Avalanche Forecast

Wednesday night: Cloudy with clear periods, scattered flurries with up to 5 cm of snow accumulation, moderate northwest wind, alpine high temperature -12 C, freezing level at valley bottom.

Thursday: Mostly cloudy with isolated flurries, light northwest wind, alpine high temperature -13 C, freezing level at valley bottom.

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

Saturday: Mostly sunny with some clouds, moderate northeast wind, alpine high temperature -20 C, freezing level at valley bottom.

New snow and wind on Tuesday built reactive storm and wind slabs and 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 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. 

The recent storm delivered up to 25 cm in the north of the region and up to 50 cm in the south of the region with strong southerly winds. The snow surface is expected to be wind affected in the alpine and at treeline in wind exposed areas with reactive wind slabs on lee features. The new snow is not expected to bond well with 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.

• 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.
• Minimize your exposure time below cornices.