Sawtooth Avalanche Center

Pro Field Report

Basic Information

Observation Details

Observation Date:
December 26, 2020
Submitted:
December 26, 2020
Observer:
Chris Lundy
Zone or Region:
Galena Summit and Eastern Mtns
Location:
4th of July Lake (9000-9700', N-W)

Signs of Unstable Snow

Recent Avalanches? 
None Observed
Cracking? 
Isolated
Collapsing? 
Isolated
A handful of medium-sized collapses, primarily in upper elevation terrain with some wind effect.

Snow Stability

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

Bottom Line

New snowfall is continuing to slowly load our buried facet layer. Instability is not yet widespread, but I'm fairly certain you could have triggered a slide on many steep slopes with the right characteristics: wind-stiffened slab over the facet layer.

Media/Attachments

Remotely triggered cracking along a stream bank.

Advanced Information

Weather Summary

Cloud Cover:
Obscured
Wind:
Light

The storm looked like it was breaking up late morning, only to come back harder around noon. From noon to when I left the field around 2pm, it was snowing S1-2. New snow in this area seemed to be around 15cm.

Avalanche Observations

Visibility wasn't great and light was flat, but I did see a fair bit of avalanche terrain and I did not see any slides.

Snowpack Observations

The storm from earlier this week (12/20) appears to have been much colder in the White Clouds. There was no sign of a rain crust, even at mid-elevations, and the recent storm snow was much softer. Quite a dramatic difference from other place's I've seen. Shot in the dark, but storm totals from 12/20 storm were likely similar to Galena Summit.

The result of this difference is that the slab atop the 12/11 layer is still very soft (F to F+) and with today's storm, averages about 40cm thick. On sheltered slopes, the slab was soft enough that skis penetrated through the slab making trail-breaking tough. On a sled, I was leaving a 60cm trench.

I did remotely "trigger" some cracking/sliding along a short/steep creek bank. I looked for SH but did not find any, it was breaking on the 12/11 FC.

@9500', N, 20*: sheltered location in tree opening. HS 100-105cm. 40-45cm slab, F+ at base, over F 12/11 FC. ECTX x2 - slab just seemed too soft. Basal facets present in this area, but showing some sign of strengthening and were 1F to 4F.

@9700', N: exposed slope near treeline. Slab 40cm and slightly stiffer (4F at base) - which made all the difference. ECTP13 & 15, see photo below.

A very faint crust could be felt beneath the new snow from yesterday evening's freezing rain.

9700', N. ECTP13&15 down 40cm on 12/11 FC.

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: 40cm
Weak Layer(s): Dec 11, 2020 (FCsf)
Comments: Sensitivity is reactive where a slightly stiffer slab exists.

I did not get into exposed terrain to assess wind loading.

Terrain Use

I avoided avalanche terrain, including runout zones.