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Avalanche Forecast

Archived

Feb 21st, 2020–Feb 22nd, 2020

Alpine
Natural avalanches unlikely, human triggered possible.
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, 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.

New wind slabs are likely forming up high. Use added caution on steep slopes in open trees as a slab of snow may rest on surface hoar, particularly in the eastern part of the region.

Confidence

High -

Weather Forecast

FRIDAY NIGHT: Increasing clouds, moderate to strong southwest wind, alpine temperature -5 C.

SATURDAY: Mix of sun and cloud with isolated flurries, accumulation 1 to 3 cm, moderate west wind, alpine temperature -5 C, freezing level 1300 m.

SUNDAY: Cloudy with snowfall, accumulation 5 to 10 cm, moderate southwest wind, alpine temperature -6 C, freezing level 900 m.

MONDAY: Morning snowfall and afternoon clearing, accumulation 2 to 5 cm, light to moderate northwest wind, alpine temperature -7 C, freezing level 1000 m.

Avalanche Summary

A few slab avalanches were triggered by skiers on Thursday. They were both on northerly aspects. One of them was a wind loaded feature and the other was suspected to have failed on the weak layer described in the snowpack summary, with a slab depth of about 30 cm.

Snowpack Summary

A dusting of snow is forecast for Saturday, along with strong southwest wind. New wind slabs are likely to form in lee terrain features. The new snow will accumulate onto a widespread layer of feathery surface hoar crystals or a melt-freeze crust on southerly aspects.

A 20 to 30 cm thick slab has been reactive to human traffic since last weekend, where the snow overlies a weak layer of surface hoar. The slab has been most reactive in open trees in the eastern part of the region.

The remainder of the snowpack is well-settled.

Terrain and Travel

  • Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.

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.