Michigan's heat wave this week will feel even warmer because of high humidity. Here's how the heat index works.

Extreme levels of heat and humidity are forecast to spread across the country over the next two weeks, blanketing the Southwest, Midwest, and East Coast with high temperatures beginning this June 19 ...

What is heat index and how does it affect how stifling excessive heat feels?

The heat index shows how humidity makes hot days feel hotter, and why direct sun can push dangerous conditions even higher.