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Avalanche Forecast

Archived

Nov 24th, 2020–Nov 25th, 2020

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

Regions

Banff Yoho Kootenay.

Some new snow and wind may bump up the avalanche danger for Wednesday. Watch locally for snow amounts and wind effect. There is uncertainty as to what will make the Nov. 5 crust/facet layers become reactive.

Weather Forecast

Strong to Extreme winds will continue overnight into Wednesday, then decrease to the moderate range in the alpine. Expect 5-15cm at higher elevations along the divide and West, with less East of the divide. Temperatures will be in the -6 to -8C range at valley bottom and -12 to -15C at 3000m.

Snowpack Summary

Wind slabs present at treeline and above from W-SW winds. At treeline 20-50 cm of storm snow sits over a layer of preserved stellars. The Nov. 5 facet/crust combo is down 50-80 cm and producing variable test results from easy to hard. 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

Ski hills reporting small wind slabs with explosive control Tuesday. A slide above Sacre Bleu on Mt. Rundle was observed as well, but hard to tell what the trigger was.

Confidence

Forecast snowfall amounts are uncertain on Wednesday

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.