Avalanche Forecast

Issued: Jan 10th, 2022 4:00PM

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.

Avalanche Canada ldreier, Avalanche Canada

Email

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: Increasing cloud coverage, trace of new snow, strong southwest wind, treeline low around -8 °C, freezing level below valley bottom. 

Tuesday: Mix of sun and cloud, up to 5 cm new snow, strong southwest wind, treeline high around -3 °C, freezing level rising to 1000 m, possible inversion.

Wednesday: Mix of sun and cloud, 5-10 cm new snow, strong southwest wind, treeline high around 0 °C, freezing level rising to 1500 m, possible inversion. 

Thursday: Sunny with cloudy periods, up to 5 cm new snow, strong southwest wind, treeline high around +1 °C, freezing level around 2000 m, inversion. 

Avalanche Summary

On Sunday, a natural size 2 wind slab avalanche that released in extremely steep terrain was observed. A few small (up to size 1.5) wind slab and dry loose avalanches were triggered by skiers.  

On Saturday, several wind slab avalanches up to size 2 released naturally and were triggered by explosives. A small size 1.5 wind slab avalanche was triggered remotely by a skier. 

On Friday, explosives triggered storm stab avalanches to size 2, on average 20 cm deep. A rider triggered a size 2 wind slab avalanche 30 cm deep. Skiers triggered numerous small (size 1) avalanches. A natural avalanche cycle to size 1.5 occurred Thursday-Friday night with rapid loading of new snow.

An increasing amount of large, persistent slab avalanches was reported on Sunday. Almost all the reported avalanches over the past week 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, two size 3 and 3.5 deep persistent avalanches were triggered with explosives up to 1 m deep. They released at an elevation around 1900 m on SE and SW aspects. And a persistent slab avalanche 2 m deep and 200 m wide was reported in this MIN report
  • Last Tuesday just east of the region in the Rockies near Invermere, a size 3.5 (very large) persistent slab avalanche was triggered remotely by a skier on an alpine ridge top. The resulting crown was 2-3 m deep and the avalanche ran about 1 km to the valley bottom. More details in this MIN report. 

Notable persistent slab avalanches in neighbouring regions feature in our latest blog, Photos of recent persistent slab avalanches in the southern interior.

Snowpack Summary

40-60 cm of recent storm snow fell with southwesterly wind and warming temperatures. In open terrain and upper elevations, wind developed more reactive deposits around lee and convex features. An accumulated total of 40-90 cm of new and recent snow sits now over variable and potentially weak snow surfaces including widespread facets, wind affected snow, and/or surface hoar up to 3 mm in sheltered areas.

The most notable layer of concern in the snowpack is a crust that was formed in early December and is now down 90-160 cm. Activity on this layer has been sporadic. It has generally been triggered on steep, rocky slopes, with a shallow or thin-to-thick snowpack. This layer has created a low likelihood, high consequence scenario which is best managed through conservative terrain choices and disciplined backcountry travel techniques.

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

Strong southwest wind will continue to redistribute the recent snow and form fresh wind slabs. Be especially mindful around steep and convex openings in the trees and ridge features in the alpine. The new and recent snow may overlie a weak interface which could result in deeper and touchier than expected slabs.

Aspects: North, North East, East, South East, North West.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1.5 - 2.5

Persistent Slabs

An icon showing Persistent Slabs

A persistent slab problem formed by a crust down 90-160 cm has created a low likelihood, high consequence scenario that is difficult to forecast. Avoid likely trigger spots such as steep, rocky slopes with a shallow or thin-to-thick snowpack. Smaller storm slabs or wind slabs have the potential to step down to a deeper weak layer. 

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

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