Avalanche Forecast
Issued: Jan 12th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
swerner,
Avalanche Canada
Widespread avalanche activity is expected avoid avalanche terrain including overhead hazards. The new load and stress on the snowpack may be enough to trigger deep weak layers.
Summary
Confidence
Weather Forecast
The storm will start to diminish overnight as a ridge of high pressure builds on Wednesday bringing dryer and cooler conditions.
Tuesday Night: Snow 20-30 cm with freezing levels rising to 1500 m and possibly spiking to 2000 m early Wednesday morning. Ridgetop wind strong from the southwest.
Wednesday: Cloudy with possible sunny periods. Treeline temperatures near -2 and freezing level 1400 m.
Thursday/ Friday: Mix of sun and cloud. Treeline temperatures -4 and freezing level 900 m rising to 1100 m on Friday.
Avalanche Summary
On Tuesday, explosive control triggered numerous size 2-2.5 slab avalanches and human triggered avalanches up to size 1.5 were also reported.
Natural and human triggered slab avalanches will continue to exist on Wednesday.
Of note, a naturally-triggered size 3 deep persistent slab avalanche released on a southeast aspect at 2200 m in the Rossland range last Tuesday or Wednesday. The avalanche likely failed on the weak layers described in the Snowpack Summary and scrubbed to ground. Persistent slab avalanche activity has quieted in the past few days since this report. Although the likelihood of triggering these layers has reduced, the consequence of doing so remains high.
Snowpack Summary
Up to 30 cm of new snow fell on Tuesday with another 20-30 cm forecast for overnight into Wednesday. The new snow accompanied by strong winds are building reactive storm and wind slabs. These will likely be extra sensitive where they overlie surface hoar in sheltered terrain.
Two weak layers are buried in close proximity to one another. They are 70 to 100 cm deep around Nelson and 50 to 80 cm deep around Rossland and other western parts of the region. The layers are composed of surface hoar and faceted grains and they overlie a hard melt-freeze crust. Many MIN reports describe these layers and their snowpack test results. The results suggest that it remains possible for riders to trigger these layers.
Another layer of faceted grains above a melt-freeze crust that formed in early November is upwards of 200 cm below the surface. This has been the suspected failure layer of a few very large avalanches that released last week in the Rossland range.
Terrain and Travel
- Storm slabs in motion may step down to deeper layers resulting in large avalanches.
- Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
- Cornice failure may trigger large avalanches.
Problems
Storm Slabs
The new snow/ rain load will destabilize the snowpack and natural avalanches are likely on Wednesday. New wind slabs are expected to form at higher elevations due to strong southerly wind.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
Weak surface hoar and/or faceted grains sit above a melt-freeze crust around 70 to 100 cm deep. The likelihood of triggering a persistent slab has reduced, but the consequence of doing so remains high.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Jan 13th, 2021 4:00PM
