Pro Field Report

Basic Information

Observation Details

Observation Date:
December 21, 2022
Submitted:
December 21, 2022
Observer:
SAC - Davis
Zone or Region:
Soldier and Wood River Valley Mtns
Location:
Adam's Gulch/ Warm Springs Divide (N-E-S, 5,900-7,600')

Signs of Unstable Snow

Recent Avalanches? 
Yes
Cracking? 
Isolated
Collapsing? 
Isolated
Locally, cracking and collapsing was isolated to 15-25cm drifts along ridges. Collapses occurred under new snow on S-facing slopes in a layer of facets and surface hoar resting on a crust. Regionally, this drifting caused a handful of very large wind slab avalanches and several smaller wind slab avalanches on a variety of aspects and elevations.

Snow Stability

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

Bottom Line

Wind loading caused a handful of very large wind slab avalanches and several smaller wind slab avalanches on a variety of aspects and elevations.

Media/Attachments

There was plenty of wind transport at upper and middle elevations around Ketchum. Wind transport at lower was less widespread but it was essentially a ground blizzard at the mouth of Lake Ck all day.
NNE @ 7,600' above Adam's Gulch. CPST27/100 end. You can see the layer that is failing is below the obvious surface hoar at (11/27). This pit location saw previous wind loading.
NNE @ 7,600' above Adam's Gulch. This is some of the 6mm surface hoar found at (12/8). Flakes were visible in the pit was. The layer was down 65 cm and produced no results in repeated ECTs.
NNE @ 7,600' above Adam's Gulch. This is the top of the November facet stack. (11/27) is visible as a low density stripe. All ECTs propagated with additional loading steps on a weaker layer of facets under the surface hoar (bottom of crystal card). The slab was 85 cm thick here 1F at the base, 4F below the weak layer.
Cracking in freshly formed soft slab. It was generally confined to ridge tops in this location, failing 15-25 cm deep on facets above a crust. S-facing slope at 7,600'.

Advanced Information

Weather Summary

Cloud Cover:
Clear
Temperature:
Low 20s
Wind:
Moderate , NW
New/Recent Snowfall:
HST = 15 cm

Blustery moderate NW wind with occasional strong gusts. Wind affect was evident to the valley floor. Drainage winds along hiway 75 seemed to ease midday but the mouths of drainages like Lake Ck and portions of Warm Springs as well as most middle to upper elevations remained windy most of the day.

Avalanche Observations

 #  Date Location Size Type Bed Sfc Depth Trigger Photos Details
1 Dec 21, 2022
(+/- 1 day) 		Headwall of Eagle Ck
S 10000ft 		D2 SS-Soft Slab N-Natural
A set of impressive wind slab avalanches on the headwall of Eagle Ck N. of Ketchum. SW and S @ 10,000'.
Report
1 Dec 21, 2022
(+/- 1 day) 		Headwall of Eagle Ck
S 10000ft 		D2.5 SS-Soft Slab N-Natural
A set of impressive wind slab avalanches on the headwall of Eagle Ck N. of Ketchum. SW and S @ 10,000'.
Report
1 Dec 11, 2022
(+/- 3 days) 		Adam's Gulch
NE 8300ft 		D2 SS-Soft Slab N-Natural
Adam's Gulch NE @ ~8,300'. Large avalanche from the 12/11 storm.
Report
1 Dec 11, 2022
(+/- 3 days) 		Adam's Gulch
NE 7200ft 		D2 SS-Soft Slab N-Natural
NE @ 7,200'. Large avalanche from the 12/11 storm.
Report
Headwall of Eagle Ck
Headwall of Eagle Ck
Adam's Gulch
Adam's Gulch

Snowpack Observations

I set out to observe wind affect and assess the 12/19 new/old interface. Wind affect and associated avalanches are explained elsewhere.

"New/old" (12/19): I found this interface to be touchy on S-facing slopes where it presented as a mix of facets and surface hoar on a stout crust. Elsewhere it was simply small facets. These areas didn't look particularly worrisome in the long term. I did not observe the (12/11) rain layer anywhere which was a little perplexing as it was reported on Baldy.

NNE @ 7,600' HS = 120cm. This pit was located in an area that received previous wind affect. The slab was thinner and closer to 4F at the base in nearby areas that I probed. On ascent the slab was quite weak (maybe only 4F- at the base). 15 cm of storm snow sat on small facets. (12/8) was down 65cm. It presented as 6mm SH but produced no results in multiple ECTs (including additional hits). The (11/27) layer was down 85cm. The slab graded from 4F to 1F at the base. It presented as 6mm SH that was faceted and "crispy" and felt sturdy. ECTs propagated in weaker facets 5cm below this interface with additional loading steps. It also produced a CPST27/100 end.

S @ 7,300' HS 45-65cm. I traversed and dug along the S-face. It was notably shallow. Grass and small shrubs protruded. New snow and Dec. 11 snows sat atop a sandwich of crusts and facets to the ground.

Avalanche Problems

Problem Location Distribution Sensitivity Size Comments
Persistent Slab
Isolated
Specific
Widespread
Unreactive
Stubborn
Reactive
Touchy
 Weak Layer(s): Nov 27, 2022 (FC)
Comments: Shaded where I expected the problem to be at it's worst. ECTXs that propagated with additional loading steps. CPST27/100 end.
Wind Slab
Isolated
Specific
Widespread
Unreactive
Stubborn
Reactive
Touchy
 Layer Depth/Date: 30cm
Comments: Shaded where most likely. Regionally there appeared to be enough wind-loading to produce numerous D1.5s at low elevation.

Terrain Use

I avoided avalanche terrain due to solo travel.