Avalanche Forecast
Issued: Jan 16th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs, Persistent Slabs and Deep Persistent Slabs.
ahanna,
Avalanche Canada
Find the best riding in wind sheltered terrain above 2000 m but keep your guard up around steep pockets where recent storm snow may be settling over a fragile layer of surface hoar or a slippery crust.
Summary
Confidence
Weather Forecast
Saturday night: Flurries, a few cm, moderate southwest ridgetop wind, freezing level valley bottom.
Sunday: Flurries, a few cm, moderate northwest ridgetop wind, freezing level 800 m.
Monday: Sunny, light northerly ridgetop wind, freezing level 800 m.
Tuesday: Mix of sun and cloud, ridgetop wind shifting southwest, building to strong, freezing level 800 m.
Avalanche Summary
A couple of natural avalanches since the storm are suspected to have run on the surface hoar 20-40 cm down, including a size 2.5 storm slab out of a northwest facing gulley feature around 2000 m near Nelson.
On Wednesday, a widespread natural avalanche cycle up to size 2.5 was reported. A recent MIN report observed from Rossland shows a size 3 natural persistent slab avalanche that occurred during or post-storm.
Last week, a naturally-triggered size 3 deep persistent slab avalanche released on a southeast aspect at 2200 m in the Rossland range. The avalanche likely failed on the weak layers described in the snowpack summary and scrubbed to the ground.
Snowpack Summary
A surface crust exists up to around 2000 m. The top 20-40 cm of the snowpack is composed of some elevation-dependent permutation of a crust sandwich, formed by fluctuating freezing levels during the last storm.
A layer of surface hoar (and/or another crust) may be found beneath the most recent storm snow in sheltered terrain. A couple of recent avalanches are suspected to have run on this layer and where it has been found in snow profiles, it has been producing moderate to hard planar test results.
An older weak layer is buried 70 to 130 cm deep. It is composed of faceted grains over a crust. This recent MIN report observed from Rossland on Wednesday the 13th shows good evidence of a large natural slab avalanche failing on this layer during or post-storm. This suggests that it remains possible for riders to trigger this layer.
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
- Be careful as you transition into wind affected terrain.
- Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
- Conditions may have improved, but be mindful that deep instabilities are still present.
Problems
Wind Slabs
Previous wind has deposited recent snow into deeper slabs on leeward slopes at upper elevations. Wind slabs may remain reactive, particularly where they sit over surface hoar in sheltered terrain or a crust. Recent wind has varied in direction so watch for wind loading on a variety of aspects.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
20-40 cm of snow from the most recent storm has settled into a slab over weak surface hoar crystals. An avalanche cycle during the storm cleaned out this layer in many areas, but in places where avalanches have not yet run, it remains a concern. Use caution around convexities in open trees.
Aspects: All aspects.
Elevations: Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
Two crusts with weak faceted grains overtop are buried deep within the snowpack. The upper layer is 80 to 130 cm deep and the lower is near the ground. A few large avalanches have run naturally on these layers recently. The likelihood of triggering these layers is low but the consequence of doing is high.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Jan 17th, 2021 4:00PM
