Avalanche Forecast

Archived

Feb 21st, 2023–Feb 22nd, 2023

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural avalanches possible, human triggered probable.

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 possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Kananaskis, Bow Valley, Highwood Pass, North 40, Spray - KLakes.

Natural avalanches are possible and if the deep persistent layer is released, expect large destructive avalanches.

Travel in avalanche terrain is not recommended.

Road closure(highway 742) due to avalanche control on Mt. Rundle(Canmore Hill) at 1pm on Wednesday Feb 22.

Confidence

Moderate

Avalanche Summary

The field team went to Burstall Pass today and had poor visibility all day and saw one size 1.5 avalanche on a SE aspect. We are likely going through a natural avalanche cycle.

Snowpack Summary

This latest storm has left us with 40-50cm of snow. This is the first large input on the snowpack since December; this is likely to wake up the deep persistent (November facet) layer somewhere. During the storm, the winds shifted from West to East, so expect to find wind slabs on all aspects at tree line/alpine, and some thinner slabs in open areas below tree line. These East winds are suppose to continue in the 30km/hr range until Thursday morning, so expect continued wind slab formation. At tree line and below, this new snow mostly sits on top of a faceted snowpack. In the alpine, the new snow and wind slabs sits on top of a strong mid-pack where it was previously deep and on top of facets where it was not so deep. In either case, the November facets(deep persistent problem) is a big concern to create large avalanches that could go to ground.

Weather Summary

The storm has passed and the Arctic air has settled in. Wednesday will bring mostly cloudy skies with light flurries in the morning. Temperatures at tree line will be between -25c and -30c for the day. Winds will continue to be from the East at 30km/hr.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
Be aware of the potential for surprisingly large avalanches due to deeply buried weak layers.
Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

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.