Avalanche Forecast

Sunday night: Mostly clear, light west winds, alpine temperature -18 C.

Monday: Mostly clear, light southwest winds, alpine high temperature -5 C, freezing level 1000 m.

Tuesday: Increasing cloud, 5-15 cm of snow, strong south winds, alpine high temperature -4 C, freezing level 1300 m.

Wednesday: Mostly cloudy, 5-10 cm of snow overnight, alpine high temperature -4 C, freezing level 1000 m.

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. These avalanches propagated widely across terrain features, warranting conservative terrain margins. This MIN from a large, snowmobile-triggered avalanche on Friday is a helpful example. 

In the aftermath of last week's storms, a natural cycle of large to very large (size 2-3) avalanches were observed on wind-loaded aspects (northeast, east, and southeast) above 1800 m. Several were triggered by large cornices failures. If triggered, wind slabs and cornices could step down to the buried surface hoar layer, forming large avalanches. Use added caution on sun-exposed slopes during intense solar radiation, as rapidly warming snow and weakening cornices could trigger loose or slab avalanches.

Incremental snowfall and wind formed wind slabs in the alpine and open areas at treeline that may remain possible to human trigger. Cornices are large and looming after a week of successive storms. Intense solar radiation is rapidly destabilizing recent snow on steep, sun-exposed slopes and weakening cornices.

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 (check out this MIN from Sugarbowl). However, observers have identified the layer in snow profiles ranging 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. Snowfall, wind, temperatures, and solar radiation have increased the depth and slab properties of the snow above the weak layer, making it more difficult to trigger and masking obvious clues that the problem is present (i.e. cracking, whumpfing). However, if triggered, avalanches will likely be larger in size and getting caught could have more 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.

• Stay off recently wind loaded slopes until they have had a chance to stabilize.
• Surface hoar distribution is highly variable. Avoid generalizing your observations.
• Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
• Minimize exposure to steep, sun exposed slopes, especially when the solar radiation is strong.