Avalanche Forecast

Issued: Dec 29th, 2018 4:08PM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is low. Known problems include Wind Slabs and Deep Persistent Slabs.

jfloyer, Avalanche Canada

South Rockies.

Lots of recent wind has redistributed snow in exposed areas and has likely set up wind slabs that could be reactive to the weight of a rider.

Summary

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

SATURDAY NIGHT: 5-10 cm additional new snow expected. Strong southwesterly winds.SUNDAY: Light snow, 2-4 cm. Moderate northwesterly winds. Treeline temperatures around -6C.MONDAY: Dry with sunny breaks. Light northerly winds. Treeline temperatures around -14C.TUESDAY: Dry with sunny breaks. Light southwesterly winds. Treeline temperatures around -15C.

Avalanche Summary

On Thursday and Friday, the South Rockies field team found weak faceted snow, saw shooting cracks and experienced whumpfing as they traveled around the Nordstrom area south of Elkford and around the Crowsnest Pass.A great MIN report from Corbin on Thursday identifies a few slabs initiating in thin, rocky areas on a south aspect. While this is in the Lizard Range and Flathead forecast region, similar conditions should be expected around the South Rockies. Check out the report here.

Snowpack Summary

The upper snowpack consists of hard wind slabs on north aspects, scoured and a shallower snowpack on south aspects, and a mixed bag of lower density snow in more sheltered areas. In total, 60-90 cm of December snow has formed a slab that sits on a persistent weak layer of facets (sugary snow) that formed during the dry weather in early December. This layer is most likely to be triggered on steep features where the underlying ground cover is smooth, areas where the snowpack depths are variable, or on large convex features.The lower snowpack has a weak structure composed primarily of facets over a crust on the ground. It is very likely that an avalanche triggered on the persistent slab would step down to the lower facets, resulting in a full depth avalanche.

Problems

Wind Slabs

Moderate to strong winds will deposit snow in lee terrain. Watch for slabs below roll-overs, in cross-loaded terrain, and open areas.

If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Be cautious as you transition into wind affected terrain.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Deep Persistent Slabs

60-90 cm of snow sits on a weak layer of facets (sugary snow). The snow below this layer consists primarily of facets all the way to the ground. Avalanches triggered on this layer will likely step down to the ground, resulting in large avalanches.

Watch for whumpfing, hollow sounds, and shooting cracks.Be wary of slopes that did not previously avalanche.Avoid steep convexities or areas with a thin or variable snowpack.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 2.5

Valid until: Dec 30th, 2018 2:00PM