Much of that is because the season is starting earlier, and tornado alley is expanding due to a warmer climate. Tornadoes need four ingredients to form, explained Ashley: moisture, instability (which provides the energy necessary for the storms), wind shear and lift. When a powerful F-4 tornado plowed through Rolling Fork, Mississippi, in March, residents were largely unprepared. The only one that I can remember is 1971, and the tornado bypassed Rolling Fork. That's precisely why the widening of tornado alley is fast becoming a new focus for insurers.

---

Persons: Walker Scott Ashley, Ashley, Eldridge Walker, Walker, That's, John Dickson, Dickson, Eric Andersen, Aon Organizations: Climate Central, Northern Illinois University, Tornadoes, Global, U.S ., Farm, Allstate Locations: U.S, Northeast Texas, Oklahoma, Arkansas, Fork , Mississippi, Rolling, Kansas, Mississippi, Aon, California