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Avalanche Forecast

Archived

Dec 3rd, 2022–Dec 4th, 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.

Users should be cautious around steeper terrain with significant wind effect. There are fresh wind slabs and facet/crust layers near the base of the snowpack that have produced numerous avalanches over the past few days.

Confidence

Moderate

Avalanche Summary

A flight in the Lake Louise group saw a few smaller wind or persistent slabs failing within the last 24 hours. One size 2 on Mt. St. Piran appeared to initiate as a wind slab then step down to the persistent facets at the base. There was a natural size 1.5 observed above Bourgeau Left ice climb which didn't go over the climb. Lake Louise went on a heli bombing mission and got a bunch of size 2's and smaller. They were a mix of new wind slabs and persistent slabs going to ground on the facets.

Snowpack Summary

Wind effect and wind slab development due to variable winds. 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

Mostly clear skies Saturday night with ridgetop temperatures in the -15C to -20C range and moderate NW winds. Sunday will see winds shift to the E/NE with trace amounts of snow along the Eastern slopes. Winds will be 30-40kmh in the AM, weakening to 10-20kmh in the afternoon. Alpine temperatures will warm up to -5C to -10C.

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.
  • Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.

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.