Avalanche Forecast

Archived

Dec 9th, 2023–Dec 10th, 2023

Alpine

Natural and human triggered avalanches likely.

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.

Regions

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

While the hills looked pretty for a few days following the storm: the SW winds returned with a vengeance bringing a natural avalanche cycle Saturday.

Avoid exposure to overhead avalanche terrain as large natural, and remotely triggered, avalanches are expected.

Freshly formed windslabs will be sensitive to human triggering.

Confidence

Moderate

Avalanche Summary

Natural avalanches to sz 2.5 were observed around Banff Saturday afternoon as huge plumes of wind transported snow streamed off of Mt Rundle and Cascade. The Urs Hole ice climb ran sz 2.5 and Bourgeau Right-hand ran twice at sz 2.

Highway avalanche control on Friday produced results to size 2.5 on Mt Bosworth. While helicopter avalanche control work at Lake Louise produced results up to sz 3, of which one was remotely triggered from 250m away.

Snowpack Summary

Last week's 60cm+ of storm snow fell on the Dec 2 weak layer (Surface Hoar, Facets, and Sun Crusts) which capped a weak snowpack featuring several weak faceted layers and a spotty crust and depth hoar layer against the ground. While there is some separation between these weaknesses in the alpine, at treeline and below they are essentially the same layer.

A rain crust exists buried 20-40 cm at lower elevations.

80-100 cm at treeline with up to 140cm observed in alpine locations.

Weather Summary

Strong to Extreme SW winds are expected to shift W and back off into the moderate to range through the day Sunday.

Small amount s of snow can be expected as temperatures warm through the overnight period bringing alpine high temperatures near -7C Sunday.

For more information, click Mountain Weather Forecast.

Terrain and Travel Advice

If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
Remote triggering is a concern, watch out for adjacent and overhead slopes.
Avoid exposure to overhead avalanche terrain, avalanches may run surprisingly far.

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.