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Avalanche Forecast

Archived

Dec 18th, 2019–Dec 19th, 2019

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

Regions

Banff Yoho Kootenay.

Recent SW winds have stripped the alpine, and loaded lee features with wind slabs.  Good skiing can be found in sheltered areas. 

Weather Forecast

Thursday - expect light flurries, moderate SW wind, and mild temperatures in the -5 to -10 range

Friday - the next storm begins elevating the avalanche hazard as it brings warmer temps (freezing levels at 1600 m), strong SW wind, and snow (15-30 cm depending on the weather model)

Saturday -  expect another 10-15 cm

Snowpack Summary

Strong winds have formed new wind slabs at alpine and tree line. The distribution of this new load is uncertain. Beneath the recent 40-60 cm of storm 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

On Tuesday there was a Skier involvement in a size 2 windslab avalanche triggered on a convex roll at treeline (Paget Peak) and a natural size 2 windslab on a S alpine aspect of Noseum Peak.  Local ski hills continue to report small wind slabs reactive to ski cuts, although slightly less reactive compared to Tuesday

Confidence

Intensity of incoming weather systems is uncertain on Friday

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.