Professional Field Report

Basic Information

Observation Details

Observation Date:
December 11, 2019
Submitted:
December 11, 2019
Observer:
SAC - VandenBos, Davis
Zone or Region:
Sawtooth and Western Smoky Mtns
Location:
Smiley Creek

Signs of Unstable Snow

Recent Avalanches? 
None Observed
Cracking? 
Widespread
Collapsing? 
Widespread
Cracking and collapsing on specific slopes, those on the northern 3/4 of the compass that held snow before Thanksgiving.

Snow Stability

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

Bottom Line

A weak, unstable snowpack exists in the headwaters of the Salmon River. Natural and human triggered avalanches will be likely with additional loading and may be triggered remotely, from a distance above, below, and to the sides of steeper slopes.

Media/Attachments

These small persistent slab avalanches are a clear sign that the snowpack in the headwaters of the Salmon River are unstable.
This avalanche and several others like it failed in the northern Sawtooth Mtns during the December 7-8 storm. Based on nearby snowpits, these avalanches failed on either a layer of surface hoar and near surface facets that was buried on 12/7, or a layer of depth hoar near the ground that was buried on 11/26.

Advanced Information

Weather Summary

Cloud Cover:
Overcast
Wind:
Moderate , W

Occasional S-1 flurries, with no significant accumulation, 1-2cm throughout the day at most. Variable cloud cover, from broken to obscured.

Avalanche Observations

 #  Date Location Size Type Bed Sfc Depth Trigger Comments Photo
5 Smiley Creek
N 8,800-9,300 		D2 SS O-Old Snow N-Natural Observed a number of D1-D2 slides on the northerly quarter of the compass. Based on crown depth, some slides appeared to be failing on 12/7 and others on 11/26. Stability tests pointed to 11/26 as the more problematic layer.
This avalanche and several others like it failed in the northern Sawtooth Mtns during the December 7-8 storm. Based on nearby snowpits, these avalanches failed on either a layer of surface hoar and near surface facets that was buried on 12/7, or a layer of depth hoar near the ground that was buried on 11/26.

Lots of mid storm activity observed despite poor visibility. This is a snowpack that can make avalanches, and it is about to get tested by a sizable load of new snow.

Snowpack Observations

Plenty of remnant snow from before Thanksgiving to create a significant persistent slab avalanche problem in this area.

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
 Comments: DH buried 11/26
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: 12/7
Comments: SH buried 12/7. Unreactive in snowpits, but worth keeping on the problem list until proven innocent

Terrain Use

Avoided avalanche terrain and the runouts below large paths. Chose to abort our mission to work on the Upper Vienna weather station due to persistent slab avalanche and remote triggering concerns.