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Avalanche Forecast

Archived

Dec 9th, 2024–Dec 10th, 2024

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

New snow has refreshed the skiing but also created a new layer of concern. We expect this to be most reactive in alpine/ treeline terrain where the wind has created a slab above it, so heads up if you are seeking out this terrain!

Confidence

Moderate

Avalanche Summary

Clear skies today revealed more evidence of a natural avalanche cycle over the last few days:

  • A team in Field area reported several slabs on below treeline fans near the ice climbs of Twisted and Guinness Gully

  • A team in the Sunshine backcountry reported 2 size 2 slabs on steep north facing alpine/ treeline terrain. These were likely triggered by sluffing/ cornices and stepped down to the basal layers

  • A size 2 was also observed on an alpine S aspect failing above the ground

Snowpack Summary

20-30 cm of recent snow has been blown by S/SW winds into windslabs in exposed alpine and treeline locations. In sheltered areas, non-wind effected snow sits on a layer of facets, suncrust and isolated surface hoar that was buried on Dec. 7th. Below this is a weak and facetted, early season midpack with two crust/facet layers near the bottom of the snowpack (Nov. 9th and Oct. 20th interfaces). Total snowpack depths at treeline are 50-80 cm.

Weather Summary

A ridge of high pressure sits over the area bringing cooler air and stable weather for a few days. Skies should be mostly clear with few clouds, light NW winds and high temperatures of ~ -5 to -10. Another system offshore may bring some light precipitation starting Wednesday evening or Thursday.

Terrain and Travel Advice

  • Be careful with wind-loaded pockets, especially near ridge crests and rollovers.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger 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.

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.