Sawtooth Avalanche Center

Pro Field Report

Basic Information

Observation Details

Observation Date:
December 21, 2020
Submitted:
December 22, 2020
Observer:
SAC - VandenBos, Creelman
Zone or Region:
Banner Summit
Location:
Langer Area (6,600-8,600', primarily W-SW-S-SE)

Signs of Unstable Snow

Recent Avalanches? 
Yes
Cracking? 
Widespread
Collapsing? 
Widespread

Snow Stability

Stability Rating: 
Very Poor
Confidence in Rating: 
Moderate
Stability Trend: 
Improving

Bottom Line

Recent storm and warm temperatures produced widespread signs of instability, including many natural avalanches. We avoided all avalanche terrain and all runout zones.

Advanced Information

Weather Summary

Cloud Cover:
Mostly Cloudy
Temperature:
low to mid 30s F (estimated)
Wind:
Light , W

Cloud cover decreasing from X to BKN through the day. Geared up in a drizzle, rain petering out around 1100 or 1130. Cloud cover decreased but temperature continued to slowly climb through the day. Trees were dumping rime and snow that had accumulated during the storm, sounded like it was raining all day. Passing banks of low stratus mostly cleared out by nightfall, leaving CLR to FEW clouds.

Avalanche Observations

Too many avalanches to list individually at this point. May have time to record in future days.

Snowpack Observations

Hand and formal pits revealed that the combination of rain and warm temperatures had pushed an appreciable amount of water into the faceted snow that is now in the middle of the snowpack. Facets were wet at 6,600' and moist at 8,500' with a transition in between, probably close to 8,000'. Overlying slab was wet and very dense at 6,600' where it was 20-25cm thick. Somewhat less dense but still wet for upper 5cm at 8,500', 40-45 cm thick. Never found dry snow on top of the snowpack. Very curious to see what a snowpack like the one we observed today looks like as it drains it's free water and freezes. Expecting the unexpected. We experienced widespread cracking and collapsing, received unstable snowpack test scores, and observed countless natural avalanches.

Pit at 7,500' on SW, slope angle in mid teens:
HS=80-90cm
Overlying slab=35-40cm thick. Upper 10cm are wet
ECTP 2 and 4, both down 40cm
CPST 16 and 19 to END down 40cm
PST 18 and 20 to END down 40cm

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
Weak Layer(s): Dec 11, 2020 (FCsf)

Terrain Use

We avoided all avalanche terrain and the runout zones below it. "Felt" like we could have triggered avalanches easily.