The snowpack isn't a fan of rapid change. Freezing levels jumping 2000 m in a couple of hours on Wednesday is about as rapid as it gets. Hazard from wet loose slides might be the obvious problem, but an increasing likelihood of triggering a persistent slab is the most worrying.
Rider triggerable wind slabs will likely exist on east and north aspects at and above treeline. Recent strong winds may have focused slab formation at lower elevations than is typical. Warming will increase the likelihood of triggering slabs in the short term.
20 to 70 cm of snow sits over a facet-crust weak layer combination that is possible to human trigger. This problem is particularly concerning in the Duffey Lake area. Recent observations demonstrate the potential for this problem to be triggered remotely and propagate far and wide. It can be found on all aspects at treeline and is most reactive at this elevation band, but it can be found above and below.
Rapid warming on Wednesday will cause surface layers to lose cohesion and shed from steep slopes. This may occur naturally but is even more likely with a human trigger. Larger releases have potential to trigger destructive persistent slab avalanches, especially around treeline.
Tuesday night: Cloudy with isolated flurries. Moderate to strong west or southwest winds. Freezing levels remaining near 1300 metres.
Wednesday: A mix of sun and cloud. Light to moderate west winds. Treeline high temperatures around +2 with freezing levels rising to 3300 metres.
Thursday: Sunny. Moderate to strong west winds. Treeline high temperatures around +1 with freezing levels remaining near 3000 metres, falling overnight.
Friday: Sunny. Light north winds. Treeline high temperatures around +1 with freezing levels rising from surface to 2500 metres.
On Saturday a fatal avalanche occurred in the Duffey Lake area. This avalanche was a very large (size 3), skier triggered avalanche with significant propagation. It was triggered at upper treeline on a northeast aspect and it failed on a shallower layer of surface hoar before stepping down to the crust from late January discussed in our snowpack summary. A more detailed report can be found here. This layer was also responsible for several large skier triggered avalanches in the neighbouring Sea to Sky region.
We anticipate a significant increase in the likelihood of avalanches on this layer during the warming pattern from Wednesday onward.
Another bout of strong southwest wind over Sunday night may have formed new wind slab on leeward aspects at treeline and above. Slab formation was likely hampered to a degree by already extensive recent wind redistribution as well as the recent formation of surface crusts at lower elevations and on solar aspects.
The primary concern in the snowpack at present is the 20 to 70 cm of snow from the past week that is sitting above a variety of surfaces including facets and crust, but also surface hoar in more sheltered areas at mid-elevations. This layer is most prominent at treeline and above. It has been found on all aspects in the Duffey Lake area. This layer is up to about 90 cm deep in the south of the region and has been giving similar, moderate to hard, sudden results in recent snowpack tests.
