An Air Quality Alert has been issued for Northeast Illinois and Northwest Indiana for Thursday afternoon. This does include McHenry County.
Due to the higher temperatures and humidity expected Thursday the air won't have a chance to mix throughout the atmosphere, trapping ozone particulates near the surface. This will cause ozone and particulate levels to be at, or above, unhealthy levels for sensitive groups such as children and adults with Asthma. If you are sensitive to the high humidity, try to limit your time outdoors Thursday.