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Professional Observation

Basic Information

Observation Details

Observation Date:
December 10, 2019
Submitted:
December 11, 2019
Observer:
SAC - VandenBos (off duty)
Zone or Region:
Sawtooth and Western Smoky Mtns
Location:
Fishhook to Profile

Signs of Unstable Snow

Recent Avalanches? 
Yes
Cracking? 
Widespread
Collapsing? 
Widespread
Widespread collapsing where sufficient snow was preserved from pre-Thanks giving storms.

Snow Stability

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

Bottom Line

Very weak snowpack where Thanksgiving storms fell on old snow. Truly impressive rumbling collapses traveling many hundreds of feet, lasting for up to 10 seconds.

Media

This avalanche failed during the storm on December 7-8 above Profile Lake in the Sawtooth Mountains at 9,400' on a north-facing slope. Nearby snowpits indicate it failed on either a layer of surface hoar and near surface facets, or a deeper layer of depth hoar.
This avalanche failed during the storm on December 7-8 below Profile Lake in the Sawtooth Mountains at 8,700' on a northeast-facing slope. Nearby snowpits indicate it failed on either a layer of surface hoar and near surface facets, or a deeper layer of depth hoar.
A rumbling collapse that traveled many hundreds of feet in the northern Sawtooth Mtns produced these fractures on Dec 10th. The slope pictured faces SE and sits at 8,900'. The collapse that triggered this slope faces north and sits at 8,750'.

Advanced Information

Weather Summary

Cloud Cover:
Clear
Temperature:
Inverted
Wind:
Light , W

Wind found only in upper elevation, exposed terrain. Passing, isolated mid-level stratus did not significantly affect radiation picture.

Avalanche Observations

 #  Date Location Size Type Bed Sfc Depth Trigger Comments Photo
2 Past 48 hours Profile
N 8,500-9,400' 		D2 SS N-Natural Difficult to be certain on bed surface and crown depth as these failed during the storm and had been filled in slightly. Based on widespread collapsing and poor test scores on Thanksgiving FC/DH (buried 11/26) I'd have to guess that that was the culprit, but near FCsf and SH are also contenders.
This avalanche failed during the storm on December 7-8 above Profile Lake in the Sawtooth Mountains at 9,400' on a north-facing slope. Nearby snowpits indicate it failed on either a layer of surface hoar and near surface facets, or a deeper layer of depth hoar.

Snowpack Observations

Depth hoar produced repeatable ECTP scores in the low single digits (see snowpack image).

Snowpit dug at 8,600' on an E/NE aspect below Profile Lake near Thompson and Williams Peaks. Dates indicate when layers were buried.

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
 Layer Depth/Date: 11/26
FC/DH buried just before Thanksgiving (11/26)
Persistent Slab
Layer Depth/Date: 12/7
SH buried 12/7. Found in several locations. Unreactive in standard and non-standard stability tests, but probably worth keeping on the radar for a bit. Grains were standing upright and intruding into snow above.

Terrain Use

Avoided all avalanche terrain that held sufficiently connected snow prior to 11/26. Paid close attention to the terrain above me. Would not have felt comfortable entering this area without a detailed knowledge of this year's snowpack evolution.

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