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Avalanche Forecast

Archived

Dec 17th, 2021–Dec 18th, 2021

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

Regions

Vancouver Island.

Heavy snowfall and strong wind are creating very dangerous avalanche conditions. Avoid avalanche terrain, and stick to simple, low-angle slopes with no overhead hazard.

Confidence

Moderate - Forecast precipitation (either snow or rain) amounts are uncertain.

Weather Forecast

Heavy snow and strong wind on Saturday

Friday night: Overcast, 10-30 cm of snow above 900 m, areas southwest in the region could see 40 cm of snow above 1500 m, extreme southwest winds, treeline temperatures rising overnight to -1 C, freezing level rising to 900 m.

Saturday: Overcast, another 10-30 cm of snow above 700 m, areas southwest in the region could see 40 cm of snow above 1300 m, strong southwest winds, treeline temperatures cooling from -1 C to -4 C, freezing level dropping to 500 m.

Sunday: Partly cloudy, up to 5 cm of snow, winds becoming east and light, high treeline temperatures near -3 C, freezing level around 700 m.

Monday: Mainly sunny, no precipitation expected, light southeast winds, high treeline temperatures near-2 C, freezing level around 300 m. 

Avalanche Summary

Natural avalanches releasing in the new snow are likely on Saturday. These storm slab avalanches are expected to be large, widespread, and very sensitive to human triggers.

Snowpack Summary

 An intense storm is taking aim at the region, with 25-60 cm of new snow expected by Saturday afternoon. A strong storm is taking aim at the region, bringing strong southwest winds and 25-60 cm of new snow by Saturday afternoon. During the heaviest snowfall mid-morning on Saturday, freezing levels are forecast to rise to around 900 m, creating denser snow over lighter snow and potentially forming a mid-storm crust layer. Higher snow totals and freezing levels may be found in southwest parts of the region. Periods of extreme southwest wind will likely be a major contributor to the size and likelihood of Saturday's storm slab problem. Even steep opening in the trees should be treated as suspect on Saturday. 

Below up to a meter of snow from the past week, two crust layers can be found that formed in early December. Small facets (sugary snow) have been reported near these crusts that may transition into a persistent slab problem. Recent snowpack tests have demonstrated instability at this interface, though with limited propagation potential. This layer could have potential to be triggered in shallow, rocky zones near ridge tops, where the facets are more developed and where the crust layers are more accessible to the weight of a person or machine. Check out this MIN report from the Elk Mountain area on Tuesday. 

Below these crust layers, the snowpack is generally well-settled. Early season hazards such as rocks, stumps, and open creeks remain at lower elevations.

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • Use increased caution at all elevations. Storm snow is forming touchy slabs.
  • Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.

Problems

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.