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Avalanche Forecast

Archived

Dec 21st, 2020–Dec 22nd, 2020

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
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.

Avalanche control on Mt. Stephen, Mt Field and Mt. Dennis in Little Yoho. No access to these areas on Tuesday Dec. 22.

Weather Forecast

An early christmas present of 15-40 cm has started to fall as I write this bulletin. The highest amounts are on the south and east sides of the bulletin area. Mostly light S winds switching to N becoming strong at the end of the storm. Tuesday: cool with clearing skies. Wed and Thurs: sunny and cold with lows near -20 and increasing alpine winds

Snowpack Summary

30-60 cm over the last week have been blown into windslabs in the alpine and down into tree line from strong West winds. The Dec 13 and Dec 7 sun crust/surface hoar/facet layers are down ~ 35cm and ~65cm respectively. The decomposing Nov crust/facets sits at the bottom of the snowpack. Height of snow at tree line is 80-150cm.

Avalanche Summary

Minimal activity in the Lake Louise Ski Hill area but Sunshine Village ski patrol had some notable observations. A size 2.5 -3 was triggered with explosives in the "Wheelers" path above the ski out which stepped down to ground (2m in spots) and ran full path. They also reported a size 1.5 failing on surface hoar down 50 cm BTL in the Wild West area

Confidence

Intensity of incoming weather systems is uncertain

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.