Avalanche Forecast

Issued: Dec 22nd, 2018 3:37PM

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

shorton, Avalanche Canada

South Columbia.

Persistent slabs continue to be a concern and require conservative terrain choices like avoiding steep open slopes, convex rolls, and wind loaded terrain.

Summary

Confidence

High -

Weather Forecast

SATURDAY NIGHT: Scattered flurries with localized accumulations of 5-12 cm, moderate wind from the south, alpine temperatures around -10 C.SUNDAY: Isolated flurries with localized accumulations of 2-4 cm, light wind with moderate gusts from the southwest, alpine high temperatures around -6 C.MONDAY: Mostly cloudy, light wind from the southwest, alpine high temperatures around -6 C.TUESDAY: Mix of sun and cloud, light wind from the northwest, alpine high temperatures around -8 C.

Avalanche Summary

Natural avalanche activity is tapering off after a week of stormy weather. Natural avalanche activity was reported on Thursday and Friday, with small and large storm slabs avalanches (size 1-2), primarily on north and east aspects. A few natural avalanches also released on deeper persistent weak layers producing larger (size 2.5) avalanches with 100 cm thick slabs. Skiers have triggered small slabs (size 1) on all aspects in the 10-30 cm of most recent snow.Over the past week there have been a few notable large persistent slab avalanche that have been remotely triggered from skiers on adjacent slopes (most recently on Wednesday in the Valhallas). We can't rule out the possibility of deeper layers still being reactive to human triggers, as these layers are still adjusting to the weight of the new snow.

Snowpack Summary

Strong wind from the southwest has formed wind slabs in the alpine and around treeline.A week of stormy weather has deposited 50-100 cm of snow above a weak layer of facets (sugary snow), surface hoar (feathery crystals), and a sun crust (on south aspects) that formed during the dry spell in early December. This layer has been responsible for large persistent slab avalanches over the past week, particularly on north and east facing slopes above 1900 m. The potential exists for smaller avalanches to step down and trigger this deeper layer, resulting in very large avalanches.Another weak layer from mid-November is now buried up to 120 cm, but has been less active recently. It could potentially remain a concern on steep south-facing slopes where the surface hoar sits on a sun crust. At the base of the snowpack is a crust that formed in late October. The probability of triggering this layer is low, but the most suspect areas would be steep rocky alpine features with a shallow snowpack.

Problems

Persistent Slabs

A widespread weak layer buried 50-100 cm deep has the potential to produced large avalanches, especially on sheltered north and east facing slopes.

Use conservative route selection, choose moderate angled and supported terrain with low consequence.Remote triggering is a concern, watch out for adjacent slopes.Avoid open slopes and convex rolls at treeline where buried surface hoar may be preserved.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Wind Slabs

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

Use ridges or ribs to avoid pockets of wind loaded snow.The new snow will require several days to settle and stabilize.Be careful with wind loaded pockets, especially near ridge crests and roll-overs.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

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