A number of large, destructive avalanches in the SE corner of BC have been reported in the last 12 to 24 hours. Areas that received significant loads of new snow in recent days are reporting size 3 to 3.5 avalanches with crowns 200-300cm thick. In some cases these are running on relatively low angle terrain and are propagating across significant terrain features (one fracture line crossed a pronounced ridge feature SE aspect on one side, NE aspect on the other). We suspect the rapid loading and significant accumulations of new snow coupled with warm temperatures and perhaps windloading have overloaded deeply buried weak layers. The most likely suspect seems to be a rain crust/facet combo that formed in mid-January. More snow with continuing warm temps are forecast for this region and we suspect this condition will persist for at least several days after the weather abates. We are also remembering how a similar storm in mid-January continued to produce large slides during the cooling trend after the end of the storm—even though the weak layers are not quite the same, the weather pattern is similar. I personally would be careful during and for a couple of days after any cooling trend.
This condition has prompted the Canadian Avalanche Centre to issue a special public avalanche warning for the area:
Special Public Avalanche Warning for
Backcountry Recreationists in Southeast BC
March 11, 2011, Revelstoke, BC: The Canadian Avalanche Centre (CAC) is issuing a special public avalanche warning for southeast BC. This warning includes the mountainous areas from the US border north through Moyie and Cranbrook to Wasa, and east through Sparwood to the Alberta border. This warning is in effect immediately and will extend through the weekend to at least Tuesday March 15.
A recent storm dropped a large amount of snow in the area, explains Karl Klassen, Manager of the CAC's Public Avalanche Warning Service. "The warm and heavy snow has added a significant load to the snowpack," says Klassen. "Continuing warm temperatures and additional snowfall have the potential to create large and destructive avalanches, running to valley bottom."
The CAC is advising all backcountry users to avoid avalanche terrain. "Skiers and snowmobilers should be especially wary of stopping or regrouping in areas exposed to avalanche terrain from above, even in valley bottoms," adds Klassen. "This is not the time to be making aggressive terrain choices."
Every member of a backcountry party needs to be equipped with a shovel, probe and transceiver. The CAC strongly recommends that all backcountry users take an avalanche awareness course. Snowpack stability changes constantly throughout the winter; backcountry users need to check the avalanche bulletin regularly to keep informed of conditions in their area. Avalanche bulletins are can be found at www.avalanche.ca.
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For more information contact:
Karl Klassen, Manager Public Avalanche Warning Service
James Floyer, Public Avalanche Forecaster
250.837.2141 (227)