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Avalanche Forecast

Archived

Mar 7th, 2022–Mar 8th, 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 unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Kootenay Boundary.

Persistent slab avalanches on various buried weak layers have surprised riders in areas north of Nelson in recent days. Reactivity should cool down in the coming days but keep the potential for large human triggered avalanches on your radar.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast. Confidence is due to a stable weather pattern with little change expected.

Weather Forecast

Monday night: Partly cloudy. Moderate northwest ridgetop wind. Treeline low around -7 °C. Freezing level dropping to valley bottom. 

Tuesday: Scattered flurries bringing a trace. Light northerly wind. Treeline high around -5 °C. Freezing level 800 m.

Wednesday: Flurries bringing up to 5 cm. Light northwest wind. Treeline high around -7 °C. Freezing level valley bottom.

Thursday: Mostly sunny. Moderate northwest wind. Treeline high around -5 °C. Freezing level 800 m.

Avalanche Summary

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 noteable stepped down to a weak layer 100 cm deep.

On Friday and Saturday, several accidentally triggered storm slab avalanches were reported in the northeast of the region. These avalanches were:

  • Large, ranging from size 2-3
  • Triggered by skiers, snowmobiles and snow cat. At least one was remote.
  • At treeline elevations, on leeward SE-NE aspects.
  • See photos and detailed description of the remote in this MIN

Similar incidents also occurred east of Slocan in the neighboring South Columbia region, resulting in a partial burial and injury. More details and photos here. 

Small loose wet avalanches were also reported on solar aspects in the afternoon.

East of Kelowna, a natural wind slab avalanche and several explosive triggered wind slabs were reported up to size 1.5 on east through south aspects around treeline. 

Snowpack Summary

A near-surface crust may make for challenging travel conditions up to 2250 m. The crust ranges from breakable to supportive and is between 1-5 cm thick. 

20-50 cm of recent storm snow sits over a variety of surfaces including a weak layer of surface hoar in wind-sheltered areas around treeline and a crust on solar aspects.

Weak layers from mid-February and late January made up of crusts and/or surface hoar crystals can be found around 60-100 cm deep. 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.
  • A crust on the surface will help bind the snow together, but may make for tough travel conditions.

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.