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Avalanche Forecast

Archived

Dec 28th, 2024–Dec 29th, 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.

Avalanche control is scheduled for Mt Stephen Sunday. Access to this area will be closed for the day.

Our primary avalanche concern is that superficial slabs could step down to the deep, persistent weakness resulting in full-depth avalanches.

The thinner and rockier the terrain, the higher probability of triggering an avalanche.

Confidence

Low

Avalanche Summary

There have been several reports of cornices failing over the last few days at Sunshine, Hwy 93N and Sherbrooke Lake.

Friday, ski hills reported some explosive-triggered avalanches to size 2, and a few involved wind slabs that stepped down to deeper layers.

Observations from Thursday reported natural and skier-triggered avalanches near Lake O'Hara and Bow Summit.

Snowpack Summary

15-30 cm of storm snow from the past week, combined with strong W/SW winds, has aging 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

Saturday night: Cloudy with clear periods and isolated flurries. Alpine temperature: Low -12 °C. Ridge wind southwest: 15 km/h.

Sunday: Cloudy with sunny periods and isolated flurries. Alpine temperature: High -12 °C. Light ridge wind.

Monday: Cloudy with sunny periods and isolated flurries. Alpine temperature: Low -16 °C, High -13 °C. Ridge wind west: 10 km/h.

Terrain and Travel Advice

  • Avoid thin areas like rocky outcrops where you're most likely to trigger avalanches on deep weak layers.
  • Avoid freshly wind-loaded features, especially near ridge crests, rollovers, and in steep terrain.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

Problems

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.

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.