The warning is in effect until midnight for Cook, DuPage and Will counties.
By Mary Kay Kleist

(CBS) — An air-quality alert has been issued for much of the Chicago area Saturday, as stagnant, steamy air combines with temperatures in the 90s.

The alert is in effect until midnight for Cook and the collar counties, CBS 2’s Mary Kay Kleist says. People with respiratory problems are the most vulnerable during these conditions and are encouraged to limit their outdoor activities.

Temperatures will peak in the mid-90s.

Storms are possible by evening.

Sunday will offer a marked contrast to the heat of the last couple of days. Temperatures will be in the 70s.