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Avalanche Forecast

Archived

Jan 25th, 2020–Jan 26th, 2020

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

Regions

Banff Yoho Kootenay.

Forecasters have low confidence in the snowpack. There is lots of good skiing and climbing but picking low consequence terrain is the only way to manage the deeper layers as they are hard to predict. Large (size 3) avalanches are still possible.

Weather Forecast

A mix of sun and cloud with some light afternoon flurries developing on Sunday.  Freezing levels will be 1400m in the PM and alpine temperatures around -7.  There could be a slight temperature inversion with cooler temperatures down low than up high.  Alpine winds will be in the moderate range from the SW with strong gusts in some areas. 

Snowpack Summary

Recent wind slabs can be found near ridge-tops. There is 40-60 cm above the Dec 31 layer of facets, surface hoar and sun crust which is slowly becoming less reactive. The bottom layer of the snow-pack consists of weak facets and depth hoar, except for deeper snow-pack areas (over 2m) which have basal facets but not as prevalent.

Avalanche Summary

A large natural avalanche over Cascade waterfall occurred yesterday which went on the basal facets/depth hoar, possibly triggered by warm temperatures and solar input. One other size 2.5 cornice triggered wind slab stepping down to the persistent layer was observed in the last 24 hours.  This was a SE aspect in the Sunshine backcountry.

Confidence

Freezing levels are uncertain on Sunday

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.

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.

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.