Dr. Trevor Lewis, chair of emergency medicine at Cook County Health, advised that anyone going out in extreme heat should drink 8 to 12 ounces of water before going out, and replenish with 6 to 8 ounces more every 20 minutes. Lewis also advised wearing light-colored clothing, as it reflects the sun, while dark-colored clothing absorbs heat.

As residents of Chicago's Northwest Side recovered from the sweltering heat, a round of storms Thursday caused a ground stop at O'Hare and Midway airports.

A dangerous heat wave has descended on Chicagoland this week, with extreme heat and humidity to persist through Thursday. Temperatures will get well into the 90s, but heat index values will soar to around 105 or 110 degrees when the high humidity is factored in.

The National Weather Service issued Extreme Heat Watches and Flood Advisories throughout Illinois. Here's the forecast.

Rising dew point temperatures will increase humidity Tuesday evening, with a heat advisory going into effect Wednesday.

The heat index, or how it feels with humidity factored in, will rise into the triple digits for millions as the hot dome of high pressure engulfs the central and eastern states.

The heat index is expected to hit 105 to 115 degrees in the metro area on Wednesday. The setting sun won't provide much relief — temperatures will likely remain above 90 degrees into the evening hours.

The building heat and humidity comes as Chicago's air quality readings early Monday morning were "unhealthy for sensitive groups," the website AirNow.gov said. The air quality ranked as a level three of six on the Air Quality Index, with a PM2.5 of 128.

Chicago's in for a scorcher. An Extreme Heat Watch is in effect Wednesday through Thursday. Here's how to stay safe.