A dense fog advisory was issued for central Cook, Lake, DuPage and McHenry counties in Illinois and Kenosha County in Wisconsin on October 20, 2026. The advisory warned of near‑zero visibility and hazardous driving conditions and remained in effect until 9 a.m.
The fog reduced visibility to almost zero, creating dangerous road conditions during the morning commute across the affected parts of the Chicago metropolitan area. Drivers were advised to proceed with caution as the advisory covered the specified counties until the morning rush hour ended.
The advisory’s timing coincided with the typical morning travel period, prompting commuters to adjust routes or delay travel until visibility improved.