Avalanche Forecast

Issued: Dec 23rd, 2018 3:44PM

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.

Avalanche Canada shorton, Avalanche Canada

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The persistent slab problem is best managed with patience and conservative terrain choices. Read more in the new forecaster blog here.

Summary

Confidence

Moderate.

Weather Forecast

SUNDAY NIGHT: Isolated flurries with localized accumulations of 2-5 cm, light wind from the southwest, alpine temperatures drop to -8°c. MONDAY: Mostly cloudy with a few sunny breaks, light wind, alpine high temperatures around -6°c. TUESDAY: Mostly cloudy with a few sunny breaks, light wind, alpine high temperatures around -8°c. WEDNESDAY: Mostly cloudy, light wind, alpine high temperatures around -10°c.

Avalanche Summary

On Saturday, a few large (size 3) avalanches were triggered by explosives on south-facing alpine slopes. The avalanches released on persistent weak layers 60-150 cm deep. Otherwise, natural and human triggered activity has started to tapered off. Over the past week, several notable persistent slab avalanches have been remotely triggered from skiers on adjacent slopes, particularly in the Selkirks and the northern tip of the Monashees near Valemount. The most recent occurred in the Selkirks on Friday, where a size 2.5 slab was remotely triggered on a south slope at 2200 m from low angle trees. The avalanche failed on a 120 cm deep surface hoar layer.

Snowpack Summary

Strong wind from various directions has formed wind slabs in the alpine and around treeline. A week of stormy weather has deposited 80-120 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 northeast facing slopes above 1900 m and on south-facing slopes in the alpine. The potential exists for smaller avalanches to step down and trigger this layer, resulting in very large avalanches. Another weak layer from mid-November is now buried up to 150 cm, but has been less active recently. At the base of the snowpack is a crust that formed in late October. Concern for these layers has dwindled, but they may still be worth considering in places such as steep, rocky, alpine terrain.

Problems

Persistent Slabs

An icon showing Persistent Slabs
The likelihood of persistent slab avalanches is gradually decreasing, but triggering a widespread weak layer buried 80-120 cm beneath the surface has major consequences. This problem will likely linger through the holidays.
Use caution on open slopes and convex rolls at treeline where buried surface hoar may be preserved.Use conservative route selection, choose moderate angled and supported terrain with low consequence.Remote triggering is a concern, watch out for adjacent slopes.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Wind Slabs

An icon showing Wind Slabs
Watch for wind slabs in open and lee terrain.
Be careful with wind loaded pockets, especially near ridge crests and roll-overs.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Dec 24th, 2018 2:00PM