Though less common, tornadoes can form without the presence of thunderstorms

Tornado formation relies on wind shear to create a tube of rotating air

Once a horizontal vortex is created by air circulating between winds of different directions and speeds, an updraft, such as those seen in powerful thunderstorms, tilts the vortex vertically. The updraft then strengthens the vortex, which becomes a tornado upon touching the ground.

In a tornado outbreak, a single severe weather system can spawn multiple twisters

By maintaining the ingredients for tornadoes—differences in wind speed and direction across altitudes, moisture, and rising air—for long periods of time as it moves across a region, a severe thunderstorm can continuously produce tornadoes by lifting multiple columns of horizontally rotating air.

Tornadoes, or twisters, have been seen on every continent but Antarctica

Because tornadoes require rising warm air to form, some meteorologists have suggested that urban environments—locations where human landscape modification has introduced materials that trap thermal energy—can enhance the conditions needed for tornado formation. Tornadoes have been reported to cause ear "popping" due to drastic changes in air pressure.

Most tornadoes occur during the afternoon and evening hours

While there is no official national tornado season as with Atlantic hurricanes, many tornadoes form in the presence of thunderstorms, which are fueled by solar heating and the energy released by the condensation of water vapor. The airflow instabilities created from this energy build throughout the day until the sun sets.

Various types of tornadoes are distinguished by their shape, size, and location

Waterspouts form over water as long, thin columns of mist and air, while elephant trunks are tornadoes that elongate vertically as they become tilted during their formation, resembling the mammal's appendage. Wedge tornadoes are among the most powerful, often spanning a mile or more in width.

Fast-changing conditions during their formation make tornado forecasting difficult

The final steps of tornadogenesis—the process of forming a tornado—depend on near-surface details, such as local geography, which are difficult for radar to observe and affect how funnel clouds make contact with the ground. Inconsistencies in storm behavior have limited the amount of advance warning people receive before tornadoes touch down.

Nor'easters can produce thundersnow—lightning in blizzard conditions

Although thunderstorms typically require warm air to rise in updrafts and collide with heavier soft hail, which creates charge separation and eventual electrical discharge, these cyclones can replicate these conditions by churning the atmosphere through strong winds. Rarely, especially warm lakes can similarly help generate thunderstorms during the winter.

The first known instance of a fire tornado occurred in 2003

During pyro-tornadogenesis, many processes that create thunderstorms from wildfires, such as rising hot air and steam from evaporated water in forests, fuel the formation of a fire tornado. The increasing rates of wildfires due to climate change are expected to make this phenomenon and other extreme weather more common.

Tornadoes produce inaudible signals to humans hours before forming

Researchers at the National Oceanic and Atmospheric Administration have found that tornado-producing storms generate specific sounds below the range of human hearing, much like the infrasonic signals produced by earthquakes and avalanches. Although difficult to distinguish from wind noise, scientists hope to build systems that use these signals to improve tornado forecasting.

Tropical cyclone formation require warm water and limited vertical wind shear

Ocean temperatures above 27 degrees Celsius fuel rising, moist air, which releases energy through heat as water vapor condenses into clouds. Significant changes in wind speed with height can spread out these upflows, preventing the eventual formation of a central column known as the eye.

In Doppler radar imaging, a 'hook echo' helps identify a tornado-producing thunderstorm

Typically found in the right-rear part of a storm relative to its motion, the "hook" is the hallmark of a mesocyclone—a large, rotating updraft of air—within supercells, the most powerful thunderstorms. While tornadoes are known to develop within mesocyclones, they can also be detected by storm spotters trained to recognize tornado conditions in their communities.

Atmospheric processes amplify the strength of storms by coalescing clouds

Research has shown that turbulent mixing of air at the edges of clouds and other small-scale thermal activity beneath them help clouds group together, intensifying short bursts of rainfall, especially in tropical regions. Simulations reveal this produces more powerful storms than predicted by older models, though they may occur less frequently.

Hail forms in freezing temperatures thousands of feet above the ground

Even if surface temperatures are well above freezing during the summer, updrafts during thunderstorms can push raindrops high into the atmosphere, where they can freeze and form hail. Giant hailstones the size of softballs require updrafts of close to 100 mph.

Unlike hurricanes, tornadoes are not ranked based on measured wind speed

Technological limitations prevent direct measurements of wind speeds where tornadoes make contact with the ground. Instead, the Enhanced Fujita scale assigns a rating with a range of speeds based on how much damage a tornado caused to various types of structures. These types are more extensive than the original Fujita scale.

Tornado myths include suggestions to hide beneath a bridge or to open windows

Winds can accelerate due to a tunneling effect as they pass under a structure, making seeking shelter from a tornado in a mobile home or recreational vehicle highly discouraged. Significant tornado damage results from debris being picked up and hurled by strong winds, making it unsafe to be near windows that may shatter.

Stretching from Texas to the Dakotas, Tornado Alley is a US tornado hotspot

The region experiences atmospheric instability and extensive wind shear due to the convergence of warm, moist air from the Gulf with cooler, drier air from the Rockies. However, some recent data suggests tornadoes are more frequent and more powerful in the Dixie Valley, which includes much of the lower Mississippi Valley.

Watch the birth of a tornado in real time

While driving through suburban Oklahoma in May 2013, National Geographic explorer and storm researcher Tim Samaras witnessed the formation of a tornado from a thunderstorm and captured footage of the descending funnel cloud before it touched down.

The risk of tornadoes and storm surges is greatest on the 'dirty side' of a hurricane

Winds in the right-front quadrant of the storm are amplified by the hurricane's motion and its rotation, which both move air in the same direction. Upon making landfall, these winds pull water from the Gulf and Atlantic onto land, creating storm surges. Tornadoes can also be generated from large differences in wind speed and direction at various heights.

Hurricanes, which rely on air consistently spinning in the same direction, cannot cross the equator because air curves in opposite directions north and south of it.

View the various types of lightning

The most common form of lightning involves channels of electricity between oppositely charged regions within a cloud or between two clouds to reestablish electrostatic equilibrium. While cloud-to-ground lightning is understood best, research is ongoing to fully model the mechanisms behind rarer forms of lightning, such as transient luminous events.

Why aren’t there hurricanes in Europe?

Despite their proximity to the Atlantic Ocean, the effects of the subtropical jet stream make tropical storms and hurricanes unlikely to reach Europe at full strength. Their remnants, however, can combine with other weather systems to create powerful storms.

How jet streams, which reside in the troposphere, shape and confine pockets of atmospheric air

These fast-flowing ribbons of air are hundreds of kilometers wide and typically travel from west to east due to Earth's rotation, with the polar front and subtropical jets serving as major drivers of global circulation. Warmer air near the equator pushes the polar front jets toward the poles, which can buckle and deform them as they contain frigid polar vortex systems.

Dirty lightning is a thunderstorm created from friction between rising and falling flows of ash and smoke during volcanic eruptions.

Hurricanes can grow by replacing their eyewall

A second outer eyewall can form around the primary eyewall surrounding a hurricane's eye. During an eyewall replacement cycle, the outer wall can weaken, collapse, and replace the inner wall, temporarily weakening the storm before it strengthens and grows.

View the ten deadliest tornadoes in US history.

Chaos theory—informally known as the butterfly effect—is the reason why weather forecasts are presented with probabilities rather than certainties.

The sun emits a continuous stream of plasma known as the solar wind

Composed of charged particles—electrons and ions—the solar wind is deflected around the Earth by the planet's magnetic field. More powerful solar storms, known as coronal mass ejections, are short-lived but produce huge clouds of plasma that disrupt technology upon reaching Earth.

Carbon-neutral data centers may be possible if built within wind turbines

Wind turbine towers are typically hollow, housing only cables and a ladder for maintenance access. The excess electricity a wind turbine collects could power a stack of server racks more than 100 meters (328 feet) high within its tower.

Supervolcanoes can eject enough material to fill one-fourth of the Grand Canyon

Although extremely rare, their released material can trigger winters by blocking the sun and cooling the Earth’s surface for years. The Toba supereruption 74,000 years ago disrupted food chains and reduced the human population to a few thousand.

Some renewable energy sources may weaken the resiliency of electric grids by removing outage buffers provided by coal- and natural gas-fired plants, which provide the system with more time to find a new power source if a plant goes down.

Planeterrellas create artificial auroras that mimic the atmospheric displays of light by setting up an electric field between two metal balls in a jar filled with a small amount of air.

While atoms are normally made of protons, neutrons, and electrons, exotic ones have been built with antimatter—alternate versions of normal matter that live for fractions of a second and are about a billion times as rare.

All rainbows are 'raincircles' caused by water droplets separating white sunlight into a spectrum of colors, but Earth's surface blocks the bottom half of the circle from our line of sight.

The boiling temperature of water decreases with increasing elevation because the molecules need less energy to overcome the lower atmospheric pressure associated with thinner air.

Most of the observable universe's volume consists of voids and supervoids—enormous regions of space with little to no galaxies, stars, or light.

Lesser-known phobias include turophobia, or the fear of cheese, and nomophobia, the fear of being without your cell phone.

Pure water does not conduct electricity because this flow of energy requires the movement of charged particles, and water is a neutral molecule.

'Silent' fireworks have gained more interest in recent years as a quieter celebratory option.

To reduce wrinkles in clothing, research recommends gentle wash cycles with more water and tumble drying with smaller loads and longer times.

The history of many kitchen appliances involves unexpected discoveries and applications, including wartime radar turned hamster defroster and replacing an 'ice king' with heat-stealing boxes.

The United States is one of only around two dozen countries with a fully federal system of government, in which power is divided between national and state governments.

Hookworm infection, though risky, may help fight certain autoimmune conditions by tamping down the immune system's inflammatory response.

Corals are themselves not coral reefs—the term refers to the tiny marine invertebrates that build the rigid reef.

A small portion of The Winstons' 'Amen, Brother,' an obscure '60s gospel record, is the basis for thousands of hip-hop tracks, making it one of the most sampled records ever that's informally known as 'the Amen break.'

While the first exchange-traded fund (a 'basket' of different assets that can be bought and sold on a stock exchange) in the US only launched in 1993, the global ETF market has grown to more than $10T in the short time since.

Crows are believed to have intelligence on par with a seven-year-old child and demonstrate complex behaviors, from problem-solving with tools to recognizing human faces.

Waves off the coast of Nazaré, Portugal, can reach over 100 feet and are caused by the area's deep underwater canyon geography

Children are now three times more likely to say they want to be a YouTuber when they grow up than an astronaut, with some even attending 'YouTube camps' that teach kids how to create content for the platform.

In 1963, a basement renovation in Turkey revealed a passageway to a hidden, multilevel underground city that once housed as many as 20,000 people

The syncytiotrophoblast is the outer layer of the placenta and the largest human cell, spanning an area about twice that of a king-sized bedsheet.