Update 10AM CDT…
Dense fog along and west of the interstate-39 corridor and along and south of the Interstate-80 corridor has taken longer to lift than earlier anticipated. A dense Fog Advisory (gray-shaded counties on the map below) for that portion of our area is now in effect until 11AM and could well extend to noon with visibility near zero , severely restricting travel in many locations. Conditions should improve rapidly this afternoon.
Patchy dense fog will drop visibility under a quarter-mile in many areas away from the city early this Wednesday morning with near zero visibility in spots. If out driving, be aware that you may quickly encounter patches of very poor visibility. While it will be hazy, the “heat Island” effect will keep temperatures a little warmer, and probably avoid dense fog formation within the Chicago city limits.
With weak high pressure overheat and light winds, temperatures and dew-points have come together, allowing the formation of the patchy dense fog. Check the visibility map below for specific area airport locations and note the minimal temperature/dew-point differences on the other two maps.
Visibility will increase as fog lifts by mid-morning.