As temperatures rise, so does risk of avalanche

Just as the weather finally heats up for the weekend, mountain-pass highways in Washington could be forced to close because of avalanches. The North Cascades Highway (Highway 20) closed Thursday because of a snowslide on the road near Liberty Bell mountain, and it will remain closed at least until Monday.

Backcountry users in Washington's Cascades and Olympics and in Northern Oregon are being warned of high avalanche danger and to avoid recreation near any possible avalanche areas through the weekend.

For hikers, even those at lower elevations, there's danger in crossing streams and rivers that could run unexpectedly high because of sudden melting of the record-high snowpack.

Temperatures that began quickly rising Thursday are rapidly melting and destabilizing the deep snowpack and threaten to touch off extensive avalanches.

Friday's temperatures in some Washington mountain areas reached the mid-70s — 30 degrees higher than earlier in the week. Stampede Pass reached 74 degrees, and Snoqualmie Pass reached the high 70s.

Drivers should check the conditions of mountain passes before setting out.

It's not clear when the North Cascades Highway will reopen (it opened for travel on May 1).

"Our avalanche team won't go back in to reassess the conditions until Monday," said Jeff Adamson, a Washington State Department of Transportation spokesman.

The Northwest Avalanche Center cautioned backcountry skiers, hikers and others to avoid all travel near any avalanche terrain in the Cascades and the Olympics and Northern Oregon's mountains.

"Deep avalanches are possible. Some slides may release to or near the ground, involving the entire winter's snowpack," the agency warned on its Web site. "The expected large wet snow avalanches may travel very fast and run long distances, possibly to lower elevations where little or no snow cover may remain or to valley floors."

The Washington Trails Association (WTA) urged hikers to be extra cautious when crossing streams and rivers this weekend because they could rise dramatically within a few hours.

"Low- to mid-elevation hikes with river- and stream-crossing could present serious hazards in a case like this. Streams and rivers will be swollen with snowmelt and running high. Crossings should be taken with extreme care," said Lauren Braden, of the WTA.

"Remember that it was in conditions such as this that two hikers died last year while crossing a swollen stream at Mount Rainier National Park. If you have any concern about a stream crossing, turn around," Braden said.

Kristin Jackson: kjackson@seattletimes.com