Watch for fresh wind slabs in leeward terrain features on Saturday. Be prepared to take an extra step back if you find overnight snowfall has exceeded forecast amounts.
Light snowfall overnight will combine with elevated and shifting winds to build new wind slabs that will need to be managed on Saturday. Be mindful of areas where wind slab and cornice distribution overlap.
A layer of weak, sugary facets persists at the bottom of the snowpack at higher elevations. Steep, rocky alpine features where the snowpack transitions from thick to thin are the likely trigger points for this deep persistent slab problem. Easier-to-trigger wind slab avalanches or cornice falls could step down to this layer, resulting in very large and destructive avalanches.
Friday night: Cloudy with flurries bringing 5-15 cm of new snow. Light southwest winds, becoming strong at ridgetop before shifting northwest. Alpine high temperatures around -10.
Saturday: Cloudy with continuing light flurries bringing up to 5 cm of new snow. Light northwest winds shifting northeast. Alpine high temperatures around -10.
Sunday: Mainly sunny. Light west winds, becoming moderate or strong at ridgetop. Alpine high temperatures around -9.
Monday: Mainly sunny. Light west winds. Alpine high temperatures around -8.
Explosives control in the central part of the region on Thursday successfully targeted several cornices and wind slabs with a mix of small and large results (size 1-2.5). A couple of remotely triggered cornice falls were observed during the work, as well as one recent natural cornice fall that triggered a slab on the reloaded bed surface of a previous deep persistent slab avalanche.
Since the weekend storm, there were several reports of failing cornices and small wind slabs. See this MIN report for a helpful illustration. Explosive control 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.
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.
