Avalanche Forecast

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Sunday night: Mostly clear, light west winds, alpine temperature -14 C.

Monday: Mostly clear, light southwest winds, alpine high temperature -4 C, freezing level 1100 m.

Tuesday: Increasing cloud, 5-10 cm of snow, moderate southwest winds with strong gusts, alpine high temperature -5 C, freezing level 1100 m.

Wednesday: Mostly cloudy, 5-15 cm of snow overnight, moderate west winds, alpine high temperature -2 C, freezing level 1200 m. 

On Saturday, several skier-triggered storm slab avalanches were reported. These avalanches were small (size 1-1.5) and breaking 15-30 cm deep. Shallow storm slabs have the potential to step down to the buried surface hoar layer, creating very 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.

Human-triggered and remotely-triggered avalanches releasing on the February 22 surface hoar have been reported by nearly every operation region-wide over the past week. In many instances, slopes were ski cut with no results, only to have the third or fourth skier in the group trigger the slab. Observations extend 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+.

Snowfall amounts varied across the region on Saturday, with the highest totals falling in the southern part of the region. In areas that accumulated more than 20 cm, storm slabs may remain possible to human trigger. In areas where less snow accumulated, slab formation will likely be specific to where the wind has transported the snow into deeper drifts. Intense solar radiation may rapidly destabilize recent snow on steep, sun-exposed slopes and weaken cornices.

A widespread weak layer of surface hoar is buried 50-90 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. 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.

• Be aware of the potential for large avalanches due to the presence of buried surface hoar.
• Use conservative route selection and resist venturing out into complex terrain.
• Minimize exposure to sun-exposed slopes when the solar radiation is strong.
• If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.