Dense fog is likely this evening in counties away from the city of Chicago with visibility dropping to under a quarter-mile, possibly lowering to 100-feet or less in spots. With temperatures in the 20s, there could be some condensation-formed glaze on some roads, and other paved areas, complicated further by a period of light snow/sleet. With the potential slick spots in mind along with poor visibility, travel and outdoor activities will be difficult and dangerous – be careful and take your time.
A dense Fog Advisory is actually in effect until well after midnight for most of the Chicago area away from the City of Chicago (see grey-shaded area on the headlined map). A rather weak low pressure will move through northeast Illinois into NW Indiana later this evening preceded and accompanied by the period of light snow/sleet, winds shifting from SW to West and eventually NW. Visibility should improve with the passage of the low pressure, but spotty slick conditions could persist overnight.
Check current conditions with the Visibility and Regional Weather Radar Mosaic maps below.