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Avalanche Forecast

Archived

Feb 28th, 2023–Mar 1st, 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 unlikely, human triggered possible.
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.

Human-triggered wind slabs are still possible. Use caution in lee areas.

Confidence

Moderate

Avalanche Summary

Lake Louise patrol produced several size 1 wind slabs with explosives today, mostly in the alpine. They also cleaned out D-Gully with a hand charge that produced a size 2, which ran on the ground. This feature hand previously avalanched and reloaded. Sunshine patrol remotely triggered a size 2 deep slab in the Wild West that was 80m wide and 60cm deep.

Snowpack Summary

Widespread wind slabs are present in the alpine and treeline due to last week's storm snow and wind event. The wind slabs overlie the various Jan PWL interfaces of sun crusts, facets, and surface hoar down 80-120 cm. The weaker Nov 16 basal facet layer is down 100-200cm, and produces mod-hard sudden collapse results. Deeper snowpack areas west of the divide are stronger and more supportive than areas to the east.

Weather Summary

Cool temps for the next few days will show the valley not being warmer than -2 and the ridge about -15. Wind will pick up into the strong range from the SW Wednesday morning and will stay elevated through Friday. Snow beginning late on Wednesday will amount to about 10cm late on Thursday.

Terrain and Travel Advice

  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger 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.