CHICAGO -- Dense fog will drop visibility to less than a quarter-mile over much of northern Illinois into southern Wisconsin, central Illinois and northwest Indiana, including the Chicago area early this Wednesday morning.
The Dense Fog Advisory will be in effect until 9AM CST. Driving conditions will deteriorate with near zero visibility in many locations leading to a very slow-go for the morning drive.
Generally clear skies, high dewpoint air and the still cold ground/pavement will create conditions conducive to the formation and maintenance of dense fog until mid-morning, when the fog will finally improve/lift fairly rapidly.
Map of current metro-area visibility in tenths of a mile...