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Avalanche Forecast

Archived

Nov 30th, 2021–Dec 1st, 2021

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

Regions

Little Yoho.

A significant storm is expected on Wednesday. It will be best to enjoy the ski hill and avoid all avalanche terrain.

Weather Forecast

Wednesday will be a crux day for avalanches. 40-100 cm of snow is forecasted by end of day (more snow along the divide).  This snow will be accompanied by very strong winds, high freezing levels and rain at lower elevations. Thursday will see convective flurries and clearing skies overnight. Freezing levels will drop to valley bottom.

Snowpack Summary

30-60 cm recent storm snow is reacting as a storm slab in alpine and tree-line locations. A crust (Nov 15) exists in the mid-pack in most areas below 2100 m. The Nov 5 crust/facet layer exists near the ground. Snowpack depths at tree-line average 80-100 cm. Lower elevation snow (below 1600 m) is rain soaked and isothermal.

Avalanche Summary

Natural and explosive triggered storm slabs have been observed at tree-line and alpine locations in past 48 hours. Many upper elevation storm slabs are stepping down to the deep persistent layer making for large class three avalanches. At lower elevations (below 1700 m) debris is gouging into isothermal snow and again making for large avalanches.

Confidence

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.