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Backcountry Avalanche Advisory

As of Wednesday, March 18

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Alpine: Extreme through Friday

Treeline: High through Friday

Below treeline: High through Friday

Travel Advisory: Solar crusts, near surface facets and areas of wind slab have been covered by the approximately 80 cm of storm snow that has fallen since Friday night, 20 cm of which fell during the past 24 hours. Winds throughout this period were from the SW and Southeasterly directions, gusting at times to 70 km/h. Soft slabs to size 2 have built in lee start zones in the alpine terrain and they will continue to do so with the forecast for continued snowfall throughout the week. At treeline elevations and below the snow is much less consolidated. Caution is advised on any previously shallow rocky areas that are filling in with the late season snowfall. Remember that sometimes it only takes a bit of wind-transported snow, rising freezing levels, or periods of sunshine to tip the balance and to overstress a buried weakness in the snowpack. Stick to the lower angle terrain in the trees and err on the side of caution.

Avalanche Activity: Periodically during the past two weeks there have been reports of deep slab avalanches running up to size 3, stepping down to the Dec. 6 crust. Explosive and ski testing carried out during the past several days produced soft slab avalanches that were involving for the most part the storm snow only, stepping down deeper to a buried layer of facets in a few isolated areas. As previously mentioned, the snow at lower elevations remains loose and will likely sluff with the weight of a person or with rising freezing levels today and tomorrow. Bear in mind that as the load continues to increase over the various persistent weak layers buried within our snowpack, we can expect to see deep slab avalanches beginning to run again in some isolated areas.

Snowpack: The storm snow is sitting on a variety of old surfaces. In the alpine terrain there has been lots of wind affect but the slab rapidly softens as you lose elevation. The crust/facet combination that formed in early December is buried below a stiff, hard bridging layer in some areas. In other areas where the snowpack is shallow, the basal weakness is more extensive and the overlying bridge is much weaker. These layers appear to be reaching their critical threshold in some areas with reports of skier- and solar-triggered activity occurring periodically during the past two weeks in various areas of the coast range. Travel with extreme caution as the new snow-load, rising freezing levels, or possibly even the effects of brief exposure to sun may trigger another round of old snow releases.

Weather: A continual series of systems embedded in a more Westerly flow is expected to bring us periods of moderate and at times heavy snowfall throughout the week. The freezing level will rise to around 1,200-1,300 metres today, but aside from that will remain close to the valley bottom throughout this forecast period.

Conditions may vary and can change rapidly. Check for the most current conditions before heading out into the backcountry. Daily updates for the areas adjacent to Whistler/Blackcomb are available at 604-938-7676, or surf to www.whistler-blackcomb.com/weather where there is also a link to the CAA public avalanche bulletin, or call 1-800-667-1105.

- Whistler Mtn Snow Safety

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