Avalanche Forecast

Issued: Dec 22nd, 2018 3:00PM

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

Cariboos.

As we come out of a very active avalanche period it's critical to make conservative terrain choices like avoiding steep slopes, convex rolls, and wind loaded terrain.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

SATURDAY NIGHT: Scattered flurries with 5-10 cm of snow, moderate wind from the south, alpine temperatures around -12 C.SUNDAY: Isolated flurries with 2-4 cm of snow, moderate wind from the south, alpine high temperatures around -7 C.MONDAY: Mostly cloudy with isolated flurries, light wind from the south, alpine high temperatures around -7 C.TUESDAY: Mostly cloudy, light wind from the west, alpine high temperatures around -10 C.

Avalanche Summary

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 10 days 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 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 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 80-120 cm deep has produced large avalanches with wide propagations over the past week. This weakness needs more time to heal.

Use caution on open slopes and convex rolls 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: 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.

Use ridges or ribs to avoid pockets of wind loaded snow.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Use caution in lee areas. Recent wind loading has created thick wind slabs.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

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