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D awn cracked with the intermittent sound of explosives near the top of Cowboy Mountain. Stevens Pass ski patrollers, called to duty whenever more than a few inches of snow fell, had arrived to check and control the ski area’s 200 inbounds avalanche zones

 

After getting the latest assessment from the area’s full-time avalanche forecaster, more than a dozen patrollers filled their backpacks with 2.2-pound emulsion charges, shaped like cartoon dynamite. Chairlifts rumbled to life, ferrying the crews up the dark mountain.

Three two-person teams assigned to Cowboy Ridge removed their skis and filed through the boundary gate. They took turns plowing a path through the fresh snow with their bodies. Their boots forged an icy stairway to the top of the skinny ridge.

Back on their skis, facing down into the ski area and with their backs to Tunnel Creek, they spread across the ridge to stamp and destroy wind-swept cornices, small balconies of crusty snow.

“I said to Dan, ‘Do you think Tunnel will be safe today?’” Michelson said. “He said something along the lines of, ‘Yeah, those guys know the best route down.’”

There were similar conversations elsewhere. In the slope-side cabin at Stevens Pass that Rudolph arranged — he cleaned it on Friday as he spoke to his mother on the phone — the journalists from Powder magazine, Stifter and Carlsen, contemplated the day’s plans.

“We started asking questions,” Carlsen said. “‘Where are we going? Out of bounds? Didn’t it just snow nonstop for two days? How much snow?’ That’s when John pulled up the avalanche report, and he read it aloud.”  Predicting Avalanches

Mark Moore, director and lead meteorologist of the Northwest Weather and Avalanche Center, had set that day’s forecast on Saturday afternoon. A 64-year-old with graying hair pulled into a short ponytail, Moore had a feeling it could be a busy weekend.

The avalanche center, based in Seattle, is one of about 20 regional avalanche forecasting centers in the United States, most run by the Forest Service. During the winter, one of its three employees arrives in the middle of the night, analyzes weather maps and computer models, and examines data — snowfall, temperatures, wind, humidity and so on — from 47 remote weather stations scattered across the mountains, including five in the vicinity of Stevens Pass. They take calls from ski patrollers and highway crews.

The biggest storm of the season increased avalanche concerns. But it was not just the new snow that concerned Moore. It was what lay nearly three feet beneath — a thin layer of perfectly preserved frost called surface hoar. The frozen equivalent of dew, created on crisp, clear nights, it features fragile, featherlike crystals that grow skyward.

On the surface, they glimmer like a million tiny diamonds. When frosted and protected by soft blankets of fluffy snow, they are weak stilts supporting all that falls on top. When they finally give way, falling like microscopic dominoes on a steep slope, they provide an icy flume for the snow above.

A shot of rain or above-freezing temperatures, both common in Cascade winters, usually destroy the fragile crystals, melding them into the snowpack. But five days of dry, cold weather, from Feb. 3 to 7, created a perfect, sparkly layer of surface hoar. Sporadic light snow, never more than an inch or two a day, delicately shrouded it over the next 10 days.

By the weekend, as snow fell heavily over the Cascades and powder-hungry hordes took to the slopes, the old layer was long out of sight, and mostly out of mind.

Not to Moore.

“Snowpack is never static,” he said. “It’s changing, even once it’s buried.”

Changes in temperatures, precipitation, humidity and wind can turn a benign snowpack into a deadly one, and vice versa. Sometimes weather is enough to start an avalanche. But “natural” avalanches rarely kill. The majority of avalanche fatalities are in human-triggered slides — usually of the victims’ own making.

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