"Why does the U.S. get so many more tornadoes than other countries?" — David

The U.S. gets way more tornadoes than anywhere else on Earth. We average around 1,000 a year, while second place, Canada, gets only about 100 a year. It all comes down to America’s unique geography and contrasting air masses.

Severe thunderstorms that spawn tornadoes need several ingredients.

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First, you need warm and humid air. Because the nearby Gulf is a massive moisture source, it’s easy to get muggy air to flow north into the central and eastern U.S.

But you also need drier, cooler air to flow over that warm, muggy air to generate thunderstorms, what meteorologists call instability.

The western U.S. is a prime source of that drier air.

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Then you often get cooler air plunging out of Canada. This sharp temperature contrast produces a strong jet stream, the ribbon of high winds you typically find about 30,000 feet above the ground.

Winds change quickly from the ground to jet stream level, what is called wind shear. This higher wind shear provides the rotation needed for severe thunderstorms.

A recent study also found it’s the flow of humid air from flat terrain — the Gulf in the case of the U.S. — that's also a prime ingredient for more tornadoes in the U.S.

So it’s the Gulf, mountains in the West and cooler air in Canada that all make America the most tornado-prone country in the world.