Pro Field Report

Basic Information

Observation Details

Observation Date:
January 24, 2023
Submitted:
January 25, 2023
Observer:
SAC - VandenBos (off duty), O'Connor, Sackbauer
Zone or Region:
Soldier and Wood River Valley Mtns
Location:
Johnstone (6,600-9,900', primarily NE-E-SE-S-SW-W)

Signs of Unstable Snow

Recent Avalanches? 
Yes
Cracking? 
Isolated
Collapsing? 
Isolated
Recent avalanches refers to two wind slabs and larger persistent slab described below. I experienced cracking and collapsing in many small, fresh drifts and wind skins. Cracking extended up to roughly 30'.

Snow Stability

Stability Rating: 
Good
Confidence in Rating: 
Moderate
Stability Trend: 
Steady

Bottom Line

Thin wind slabs presented the most obvious hazard, but the recent natural persistent slab on Duncan Ridge is a good reminder (not that we needed one) of the weak layers deeper in the snowpack.

Media/Attachments

Debris from a wind slab avalanche in the foothills of the Pioneer mountains. This avalanche started at 7,800' on a ESE aspect. It ran roughly 1,000' vertical feet above and piled 6-9' of debris in this gully. Getting caught in terrain traps like this can have consequences, even if the avalanche is relatively small.
This recent large avalanche occurred on the shoulder of Duncan Ridge in the Pioneer Mountains. It appears to be a heavily wind-loaded slope that broke on a persistent weak layer. A smaller wind slab avalanche is visible further right in the image. 10,100', WSW.
This small wind slab avalanche occurred recently above the Hyndman Creek trailhead, likely as a result of the N-NW winds. As the avalanche moved downhill, it appears to have entrained loose surface snow that is becoming faceted, weak, and sugary. 7500', ESE.

Advanced Information

Weather Summary

Cloud Cover:
Overcast
Wind:
Moderate , NW

Afternoon wx obs: Skies partly cloudy, increasing to overcast by mid-afternoon. Gusty NW winds blowing on ridges. Never snowed on us, but looked like flakes were flying in the Pioneers by the end of the day.

Avalanche Observations

 #  Date Location Size Type Bed Sfc Depth Trigger Photos Details
1 Jan 23, 2023
(+/- 1 day) 		Duncan Ridge
W 10100ft 		D2.5 HS-Hard Slab O-Old Snow N-Natural
This recent large avalanche occurred on the shoulder of Duncan Ridge in the Pioneer Mountains. It appears to be a heavily wind-loaded slope that broke on a persistent weak layer. A smaller wind slab avalanche is visible further right in the image. 10,100', WSW.
Report
Duncan Ridge

In addition to the large persistent slab avalanche near Duncan Ridge, we observed two small wind slabs that ran quite a ways, one piled up debris deeply in a narrow gully.

Snowpack Observations

No formal obs, just moving obs. We experienced cracking and collapsing in many small, fresh drifts and wind skins. Cracking extended up to roughly 30'. Wind slabs/skins were up to 10cm thick on open slopes and 30-45cm thick near ridges. Wind-affected snow is widespread, and extends well down into middle elevations. We lost a lot of good skiing out there over the past few days... Most drifts/slabs were reactive, I don't think it would have been hard to trigger a fresh, small slab on a steep slope. I found one stiff drift at lower elevation that was stubborn, but then I hit it with an (unintentional) forecasters bodyslam, which produced a collapse and associated crack that extended 15' out from my body (FB1).

Avalanche Problems

Problem Location Distribution Sensitivity Size Comments
Wind Slab
Isolated
Specific
Widespread
Unreactive
Stubborn
Reactive
Touchy
D1
D1.5
D2
D2.5
D3
D3.5
D4
D4.5
D5
Persistent Slab
D1
D1.5
D2
D2.5
D3
D3.5
D4
D4.5
D5
 Weak Layer(s): Jan 5, 2023 (SH) Dec 26, 2022 (FC) Dec 19, 2022 (FC) Nov 27, 2022 (FC)