Pro Field Report

Basic Information

Observation Details

Observation Date:
January 10, 2023
Submitted:
January 11, 2023
Observer:
SAC - Davis, VandenBos
Zone or Region:
Banner Summit
Location:
Copper Mountain - North Side (W-N-E, 6,600-8,900')

Signs of Unstable Snow

Recent Avalanches? 
Yes
Cracking? 
Isolated
Collapsing? 
Isolated
One small D1 in a steep NE-facing slope on the N side of Banner. A handful of D2s in the Sawtooths (see below).

Snow Stability

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

Bottom Line

We found a touchy layer of surface hoar buried under ~1 foot of snow. The layer was responsible for one small natural avalanche, cracking in drifts, and poor snowpack test scores.

Media/Attachments

Storm snow sluffing off of SE-facing slopes in Prairie Ck, Smoky Mtns.
These avalanches released near 9,700' on an E-facing slope of Saviers Pk in the Smoky Mtns.
Debris of a large avalanche near Cabin Pk. Southern Sawtooth Mtns, NE aspect at 9,500'.
This large slide likely began as a tumbling cornice or a loose snow avalanche before stepping down to release a slab avalanche. Near Decker Pk, E aspect near 10,000'.
Large avalanche on Eureka Pk. ENE aspect at 10,000'.
Large wind dunes on McDonald Pk. Southern Sawtooth Mtns.
Cornice failure entraining loose storm snow. E aspect around 9,500'.
This large slide likely began as a tumbling cornice or a loose snow avalanche before stepping down to release a slab avalanche. Near Decker Pk, E aspect near 10,000'.
A touchy layer of surface hoar produced a natural avalanche and cracking in drifts along a middle elevation ridge line on the N side of Copper Mtn.
https://www.youtube.com/watch?v=p11Es8ZsPy0&t=1s

Advanced Information

Weather Summary

Cloud Cover:
Mostly Cloudy
Temperature:
Low 20sF
Wind:
Light , E
New/Recent Snowfall:
HST since (1/5) = 40 cm

Much of the mountains N of Galena Summit saw a healthy dose of sun in the morning hours. Clouds moved in midday. Very light snowfall began at Banner Summit around 4PM. Less than an inch had fallen by dark. Wind blew light from the E and SE.

Avalanche Observations

 #  Date Location Size Type Bed Sfc Depth Trigger Photos Details
1 Jan 9, 2023
(+/- 1 day) 		Near McDonald Peak
NE 9500ft 		D2 N-Natural
Debris of a large avalanche near Cabin Pk. Southern Sawtooth Mtns, NE aspect at 9,500'.
Report
1 Jan 9, 2023
(+/- 1 day) 		Near Decker Pk
E 10000ft 		D2 N-Natural
This large slide likely began as a tumbling cornice or a loose snow avalanche before stepping down to release a slab avalanche. Near Decker Pk, E aspect near 10,000'.
This large slide likely began as a tumbling cornice or a loose snow avalanche before stepping down to release a slab avalanche. Near Decker Pk, E aspect near 10,000'.
Report
1 Jan 9, 2023
(+/- 1 day) 		Eureka Pk
E 10100ft 		D2 N-Natural
Large avalanche on Eureka Pk. ENE aspect at 10,000'.
Report
Near McDonald Peak
Near Decker Pk
Eureka Pk

We had good visibility from Decker Pk south to the Headwaters. Poor visibility in the northern Sawtooths and Banner. Much of the activity was masked by continued wind-loading and snowfall.

Snowpack Observations

We set out to gather information on the storm snow of the last several days and to check back in on older weak layers in the upper meter of the snowpack. We only dug down ~1m in each location. The snow graded smoothly from F to 1F by 1m in depth. ECTPs on SH dn 30 cm in most pits.

W @ 7,300', HS = 180 cm, Mid-drainage opening in a trim line: ECTP11,14 and ECTN14 dn 30 on 2-4 mm SH, (12/26) dn 75 cm presented as an ice crust on 1 mm FC. ECTN29,30 and ECTP29.

NE @ 7,900' HS = 160 cm, Exposed finger ridge: ECTP13,13,15 dn 35 on 2-5 mm SH. (12/26) dn 55 cm presented as a hardness change with layed down 6 mm SH. No results on this layer but the slab broke when digging.

W @ 8,400', Previously drifted, exposed ridgeline: ECTN20 and 19 dn 30 on 4-6 mm SH. The presence of SH on this fairly exposed mid/upper transition ridge led us to believe it was likely alive and well in slightly protected bowls just off of alpine ridgelines.

Avalanche Problems

Problem Location Distribution Sensitivity Size Comments
Persistent Slab
Unknown
Unreactive
Stubborn
Reactive
Touchy
D1
D1.5
D2
D2.5
D3
D3.5
D4
D4.5
D5
 Layer Depth/Date: 30-40 cm
Comments: Shaded where observed, exact distribution unknown. We did not dig on sunnier aspects. I assume given the SE wind and some sun, the surface hoar is a problem in fewer locations on these aspects. The slab was mostly F to F+ in sheltered areas and as stiff as 1F to 1F+ in windier terrain. It seemed quiet possible to pull out a slab in steep sheltered terrain, but certainly more likely as you climbed into windier areas that tied the slab together.
Persistent Slab
Isolated
Specific
Widespread
Unreactive
Stubborn
Reactive
Touchy
 Layer Depth/Date: 75-85 cm
Weak Layer(s): Dec 26, 2022 (FC)
Comments: (12/26) produced mixed results where we found it as a crust + FC combination. It was harder to locate >8,000' (hardness difference). We didn't dig on sunnier slopes.

It was windy up at Copper during the last storm. Large swaths of trees from Copper to Bull Trout were stripped of snow. I assume you could find some isolated true wind slabs, but it's more likely that you'd trigger a wind-stiffened slab that sat over the recently buried layer of surface hoar (or some permutation of SH, FC, MFcr).

Terrain Use

We carefully chose a route to avoid overhead hazard. We traveled out of our way to avoid greater than 30-degree slopes, even in sheltered terrain.