11 Booming Facts About Thunderstorms

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Thunderstorms can inspire the entire range of human emotion with their vivid displays of nature's fury. Storms are used to set an ominous tone in spooky stories, even as they bring much-needed relief to parched fields or distressed humans on a hot day. These torrents are as fascinating to study as they are to watch, and as common as they are, they're actually quite complex.

1. WHAT GOES UP …

Warm, moist air is the fuel that feeds a thunderstorm the energy it needs to survive. A column of warm air quickly rising through the atmosphere is known as an updraft, and these upward winds can pack a punch. The strength of an updraft depends on how great the temperature difference is between different levels of the atmosphere. An updraft can exceed 100 mph in the strongest thunderstorms.

2. THE TOP OF THE STORM GETS SMOOSHED.

An updraft will continue skyward until the rising air is no longer warmer than the air around it. The rising air spreads out at this point, creating flat, anvil-like clouds that make a distant thunderstorm such a spectacular sight. Even more stunning are mammatus clouds, bubble-shaped formations that can develop along the bottom of anvils. Due to the strength of the storm needed to produce these vivid formations, they're often associated with severe thunderstorms.

3. RAIN DRAGS A STORM DOWN.

Once the weight of the raindrops suspended in a budding thunderstorm grows too heavy for the updraft to hold, or once raindrops fall out of the sides of the updraft, they begin falling to the ground as precipitation. The falling rain drags cooler air toward the ground, creating a downdraft, or that cool breeze you feel before and during a storm. Most downdrafts are pretty weak, but some are strong enough to cause damaging winds at the surface. A thunderstorm dies once the cool air of the downdraft cuts off the flow of warm air to the updraft, starving the storm and causing it to rain itself out.

4. THERE ARE DIFFERENT TYPES OF THUNDERSTORMS.

Not all thunderstorms are the same. There are three main types of thunderstorms. Most thunderstorms are single-cell, or a storm that pulses up, rains for half an hour, and dissipates. When that storm collapses, the wind from its downdraft can trigger more storms in a chain reaction. There are also multi-cell thunderstorms, the most common of which are squall lines. The third type of storm is a supercell, or a thunderstorm that has a rotating updraft. The twisting updraft helps supercells survive for many hours and produce more severe weather—larger hail, higher winds, and stronger tornadoes—than a normal thunderstorm.

5. HAIL BOUNCES AROUND LIKE POPCORN.

If temperatures are just right in the middle of a thunderstorm, some of the raindrops will begin to freeze as they bounce around in the updraft. The up-down motion of the newly formed hailstone will cause more liquid to accumulate on the outside of the stone, a process that causes hailstones to grow in layers like an onion. The vast majority of hail isn't large enough to cause any damage, but the updrafts in some thunderstorms are so intense that they can support hailstones the size of softballs or larger.

6. THUNDERSTORMS ARE ELECTRIFYING.

The friction between ice crystals, raindrops, and hailstones moving around in a storm can cause an electrostatic buildup between the clouds and the ground that releases its energy in a brilliant flash of lightning. Lightning is hotter than the surface of the Sun, heating the air up so fast that the shockwave radiates out in a sonic boom we hear as thunder. All thunder is caused by lightning, and all lightning causes thunder. There's no such thing as "heat lightning," a term used to describe lightning seen in the distance not accompanied by thunder. This phenomenon is simply lightning that occurs too far away for you to hear the thunder.

7. STORMS ARE PRETTY HEAVY.

Water is heavy. We look at clouds floating effortlessly through the sky and don't think about the sheer amount of weight hanging above our heads. One cumulus cloud can weigh more than 1 million pounds. When it comes to a billowing thunderstorm, though, the weight can go up tremendously depending on how much rain it's holding. We're lucky the rain doesn't all fall at once.

8. THEY BLOCK OUT THE SUN.

All of that water looming above us also has the effect of blotting out the sun. The sky gets dark before a thunderstorm because the sunshine can't make it through the vast column of water in an especially wet thunderstorm. The much-feared green sky before a storm, often thought to presage a tornado, is usually caused by sunlight refracting through both heavy rain and hailstones.

9. HUMANS CAN ACCIDENTALLY CAUSE THEM.

Humans can't control the weather, but our actions can indirectly influence where thunderstorms form. Studies have shown that increased temperatures in and around cities, due to the urban heat island effect, can trigger thunderstorms that wouldn't have otherwise formed in these areas if the city and its streets weren't there. There's also some evidence that unstable air warmed by steam released by the cooling stacks of nuclear power plants can trigger small storms.

10. IT CAN THUNDER WHEN IT'S SNOWING.

Thunder doesn't only happen when it's raining. Intense bands of snow can develop during blizzards and lake effect snow events in much the same way that a regular thunderstorm would form when it's warm out. These strong bands can produce lightning and loud cracks of thunder all while dumping copious amounts of snow in a short period of time.

11. YES, IT CAN RAIN FROGS.

There's some truth to the myth that it can rain frogs, fish, and other odd objects. If a strong tornado lofts debris high into a storm, that debris has to fall down somewhere. If a tornado sucks the water out of a pond, for example, it's very possible that the critters that used to be in the water will fall on populated areas. Hail can also form embedded with small pieces of debris like tree branches as the debris serves as a nucleus around which the water can freeze.

Why Does Humidity Make Us Feel Hotter?

Tomwang112/iStock via Getty Images
Tomwang112/iStock via Getty Images

With temperatures spiking around the country, we thought it might be a good time to answer some questions about the heat index—and why humidity makes us feel hotter.

Why does humidity make us feel hotter?

To answer that question, we need to talk about getting sweaty.

As you probably remember from your high school biology class, one of the ways our bodies cool themselves is by sweating. The sweat then evaporates from our skin, and it carries heat away from the body as it leaves.

Humidity throws a wrench in that system of evaporative cooling, though. As relative humidity increases, the evaporation of sweat from our skin slows down. Instead, the sweat just drips off of us, which leaves us with all of the stinkiness and none of the cooling effect. Thus, when the humidity spikes, our bodies effectively lose a key tool that could normally be used to cool us down.

What's relative about relative humidity?

We all know that humidity refers to the amount of water contained in the air. However, as the air’s temperature changes, so does the amount of water the air can hold. (Air can hold more water vapor as the temperature heats up.) Relative humidity compares the actual humidity to the maximum amount of water vapor the air can hold at any given temperature.

Whose idea was the heat index?

While the notion of humidity making days feel warmer is painfully apparent to anyone who has ever been outside on a soupy day, our current system owes a big debt to Robert G. Steadman, an academic textile researcher. In a 1979 research paper called, “An Assessment of Sultriness, Parts I and II,” Steadman laid out the basic factors that would affect how hot a person felt under a given set of conditions, and meteorologists soon used his work to derive a simplified formula for calculating heat index.

The formula is long and cumbersome, but luckily it can be transformed into easy-to-read charts. Today your local meteorologist just needs to know the air temperature and the relative humidity, and the chart will tell him or her the rest.

Is the heat index calculation the same for everyone?

Not quite, but it’s close. Steadman’s original research was founded on the idea of a “typical” person who was outdoors under a very precise set of conditions. Specifically, Steadman’s everyman was 5’7” tall, weighed 147 pounds, wore long pants and a short-sleeved shirt, and was walking at just over three miles per hour into a slight breeze in the shade. Any deviations from these conditions will affect how the heat/humidity combo feels to a certain person.

What difference does being in the shade make?

Quite a big one. All of the National Weather Service’s charts for calculating the heat index make the reasonable assumption that folks will look for shade when it’s oppressively hot and muggy out. Direct sunlight can add up to 15 degrees to the calculated heat index.

How does wind affect how dangerous the heat is?

Normally, when we think of wind on a hot day, we think of a nice, cooling breeze. That’s the normal state of affairs, but when the weather is really, really hot—think high-90s hot—a dry wind actually heats us up. When it’s that hot out, wind actually draws sweat away from our bodies before it can evaporate to help cool us down. Thanks to this effect, what might have been a cool breeze acts more like a convection oven.

When should I start worrying about high heat index readings?

The National Weather Service has a handy four-tiered system to tell you how dire the heat situation is. At the most severe level, when the heat index is over 130, that's classified as "Extreme Danger" and the risk of heat stroke is highly likely with continued exposure. Things get less scary as you move down the ladder, but even on "Danger" days, when the heat index ranges from 105 to 130, you probably don’t want to be outside. According to the service, that’s when prolonged exposure and/or physical activity make sunstroke, heat cramps, and heat exhaustion likely, while heat stroke is possible.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

This article has been updated for 2019.

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. 

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

This story has been updated for 2019.

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