Tornadoes

One of Earth’s most recognizable natural forms is the funnel of a tornado.

The tornado’s form is the mountain silhouette of meteorology, inspiring simultaneous awe and terror. Their sinewy, gorgeous stovepipes demand our attention while filling us with fearful dashes of the unknown.

Also called twisters, whirlwinds, or cyclones, tornadoes are revolving columns of air in contact with the ground and a cloud.

A classic tornado, like the one in the image above, features a condensation funnel and connects to either a cumulonimbus cloud or a cumulus cloud. Other types exist, namely waterspouts and landspouts, whose creation mechanisms and cloud connections differ from the conventional tornado.

The traditional version forms from a special kind of thunderstorm, called a supercell. These extreme, rare storms rotate in the sky, thanks to an engine called a mesocyclone.

Supercells form thanks to wind shear.

Wind can move in different directions and speeds at varying heights. The effect can be seen when airplanes attempt to land during adverse conditions.

Sometimes, the differing directions or speeds can cause a horizontal tube of rotating air.

This tube is ingredient one in the tornadic recipe, but twisters, of course, are not made of horizontally spinning air.

Supercells also require an updraft. During the day, the Sun heats the ground, which warms the air around it. Warm air rises. When these uplifting columns meet a horizontally spinning tube of air, the clouds begin to spin, and the creation of a mesocyclone is complete.

After the updrafts have worked to make supercells into miniature, terrestrial versions of hurricanes, the vertical spinning factors necessary for a tornado are in place.

However, not all supercells produce tornadoes. In fact, under 30% of these monster forms spawn the troublesome whirlwinds. Most supercells throw intense loads of rain, hail, lightning, and wind, even if they don’t birth a tornado, making them extremely dangerous when they appear.

One more element must occur for the creation of a twister. If the supercell begets downdrafts – cold air sinking – these columns can pull the bottom of the swirling cauldron with them. When the bottom starts to sink, it might resemble a wall or even a proto-funnel; we call these formations wall clouds and funnel clouds. Neither of these shapes means a tornado is inescapable, but they are a good sign that conditions are ripe for one.

If the downdrafts pull the maelstrom to the ground, a tornado is officially born.

The average tornado is frightening, though they might seem tame compared to the gargantuan ones.

Most are about 250 feet across, have winds under 110 miles per hour, and dissipate after traveling a few miles. Considering these statistics relatively tame might seem crazy: imagine a revolving mass nearly the width of an American football field coming at you with hurricane-force winds, and it doesn’t stop for a few miles.

Yet the true tornadic denizens do make these figures seem tiny.

The highest wind speed ever recorded on Earth came from a tornado in 1999 that ravaged parts of Oklahoma: 301 miles per hour. The largest tornadoes have spanned 2.6 miles in diameter. The Tri-State tornado of 1925 remained continuously on the ground for 219 miles, across Missouri, Illinois, and Indiana. If those details weren’t bad enough, they can move in forward lines at speeds of 75 miles per hour!

Though the prototypical tornado looks like the image above, they can take many forms. The common conception of a twister, long and tight, is called a stovepipe tornado, but many of the most destructive versions are wedges, a much broader form.

Even the colors of tornadoes can vary. If the Sun is behind a viewer, the funnel might appear bright; if the tornado is back-lit, it might present as extremely dark. Depending on the area, the clouds can take odd colors. If a tornado hits water, it can become whitish-grey or blue; in certain areas with redder soils, the funnels can become ruby; tornadoes on snowy climes can look cleanly white. Even worse is the “invisible” tornado. Not all twisters develop a condensation funnel. Sometimes, the swirling winds from a supercell reach the ground without the telltale sign of a funnel, making them extremely difficult to spot as they approach. Other times, the condensation funnel is much smaller than the sphere of twisting winds, again complicating spotting.

Tornadoes are famous for their acoustics. Those in the path have often described roars that sound like freight trains, jet engines, or massive waterfalls.

Funnel clouds can also produce sound, which is sometimes reported to be akin to whistling, humming, whining, or swarms of bees.

The United States experiences the most tornadoes of any nation, thanks to unique geographical elements. The Rockies, which run north and south, form a massive atmospheric barrier. The air that crosses the mountains tends to be cold and dry. In the south, warm, moist air streams northward from the Gulf of Mexico. When the two meet, instability flourishes, producing a breeding ground for supercells.

This area of the U.S. Midwest is known as Tornado Alley.

Various definitions of this region exist. Some models restrict it to the middle of the nation, while others extend the reach into the Great Lakes areas. Some meteorologists believe Tornado Alley is slowly moving eastward and southward as the climate changes, sometimes even including the Deep South states.

Each year, approximately 1,200 tornadoes touch down in the United States. By contrast, only around 100 hit Canada next door.

Though the United States dominates in tornado volume, they are far from the only affected nation.

The Netherlands and the United Kingdom have the highest number of tornadoes per unit area. Despite the large number of strong tornadoes in the United States, many parts of Tornado Alley are sparsely populated, leading to lower deaths than the storms might merit. Bangladesh suffers from the opposite problem. This densely populated nation leads the globe in tornado deaths: 179 per year on average.

As technology improves, our ability to predict and detect tornadoes has improved greatly. Today, weather radars can spot rotation and morphologies (e.g., hook echoes, notches, debris fields) often before a person can visually identify a tornado, allowing authorities and media to disseminate life-saving information.

A few myths about tornado safety persist. Inside strong tornadoes, pressure drops massively, prompting the age-old advice to open a house’s windows during the event to prevent them from breaking. The pressure drop is not strong enough to shatter windows; most damage from tornadoes occurs due to debris thrown at high speeds. Taking shelter in an underpass on a highway is another common notion, but this idea is more dangerous than lying in a nearby ditch. Thanks to a phenomenon known as the Venturi effect, wind speeds in confined spaces actually accelerate. One partially correct attribute relates to sky color. Folk knowledge touts that green skies can presage a tornado. While green skies are associated with severe thunderstorms, they do not necessarily mean a tornado will occur.

If you’re ever caught in an oncoming twister, getting to shelter is paramount. Basements are ideal, but the lowest, most central area in a building is the best place to be, perhaps under a stairwell. If you’re caught in the open, getting as low as possible is your best bet. Debris is the worst enemy in a tornado. Anything you can do to keep yourself from being struck will help your odds of survival.

And, no, attaching yourself to a piece of pipe with a belt, as in the 1996 film Twister, in an attempt to survive a behemoth tornado will not work. Even if the strap keeps you from flying off, the debris will certainly make life tough.

These marvels of Earth are mesmerizing. It’s hard to square watching something incredible in the distance, knowing it might be deadly. Nature often packages resplendence and menace together. The tornado is a swirling harbinger of beauty and lethality.