Wildfire smoke near Warm Springs.Beth Nakamura/The Oregonian

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Air quality throughout most of Oregon remains poor Wednesday, but pockets of cleaner air offer hope for days to come.

Air quality in the Portland area, along the Interstate 5 corridor and elsewhere ranges from unhealthy to hazardous. But portions of the coast offer cleaner air — a sign of better conditions that are on the way amid Oregon’s historic spate of wildfires.

The National Weather Service has said hazardous air quality is expected through Thursday for inland valleys. Air quality is expected to improve starting Friday, the agency said, but that improvement could be gradual.

All of Oregon is under an air quality advisory until Thursday, and Portland again has the worst conditions among major cities worldwide. Seattle and Vancouver, British Columbia, had the second- and third-worst air quality among major cities early Wednesday.

Forecasters say Wednesday will be dry in Portland, with temperatures topping out near 74 degrees.

A 30% chance of showers is expected Thursday, mainly after 11 a.m.

The weather service predicts showers overnight Thursday and during the day Friday. Thunderstorms are also possible.

Showers are likely to continue Friday night, mainly before 11 p.m., and again Saturday.

— Jim Ryan

jryan@oregonian.com; 503-221-8005; @Jimryan015