Regulators have issued an Air Quality Alert for Saturday in Metro Louisville and Southern Indiana.
The high temperatures (around 90 degrees) and light winds mean there could be high ozone levels in the area. The air is predicted to be unhealthy for sensitive groups, such as the elderly, young children, and people with lung disease.
Ozone is formed when the pollution from motor vehicles and factories cooks under the sun.
For updates on local air quality, click here.