New snow and wind are expected to build increasingly reactive wind slabs. Weak layers near the bottom of the snowpack remain possible to trigger.
Up to 20 cm of new snow is forecast to accumulate by late Friday in favored areas. Moderate to strong southwest winds may redistribute the new snow into reactive slabs on lee features.
Very large avalanches over the past few days suggest that a buried crust formed in early November and weak snow at the ground are reactive persistent and deep persistent weak layers. We have limited information about the distribution of this snowpack structure in the region. Keep in mind that easy-to-trigger avalanches in the new storm snow have the potential to step-down to these deeper layers, producing large, destructive avalanches.
Thursday night: Mostly cloudy, up to 5 cm of snow, moderate southwest wind, freezing level around 700 m.
Friday: Overcast, 5-15 cm of snow, moderate southwest wind with strong gusts, freezing level rising to 1200 m
Saturday: Overcast, 10-20 cm of snow above 1500 m, moderate southwest wind with strong gusts.
Sunday: Mostly cloudy, 5-10 cm of snow above 1500 m, moderate southwest winds.
A series of notable avalanches have been reported in the northern half of the region. These were both explosive-triggered and natural releases that resulted in very large deep persistent slab avalanches (size 3-3.5), failing on weak snow near the ground. The extent of this snowpack structure in the region is not well-known.
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Up to 20 cm of new snow is forecast to accumulate by late Friday in favored areas. Moderate to strong southwest winds may redistribute the new snow into reactive slabs on lee features. The new snow is accumulating above a melt freeze crust and hard, wind-affected snow and may not bond well.
Reports suggest the bottom half of the snowpack consists of weak snow interrupted by a crust from early November. Further north in the region, we're learning that weak snow developing near the ground has produced very large deep persistent slab avalanches. Although we lack data on the distribution of this problem, the bottom line is that easy-to-trigger wind slabs have the potential to step-down to deeper layers and trigger destructive avalanches.
Snowpack depths are variable across the region, ranging from 60 cm in eastern parts of the region up to over 100 cm in western parts of the region. Lower elevation terrain may still be below the threshold for avalanches.
