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Originally published May 1, 2013 at 9:53 PM | Page modified May 2, 2013 at 10:00 AM

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Forecast heats up, avalanche danger does, too

People headed into the mountains to enjoy spring’s warmest weather so far should be on the lookout for avalanches.

Seattle Times science reporter

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With temperatures expected to approach the 80s across Western Washington this weekend, snow won’t be foremost on most people’s minds.

But for those who plan to head into the hills to hike, snowshoe, ski or snowboard, the Northwest Weather and Avalanche Center warns that conditions are ripe for some of the season’s biggest avalanches.

The unusually warm weather that will start on Thursday and persist for at least five days comes on the heels of a series of storms that dumped up to two feet of snow in some areas earlier this week, said the avalanche center’s Scott Schell.

“Now we’re experiencing rapid warming, which weakens the snowpack,” he said. “You can think of it as loosening everything up.”

The center issued an advisory Tuesday that covers the Cascade and Olympic mountains. The advisory is a general warning, rather than the type of detailed avalanche assessments the center provides during the winter and early spring.

“We’re just saying: Be aware of these conditions,” Schell said.

This avalanche season was uncommonly quiet until mid-April, when two people died in separate slides near Snoqualmie Pass on the same day.

“We thought we were going to make it through the season with no fatalities, which would have been the first time in a long time,” said Kenny Kramer, the center’s director.

The body of one victim still hasn’t been recovered because of fresh snow and continued avalanches in the area, said Sgt. Cindi West of the King County Sheriff’s Office.

January and February are usually the region’s deadliest avalanche months, but there’s often a spike in May that corresponds with the onset of warmer weather, Kramer explained.

Conditions are particularly dicey when that first warming flush is preceded by a dump of fresh snow.

The fresh snow settles atop the crust of the existing snow pack, which automatically creates a risk that the new layer will slide.

Going into this weekend, the risk will be elevated as the new snow turns to heavy, wet slush.

“Then you put that on a slope and you start with a small amount sliding down, it can gather a lot of momentum and gouge down and pick up more and more snow ... and all of a sudden it’s scary,” Kramer said.

The result can be what are called climax avalanches, which rip deep into the snowpack and can even extend to bare ground.

Since they tend to hit in the spring, these powerful avalanches often take people by surprise.

“You’ve got really nice weather and you head into the mountains, you’re not thinking about avalanches,” Schell said.

Temperatures are expected to peak on Sunday, but the region will stay warm through Tuesday, said National Weather Service meteorologist Jeff Michalski.

“Across the whole area we should be 15 to 20 degrees above normal,” he said.

The forecast calls for a high of 79 degrees in Seattle on Sunday and reach the 80s in some surrounding areas. The forecast for Snoqualmie Pass is for highs in the 60s and lows in the 40s.

Michalski added his own cautionary note, advising outdoor adventurers to be aware that melting snow will pump up the volume in area streams and rivers.

But that’s enough about nature’s dark side.

After shivering while the rest of the country basks, it’s the Northwest’s turn for heat — and it’s going to be spectacular, said University of Washington meteorologist Cliff Mass. “People are going to be delighted and happy and they will be out there sunbathing,” he said.

Mass posted a map on his website that shows the tables turning.

Instead of the usual pattern, where Washington and Oregon comprise the sole patch of blue in a sea of warm tones, this map has an orange bull's-eye centered between the two states — the region that will, at least for a few days, be enjoying the nation’s most anomalously warm temperatures.

“The weather here is going to be better than California,” Mass said.

Sandi Doughton at: 206-464-2491 or sdoughton@seattletimes.com

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