By Randy Mertens, University of Missouri
Tornado Alley will probably see slightly fewer tornadoes this storm season, while areas to its east will see a more than average number of tornadoes, says a climate expert at the University of Missouri.
Tony Lupo, professor and chair of atmospheric science at the College of Agriculture, Food and Natural Resources, said that higher sea temperatures in the central Pacific Ocean will shift the jet stream pattern eastward over Tennessee, Kentucky, eastern Missouri, Illinois and Indiana.
The jet stream will funnel more moisture and instability over these areas, creating ingredients for strong thunderstorms that spawn tornadoes.
Typically during storm season – March through June – the jet stream passes over Tornado Alley, a swath of the Great Plains states from Texas and Oklahoma into Kansas and Nebraska.
The increase in Pacific Ocean temperatures is causing a trend away from a La Niña weather pattern and toward what climatologists call a neutral weather pattern.
For the past few years, these sea temperatures have been 3–5 degrees Celsius lower than normal, creating a La Niña weather pattern that sends the jet stream and its accompanying storms more northward than average. The La Niña was a contributor to the Midwestern drought.
Because of the comparative weakness of this neutral pattern, Lupo does not expect the upcoming storm season to be more severe or longer than average. He said the storm season is getting a later start than usual as the shift from a La Niña pattern to a neutral pattern in early 2013 prolonged winter conditions over much of the Midwest.
"This doesn’t mean that we won’t see strong and destructive storms in the traditional Tornado Alley," Lupo said. "There will be statistically fewer of them this year."
Average number of tornadoes each year by state, 1991-2010. Credit: National Oceanic and Atmospheric Administration