Across much of the world, hotter days are no longer arriving alone. The air itself is changing, sometimes turning from dry ...

It’s a T-shirt kind of day in Washington, DC: 85 degrees with 63 percent humidity. We all know those numbers mean hot, but what exactly does that humidity percentage tell us? And why should we care?

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 ...