WHITEFISH - Backcountry skiers already are triggering avalanches this year, with three western Montana slides reported in as many weeks.

In his narrative of the most recent - a slab slide on Big Mountain's north face - avalanche expert Stan Bones wrote that "from the time of the falling of the first snow crystals to the melting of the last ice grain, it is imperative that we constantly keep snow stability and avalanche safety in the front of our minds, screaming in our ears and dangling in front of our eyes."

That's an especially important reminder, slide experts said, as the region enters what's predicted to be a snowy weekend.

The Big Mountain slide was reported to Bones on Nov. 9, but probably cut loose early in the weekend of Nov. 6.

Bones, who monitors snow and avalanches for the U.S. Forest Service, said wind-loaded snow near the summit had been deposited on an icy layer beneath, and broke loose under the weight of a skier.

"The size of the slide," he reported to the Glacier Country Avalanche Center, "was such that it could have shallowly, but totally, buried a person."

More likely, though, was the risk of trauma injuries - colliding with trees and rocks. The unknown skier did not report the incident, Bones said, so he assumes any injuries were minor.

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Skiers did, however, report a pair of avalanches elsewhere in western Montana, including one not far south of Missoula. A narrative of that incident was posted on the Missoula Avalanche Center Web site, www.missoulaavalanche.org.

That Oct. 24 slide swept four Missoula-area skiers down a slope in the Gem Lake area of Trapper Peak, in the southern Bitterroot Mountains. They were climbing into the Gem Lake couloir, digging shallow pits to assess snow conditions, when they "discovered relatively poor bonds" between new snow and the crustier base.

One skier said the deeper snow "felt like Styrofoam" beneath the wind slab.

They were approaching a "safe zone" when the lead climber "weighted my left foot and felt a massive settlement. A very brief moment passed and the whole slope began to pull out."

As he tumbled, trying to keep his crampons from catching, "I remember it being surprisingly dark and amazingly powerful."

In a matter of seconds the snow carried the skiers about 60 feet. All were at least partially buried, but dug themselves out.

"We were pretty banged up, but in good shape considering the circumstances."

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Skiers also were banged and bruised during an early-season avalanche on Granite Peak, in the Tobacco Root Mountains of southwest Montana. The Halloween-day slide - reported to the Gallatin National Forest Avalanche Center - swept down the east face of the mountain, carrying three Bozeman-area skiers over a rocky talus slope.

The group had dug several pits, to assess conditions, and "found the layers to be bonded and stable."

They made one run, then climbed up for a second. This time, though, they chose a different route, confident that their earlier tests and the success of their first run indicated safe conditions.

They did note, however, that the snowpack was changing, and made plans to reassess once reaching a "safe spot" just 30 feet above them.

"When the lead climber was approximately 100 feet from the summit, the entire slope whoomped" - sounding like "dropping a stack of plywood flat onto a hard surface."

A slab 300 feet wide and considerably more than a foot deep "caught all three of us and dragged us over exposed talus for 300 feet until we were strained out of the slide on top of the rocks."

It lasted less than 10 seconds, "sounded like a jet engine taking off," and left them bruised and scraped. One skier sustained two cracked ribs.

Bones noted that all three avalanches shared several commonalities - namely, they came early in the season, in a shallow snowpack, and involved isolated pockets of wind-loaded snow. In addition, in at least two of the slides the skiers recognized instabilities but nevertheless continued on.

"Never let your enthusiasm blind you to the threats present," Bones advised. "Although not likely fatal, all three of the incidents could have spelled the end of someone's skiing or snowboarding experience for the season, or even a lifetime."

"Bullets were dodged," he concluded, "but not by skill or design; only by luck."

Reporter Michael Jamison can be reached at (406) 862-0324 or at mjamison@missoulian.com.