Avalanche Forecast

Archived

Dec 23rd, 2024–Dec 24th, 2024

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Banff Yoho Kootenay, Little Yoho, Banff, East Side 93N, Kootenay, Lake Louise, LLSA, Sunshine, West Side 93N, Field.

While the avalanche hazard is slowly dropping, human triggering remains possible.

The recent snow has helped the ski quality, but strong alpine winds have created new wind slabs in lee areas. The primary concern is the threat of superficial slabs stepping down to the deep persistent weakness resulting in full-depth avalanches.

Confidence

Moderate

Avalanche Summary

The ski hills continue be able to trigger deep persistent slabs with explosives up to size 2, failing on the basal facets/crust. One was on a relatively low angle slope of 30-34°. They have also used explosives or ski cutting to trigger small windslabs in steep lee areas but these are becoming stubborn.

Natural avalanche activity has slowed down in the past couple days with a couple of wind triggered avalanches in steep lee alpine terrain on Sunday and no new reports on Monday.

Snowpack Summary

Thin sun crust on steep solar aspects. 15-20 cm of storm snow from the past week combined with strong W/SW winds, has formed wind slabs in alpine lee areas and down into treeline.

The mid and lower snowpack is faceted and weak, with facet/crust interfaces near the ground. This is more pronounced east of the divide, while western regions display a deeper snowpack with fewer facets.

Snowpack depths at tree-line are about 60 cm in eastern areas and 100 cm west of the divide.

Weather Summary

SW ridgetop winds will increase by Tuesday morning and slowly drop into Wednesday. Like the events over the last weekend, this system remains relatively dry and only a few cm of snow is forecast Tuesday into Wednesday. A mix of sun and cloud on Tuesday with more cloud to the west, and treeline temperatures between -4°C and -7°C.

Terrain and Travel Advice

Avoid freshly wind-loaded features, especially near ridge crests, rollovers, and in steep terrain.
If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
Avoid thin areas like rocky outcrops where you're most likely to trigger avalanches on deep weak layers.

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.