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Avalanche Forecast

Archived

Feb 8th, 2023–Feb 9th, 2023

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

Regions

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

An avalanche cycle is underway, evidenced by today's avalanche control results and observations of natural avalanches. Avalanche control is planned for Thursday, February 9 on Hwy 93S (Mt Whymper, Vermillion Peak & Simpson) so no access to these areas on Thursday. We expect this current peak in avalanche danger to last for a few days while the snowpack adjusts. Human triggering is likely avalanche starting zones.

Confidence

High

Avalanche Summary

Lots of avalanches were observed today, both natural and explosive triggered. Field teams observed widespread activity up to size 3 on the Icefields Parkway with propagations up to 300 meters. Avalanche control on the Sunshine road produced excellent results up to size 3 and the Emerald Lake Slide path has a size 2 near the summit.

Snowpack Summary

Regional snowfall totals since Feb 1: Bow Summit 43 cm, Bosworth 37 cm, Sunshine 34 cm, Simpson 31 cm, Stanley 22 cm.

Strong winds have moved this new snow into widespread, reactive windslabs at higher elevations, confirmed by today's avalanche control. Two crusts are buried within the upper snowpack and the November facets remain near the base. These buried weak layers are now producing avalanches, including a wake-up of the November facets. Minimal reactivity has been observed below treeline.

Weather Summary

After a short clearing on Wednesday, another system crosses the area starting Thursday afternoon and evening. This next system brings only 5 cm of snow, but with 50-60 km/hr winds and temperatures remaining in the -5 to -10 range for alpine areas. Longer term, the systems keep coming, but no significant snowfall amounts are predicted for the next week.

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.

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.

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.