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Avalanche Forecast

Archived

Dec 18th, 2024–Dec 19th, 2024

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.
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.

Avalanche control on Mt. Stephen is planned for Thursday, December 19; all climbing routes here are closed.

Up to 20cm of storm snow, rising temps and strong SW winds have combined to produce windslab avalanches and a mini avalanche cycle that peaked on Wednesday. Watch for winds continuing to transport snow in the wake of this storm.

Confidence

Moderate

Avalanche Summary

Avalanches were reported at both ski areas (Sunshine and Lake Louise) today, mostly size 1 but several size 2 windslabs at Sunshine, both natural and explosive triggered. Loose snow avalanches were reported on Mt Stephen, running through steep terrain and over the ice climbs.

Snowpack Summary

10-20 cm of storm snow has fallen across the region over the past 36 hours, accompanied by rising temperatures and strong winds - this is the recipe for windslab formation in many open areas. This additional weight will likely overload weak layers at the base of the snowpack, resulting in larger avalanches running on the ground. Avoid all steep, windswept alpine terrain for the next 24 hours as the storm snow settles.

Weather Summary

Wednesday night: The storm is over, clearing overnight with isolated flurries and winds continuing moderate SW.

Thursday: There will be sun and clouds, with some overcast skies and isolated flurries. No significant accumulations are expected. The temperature will range from -5 to -10, and winds will decrease.

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.

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.