As winds pick up ahead of the next storm, fresh, reactive wind slabs will likely form at upper elevations. The region continues to deal with a tricky persistent slab problem and very large avalanches remain possible. Conservative terrain selection remains essential.
Plenty of recent, low density snow is available for transport as winds pick up ahead of the next storm. Fresh wind slabs overlie a weak interface which could result in them being particularly touchy and remaining reactive for longer than usual.
A persistent slab problem formed by a crust down 70-150 cm has created a low likelihood, high consequence scenario that is difficult to forecast. Avoid likely trigger spots such as steep, rocky slopes with a shallow or thin-to-thick snowpack. Smaller storm slabs or wind slabs have the potential to step down to a deeper weak layer.
Wednesday night: Increasing cloud. Light NW wind switching SW. Treeline temperature around -16 °C.
Thursday: Snowfall 4-8 cm. Moderate to strong SW wind. Treeline high around -12 °C.
Friday: Snowfall 5-15 cm. Strong SW wind. Treeline high around -8 °C.
Saturday: Light snowfall up to 5 cm. Moderate SW wind. Treeline high around -8 °C.
Reports from throughout the region Monday include natural, explosive and skier triggered wind slabs up to size 2. This MIN report from the south of the region shows an example of the instability in the storm snow and good decision making. Wind slabs remained reactive around Invermere into Tuesday, with continued natural and human triggered activity up to size 2.
On Tuesday just east of the region in the Rockies near Invermere, a size 3.5 (very large) persistent slab avalanche was triggered remotely by a skier on an alpine ridgetop. The resulting crown was 2-3 m deep and the avalanche ran about 1 km to the valley bottom. More details in this MIN report. This and other notable persistent slab avalanches in neighboring regions feature in our latest blog, Photos of recent persistent slab avalanches in the southern interior.
As winds pick up in advance of the next storm, 30-40 cm of recent snow will likely see redistribution into reactive slabs in lee terrain features. The recent snow sits over variable and potentially weak snow surfaces including widespread facets, wind affected snow, and/or surface hoar up to 3 mm in sheltered areas. Reactivity at this interface may persist for longer than usual.
The most notable layer of concern in the snowpack is a crust that was formed in early December and is now down 70-150 cm. Activity on this layer has been sporadic. It has generally been triggered on steep, rocky slopes, with a shallow or thin-to-thick snowpack. This layer has created a low likelihood, high consequence scenario which is best managed through conservative terrain choices and disciplined backcountry travel techniques.
