Avalanche Forecast

Friday night: Mostly cloudy, scattered flurries with up to 5 cm snow accumulation, moderate easterly wind, alpine high temperature -20 C, freezing level at valley bottom.

Saturday: Mix of sun and cloud with isolated flurries, moderate easterly 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 1200 m.

Numerous wind slab and storm slab avalanches up to size 3 were triggered naturally and by humans on Tuesday and Wednesday. Many released on the old snow surface which consists of a weak surface hoar layer and a sun crust on steep solar aspects. Reports of avalanches releasing on this layer continued into Thursday. Some of these avalanches stepped down to the persistent weak surface hoar layer from February 22 and resulted in large avalanches up to size 3. 

Reports of large (size 2-3) human, remotely and explosive-triggered avalanches releasing on the February 22 surface hoar layer continued over the 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 (see this Instagram report as a good example). 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 20-40 cm of snow with strong southwest winds which then shifted via northwest to northeast winds. 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 60-120 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.
• If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.
• Be aware of the potential for large avalanches due to the presence of buried surface hoar.