Fresh wind slabs in exposed areas will be the primary concern for Saturday, so seek out sheltered low density snow. Recent snowfalls varied widely across the region, so make local observations of new snow depth to determine the scale of the wind slab problem in your area.
Wind slabs that formed in response to light snowfall and southwest wind over the last week may remain sensitive to human triggering on Saturday, especially near ridgecrest.
Triggering large, deep persistent slab avalanches is a low likelihood but high consequence problem that is most likely to trigger in shallow, rocky start zones.
Friday night: Cloudy with scattered flurries bringing up to 5 cm of new snow. Light west winds.
Saturday: Mainly cloudy with isolated flurries and a trace of new snow. Light southwest winds, becoming moderate at ridgetop. Alpine high temperatures around -5 with freezing levels to 1400 metres.
Sunday: Cloudy with light flurries beginning in the afternoon. Light to moderate southeast winds. Alpine high temperatures around -5.
Monday: Cloudy with isolated flurries and a trace of new snow. Light southwest winds. Alpine high temperatures around-5.
Reports from Thursday showed ski cuts producing small (size 1) 20-25 cm-deep storm slab releases in the south of the region. Further north in the Golden area where less new snow exists, ski cuts produced numerous smaller 2-5 cm-deep wind slab releases.
On Wednesday, a few deep persistent slab avalanches were reported in the Purcells west of Invermere. These were triggered by skier traffic, ski cutting, and remotely from a group traveling nearby. They ranged from size 1-2, with the smaller example being a wind slab that reloaded the basal snowpack where it had already avalanched. The larger two had 100 cm-deep crown fractures.
Over the past week there have been a few other reports of natural and explosives triggered avalanches reaching size 3. A few of these were also deep persistent slab avalanches that failed near the base of the snowpack.
Light snowfalls over the past week brought around 15-20 cm of snow to the region. Bouts of strong southwest wind over the same period formed new wind slabs on leeward slopes at higher elevations while warm temperatures caused surface snow to melt below about at least 1500 metres and in some areas created moist snow up to 2000 metres.
A layer of surface hoar that formed in late December appears to be gaining strength. It can be found 70 cm deep around Golden, 30 cm deep around Invermere, 70 cm deep around Kimberley, and 100 cm deep along Kootenay Lake.
As usual for the Purcells, the base of the snowpack contains basal facets and it remains possible to trigger these deep weak layers in shallow rocky start zones or from a heavy trigger such as a cornice fall or explosives.
