Is the Heat Index Real?

iStock
iStock

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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Lake Michigan Has Frozen Over, and It's an Incredible Sight

Scott Olson, Getty Images
Scott Olson, Getty Images

A polar vortex has brought deadly temperatures to the Midwest this week, and the weather is having a dramatic effect on one of the region's most famous features. As the Detroit Free Press reports, parts of Lake Michigan have frozen over, and the ice coverage continues to grow.

The Lake Michigan ice extent has increased rapidly throughout January, starting around 1 percent on the first of the month and expanding to close to 40 percent by the end of the month. Yesterday was the coldest January 30 in Chicago history, with temperatures at O'Hare Airport dropping to -23°F. Even though it's frozen, steam can be seen rising off Lake Michigan—something that happens when the air above the lake is significantly colder than the surface. You can watch a stream of this happening from a live cam below.

Lake Michigan's ice coverage is impressive, as these pictures show, but it's still far from breaking a record. Though Lake Michigan has never frozen over completely, it came close during the winter of 1993 to 1994 when ice reached 95 percent coverage.

Midwestern states like Wisconsin, Michigan, Illinois, and Indiana aren't the only places that have been hit hard by the cold this winter. At the United States/Canada border, Niagara Falls froze to a stop in some spots, a phenomenon that also produced some stunning photographs.


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[h/t Detroit Free Press]

Why You Need to Keep Your Car's Gas Tank Full in Cold Weather

iStock.com/Chalabala
iStock.com/Chalabala

Schools, trains, and the U.S. Postal Service have shut down this week as a polar vortex brings negative double-digit temperatures to the Midwest. Even if residents won't be doing much traveling as long as the dangerous weather persists, they'd benefit from keeping a full tank of gas in their cars: According to the Detroit Free Press, it's an easy way to prevent fuel lines from freezing.

One common reason cars struggle to start in cold weather is blocked-up fuel lines. These tubes are thin, and if there's any moisture in them when temperatures drop to extreme levels, they can freeze, causing blockages that prevent fuel from flowing.

Gasoline, on the other hand, doesn't freeze as easily. It maintains its liquid state in subzero temperatures, like those currently hitting parts of the U.S., so when a gas tank is full, those fuel lines are better equipped to handle to the cold.

If you filled up your tank before the recent cold snap and your car still won't start, it may have something to do with your antifreeze levels. Your car's radiator needs water to work properly, and antifreeze is what keeps the water liquid when temperatures dip below 32°F.

Of course, if temperatures have already dropped to dangerous levels in your area, it's not worth it to drive to the gas station to refuel or run out to stock up on antifreeze. Instead, keep these car maintenance tips in mind for the next time an arctic blast rolls in to town. And when it is safe enough to drive again, resist heating up your engine in the driveway: Letting your car idle in the cold can actually shorten the engine's lifespan.

[h/t Detroit Free Press]

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