Avalanche Forecast

High - Uncertainty is due to the fact that deep persistent slabs are particularly difficult to forecast. Confidence is due to a stable weather pattern with little change expected.

TUESDAY NIGHT - Cold and cloudy / light north wind / alpine low temperature near -30

WEDNESDAY - Cold, partly cloudy and isolated flurries / light northeast wind / alpine high temperature near -26

THURSDAY - Cold and mostly sunny / moderate and increasing northeast wind / alpine high temperature near -26

FRIDAY - Cold and sunny / moderate northeast wind / alpine high temperature near -20

On Monday, skiers accidentally triggered 2 small (size 1) avalanches down 45 cm, likely on surface hoar.

On Sunday a cornice failure triggered a small (size 1) avalanche with a 50 cm crown. Skiers reported sudden results in test profiles on prominent surface hoar on a variety of aspects buried 50 cm deep.

Last week was busy for avalanche activity, on Wednesday (Feb 3) persistent slab avalanche activity really picked up with reports of natural, human, and explosives triggered storm and/or persistent slab avalanches up to size 2 everyday through Saturday (Feb 6). 

On Saturday (Feb 6) riders continued to trigger slab avalanches 20-60 cm deep, documented in a handful of MIN reports (Trespass, Mammoth, Spicy, Different Day). Explosives triggered several large (2-2.5) persistent slab avalanches on northerly aspects below 2000 m.

On Friday (Feb 5), there were numerous reports of natural and human triggered persistent slab avalanches up to size 2.5. Some of these were triggered remotely, as outlined in a MIN report that can be viewed here. There were also numerous natural and explosives triggered dry loose, and storm slab avalanches reported up to size 2. 

Many thanks for all of the great MIN reports over the past week!

Surface faceting and surface hoar growth is occurring with clear nights and frigid temperatures. Recent northerly and shifting winds have reverse loaded features, slabs may be found in lee terrain on a variety of aspects. 

A persistent weak layer lurks 30-70 cm below the surface, consisting of surface hoar, facets, and a crust buried in late January. This layer has been responsible for the majority of recent avalanche reports and has been easily found on all aspects, reports suggest it is touchiest on northerly and easterly aspects. It's likely that reactivity will decrease with the cold and calm weather, however any inputs (like wind or snow) encouraging a slab to form could quickly make this layer reactive.

Below 1600 m a hard melt-freeze crust is underneath 20-40 cm recent snow. A solid mid-pack sits above a deeply buried crust and facet layers near the bottom of the snowpack (150-200 cm deep), which is currently unreactive. 

• Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
• Avoid terrain traps such as gullies and cliffs where the consequence of any avalanche could be serious.
• Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
• Be aware of highly variable recent wind loading patterns.