Avalanche Forecast

Issued: Apr 19th, 2012 10:33AM

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

jlammers, Avalanche Canada

Purcells.

Summary

Confidence

Fair - Intensity of incoming weather is uncertain on Thursday

Weather Forecast

A frontal system is expected to arrive Thursday night bringing moderate amounts of precipitation, strong southwest winds at higher elevations and freezing levels to about 1600m. Light flurries should persist through Friday, but will give way to a ridge that will bring clear skies to the region over the weekend. Freezing levels on Saturday are expected to be at around 2000m, climbing up to about 2800m on Sunday.

Avalanche Summary

In the last few days there have been several natural avalanches at higher elevations to size 1.5 running within recent storm snow. There was also a size 2 natural glide crack release at 2000m. With forecast weather, I expect new wind slab activity at higher elevations.

Snowpack Summary

On the surface, light to moderate amounts of recently fallen snow override melt-freeze crusts at higher elevations. At lower elevations, the snowpack is generally isothermal. 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

Wind Slabs

New wind slabs are expected with forecast weather. They may not bond well to newly formed crusts where they exist.

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

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

Loose Wet

Loose wet snow avalanches are expected during periods of daytime warming or if periods of rain showers persist. Loose snow avalanches may entrain a great deal of mass and may trigger deep weak layers.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

2 - 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

Expected Size

3 - 7

Valid until: Apr 20th, 2012 9:00AM