Colorado Department of Transportation workers watch a shell fly out of a truck-mounted "Avalauncher" on Vail Pass, to trigger an avalanche on I-70 near Vail, Colorado. Avalanches have killed 15 skiers and snowmobilers in Western states in less than two months. REUTERS/Rick Wilking/Files

Salmon, Idaho - Fresh powder in the US West has lured thousands of skiers, snowboarders and snowmobilers to the high country at a time the risk of avalanches has been heightened by weather patterns that are making the snowpack less stable, winter recreation experts said.

Avalanches have killed 15 skiers and snowmobilers in Western states in less than two months - well over the nine deaths recorded in the same period last year - most recently when a massive slide raced 1,400 feet down an Idaho mountainside and killed a snowmobiler at the weekend.

Government specialists say the uptick in killer avalanches stems in part from unusually dense and wet snows that have lately blanketed the mountain West after an extended dry spell weakened a base layer of snow laid early in the season.

“Storms in the past month have placed very strong, heavy snow on top of a layer that had the consistency of rock salt and the strength of potato chips. It's always a bad combination,” said Craig Gordon, forecaster with the Forest Service Utah Avalanche Center.

Federal avalanche centers in states such as Idaho, Montana and Colorado have in recent days stepped up warnings to winter recreationists, whose numbers in the snowy backcountry have grown in the last decade alongside advances that have made treks possible to steep winter terrain that was once nearly inaccessible.

US avalanche deaths have increased over the past two decades, hitting a record number of 36 twice since 2007 in seasons that typically span late fall to late spring, peaking in January and February, according to federal figures.

Avalanches are common in the snowcapped peaks of the mountainous West, where 100-yard (91-meter) slides the length of a football field can travel at speeds of 50 to 250 miles an hour (80.5 to 402 km an hour). Most deadly avalanches are triggered by snowmobilers and skiers on federal land in the Rockies, Cascades and High Sierras that offers prime and mostly unregulated access to snow.

Winter recreation experts link the recent fatalities to gear advances that allow even the less-skilled to venture into danger zones.

“A big factor in the spate of deaths in the last month is an explosion of activity in the backcountry. Bigger, fatter skis and lighter, faster snowmobiles mean you can go anywhere, even into harm's way,” said Michael Berry, president of the National Ski Areas Association, a trade group.

US land managers routinely issue avalanche warnings during winter months but do not prohibit or penalize people for venturing into avalanche-prone areas at their own risk.

“Powder snow is a powerful drug and it's one a lot of people can't resist, even when the avalanche danger is high,” said Steve Karkanen, director of the West Central Montana Avalanche Center.

“In a lot of cases, it takes backcountry skiers and snowmobilers hours to get to a summit or a high-line ridge,” he said. “It's a difficult decision to look at a big, long run and say: 'I'm not going to do it, it's not safe.'“

Land managers advise backcountry recreationists to take advantage of hazard-mitigating equipment, including transceivers to pinpoint the location of anyone buried by a slide, airbags that allow people to float to the surface, and lighter weight shovels and probe poles used to assess snowpack structure and locate victims beneath the snow.

Ski resorts across the US West lessen the risks of avalanches by using explosives to set off slides on unoccupied slopes. But many developed ski areas in the West are on federal land and cannot ban skiers from venturing into the backcountry outside resort boundaries, said the ski association's Berry.

Ski areas like Montana's Whitefish Mountain Resort post signs showing the development's perimeter.

“If you're going out of bounds, you're on your own,” spokeswoman Riley Polumbus said.

Vail Resorts in Colorado allows skiers access the backcountry from designated points. Those who ignore that rule lose resort ski privileges, said spokesman Russ Pecoraro.

Still, for some, there is no experience equivalent to out-of-bounds skiing.

“It's a real thrill to go through uncut powder. You're back there by yourself with fresh snow and no crowds,” said Idaho skier Shannon Page, who sometimes skis in out-of-bounds areas but said she exercises caution about risks.