Is the Heat Index Real?

MarianVejcik/iStock via Getty Images
MarianVejcik/iStock via Getty Images

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.

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.  

In 2016, a city in Kuwait 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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This story has been updated for 2019.

Denver's Temperature Dropped a Record 64 Degrees In 24 Hours

Leonid Ikan/iStock via Getty Images
Leonid Ikan/iStock via Getty Images

One sure sign summer is over: On Wednesday, residents of Denver, Colorado were experiencing a comfortable 82-degree day. Just before midnight, the temperature dropped to 29 degrees. Between Wednesday and Thursday afternoon, the Denver airport recorded a differential of 79 degrees down to 24 degrees. At one point on Wednesday, a staggering 45-degree drop was seen in the span of just three hours.

All told, a one-day span saw a 64-degree change in temperature, from a high of 83 to a low of 19, a record for the state in the month of October and just two degrees shy of matching Denver’s all-time record drop of 66 degrees on January 25, 1872. On that date, the temperature plummeted from 46 degrees to -20 degrees.

Back to 2019: Citizens tried their best to cope with the jarring transition in their environment, to mixed success. On Wednesday, the city’s Washington Park was full of joggers and shorts-wearing outdoor enthusiasts. Thursday, only the most devoted runners were out, bundled up against the frigid weather.

The cold snap also brought with it some freezing drizzle which prompted several vehicular accidents, including 200 reported during Thursday's morning commute. It’s expected to warm up some in the coming days, but residents shouldn't get too comfortable: Melting ice could lead to potholes.

[h/t KRDO]

Fall Foliage Is Running Late This Year

Free art director/iStock via Getty Images
Free art director/iStock via Getty Images

The August arrival of the pumpkin spice latte might have you feeling like fall is in full swing already, but plants aren’t quite so impressionable. According to Travel + Leisure, the best fall foliage could be coming a little later than usual this year.

Historically, the vibrant transformation starts to sweep through northern regions of the Rocky Mountains, Minnesota, and New England in mid-September, and reaches its peak by the end of the month. Other areas, including the Appalachians and Midwest states, don’t see the brightest autumn leaves until early or mid-October. The Weather Channel reports that this year, however, the forecast from the National Oceanic and Atmospheric Administration predicts unseasonably warm temperatures for the next two weeks, which could impede the color-changing process.

Warm temperatures aren’t necessarily bad for fall foliage, as long as they occur during the day and are offset by cool nights. Since meteorologists don’t expect the overnight temperatures to drop off yet, plants will likely continue producing enough chlorophyll to keep their leaves green in the coming days.

The good news is that this year’s fall foliage should only be about a week late, and meteorologist David Epstein thinks that when leaves do start to change color, we’re in for an especially beautiful treat. If the current weather forecast holds, he told Boston.com, we'll "see a longer season than last year, we’d see a more vibrant season than last year, and it would come on a little earlier than last year, which was so late.”

Though poor weather conditions like early snow, heavy rain, drought, or strong winds can cause leaves to fall prematurely, most trees right now are in a good position to deliver a brilliant display of color after a healthy, rain-filled summer.

Find out when you’ll experience peak fall foliage in your area with this interactive map.

[h/t Travel + Leisure]

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