The team believes that the reduction in tornado activity boils down to how the diminishing Arctic sea ice controls the path of the jet stream. As Arctic sea ice retreats, the jet stream migrates from its traditional summer path over states like Montana and South Dakota to areas farther north, and the atmospheric conditions that are favorable for tornado formation follow suit.
"Tornadoes and their parent thunderstorms are fueled by wind shear and moisture," Trapp said. "When the jet stream migrates north, it takes the wind shear along for the ride, but not always the moisture. So, even though thunderstorms may still develop, they tend not to generate tornadoes because one of the essential ingredients for tornado formation is now missing."
https://www.sciencedaily.com/releases/2018/08/180806104253.htmhttps://news.illinois.edu/view/6367/679821DOI: 10.1038/s41612-018-0025-9
