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Avalanche Forecast

Archived

Jan 15th, 2021–Jan 16th, 2021

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Kootenay Boundary.

Find the best riding in wind sheltered terrain above 2000 m but keep your guard up around steep pockets where storm snow may be settling over a fragile layer of surface hoar or a slippery crust. 

Confidence

Moderate -

Weather Forecast

Friday night: Clear, light northwest ridgetop wind, freezing level valley bottom.

Saturday: Mix of sun and cloud, light northwest ridgetop wind, freezing level 600 m.

Sunday: Flurries, moderate northwest ridgetop wind, freezing level 800 m.

Monday: Sunny, light northerly ridgetop wind, freezing level 800 m.

Avalanche Summary

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 (or another crust) may sit beneath the recent storm snow in sheltered terrain.

Two weak layers are buried in close proximity to one another. They are 70 to 130 cm deep. The layers are composed of surface hoar and faceted grains and they overlie a hard melt-freeze crust. This recent MIN report observed from Rossland on Wednesday the 13th shows good evidence of a large natural slab avalanche failing on the early December persistent layer during or post-storm. This suggests 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

  • Be careful as you transition into wind affected terrain.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.