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Avalanche Forecast

Archived

Dec 10th, 2019–Dec 11th, 2019

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

Regions

Banff Yoho Kootenay.

Lots of recent snow over a weak base, now being moved by west wind into reactive wind slabs. Stick to conservative lines and allow some time for the snowpack to adjust and bond.

Weather Forecast

Continued moderate West alpine winds are expected overnight and increase to strong on Thursday. This will add to existing wind slabs and keeping the alpine hazard at Considerable. Temperatures should remain seasonal in the -10 range at tree line. Minimal snow, and a mix of sun and cloud for Wednesday and up to 5 cm on Thursday.

Snowpack Summary

Moderate winds in the alpine are adding to the wind slabs problem in the alpine. Beneath the recent 40-60 cm of recent snow, the snowpack structure is generally weak, consisting of facets and depth hoar. The Nov crust is present up to 2500m and ~30 cm up from ground. Snowpack depths at treeline range from 80-160 cm.

Avalanche Summary

Avalanche control today continues to produce windslab avalanches. Sunday and Monday's control produced up to size 3 avalanches with propagations across terrain features and stepped down to the Nov crust and basal facets. A skier accidental size 2.5 on the basal weakness occurred in West Bowl at Lake Louise Sunday.

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.