The Tameside tornado: What is a 'supercell thunderstorm' and how common are they in the UK?

The tornado which damaged around 100 homes as it ripped through Tameside on Wednesday night was the strongest in the UK in almost 20 years. But while the destructive phenomenon might be more commonly associated with the the wide open plains of the USA, it's surprisingly frequent in this country too.

About 30 tornadoes a year are reported here, according to the Met Office, but they tend to be small, less violent and short-lived. In fact research by the University of Manchester found the UK experienced a higher density of tornados per 10,000 square kilometres than the US.

"The numbers are higher for American states in 'Tornado Alley' such as Oklahoma or Kansas," David Schultz, a professor of synoptic meteorology wrote earlier this year. "Nonetheless, a random location in the UK is more likely to experience a tornado than a random location in the US."

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So why was the Tameside tornado so destructive? It was the result of a thunderstorm known as a 'supercell', which causes some of the most extreme weather on the planet.

It's rare, but given the right environmental conditions supercells - rotating thunderstorms often tens of kilometres across – can form here in the UK. According to the Met Office website tornadoes occur when the updraft - a current of air that pulls moisture in from the surrounding area - begins to twist around 'in the same sense as the rotation of a merry-go-round'.

"Eventually the rotation may become so strongly focused that a narrow column of violently rotating air