A spotty but consequential problem

Date

Thursday, March 17, 2022

The weak layer varies depending on slope aspect and elevation. It may be surface hoar in areas sheltered from the wind or faceted snow, sometimes associated with a hard melt-freeze crust, on sun-exposed slopes. It formed in early March and is buried anywhere from 50 to 100 cm beneath the snow surface. What we know is that large avalanches on this layer have been triggered in:

• southern parts of the Northwest Coastal region (e.g., around Terrace, Rosswood)
• areas of the North Rockies region with deeper snowpacks (e.g., Pine Pass, Renshaw)
• the Cariboos and North Columbia regions along the McBride, Valemount, and Blue River corridors
• the North Columbia region around Malakwa (e.g., Queest/Gorge) and Highway 23 North (e.g., Downie Creek and Goldstream FSR’s)
• the South Columbia region along the Nakusp to Kaslo corridor (e.g., Goat Range) and north of Nelson (e.g., Kokanee Glacier)
• the western side of the Purcells (e.g., Bugaboos)
• the eastern side of the Kootenay Boundary (e.g., around Nelson and Kootenay Pass)

The layer likely exists elsewhere in these regions and could start to produce large avalanches this week.

A rider-triggered avalanche that propagated far on March 13 near Pine Pass in the North Rockies. Photo credit North Rockies field team.

Numerous avalanches that failed on the layer of concern in the Cariboos on March 15 . Photo credit Bob Rankin.

The spotty nature of this weak layer increases the uncertainty. We strongly recommend following good travel habits:

• Continually look for signs of snowpack instability, including avalanche activity, whumpfing, or cracking snow. Don’t let your guard down throughout the day.
• Test small, low-consequence slopes before committing to larger, more consequential terrain. Make sure they are the same aspect and elevation as the larger terrain you’re considering riding.
• Travel one at a time when exposed to avalanche terrain and regroup in safe spots well away from overhead hazard.
• Avoid exposure to terrain traps such as gullies, cliffs, and trees to reduce the consequence of being caught in an avalanche.

Ride small, low consequence slopes first. If these release, avoid any higher consequence terrain in the area. Photo credit North Rockies field team.

Continue to follow the daily bulletins for the latest information on this evolving problem.

- Mike Conlan

Definitions and further learning

• Surface hoar
• Faceted snow
• Melt-freeze crust
• Terrain traps