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Avalanche Forecast

Archived

Jan 14th, 2021–Jan 15th, 2021

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

Regions

Kootenay Boundary.

Strong and shifting winds should refresh surface instabilities in exposed terrain. Seek out sheltered snow 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 - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

Thursday night: Increasing cloud, moderate to strong southwest ridgetop wind, freezing level valley bottom.

Friday: Mostly cloudy, light to moderate northwest ridgetop wind, freezing level 1000 m.

Saturday: Mix of sun and cloud, moderate northwest ridgetop wind, freezing level 700 m.

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

Avalanche Summary

On Wednesday, a widespread natural avalanche cycle up to size 2.5 was reported on all aspects and elevations. 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

20-40 cm of recent storm snow accompanied by strong to extreme westerly wind has built reactive storm and wind slabs at upper elevations. These slabs may be extra sensitive where they overlie surface hoar in sheltered terrain or a crust on solar aspects. Warmer temperatures and a period of rain overnight Tuesday has formed a thin surface crust up to around 2000 m.

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

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.
  • 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

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.