Avalanche Forecast

Issued: Dec 23rd, 2018 4:39PM

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

High - Due to the number and quality of field observations.

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 -8°c. TUESDAY: Mix of sun and cloud, light wind, alpine high temperatures around -10°c. WEDNESDAY: Mostly cloudy, light wind, alpine high temperatures around -10°c.

Avalanche Summary

Preliminary reports from Sunday indicate the most recent 20 cm of new snow was reactive to skiers on steep and convex features. No significant avalanche activity was reported on Saturday, as natural and human triggered activity has started to tapered off. However, as recent as Friday, large (size 2-3) persistent slab avalanches were occurring naturally. There have also been a few notable persistent slab avalanches remotely triggered from skiers on adjacent slopes. Most recently, a few large (size 2-2.5) avalanches on north-facing slopes at treeline elevations were remotely triggered by skiers in the Selkirks on Wednesday.

Snowpack Summary

Recent 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 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 120 cm, but has been less active recently. At the base of the snowpack is a crust that formed in late October.

Problems

Persistent Slabs

An icon showing Persistent Slabs
The likelihood of persistent slab avalanches is gradually decreasing, but triggering a widespread weak layer buried 50-100 cm beneath the surface has major consequences. This problem will likely linger through the holidays.
Avoid open slopes and convex rolls at treeline where buried surface hoar may be preserved.Remote triggering is a concern, watch out for adjacent slopes.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: Alpine, Treeline.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

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