<h2 class=" eplus-wrapper" id="crosshead">Twister mystery</h2>

At first the high winds hitting Vail High School seemed like a bit of a laugh. They had caused a power cut, and the students giggled as they used their phones to light their classrooms. But then a teacher opened a door to see what was going on - and was immediately sucked out and thrown to the ground. Her pupils rushed to help her.

Luckily she was not badly hurt. But it vividly illustrated the power of the tornado that hit Los Angeles last Wednesday. With winds reaching 110 miles per hour, it damaged 17 buildings and many cars.  

But this was nothing compared to the tornado that MississippiA state in the south of the USA with a population of nearly 3 million. experienced on Friday night. One weather forecaster almost broke down as he tracked its progress on live TV. "Dear Jesus, help them," he prayed.

In the small town of Rolling Fork the tornado caused at least 26 deaths and left a scene of almost unimaginable devastation. Houses were flattened, trees shredded and lorries piled on top of wrecked buildings.

"The Family Dollar store was practically new. It's gone, and I think there was loss of life there," said local resident Jack Burkhalter. "The flower shop, beauty shop, barber, law offices just down the street are all gone."

The tornado was estimated to be a mile wide, and brought with it hail stones the size of golf balls. Tracy Hardin, the owner of a dairy business, had a narrow escape along with her husband and seven others.

"One of my cashiers came to me running and said, 'My mom is on the phone, and she said, there's a tornado,'" she remembers. "And at that moment, the lights flickered, and I just hollered, 'Cooler!'"

The cooler was a large, sturdy metal structure for storing ice cream. With all nine people inside, Hardin's husband struggled to close the door; then he looked up: "He said, 'I see the sky.' And that just let us know that the roof was gone, and this is more serious than we could have imagined."

When the tornado had passed, "The building was gone, but we stepped out through what would have been the back door, and our vehicles were totalled... what used to be two motel buildings and 35 or more trailer houses are all gone."

Relative to its size, Britain has more tornadoes than any other country - an average of 33 per year.¹ But altogether the US has the most - around 1,000 per year - and the strongest.

Tornadoes are created by thunderstorms which form when warm, humid air comes into contact with cold, dry air. The warm air rises through the cold air, resulting in a change of wind direction.

If the winds blow at very different speeds or in very different directions, a funnel forms, drawing in more warm air and eventually stretching from the ground to the clouds.

Some people believe that climate change is making tornadoes worse, but it is very hard to say for sure. Global warming means that the atmosphere can hold more moisture, increasing the likelihood of thunderstorms. But it also means that wind shears - sudden changes in wind speed and direction - are less likely.  

Yes: The most destructive tornadoes are spawned by severe thunderstorms known as supercells. Studies show that we are likely to have more of these in future because of climate change.

No: There have always been tornadoes. The most violent one on record took place in 1925, when global warming was much less extreme: it travelled 219 miles and devastated three states of the US.

Or... It is impossible to say. Because most tornadoes are very short-lived, and the keeping of detailed records began comparatively recently, it is difficult to make comparisons between past and present.

Mississippi - A state in the south of the USA with a population of nearly 3 million.