Tornado Alley is undergoing a transformation.
The number of days that damaging tornadoes occur has fallen sharply over the past 40 years, a study published recently in the journal Science shows. But the number of days on which large outbreaks occur has climbed dramatically.
“It’s really pretty shocking,” said Greg Carbin, warning coordination meteorologist with the Storm Prediction Center in Norman, Okla.
In the early 1970s, there was an average of 150 days each year with at least one F1 tornado. That number has dropped to about 100 days each year now.
There were just six days in all of the 1970s with at least 30 F1 tornadoes. But that number has jumped to three a year now.
“The areas that will support a tornado – we get fewer of those areas than we used to,” said Harold Brooks, a researcher with the National Severe Storms Laboratory in Norman who co-authored the study with Carbin.
This year is following that trend, Carbin said. There have been 66 days with EF1 tornadoes and two days with 30 or more EF1 tornadoes: April 28 and June 30.
The April 28 outbreak came from the same storm system responsible for an EF2 tornado that tore through the center of Baxter Springs in southeast Kansas late the day before. The tornado injured 34 people and damaged more than 100 homes and businesses in the Cherokee County town of 4,200 residents.
For the year, preliminary data from the Storm Prediction Center indicates there have been 1,017 tornadoes reported around the country, the second-fewest since 2005 and 25 percent below the average of the past 10 years.
Despite seeing fewer tornado days, researchers say, the average number of tornadoes each year has remained about the same – though three relatively quiet years have followed the record-breaking 2011.
“Somehow the atmospheric pattern has changed,” Brooks said.
The cause of that change is not clear, he said. There is considerable discussion about whether the melting of ice in the Arctic has influenced the jet stream, changing the waves the jet stream rides as it crosses North America.
The size and intensity of those waves are apparently different than they were 40 years ago, Brooks said. Those changes affect when, where and how often the ingredients needed to produce tornadoes come together.
“The physical cause of that change is controversial,” he said. “Most people in the field accept that there has been a change, but not everyone is convinced there is a connection to the melting of the Arctic.”
The shift in tornado patterns is more than an academic debate among weather researchers, Brooks said: It could have significant effects for insurers and emergency managers around Tornado Alley and the Deep South.
“It may change the way they have to handle their resources,” Brooks said. “They have to have resources to handle the big day.
“Responding to a 30-tornado outbreak is a whole lot different than if it’s 30 days with one tornado.”
Emergency management officials in Kansas say they are well-prepared in the event of a massive outbreak striking the Sunflower State.
“We have been planning for multiple events for many years, and not only planning, but actually responding to multiple events that have happened in Kansas,” Sharon Watson, spokeswoman for the Kansas Division of Emergency Management, said in an e-mail response to questions.
“We’ve had to respond to tornadoes and blizzards at the same time, tornadoes and floods, and tornadoes and wildfires at the same time.”
On the same day that Greensburg was obliterated by an EF5 tornado on May 4, 2007, she said, northeast Kansas was dealing with major flooding.
Several times in recent years, training exercises have featured scenarios involving multiple disasters, Watson said. A large-scale field exercise in August called Vigilant Guard involved a scenario in which tornadoes hit several cities, including Emporia, Manhattan and Salina.
Along with the damage from multiple tornadoes, participants had to deal with chemical spills and fires. The exercise tested how quickly requests for additional resources from other states and the federal government were made, Watson said.
On a local level, Sedgwick County Emergency Management director Randy Duncan said mutual aid agreements in place should help officials receive whatever assistance they need should several tornadoes strike in the same region.
“My first hope is we don’t ever see anything like that happen in our area,” Duncan said. “I’m also a realist. When that event does happen, we’ll be ready to ask for that level of support.”