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Avalanche Forecast

Archived

Mar 19th, 2023–Mar 20th, 2023

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.
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.

Following a week full of avalanche activity and incremental warming through the weekend with strong solar inputs, cloudy skies and cooling will limit the potential for natural avalanche activity into the start of the week.

Human triggering of the lingering persistent and deep persistent layers remains a concern.

Confidence

Moderate

Avalanche Summary

Since the latest storm, we have seen avalanches almost every day failing on the deep persistent layers.

See the other bulletin for the region for Saturday's avalanche control results in Yoho NP.

Friday avalanche control on Mt Whymper produced avalanches with every shot: Small slab results were observed with the March 12 Persistent Layer. Large slabs to sz 3 were observed on the Deep Persistent Layer, several of which initiated directly to the base of the snowpack. Finally, several pockets: slabs to sz 2 in themselves, were sympathetically triggered by other avalanches in motion on SW facing features. These were initiating on the January Persistent Layer of crusts.

Snowpack Summary

10-20 cm of snow buries a layer of surface hoar, facets and sun crust (March 12). Suncrusts are forming on steep solar slopes in the alpine and are more widespread below.

The midpack comprises various Jan crust layers that are now down 40-110 cm.

The weak Nov. 16 basal facet layer is down 50-130 cm producing sudden results in snowpack tests.

Weather Summary

A trough will bring cloudy skies, cooler temperatures and some light snow accumulations through Tuesday.

Monday, freezing levels around 1800m winds will be light.

Tuesday, freezing level will stay near valley bottom.

Terrain and Travel Advice

  • Uncertainty is best managed through conservative terrain choices at this time.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

Problems

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.

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.