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Avalanche Forecast

Archived

Mar 12th, 2024–Mar 13th, 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 and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.

Regions

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

Stick to mellow terrain, and avoid travelling in or under large, open slopes.

Rider or sun-triggered avalanches could become very large if they step down to a deeper weak layer.

Confidence

Moderate

Avalanche Summary

On Monday, several small to large (up to size 2.5) natural and rider triggered wind and storm slab avalanches were reported at treeline and below. See photo for example.

Limited 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 40-60 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

Tuesday Night

Cloudy. 15-25 cm of snow expected, but only 5-10 in the northwest and southeast corners of the forecast area. Light to moderate southwest ridgetop wind. Freezing level around 1000 m, with treeline temperatures around -6 °C.

Wednesday

Mostly sunny. No new snow expected. Light northwest ridgetop wind. Freezing levels rise to 1700 m, with treeline temperatures around -3 °C.

Thursday

Sunny. No new snow expected. Light northwest ridgetop wind. Freezing levels rise to 2000 m, with treeline temperatures around 0 °C.

Friday

Sunny. No new snow expected. Light to moderate northwest ridgetop wind. Freezing levels rise to 3000 m, with treeline temperature around 5 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Dial back your terrain choices if you are seeing more than 20 cm of new snow.
  • Avoid avalanche terrain during periods of strong sun.
  • Be mindful that deep instabilities are still present and have produced recent large avalanches.
  • 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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.