Indiana State Police warns drivers to add extra time to their commute as dense and patchy fog will lower visibilities Thursday morning on the roads.

A Dense Fog Advisory is in effect for much of central Indiana–and some school districts are delayed as a result. The advisory, which runs through 9 a.m. ET, means visibility could be limited to one quarter mile or less in areas with dense fog.

During the morning hours, the Federal Aviation Administration warned that ground stops at both O'Hare and Midway International Airports were possible due to weather conditions.