Sawtooth Avalanche Center

Pro Field Report

Basic Information

Observation Details

Observation Date:
February 7, 2021
Submitted:
February 8, 2021
Observer:
SAC - VandenBos (off duty)
Zone or Region:
Banner Summit
Location:
Langer Area (6,500-9,400')

Signs of Unstable Snow

Recent Avalanches? 
Yes
Cracking? 
Isolated
Collapsing? 
Isolated
Very isolated cracking and collapsing in fresh wind drifts. Avalanches observed refer to small crowns and small fresh(ish) debris piles that appeared to be from small wind slabs.

Snow Stability

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

Advanced Information

Weather Summary

Cloud Cover:
Overcast
Wind:
Moderate , NW
New/Recent Snowfall:
15-20cm

Winds blowing MgS, digging well down into terrain that is generally sheltered. Highway was drifted almost to the centerline with 1-2' drifts in places.

Avalanche Observations

Saw evidence of small wind slabs that had failed naturally (thin crowns and small, recent debris piles). No evidence of slides failing on deeper weak layers, but visibility was pretty bad.

Snowpack Observations

Went looking for the behavior of 1/27 interface and the effect of the wind. 1/27 is buried ~75 cm down, but is difficult to differentiate in many places. Too deep and subtle for handpits to be effective. Dug two pits at ~7,000' and two around 8,000' on solar and shaded aspects. Did not find any thick layers of standing surface hoar, but did find some SH xtals at this interface. Did not get propagating results in any of my ECTs, just a mixture of ECTNs with hard force (on solars, where coupled with a crust) and ECTXs (on shaded slopes). In one pit dug at 8,200' the 1/27 interface manifested itself as nothing more than a dusty stripe with some pine needles and produced ECTXs. HS ranged from 160cm on lower elevation pits on solars to over 200cm on higher elevation shaded slopes.

It was about as windy as I've seen the Banner Summit area, with drifts covering almost one lane of the highway on the drive north from Stanley. After I left the highway, the wind was moving snow at all elevations, but only really building slabs in exposed middle and (mostly) upper elevation terrain. Wind slabs that I encountered were stubborn to unreactive, with some producing short cracks and others doing nothing at all when stomped on. Impressive cornice formation at upper elevations provided me with some good slope testers - I was able to safely kick off some multi-hundred pound chunks of snow that produced no results when they impacted the slope below aside from some short cracks.

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
Layer Depth/Date: down 30-60cm
Comments: Rose filled out based on where I encountered the problem at its worst. Sensitivity between stubborn and unreactive.
Persistent Slab
Isolated
Specific
Widespread
Unreactive
Stubborn
Reactive
Touchy
D1
D1.5
D2
D2.5
D3
D3.5
D4
D4.5
D5
Weak Layer(s): Jan 27, 2021 (FCsf)
Comments: Rose filled out based on where I would suspect problem to be at its worst.

Terrain Use

Off duty tour, felt comfortable on supported slopes in the low 30s without sensitive wind slabs. Might have convinced myself to push slope angle up a bit in similar terrain, but I don't mind low angle pow. Plenty of wild, steep skiing to be done later.