch out for adjacent and overhead slopes.
• In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.