Avalanche Forecast

Issued: Dec 18th, 2021 1:00PM

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

Avalanche Canada JSmith, Avalanche Canada

Touchy storm slabs that formed on Saturday will remain reactive to human triggers through the weekend; especially in wind affected terrain.

The new snow will increase the likelihood of triggering the persistent slab problem. Learn more HERE.

Summary

Confidence

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

Weather Forecast

SATURDAY NIGHT: Flurries; 3-5 cm / Light northwest wind / Low of -19

SUNDAY: Clearing skies with a mix of sun and cloud / Light north wind / High of -16

MONDAY: Mix of sun and cloud / Light west wind / High of -17

TUESDAY: Increasing cloudiness with flurries; 3-5 cm / Strong west wind / High of -14

Avalanche Summary

Fresh storm slabs formed on Saturday will likely remain reactive to human triggers through the weekend, especially in wind affected terrain.

A skier triggered size 2.5 persistent slab was reported on Tuesday. This avalanche failed on the crust layer down 40-150 cm. The photo of this avalanche in our recent blog demonstrates the layer's ability to propagate large distances, resulting in large and destructive avalanches.

Snowpack Summary

15-25 cm of new snow and strong southwesterly winds on Saturday formed touchy storm slabs that will remain reactive to human triggers though the weekend; especially in wind affected terrain.

Below the new snow, the prominent layer of concern in most of the region is a crust that was formed in early December and is now down 40-150 cm, which is prime depth for human triggering.

This layer has created a persistent slab problem that has recently surprised riders with large avalanches.

Another crust layer near the bottom of the snowpack has not produced any recent avalanches but may be possible to trigger by hitting a shallow spot in the snowpack on a large alpine feature.

Terrain and Travel

  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.

Problems

Storm Slabs

An icon showing Storm Slabs

Fresh storm slabs formed on Saturday will remain reactive to human triggers through the weekend, especially in wind affected terrain.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1.5 - 2.5

Persistent Slabs

An icon showing Persistent Slabs

 A layer of weak facets (sugary snow) can be found down 60-150 cm near a crust layer that formed in early December. This persistent slab problem has recently been most reactive at treeline elevations and is possible to human trigger on some slopes. Avoid likely trigger spots such as steep, convex slopes, with a shallow or thin to thick snowpack.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible

Expected Size

2 - 3

Valid until: Dec 19th, 2021 1:00PM