Avalanche Forecast

Issued: Dec 28th, 2018 3:56PM

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

dsaly, Avalanche Canada

South Rockies.

Extreme winds will redistribute any and all loose snow. Expect to see scouring, hard wind slabs, and snow transport. Keep the persistent weak layer in mind, it may be easier to trigger in areas affected by wind.

Summary

Confidence

Low - Due to the number of field observations

Weather Forecast

FRIDAY NIGHT: Cloudy with isolated flurries, up to 5 cm accumulation. Moderate west wind. Alpine low of -13C.SATURDAY: Cloudy with scattered flurries, trace to 10 cm accumulation. Moderate west wind gusting strong to extreme. Alpine high -4, freezing level rising about 1500 m. Environment Canada has issued a wind warning for the area around Crowsnest Pass and the front ranges here.SUNDAY: Mix of sun and cloud. Light northwest wind with occasional moderate-strong gusts. Alpine high -6C.MONDAY: Mix of sun and cloud. Light northwest wind with occasional moderate gusts. Alpine low -16C.

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.Over the last weekend, the persistent weak layer was active, explosives triggered avalanches to size 2.5 and a cornice triggered a size 2 avalanche. Skier traffic was also able to trigger wind slab avalanches to size 2. Though avalanche activity on this layer has slowed, avalanches failing on this layer have the potential to be large and destructive.

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. Though avalanche activity on this layer has slowed down in recent days, it may still be easy for humans to trigger avalanches on this layer in certain terrain features. Steep features where the underlying ground cover is smooth, places where the snowpack depths are variable, and large convex features are some of the more likely places to trigger this layer.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

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.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

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.

Be cautious as you transition into wind affected terrain.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 29th, 2018 2:00PM