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Avalanche Forecast

Archived

Feb 26th, 2025–Feb 27th, 2025

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

The snowpack is slowly adjusting, but human triggering remains a risk. The strong to extreme wind and warm temperatures forecast for Thursday will add to the slab development.

Confidence

Moderate

Avalanche Summary

On Thursday, helicopter avalanche control on Mt. Field, Stephen, and Dennis produced slab avalanches up to size 3. Any spot that looked like it could avalanche, did. Many avalanches triggered slabs from the side walls of the path.

On Wednesday, a skier triggered a size 1.5 avalanche in Lipalian 3, just outside the Lake Louise ski area boundary. One skier was carried 60 m but remained on the surface, uninjured. Sunshine patrol triggered a size 2 deep slab with explosives.

Snowpack Summary

10-30 cm of storm snow has fallen with mild temps and recent strong S-SW winds helping to form wind and persistent slabs. This snow sits over a layer of weak facets, surface hoar or sun crust from the cold snap.

The mid-pack is generally weak facets, while depth hoar and crusts form an even weaker base. The snowpack is the weakest in eastern areas where snow depths are low. In these areas, the basal weaknesses should be carefully considered.

Weather Summary

For Thursday - Friday, flurries with showers at lower elevations are forecast. Freezing levels are 1900 m on Thursday and 2200 m on Friday. Only trace accumulations are expected in the region. Winds will be strong to extreme on Thursday from the west.

Terrain and Travel Advice

  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and slopes above cliffs.

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.