In news that shouldn't surprise anyone with access to a window, the air quality in Portland is horrendous right now—and likely to get worse.

Due to the wildfires continuing to rage across Oregon and parts of Washington, Portland is currently competing with San Francisco for the worst air quality of any major city in the world, according to IQAir, a Swiss company that tracks global air quality.

The Oregon Department of Environmental Quality has issued an advisory for the entire state, with the air in the Willamette Valley being classified as "unhealthy"—though it's worse in the areas closest to the fires, such as Salem, Eugene, the Rogue Valley and Roseburg, which are currently deemed "hazardous."

The advisory is expected to hold through Monday afternoon, which might seem surprising given that the high winds that have fueled the blazes the past three days have died down. But while that's good for fighting fires, it's bad for air quality.

"What everyone's been hoping for is the winds to stop coming out of the east," says Dylan Darling, a spokesperson for DEQ, "but when it does that, there's a chance it might blow smoke north to Portland, or the smoke that is going due west will turn around and come back into Portland."

The National Weather Service offered a similar analysis on Twitter, writing that "the fires likely will grow with time until they are fully contained" and "any drastic wind shifts that would move the smoke out of western Oregon" are not expected.

Darling says the intensity, duration and spread of the fires has the potential to make the air quality the worst the Willamette Valley has ever seen.

DEQ is advising residents stay inside with windows closed, particularly those with heart and respiratory ailments. The agency also notes that cloth, dust and surgical masks are not effective in protecting from harmful smoke inhalation—only properly worn N95 respirators provide enough protection.