Expect the blue skies of Central Oregon to turn gray and the air quality to dip to unhealthy — or even hazardous — levels for sensitive groups as winds shift from the southeast to the northwest by Friday.

The unprecedented poor air quality caused by a record number of wildfires around the state will be begin to blanket the region and parts east and last through the weekend, according to weather service and fire officials.

“It could be pretty thick in the area,” said Dan Slagle, a National Weather Service meteorologist in Pendleton. “We could see it limiting visibility quite a bit. You might not be able to see the sun.”

For 72-year-old Louie Pitt Jr., director of government affairs and planning for the Confederated Tribes of Warm Springs, poor air quality means he’ll be staying home next to his air purifier.

As someone who experiences asthma and allergies, Pitt said he’s worried about how the smoke will affect his breathing.

“We’ve learned the hard way from the last fire about the air quality,” Pitt said Thursday. “There were times when I couldn’t see across the road to the hill on the other side.”

Health officials are telling people to stay indoors, seal up their windows and doors and turn their air conditioners to recycle to protect themselves from the unhealthy conditions.

Areas closest to fires — such as Salem, Eugene, the Rogue Valley and Roseburg in Oregon, and Woodland in Washington — are having the worst smoke impacts.

“We’re telling people to limit their exposure,” said Emily Wegener, Jefferson County Public Health preparedness and response coordinator. “They should reduce the amount of time they spend outside.”

Normally officials would tell residents to seek cleaner air in air-conditioned venues like movie theaters, libraries or other indoor facilities, but the threat of COVID-19 means people should just stay home, Wegener said. If non-household members move in temporarily because of fire threats, maintain physical distances and wear cloth masks indoors, she said.

Unhealthy or hazardous air quality means that minute particles, smaller than the diameter of a hair follicle, are airborne and can go deep into the lungs, said Laura Gleim, Department of Environmental Quality spokeswoman. These particles are so small they can get into the bloodstream.

“PM 2.5 (particulate matter air pollutant) can go deep into the lungs and cause coughing, chest pain and exacerbate heart and lung conditions,” Gleim said.

Cloth face coverings, while recommended to stop the spread of droplets that might contain COVID-19, do not keep out this particulate pollution, Gleim said. Only well-fitted N95 masks can keep out these fine particles, she said.

And while not everyone can afford a high-efficiency filter that captures particulate pollution, health officials said that residents can build an equivalent themselves using a standard window box fan with a MERV (Minimum Efficiency Reporting Values filter) rated filter of 13 and above taped to one side for about $40, said Morgan Emerson, Deschutes County Health Services spokeswoman.

“This is a nice affordable option,” Emerson said. “Even if you have an N95 respirator, call your doctor and make sure you have a plan. If you’re running low on your inhaler, now’s the time to refill your prescription.”