On a sticky, hot day, have you ever heard someone complain, “It’s not the heat, it’s the humidity?” If you’re in one of the 40 US states predicted to get stifled by extreme humidity over the next couple weeks, you may say it yourself. Warm, damp air funneled up from the Atlantic Ocean and Caribbean Sea will settle like a wet blanket across the South, Midwest, and East in the coming days. Experts predict it will stick around for a while, too. An area of high pressure will trap it in place in a weather event called a “heat dome.” That means 170 million people in the US are in for a sweaty start to their July. Heat can be bad for one’s health. But when it's combined with humidity, it can be particularly dangerous. Humidity is the amount of water vapor present in the air. It can interfere with the body’s natural cooling process. When we get hot, we sweat. When sweat evaporates off our skin, it sheds heat. But if the air is already saturated with water vapor, our sweat has no place to go. We stay soaked, and we stay hot. And that can lead to heat exhaustion. “If you’re seeing heavy sweating, cramps, weakness—stop what you’re doing, drink cool beverages, and rest,” Suzanne Beavers told Popular Science. She's an epidemiologist at the US Centers for Disease Control and Prevention. “(And) seek medical attention right away if you have changes in mental status.” Humidity is measured by the “dew point.” That's the temperature at which the air becomes saturated with moisture. Over the next two weeks, dozens of US cities will reach “extreme” on the dew point scale. Their dew points will be similar to those of a tropical rain forest. Reflect: How would you feel and react if the weather was very hot and humid, and what would you do to stay comfortable or safe?
