Wind slabs have been reactive this week and they may remain sensitive to human triggering Friday. Be mindful of the potential for wind slab avalanches to step down to deeper weak layers.
Wind slabs have been reactive on a variety of aspects due to variable wind direction. In sheltered terrain, the recent snow may also still be reactive to human triggers until it bonds to the snowpack.
Weak layers of surface hoar and/or faceted grains may be found above a hard melt-freeze crust. Recent reports suggest the weak layers may be less prevalent in the south of the region, but still exist in localized pockets.
Thursday night: Clear skies, moderate southwest wind, above-freezing layer dissipating, freezing level valley bottom.
Friday: Increasing cloud, up to 5 cm new snow, light southwest wind, alpine temperature -5 C, freezing level 600 m.
Saturday: Up to 5 cm overnight, cloudy with flurries, moderate to strong southwest wind, alpine temperature -2 C freezing level 1500 m.
Sunday: Clearing, moderate southwest wind, alpine temperature -2 C, freezing level 1500 m.
Numerous skier triggered wind slab avalanches size 1-2 have been reported throughout the region over the last few days. Typically they are being triggered on wind loaded convex terrain features at alpine and treeline elevations.
A few persistent slab avalanches were triggered in the past few days, mostly in the north of the region near the Hurley, but also near Allison Pass. They were triggered by riders, heavy machinery, and naturally. The slabs were generally 60 to 90 cm deep, around 2000 m, and released on the weak layers described in the snowpack summary.
Early this week, around 60 cm of snow fell near Coquihalla and Manning Park and 15 cm near Duffey Lake. Since then, at upper elevations, strong wind from variable directions has formed wind slabs in exposed terrain, and warm air and sunshine may have formed a melt-freeze crust on solar aspects.
A hard melt-freeze crust from early December is found around 40 to 120 cm deep in the snowpack. This crust may have weak layers above it, consisting of feathery surface hoar or sugary faceted grains. These weak layers are most prevalent in the north (e.g., Duffey Lake, Hurley) and found to a lesser extent in the south of the region. The snowpack should be treated as suspect anywhere you find either surface hoar or faceted grains above the crust.
The remainder of the snowpack is well-settled in the south of the region. In the north, another melt-freeze crust with associated faceted grains around it may be found near the ground. Without evidence of recent avalanche activity, the layer appears to be dormant at this time.
