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Avalanche Forecast

Archived

Dec 28th, 2020–Dec 29th, 2020

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 unlikely, human triggered possible.
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.

Keep the presence of a buried weak layer in your mind and continue to choose conservative terrain.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

Monday night: Mostly dry, light flurries possible. Winds light, northwesterly.

Tuesday: Dry during the day. Treeline temperatures around -9 C. Winds light northwesterly.

Wednesday: 2-5 cm new snow. Treeline temperatures around -8 C. Winds light southerly.

Thursday: 5-10 cm snow ending in the morning. Treeline temperatures around -5 C. Winds light southwesterly.

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 appears to have diminished, I wouldn't rule out the possibility of seeing more persistent slab avalanches.

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 aware of the potential for large avalanches due to the presence of buried persistent weak layers.
  • Uncertainty is best managed through conservative terrain choices at this time.

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.