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Avalanche Forecast

Archived

Dec 30th, 2021–Dec 31st, 2021

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

Regions

Banff Yoho Kootenay.

Another bitterly cold, clear, calm day on Friday before winds pick up for the weekend. The moderate rating at treeline and below is due steep, unsupported terrain where the Dec. 2 crust and facets may be triggered.

Weather Forecast

Expect temperatures Friday AM to be around -30C with clear skies and light winds. On Saturday winds will really pick up midday and last for the weekend with some warming temperatures. Temperatures and winds drop again for next week.

Snowpack Summary

10-40 cm of snow last week and recent wind from various directions has developed wind slabs in the alpine. There is 50-70 cm over the Dec. 2 crust/facet combo which exists below 2200m, which we are monitoring closely. Shallow areas (<100 cm) have weaker basal facets.

Avalanche Summary

There was a skier triggered size 2 avalanche below treeline in Kootenay today. This may have been on the Dec. 2nd crust/facets. Sunshine ski hill saw a natural wind slab avalanche (size 2) possibly triggered by a cornice. Lake Louise triggered a few size 1.5 and a 2 with explosives that were new wind slabs from winds Wednesday night.

Confidence

Due to the number and quality of field observations on Thursday

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.