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Avalanche Forecast

Archived

Dec 28th, 2022–Dec 29th, 2022

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

Regions

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

Human triggering remains a possibility. Conservative terrain choices will be important to sustain for the near future.

Avalanche control is being conducted on Mt. Whymper and the Simpson slide paths on Dec 29, 2022. These areas are closed during this time.

Confidence

Moderate

Avalanche Summary

Avalanche control on the Sunshine road produced results up to size 2.5. Typically the slabs were thin and didn't run far, but propagated widely. Lake Louise patrol managed to trigger a size 2.5 deep slab that scrubbed to the ground but received no results on similar adjacent features. Sunshine patrol also reported triggering deep persistent slabs up to size 2 with explosives, although they were only about 30cm deep.

Snowpack Summary

Windslabs remain in the alpine and some treeline areas. These slabs sit atop a weak layer of facets and surface hoar (Dec. 17th interface) and have been producing skier-triggered avalanches to size 2. Below this, the snowpack is generally facetted with the largest facets and depth hoar near the bottom. Snowpack depths at treeline range from 80-140 cm throughout the region.

Weather Summary

A slight cooling trend is expected on Thursday, with temperatures around -10 at the ridge and -5 at the valley. Very light snow is expected with accumulations of a few centimeters. The biggest factor will be the wind which will blow from the SW into the strong range at higher elevations.

Terrain and Travel Advice

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Uncertainty is best managed through conservative terrain choices at this time.

Problems

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.

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.

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.