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Avalanche Forecast

Archived

Dec 12th, 2020–Dec 13th, 2020

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

Regions

Little Yoho.

Watch for power sloughing of the faceted surface snow in steep terrain. Although fairly small, they can travel far and fast. In extreme terrain these could extend below treeline as was observed on Pilsner Pillar today.

Weather Forecast

Mainly cloudy with continued colder temperatures (-18 to -20C in the AM) with a slight increase in wind which could gust moderate above 3000m. Some flurries possible but only trace amounts. Winds will increase on Monday and especially Tuesday.

Snowpack Summary

20-40 cm of faceted snow sits on the Dec 7th layer of sun crust, facets or surface hoar depending on your location. The Nov. 5th crust / facet layer persists at the bottom of the snowpack, but less prominent in deeper snowpack areas in Little Yoho. Snowpack depths are 90-160cm at tree line.

Avalanche Summary

There were numerous reports of loose, dry avalanches up to sz 2 in steeper alpine features like gullies which were running far on Saturday (Pilsner Pillar and other Mt. Dennis paths).The theory is the 20-40cm received last week has faceted and not been exposed to any wind. Even light winds today may have initiated these.

Confidence

Wind speed and direction is uncertain

Problems

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.

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.