Avalanche Forecast

Thursday night: Mostly cloudy with clear periods, isolated flurries, light northerly wind, alpine high temperature -12 C, freezing level at valley bottom.

Friday: Mix of sun and cloud, isolated flurries, moderate northeast wind, alpine high temperature -18 C, freezing level at valley bottom.

Saturday: Mix of sun and cloud with isolated flurries, moderate northeast wind, alpine high temperature -22 C, freezing level at valley bottom.

Sunday: Sunny, light northeast wind, alpine high temperature -15 C, freezing level at valley bottom.

Numerous slab avalanches up to size 2.5 and many small dry loose avalanches were reported on Tuesday and Wednesday. Many of these avalanches released on the old snow surface consisting of a weak surface hoar layer which the new storm snow covered on Tuesday.  

A few natural cornice failures and wind slab avalanches up to size 2.5 were reported on Monday.

Reports of large (size 2-2.5) human-triggered and explosive-triggered avalanches releasing on the February 22 surface hoar layer continued throughout last weekend from operators region-wide. This layer continues to surprise people with remote-triggered activity, wide propagation, and a false sense of stability from unreactive ski cuts or from multiple people moving through the terrain before an avalanche releases. Observations have extended to all aspects and elevations, but north to east aspects near treeline have been a hot-spot for reactivity. Avalanches have also occurred at unusually high elevations for surface hoar, with several cases of wind slabs stepping down in the alpine. While the number of reported avalanches has decreased, the size has increased, with more of the activity releasing size 2+.

The recent storm delivered 15-30 cm of snow with strong westerly winds. The snow surface varies from soft snow to wind pressed in the alpine and at wind exposed treeline elevations. The recent snow may sit on a surface hoar layer and a sun crust on steep solar aspects. The new snow is not expected to bond well with these previous surfaces. 

A widespread weak layer of surface hoar is buried 60-100 cm deep. On solar aspects, this layer may sit over a crust. This persistent slab problem is transitioning into a low probability/high consequence scenario. The snow above the weak layer has increased in depth and slab properties, making avalanches more difficult to trigger and masking obvious clues that the problem is present (i.e. cracking, whumpfing). However, if triggered, avalanches will be large and getting caught could have serious consequences. Managing this problem requires a patient and diligent mindset, implemented by avoiding suspect slopes and maintaining conservative terrain margins. This persistent weak layer will likely pose the threat of a low probability/high consequence avalanche until there is a substantial change in the snowpack. Read more about surface hoar on our forecaster blog.

• Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
• Recent wind has varied in direction so watch for wind slabs on all aspects.
• Be aware of the potential for large avalanches due to the presence of buried surface hoar.
• Storm slabs in motion may step down to deeper layers resulting in large avalanches.