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Avalanche Forecast

Archived

Feb 20th, 2023–Feb 21st, 2023

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

Snow and wind on Monday night will hold the danger rating at HIGH in the alpine and treeline, with several natural large avalanches observed running to the valley bottom in the past 24 hrs.

Minimize exposure to avalanche terrain until things improve!

Confidence

High

Avalanche Summary

Numerous natural avalanches up to size 4 were observed on Monday with debris reaching the bottom of the runout zones in some paths. Ski areas also triggered numerous avalanches with ski cutting and explosives. With additional weather inputs Monday night, forecasters expect the avalanche cycle to continue into Tuesday.

Snowpack Summary

15 to 50+ cm of snow over the past 72hrs with moderate to strong SW-W winds have created extensive wind effect in the alpine and contributed to wind slab development. Several persistent weak layers exist 40-80 cm below the surface. These weak layers include crusts, facets and surface hoar buried in January, producing sudden test results in some locations. Deeper in the snowpack, the November crust/facet layer is found about 40 cm above the ground and continues to produce sudden test results.

Weather Summary

An additional 10-20 cm of snow is expected Monday night and into Tuesday. The wind will drop to the light to moderate range and switch to a more easterly direction. Temperatures will also start dropping with alpine highs in the -16 to -24°C range as a cold arctic airmass arrives.

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

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.