Avalanche control is scheduled for Mt Stephen Sunday. Access to this area will be closed for the day.
Our primary avalanche concern is that superficial slabs could step down to the deep, persistent weakness resulting in full-depth avalanches.
The thinner and rockier the terrain, the higher probability of triggering an avalanche.
Moderate to strong W and SW winds over the past week promoted cornice development and built wind slabs and in lee features in the alpine and down into treeline. These slabs are a concern where they sit over weak facets that could "step down" to the basal layers.
Weak facets and depth hoar associated with crusts near the base of the snowpack have resulted in avalanches 60-100 cm deep. Any area with a stiffer slab over the facetted lower snowpack can generate a larger avalanche that steps down to the ground.
There have been several reports of cornices failing over the last few days at Sunshine, Hwy 93N and Sherbrooke Lake.
Friday, ski hills reported some explosive-triggered avalanches to size 2, and a few involved wind slabs that stepped down to deeper layers.
Observations from Thursday reported natural and skier-triggered avalanches near Lake O'Hara and Bow Summit.
15-30 cm of storm snow from the past week, combined with strong W/SW winds, has aging wind slabs in alpine lee areas which extend down into treeline.
The mid and lower snowpack is faceted and weak, with facet/crust interfaces near the ground. This is more pronounced east of the divide, while western regions display a deeper more settled snowpack.
Snowpack depths at tree-line are about 60 cm in eastern areas and 100 cm west of the divide.
Saturday night: Cloudy with clear periods and isolated flurries. Alpine temperature: Low -12 °C. Ridge wind southwest: 15 km/h.
Sunday: Cloudy with sunny periods and isolated flurries. Alpine temperature: High -12 °C. Light ridge wind.
Monday: Cloudy with sunny periods and isolated flurries. Alpine temperature: Low -16 °C, High -13 °C. Ridge wind west: 10 km/h.
