Poor air quality is continuing in much of Oregon and southwest Washington, but more rain in the forecast could improve that.

Oregon’s Department of Environmental Quality issued an air quality advisory earlier this week that has been extended until at least Tuesday.

Matthew Cullen with Portland’s National Weather Service said the continued advisory is because of a high-pressure weather pattern that’s creating stagnant air in much of the region.

“The general idea is that you have what we call an inversion,” Cullen said. “Basically, temperature increases with height, as you go up from the ground, and that actually provides kind of a stable layer that keeps the particulates in the air close to the surface.”

More rain and wind could help end that inversion, he said.

“In general, it looks like we’ll see some increasing winds at times,” Cullen said, “and some increasing clouds and some rain at times. All those would bode well for kind of breaking down this persistent high-pressure pattern we’ve had.”

Oregon’s DEQ is recommending that people avoid wood-burning stoves, if possible, in the meantime, and it warns that particles in the air could make breathing difficult for sensitive groups like children and people with heart and lung problems.