Pro Field Report

Basic Information

Observation Details

Observation Date:
January 1, 2021
Submitted:
January 1, 2021
Observer:
SAC - Chris Lundy (off duty)
Zone or Region:
Banner Summit
Location:
Cape Horn Summit (7300-8400', NE-ESE)

Signs of Unstable Snow

Recent Avalanches? 
None Observed
Cracking? 
Isolated
Collapsing? 
Widespread
Widespread medium to large collapses. These seemed most common on E and ESE aspects at mid-elevations. Many were accompanied by a physical drop of the snow surface, and a slight shift in the slope if the angle was over 25*. At least one rattled snow from a tree 75' away.

Snow Stability

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

Bottom Line

Poor snowpack test scores and widespread collapsing indicated that the snowpack in this area seemed worse than observed elsewhere in the Banner Summit zone. The weak facet layer is buried beneath an 18-20" thick, dense slab.

Advanced Information

Weather Summary

Cloud Cover:
Overcast
Wind:
Light

Generally overcast, but occasionally obscured. There was one brief period when the sun poked out. Ski pen around 20cm.

Snowpack Observations

Was surprised by the widespread collapsing given the lack of recent loading. Collapsing seemed most widespread on E and ESE aspects where there were more distinct crusts present in the slab and a weakening crust near the 12/11 facet layer. Hard to confirm/deny this theory with the little data we had. Collapsing was less common on NE and at higher elevations where the slab was thicker, stronger, and likely more difficult to impact the weak layer.

@8100', NE: HS 105cm. 12/11 down 55cm. Slab 1F hard at base over F/F+ FC. ECTP21.

@7700, ESE: HS 95cm. This slope collapsed as we approached it. 12/11 down 50cm. Slab 4F hard at base over F FC - weaker than first pit. There was a thicker crust from the solstice rain, and a few other crusts below it in the slab. There was also a very faint/deteriorated crust just above 12/11. ECTP13 just below that crust. I think these crusts were playing a role in the collapsing on the E and ESE aspects.

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: 50-55cm
Weak Layer(s): Dec 11, 2020 (FCsf)
Comments: Collapsing most widespread on E and ESE. Propagating ECTs on N and ESE.

Terrain Use

Went out planning to avoid terrain over 35*. Widespread collapsing caused us to step back, and we basically avoided avalanche terrain.