Avalanche Forecast

Issued: Mar 23rd, 2012 10:24AM

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

pgoddard, Avalanche Canada

Purcells.

Avalanche danger could spike to HIGH at treeline this weekend during times of rapid temperature change.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain

Weather Forecast

Saturday/Sunday: Clear and sunny. Light winds. Freezing level dropping to valley floor at night and climbing to around 1700 m on Saturday and 2000-2500 m on Sunday.Monday: Cloud developing in the morning. Light precipitation is possible by afternoon. Freezing level near 2000 m.

Avalanche Summary

There have been four close calls in the Purcell Mountains this week, all involving very large slabs releasing either from a distance or with a light load. This is a scary situation. 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/GKumsT). 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. In the Dogtooth Range on Tuesday, a size 3 slab was triggered by a skier on a north aspect. It's suspected to have initiated on the February weakness, and stepped to ground. Two large slabs (size 2-2.5) also released naturally on north to north-east aspects, up to 1 m deep. On Sunday, there were two snowmobile-triggered size 3 avalanches on west aspects in the southern Purcells near Kimberley (read more in 'related incidents' on this page). Strong solar warming forecast for the weekend is only going to make conditions trickier, decreasing stability on solar aspects which could step down to persistent weaknesses and create very large avalanches. All other aspects have also proven that they can fail as deep persistent slabs. Very conservative terrain choices would be wise.

Snowpack Summary

Recent snow and wind created mostly small, soft wind slabs. Sunshine is expected to destabilize surface snow and weaken cornices, which are large and threaten slopes below. Deeper in the snowpack, 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

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

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

Solar warming may trigger loose wet avalanches, particularly on steep, rocky, south-facing terrain.

Aspects: North, North East, East.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 5

Valid until: Mar 24th, 2012 9:00AM