More than 500 twisters reportedly touched down across the country last month.
The United States experienced a record-breaking rash of tornadoes in May, with hundreds of twisters reported from coast to coast.
It was the third-highest month of reported tornado activity since 2000. Eyewitnesses reported more than 530 of the violent storms to the National Oceanic and Atmospheric Administration’s Storm Prediction Center in May alone. The only other months with more reports were in April 2011 and May 2003.
Last month also saw a historic tornado streak, with eight twisters each consecutive day from May 17-29, according to NOAA data. The last biggest streak occurred in 1980 with 11 consecutive days.
In general, tornadoes are rare. Between 1,500 and 2,000 are recorded globally each year, with 90 percent occurring in the United States.
Because of this, there isn’t enough data to attribute the influx of storms to climate change or other causes, experts said, but they have worked to identify some patterns within the existing numbers.
For example, the United States now experiences fewer days of tornado activity than in previous years. But when those days come, they bring with them a greater number of the violent storms.
“We’re having more outbreaks when they do occur,” said Patrick Marsh, warning coordination meteorologist for NOAA’s National Weather Service Storm Prediction Center.
Experts are also seeing a change in the locations of tornadoes.
“There is a spatial shift that’s happening,” Marsh said. “We’re seeing a decrease in Southwest Oklahoma and Texas and an increase in Kentucky, western Tennessee and northeast Arkansas.”
Though May traditionally experiences a large number of twisters, the frequency of this year’s activity was much higher compared tornado seasons of the past.
“There are four ingredients you need for tornadoes: moisture, instability, lift and wind shear,” Marsh said. “We’ve had all four of these ingredients that we need for severe thunderstorms and tornadoes over the central United States.”
In May 2018, eyewitnesses reported 166 tornadoes to the NOAA. The May before that, they reported 295.
The NOAA must confirm all reports before issuing the final count. Once it does, the difference between preliminary and confirmed counts can vary.
“A lot of it has to do with how the tornadoes occur,” Marsh said. “Really long tornadoes are more likely to be counted multiple times. In the heat of the moment we don’t know if that’s the same tornado or separate tornadoes.”
Texas bore the brunt of last month’s tornado activity with at least 107 reported twisters. Kansas and Oklahoma saw the next highest counts with 81 and 63, respectively, followed by Missouri, Ohio, Nebraska and Iowa.
All seven of those states are located in “Tornado Alley” — a region known for having a disproportionately high frequency of tornadoes.
Some of the storms have been fatal. Out of the 38 tornado-related deaths reported this year, seven occurred last month.
Three fatalities were reported in Barton County, Missouri and one in Adair County, Iowa as a result of tornadoes on the evening of May 22. Two were reported in El Reno, Oklahoma on May 25.
At least eight tornadoes barrelled through Ohio beginning late Memorial Day and continuing into Tuesday. One person was killed in Mercer County, Ohio.
The number of tornadoes is expected to decrease in June, which typically sees an average of 210 twisters, based on eight years of data. That’s compared to May’s average of 275.
Beth Burger and Ben Deeter of the Columbus Dispatch contributed to this report.