Dense fog advisory until 9 a.m.

A dense fog advisory has been issued until 9 a.m. by the National Weather Service.

Cook, DuPage, Kane, Lake and McHenry counties are in the advisory area.

Visibility will be less than a quarter mile, officials said.

Areas of low visibility will cause hazardous driving conditions.

People are urged to reduce speeds when driving, use headlights and leave plenty of distance between you and other cars.