Pro Field Report

Basic Information

Observation Details

Observation Date:
February 11, 2020
Submitted:
February 11, 2020
Observer:
SAC - Davis, Stefan
Zone or Region:
Banner Summit
Location:
Copper Mountain

Signs of Unstable Snow

Recent Avalanches? 
None Observed
Cracking? 
Isolated
Collapsing? 
None Experienced
We stomped and walked through whatever wind-loaded terrain we could find and experienced only very isolated cracking.

Snow Stability

Stability Rating: 
Very Good
Confidence in Rating: 
Moderate
Stability Trend: 
Steady

Bottom Line

A slab avalanche was observed yesterday near Copper. We set out to determine what the slide failed on and whether the weak layer could be found in other areas.

The slide failed on an east-facing slope at 8,800’. It occurred at the tail end of the last storm (over the weekend) on a thin layer of preserved low-density snow. We also found this layering on sheltered S-facing slopes. Based on our observations today this layer currently appears to be unreactive.

Media/Attachments

This avalanche failed sometime over the weekend at the tail end of our most recent storm. The slide was colocated with a deeper persistent slab avalanche that occurred in January. You can see the clean-looking, shallower crown at the center-right portion of the slide and the older crown face slightly above that closer to the ridge. Banner Summit Zone - Copper Mountain, 8,800', E-facing slope.
The slide was 40 cm deep and failed in a layer of preserved low-density and lightly faceted snow. This photo was taken after stomping above the crown to expose a clean section of the crowns face. Banner Summit Zone - Copper Mountain, 8,800', E-facing slope.
Wind-loading in the Northern Sawtooths.

Advanced Information

Weather Summary

Cloud Cover:
Mostly Sunny
Wind:
Moderate , SW

Decreasing clouds throughout the day. Warm near the road at Banner Summit (32 F) while still 16 F in Stanley at 3 PM. Wind blew light to moderate from the SW at the ridge top of Copper Mountain. Wind speeds increased throughout the day and blew around a substantial amount of snow at upper elevation in the northern Sawtooths. Wind was not moving much snow in the Southern Sawtooths or near Galena Pass.

Snowpack Observations

Surface Conditions:
Surface hoar on north-facing slopes. Breakable 3 cm crust on most S-SW-W. Generally light faceting elsewhere.

8,116’, South (170 deg.), HS 145 cm:
Martin and I both found subtle weak layers in the upper 35 cm of the snowpack. The most notable was a layer of well preserved and lightly faceted low-density snow sandwiched between layers of slightly stronger snow. This was the same layer responsible for the slide shown in the photo. CT16, ECTN down 35 cm

Avalanche Problems

Problem Location Distribution Sensitivity Size Comments
Wind Slab
Isolated
Specific
Widespread
Unreactive
Stubborn
Reactive
Touchy
D1
D1.5
D2
D2.5
D3
D3.5
D4
D4.5
D5
 Layer Depth/Date: 30-40 cm
Comments: The recently formed wind slabs we encountered were 4F-1F. Only minor cracking.

We did not assess weak layers near the ground.