Reverse wind-loading and a buried weak layer warrant careful terrain choices. Keep in mind that cold temperatures can increase the consequences of an incident. Seek out softer conditions wind-sheltered areas.
Recent winds have shifted from south to north with an ample supply of light, cold snow to drift into reactive slabs. Watch for unusual cross-loading or reverse-loading patterns in wind-exposed areas, and anticipate reactive wind slabs on a variety of aspects. 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. Cornice falls or wind 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
Sunday night: Decreasing cloudiness, a trace of new snow possible, moderate northeast winds, treeline low temperatures near -30 C.
Monday: Mix of sun and cloud, no new snow expected, moderate west winds becoming northwest and increasing to strong, treeline high temperatures near -20 C.
Tuesday: Mainly cloudy, a trace of snow possible, moderate northwest winds with strong gusts in the alpine, treeline high temperatures near -14 C.
Wednesday: Increasing cloudiness, no new snow expected, moderate northwest winds increasing to strong in the alpine, treeline high temperatures near -16 C.
Wind slab avalanches will likely be sensitive to triggering on Monday, especially near ridge crests and roll-overs. On Sunday, operators reported small to large (size 1-2) wind slabs releasing naturally on southwest through southeast aspects. Since Thursday, backcountry travelers have reported small wind slabs on a variety of aspects near the Cayoosh glacier (check out this MIN and this MIN).
Cornices are large and looming and have the potential to trigger large avalanches on slopes below. Several large (up to size 2) cornices have been both human-triggered and explosive-triggered in the neighbouring Sea-to-Sky region.
It remains possible to human-trigger large persistent slab avalanches, particularly in shallow snowpack areas at treeline and low alpine elevations. 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.
Since Friday, 20-35 cm of low density snow has fallen a variety of surfaces, including well-settled snow, wind-packed or wind-scoured surfaces, and a possible surface hoar or rime crust layer.
Northerly outflow winds have an ample supply of light, cold snow to drift into reactive slabs on leeward slopes. Watch for unusual cross-loading or reverse-loading patterns in wind-exposed areas, and anticipate reactive wind slabs on a variety of aspects. Sensitivity to triggering will be greatest near ridge crests and roll-overs. Monitor for changing slab conditions as you move into wind-exposed terrain, and give cornices a wide berth.
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 2-3) 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.
