Southern California residents stacked sandbags Thursday and authorities ordered thousands of people to evacuate ahead of possible flash flooding and mudslides in areas burned bare by recent wildfires.

Orange County sheriff's patrol cars broadcast warnings through loudspeakers throughout the day, urging about 2,000 people to get out of three canyons because some of the heaviest rainfall in more than a year was expected to hit the area overnight.

The evacuations became mandatory in the evening as the storm approached, sheriff's spokesman Jim Amormino said. Authorities closed several roads and restricted access in and out of the canyons.

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But he urged people not to wait until deputies went door to door, ordering people out.

"It's much better to do it early than wait for the slides to start," he said. "The canyons are narrow; the roads are narrow. Sometimes if you wait too long, it's potentially dangerous."

In the Pacific Northwest, thousands remained without power or clean drinking water after a deadly wave of storms there.

Six people died in Washington, and another two died in Oregon. An elderly man was missing after he was believed to have fallen into a raging creek behind his house in rural Winlock, Wash.

About 640 people were still in shelters, 33,000 customers lacked power and about 18,900 had no safe drinking water, Gov. Chris Gregoire said. Fourteen water systems were shut down and people served by nine others were under orders to boil water. Some areas requested vaccines, especially for tetanus.

Helicopters took flood-stranded residents to safety at the height of the storm. By the time helicopter operations ended Wednesday evening, at least 300 people had been taken to safety in what Gregoire described as Washington state's largest aerial search-and-rescue operation in a decade.

"Those folks who are literally homeless today still have a spirit in them," the governor said. "They are determined to get back to their homes and get their lives back together again."

Recalling scenes of blown-down trees, Gregoire said, "The visual is nothing like I've ever seen other than my recollection of Mount St. Helens" after the volcano's devastating 1980 eruption.

Interstate 5, the West Coast's main north-south route, reopened Thursday with one lane of traffic in each direction but was limited to freight haulers.

The freeway, which has been closed since Monday about 30 miles south of the Washington capital of Olympia, is not expected to reopen to passenger vehicles until Friday.

Amtrak service resumed Thursday between Portland and Vancouver, British Columbia.

Damage is likely to reach into the billions of dollars but remains to be tallied.

The governor filed a formal request for a White House emergency declaration in two counties, with other counties to be added as damage assessments come in. An emergency declaration would trigger money for temporary lodging, rental assistance, money for home repairs and crisis counseling, and small-business loans.

An aide to Oregon Gov. Ted Kulongoski said that state would also seek a federal disaster declaration.

In Hawaii, residents also were cleaning up from this week's stormy weather that brought 70-mph winds and heavy rain. Twenty-seven of 83 public schools were still closed Thursday because of the lack of electricity, fallen trees and blocked roadways.

In California, the National Weather Service issued a flash-flood watch for coastal and mountain areas through Friday afternoon. As much as an inch of rain in urban areas and as much as 3 inches in the mountains was predicted, said Stuart Seto, a Weather Service specialist.

The Weather Service also issued a high wind warning for mountain areas and in a valley in north Los Angeles county. Gusts as high as 60 mph were expected, said meteorologist Todd Hall.

Southern California has had a very dry rainy season, and it will be the first time since April 2006 that so much rain has fallen from a single storm, Seto predicted.

Areas denuded by fires were a special concern. Wildfires this year have stripped vegetation from thousands of acres of land. That land is now susceptible to excessive runoff and erosion.

"It doesn't take much to set off those mud and debris flows," Seto said.

In Los Angeles County, crews sandbagged hillsides in Griffith Park, where about 1,200 acres were scorched in May. Work was also under way in Malibu, where a wildfire destroyed 53 homes in November.