Avalanche Forecast

Issued: Feb 11th, 2017 4:53PM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Storm Slabs and Persistent Slabs.

Avalanche Canada mgrist, Avalanche Canada

Touchy storm slabs are reactive to human triggers. Use small slopes with low consequence to test the bond of the storm snow.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Seasonal temperatures and isolated flurries through the weekend. Significant alpine warming Tuesday afternoon. SUNDAY: Cloudy / Light - moderate southwesterly winds / Freezing level around 900 m. MONDAY: Sunny with cloudy periods, warming with highs to +1Celsius / Moderate southeasterly winds / Freezing level around 1200 m. TUESDAY: Mostly cloudy / High temperatures to +3 Celsius / Light-moderate southwesterly winds/ Freezing level near 2000m.

Avalanche Summary

Near Nelson, several persistent slab avalanches to Size 3 (average depths ranging from 60cm to 100cm) were triggered on virtually all aspects above 1900m with explosives on Saturday. See Whitewater Ski Patrol's great video (here) posted on the Backcountry Skiing Canada web site for a concise summary of details to Feb 9th, and some excellent video footage of a Size 2.5 avalanche running on the Goat Slide path near Whitewater (with crown height to 2.5m).

Snowpack Summary

Another 20-30 cm of wet snow fell up to 1900m on Thursday and ended with a 1-2cm thick crust on all aspects below this elevation. Since then, up to 30cm additional snow has fallen (mostly near Nelson) and brings the recent storm snow total to 65-100cm, creating touchy storm slabs at all upper elevations and aspects. Snowfall amounts have been highest around Kootenay Pass. Slabs have been reported as very reactive to human triggers and are sitting on a variety of surfaces; including scoured surfaces in wind exposed terrain, surface hoar (size 2-3 mm) in sheltered locations, and sun crust on steep solar aspects. Snowpack tests near the Valhallas have given moderate, propagation-likely results down 50-70cms on the Feb 3rd interface. Areas with a shallower snowpack (less than 150 cm) have a generally weak snowpack structure with sugary facets near the ground. This includes shallow alpine slopes and most of the Rossland range. It is possible for storm slab avalanches to step-down to these deeper weak layers, resulting in large, destructive avalanches.

Problems

Storm Slabs

An icon showing Storm Slabs
Thursday's storm started cold and ended warm. This creates a dangerous condition where warmer heavy snow is sitting on-top colder snow, making storm slab avalanches much more likely.
Watch for signs of instability such as whumpfing, shotting cracks, or recent natural avalanching.Use small slopes with low consequence to test the bond of the storm snow.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

An icon showing Persistent Slabs
Storm slabs may step-down to deeper weak layers, resulting in large, destructive avalanches.
Avoid likely trigger spots such as steep and rocky areas with a shallow snowpack.Wait to see how the snowpack responds to increased loads before venturing out into bigger terrain

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Feb 12th, 2017 2:00PM