Avalanche forecast

Kootenay Boundary

Jan 12 – 13, 2022Avalanche Canada
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Avalanche danger

Fri
Sat
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Up to 35 cm by the end of the day Wednesday combined with wind and warming temperatures elevate the avalanche hazard. There is uncertainty whether deeper weak layers will become more reactive. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    A persistent slab problem formed by a crust down 120-200 cm has created a low likelihood, high consequence scenario that is difficult to forecast. The deeply buried weak layer has produced a number of large and surprising avalanches in the past two weeks. 

    This problem is most likely to be triggered from thin or variable depth snowpack areas such as wind affected features, ridge crests, and near rocky outcroppings. Large additional loads like small avalanches or failed cornices can trigger deeper weak layers. The same feature or path can slide repeatedly when the persistent weak layer is reloaded with new snow.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    1.5–2.5

    10-20 cm are forecast by Wednesday morning and another 5-15 cm during the day. The snow will fall with warm temperatures, forming cohesive storm slabs. Moderate southwest wind will redistribute the new snow, developing fresh wind slabs.

    Be especially mindful around steep and convex openings in the trees and ridge features in the alpine. Smaller avalanches might step down and trigger deeper weak layers, resulting in large and destructive avalanches.

Confidence

Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

Tuesday night: Cloudy, 10-20 cm new snow in the east of the region and 10 cm in the west of the region, moderate southwest wind, treeline low -3 °C, freezing level around valley bottom.

Wednesday: Cloudy, 5-15 cm new snow, light to moderate southwest wind, treeline high around 0 °C, freezing level rising to 1000 m. 

Thursday: Mix of sun and cloud, trace of new snow, light southwest wind, treeline high around +2 °C, inversion develops Wednesday-Thursday night bringing above 0 °C to an elevation of 2600 m, freezing level drops to 1600 m during the day.

Friday: Mostly cloudy, trace of new snow, light southwest wind, treeline high around -1 °C, freezing level around 1000 m.

Avalanche Summary

On Monday, a couple small (up to size 1.5) wind slab avalanches were triggered by skiers.

On Sunday, explosives triggered several avalanches of size 2 to 3. A few of these were persistent slab avalanches and released on the early December layer. A large size 2.5 wind slab avalanche released naturally.

On Saturday, numerous storm slabs up to size 2.5 were triggered by explosives. 

A natural avalanche cycle to size 2 occurred overnight Thursday-Friday with accumulating snowfall and wind. On Friday morning, explosives easily triggered storm slabs to size 2.5. Several natural slab avalanches of size 2 and one size 3 released naturally. 

There has been an alarming pattern of large, persistent slab avalanches being consistently reported over the past two weeks. Almost all of these avalanches ran on the early December weak layer. Deeply buried persistent problems like these don't go away overnight, and it remains a serious concern. 

  • On Sunday, a few size 2 to 3 persistent slab avalanches were triggered by explosives. One avalanche released at 1900 m and was more than 1 m deep and 150 m wide. 
  • On Saturday, a large (size 2.5) persistent slab avalanche was triggered by explosives on the early December layer that was reloaded with new snow.
  • On Friday, a natural persistent slab avalanche of size 3 released 1-2 m deep on the early December layer at 2100 m on an E aspect in the north of the region. A size 2 persistent slab avalanche occurred naturally and failed on the same layer 30 cm deep. The feature had slid previously, and new snow reloaded the persistent weak layer.
  • On Tuesday, explosive control work near Rossland produced a size 2.5 persistent slab avalanche on a layer of surface hoar from late December. 
  • A few notables from last week feature in our latest blog Photos of recent persistent slab avalanches in the southern interior. 

Snowpack Summary

15-30 cm of recent storm snow fell with southwesterly wind and warming temperatures, resulting in a denser slab forming over lower density snow. An accumulated total of 60-80 cm of new and recent snow now sits over variable and potentially weak snow surfaces including widespread facets, wind affected snow, and/or surface hoar up to 5 mm in sheltered areas.

The early December crust/facet layer has been responsible for sporadic but very large, persistent slab avalanches over the past two weeks. The crust is now buried 120-200 cm deep except in thin, wind affected areas near ridgetops where nearly all of the recent avalanches have been triggered. 

Terrain and Travel

  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

Regions covered