Steady light snowfalls have been keeping wind slab problems active in the region, and Friday's forecast calls for more of the same. Be prepared to dial back your terrain selection if more than 20 cm of new snow accumulates in your area by the afternoon.
Fresh wind slabs may begin to form Friday as light new snow combines with southwest winds. Older wind slabs formed over the last week may also remain sensitive to human triggering, 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.
Thursday night: Cloudy with scattered flurries bringing 5-10 cm of new snow. Light to moderate southwest winds. Freezing levels remaining near 1500 metres.
Friday: Cloudy with continuing flurries bringing 5-15 cm of new snow. Light to moderate southwest winds. Alpine high temperatures around -2 with freezing levels to 1600 metres.
Saturday: Cloudy with isolated flurries and a trace of new snow. Light southwest winds. Alpine high temperatures around -4 with freezing levels to 1300 metres.
Sunday: Broken skies, becoming cloudy with isolated flurries and a trace of new snow. Light southeast winds. Alpine high temperatures around -5.
With more moderate winds and fresh snow in the forecast, new wind slabs are expected to form again on Friday and they may become increasingly reactive throughout the day.
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 three days 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. Strong southwest winds on Thursday likely formed new wind slabs on leeward slopes at higher elevations while warm temperatures caused surface snow to melt below about 1500 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.
