Avalanche Forecast

Issued: Apr 20th, 2012 10:19AM

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

jlammers, Avalanche Canada

Purcells.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain

Weather Forecast

Saturday: Clear skies / light to moderate southwest winds / freezing level at 2000m Sunday: Light precipitation / strong southwesterly winds / freezing level at about 2800m Monday: light precipitation / strong southwest winds / freezing level at about 2800m

Avalanche Summary

On Thursday, a size 2.5 natural cornice fall was reported. A smaller cornice fall triggered a size 2 wind-loaded slab on the same day. Wet sluffing to size 2 was also reported on solar aspects. I expect continued wind slab reactivity in the wake of Thursday night's storm with a transition to increased wet avalanche activity with warm temperatures forecast for the weekend.

Snowpack Summary

On Thursday night, light to locally heavy amounts of snow fell forming wind slabs that overlie a variety of surfaces that include: well settled powder, melt-freeze crusts and wet grains. At lower elevations, rain has continued to penetrate and weaken the isothermal snowpack. Deeper in the snowpack there are layers that may not be reactive with cooler temperatures, but should be on your radar as spring brings more prolonged periods of warm weather. These layers include near surface crusts, the early-February surface hoar (about 100-170cm down) and basal facets. Cornices in region are also large and will become weak with warm temperatures.

Problems

Loose Wet

Loose wet snow avalanches are expected with warming forecast for the weekend. Loose snow avalanches may entrain a great deal of mass and may trigger deep weak layers.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 5

Wind Slabs

Fresh wind slabs exist in some parts of the region. They may not bond well to recently formed crusts where they exist.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Deep Persistent Slabs

Avalanches may release on the deeply buried weak layers from February or from depth hoar that developed early winter. The likelihood will increase if warm temperatures persist and there is no overnight freeze.

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

3 - 7

Valid until: Apr 21st, 2012 9:00AM