Dense storm snow and buried Surface Hoar

Date of Observation: 12/28/2022
Name: Eric Murrow Zach Kinler

Zone: Northwest Mountains
Route Description: Kebler Pass to Anthracites standard skin track.

Observed avalanche activity: Yes
Avalanches: No natural avalanches. Observed two small human-triggered avalanches by other parties on east and northeast aspects. We remotely triggered 3 separate avalanches, D1 and D1.5, on northeast, southeast, and south aspects. All of the avalanches we triggered failed on Surface Hoar immediately beneath the storm snow.
Weather: Mostly cloudy skies with light snowfall throughout the day. The height of storm snow at 2pm was about 13 inches with 1.3″ of water. Winds remained light at the ridgetop with no drifting observed.
Snowpack: In each place we looked, northeast through east through southeast through south near and below treeline, we found 6 – 9 mm surface hoar beneath the storm snow. The collapses that triggered the avalanches mentioned were quiet and hard to hear or notice. One of the avalanches on a southeast aspect was triggered from 150 feet away. Whether the weak layer was buried surface hoar, the 12/20 facets, or within the storm snow, it seemed likely to trigger a small avalanche in the surface snow (some long slopes could have approached D2 size). On southerly slopes, a melt-freeze crust formed in the past few days that have the potential to collapse and produce avalanches with more snowfall this weekend. Below the crusts, the snowpack was only lightly faceted but remains soft and collapsable. The biggest takeaway was buried surface hoar, in open areas, beneath the recent storm snow on most aspects near and below treeline in this area.