More rain, snowmelt; look for rising streams, water pooling in streets

An inch of rain a day is expected for the next few days in the Seattle area, and a flood watch remains in effect for most of Western Washington through Sunday morning, according to the National Weather Service.

A strong, warm and wet Pacific storm will produce lowland showers into next week, meteorologist Johnny Burg said.

"An inch of rain a day isn't too outlandish," he said. "Getting a quarter-inch every six hours is kind of the typical, wet winter system we get."

The potential remains for small streams to flood and for water to pool on streets as the last of our snow is melted by the rain and warming temperatures -- a bigger concern for urban areas. Today's high is expected to reach 44 degrees, a welcome change from recently frigid temperatures and the more than 12 inches of snowfall reported at Seattle-Tacoma International Airport between Dec. 13 and Christmas Eve.

In anticipation of the predicted rain and resulting snowmelt, Seattle Public Utilities has put in motion its Urban Flood Response Plan, with extra crews on duty and observers in place at sections of the city where flooding is likely. To report an emergency drainage problem in Seattle, call 206-386-1800.

Residents have been advised to help clear storm drains and remove snow and slush from flat roofs.

A Bothell firefighter responding to an emergency call at the Green Acres mobile home park was rushed to Harborview Medical Center Friday night after a portion of the carport roof collapsed on him. Heavy accumulation of snow was also to blame for the Christmas Day collapse of a carport at a Bothell apartment complex and a portion of the roof at an Olympia high school closed for winter break.

In Tumwater, Thurston County, a roof sagging beneath a heavy load of snow and water led to the evacuation of dozens of people at a retirement home Friday night.

Authorities were summoned after a resident on the second floor of the Olympics West Retirement Inn had trouble opening a door and saw that part of the floor was sagging, according to Fire Lt. Dale Britton.

About 65 seniors at the assisted-living complex were taken to a part of the building that is safe.

Britton says a municipal building official was summoned and told maintenance personnel to shovel snow off the roof. He said a collapse of the roof did not appear to be imminent.

By Sunday, all lowland snow should be gone, and with it the possibility of urban flooding, Burg said. But in the event snow continues to clog a street, the city of Seattle says residents may call 206-386-1218. Requests for snow clearing will be met on a case-by-case basis.

Passable conditions have been achieved on all of the city's primary arterials. Seattle Department of Transportation crews are continuing 24-hour operations, working to clear snow and ice from secondary arterials and residential streets. The work will be prioritized based on police, fire and life-safety concerns.

The Skokomish River in Mason County could flood, as it does frequently in the winter, Burg said. River levels across the region also may rise after consecutive days of rain, but "it's not something we're worried about yet," he said. "It's just something I always keep in the back of my mind."

The same Pacific storm that's supposed to soak Seattle will dump 3 or more feet of heavy, wet snow in the mountains this weekend, said Mark Moore, director of the Northwest Weather and Avalanche Center.

The new snow is sure to entice skiers and snowboarders, but Moore said the avalanche danger is so severe that backcountry enthusiasts should "go to the mall and exchange their gifts or shovel their driveways" instead of venturing outside ski areas.

Moore said the Cascades snowpack is the weakest he's seen in 20 years. Until now, the mountain snow has been light and fluffy, the kind that falls only when temperatures are very cold. As a result, the snowpack is shallow and the bonds between snow crystals have disappeared, he said.

"If you were to step off your skis or snowboard, you could easily sink to the ground or very near the ground. It won't support much weight," Moore said.

Adding heavier, wet snow to the fragile snowpack "is a very scary situation," he said. "It tends to bring down the whole deck of cards. It's like potato chips loaded with a brick."

The heavier snow will create a more stable surface, but it won't take much to trigger a slide because of the weak snow below, Moore said. Avalanches, either natural ones or those caused by people, are likely to "involve snow all the way to the ground" and cover much greater swaths of terrain than usual, he said.

Depending on how the rest of the winter unfolds, avalanches could be a big problem during the spring thaw, Moore said.

The extreme danger this winter comes a year after the deadliest avalanche season in 30 years in Washington state. Between December 2007 and January 2008, eight people were killed or presumed dead in avalanches between Crystal Mountain and Mount Baker.

Seattle Times reporter Jack Broom and The Associated Press contributed to this report.

Sara Jean Green: 206-515-5654 or sgreen@seattletimes.com