Dear Alice,
Have you ever felt a warm wind blow by you, followed by a cold gust of air? You can’t see it, but you can sense it on your skin. Invisible to you, winds mix together.
Usually, these winds are harmless. But under the right conditions, they can also be the main ingredients for a tornado.
To learn more, I chatted with Jon Contezac, Craig Oswald, and Joe Zagrodnik, a team of Washington State University scientists who are very curious about the weather.
To make a tornado, they explained, you need two big things: rising air and rotating air.
“When you have the right amount of both, a storm is more likely to produce a tornado,” Zagrodnik said. “That’s no guarantee—you’re just more likely to have a tornado under those conditions.”
A special storm called a “supercell” often has those ingredients. Supercells form as a rotating mass, with air rising quickly within.
Different temperature winds can cause rising and rotation. Warm air rises, but cool air sinks. Warm air trapped near the surface can rise fast if there’s much cooler wind above it. When these winds cross paths from different directions, they may spin skyward.
Rising, rotating air can form a funnel cloud: the first visible sign of a potential tornado. Funnel clouds look like an ice cream cone pulling down from the sky. They’re usually dark gray, made of condensed water like other clouds.
Tornadoes get their color from moisture, plus things picked up along the way. “It’s like a cloud at some point,” Oswald explained. “If it reaches the ground and starts to stir up dirt, it will lift that dirt up into the funnel and turn it dark.”
If a funnel cloud’s rotation touches the ground, it becomes a tornado. But many funnel clouds never do. Their rotation fades, and they disappear without causing damage.
Tornadoes aren’t the only weather patterns to form from twirling wind. Where I live in Washington, I sometimes see dust devils: spirals of swirling dirt. But they’re different from tornadoes.
“Tornadoes’ rotation comes from the cloud and goes down to the surface,” Contezac said. “But dust devils have pockets of intense hot air at the surface, and air spins rapidly around those pockets. They’re generated from the surface upward.”
Not all rotating storms cause tornadoes. But it’s important to know how to stay safe if a tornado happens near you. A watch means the ingredients to produce a tornado exist. A warning means a tornado has actually been created.
During a tornado watch, you should be on the lookout for storms in your area. A tornado warning is when you should go to a safe location, like a basement or bathroom. Talk to grown-ups you live with about where to go.
Although scientists know tornadoes’ general recipe, they still hold a lot of mystery. We’re still trying to learn why some storms make tornadoes and others don’t. Maybe someday you can help uncover the answer.
Sincerely,
Dr. Universe