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Avalanche Forecast

Archived

Feb 15th, 2023–Feb 16th, 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.

Dangerous avalanche conditions persist with continued evidence every day - on Thursday it was more avalanche control results where "every shot we got a slab" plus observations of large natural avalanches with long fracture propagations in the last 36 hours.

Confidence

High

Avalanche Summary

Observations of natural and explosive-triggered avalanches continued today during an avalanche control mission to the Icefields Parkway. In addition to recent naturals (last 36 hrs), every shot placement resulted in an avalanche, some up to size 3. Most are failing on a mid or lower snowpack persistent weak layer, with long propagations up to 600 m noted in the Cirque Peak area.

Snowpack Summary

Slab avalanches up to 60 cm deep were formed from last week's storm and extreme winds. These slabs overlie several persistent weak layers in the upper snowpack: crusts, facets and surface hoar formed and buried in January and are producing sudden test results. Deeper in the snowpack, the November crust/facet layer 40 cm above the ground also continues to produce sudden test results.

Weather Summary

A ridge of high pressure with a NW flow will keep the region mostly clear and cool until Thursday afternoon when clouds and flurries will begin. Expect the winds to come up on Thursday with the approach of the next system and potentially 5 cm by Friday.

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

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.

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.