Avalanche Forecast

Issued: Apr 17th, 2017 4:20PM

The alpine rating is moderate, the treeline rating is low, and the below treeline rating is low. Known problems include Cornices, Wind Slabs and Loose Wet.

jsmith, Avalanche Canada

Purcells.

Minimize exposure to slopes with large cornices overhead when it is cool and cloudy and completely avoid them if it is warm and/or sunny.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

TUESDAY: Cloudy with isolated flurries. Light to moderate southwesterly ridgetop winds. Freezing level around 2100m.WEDNESDAY: Mostly cloudy. Moderate southwesterly ridgetop winds. Freezing level around 2100m.THURSDAY: Mix of sun and cloud. Light southwesterly ridgetop winds. Freezing level around 2200m.NOTE: The convective flurries which are common during this time of year can result in widely varying snowfall amounts throughout a region. These spring squalls routinely drop 20+ cm of snow in one valley while the adjacent drainage remains dry. For this reason, the distribution of avalanche problems associated with new snow, such as wind slabs, can vary greatly within a region.

Avalanche Summary

Numerous cornice triggered, large slab avalanches up to size 3 were reported on a variety of aspects in this region on Sunday. Falling cornices triggering large avalanches is currently our primary concern in this region.

Snowpack Summary

Triggering large avalanches on facets near the bottom of the snowpack is currently our primary concern. On high north facing terrain, which is currently where the best skiing can be found, the problem is the possibility that if a large cornice falls on a steep slope, it will trigger this layer. On solar aspects, the problem is small loose wet or wind slab avalanches stepping down to this layer or skier triggering the layer by hitting a shallow spot in a large, steep, and rocky alpine face. Additionally, convective flurries and moderate southwest winds may form fresh wind slabs on lee features at Treeline and above on Tuesday. Fresh snow combined with warm temperatures will increase the likelihood of small loose wet avalanches on all aspects at Treeline and below.

Problems

Cornices

Minimize exposure to slopes with large cornices overhead when it is cool and cloudy and completely avoid them if it is warm and/or sunny.

Cornice failures could trigger large avalanches on sugary facets near the bottom of the snowpack.Cornices often break further back than expected; give them a wide berth when traveling on ridgetops.

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

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Wind Slabs

Convective flurries and moderate southwesterly winds may create small wind slabs in lee features below alpine ridgetops.

Use ridges or ribs to avoid pockets of wind loaded snow.Be cautious with wind loaded pockets near ridge crests and roll-overs.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 2

Loose Wet

Small loose wet avalanches can still have big consequence if they push you into terrain traps such as cliffs and gullies.

Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Apr 18th, 2017 2:00PM