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Avalanche Forecast

Archived

Dec 6th, 2024–Dec 7th, 2024

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
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.

The degree the hazard increases greatly depends on how much snow we receive. The greatest amount of snow is expected in the Northern part of the region and along the Divide and west. Watch for building hazard through the day with strong winds forecast.

Confidence

Low

Avalanche Summary

No new avalanches were observed on Friday.

The common theme from avalanches over the week was small avalanches that then gouged down to basal facets and ran further than expected. Lake Louise got two explosive-triggered avalanches in a steep N to E aspects, failing on the Nov 9 weak layer 40 cm above the ground. The snowpack foundation is weak.

Snowpack Summary

Expect the hazard to increase through Saturday as new snow accumulates and the strong to extreme winds create easily triggered surface slabs; some may fail on the ground.

As of Friday, the snow surface is a mix of sun crust, 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.

Weather Summary

We are on the southern edge of a warm Atmospheric River that will spill into Alberta Friday night and all day Saturday. Expect strong W to SW winds (40-60 km/hr) and 5-15 cm by the end of Saturday and another 5-10 cm Saturday night. The greatest amounts will be in the northern part of the region, along and West of the Continental Divide. Freezing levels should be at the valley bottom (1400 m).

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.

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.