© Nature



Over the past few decades tornadoes have been shifting - decreasing in Oklahoma, Texas and Kansas but spinning up more in states along the Mississippi River and farther east. But scientists aren't quite certain why.Tornado activity is increasing most in Mississippi, Arkansas, Tennessee, Louisiana, Alabama, Kentucky, Missouri, Illinois, Indiana, Wisconsin, Iowa and parts of Ohio and Michigan. There has been a slight decrease in the Great Plains, with the biggest drop in central and eastern Texas. Even with the decline, Texas still gets the most tornadoes of any state.The shift could be deadly becauseAlso more people live in vulnerable mobile homes and tornadoes are more likely to happen at night in those places.Even though Texas, Kansas and Oklahoma get many more tornadoes, the four deadliest states for tornadoes are Alabama, Missouri, Tennessee and Arkansas. More folks are generally at risk because of that eastward shift.Because tornadoes sometimes go undercounted, especially in the past and in less populous areas, scientists don't like to study trends by using counts of tornadoes. NowThe more of those three ingredients, the more likely tornadoes will form.Why is this happening?We don't know. But here's my guess: As the Great Plains dry out, there's less moisture to have the type of storms that spawn tornadoes. Tornadoes form along the "dry line" where there are more thunderstorms because there's dry air to the west and moist air from the Gulf of Mexico to the east. That dry line is moving east.