Avalanche Occurrence

View Associated Field Report

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

Observer:

SAC Forecaster

Verified by SAC?

Yes

Occurrence Date:

Dec 20, 2021 (+/- 1 day)

Location:

McDonald Peak

Comments:

Persistent slab avalanches in heavily wind-loaded terrain.

# of Avys:

2

Aspect:

E (NE,E)

Start Zone Elev:

9500ft

Size:

D2.5

Type:

HS-Hard Slab

Trigger:

N-Natural

Bed Surface:

O-Old Snow

Width:

160ft

Weak Layer:

Dec 11, 2021 (FC)

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.