Be on the lookout for areas where recent snow has formed a slab from either wind or settlement. A wind slab release or cornice fall in a shallow rocky start zone could be the trigger for a large deep persistent slab avalanche.
Winds have drifted recent snow into slabs on leeward features that may be possible to trigger. Winds have changed in strength and direction from extreme out of the southwest to moderate out of the northwest, creating a tricky loading pattern. Be mindful of areas where wind slab and cornice distribution overlap.
A layer of weak, sugary facets persists at the bottom of the snowpack. Areas where the snowpack transitions from thick to thin may still harbor this deep persistent slab problem, like shallow, rocky alpine start zones. Easier-to-trigger wind slab avalanches or cornice falls could step down to this deeper layer, resulting in very large avalanches.
Thursday night: Becoming cloudy. Light northwest winds.
Friday: Mainly cloudy with light flurries bringing a trace of new snow before increasing overnight. Light northwest winds shifting southwest. Alpine high temperatures around -10.
Saturday: Cloudy with continuing light flurries bringing up to 5 cm of new snow, up to 15 cm with the previous night's accumulations. Light northwest winds shifting northeast. Alpine high temperatures around -9.
Sunday: A mix of sun and cloud. Light west winds, becoming moderate or strong at ridgetop. Alpine high temperatures around -9.
Since the weekend storm, there have been several reports of failing cornices and small wind slabs. See this MIN report for a helpful illustration. Explosive triggers have also released several large avalanches breaking on deeply buried weak layers on a variety of aspects above 2200 m. This activity is a good reminder that this layer remains a problem in the region. Easier-to-trigger wind slab avalanches or cornice fall may have the potential to step-down to this layer.
During the weekend storm, numerous size 2-3.5 slab avalanches released naturally. A few were thought to have stepped down to deeper layers. These avalanches primarily occurred on leeward aspects at treeline and alpine elevations. Below tree line, wet loose avalanches ran naturally during the warm temperatures on Saturday.
20-40 cm of snow from the early part of the week now overlies older wind-affected snow at high elevations, or over a widespread melt-freeze or rain crust with a variable upper extent of 1800-2000 metres in elevation. The recent snow has mainly shown reactivity where winds have had a chance to redistribute it into new slabs. A few reports from adjacent regions have shown poor bonding with the buried crust where it exists.
A weak layer of surface hoar may still be found about 90 cm deep around Golden and Kimberley, 50 cm deep around Invermere, and 130 cm deep along Kootenay Lake. Recent reports from the Golden area suggest a positive stabilizing trend. At lower elevations this layer has likely been bridged over by the above-mentioned crust.
As usual for the Purcells, the base of the snowpack contains basal facets. It remains possible to trigger these deep weak layers in shallow rocky start zones or from a heavy trigger such as a cornice fall. Given this layer is most prominent in the alpine, it is unlikely to be effectively bridged over by our most recent crust.
