Cold snap cause for snowpack concerns

Persistent weak layers and early season hazards biggest dangers in backcountry

With the Coast Mountains having received around 50 per cent of the usual snowfall for this time of year, avalanche activity has been minimal thus far. But a mix of recent cold weather and a thin snowpack could spell dangerous conditions when the next sizeable storm arrives.

"It's a little too early to tell right now, but we definitely have the potential for some of these layers to become persistent weaknesses, and they may be with us for some time," said Whistler Mountain avalanche forecaster Anton Horvath.

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"Because the snowpack got so cold we had what's called 'faceting' taking place. When you have faceting associated with crusts, there's the potential for a persistent weakness once you get a big load on top of it."

Faceting is a rapid growth of snow crystals due to the temperature gradient in the snow pack, and in this case the difference between the warmer ground temperature and the cold air temperatures was the below -20C cold snap experienced over the last few weeks. When snow crystals grow and change shape they don't bond to each other as well, forming weak layers that can release when loaded with a large enough snowfall.

With small amounts of snow arriving this week, and another sunny, high-pressure system to follow, Horvath urged all backcountry travellers heading out to take the time and observe the snowpack themselves.

"In addition to reading the bulletin, everybody should be out there digging pits themselves and seeing what's going on," he said.

"They should be observing to see what kind of shears we are getting on these buried weaknesses and observing what's going on at the interfaces."

But buried layers in the snowpack are not the only concern when travelling in the backcountry right now. With half of the usual December snowpack on the ground, early season hazards are just as prevalent in the backcountry as they are in the resort.

"On the glaciers, the crevasses are far more open than they would normally be at this time of year," said Eirik Sharp, forecaster for the avalanche warning service at the Canadian Avalanche Centre.

"A small avalanche can also drag you into a boulder field or into some trees. The early season hazards are lingering this year and definitely magnifying the effects of getting caught in an avalanche. Even a small avalanche bullying someone into a crevasse is going to make it a lot more dangerous than what it would be normally."

Sharp added that while snowfalls are currently near record lows, conditions can still turn around this early into the season.

"We're not looking at an El Nino or La Nina cycle, we're looking at an average winter in terms of large scale weather patterns. It's off to a slow start, but that could change."

For more information on the local avalanche and snowpack conditions go to http://www.whistlerblackcomb.com/the-mountain/backcountry/avalanche-advisory or http://www.avalanche.ca/cac/bulletins/latest

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