Collapses on the flats and another preserved surface hoar layer

CBAC CBAC Observations

Date of Observation: 12/17/2021
Name: Zach Guy

Zone: Northwest Mountains
Route Description: Traveled on NE to SE aspects near and below treeline, lower Slate.

Observed avalanche activity: Yes
Avalanches: Nothing recent. Documented more activity from last cycle.
Weather: Very light snowfall at times. Mostly cloudy skies, light winds, no transport observed.
Snowpack: We found about 6″ to 10″ of recent snow over a preserved surface hoar layer that somehow survived the wind event and was buried on 12/15. I found this layer consistently in hand pits up to about 10,000 ft in sparsely gladed, wind sheltered terrain on northerly aspects. I didn’t see it near ridgeline start zones. Not enough snow on this surface hoar layer for slab concerns at the moment..
We experienced a handful of collapses on basal facets near valley bottom on low angle terrain, some were localized, some radiated up to 100 ft. Many occurred after the second or third skier in the skin track had crossed. Stability tests near and below treeline on shady aspects produced hard, propagating results on the 12/6 facets. Almost all of the steep terrain that we passed by today had slid naturally during the previous cycle. Those slopes did not show signs of instability.
There were small, localized drifts from the 12/15 wind event behind tree fences and near ridges. Ski cuts and cornice drops didn’t produce any signs of instability with these wind slabs.

Photos:

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