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Avalanche Forecast

Archived

Mar 11th, 2023–Mar 12th, 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 and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
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, Banff, East Side 93N, Kootenay, Lake Louise, LLSA, Sunshine, West Side 93N, Field.

Despite limited inputs that can be expected to influence the snowpack this weekend, the avalanche hazard remains elevated.

Forecasters have very little faith in the buried persistent weak layers given the amount of avalanche observed this past week - despite the relatively benign weather.

Choosing terrain with modest slope angles, of limited slope size, and with limited overhead hazard remains the best way to manage your exposure while travelling.

Watch for hazard ratings to rise Monday with a warm, wet Pacific flow incoming.

Confidence

Moderate

Avalanche Summary

We are still getting large settlements, or whumpfs, and occasional natural and skier triggered avalanches on the deeper weak layers in the snowpack.

A cornice triggered size 3 avalanche reported by Mt. Norquay ski hill occurred in the past 72hrs. Friday, the avalanche control team at Sunshine Village produced a sz 2 in steep terrain with explosives as well as a second sz 2 that was remote triggered by the same shot. On Saturday, SSV noticed a sz 2 cornice triggered east-facing slab in the surrounding alpine terrain.

Snowpack Summary

A sun crust is present on steep solar slopes at treeline and below while10-30 cm of soft snow can be found on northerly aspects. The various Jan PWL interfaces (sun crusts, facets, and surface hoar) are now down 40-80 cm. The weaker Nov. 16 basal facet layer is down 50-120 cm and continues to produce whumpfing and moderate to hard sudden collapse results in tests.

Weather Summary

Mainly cloudy skies with scattered flurries yielding 2-5cm of accumulation will persist overnight Saturday through Sunday with southwest winds in the light range and alpine temperatures warming a bit to between -10 and -15C.

Sunday evening snowfall will increase to bring 5cm overnight as winds increase to 40km/h and a strong Pacific flow of moisture begins.

10-20cm of snow is expected Monday with freezing levels approaching 2000m and winds increasing to beyond 50km/h.

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.