The ozone advisory predicts higher pollution levels. It follows a similar one for the city on Friday.
Authorities say the summer-like heat can lead to formation of ground-level ozone, a major component of smog. People should consider limiting strenuous outdoor activities.
Automobile exhaust and out-of-state smokestack emissions are primary causes.
The air quality warning lasts until 11 p.m. Saturday.
The third straight day of temperatures hitting 90 officially makes it the first heat wave of the season.