Avalanche Forecast

Archived

Mar 11th, 2024–Mar 12th, 2024

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Kootenay Boundary, Bonnington, Grohman, Kootenay Pass, Norns, Rossland, Ymir, Crawford, Moyie, St. Mary, Kokanee, Valhalla.

It's not time to step out yet, resist the temptation of large, open terrain.

Storm snow is reactive to human triggers and buried weak layers remain capable of producing very large avalanches.

Confidence

Moderate

Avalanche Summary

Small slabs were reactive to rider traffic on Sunday within the storm snow, sitting over facets and surface hoar.

No persistent slab activity has been reported since Thursday, however, avalanches within the last week have been large and destructive, running full path. The photos below show an explosive triggered avalanche near Nelson, and a rider triggered avalanche in the Bonningtons, both several days old.

Snowpack Summary

Storm totals are expected to reach 30-40 cm by Tuesday afternoon. Storms slabs are currently not bonding well with the old snow surface - a crust on sun affected slopes, surface hoar in sheltered terrain, and wind affected snow in exposed areas.

A widespread crust with weak facets above is buried 100-150 cm deep and remains a very concerning layer for human triggering. While reports suggest this layer is becoming harder to trigger, it has produced very large avalanche activity this week.

The snowpack below the crust is generally strong.

Weather Summary

Monday Night

Cloudy with up to 15 cm of snow overnight in the Selkirks, and 5 cm in the Purcells. 30-40 km/h southwest ridgetop wind. Freezing levels remain above 1000 m.

Tuesday

Cloudy with another 10 cm of snow for the Selkirks and flurries for the Purcells. 30-40 km/h southwest ridgetop wind. Freezing levels rise to 1500 m, with treeline temperatures around -3 °C.

Wednesday

Mostly clear skies. 10 km/h northwest ridgetop wind. Freezing levels rise to 1800 m, with treeline temperatures around -1 °C.

Thursday

Clear skies. 20-40 km/h northwest ridgetop wind. Freezing levels spike to 2000 m, with treeline temperatures around +1 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Be careful to keep storm day fever from luring you out into bigger terrain features.
Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
Storm slabs in motion may step down to deeper layers resulting in large avalanches.

Problems

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.