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Avalanche Forecast

Archived

Dec 4th, 2022–Dec 5th, 2022

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

Regions

Banff Yoho Kootenay, Little Yoho, Banff, East Side 93N, Kootenay, Lake Louise, LLSA, Sunshine, West Side 93N, Field.

The recent wind has created wind slabs, particularly in the alpine. If triggered these slabs will entrain facets as they progress downslope. Approach steep terrain with caution.

Confidence

Moderate

Avalanche Summary

A size 1.5 wind slab was observed in the cliffs above Bow Summit. It is estimated to be between 24 and 48 hours old. Both Sunshine and Lake Louise ski patrol reported triggering hard wind slabs up to 1.5 with explosives.

Snowpack Summary

Wind effect and wind slab development due to variable winds in the past 36 hours. 20-40 cm of recent snow sits over a very weak layer of facets, surface hoar, or sun crust on steep south aspects. 40-80 cm of total snow exists at treeline throughout the region, with up to 120 cm in loaded alpine features.

Weather Summary

On Monday, the region will encounter cooling temperatures into the range of -5 in the valley and -20 at the ridge. Additionally, small amounts of precipitation (4cm) will be accompanied by an increase in the wind from the SW in the strong range.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • If triggered, loose dry avalanches may step down to deeper layers resulting in large avalanches.

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.