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Avalanche Forecast

Archived

Dec 27th, 2020–Dec 28th, 2020

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

Regions

Kootenay Boundary.

Watch out for lingering wind slabs which may remain sensitive to human triggers. Be mindful that buried weak layers are still present and are best managed through conservative terrain selection.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

Sunday night: Partly cloudy, light southwest wind, freezing level valley bottom.

Monday: Sunny, light northwest wind, alpine temperature -7 C, freezing level valley bottom.

Tuesday: Increasing cloud, light northwest wind, alpine temperature -7 C, freezing level valley bottom.

Wednesday: Cloudy, light to moderate southwest wind, alpine temperature -6 C, freezing level valley bottom.

Avalanche Summary

A couple of skier triggered size 1 avalanches were reported over the weekend, a wind loaded pocket below a roll-over (here) and isolated loose dry sluffs in the new snow.

Many storm and persistent slab avalanches were observed last 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. Although avalanche activity is becoming smaller and more sporadic, the potential to trigger buried weak layers remains.

Snowpack Summary

5-15 cm of recent snow sits over surface hoar in wind sheltered areas. Lingering wind slabs formed last week may remain reactive on a variety of aspects due to shifting winds.

Two weak layers are buried in close proximity to one another, around 50 to 80 cm deep. The layers are composed of feathery surface hoar and sugary faceted grains and they overly a hard melt-freeze crust. Last week saw substantial avalanche activity on these layers from natural and human triggers. Although reports of such avalanches have been dwindling, these weak layers remain a concern, as they can produce large and destructive avalanches.

Terrain and Travel

  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Uncertainty is best managed through conservative terrain choices at this time.

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.