Avalanche Forecast

A building ridge of high pressure will usher in clear skies and warm temperatures. 

Thursday Overnight: Clearing. Ridge winds 20-60km/h from the northwest. Freezing level dropping to valley bottom.

Friday: Mainly clear. Ridge winds 20-40 km/h from the west. Freezing level rising to 1500 m.

Saturday: Mainly clear. Ridge winds 10-40 km/h from the northwest. Freezing level rising to 1700 m.

Sunday: Increasing cloud cover. Light ridgetop winds. Freezing level rising to 2000 m.

Over the past week, a persistent weak layer of buried surface hoar has produced numerous large human-triggered avalanches, surprising both professionals and recreationists. This layer has shown the most reactivity between 1600-2200 m, with the most reactivity observed in open areas in the trees, in cut blocks and on steep convexities. Check out some good example photos here. Compelling observations on this layer in the neighbouring Glacier National Park can be seen here. 

Overnight, clear skies and cooling temperatures will refreeze the surface of the snowpack at lower elevations where it has been affected by rain and warm temperatures. A sun crust has formed on sun-exposed slopes at all elevations. In the alpine and exposed treeline, strong winds throughout the week have created a variety of wind-affected surfaces. Expect to find old and new wind slabs on a variety of aspects, with the most recent and reactive slabs formed in terrain features lee to the northwest. 

A weak layer of surface hoar exists 60 to 100 cm deep in the snowpack, which is a prime depth for human triggering. The layer is most prominent in areas sheltered from the wind. Example terrain features to treat as suspect include the lee side of protected ridges, openings in the trees, cut blocks, and burns. The layer may not exist on steep sun-exposed slopes, where a melt-freeze crust may be found instead.

The facet/crust layer that formed in early December is buried around 120 to 250 cm. The last reported avalanche was on January 31 from a large explosive, and before that on January 23. Although unlikely, the layer could be triggered from a large load like a cornice fall or a shallower slab avalanche could step down to this layer. Humans are unlikely to trigger it, with perhaps the exception in thin, shallow snowpack areas. Check out the forecaster blog for more information.

• Be aware of the potential for large avalanches due to the presence of buried surface hoar.
• Surface hoar distribution is highly variable. Avoid generalizing your observations.
• Cornice failure may trigger large avalanches.
• Uncertainty is best managed through conservative terrain choices at this time.