A string of destructive tornadoes ripped through huge swaths of the country in recent weeks, with experts saying a warmer-than-usual winter across the South likely fueled what has been one of the busiest recorded starts to the tornado season.
There have been at least 478 tornado reports this year across 25 states as of Wednesday, according to the National Weather Service. Only 2017, with 503 tornado reports, and 2008, with 523, had more at this point in the year.
Pinning down how tornado activity will change in a warming world — if at all — is an active area of research, and more data is needed. But a picture is emerging of how risks are changing across parts of the country, particularly in areas where social factors compound vulnerabilities to extreme weather.
This year’s active start can be blamed, at least in part, on the mild winter conditions experienced across much of the country, said Harold Brooks, a senior research scientist at the National Oceanic and Atmospheric Administration’s National Severe Storms Laboratory.
Warmer-than-usual winters create the type of atmospheric instability in early spring that is a key ingredient for severe storms, including those that spin up tornadoes.
“If you don’t get the cold fronts across the Gulf, all you need is a little bit of wind to bring in a lot of warm, moist air,” Brooks said. “And this has been a year where cold fronts really haven’t gotten that far south. The southern part of the U.S. was not particularly cold this winter.”
This dynamic is why tornadoes in the South occur more commonly in the cooler months, from late fall through winter and into early spring. It’s also why this part of the country may become more vulnerable as the world warms.
A study published last week in the Bulletin of the American Meteorological Society found that supercell storms, which can produce violent tornadoes, will increase as the world warms. These storms are also projected to hit Southern states like Alabama, Mississippi and Tennessee more frequently in the future, according to the research.