Avalanche Forecast

Archived

Mar 6th, 2023–Mar 7th, 2023

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.

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

We continue to have skier triggered avalanches and large whumpfs on the deeper weak layers in the snowpack, especially in thin snowpack areas. Moderate terrain choices with minimal overhead hazard continue to be a good idea for dealing with a weak snowpack like this.

Confidence

Moderate

Avalanche Summary

We continue to see skier, natural and explosive triggered avalanches. A size 3 skier triggered avalanche was observed on an east aspect of Mt. Fairview failing on the basal facets, and a smaller skier triggered slab was observed on Lipalian on Sunday. Several naturals to size 2 were observed including cornice failures in the past 48 hrs, and explosive control at local ski areas produced slabs up to size 2.5 with some stepping down to the basal facets.

Snowpack Summary

Alpine and exposed treeline areas are wind effected with wind slabs that are slowly becoming less reactive. Steep solar slopes at treeline and below have a thin sun crust. The the various Jan PWL interfaces of sun crusts, facets, and surface hoar are now down 40-80 cm. The weaker Nov. 16 basal facet layer is down 50-120 cm and produces moderate to hard sudden collapse results in tests.

Weather Summary

A stable weather pattern continues with treeline highs of -8°C and overnight lows of -20°C. Winds will be calm to light from the W/SW. The skies will be mostly clear with some scattered clouds.

For a more detailed weather forecast, click here.

Terrain and Travel Advice

If triggered, wind slabs avalanches may step down to deeper layers resulting in larger 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.

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.

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.