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Avalanche Forecast

Archived

Jan 5th, 2020–Jan 6th, 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 and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
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 possible, human triggered probable.

Regions

Kootenay Boundary.

Recent strong wind has formed wind slabs. Don't discount the multiple buried weak layers in the snowpack.

Confidence

High -

Weather Forecast

SUNDAY NIGHT: Partly cloudy with isolated flurries, local amounts 2 to 5 cm, moderate northwest wind, alpine temperature -10 C, freezing level below valley bottom.

MONDAY: Mix of sun and cloud with afternoon snowfall, accumulation 2 to 10 cm, light to moderate west wind, alpine temperature -8 C, freezing level 500 m.

TUESDAY: Cloudy with snowfall, accumulation 15 to 25 cm, moderate to strong southwest wind, alpine temperature -3 C, freezing level 1100 m.

WEDNESDAY: Morning snowfall and afternoon clearing, accumulation 10 to 15 cm, light northwest wind, alpine temperature -6 C, freezing level 1000 m.

Avalanche Summary

Numerous small to large storm and wind slab avalanches were triggered naturally, by humans, and by explosives on Saturday. They were generally on northwest to northeast aspects and at treeline and alpine elevations. The slabs were most commonly 10 to 20 cm thick.

Snowpack Summary

Around 40 to 60 cm of recent storm snow has been redistributed by strong westerly wind, forming wind slabs in lee terrain features. The slabs may overly a thin layer of ice formed early January.

There are multiple weak layers buried in the snowpack. A weak layer of feathery surface hoar is buried around 30 to 50 cm. Around 80 to 120 cm deep, two more surface hoar layers may be found. Near the bottom of the snowpack, weak faceted snow may be found. This fundamentally unstable snowpack structure remains a concern, as it is capable of producing large and destructive avalanches. It is possible that wind slab avalanches could step down to these deeper layers or the layers could be triggered in areas where the snowpack is relatively thin.

Terrain and Travel

  • Make conservative terrain choices and avoid overhead hazard.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.

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.