Avalanche Forecast

Issued: Dec 24th, 2018 3:20PM

The alpine rating is moderate, 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 - The weather pattern is stable

Weather Forecast

MONDAY NIGHT: Mostly cloudy with isolated flurries, light wind from the northwest, alpine temperatures drop to -12 C.TUESDAY: Mostly cloudy with sunny breaks in the afternoon, light wind from the northwest, alpine high temperatures around -10 C.WEDNESDAY: Mostly cloudy with isolated flurries, light wind, alpine high temperatures around -12 C.THURSDAY: Mix of sun and cloud, moderate wind from the northwest, alpine high temperatures around -12 C.

Avalanche Summary

A few large (size 2-3) natural persistent slab avalanches were reported on Sunday. These avalanches were reported south aspects in the alpine and failed on failed on weak layers 150 cm below the surface. Natural activity has tapered off after an active period last week, when numerous persistent slab avalanches (up to size 3) were reported on all aspects (a few that even destroyed mature trees). The persistent slabs were 50-150 cm thick and likely failed on the early December weak layer. The same layer was responsible for several large human triggered avalanches earlier this month (see this MIN report for an example), and although there are no recent reports of human triggered avalanches, professionals are still being very cautious with their terrain choices because of this layer.

Snowpack Summary

Low density snow from the past few days sits above wind affected snow in the alpine and around treeline.A weak layer that formed during the dry spell in early December is now 80-120 cm deep. The layer is composed of weak facets, surface hoar, and a sun crust on steep south-facing slopes. This layer has been responsible for large persistent slab avalanches over the past two weeks, particularly on northeast facing slopes between 1900-2300 m and on steep south-facing slopes in the alpine.Another weak layer from mid-November is now buried up to 150 cm and a crust that formed in late October is found near the bottom of the snowpack. The probability of triggering these deeper layers is low, but the most suspect areas would be shallow spots in steep rocky terrain.

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.Use caution on open slopes and convex rolls at treeline where buried surface hoar may be preserved.Minimize exposure to steep, planar, south-facing alpine slopes

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Wind Slabs

Watch for wind slabs in open and lee terrain.

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.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Dec 25th, 2018 2:00PM