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Avalanche Forecast

Archived

Dec 3rd, 2021–Dec 4th, 2021

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

We are out the other side of the storms with a blast of cold and clear but slabs remained reactive to explosive control Friday. Expect a low on Saturday to stir things up again particularly as west winds start to redistribute the recent snow.

Weather Forecast

Friday night will bring overnight low temperatures approaching -20C at treeline with almost calm winds. Saturday, expect a low pressure system to affect the region as light precip starts in the morning and  temps warm to -10C midday. Alpine winds will build from the southwest and may reach strong before shifting NW late in the day.

Snowpack Summary

The storms from the end of November and first days of December brought up to a meter of settled snow at treeline and periods of rain as high as 2200m. Cold temps starting Thursday afternoon froze low elevation snow. The snow from these storm sits on the Nov.15 interface (a crust below 2100m) and the Nov. 5 crust/facet layer found near the ground.

Avalanche Summary

With Thursday's clearing and avalanche control flights we have seen widespread evidence of a natural cycle up to sz 4. Many of these started as full depth avalanches in the alpine and resulted in loose wet debris piles at valley bottom. Avalanche control has produced storm slabs averaging 50-100cm deep as well as full depth slabs treeline and above

Confidence

Timing, track, or intensity of incoming weather system is uncertain on Saturday

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.