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Avalanche Forecast

Archived

Feb 25th, 2023–Feb 26th, 2023

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
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, Little Yoho, Banff, East Side 93N, Kootenay, Lake Louise, LLSA, Sunshine, West Side 93N, Field.

Wind transport, new snow, and deeper buried weak layers will keep the avalanche hazard elevated on Sunday.

Conservative terrain choices with minimal overhead hazard are recommended until the winds diminish and the snowpack adjusts to the recent loading.

Confidence

Moderate

Avalanche Summary

Natural avalanche activity slowed slightly on Saturday, but numerous natural wind slabs, persistent slabs and deep persistent slabs up to size 3+ have been observed over the past several days. Ski hills also continue to trigger wind slabs with explosives and ski cutting, with some avalanches stepping down to the deeper layers in the snowpack.

Snowpack Summary

20-50 cm of recent storm snow is now faceting and being redistributed by strong SW winds at alpine and treeline elevations. Wind effect and new wind slabs exist on most aspects above treeline. These windslabs overlie the various Jan PWL interfaces of sun crusts, facets and surface hoar down 70-110 cm. The weaker Nov 16 basal facet layer is down 100-180 cm and still produces mod-hard sudden collapse test results. Deeper snowpack areas west of the divide have a stronger and more supportive lower snowpack than areas to the east.

Weather Summary

Sunday will see light snow flurries for most of the region with a few cm's of new snow in eastern regions and perhaps as much as 5 to 10 cm in areas along the divide. Ridgetop winds remain in the moderate to strong range out of the SW. Alpine temperatures are expected to be between -10 to -15°C.

Terrain and Travel Advice

  • Make conservative terrain choices and avoid overhead hazard.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Cornice failure may trigger 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.

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.