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Avalanche Forecast

Archived

Dec 24th, 2024–Dec 25th, 2024

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.

While the avalanche hazard is slowly dropping, human triggering remains possible. The primary concern is the threat of superficial slabs stepping down to the deep persistent weakness which could result in full-depth avalanches.

Confidence

Moderate

Avalanche Summary

Ski hill reported continued wind slab and cornice development. Explosive control triggered wind slabs up to size one. Sunshine reported one deep persistent explosive triggered avalanche in Delirium.

On Monday a large cornice failure on Ptarmigan Peak (SE aspect) triggered a 250 m wide windslab that scoured down into the basal facets. (See photo)

A skier triggered deep-persistent avalanche was reported from a shallow west facing aspect above Sherbrook Lake on Monday.

Snowpack Summary

15-20 cm of storm snow from the past week, combined with strong W/SW winds, has formed wind slabs in alpine lee areas which extend down into treeline.

The mid and lower snowpack is faceted and weak, with facet/crust interfaces near the ground. This is more pronounced east of the divide, while western regions display a deeper more settled snowpack.

Snowpack depths at tree-line are about 60 cm in eastern areas and 100 cm west of the divide.

Weather Summary

The forecast is for a mix of sun and cloud on Christmas Day followed by light flurries along the Continental Divide on Boxing Day. Ridgetop winds will be from the west/southwest in the moderate range with stronger gusts. Day-time high temperatures at treeline forecasted to be around -8.

Terrain and Travel Advice

  • Avoid freshly wind-loaded features, especially near ridge crests, rollovers, and in steep terrain.
  • Avoid thin areas like rocky outcrops where you're most likely to trigger avalanches on deep weak layers.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.