Dense fog, heavy rain causes trouble during AM commute

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Counties affected by Dense Fog Advisory

CHICAGO — A Dense Fog Advisory is in effect until Noon CST Tuesday for all but southernmost portions of the Chicago area (grey-shaded counties on highlighted map to the right). Visibility will vary widely across our area, improving where showers/thunderstorms are occurring and then possibly reforming in lighter rain/drizzle.

A center of low pressure will track east-northeast across northern Illinois this morning with precipitation ending from the west and visibility gradually improving from west to east later this morning. Temperatures will rise into the 50s to the south, while remaining in the upper 30s to lower 40s north.

Continue to monitor current visibility and showers/thunderstorms on the maps below.

The Chicago National Weather Service Forecast Office has issued a Dense Fog Advisory (grey-shaded area on highlighted map above) for northeast Illinois and northwest Indiana calling for visibility a quarter mile or less tonight into as late as midday Tuesday. Moisture-laden southerly flow associated with low pressure and a warm front approaching our area from the west and south respectively has caused dew points to rise to ambient air temperatures, resulting in nearly 100% relative humidity and the formation of dense fog over much of our area this evening. The Dense Fog Advisory also extends to the west as well as north into southern Wisconsin and south into central Illinois.

In addition, showers and thunderstorms will be developing in this moist air mass overnight into the Tuesday morning hours. In some cases the resulting instability may actually improve visibility for a while in affected areas, but the dense fog will still be a threat until the low pressure and associated warm and cold fronts finally push through and east of our area Tuesday. Fog could improve earlier (Dense Fog Advisory expires at 6AM CST Tuesday) in southernmost sections of our area (Kankakee, Livingston, Iroquois and Ford Counties in Illinois and Newton, Jasper and Benton Counties in Indiana).

See the current visibility map below and track shower and thunderstorm development on the current Metro Weather radar display below.

Current visibility (in miles and tenths of a mile)...

Current Metro weather radar Mosaic...