Sawtooth Avalanche Center

Pro Field Report

Basic Information

Observation Details

Observation Date:
April 2, 2020
Submitted:
April 2, 2020
Observer:
SAC - Lundy
Zone or Region:
Galena Summit and Eastern Mtns
Location:
Avalanche Peak

Signs of Unstable Snow

Recent Avalanches? 
Yes
Cracking? 
None Experienced
Collapsing? 
None Experienced
A few unreported slides observed in the White Clouds behind Horton Peak.

Snow Stability

Stability Rating: 
Fair
Confidence in Rating: 
Moderate
Stability Trend: 
Steady

Bottom Line

Investigated the remotely-triggered slide on the east face of Avalanche Peak. The slide released on a slope that faced from E to NE and broke 16 inches deep on a persistent weak layer of faceted snow that formed in mid-March. There is another persistent weak layer down nearly 3 feet that also looks concerning. Triggering a large persistent slab avalanche remains on the table on aspects facing E through N through NW.

Advanced Information

Weather Summary

Cloud Cover:
Mostly Cloudy
Wind:
Light , NW

Enough cloud cover and cold temps to prevent snow surface from getting too wet, but solars still have a surface crust. Settled storm snow from 3/29 storm was around 30cm.

Avalanche Observations

 #  Date Location Size Type Bed Sfc Depth Trigger Comments Photo
Several Behind Horton Peak
W 9600
D2 SS Included these as nothing on the White Cloud side of the valley has been reported. Unsure of depth, trigger, etc. Didn't see any activity in the ~W facing paths on Horton proper.
1 Avalanche Peak East Face
E 9300
D2 SS O-Old Snow 40-50cm AS-Skier
r-Remote
This has been reported but adding measured depth and that it ran in an older persistent weak layer. None

Other observed slides had been reported or were very similar and fit the pattern of those that were.

Snowpack Observations

The avalanche was interesting in that the weak layer had a different configuration as you wrapped from the lookers right (E facing) to lookers left (NE facing). On the E facing side, it failed at the bottom of 5-7cm facet layer sandwiched between two crusts. On the NE facing side, there were no crusts and it was a 5cm layer of F facets below a 4F slab. I believe these weak layers both have the same date, although I'm having a tough time dating them—maybe 3/14 or 3/17?

I did a crown profile on the lookers L flank on a NE aspect. I had ECTP23 and 25 down 45cm on the layer described above.

On the NE aspect, there is a more prominent/thicker layer of larger grained F facets (3/7?) down 85cm that was likely responsible for the slides in Owl Creek and the Headwaters prior to the 3/29 storm. Scott also saw this in his ob from 3/31. I did not have time to perform tests on this layer, but it looked bad enough I didn't need to.

Both of these layers looked concerning and seem ripe for human-triggering.

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: early to mid March, 40-85cm
Comments: Sensitivity is based on limited obs from today, likely reactive in spots