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.

shorton, Avalanche Canada

Cariboos.

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

Summary

Confidence

Moderate - Due to the number of field observations.

Weather Forecast

SUNDAY NIGHT: Scattered flurries with localized accumulations of 3-8 cm, light wind from the southwest, alpine temperatures drop to -10Â°c. MONDAY: Mostly cloudy with isolated flurries, light wind from the south, alpine high temperatures around -7Â°c. TUESDAY: Mostly cloudy, light wind, alpine high temperatures around -10Â°c. WEDNESDAY: Mostly cloudy, light wind, alpine high temperatures around -12Â°c.

Avalanche Summary

No recent avalanches have been reported, but evidence of a natural avalanche cycle was reported on Friday. Numerous large (size 2) storm slabs and wind slabs were reported, primarily on north and east aspects. Larger persistent slab avalanches (size 3) were also reported on all aspects, a few even destroying mature trees. The persistent slabs were 50-150 cm thick and likely failed on the early December weak layer. Over the past week numerous large natural and human triggered avalanches (size 2-3) have been reported, several of which were triggered remotely (from a distance). A notable human triggered size 2.5 avalanche occurred on a northeast facing slope in Allan Creek last weekend. See details in this MIN report.

Snowpack Summary

Strong wind from the southwest has formed wind slabs in the alpine and around treeline. Stormy weather over the past two weeks 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, 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 150 cm, but has been less active recently. At the base of the snowpack is a crust that formed in late October. The probability of triggering these deeper layers is low, but the most suspect areas would be steep rocky alpine features with a shallow snowpack.

Problems

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 conservative route selection, choose moderate angled and supported terrain with low consequence.Remote triggering is a concern, watch out for adjacent slopes.Use caution on open slopes and convex rolls

Aspects: All aspects.

Elevations: All elevations.

Likelihood

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.

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.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

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