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Avalanche Forecast

Archived

Feb 8th, 2012–Feb 9th, 2012

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

Regions

Kootenay Boundary.

Confidence

Good - -1

Weather Forecast

A series of weak frontal systems are expected to bring 3-10cm to the region each day and particularly Thursday afternoon, but the timing is uncertain. Winds are expected to be generally light southwesterlies, but winds associated with snow squalls could get quite gusty. Freezing levels could reach as high as 1500m with the passage of warm fronts.

Avalanche Summary

Fresh hard wind slabs on west through northeast aspects are very touchy with natural and skier-triggered avalanches up to size 2. Loose faceted surface snow is sluffing readily in steep terrain and gaining considerable mass. Check out the incident database (under the Bulletins tab) for reports of recent avalanche involvements in the region, and search vimeo.com for helmet-cam footage of the Feb. 3rd incident near Nelson.

Snowpack Summary

The current snow surface is well on its way in becoming a dangerous weak layer once a sufficiently cohesive slab develops. Surface hoar is continuing to develop on sheltered slopes at all elevations combined with near-surface facets at lower elevations and surface crusts on sun-exposed slopes. There is still dry snow on northerly aspects at higher elevations, but it is likely wind-affected and variable in exposed areas. Concerns remain for the mid-December surface hoar layer. Basal facets were recently responsible for a large whumpf on a shallow south facing treeline slope in the Rossland Range and gave very easy and sudden compression tests results where they were found down 60cm.

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.