Avalanche Forecast
Issued: Jan 17th, 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
Watch for small but reactive fresh wind slabs in atypical terrain features after redistribution of recent snow by overnight wind from the northwest.
Summary
Confidence
Weather Forecast
Sunday night: Partly cloudy, moderate to strong northwest ridgetop wind, freezing level valley bottom.
Monday: Sunny, light northerly ridgetop wind, freezing level 800 m.
Tuesday: Mix of sun and cloud, southwest ridgetop wind building to strong, freezing level valley bottom.
Wednesday: Mix of sun and cloud, moderate northwest ridgetop wind, freezing level valley bottom.
Avalanche Summary
A couple of natural avalanches since last week's 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.
Last week, 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.
Over a week ago, 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
10-15 cm of new snow sits over extensively wind affected surfaces at upper elevations, a crust below 2000 m and large surface hoar crystals in wind sheltered areas around treeline. The upper snowpack is composed of some elevation-dependent permutation of 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 carefull around freshly wind loaded features.
- Recent wind has varied in direction so watch for wind slabs on all aspects.
- Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
Problems
Wind Slabs
Overnight wind from the northwest has likely blown new snow into fresh wind slabs in atypical terrain features. These will be especially reactive where they sit over a rain crust or large surface hoar crystals.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
30-50 cm of snow has settled into a slab over weak surface hoar crystals. An avalanche cycle 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. This problem is most prominent in thinner snowpack areas in the west of the region.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Jan 18th, 2021 4:00PM
