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Jessi: The weather is a funny thing. One day it can be sunny and warm, perfect day for sunglasses and flip-flops the next day it can be cold and rainy. Most of the time the weather doesn't give us anything that we can't handle with maybe some sunscreen or an umbrella or a snow shovel, but sometimes and in some places there can be extreme weather, like big thunderstorms or hurricanes or snowstorms.

And one of the most powerful kinds of extreme weather out there is a type of a storm that scientists pay close attention to: tornadoes. A tornado is a fast-spinning column of air that stretches all the way from a thunderstorm cloud in the sky down to the Earth's surface. Because tornadoes turn and twist as they move, they're sometimes called twisters.

They form inside really big thunderstorms when cold, dry air moving from one direction bumps into warm, wet air coming from a different direction. Because the cold air is heavier, it slides down under the warm air and pushes it up really fast. All this fast-moving air rushing up and down can create a sort of spinning thunderstorm, and it can eventually keep going to form a tornado.

And when a tornado forms, it can be one of the most powerful forces in nature. Tornado winds are the strongest in the world, even stronger than hurricanes. In some twisters, we know that the wind can blow to almost 500 kilometers and hour, strong enough to lift heavy things like cars and trucks into the air.

And they're loud too. People who have seen them or even been in them say they sound like giant roaring trains, but they don't move as fast as a speeding train. Usually tornadoes travel across the land at about 50 kilometers an hour, slower than most cars go.

Now, weather can be really unpredictable, which means that you just can't predict or know what's going to happen before it happens, and that's especially true for tornadoes. These windy storms can speed up, slow down, change direction or even stand still and they can last anywhere from a few seconds to as long as an hour.

While tornadoes can happen all over the world, they're most common in the United States. About 2/3 of all the tornadoes in the world happen right down the middle of the country, from the Dakotas down to Texas, especially in the last Spring and early Summer.

Because tornadoes are so powerful and so unpredictable, meteorologists spend a lot of time studying them. They want to stand more about exactly how and when tornadoes can form, and hopefully predict when they'll show up.

There are even people called storm chasers who follow big storms around the middle of the US hoping to spot one as it turns into a tornado, so we can get a better picture of what really happens when a twister forms.

Scientists still don't know for sure when a tornado is going to happen, but they have gotten better at predicting which thunderstorms might be strong enough to create one, and if they spot a bad looking storm early enough, then they can give people who live nearby a warning that a twister might be coming.

That's one of the most important jobs that a meteorologist has: helping people get ready for extreme weather. So the more they learn about tornadoes, the better we can prepare for them and the more they can help us understand how our weather works, even when it's not so extreme.

I hope the weather is nice where you are, and if you have any questions for any of us here at the fort about weather, animals, space, or anything, just let us know by leaving a comment or emailing us at kids@thescishow.com. Thanks for joining us and see you next time.

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