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Is the Heat Index Real?

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Complaining about the humidity is a mainstay of small talk. “It’s not the heat that gets you, it’s the humidity” is a common refrain around the South, just as “it’s a dry heat” is a go-to line in the desert Southwest. The clichés aren’t wrong on this one—a hot and humid day can have a dramatic effect on both your comfort and your health. We can measure this very real impact on your body using the heat index. 

The heat index is the temperature it feels like to your body when you factor in both the actual air temperature and the amount of moisture in the air. If the heat index is 103°F, that means that the combination of heat and humidity has a similar physical impact on your body as it would if the actual air temperature were 103°F. Even though it’s tempting to think of the heat index as an exaggerated temperature that only exists to make the heat sound worse than it really is, scientists came up with the measurements after decades of medical and meteorological research devoted to studying the impact of heat and humidity on the human body. It’s the real deal.

The dew point is an important component of the heat index. The dew point is the temperature at which the air would reach 100 percent relative humidity, or become fully saturated with moisture like on a foggy morning. Since cooler air can’t hold as much moisture as warmer air, lower dew points reflect lower moisture levels and higher dew points indicate higher moisture levels. Dew points below 60°F are comfortable, while readings reaching 70°F and even 80°F range from muggy to downright oppressive.

A chart for finding the heat index based on the temperature and dew point. Image credit: National Weather Service

Measuring humidity on a hot day is important because moisture is how your body naturally cools itself off. Your sweat cools the surface of your skin through a process known as evaporative cooling. If the air is packed with moisture, it takes longer for your sweat to evaporate than it would in more normal conditions, preventing you from cooling off efficiently. The inability to lower your body temperature when it’s hot can quickly lead to medical emergencies like heat exhaustion or heat stroke, which is why the heat index is such an important measurement to pay attention to during the summer months.

The heat index is generally considered “dangerous” once the value climbs above 105°F, and your risk of falling ill increases the higher the heat index climbs.

Dry climates can have the opposite effect on your body, with the distinct lack of moisture in the air making it feel cooler to your body than it really is. Summers get oppressively hot in places like Arizona and Iraq, but the heat doesn’t affect residents as severely because the air is extremely dry. Dew points in desert regions can hover at or below 32°F even when the air temperature is well above 100°F, which is about as dry as it can get in the natural world.  

A city in Kuwait recently measured the all-time highest confirmed temperature ever recorded in the eastern hemisphere, where temperatures climbed to a sweltering 129°F during the day on July 21, 2016. The dew point there at the same time was nearly 100 degrees cooler, leading to a heat index of just 110°F, much lower than the actual air temperature. That’s not necessarily a good thing. Extreme heat combined with extreme aridity can make your sweat evaporate too efficiently, quickly dehydrating you and potentially leading to medical emergencies similar to those you would experience in a much more humid region of the world. 

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Henrik Djärv, Flickr // CC BY-NC 2.0
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Weather Watch
It's So Cold In One Part of Russia That People's Eyelashes Are Freezing
Henrik Djärv, Flickr // CC BY-NC 2.0
Henrik Djärv, Flickr // CC BY-NC 2.0

Oymyakon, a rural village in the eastern Russian region of Yakutia, is one of the coldest inhabited spots in the world. While some schools in the U.S. cancel classes as temperatures approach zero, schools in Oymyakon remain open in -40°F weather. But recently temperatures in the region have dropped too low even for seasoned locals to handle. As AP reports, the chill, which hit -88.6°F on January 16, is cold enough to break thermometers and freeze eyelashes.

Photos shared by residents on social media show the mercury in thermometers hovering at -70°F, the lowest temperature some are built to measure. When thermometers fail, people in Oymyakon have other ways of gauging the cold. Their uncovered eyelashes can freeze upon stepping outside. Hot water tossed in the air will also turn to snow before hitting the ground.

To Oymyakon's 500-odd citizens, the most recent cold snap is nothing out of the ordinary. Temperatures are perpetually below freezing there from late October to mid-May, and average temperatures for the winter months frequently reach −58 °F. On Tuesday, residents were advised to stay inside and stay as warm as possible. Of course, that directive wasn't enough to stop some adventurous locals from sneaking outside for selfies.

[h/t AP]

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Amazon
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Weather Watch
Heated Mats Keep Steps Ice-Free in the Winter
Amazon
Amazon

The first snow of the season is always exciting, but the magic can quickly run out when you remember all the hazards that come with icy conditions. Along with heating bills, frosted cars, and other pains, the ground develops a coat of ice that can be dangerous for pedestrians and drivers alike. Outdoor steps become particularly treacherous and many people find themselves clutching their railings for fear of making it to the bottom headfirst. Instead of putting salt down the next time it snows, consider a less messy approach: heated mats that quickly melt the ice away.

The handy devices are made with a thermoplastic material and can melt two inches of snow per hour. They're designed to be left outside, so you can keep them ready to go for the whole winter. The 10-by-30-inch mats fit on most standard steps and come with grips to help prevent slipping. A waterproof connector cable connects to additional mats so up to 15 steps can be covered.

Unfortunately, this convenience comes at a price: You need to buy a 120-volt power unit for them to work, and each mat is sold separately. Running at $60 a mat, the price can add up pretty quickly. Still, if you live in a colder place where it's pretty much always snowing, it might be worth it.

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