Tornadoes Are Coming in Bunches. Scientists Are Trying To Figure Out Why.

The number of tornadoes so far in the United States this year is just above average. But their distribution is changing. From a report: Tornadoes tend to travel in packs these days, often with a dozen or more forming in the same region on the same day. On the worst days, hundreds can form at once. More than a dozen tornadoes were reported on both Monday and Tuesday this week across the Great Plains and the Midwest, according to the Storm Prediction Center run by the National Oceanic and Atmospheric Administration. Two weeks ago, on the most active day in April, 105 tornadoes were reported. While outbreaks like these have always happened, they have become more common in recent decades. The total number of tornadoes in the United States each year has stayed relatively consistent over the last several decades, but they now happen in more concentrated bursts over fewer days during the year. In the 1950s through the 1970s, on average about 69 percent of tornadoes in the United States happened on days with fewer than 10 tornadoes, and about 11 percent happened on days with 20 or more tornadoes. These percentages have shifted significantly in recent decades, according to a 2019 study. The researchers found that since 2000, on average only about 49 percent of tornadoes have happened on less busy days and about 29 percent have happened on days with 20 or more tornadoes. "Now when tornadoes happen, they often happen in an outbreak environment," said Tyler Fricker, an assistant professor of geography at the University of Louisiana Monroe and one of the authors of the study. While the timing of this trend lines up with the planet's rising temperatures, scientists are hesitant to definitively attribute tornadoes' clustering behavior to human-caused climate change.

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