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Avalanche Forecast

Archived

Nov 29th, 2021–Nov 30th, 2021

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

Regions

Little Yoho.

Avalanche Control is planned for the Sunshine Road on Nov. 30th. No access to Mt Bourgeau or Eagle Mountain zones.

Weather Forecast

Temperatures will cool Mon night, but then warming as the next storm arrives. Winds will rise to strong to extreme from the west and freezing levels are forecasted to be in the 2000m range. Models are forecasting ~20 cm by end of Tues, ~ 60 cm by end of Wed, and another ~ 10 cm as the system passes and cools on Thurs. Rain in valley bottoms.

Snowpack Summary

30-60 cm of snow in the last storm is reacting as a storm slab in alpine and treeline terrain. The Nov 15 crust is below this and present below 2100 m. The Nov 5 crust/facet layer exists near the ground. Snowpack depths at tree-line average 80-110 cm. Lower elevation snow (below ~ 1500 m ) is rain- soaked.

Avalanche Summary

Natural activity to size 3 as a result of the weekends storm was observed on Monday. Results from avalanche control in Kootenay showed touchy storm slabs at treeline and in the alpine with higher elevation avalanches stepping down to the deep persistent layer. At lower elevations, (below ~ 1700m), these were entraining loose wet snow.

Confidence

Timing, track, or intensity of incoming weather system 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.