There is uncertainty about the trajectory of our persistent slab problem, but the recent evidence is compelling. Make sure your route selection accounts for the possibility of very large avalanches on suspect features. Wind slab or cornice releases could be sufficient triggers.
A shift to northwest winds and an ample supply of loose surface snow is likely to expand wind slab distribution across all aspects. Wind slab releases around steep, rocky features at ridgecrest may carry the risk of triggering a deeper weak layer.
A concerning number of large, deep and destructive avalanches have been human triggered and have ran naturally on deeply buried weak layers in the last two weeks. Large alpine features that have not yet slid need to be treated as suspect, especially if they have seen significant recent wind loading. Wind slab or cornice releases are likely triggers for this problem. Human triggering is most likely in shallow, rocky areas where the snowpack transitions from thick to thin.
Thursday night: Cloudy with continuing scattered flurries bringing a variable trace to 10 cm of new snow. Light to moderate northwest winds.
Friday: Cloudy with scattered flurries and up to 5 cm of new snow. Moderate northwest winds. Alpine high temperatures around -11
Saturday: Cloudy with continuing light flurries bringing up to 5 cm of new snow, easing overnight. Moderate southwest winds, easing overnight. Alpine high temperatures around -9.
Sunday: Mainly cloudy with isolated flurries and a trace of new snow. Light southwest winds shifting west and increasing. Alpine high temperatures around -11.
Another recent large (size 2.5) persistent slab avalanche, triggered by a large snow machine, was observed in the Kispiox area on Tuesday, this time failing on a southeast-facing slope at about 1600 metres. No new avalanches were reported on Wednesday.
Since February 3rd there have been many very large and destructive avalanches failing on deeply buried surface hoar and crust/facet layers near the bottom of the snowpack. The bulk of the activity has been above treeline on north through east facing aspects, but all alpine slopes that have not yet avalanched need to be treated as suspect. A few examples of the most recent activity are reported here:
Feb 9: Very large avalanche on the Kathlyn Face near Smithers. Details/Photos here and here.
Feb 9: Large avalanche in the French Peak Complex. Details/Photos here.
Feb 9: Very large avalanche near the Pine Creek Trail. Details/Photos here.
Feb 8: Large snowmobile triggered avalanche in the Babines. Details/Photos here.
Feb 8: Very large avalanche on Mt. Elmstead above Silver King Basin Trail in the Babines. Details/Photos here.
Open terrain continues to be heavily affected by west and northwest wind, which has been actively loading lee terrain features and seems to have pushed our region's persistent weak layers to their breaking point. In sheltered areas, about 10-15 cm of new snow now overlies crusts that can be found up to roughly 1200 m as well as on open south-facing slopes.
A weak layer of faceted snow that formed during cold weather in mid January is one likely failure plane responsible for the recent rash of very large avalanches in the region. Depending on location this layer may be composed of soft facets, surface hoar, or both. It is buried approximately 60-120 cm below the surface. As a product of previous widespread cold temperatures, the faceted snow associated with this layer exists all over the region, however it may be bridged over by a firm crust at lower elevations.
An older Crust/facet layer from November, lurking at the base of the snowpack, is the more widely observed culprit in recent persistent slab activity, having produced many very large avalanches since February 3rd. As a product of old, weak snow from the early season, this layer is most likely to be found at high elevations.
The most recent activity with these deeper snowpack layers has been around Smithers, Hazelton, Kispiox and the Babines, but it should be assumed that they are widespread problems.
