Pro Field Report

Basic Information

Observation Details

Observation Date:
December 21, 2021
Submitted:
December 21, 2021
Observer:
SAC - Savage
Zone or Region:
Sawtooth and Western Smoky Mtns
Location:
glassing Hailey-Stanley-Banner Summit (all elevations and most aspects)

Signs of Unstable Snow

Recent Avalanches? 
Yes
Cracking? 
None Experienced
Collapsing? 
None Experienced
I saw fresh, small and large avalanches. Cracking and collapsing data is N/A as all snow observations were roadside.

Bottom Line

Very large, recent natural avalanches on McDonald Peak in the southern Sawtooths...several smaller wind slab avalanches releasing at/near ridgelines in the Smoky and Sawtooth Mtns (cornice fall triggered some)...pinwheels and rollerballs on some steep southerly-facing slopes. The little storm a couple of days ago and wind transported snow over the past 36 hours was enough to keep the snowpack very much on edge.

Media/Attachments

Wind effects and critter tracks in the upper reaches of the Eagle Creek drainage north of Ketchum.
These very large avalanches were observed this morning on McDonald Peak in the southern Sawtooths. The starting zones range from about 9,200' to 9,700' and they face predominantly E/NE. The slides occurred sometime in the past 12-24 hours. 4-6" of snow fell in this area on Sunday and was drifted by moderate to strong winds during the storm Sunday and yesterday. This small load was all it took to break the proverbial camel's back. As we look ahead at an extended period of snowfall we can be certain that stability will decrease and the likelihood of these types of avalanches will increase. Persistent slab avalanches, like the ones pictured here, fail in surprising ways, breaking much wider than you might expect and wrapping around terrain features. They can be triggered remotely—from below, above, and to the sides of steep slopes.

Advanced Information

Weather Summary

Cloud Cover:
Partly Cloudy
Temperature:
20s and low30s F
Wind:
Light
New/Recent Snowfall:
No new snow in the previous 24 hours.

Fair amount of evidence of recent wind transport in upper elevation terrain: dunes, pillows, cornice fall, etc. No active wind loading or transport occurred from noon-4PM today.

Avalanche Observations

 #  Date Location Size Type Bed Sfc Depth Trigger Photos Details
2 Dec 20, 2021
(+/- 1 day) 		McDonald Peak
E 9500ft 		D2.5 HS-Hard Slab O-Old Snow N-Natural
These very large avalanches were observed this morning on McDonald Peak in the southern Sawtooths. The starting zones range from about 9,200' to 9,700' and they face predominantly E/NE. The slides occurred sometime in the past 12-24 hours. 4-6" of snow fell in this area on Sunday and was drifted by moderate to strong winds during the storm Sunday and yesterday. This small load was all it took to break the proverbial camel's back. As we look ahead at an extended period of snowfall we can be certain that stability will decrease and the likelihood of these types of avalanches will increase. Persistent slab avalanches, like the ones pictured here, fail in surprising ways, breaking much wider than you might expect and wrapping around terrain features. They can be triggered remotely—from below, above, and to the sides of steep slopes.
Report
McDonald Peak
 #  Date Location Size Type Bed Sfc Depth Trigger Comments Photo
2 McDonald Peak
E alpine 		D2.5 HS O-Old Snow N-Natural None
1 McDonald Peak
NE alpine 		D2 SS I-New/Old Interface N-Natural None
4 Prairie Ck and West Fork Prairie Ck
NE alpine 		D1.5 SS S-New Snow N-Natural Several D1-1.5 wind slabs, releasing at/near ridgeline or where small cornice fall hit the slopes below. None

The light was flat in the northern Sawtooths, but I think I saw fresher slides near Decker Peak, Merritt Peak, Crooked Ck, and McGown Peak.

Snowpack Observations

Roadside observations: Steep solar surfaces were moist or crusts in the process of refreezing. Many locations had small surface hoar crystals on the surface, but I didn't see any larger than about 3mm. I did not much SH that was standing upright.

Terrain Use

Roadside observations.