The Purcells would be headed into a low danger scenario if it weren't for our terrible basal snowpack structure. Regular reports of deep persistent slabs should keep this problem top of mind. A cornice or wind slab release could be a sufficient trigger.
Wind slabs that formed in response to light snowfall and southwest wind over the past week may remain sensitive to human triggering near ridgecrest. Deeper, more reactive slabs may be found in western parts of the region where greater recent snow amounts exist.
Triggering large, deep persistent slab avalanches is a relatively low likelihood but high consequence problem that is most likely to trigger in shallow, rocky start zones. A small wind slab release could be a sufficient trigger.
Sunday night: Cloudy with isolated flurries and a trace of new snow. Light to moderate southwest winds.
Monday: Cloudy with scattered flurries and a variable trace to 10 cm of new snow. Light southwest winds. Alpine high temperatures around-5 with freezing levels to 1400 metres.
Tuesday: Mainly cloudy with isolated flurries. Light southwest winds shifting west. Alpine high temperatures around -5.
Wednesday: Increasingly cloudy with light flurries beginning in the afternoon and continuing overnight. Light to moderate southwest winds, increasing overnight. Alpine high temperatures around -6.
Reports from Thursday through Saturday showed ski cuts producing small (size 1) 20-25 cm-deep storm slab and wind slab releases in deeper snow areas of the region (Bugaboos, west slope). Further north in the Golden area where less new snow exists, ski cuts were producing numerous smaller 5 cm-deep wind slab releases a few days ago.
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. Another size 1.5 deep persistent slab was controlled with explosives in the same area on Friday.
Light snowfalls over the past week brought around 15-30 cm of snow to the region, with a focus toward the south and west of 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.
