Kootenay Boundary Avalanche Forecast

Issued: Jan 10th, 2022 4:00PM

Tue Jan 11th Current Conditions
Alpine Considerable Treeline Moderate Below Treeline Moderate
Wed Jan 12th 2 Day Outlook
Alpine Considerable Treeline Considerable Below Treeline Moderate
Thu Jan 13th 3 Day Outlook
Alpine High Treeline High Below Treeline Considerable

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Wind Slabs and Persistent Slabs.

Fresh wind slabs will form in lee terrain features and below ridge crests. Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches. 

Summary

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

Monday night: Mostly cloudy with flurries, moderate southwest wind with strong gusts, treeline low around -8 °C, freezing level below valley bottom.

Tuesday: Cloudy, 5 cm new snow, strong southwest wind, treeline high around -3 °C, freezing level rising to 700 m. 

Wednesday: Cloudy, 20-30 cm new snow, strong southwest wind, treeline high around +1 °C, freezing level rising to 1000 m. 

Thursday: Mostly sunny, trace of new snow, light southwest wind, treeline high around +4 °C, freezing level rising to 2600 m.

Avalanche Summary

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.

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. 
  • On Monday in the neighbouring South Columbia region, a natural size 2.5 persistent slab avalanche was reported on a NE aspect at 2200 m failing 80 cm deep on the early December layer.
  • 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

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • 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.

Problems

Wind Slabs

An icon showing Wind Slabs

Likelihood

Likely

Expected Size

1 - 2

Moderate to strong southwest wind will continue to build fresh slabs. Be especially mindful around steep and convex openings in the trees and ridge features in the alpine.

Cornices will continue to grow and might fail with the additional load. 

Aspects:

North, North East, East, South East, North West.

Elevations:

Alpine, Treeline.

Persistent Slabs

An icon showing Persistent Slabs

Likelihood

Possible

Expected Size

2 - 3

A 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.

The same feature or path can slide repeatedly when the persistent weak layer gets reloaded with new snow. 

Aspects:

All aspects.

Elevations:

All elevations.

Valid until: Jan 11th, 2022 4:00PM

Forecast Trend

The latest forecast danger ratings, broken down to elevation. See how an elevation is trending.