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Avalanche Forecast

Archived

Mar 9th, 2022–Mar 10th, 2022

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Kootenay Boundary.

Use extra caution in the north of the region and above 2100m in the south where the early March crust is not present. The likelihood of triggering a persistent slab avalanche is greater in these areas.

Confidence

Moderate - Uncertainty is due to the complexity of the snowpack’s structure.

Weather Forecast

Wednesday night: No new snow expected. Light to moderate northwest winds and a Low of -14 at 1500m.

Thursday: a mix of sun and cloud with Light to moderate northwest wind. High of -5 at 1500m. 

Friday: cloudy with up to 5cm of new snow. Moderate west wind. High of -2 at 1500m. 

Saturday: cloudy with up to 10cm of new snow. Moderate southwest winds and a high of -1 at 1500m.

Avalanche Summary

No new avalanche activity reported on Monday or Tuesday. The current cooling trend has helped calm down avalanche activity on buried weak layers, old and new. But the many reports of avalanches over the warm sunny period on the weekend indicate that our various weak layers are still triggerable under the right conditions.

On Sunday a size 1.5 skier triggered persistent slab avalanche was reported in an treeline elevation start zone north of Nelson. Good visibility allowed observation of a 2 day old widespread avalanche cycle in the Valhallas size 2-3.5. One notable stepped down to a weak layer 100 cm deep.

Snowpack Summary

South of Nelson, around 10 cm of wind-affected snow sits over a near-surface crust up to 8 cm thick which may make for challenging travel conditions as high as 2250 m. Further north where the crust does not exist, more surface snow is available for wind transport so we anticipate more substantial wind slab development at upper elevations.

A recently buried weak layer sits 20-50 cm deep. It consists of surface hoar crystals in shady, wind-sheltered areas around treeline and a crust on solar aspects. This layer was reactive to human triggers over the weekend in areas where it was not bridged by the above-mentioned crust.

Weak layers from mid-February and late January made up of crusts and/or surface hoar crystals can be found around 60+ cm and 100+ cm deep, respectively. Some recent persistent slab avalanches on this layer have surprised riders, so keep this type of avalanche in mind when making terrain choices.

Terrain and Travel

  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Avoid steep convexities or areas with a thin, rocky, or variable snowpack.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.

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.