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Avalanche Forecast

Archived

Feb 21st, 2023–Feb 22nd, 2023

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
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

Kootenay.

Avalanche control will occur in the Simpson and Wardle zones on Wednesday, February 22. Access to these areas is closed.

A significant avalanche cycle is underway with large, destructive avalanches running full path observed every day this week. Overhead hazard is significant, so even travel below the treeline should avoid avalanche runout zones. With the onset of arctic air, we expect the natural activity to taper, but human triggering will remain almost certain on Wednesday.

Confidence

High

Avalanche Summary

Natural avalanches up to size 4 have been observed in the past 48 hours, including multiple size 3 and 3.5 avalanches in Kootenay and Yoho parks on Tuesday. Numa Peak, Mt. Dennis, Mt. Field, and Mt Burgess all had size 3 natural avalanches on Wednesday. We expect the natural avalanche cycle to taper with the onset of arctic air, but human triggering will remain almost certain for Wednesday.

Snowpack Summary

The five-day storm snow totals are Simpson 81cm, Sunshine 60cm, Stanley 38cm, Bosworth 69cm and Bow Summit 23cm. All of this fell accompanied by strong winds, creating an unstable snowpack across the region. Natural and explosive-triggered avalanches have been widespread, some running full path, with slab avalanches failing in the storm snow, crusts in the upper meter and deep avalanches on the ground. Natural activity should taper with the onset of cold temperatures, but human triggering remains almost certain.

Weather Summary

The storm has ended and an arctic air mass has arrived. Wednesday and Thursday will reach lows of -25 to -30 with light snow and gusty east winds. Not your typical bluebird cold snap - this one looks nasty with swirling winds and frigid temps. The good news is that it's short-lived as warmer air returns on 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.
  • Cornice failure may trigger large 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.