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Avalanche Forecast

Archived

Feb 17th, 2023–Feb 18th, 2023

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural and human triggered avalanches likely.
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.

There has been continued natural, explosive and human-triggered avalanches, with many starting or stepping down to the deep persistent layer. Continued inputs of snow and/or wind this weekend will keep the hazard elevated.

Confidence

Moderate

Avalanche Summary

A flight in the Northern part of the park Friday saw continued natural activity over the past 24 hours. Mainly wind slabs with some stepping down to persistent or deep persistent layers. Lake Louise observed a natural size 2.5 on "Speed run", and a natural size 3 in Richardson's bowl. Both initiated on the basal facets. As well, lots of recent explosive triggered and natural avalanches.

A size 2.5 deep persistent natural avalanche at Quartz ridge was triggered by a cornice on Thursday. There was also a MIN report of a skier remote triggering a size 2.5 avalanche in the Healy Creek area on Wednesday from 100m away showing continued reactivity to a skier's weight.

Snowpack Summary

5-20cm over the last 24 hours (average 10cm). New and previous wind slabs have formed from strong winds over the past week. These slabs overlie several persistent weak layers that exist 30-60cm below the surface. These weak layers are a combination of crusts, facets and surface hoar formed and buried in January and are producing sudden test results. Deeper in the snowpack, the November crust/facet layer ~40 cm above the ground also continues to produce sudden test results.

Weather Summary

Saturday: 5cm with decreasing West winds 40-60km/h to NW 20-30km/h in the afternoon. Freezing levels 1300-1500m and alpine temperatures -10C to -15C.

Sunday: Strong winds return as another system arrives with 10-20cm in the forecast. Freezing levels 1600-1800m and alpine temperatures -5C to -10C.

More details can be found in the Mountain Weather Forecast.

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

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.