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Avalanche Forecast

Archived

Dec 30th, 2019–Dec 31st, 2019

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.

The avalanche hazard is increasing with the arrival of new snow and wind. We also have a lot of uncertainty about where the deep persistent layer might be triggered. As a result it is a good time to be patient and make conservative terrain choices.

Weather Forecast

A series of systems will reach the forecast region with light snowfall over each of the next few days. Amounts of about 5 cm each day are expected, though Western regions could see more. Winds will remain strong in the alpine for Tuesday and start to taper off on Wednesday. Treeline temperatures remain mild and steady between -10 and -5 'C.

Snowpack Summary

New snow and moderate to strong SW winds are creating new wind slabs in lee areas at and above treeline. In most areas the upper snowpack of denser snow sits over a weak mid and lower snowpack consisting of facets, depth hoar and crusts. In deeper snowpack areas these weaknesses are less pronounced. Snowpack depths at treeline average 100-160 cm.

Avalanche Summary

No new avalanches observed or reported on Monday. Reports of whumpfing, as well as explosive and skier triggered avalanches up to size 2 on the deep persistent layer of facets and depth hoar have occurred in the last several days, and we expect this layer to continue to be problem for a while. A few smaller wind slabs were also reported recently.

Confidence

Forecast snowfall amounts are uncertain

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.