Avalanche Forecast

Thursday night: Mostly cloudy with clear periods, scattered flurries with up to 5 cm of snow accumulation, moderate northeast wind, alpine high temperature -15 C, freezing level at valley bottom.

Friday: Mix of sun and clouds with isolated flurries, moderate to strong northeast wind, alpine high temperature -25 C, freezing level at valley bottom.

Saturday: Sunny with some clouds, 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.

The recent snow is reactive to human traffic especially where it is wind affected. A natural avalanche cycle occurred most likely during the storm on Tuesday with avalanches up to size 3. The new snow and wind added a new load to cornices. Shallow storm slab avalanches or cornice falls have the potential to step-down to deeper layers and produce very large avalanches.

Many large to very large avalanches (size 2-3) releasing on the February 22 surface hoar have been observed over the past two weeks. These avalanches primarily occurred on north, northeast, and east aspects between 1400-2100 m and in the southern part of the region. Characteristics of these avalanches included remote-triggers, wide propagation, and a false sense of stability from unreactive ski cuts or from multiple people moving through the terrain before avalanches released. This MIN from a large, snowmobile-triggered avalanche last Friday is a helpful example. Even though avalanche observations on this weak layer decreased in the past week this layer might still be reactive to human triggers. 

The recent storm delivered 20-60 cm with strong southerly winds which shifted to northwest on Wednesday. The snow surface varies from soft snow to wind pressed in the alpine and at wind exposed treeline elevations. The recent snow sits 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 weak layer of surface hoar may be found 50-100 cm deep. Reports indicate that this layer may be absent in the northern tip of the region (see this MIN from Sugarbowl). However, observers have identified the layer in snow profiles from Barkerville to Valemount (see this MIN from Mt Greenbury, this MIN from the Trophy Mountains, and this MIN from Allan Creek). Sheltered north, northeast, and east facing slopes near treeline are the most suspect.

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.

• Recent wind has varied in direction so watch for wind slabs on all aspects.
• Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
• 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.