Friday, December 3, 2010

Accumulation and advisories

1st avalanche advisory launches tomorrow


By KATHERINE WUTZ
Express Staff Writer

Fresh accumulation on Baldy over the past few days might lure skiers out this weekend, but the Sawtooth Avalanche Center has one message: start slowly.

"The avalanche risk over the next few days is just going to be increasing," said Chris Lundy, the center's director. "Start the season off on a good note, just take it easy."

Lundy said conditions tend to be unstable early in the season due to snow on top of weak and faceted snow layers. A layer of grainy, sugar-like snow can cause slides if disturbed, sending more densely packed slabs of snow downhill.

The ideal situation, Lundy said, is exactly what the valley experienced through much of yesterday—slow, steady snowfall that builds up and crushes the weak layer.

"Everybody likes the firehose, when we get a huge storm with all the fresh powder," he said. "But the snowpack doesn't like that. It likes the leaky faucet—just drip, drip, drip."

The center's first daily avalanche advisory will be sent out on Saturday morning, and Lundy said Thursday's storm system would definitely impact his forecast.

"Regardless of how much snow we get, I'd urge people to stick to lower-angle terrain," he said. "Everywhere where there's enough snow for people to recreate is going to have that [weak] layer."

Terrain thus far has been limited due to snow cover, which is why the first avalanche advisory is not being launched until this weekend. The advisories are daily e-mails and posts on the center's website that outline trouble spots for backcountry skiers, snowboarders, snowshoers and snowmobilers.

The advisories include a "bottom line," or a summary of general avalanche conditions. The advisories also include a detailed description of the type of avalanche problem that backcountry recreationists can expect to encounter.

Lundy said the two most common problems are persistent weak layers and wind slabs. The latter occurs when strong winds blow snow along a ridge, overloading underlying layers of weak snow.

The former is a layer of unstable snow, normally formed during dry spells that change the snow's consistency. If fresh snow falls on a weak layer, it can easily separate from the rest of the snowpack and take a person with it.

"Every [big] avalanche we've had since I've been here has been due to a persistent weak layer, except one," Lundy said. "Those are the ones that kill."

The accuracy of the daily avalanche reports depend on the expertise of the center's forecasters and on public input. The center's three forecasters can only cover so much terrain, Lundy said, and observations from backcountry recreationists are key.

Lundy said the center doesn't get enough layperson observations, in part because he said he thinks people are intimidated.

"Any information we get from people, we're always excited to get," he said. "We never say, 'Oh, God, that was a pretty stupid comment.'"

The center takes comments both via webform and hotline, both of which are available at www.sawtoothavalanche.com.

Katherine Wutz: kwutz@mtexpress.com




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