Dense fog in Chicago may slow first half of evening commute south and east of Chicago into northwest Indiana

Update 4:30PM CST…

Dense Fog Advisory extended until 6PM CST for portions of the Chicago area south and east of Chicago, mainly in northwest Indiana where poor visibility could persist into the evening hours. 

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CHICAGO — A Dense Fog Advisory for the entire Chicago area has been extended until 4 p.m. CST this Thursday afternoon.

Visibility will vary from near zero to a quarter-mile in many locations. Those traveling need to plan for a slowed, longer drive, and very low visibility during that time. The fog will impact at the the first half of the afternoon commute and could extend into the evening, especially in areas south and east of Chicago.

(Areas affected by the fog advisory are shaded in grey on this map)

Timing on the end of the dense fog coincides with the passage of a cold front that is forecast to move through northern Illinois into northwest Indiana later this afternoon or in the early evening.

Southerly winds are carrying mild and moist air with dew points in the upper 30s over the still-thick snow cover with fog forming quickly, as the higher dew point air comes in contact with the 32-degree air at snow level.

Around 7 a.m. Thursday, visibility ranged from near zero to a quarter-mile or less in the Chicago area. While conditions did slowly improve, patchy and dense fog persisted in some places into the afternoon. Conditions have improved enough to drop the Dense Fog Advisory across southern Wisconsin.

As the cold front passes through our area, it could turn into a mixture of wet snow and rain, which would improve visibility, but could lead to icy conditions on roads.

Here’s the latest visibility, as of 1 p.m. Thursday: