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Avalanche Forecast

Archived

Jan 20th, 2020–Jan 21st, 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 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, human triggered possible.

Regions

Banff Yoho Kootenay.

A continued cautious approach to terrain is a good idea. We still have lots of uncertainty about how the snowpack will react in steep terrain due to the deep weak layers in the snowpack. Be patient!

Weather Forecast

Temperatures will start to gradually cool on Tuesday though valley bottoms may reach the freezing mark. Winds will drop into the light to moderate range out of the West and a few flurries are expected to start in the afternoon. Wednesday and Thursday continue to cool and will see flurries continue through the day.

Snowpack Summary

Warming temperatures and moderate to strong Southerly winds continue to build wind slabs in the alpine and at ridge tops at tree line. There is 40-60 cm above the Dec 31 layer of facets, surface hoar and sun crust which is slowly becoming less reactive. Concern remains for the weak layers of facets and depth hoar near the base of the snowpack.

Avalanche Summary

A few new natural avalanches observed on Monday up to size 2.5 from wind loading including one cornice failure on Crowfoot Peak. On Sunday a skier triggered a size 2.5, 200 m wide on Lipalian Mountain (near Lake Louise). The slab stepped down through multiple layers eventually releasing on the basal facets.

Confidence

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.