The storm claimed at least two lives - a child whose body was pulled from an Oregon creek where a car was swept away from a grocery store parking lot and a person killed by a falling tree east of Seattle.
Rescuers also searched Thursday for the Oregon child's mother, who is missing in the creek in the Willamette Valley community of Albany, about 70 miles south of Portland, said fire department spokeswoman Wanda Omdahl.
Washington Gov. Chris Gregoire declared a state of emergency, authorizing the use of National Guard troops if necessary.
On the icy interstate north of Seattle, a transportation department worker responding to an accident was injured in crash. He was taken to a Seattle hospital; no details were available on his condition or how he was injured.
Freezing rain and ice pellets caused numerous accidents in the Seattle area, where drivers are mostly inexperienced with driving in snow or ice. The last widespread freezing rain in Seattle was in December 1996, said meteorologist Jeff Michalski at the Weather Service office in Seattle.
The National Weather Service used the Emergency Alert System to break into Thursday morning broadcasts with an ice storm warning until noon for the Seattle area and southwest Washington. Among the concerns were widespread power outages and the threat that structures could collapse under the weight of ice. The Washington State Patrol said some if its troopers brought chain saws to work Thursday, so they could quickly remove downed trees on highways and roads.
Authorities are also worried about flooding in the coming days as temperatures warm up.
"It's a very dangerous situation," with a major impact on roads, said Brad Colman, the meteorologist in charge of the Weather Service office in Seattle. "We're expecting a significant impact on power."
Ice closed Sea-Tac Airport completely in the early morning before one runway was reopened, but taxiways remain a problem even as runways were deiced.
Reader-boards showed the vast majority of flights canceled or delayed, leaving lines hundreds of people long snaking around nearly every ticket counter and many would-be passengers on their cell phones trying furiously to rebook their flights.
Brandon Pederson, the chief financial officer of Alaska Airlines, loaded a sport-utility vehicle with bottles of water at a nearby grocery store and joined others from the company's headquarters in passing them out to stranded travelers.
Forecasters expect up to 0.4 inch of ice before temperatures rise above freezing by afternoon.
The state Transportation Department closed one highway because of falling trees that also took out power lines. Puget Sound Energy reported 90,000 outages at about 9:30 Thursday, after crews had already brought 46,000 customers back on line since Wednesday.
"It's like a storm in slow motion that keeps happening again and again," said PSE spokesman Roger Thompson.
The ice follows a huge snowfall on Wednesday. Nearly a foot of new snow fell in Olympia, Wash., where 11 inches was measured at the airport. The record is 14.2 inches on Jan. 24, 1972.
Oregon didn't receive the snowfall that Washington did - but got plenty of rain.
Rising water from heavy rains swept a car carrying four people into an overflowing creek in Albany. Two people - a father and his 5-year-old son - escaped, but the body of 20-month-old Aiden McLaughlin was recovered and his mother, Catherine McLaughlin, was still missing.
"The water just got high so fast," Omdahl said. "It's a big tragedy."
Near Issaquah, Wash., a person backing an all-terrain vehicle out of a shed was killed by a falling tree, King County sheriff's Sgt. Cindi West said.Other details about the incident weren't immediately available.
Washington State University in Pullman was closed. The University of Washington also cancelled Thursday classes at three campuses, including Seattle. Seattle schools were also closed again Thursday, as were schools in Bellingham in northwest Washington, and in southeast Washington's Pasco, Kennewick and Richland.
Lewis County, south of Olympia, had the highest snowfall amounts, ranging from 12 to 17 inches.
"It's unusual to get this much snow for western Washington," said Dennis D'Amico, a meteorologist at the National Weather Service in Seattle.
Forecasters warned that heavy rain combined with snowmelt could lead to some Washington river flooding.
In Oregon, high winds hammered parts of the coast and caused power outages that initially affected tens of thousands of customers, with reports of gusts as high as 113 mph.
Karina Shagren, a spokeswoman for Gregoire, said even though an emergency declaration has been issued, the National Guard has not been called up.
"This is purely a precautionary move," she said. "At this point, we have not received any requests from cities or counties for state help, but we know weather conditions are changing rapidly so we want to be prepared."
Shagren said that what sparked the proclamation was concern over truck drivers carrying dairy products not being able to drive more than 12 hours a day due to federal regulations.
"In order to supersede that, the governor need to order an emergency," she said.
___Associated Press writers Doug Esser and Gene Johnson in Seattle, Ted Warren in Tacoma, Wash., and Jonathan J. Cooper in Portland, Ore., contributed to this report.
