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Avalanche Forecast

Archived

Dec 4th, 2021–Dec 5th, 2021

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.

Natural avalanche activity has tapered since last weeks storm. The snowpack is still adjusting to the significant load, and considerable hazard remains at upper elevations.

Weather Forecast

A cooling trend will continue into Monday with evening lows dropping to -20 near valley bottom. Ridge winds will be light to moderate from the North West for the next few days. Light snow fall is expected overnight Saturday with accumulation amounts up to 5cm. Mix of sun and cloud forecasted for Sunday.

Snowpack Summary

The storms from last week brought up to a meter of settled snow at treeline and periods of rain as high as 2200m. Cold temps this weekend have now formed a crust near the surface below 2200m. The new storm snow now over layers the lingering Nov.15 interface and the Nov. 5 crust/facet layer found near the ground.

Avalanche Summary

Evidence of a recent widespread avalanche cycle to size 4 is evident though the forecast region. No new natural avalanche were observed today. Local ski hill reported triggering avalanches to size 2.5 with explosives.

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.