Avalanche Forecast

Issued: Mar 25th, 2012 11:12AM

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

Avalanche Canada triley, Avalanche Canada

There is a possibility of higher than forecast freezing levels combined with precipitation that might be rain. If it is raining above 1500 metres in your area, then the danger ratings may be closer to HIGH.

Summary

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain on Monday

Weather Forecast

High cloud moved across the region on Sunday afternoon that limited the extent of solar warming, but trapped warm air beneath the cloud layer that raised the alpine temperatures to near zero. The freezing level is expected to drop down to near valley bottom by Monday morning. A moist system is forecast to move north from south of the border on Monday morning. Some models show a narrow band of precipitation and warm air moving up into the Purcells. If this happens, the region may see 20-25 cm of snow at higher elevations, and rain below 1400 metres. Tuesday should continue to be unsettled as southwest winds increase during the day and the freezing level stays at about 1500 metres. Precipitation should start again on Wednesday morning and build to heavy by evening.

Avalanche Summary

A natural cornice fall size 2.5 was reported from the high alpine on a NW aspect on Saturday. On Friday, a very large avalanche was triggered by a cornice in Gorman Lake (Dogtooth Range). It was wide, deep and covered sled tracks. Photos here: http://bit.ly/GMOYCv . There have been four other close calls in the Purcell Mountains this week, all involving very large slabs releasing either from a distance or with a light load. On Thursday, a snowmobiler remotely triggered a size 3.5 slab on an east aspect at 2400m at Oldman Creek, east of Quartz Creek (video here http://bit.ly/GLHIbg). It failed 1-2 m deep, was 200-300 m wide and ran full path, taking out mature timber. A second slope also failed, either remotely or sympathetically.

Snowpack Summary

Warm alpine temperatures combined with strong solar radiation on Sunday caused moist snow up to about 2400 metres. The major concerns are the mid-February persistent weak layer, buried 1-2 m deep, and facets at the base of the snowpack. The February layer demands respect right now. It is very touchy and can be triggered remotely or by a light load on a variety of aspects, creating frighteningly large avalanches.

Problems

Deep Persistent Slabs

An icon showing Deep Persistent Slabs
Very large avalanches have been failing on a weak layer up to 2 m deep with alarming ease. This problem demands respect. Choose very conservative terrain, as the consequences of triggering this layer could be huge.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

4 - 8

Cornices

An icon showing Cornices
Large cornices are looming above many slopes. These may weaken with fluctuating temperatures and could act as a trigger for a very large avalanche. Variable wind slabs can also be found behind ridges and terrain breaks.

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

Elevations: Alpine.

Likelihood

Likely

Expected Size

1 - 4

Loose Wet

An icon showing Loose Wet
Previous solar warming may not get a chance to recover overnight. Forecast rain up to about 1400 metres may weaken the snowpack. Loose wet releases at treeline may step down to the deeply buried weak layer.

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 5

Valid until: Mar 26th, 2012 9:00AM

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