STATELINE, Nev. — Summer is nearly here, but the threat of avalanche lingers in many Western mountain ranges where it's been an unusual season for one of nature's more unpredictable phenomena.
Since late October, 27 people have died in the United States in avalanches, which is about average. What's unusual is that two deaths occurred in developed ski areas, including in May in Colorado and another in January when a teenager was swept off a ski lift near Las Vegas.
In the previous 19 years, just three of the 416 known avalanche deaths in the nation -- less than 1% -- occurred within ski areas, according to the National Avalanche Center, in part because operators patrol their slopes.
"We at Squaw Valley have a group of us ... if it's a beautiful day or if it's a storm day, we communicate before we send anybody up onto the hill," said Jimmy King, mountain manager at Squaw Valley USA.
On a stormy day -- and winds can hit 150 mph at the resort on Lake Tahoe's California side -- workers start at the top with explosives to break up cornices and slabs of snow that fall harmlessly down the slopes.
"If I've got even just one single patroller that goes up there and says, 'I've got a problem, I don't like it,' we stop. We don't open to the public," King said.
Last month's slide at Arapahoe Basin near Breckenridge, Colo., occurred in the morning, when snow usually is more stable. But in this case, warm overnight temperatures had melted the snowpack, creating heavy wet slabs of snow, according to Scott Toepfer of the Colorado Avalanche Information Center.
In southern Nevada, an expert said there may have been no way to predict the slide that killed a 13-year-old snowboarder at Mt. Charleston.
"When this avalanche released, it was unprecedented," said Doug Abromeit, director of the U.S. Forest Service's National Avalanche Center in Ketchum, Idaho, who investigated the slide.
While forecasting avalanches is nearly as unlikely as predicting an earthquake, there are conditions that accompany slides, said Bruce Tremper, director of the U.S. Forest Service Avalanche Center in Salt Lake City.
Almost all avalanches occur on slopes of 35 to 45 degrees and are most likely after a heavy snowfall is followed by clear weather that lets ice crystals form, producing an unstable layer below the next heavy snow.
Wind also forms drifts and cornices that are avalanche-prone.
