PORTLAND — Forecasts for triple-digit heat caused a minor panic across the Pacific Northwest on Wednesday, a region famous for cool weather where many people didn't have air conditioning to help them endure the rare furnace-like blast.

Many concerned communities in Oregon and Washington opened cooling centers and warned residents to stay hydrated, avoid strenuous activity and keep their dogs out of parked vehicles.

The National Weather Service slightly dialed back its forecast for Portland to match or break its record high of 107 degrees. Meteorologist David Bishop said the city was looking at 104 or 105 degrees on Wednesday and today.

"With little to no cloud cover at night, the higher temperatures kind of hang around a little bit," Bishop said. That creates a cycle in which "the next day is going to be a little bit warmer because we're already starting off warmer than the previous day."

The latest forecast for Seattle also showed predicted highs easing a bit from earlier predictions. The weather service said the high for Wednesday would be 91 degrees and 94 today.

The Northwest is better known for its fall, winter and spring rainy seasons. Even July and August are relatively mild months. But the powerful high-pressure system arrived just at the height of summer.

Portland's light-rail trains are operating at slower speeds amid concern that the heat will cause tracks to expand and risk a derailment. In exchange for the slow service, fare inspectors are not checking riders for tickets.

Hun Taing uses the train to get to her job in downtown Portland, but she switched to an air-conditioned car because of the delays. She and a co-worker, Heather Heater, had a casual work meeting Wednesday at Director Park, dipping their toes in the fountain as children splashed in the water.

They both have air conditioning at home — something they once lacked — and expressed more concern for the homeless and elderly than for their personal comfort.

"I was in an apartment without A/C when I just had my twins, and it was really difficult," Taing said. "We had to pack ourselves in the car and just go somewhere, drive somewhere, because that apartment on the second floor was too hot for the infants."

Heater, who endures jokes about her last name, said having air conditioning was a requirement when she moved to the fourth floor in a recently constructed apartment building.

Anna Miller, 27, lives in an older brick building — a situation faced by many young renters in Portland.

"It's going to be pretty warm, but I'll probably just go to a bar before going home," said Miller, who wore a scarf and long sleeves outdoors Wednesday because the morning was chilly and she works in an air-conditioned office as an administrative assistant.

Forecasters had warned that Seattle could see its highest temperatures since the 1890s. The city has recorded only three days at 100 degrees or higher in the more than a century, according to the weather service.

The Pacific Northwest's largest city opened about 30 cooling centers in air-conditioned libraries and senior centers. Seattle officials also encouraged people to use more than two dozen wading pools and spray parks.