Avalanche Forecast

Archived

Apr 22nd, 2023–Apr 23rd, 2023

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Below Threshold.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Below Threshold.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Below Threshold.

Regions

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

Despite the slow down in natural activity, the deep persistent slab problem remains a serious concern for human triggering. Avoiding steep terrain, especially in shallow snowpack areas, is the only way to manage this reality.

A warm up over the next two days may make these slabs more sensitive.

Confidence

Moderate

Avalanche Summary

A group of skiers triggered a size 2.5 in the West Bowl at the Lake Louise ski area today (which has been closed all season). This was 550m long, 200m wide, and 40- 50cm deep. This avalanche failed on the ground and cleared all snow off of the slope until it came to rest at the deposit. One skier was almost completely buried while a second was fully buried and did not survive.

Snowpack Summary

Almost daily accumulations of new snow are competing with new sun crust formation on solar aspects with multiple buried crusts present in the upper snowpack. On northerly aspects, up to 40cm of recent snow remains preserved with buried temperature crusts as high 2200m. The basal snowpack remains weak with facets and depth hoar.

Weather Summary

A cold front approaches the region Sunday afternoon. 2-5mm of rain below 2000m with freezing levels rising to 2100- 2400m. Winds will increase to 30 to 40km/hr SW.

Overnight freezing levels only drop to around 1700m with overcast skies as winds will decrease to 20-30km/h. This will lead to less crust recovery than has been seen for several days.

Terrain and Travel Advice

Avalanche hazard may have improved, but be mindful that deep instabilities are still present.
Cornice failures could trigger very large and destructive avalanches.
Storm slabs in motion may step down to deeper layers resulting in large avalanches.

Problems

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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.