Avalanche Forecast

Issued: Dec 11th, 2021 4:00PM

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

Avalanche Canada astclair, Avalanche Canada

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Incremental snow and sustained wind will keep avalanche hazard elevated. Avoid freshly wind-drifted areas and continue to make conservative terrain choices while the storm snow gains strength.  

Summary

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

Saturday night: Cloudy, up to 10 cm of snow, strong southwest wind, treeline temperatures dropping to -8 C, freezing level at valley bottom.

Sunday: Mainly cloudy, up to 5 cm of snow, moderate southwest wind, treeline temperatures near -9 C, freezing level around 500 m. 

Monday: Mainly cloudy, up to 5 cm of snow, moderate winds becoming east, treeline temperatures near -8 C, freezing level around 500 m.

Tuesday: Mix of sun and cloud, light variable winds, treeline temperatures near -10 C, freezing level at valley bottom.

Avalanche Summary

Human-triggered avalanches remain likely on Sunday.

Early Saturday morning, operators reported a natural avalanche cycle releasing several large (up to size 2.5) and one very large (size 3-3.5) avalanches breaking within the storm snow.

Snowpack Summary

Intense bands of precipitation are forecast to bring another 10-20 cm of snow to the mountains in a highly localized pattern. Sustained southwest winds will have a sufficient supply of snow to drift into reactive wind slabs at upper elevations. Avoid freshly wind-loaded terrain features on Sunday (for example, down-wind of ridges and roll-overs).

A powerful storm on Friday night brought strong southwest winds and 25-50 cm of new snow to the mountains, favoring areas in the south of the region. A gradual temperature rise during the storm created warmer denser snow over colder lighter snow, and in many locations, storm accumulations sit on crust layers that formed in early December. This tricky combination of slab and sliding surface may require more time to recover and gain strength and warrants careful evaluation and cautious routing-finding.

In the north of the region, the snowpack near upper treeline elevations is complex and warrants conservative route selection. Weak faceted snow can be found near two possible crust layers that formed in early December, which may become reactive with loading from new snow. Our models suggest that this layer may be most pronounced at elevations between 1400-1800 and in areas north in the region, like the Hurley.  

The south of the region has seen substantially higher snow totals over the past week, with areas near the Coquilhalla seeing over a meter of accumulation since Monday. Expect to find deeper snow accumulations above the December crust and anticipate larger storm slab avalanches. Having endured warmer temperatures and more rainfall, the southern part of the region is just reaching the threshold for avalanches at most elevations. 

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Choose low-angled, sheltered terrain where new snow hasn't been wind-affected.
  • Keep in mind that human triggering potential persists as natural avalanching tapers off.

Problems

Wind Slabs

An icon showing Wind Slabs

Sustained southwest winds have a sufficient supply of snow to continue to drift into wind slabs on lee slopes at upper elevations. These wind slabs will likely be reactive to human triggering. 

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Storm Slabs

An icon showing Storm Slabs

25-50 cm of recent storm snow has formed a widespread storm slab problem that may remain possible to human trigger. Closely monitor how the recent storm snow is settling and bonding to the old surface.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 2.5

Persistent Slabs

An icon showing Persistent Slabs

In the north of the region, a layer of weak facets (sugary snow) can be found near crust layers that formed in early December. It is possible that this facet-crust combination will react as a persistent slab problem with rapid loading from recent snow. This potential persistent slab problem warrants diligent, conservative route selection at treeline elevations. Avoid open slopes and convex rolls near treeline where weak layers may be preserved.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible

Expected Size

1.5 - 3

Valid until: Dec 12th, 2021 4:00PM