Avalanche Forecast

Issued: Dec 22nd, 2018 4:14PM

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

shorton, Avalanche Canada

Purcells.

The primary concern is persistent weak layers lurking in the snowpack. These types of problems take time to heal, and are best managed with patience and conservative terrain choices.

Summary

Confidence

Moderate - The weather pattern is stable

Weather Forecast

SATURDAY NIGHT: Isolated flurries with trace amounts in northern and eastern parts of the region and up to 6 cm in southwestern parts of the region, moderate wind from the southwest, alpine temperatures drop to -12 C.SUNDAY: Isolated flurries with localized accumulations of 2-4 cm, light wind with moderate gusts from the southwest, alpine high temperatures around -8 C.MONDAY: Mix of sun and cloud, light wind from the west, alpine high temperatures around -8 C.TUESDAY: Mix of sun and cloud, light wind from the west, alpine high temperatures around -10 C.

Avalanche Summary

Large persistent slab avalanches continue to be reported on a regular basis. Natural activity quieted down on Saturday, but large persistent slabs were still reactive to explosive triggering.A widespread natural cycle occurred on Thursday and Friday with large (size 2-3) persistent slab and storm slab avalanches on all aspects. Some of these avalanches involved the full depth of the snowpack with up to 200 cm thick crowns.Over the past week there have been several notable large persistent slab avalanche that have been remotely triggered from skiers on adjacent slopes, particularly in the Golden area. Given this weak snowpack structure, human triggering will likely continue to be a concern on slopes with thin or variable snow depth and on slopes that did not previously avalanche.

Snowpack Summary

Strong wind from the southwest and northwest has formed wind slabs in the alpine and around treeline. Approximately 50-100 cm of recent snow sits on a weak layer of facets (sugary snow), surface hoar (feathery crystals), and a sun crust (on south facing slopes) that formed during the dry spell in early December. Another similar weak layer is buried 80-150 cm. Finally, the base of the snowpack has weak facets layers at alpine and treeline elevations. All of these weak layers have been producing large avalanches over the past week. Human triggering any of these layer is most likely on slopes that didn't previously avalanche and on slopes that have variable snowpack depth (such as rocky alpine features).

Problems

Persistent Slabs

Persistent weak layers have become very sensitive under the weight of the new snow and have produced numerous large avalanches. It's critical to give these layers more time to heal.

Avoid convexities or areas with a thin or variable snowpack.Be wary of slopes that did not previously avalancheUse conservative route selection, stick to moderate angled terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 3

Wind Slabs

Recent snowfall accompanied with strong wind from various directions has left open and lee terrain covered with wind slabs.

If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Use ridges or ribs to avoid pockets of wind loaded snow.The new snow will require several days to settle and stabilize.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Dec 23rd, 2018 2:00PM