Dense Fog Advisory for far western portions of Chicago area until 9 a.m. Thursday

A Dense Fog Advisory (gray-shaded counties on the headlined map) calling for visibility at or below a quarter-mile is in effect for Winnebago, Boone, Lee, Ogle, DeKalb and LaSalle Counties until 9AM CDT this Thursday morning.

The dense fog is not continuous, but more patchy making for quick changes in visibility and additionally dangerous driving conditions. Note on the visibility map below, visibility well less than a quarter mile has also developed in spots in Livingston, Grundy, Kendall and Kane Counties.

The Dense fog Advisory also extends north into Wisconsin, south into downstate and west beyond the Mississippi River.

Conditions are expected to improve rapidly by mid-morning.

Map with latest airport visibility observations…