The National Weather Service Has Issued an Air Stagnation Advisory for Portland

Just when you thought it was safe to breathe again, more bad news arrives for your lungs: The Portland area will be under an air stagnation advisory through the weekend.

According to Jon Bonk, a meteorologist with the National Weather Service office in Portland, Northwest Oregon and Southwest Washington are experiencing a strong "temperature inversion," in which a layer of warm air sits atop the cool air that's normally near the surface, acting "like a lid on a pot" and trapping particulates in the atmosphere.

The wildfire smoke that drifted in from California this week is partially to blame. While the smoke has remained high in the atmosphere, the haze is blocking 25% to 30% of incoming sunlight—enough that the ground isn't warming enough to assist with "vertical cleansing." Other conditions, such as low winds, are contributing as well.

"A lot of times we can still get wind under the inversion and help keep the air clean," Bonk says, "but we don't see that happening over next several days."

Most of the particulate matter, however, is not from the smoke but more local sources of pollution, such as cars and backyard fires.

So what does that mean for the air quality? Dylan Darling, a spokesperson for the Oregon Department of Environmental Quality, says it's unlikely based on current forecasts that an air quality advisory will be issued, but it's possible conditions could degrade enough to create problems for people with respiratory ailments.

The stagnation advisory is in effect from now until 6 pm Monday for inland areas below 2,000 feet.