Wind-drifted snow and a buried weak layer warrant careful terrain choices. Keep in mind that cold temperatures can increase the consequences of an incident. Enjoy the winter wonderland in low consequence, wind-sheltered areas.
Moderate to strong winds have varied in direction and have redistributed the recent snow into slabs on leeward terrain features. These wind slabs may remain possible to human trigger, particularly near ridge-crests and roll-overs. Cornices may be reaching their breaking point and have the potential to act as triggers on slopes below.
A layer of weak facets (sugary snow) can be found down 70-150 cm near a crust that formed in early December. Storm slabs in motion may step down to this layer and trigger large destructive avalanches. It is more likely to human trigger this persistent slab in thin areas at tree line elevations.
Cold, Arctic air and north winds take the reins
Saturday night: Decreasing cloudiness, isolated flurries with trace accumulations, winds becoming north and decreasing to light, treeline low temperatures near -23 C.
Sunday: Mix of sun and cloud, a trace of snow possible, light north winds, treeline high temperatures near -23 C.
Monday: Sunny in the morning, cloudy by the afternoon, no new snow expected, winds becoming northwest and increasing to moderate, treeline high temperatures near -21 C.
Tuesday: Mix of sun and cloud, a trace of snow possible, moderate north winds gusting strong at higher elevations, treeline high temperatures near -18 C.
It remains possible to trigger to wind slab avalanches on Sunday, especially near ridge crests and roll-overs. Cornice falls and wind slab avalanches have the potential to step-down to deeper layers, triggering large, destructive avalanches.
On Thursday, operators reported a large (size 2.5) explosive-triggered avalanche releasing in the storm snow. Additionally, several large (up to size 2) cornices have been both human-triggered and explosive-triggered in the neighbouring Sea-to-Sky region.
On Friday, a large (size 2.5) persistent slab avalanche was skier-triggered in the backcountry near Blackcomb in the Sea-to-Sky region. It released 110 cm deep on the early December crust layer on a northwest facing slope around 2100 m in a shallow rocky start zone. Last week's forecaster blog is still relevant.
Over the past week, the mountains picked up 45-90 cm of new snow, with the final 10-20 cm coming in very cold and light. Strong south winds have had an ample supply snow to drift into reactive slabs on leeward slopes, and cornices may be reaching their breaking point. Winds are forecast to shift to the north and decrease to light, which may have the potential to create an unusual cross-loading or reverse-loading pattern in wind-exposed areas. Watch for local variation in wind directions. For example, this MIN report from the Cayoosh area on Thursday describes wind slabs on northwest aspects. In this MIN report from the Cayoosh area on Friday describes a wind slab on a convexity on a southeast aspect.
Start simple and gather information as you go. Monitor for changing slab conditions as you move into wind-exposed terrain and assess the bond of the new and old snow interface. Seek out softer conditions in wind-sheltered areas.
A concerning layer of facets (sugary snow) can be found over a widespread crust that formed in early December (down 70-150 cm). This layer has been particularly reactive at treeline and low alpine elevations, between 1500-2100 m. Large size 2 and 3 avalanches have been reported recently in the neighbouring Sea-to-Sky region. This problem is particularly hard to predict and tricky to manage. Get more details and photos in our forecaster blog.
