Avalanche Forecast

Archived

Feb 7th, 2012–Feb 8th, 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

Wednesday: A weak weather system is expected to pass through the region in the morning bringing a few flurries and moderate westerly winds mainly over the West Kootenays. Freezing levels are expected to rise to 1000 m in the afternoon. Thursday and Friday: A series of weak frontal systems are expected to bring 3-10cm to the region each day starting Thursday afternoon, but the timing is uncertain. Freezing levels could reach as high as 1500m.

Avalanche Summary

One notable Size 2 skier triggered avalanche occurred outside the ski area boundary near Whitewater. This was on a North aspect @1985m. It was a variable 40-60cm thick slab in cross-loaded terrain and 2 skiers were involved, but sustained no injuries. Check out the incident database (under the Bulletins tab) for other 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. Mid-day pin-wheeling and other signs of moist snow have been observed on solar aspects at and above treeline. A couple of thin crusts down 30-50cm have been producing moderate to hard shears in tests. Some areas are still getting sudden planar shears on the mid-December surface hoar layer. Basal facets were 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.