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Wallowa Avalanche Center

Professional Observation

Basic Information

Observation Details

Observation Date:
December 22, 2020
Submitted:
December 23, 2020
Observer:
WAC - Caleb Merrill
Zone or Region:
Elkhorns
Location:
Angel Basin

Signs of Unstable Snow

Recent Avalanches? 
None Observed
Cracking? 
None Experienced
Collapsing? 
None Experienced

Bottom Line

At this location, the Rain Crust that developed during the winter solstice was supportive to the weight of a person. As we dug deeper in the snowpack, there was clearly a cohesive (strong) slab of snow above a weak crust/sugar snow combination (from 12/9) that was found 20-30" below the snow surface. This layer produced sudden, energetic, and propagating results in our snowpack tests.

Advanced Information

Weather Summary

Cloud Cover:
Obscured
Wind:
Moderate , NE

During our tour, we experienced new snowfall at light to moderate rates. Graupel snow- that dense form of snow that looks like small styrofoam pellets was observed on the snow surface. Temperatures were in the teens, and light to moderate winds were blowing the new snow around on the firm crust surface.

Snowpack Observations

We observed a firm crust surface with areas of wind drifted new snow up to 6" deep. At this time, and at this location, this "Solstice Rain Crust" was a series of 3 pencil hard crusts with softer snow sandwiched between. Perhaps this formed due to dynamic freezing levels during the rain/snow event at this elevation. This crust is able to support the weight of a person at this time. In areas where this crust is thinner, or as it breaks down over time, the weight of a person and/or machine may be able to more easily impact weaker sugar snow deeper in the snowpack. Snowpack test results produced easy, clean, and energetic shears within these facets that were found below a crust from December 9th. Compression Test Results: CTE SC down 50 cm below 12/9 crust. PST results 30/100 (END) down 50cm on 20201209.

Avalanche Problems

Problem Location Distribution Sensitivity Size Comments
Persistent Slab
Isolated
Specific
Widespread
Unreactive
Stubborn
Reactive
Touchy
D1
D1.5
D2
D2.5
D3
D3.5
D4
D4.5
D5
Layer Depth/Date: December 9th Crust/20-30" (50-70cm) from surface

Terrain Use

We stayed in simple terrain void of large avalanche paths and terrain traps.

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