Wednesday, December 21, 2005

Avalanche risk heightened by dry, cold weather

Snow is 'rotten,' and backcountry skiing is less than desirable


By STEVE BENSON
Express Staff Writer

Winter's prelude was promising—6 inches of snow here, 10 inches there, a foot and a half to kick off December.

The early-season storms deposited almost 8 feet of snow on Baldy by the first week of December, arousing powder junkies from hibernation and laying the foundation for a stable backcountry ski season.

But three weeks ago, a stubborn high-pressure system crashed the party with frigid, dry air, setting the stage for a dangerous backcountry avalanche scenario that could lurk for weeks, or months, before rearing its ugly head.

The early-December storm dumped 12 to 16 inches of snow on the Wood River Valley and surrounding peaks. It was followed by strong wind events, which formed dangerous wind slabs in the mid-to-upper elevation areas of the backcountry.

"Wind slabs can be very hard and drum like, and it was possible to trigger some of those," said Janet Kellam, director of the Sawtooth National Forest Avalanche Center, in Ketchum. "But now that we've sat so long without precipitation, the snowpack has stabilized."

For the past couple weeks, the daily avalanche advisory from the Sawtooth National Forest Avalanche Center, in Ketchum, has been low to moderate, and as long as the weather remains unchanged, so should the advisory.

But although it is somewhat stable, the snow is "rotten," and the backcountry skiing less than desirable.

"It's really weak, rotten snow with lots of rocks and (other hazards)," Kellam said. "These cold temperatures cause the snowpack to weaken and deteriorate. The snow becomes less cohesive, very granular and sugary—you can't make a snowball."

That means that when (hopefully not if) the dry high pressure does break down, allowing storms to spin back into the area, the avalanche dangers could be extreme.

"(The snowpack) has got a very weak base, so once we get new snow on top of it, it will be top heavy," Kellam said—creating the old bricks-on-potato-chips scenario. "We expect to see some avalanche activity."

The same conditions developed last winter.

After a series of massive storms pummeled Sun Valley through the holiday season, a huge high-pressure zone developed over Idaho and the Northwest, where it stubbornly sat for eight weeks.

When snows returned in March, the stage had been set for disaster, as the new snow did not bond well to the weak, underlying layer.

On March 25, Ketchum resident Steve Waltcher was seriously injured after triggering an avalanche while backcountry skiing in the Titus Ridge area, near Galena Summit, north of Ketchum.

Among other injuries, Waltcher broke both of his femurs, his left fibula, right wrist and pelvis.

A week later, a snowmobiler was buried in an avalanche north of McCall, and luckily survived.

Kellam said what often compounds the danger is the hunger for powder that develops during prolonged periods of high pressure.

"Once we get starved for good powder snow it's sometimes hard for people to hold back and make really rational decisions," Kellam said. "We talk about decision making and how often decisions can get influenced by a lot of other factors. It's easy to get drawn into the powder frenzy that can happen.

"I just urge people to check current conditions and get a little bit of a better understanding of what's going on in the snowpack."

Kellam said she advises backcountry travelers to reference what she calls "Mother Nature's billboard of clues," such as cracking or collapsing snow, or signs of natural avalanches.

"I like to look at steep little road cuts," she said. "If those little slopes are sliding, the big slopes will slide too."

What's frightening is that the problems created by the high pressure may lurk well into the winter. A series of small storms could accumulate on the weak layer and not release, at least not initially. Then, days or weeks down the line, the weight of a backcountry skier or snowmobiler could trigger a large avalanche.

But there are a number of other scenarios that could develop, with the most optimal involving "a big, wet storm that saturates the underlying snow and helps to basically consolidate everything," Kellam said.

Even then, the initial conditions will be dangerous, with significant avalanche activity possible.

Perhaps the safest slopes will be south-facing, where much of the snow has already melted, reducing concerns about the weak, underlying layer and slab releases.

"Once we get new snowfall, those may be the safer aspects to ski," Kellam said.

But, she added, "at this point it's almost like anything goes, it depends on what Mother Nature wants to deal."

In the end, Kellam said the best bet is to keep an eye on the daily backcountry advisories from the Sawtooth National Forest Avalanche Center, which can be accessed online at www.avalanche.org/~svavctr/, or by calling 622-8027.

The avalanche center also offers numerous classes for backcountry enthusiasts, including snowmobilers, throughout the winter. The next classroom session for avalanche basics will be held at the Hailey Community Campus Jan. 3, from 6 to 9 p.m.




 Local Weather 
Search archives:


Copyright © 2019 Express Publishing Inc.   Terms of Use   Privacy Policy
All Rights reserved. Reproduction in whole or in part in any form or medium without express written permission of Express Publishing Inc. is prohibited. 

The Idaho Mountain Express is distributed free to residents and guests throughout the Sun Valley, Idaho resort area community. Subscribers to the Idaho Mountain Express will read these stories and others in this week's issue.