Work and World

Why The US Has So Many Tornadoes

Hollywood loves a good tornado. Like most things Hollywood it’s all a little dramatic, but flying cows aside there is
something accurate about the setting. “I have a feeling we’re not in Kansas anymore.” You’re not. But the tornado started there,
which makes sense. Tornadoes are far more common in the US than anywhere else. For perspective all of Europe records around 300 tornadoes per year whereas the US
records well over a thousand. If we move in a bit closer, you’ll see that most of
the world’s tornadoes are happening here, in an area called Tornado Alley —
a place that’s absolutely perfect for twisters. Tornado Alley doesn’t have any
“official” boundaries but it’s typically considered this area that extends from
northern Texas through Oklahoma, Kansas, Nebraska, Colorado, and South Dakota.
Some people extend it even further east. While most states in the US have
recorded at least one tornado, this area is really a hotbed and the main reason
for that is geography. The central part of the US is unique in the fact that there’s this really large warm area of water just to the South and the wide
high range of mountains that extend a long way from north to south. Harold Brooks is the senior research scientist at the National Severe Storms
Laboratory. He used to chase tornadoes now he studies them from Norman, Oklahoma in the heart of Tornado Alley. A tornado requires a couple of special ingredients — ingredients that tornado alley is full of. First, we need a thunderstorm, which
we’re going to make right now. Sort of … To make a thunderstorm the things we need are warm moist air at low levels, cold dry air above that, and some mechanism to lift that warm moist air up. In Tornado Alley, lots of warm moist air flows into the plains from the Gulf of Mexico and cool dry air flows from over the Rocky
Mountains here in the West. Eventually a change in temperature or pressure will
arrive and lift that warm air up into the cool air forming an updraft. Once
these two meet, the moisture from the warm air begins to condense, forming clouds,
and a thunderstorm begins. Under normal conditions, rain would fall
from these clouds and cool the warm air breaking the storm, but in tornado alley
there’s a strong air current flowing from west to east known as the jet
stream. This, paired with the cool mountain air, blows the rain away keeping
the air in the updraft warm and wet, which allows the storm to intensify and
brings us the step two: getting the storm to rotate. To make that happen we need
winds moving at different speeds and directions. As you can see Tornado Alley
has that in abundance. The air coming from the Gulf moves slowly into the
plains, meanwhile the jet stream from the mountains provides a steady stream of
high fast-moving air flowing east. Because the jet stream is flowing faster
and in a different direction it causes the Gulf when below to rotate like a
spinning football. When the spinning air gets pulled into the updraft it’s tilted,
but continues to spin – causing the entire updraft to rotate. Storms like this are
known as “supercells” and they create prime conditions for tornadoes. They’re
rare but most commonly occur in … You guessed it – Tornado Alley. As the supercell grows the
spiraling updraft begins to stretch towards the ground and forcefully pulls
air into the cyclone. Air rushes in from the sides and a spinning dust cloud
forms below, which brings us to the final stage – getting the vertically spinning
air to the ground. Stage three is the friction in the tea cup. It’s like using a spoon to swirl tea leaves at the bottom of a cup. The tea leaves rush into the
center and are pulled up through the middle of the tea cyclone. In a real
tornado everything around the cyclone is sucked up – air, dirt, debris, cows …
As more and more air is pulled in tightly, pressure builds and the faster and
longer that tornado gets. It stretches closer to the ground until it eventually
meets with that dust cloud. And then, it touches down. We see most tornadoes in the central
part of the US because of the ingredients that are necessary for a
tornado come together there more often than any other place. The United States isn’t the only place that gets tornadoes. Southeastern Brazil in northeastern
Argentina have some of the same ingredients Tornado Alley does: cool
mountain air coming over the Andes, and warm moist air coming from the Amazon.
But even still, the frequency of tornadoes is scores behind the US. While
the right conditions come together sometimes the geography isn’t exactly
right. In South America the Andes aren’t as wide as the Rockies and the Amazon isn’t as good of a moisture source as the Gulf of Mexico is because it’s land. It’s sort of a Goldilocks problem And a delicate recipe. Most people will go
their entire lives without ever seeing a tornado and some would consider that
lucky. Others actively seek them out – and those that do start in Tornado Alley, where the geography is just right. Just knowing what makes a tornado isn’t enough to anticipate when and where it’ll happen, so if you want to know how
meteorologists try to predict these dangerous storms check out the
documentary tornado season on CuriosityStream. CuriosityStream is a
subscription streaming service that offers thousands of documentaries and
nonfiction titles from some of the world’s best filmmakers. You can get
unlimited access starting at $2.99 a month and because you’re a Vox fan the
first 31 days are free if you sign up at
and use the promo code Vox. CuriosityStream doesn’t affect our
editorial but their support does make videos like this one possible, so go
check them out.
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