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Backcountry Avalanche Advisory

As of Wednesday, April 29

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Alpine: Considerable through Friday

Treeline: Moderate through Friday

Below Treeline: Low through Friday

Travel Advisory: The crust that has helped hold everything together is expected to begin to fail today. Temperatures have not gone above zero in the alpine since April 21 when we recorded the last observed size 2.5 deep slab avalanche. Warm clear days will cause temperatures on solar exposed slopes to soar, breaking down the crust and initiating wet avalanche activity. Cornices will also become weak so give them a wide berth from above and below. Lately, every time a significant weather event occurs, the snowpack responds with deep slab avalanche activity. This pattern will continue as long as the 2008-09 snowpack hangs around.

Avalanche Activity: There have been no reports of natural or human triggered avalanche activity since the 21st of April. However, two days of above freezing temperatures on the 20th and 21st resulted in at least one observed full depth natural avalanche. The snowpack is expected to awaken once again with temperatures forecast to rise significantly over the next few days. Wet avalanches can be expected later in the day on direct solar aspects. In the past several weeks there have been natural avalanches occurring periodically up to size three and four. The Dec. 6 weakness has definitely not gone away, and it will continue to produce large avalanches periodically throughout the spring season.

Snowpack: There is as much as 30 cm of hard crust on all aspects in the alpine and at treeline. During the recent cool weather the direct solar exposures and daytime warming has broken down the crust on South exposed slopes only. The snowpack is very wet and weak below this crust. The persistent weak layers in the snowpack are all at or near their threshold.

Weather: We are settling into a spring freeze-thaw cycle. Daytime temperatures are forecast to shoot above 2,200 metres on Wednesday and get even higher through Friday. Overnight cooling will also diminish and may only reach zero at 1,800 metres on Saturday.

Regular updates are still available at www.whistlerblackcomb.com or www.avalanche.ca.

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