Dense fog is expected through Sunday evening in the Chicago area.

The National Weather Service issued a dense fog advisory about 8:40 a.m. Sunday, that will remain in effect until 9 p.m.

In some areas, visibility is expected to drop to 1/4 mile or less, according to the advisory.

The fog will continue to gradually spread north Sunday morning, covering Cook County and spreading into DeKalb County, the weather service said.

Drivers are advised to allow for additional travel time, reduce speed, increase following distance and use low beams.