Jay Albrecht, a meteorologist with the service, said it's the hottest it has been in Seattle since records dating to 1891.
Meanwhile, Portland ventured into its third day of triple-digit heat Wednesday, hitting 104 degrees by midday. Forecasters said there's a slight chance the city could reach or even surpass its all-time high of 107 degrees, hit four times, most recently in 1981.
Doug McDonnal, a meteorologist with the National Weather Service in Seattle, said the stretch of hot weather has lasted longer than usual. Wednesday was the fifth consecutive day above 85 degrees for Seattle, he said.
Throughout the region, shade, icy treats, ice-cold water, air conditioning units and fans were in high demand.
Geno Garcia, 40, a Boeing machinist, headed straight for Sears in Seattle early Wednesday when the family's air conditioning unit broke down.
"We could have lived without it, but it would have been uncomfortable," he said, as he stood in line with about 100 others who bought air conditioners.
Garcia said his family plans to keep cool by hunkering down in the one bedroom that's air conditioned. They've already moved their TV, games and other necessities into that room, and have been eating meals there.
Darren Wilson, 38, a concrete finisher from Puyallup, Wash., started his Seattle street paving job at 5:30 a.m., three hours earlier than usual, to beat the heat.
"I'm drinking lots of water," he said. "When I get off work, I'm going to my buddy's house and jump in his pool."
Portlanders were trying to stay cool every which way. Public fountains were clogged with children. Libraries swelled with people trying to stay out of the sun. And cooling centers for seniors were open late.
Shirley Markstaller, 71, parked herself in front of a fan and read the morning paper at a cooling center in downtown Portland.
She doesn't have an air conditioner at home, so she's been coming to the center every day for the past week or so. "I just thought, where's the coolest place?" she said.
The weather throughout the Willamette Valley wasn't much better.
Temperatures hit triple digits in Medford, Eugene and Salem by Wednesday afternoon.
Coastal cities were cooler, including Astoria and Newport. Temperatures in Bend, Pendleton and La Grande had already reached the 90s by midday.
Forecasters have issued an excessive heat warning for much of western Washington through Friday. A heat advisory is in effect through Thursday in parts of eastern Washington, including the Yakima Valley and lower Columbia Basin.
Temperatures in western Washington were expected to cool off somewhat on Friday but will still be in the 80s, about 10 degrees higher than usual, McDonnal said.
In Olympia, a group of visitors were hoping to cool off at the popular Heritage Park Fountain, but were disappointed to find that the water had been turned off for regular weekly maintenance.
"We were expecting it to be working," said Lucina Hernandez, 24, of Barcelona, Venezuela. "This is very bad."
At the Tails-A-Wagging doggie day care in Bellingham, Wash., owner Angi Lenz and her staff kept dogs comfortable with special cooling fans, air conditioning, ice toys and water slides. "We have a waiting list to get in this week because of the heat," Lenz said.
Not everyone was avoiding the outdoors. Enes Parker, manager of the Lacey Senior Center, said she found indoor air conditioning too cold. Lacey is in Washington, near the state capital of Olympia.
"I'm one of the few who like the heat," Parker said. "I go outside every so often to warm up. I love the heat. It's always too cold here."
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