Pro Field Report
Basic Information
Observation Details
Observation Date:
December 21, 2020Submitted:
December 22, 2020Observer:
SAC - VandenBos, CreelmanZone or Region:
Banner SummitLocation:
Langer Area (6,600-8,600', primarily W-SW-S-SE)Signs of Unstable Snow
Recent Avalanches?
YesCracking?
WidespreadCollapsing?
WidespreadSnow Stability
Stability Rating:
Very PoorConfidence in Rating:
ModerateStability Trend:
ImprovingBottom 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 CloudyTemperature:
low to mid 30s F (estimated)Wind:
Light , WCloud 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
|
|
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.