the United States are experiencing the devastation attributable to tornadoes. At least five people died Wednesday as a tornado swept through southeastern Missouri. It happened six in New Jersey and one in Delaware, which killed an individual and have become the widest state in history. Tornado batches killed greater than 30 people within the South and Midwest over the weekend. And January saw 168 initial tornado reports, nearly five times the month’s average from 1990 to 2010.
It was a busy and deadly begin to tornado season, with the tornado hitting regions which can be often spared. We know that a warming climate causes moisture and air instability, two aspects that spur tornado formation. But experts warn it’s too early to link one major event – or perhaps a season – to climate change. What they see are changes in when and where the tornado strikes, which could put more people in danger.
“We’re still unsure what the long run holds,” says Jana Houser, professor of meteorology at Ohio State University. Meteorologists can take a look at increased humidity and warming, in addition to changes within the jet stream, and see how these can affect storms that produce tornadoes. But, says Houser, “we actually cannot say exactly what we expect to see when and where tornadoes will occur.”
Most tornadoes are formed by unusual supercell thunderstorms. In order for tornadoes to form, they need moist, warm air near the bottom. But additionally they need strong, vertical wind shear, which is attributable to a change in wind direction and speed between the bottom and better elevations. The air begins to swirl horizontally in the form of a cylinder. As it rises and gains speed, it narrows and forms a menacing funnel we recognize as a tornado.
To understand how tornado patterns can change, meteorologists take a look at trends of their parent supercell storms. More heat within the atmosphere results in more moisture and more instability. However, wind shear, the opposite component of a tornado, may decrease over time with climate change. The jet stream may weaken as temperature differences between Arctic and mid-latitude air decrease, affecting wind shear. The final result of those changes mixing within the atmosphere isn’t clear.
“We’re in the course of an experiment,” says Walker Ashley, a professor of meteorology at Northern Illinois University who recently wrote a paper paper concerning the changing patterns of tornadoes. “When we take a look at the essential ingredients that make up a robust storm, now we have changes. The query is how much and on what scale?”
Experts say supercell storms will hit the United States more continuously within the late winter and early spring, and grow to be less frequent within the late summer and fall. The territory of the tornado also changes. Tornado Alley, a strip of land that features parts of Texas, Louisiana, Oklahoma, Kansas, South Dakota, Iowa and Nebraska, has long been a breeding ground for twisters. But drought conditions result in fewer storms, says Robert Trapp, professor and chair of the Department of Atmospheric Sciences on the University of Illinois at Urbana-Champaign.
