Wildfires in Oregon and a heat wave will leave the air smoky and dirty in Pierce County on Friday, while temperatures in Tacoma are expected to reach 90 degrees Fahrenheit.

A heat warning is in effect.

According to Harrison Rademacher, a meteorologist with the National Weather Service, a red sun rose in a tobacco-colored sky on Friday as a result of a temperature inversion.

Normally, warm air near the ground would rise, carrying with it the unhealthy small particles from vehicle emissions and other sources. The heat inversion traps that bad air closer to the ground.

Meanwhile, smoke from the Oregon fires remains largely in the air, Rademacher said, except for Mount Rainier. The smoke will increase in density through Saturday, he said.

Dirty air

Pierce County was hit harder by dirty air than King County on Friday, according to the Puget Sound Clean Air Agency.

“Pierce County and the Cascade Hills can sometimes be unhealthy for sensitive groups,” the report said.

It advised people with sensitivity to dirty air to stay indoors. The same conditions are expected on Saturday, the agency said.

Enlightenment in sight

Temperatures will drop Saturday as northwesterly winds bring cooler air from Canada. Highs in Tacoma on Saturday will be between 85 and 88 degrees, Rademacher said.

On Sunday, temperatures will be around 27 degrees Celsius, while temperatures will continue to cool.

Next week will look more like autumn weather, with temperatures around 21 degrees Celsius and a chance of showers.