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Avalanche Forecast

Archived

Dec 5th, 2024–Dec 6th, 2024

Alpine
Natural avalanches unlikely, human triggered possible.
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.

One more day of clear skies and warm temperatures on Friday, with freezing levels up to 1900 m triggering loose wet avalanches into gullies. Ice climbers avoid south-facing terrain. Conditions change starting Friday night with extreme winds, then a storm day on Saturday with snow and rain throughout the day.

Confidence

Moderate

Avalanche Summary

Observations from across the park on Thursday of avalanches up to size 2 releasing on sunny exposures, both in the ski areas and backcountry. The common theme is moist snow releasing a small slab, then gouging down to facets and running further than expected. Lake Louise got one explosive-triggered avalanche in a steep N aspect, failing on the Nov 9 layer 40 cm above the ground.

Snowpack Summary

Two warm and clear days have left the snow surface a mix of wet snow, suncrust, wind crust and facets. This overlies a mostly faceted snowpack 40-90 cm deep with two weak layers near the base (Oct 20 and Nov 9 crusts). These crusts continue to produce isolated avalanches. No new snow is expected on Friday, but by Saturday expect new snow and wind to create easily triggered surface slabs, some may fail on the ground.

Weather Summary

Some active weather is coming our way as a warm Atmospheric River comes onto the coast of BC and spills over into Alberta starting Friday night and all day on Saturday. Expect extreme winds (>100 km/hr) on Friday night, rain and snow through Saturday and freezing levels to 1900 m, then clearing and cooling on Sunday as the system exits the region.

Terrain and Travel Advice

  • Rocks will heat up with daytime warming and may become trigger points for loose wet avalanches.
  • Pay attention to the wind; once it starts to blow, sensitive wind slabs are likely to form.
  • Be mindful that deep instabilities are still present in the snowpack.

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.