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Avalanche Forecast

Archived

Dec 24th, 2020–Dec 25th, 2020

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

Regions

Kootenay Boundary.

The snowpack may take a while to equilibrate to the recent snow load. Conservative terrain travel is essential at this time until we have clear evidence that buried weak layers have stabilized. 

Confidence

Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

Thursday night: Clear skies, moderate southwest wind, freezing level valley bottom.

Friday: Sun and cloud, light southwest wind, alpine temperature -6 C, freezing level valley bottom.

Saturday: Sun and cloud, moderate southwest wind, alpine temperature -4 C, freezing level 1000 m.

Sunday: 10-20 cm new snow, strong southwest wind, alpine temperature -1 C, freezing level 1800 m.

Avalanche Summary

Many storm and persistent slab avalanches have been observed this week across the region. They were generally large (size 2), on west, north, and east aspects, 20 to 70 cm thick, and between 2000 and 2300 m. The likelihood of triggering the layers described in the snowpack summary remains.

Snowpack Summary

A hefty storm impacted the region Monday, with around 30 to 40 cm of snow accumulation. Strong wind accompanied the storm, blowing from variable directions. Expect to find storm and wind slabs across the region until they bond to the snowpack. 

This snow is loading two weak layers around 50 to 100 cm deep. The layers are composed of feathery surface hoar and sugary faceted grains and they overly a hard melt-freeze crust. There has already been substantial avalanche activity on this layer from natural and human triggers. This layer remains a major concern, as humans may be able to trigger large and destructive avalanches on it. There has been less avalanche activity reported west of Castlegar but a similar snowpack exists so the possibility remains.

Another crust with associated faceted grains may be found near the base of the snowpack. There haven't been recent avalanches reported on this layer but it remains on our radar. The most likely place to trigger it would be from shallow, rocky terrain. 

Terrain and Travel

  • Make conservative terrain choices and avoid overhead hazard.
  • Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
  • Give the new snow time to settle and stabilize before pushing into bigger terrain.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.

Problems

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.

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.