Avalanche Forecast

Issued: Dec 21st, 2018 4:29PM

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.

Avalanche Canada shorton, Avalanche Canada

Triggering large avalanches on a 1m deep weak layer is a serious concern in the region. Avoid steep open slopes, convexities, and terrain traps.

Summary

Confidence

Moderate - Due to the number of field observations.

Weather Forecast

FRIDAY NIGHT: Mostly clear skies, moderate wind from the northwest, alpine temperatures drop to -18°c. SATURDAY: Clear in the morning then increasing cloud throughout the day, light wind from the south, alpine high temperatures around -8°c. SUNDAY: Mostly cloudy with isolated flurries, 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.

Avalanche Summary

Limited observations from Friday suggest some large (size 2) wind slab avalanches released naturally from north and east aspects. 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 in Allan Creek on last weekend. The avalanche was triggered on a northeast facing alpine slope. A report of this avalanche can be found on the Mountain Information Network here.

Snowpack Summary

Strong wind from the southwest has formed fresh wind slabs in the alpine and around treeline. A week of stormy weather 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

An icon showing Persistent Slabs
A widespread weak layer buried 80-120 cm deep has produced large avalanches with wide propagations over the past week. This weakness will take time to heal.
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 - 3.5

Wind Slabs

An icon showing Wind Slabs
Recent snowfall accompanied with strong wind from the southwest has left open and lee terrain covered with touchy wind slabs.
Use caution in lee areas. Recent wind loading has created thick 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 - Likely

Expected Size

1 - 2

Valid until: Dec 22nd, 2018 2:00PM