CHICAGO (CBS) -- An isolated shower or storm is possible until 7 p.m. on Tuesday, then expect a mostly clear and warm evening with temperatures in the upper 70s and low 80s to close out the 4th of July. 

Overnight temperatures will fall only to the low 70s under a mostly clear sky.

An Air Quality Alert has been posted for Wednesday. Elevated amounts of ozone pollution will reduce air quality to possibly the "unhealthy" category.

Wednesday will start mostly clear, then we'll have increasing clouds by midday. Highs will be hot in the low 90s. 

A cold front will approach the area by late in the day, and will be the focus for scattered thunderstorms, especially after 4 p.m. 

A few storms could be severe, producing hail and gusty winds.

Cooler air for late week and weekend, with highs in the upper 70s and low 80s. Shower chances return by the weekend.

TONIGHT: An early evening shower or storm is possible, then mostly clear overnight. Low 71°

WEDNESDAY: Increasing clouds and hot. Thunderstorm chances increase by the late afternoon. A few storms could be severe. High 91°

THURSDAY: Mostly cloudy and cooler. A slight chance for rain. High 77°