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Avalanche Forecast

Archived

Nov 25th, 2020–Nov 26th, 2020

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

Banff Yoho Kootenay.

Strong to extreme winds and recent snow will keep the avalanche hazard elevated in the alpine.

Watch for sluffing in steep, confined terrain.

Uncertainty surrounds the Nov 5 crust /facet layer and what it will take to become reactive.

Weather Forecast

Mainly cloudy for Thursday with isolated flurries accumulating up to 2cm of snow. Winds will be from the West - North West in the 30-70km/hr range. Temps will range from 0 in valley bottoms to -9 in the alpine. Friday will see a further increasing winds, up to 100 km/hr from the West, small amounts of snow and slightly warmer temperatures.

Snowpack Summary

10-20cm of new snow, along with 25-40km/hr W-SW winds is building wind slab at treeline and above. The Nov 5 facet/crust combo is down 50-80 cm and producing variable test results from easy to hard, but 'sudden' in fracture character. The Nov crust extends up to 2500 m on N aspects and higher on solar aspects. Snow depths at treeline are 50-130 cm.

Avalanche Summary

Natural wind slab avalanche activity observed up to size 2 from steep rocky terrain in the Ogden area today.

Local ski areas reporting wind slabs up to size 1.5 from explosive control work.

Confidence

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.