Pro Field Report

Basic Information

Observation Details

Observation Date:
January 20, 2021
Submitted:
January 20, 2021
Observer:
SAC - Davis, VandenBos
Zone or Region:
Soldier and Wood River Valley Mtns
Location:
Shaw (S-E-N, 7,200-8,800')

Signs of Unstable Snow

Recent Avalanches? 
None Observed
Cracking? 
Isolated
Collapsing? 
None Experienced
<10' cracks in isolated wind-affected pockets at middle elevations.

Snow Stability

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

Bottom Line

We saw natural, persistent slab avalanches (from last week's storm) and noted repeatable unstable snowpack test scores. The primary weak layer of concern is the same layer of facets we've seen produce the vast majority of natural avalanches all across the forecast area.

While only about 15 miles to the west of Ketchum, this area possesses a deeper snowpack that's formed a stiffer slab over a better developed (weaker) layer of facets. The snowpack changes quickly as you leave the Wood River Valley. Your odds of triggering an avalanche increase in areas with this poor structure.

Media/Attachments

Persistent slab avalanches on a NE-facing slope at ~8,100' near Boyle Mountain.
Persistent slab avalanche on a south-facing slope at ~9,000' in Placer Ck.
Persistent slab avalanche on a SE-facing slope at about ~9,500' at the head of Placer Ck.
Persistent slab avalanche on a SE-facing slope at ~9,100' at the head of Left Fork Placer Ck.
This slide appears to have started as a loose snow and tried to break into small slab pockets. NW-facing slope at ~8,300' near the head of Rough Canyon.
https://www.youtube.com/watch?v=o7r2U-f9ris

Advanced Information

Weather Summary

Cloud Cover:
Partly Cloudy
Wind:
Light
New/Recent Snowfall:
1" SWE from last week's storm

Mild (mid-20s F), light wind, bouts of clouds and sun.

Avalanche Observations

 #  Date Location Size Type Bed Sfc Depth Trigger Photos Details
1 Jan 13, 2021
(+/- 1 day) 		Rough Canyon
NW 8300ft 		D2 U-Unknown
This slide appears to have started as a loose snow and tried to break into small slab pockets. NW-facing slope at ~8,300' near the head of Rough Canyon.
Report
2 Jan 13, 2021
(+/- 1 day) 		Warm Springs Ck
NE 8100ft 		D1.5 U-Unknown
Persistent slab avalanches on a NE-facing slope at ~8,100' near Boyle Mountain.
Report
1 Jan 13, 2021
(+/- 1 day) 		Placer Creek
SE 9500ft 		D2 U-Unknown
Persistent slab avalanche on a SE-facing slope at about ~9,500' at the head of Placer Ck.
Report
1 Jan 13, 2021
(+/- 1 day) 		Placer Creek
S 9000ft 		D2 U-Unknown
Persistent slab avalanche on a south-facing slope at ~9,000' in Placer Ck.
Report
1 Jan 13, 2021
(+/- 1 day) 		Left Fork Placer Ck
SE 9100ft 		D2 SS-Soft Slab U-Unknown
Persistent slab avalanche on a SE-facing slope at ~9,100' at the head of Left Fork Placer Ck.
Report
Rough Canyon
Warm Springs Ck
Placer Creek
Placer Creek
Left Fork Placer Ck

We also observed ~6-10 small wet snow/rain induced slides below about 7,800'.

Snowpack Observations

Approximate rain line up to 7,800' from 1/13. Crust was softening during the day on sunnier slopes. Overall poor structure with F to 4F- slab over 12/11 facets.

8,000' NE, HS=90 cm:
90-80 F-
80-55 F to F+
55 = Solstice rain crust
55-35 4F-
35-30 F- to F (12/11 facets)
30 = (11/17) crust
30-0 F

Avalanche Problems

Problem Location Distribution Sensitivity Size Comments
Persistent Slab
Isolated
Specific
Widespread
D1
D1.5
D2
D2.5
D3
D3.5
D4
D4.5
D5
 Weak Layer(s): Dec 11, 2020 (FCsf)
Comments: Numerous CPSTs in the upper 20s, PSTs in the mid-20s, ECTPs in the upper teens. Rose is shaded where problem was observed. Natural activity and previous obs from this area suggest it's prevalent around the compass at middle and upper elevation.