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Avalanche Forecast

Archived

Dec 22nd, 2019–Dec 23rd, 2019

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
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 storm has quieted but avalanche conditions remain very dangerous. The recent snow will remain touchy and it is resting on a few weak layers. Read more about this concern here. Avoid alpine avalanche terrain and conservative decision-making is essential at and below treeline.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

SUNDAY NIGHT: Mostly cloudy with isolated flurries, accumulation 1 to 3 cm, light southwest wind, alpine temperature -3 C, freezing level 1400 m.

MONDAY: Cloudy with light snowfall, accumulation 2 to 5 cm, light southwest wind, alpine temperature -5 C, freezing level 1200 m.

TUESDAY: Mostly cloudy with isolated flurries, accumulation 1 to 3 cm, light southwest wind, alpine temperature -8 C, freezing level below valley bottom.

WEDNESDAY: Mix of sun and cloud, light north wind, alpine temperature -9 C, freezing level below valley bottom.

Avalanche Summary

A widespread avalanche cycle occurred on Saturday and potentially continued into Sunday. Many of the avalanches released within the storm snow, producing large avalanches on all aspects and generally above 2000 m. One avalanche was triggered by explosives on the late-November layer described in the Snowpack Summary. It is likely that more occurred on this layer as well, but were not observed due to limited visibility.

Snowpack Summary

The storm is calming down but has deposited around 60 to 90 cm of snow in the region, with strong west wind. This snow has loaded multiple weak layers, including:

  • a feathery surface hoar layer buried around 60 to 100 cm.
  • a surface hoar layer buried about 80 to 120 cm, with an associated melt-freeze crust on steep south aspects.
  • a complex layer of weak and sugary faceted snow, surface hoar, and melt-freeze crusts in the bottom half of the snowpack buried late November.

There is uncertainty on which of these layers will remain a problem after the storm. However, given the weak nature of these layers, it is prudent to expect that they could still produce large and destructive avalanches. 

Terrain and Travel

  • Travel in alpine terrain is not recommended.
  • Don't let the desire for deep powder pull you into high consequence terrain.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.

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.