Above and beyond the wildfires of Southern and Central Oregon and California, smoke from fires as far north as Washington and British Columbia has moved in to blanket the state.
The yellow haze in the air on Friday was smoke from the Ranch Fire and other Northern California and OR fires, the San Joaquin Valley Air Pollution Control District said.
Shifting winds from the west Wednesday night started the process of clearing smoke from the Portland metro area, according to KGW chief meteorologist Matt Zaffino.
"We did have a break over the past 48 hours, but it doesn't take a ton of smoke", Schultz said.
Unhealthy for Sensitive Groups (orange): Increasing likelihood of respiratory symptoms in sensitive individuals, aggravation of heart or lung disease and premature mortality in persons with cardiopulmonary disease and the elderly.
Henderson suggested using portable air cleaners indoors to keep the air as clean as possible during smoky conditions.
The National Weather Service warned that because wildfires are still burning in Eastern Washington and Canada, the Puget Sound area will continue to see smoke from time to time.
Smaller fires also erupted in urban parts of B.C. on Monday.
Skies briefly cleared in the city before another advisory was issued on Wednesday. Portland Public Schools suspended all outdoor sports practices.
Air quality returned to "good" in Tacoma on Thursday as winds pushed large amounts of wildfire smoke out of the region.
Hundreds of flights have been grounded at Seattle-Tacoma International Airport due to the poor visibility.