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Wallowa Avalanche Center

Professional Observation

Basic Information

Observation Details

Observation Date:
January 1, 2021 - January 1, 2021
Submitted:
January 2, 2021
Observer:
WAC - Michael Hatch
Zone or Region:
Elkhorns
Location:
East Shoulder of Lee's Peak - 8400'

Signs of Unstable Snow

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

Snow Stability

Stability Rating: 
Fair
Confidence in Rating: 
High
Stability Trend: 
Worsening

Bottom Line

The existing snowpack in the Northern Elkhorns exhibits weak strength and poor structure. The bottom 2' of the snowpack is composed of rounding facets (sugar snow) and a facet/crust combo about 18" from the surface demonstrated propagation propensity. The addition of 1-2' of new snow in the next 24-48 hours will stress the existing weak snowpack and likely lead to widespread storm slab instability.

Advanced Information

Weather Summary

Cloud Cover:
Overcast
Temperature:
26
Wind:
Light , SW

The weather was fairly mild through the early afternoon with temps in the mid-20's and light SW winds. Overnight the area had received about 15cm (6") of new snow. In the late afternoon the SW wind began to increase to moderate intensity (15-25mph) as the storm front rolled into the area.

Snowpack Observations

As mentioned above the overall snowpack structure is weak with numerous persistent weak layers existing throughout the snowpack. The most reactive layer in our snowpack tests was at a facet/crust combo about 50cm down or 18" from the surface. This crust is what we are calling the Solstice Rain Crust (SRC). It was formed during the warm front passage on 12/21 that brought rain up to at least 8500' in the Elkhorns. This is where we found a propensity for propagation in our tests - ECTP26 - where it failed below the SRC on 2mm facets.

Below the stout Solstice crust is a melt-freeze jarble consisting of about three facet/crust combos likely the result of a fluctuating rain line during the warm front passage. Below the jarble is about 2' of basal facets that are slowly rounding and gaining strength.

ECT Results from Lee's Peak in N. Elkhorns

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: 50cm/1-1-21
None Specified

Terrain Use

Although the new snow totals (6") were not at threshold levels to cause widespread storm slab instability the persistent weak layers (especially the facet/crust combo down 18") demonstrated continued ability to propagate a fracture once initiated. We kept our slope angles below 35 degrees due to the uncertainty of reactivity of this PWL to the weight of a skier or rider. This layer will become increasingly reactive with the addition of 1-2' of new snow in the forecast.

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