Avalanche Forecast

Friday night: Cloudy with clear periods, moderate northeast wind, alpine high temperature -25 C, freezing level at valley bottom.

Saturday: Mix of sun and cloud, moderate northeast wind, alpine high temperature -20 C, freezing level at valley bottom.

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

Monday: Sunny, light southwest wind, alpine high temperature -10 C, freezing level at 1000 m.

Numerous slab avalanches up to size 2.5 and many small dry loose avalanches were reported during and after the recent storm. Many of these avalanches released on the old snow surface consisting of a weak surface hoar layer which the new storm snow covered. Even though reports on that layer have decreased it is till possible to trigger an avalanche on this layer. 

Reports of large (size 2-3) human-triggered and explosive-triggered avalanches releasing on the February 22 surface hoar layer continued over past week 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 which now shifted to northeast forming fresh wind slabs on previously windward slopes. The snow surface varies from soft snow and wind pressed in the alpine and at wind exposed treeline elevations to sun crust on steep solar aspects. The recent snow may sit on a surface hoar layer and a sun crust on steep solar aspects. This layer is responsible for many avalanche releases and might develop into a persistent weak layer. 

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.

• Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
• Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
• Storm slabs in motion may step down to deeper layers resulting in large avalanches.
• Be aware of the potential for large avalanches due to the presence of buried surface hoar.