Avalanche Forecast

Tuesday night: Mostly cloudy, 10 cm of snow, extreme strong westerly wind, alpine high temperature -6 C, freezing level 500 m.  

Wednesday: Mostly cloudy, scattered flurries with up to 5 cm of snow, moderate west winds, alpine high temperature -7 C, freezing level 500 m.

Thursday: Mix of cloud and sun, scattered flurries with up to 5 cm of snow, light west winds, alpine high temperature -10 C, freezing level at valley bottom.

Friday: Mix of sun and cloud, light easterly wind, alpine high temperature -12 C, freezing level at valley bottom.

Many large to very large avalanches (size 2-3) releasing on the February 22 surface hoar have been observed over the past week. 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 on Friday is a helpful example. 

New snow and wind on Tuesday may build reactive storm slabs and add 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. 

A storm moved into the region on Tuesday and is expected to bring 20-40 cm of snow with strong to extreme southwest winds by Wednesday morning. The new snow is not expected to bond well with previous surfaces and may become increasingly touchy as snow accumulates. The new snow will develop a slab on lee features at upper elevations, where westerly winds transport the snow into deeper, more cohesive drifts.

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.

• Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
• Dial back your terrain choices if you are seeing more than 20 cm of new snow.
• 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.