Pro Field Report

Basic Information

Observation Details

Observation Date:
December 15, 2021
Submitted:
December 16, 2021
Observer:
SAC - VandenBos, Davis
Zone or Region:
Galena Summit and Eastern Mtns
Location:
Galena Peak (7,3000-9,900, primarily SW-W-NW-N)

Signs of Unstable Snow

Recent Avalanches? 
Yes
Cracking? 
Isolated
Collapsing? 
Widespread
Snowpack collapses were pretty widespread. Cracking was only observed in recently formed wind drifts.

Snow Stability

Stability Rating: 
Poor
Confidence in Rating: 
Low
Stability Trend: 
Steady

Bottom Line

We found sensitive conditions that, based on the character of the weak layer, are likely to exist for sometime.

Media/Attachments

This large avalanche failed near the tail end of the big storm in mid-December. This peak is in the Prairie Creek drainage of the Smoky Mountains, northeast of Norton Peak. The crown spans nearly 500' wide (the portion that is visible at least, there may be more hidden out of sight to the right). This slope faces northeast at 9,600'.
Crown of a large avalanche that failed near the tail end of the big storm on a north-facing slope at 9,400'. This slope is in the Cabin Creek drainage in the southern Sawtooths, north of Alturas. The crown is an estimated 300+' wide. Another slide that failed earlier in the storm is also visible near the ridgeline further right of the obvious crown.
https://www.instagram.com/tv/CXhvRALlul3/

Advanced Information

Weather Summary

Cloud Cover:
Overcast
Temperature:
cold
Wind:
Light , NW
New/Recent Snowfall:
60cm settled HST

High stratus streaming through by sunrise, overcast by 1000, low clouds bring S-1 precip across the Smoky crest and the headwaters of the Salmon by 1200. Calm winds becoming light out of NW in the early afternoon.

Avalanche Observations

 #  Date Location Size Type Bed Sfc Depth Trigger Photos Details
3 Dec 14, 2021
(+/- 1 day) 		Saviers Peak
NE 10000ft 		D2 SS-Soft Slab N-Natural Report
1 Dec 14, 2021
(+/- 1 day) 		Prairie Creek
NE 9600ft 		D2.5 SS-Soft Slab N-Natural
This large avalanche failed near the tail end of the big storm in mid-December. This peak is in the Prairie Creek drainage of the Smoky Mountains, northeast of Norton Peak. The crown spans nearly 500' wide (the portion that is visible at least, there may be more hidden out of sight to the right). This slope faces northeast at 9,600'.
Report
2 Dec 14, 2021
(+/- 1 day) 		Cabin Creek
N 9400ft 		D2 SS-Soft Slab N-Natural
Crown of a large avalanche that failed near the tail end of the big storm on a north-facing slope at 9,400'. This slope is in the Cabin Creek drainage in the southern Sawtooths, north of Alturas. The crown is an estimated 300+' wide. Another slide that failed earlier in the storm is also visible near the ridgeline further right of the obvious crown.
Report
Saviers Peak
Prairie Creek
Cabin Creek

We saw a large number of D2 and D2.5 avalanches along the Smoky crest and in the mountains and hills to the east of the crest. Most of these slides failed in wind affected terrain and exhibited persistent slab characteristics, likely indicating that they failed on or near the 12/11 interface. We also observed some smaller slides in more sheltered terrain that appeared to have failed on this interface.

While I have seen many of these paths produce larger avalanches, this was about as widespread of a cycle as I've seen in the Smoky Mountains.

Snowpack Observations

Dug on SW at 8,500' where HS=85cm, looking to see how new/old interface is behaving on solar/solar margins. Received ECTP2 and 3 down 60cm at the base of the new snow on a thin layer of facets on top of the icy/melt-freeze polycrystal mess that was well adhered to the ground. As we climbed higher and onto more shaded aspects this layer of facets became thicker. Where the snowpack was not capped with a stiffer wind slab we received a number of generally localized collapses. Where stiffer slabs existed on the surface it was more difficult to impact the weak layer.

Avalanche Problems

Problem Location Distribution Sensitivity Size Comments
Persistent Slab
Isolated
Specific
Widespread
D1
D1.5
D2
D2.5
D3
D3.5
D4
D4.5
D5
 Layer Depth/Date: down 60cm
Weak Layer(s): Dec 11, 2021 (FC)
Comments: Rose is shaded both based on where problem was observed directly and where it was assumed to exist based on previous observations in similar snowpacks. The character of this interface varies by aspect but the layer is problematic everywhere I've looked at it. I'd imagine that upper elevation solars could make avalanches on this layer as well, but I don't have any data on this. On those aspects it likely manifests as a slick, icy crust with or without facets. Based on the pattern of observed activity this layer is much less reactive on solars.
Wind Slab
Comments: Some thinner slabs extended down into middle elevations in places, but were much larger and likely more sensitive at higher elevations. We had no interest in poking into terrain where these would be a problem, the persistent slab problem is pretty terrain limiting.

Terrain Use

We planned to avoid avalanche terrain and we stuck with this plan.