Avalanche Forecast

Issued: Dec 23rd, 2018 4:37PM

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

Purcells.

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: Cloudy with clear periods, some isolated flurries in the southern Purcells, light wind from the west, alpine temperatures drop to -10°c. MONDAY: Mix of sun and cloud, light wind from the west, alpine high temperatures around -9°c. TUESDAY: Mix of sun and cloud, light wind from the west, alpine high temperatures around -10°c. WEDNESDAY: Mix of sun and cloud, light wind from the west, alpine high temperatures around -12°c.

Avalanche Summary

Natural avalanche activity has started to taper off, but large persistent slabs continue to be reactive to explosive triggers. On Sunday, a very large (size 3.5) avalanche was triggered by explosives on a northeast-facing slope that involved the full depth of the snowpack. Explosive control on Saturday produced slab avalanches (ranging from size 1-3) on several different weak layers. Over the past week, several notable persistent slab avalanches were remotely triggered from skiers on adjacent slopes, particularly in the Golden area. Given this weak snowpack structure, human triggering will likely continue to be a concern on slopes with thin or variable snow depth and on slopes that did not previously avalanche.

Snowpack Summary

Strong wind from the southwest and northwest has formed wind slabs in the alpine and around treeline. Approximately 50-100 cm of recent snow sits on a weak layer of facets (sugary snow), surface hoar (feathery crystals), and a sun crust (on south facing slopes) that formed during the dry spell in early December. Another similar weak layer is buried 80-150 cm. Finally, the base of the snowpack has weak facets layers at alpine and treeline elevations. All of these weak layers have been producing large avalanches over the past week. Human triggering any of these layer is most likely on slopes that didn't previously avalanche and on slopes that have variable snowpack depth (such as rocky alpine features).

Problems

Persistent Slabs

The likelihood of persistent slab avalanches is gradually decreasing, but triggering one of the weak layer layers in the lower snowpack has major consequences. This problem will likely linger through the holidays.

Use conservative route selection, stick to moderate angled terrain with low consequence.Be wary of slopes that did not previously avalancheAvoid convexities or areas with a thin or variable snowpack.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 3

Wind Slabs

Watch for wind slabs in lee and open 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 24th, 2018 2:00PM