鈥淰ery large avalanches are almost certain鈥� on Friday, Jan. 3, warned Avalanche Canada in an uncommon extreme avalanche warning issued for the Sea-to-Sky mountains.
In a statement, the organization said it 鈥渞arely sees鈥� the danger rating rise to extreme, and, on its website, urged the public to avoid all avalanche terrain as 鈥渋ntense precipitation will form large storm slabs and add tremendous stress to an already wet snowpack.鈥�
鈥淲e typically see extreme ratings about once or twice per year and that鈥檚 across all of Western Canada,鈥� added Avalanche Canada forecaster Simon Horton in a follow-up call.
The extreme danger rating for Friday applies to the treeline and alpine areas in the backcountry, and lowers to 鈥渉igh鈥� through the weekend.
It went on to say that avalanches have the potential to run long distances and destroy mature timber. It鈥檚 the combination of 鈥渁 very high probability of avalanches and the fact that the avalanches are expected to be very large鈥� that has resulted in the rare extreme rating, Horton explained.
While the greatest risk was posed during the 鈥減eak intensity鈥� of Friday morning鈥檚 storm, large natural avalanches are 鈥渓ikely鈥� through the day and the rest of the weekend, Avalanche Canada said.
Approximately 40 centimetres of snow fell around Whistler between Thursday night and midday Friday, combining with freezing rain and strong southwesterly winds.
A weaker New Year鈥檚 Day storm deposited about 40 cm of snow above a layer of surface hoar, which led to 鈥渞eactive storm slabs鈥� in the past few days. Multiple weak layers are buried deeper in the snowpack, the forecast said, including a variable layer of surface hoar and crust from mid-December as well as 鈥渁 deeper layer of sugary facets and crust鈥� from late-November.
"It鈥檚 been quite stormy for the last few weeks but the fall was relatively dry, so that set up a weak snowpack structure, so when there was little snow on the ground in November and early December, it formed a lot of weak snow, and since then, these past few weeks when it鈥檚 been snowing harder, the bottom of the snowpack isn鈥檛 able to support the weight of this new snow,鈥� Horton noted. 鈥淲e鈥檝e seen what we call 鈥榩ersistent slab avalanches,鈥� which are much thicker than what you鈥檇 typically get just during a storm.鈥�
A second intense storm is in the forecast for Friday evening, expected to bring another 30 to 50 cm of snow above 700-metre elevation by Saturday afternoon. Another storm is expected to bring 15 to 30 cm of snow on Sunday.
At Whistler Blackcomb, all upper alpine terrain remains closed. Both the Peak 2 Peak and the upper portion of the Blackcomb Gondola are also closed. At press time, all skiing and riding has been relegated to 鈥渞estaurant-level and below,鈥� said Marc Riddell, Vail Resorts鈥� West Coast communications director.
Riddell advised the public to obey all signage and rope lines to stay safe. 鈥淭hey鈥檙e there for a reason,鈥� he said.
Avalanche mitigation will likely continue at Whistler Blackcomb on Friday and Saturday 鈥渂efore we make any decision as to whether or not we鈥檙e going to open the alpine,鈥� Riddell noted.
To read the full avalanche warning and forecast, visit .
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