Avalanche Forecast

Archived

Dec 17th, 2022–Dec 18th, 2022

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches possible, human triggered probable.

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.

Recent new snow and wind combined with the weak basal facets are keeping the avalanche hazard elevated this weekend.

A deep freeze has arrived with treeline temperatures staying in the -20 to -30°C range. Be prepared for the unexpected with extra warm clothing!

Confidence

Moderate

Avalanche Summary

Over the past few days, local ski hills have triggered deep persistent slabs up to size 2 with explosives, and sometimes with a ski cut after the explosive failed to trigger the slope. Parks Canada forecasters noted large whumpfs in the Sunshine Backcountry on Tuesday and in the O'Hara region on Thursday. No new naturals have been observed for the past few days.

Snowpack Summary

5-15 cm of new low density snow sits over a layer of recent surface hoar, with NW winds forming small new wind slabs in lee areas of the alpine. The upper 20-60 cm of snow has formed a soft slab over the very weak base of facets and depth hoar. Snowpack depths at treeline range between 60 and 120 cm. Below treeline the entire snowpack is weak and faceted and dry loose sluffs may be triggered in steep features.

Weather Summary

A surface ridge of high pressure will continue to build on Sunday with a few flurries expected in the moring as the ridge establishes itself. Winds will be light and temperatures will reamin COLD with alpine highs of -25 to -30°C.

Terrain and Travel Advice

Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
Uncertainty is best managed through conservative terrain choices at this time.

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.

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.

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.