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Avalanche Forecast

Archived

Feb 24th, 2023–Feb 25th, 2023

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, Little Yoho, Banff, East Side 93N, Kootenay, Lake Louise, LLSA, Sunshine, West Side 93N, Field.

A return to gusty west winds Friday has generated fresh avalanche activity.

These winds, and the associated Pacific System approaching the region, will bring a slow, steady reprieve from the arctic temperatures... but will keep the avalanche hazard elevated through the weekend.

Confidence

Moderate

Avalanche Summary

With the increase in west winds Friday, fresh avalanche activity was evident in the Banff area.

Lake Louise avalanche control described triggering several small wind slabs with explosives including some hard slabs and thought there was evidence of fresh natural activity in the surrounding backcountry.

One notable avalanche at Bow Summit ran onto the standard traverse track Thursday. See MIN.

Snowpack Summary

Following last weekend's storm, a settled 20-50cm of snow has been redistributed by east, then north and now west winds. Expect extensive wind effect in the alpine and fresh wind slabs in some unusual locations down into the trees.

The upper snowpack been subject to the surface faceting process during the extended cold temperatures this week and is starting to sluff in very steep terrain.

On steep solar slopes, there are crusts in the middle of the snow pack now down 40 to 110cm while facets and isolated surface hoar will be found on these interfaces elsewhere.

The bottom 30- 50cm of the snowpack remains weak and faceted as is providing poor support for the entire snowpack above.

Weather Summary

A Pacific system began its approach Friday and was heralded by winds shifting back to the westerly and increasing to the moderate to strong range. Temperatures followed, however overnight alpine temperatures will still drop to -20 to -25C.

Cloud will develop into flurries Saturday with a few cm expected north of Lake Louise as temperatures rise to -10 to-15C in the alpine during the day.

Overnight Saturday, up to 5cm is expected along the divide as the system passes the region. Temperatures should hold in the -10 to -15C range in the alpine.

Terrain and Travel Advice

  • Make conservative terrain choices and avoid overhead hazard.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Cornice failure may trigger large avalanches.

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.