Avalanche Forecast

Issued: Apr 21st, 2012 10:13AM

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

jlammers, Avalanche Canada

Purcells.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain

Weather Forecast

The region will see mostly scattered cloud on Sunday with the possibility of light rain on Monday. Freezing levels will sit at about 3000m for both days with moderate southwesterly ridgetop winds.

Avalanche Summary

Several size 2 point releases and slab avalanches were observed running within the storm snow on Friday. There will be a shift to wet loose and wet slab instabilities on Sunday and Monday as freezing levels rise.

Snowpack Summary

On Thursday night, light to locally moderate amounts of snow fell forming wind slabs that most likely settled considerably or turned to wet slabs with warming on Saturday. The recently fallen snow overlies well settled powder, melt-freeze crust sandwiches and wet grains. At lower elevations, warm temperatures continue 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. Watch for increased activity in steep, sun-exposed rocky terrain. Loose snow avalanches may entrain a great deal of mass and may trigger deeper weak layers.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely - Certain

Expected Size

1 - 5

Wet Slabs

With warming forecast for Sunday and Monday, wet slabs become more likely. A number of crusts in the upper snowpack may act as a suitable sliding layer for wet slabs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 5

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 - Possible

Expected Size

3 - 7

Valid until: Apr 22nd, 2012 9:00AM