Several rural towns suffered significant damage including Rolling Fork on the Mississippi Delta which was near obliterated.
The first issue is that tornadoes are tricky to study, partly because they are short-lived compared to other weather events like heatwaves or hurricanes.
US tornado records date back only to the 1950s and in the years before cameraphones, data largely relied on people spotting tornadoes and calling them into the National Weather Service.
Tornadoes are whirling, vertical air columns that spawn out of severe thunderstorms and travel with ferocious speed.
Thunderstorms occur when cold, dry air is pushed over warm, humid air - which scientists call atmospheric instability - to create an updraft. When winds vary in speed or direction at different altitudes — a condition known as wind shear — the updraft will start to spin.
For especially strong tornadoes, changes are needed in both wind speed and direction. In an average year, 800 tornadoes are reported in the US, according to the National Weather Service.
Less than 10 per cent of severe thunderstorms produce tornadoes, which makes drawing conclusions about climate change tricky, said Harold Brooks, a tornado scientist at the National Severe Storms Laboratory.
However scientists have observed changes taking place in the basic ingredients of a thunderstorm as the planet heats up, and extreme storms are becoming more common due to more warmer air masses in typically cooler season.
One study in 2014 from the National Severe Storms Laboratory found that in the past 50 years, clusters of tornadoes have become more common.
A separate 2018 study found that over the past four decades, America’s “Tornado Alley” appears to be shifting towards the East Coast, away from typical paths through Kansas and Oklahoma, and into states such as Kentucky, Illinois, Arkansas, Missouri.
With the Associated Press
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