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Avalanche Forecast

Archived

Jan 9th, 2020–Jan 10th, 2020

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

Regions

Banff Yoho Kootenay.

Problems within the snowpack are complex and likely will persist for some time. There is great skiing, but now is the time for conservative decision making.

Weather Forecast

A frontal system from BC will push into Alberta on Friday bringing light snow along the Divide (5-10 cm).  Temperatures will remain cool with day time highs only rising to -11 in Lake Louise. On Sunday a ridge of cold arctic air will descend bringing a significantly colder air mass to the area.

Snowpack Summary

30-50 cm of storm snow since Jan 1 sits over a variety of surfaces including facets and surface hoar. Field tests throughout the region show easy to moderate results on this interface. Reactive wind slabs exist in alpine and some treeline locations. In most areas there is a well settled mid-pack over top of a weaker basal layer.

Avalanche Summary

Field trip to Bow Summit showed evidence of a wide-spread cycle up to size 3 on all aspects tree-line and above from past 48-72 hours. A size 3 natural on Thursday was observed on the east face of Bow Peak. There were also reports of large naturals in the Sunshine area (above Bourgeau Right ice climb) and on Mt Rundle.

Confidence

Problems

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.

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.