Violent storms have cut through a wide swath of the South and Midwest, spawning tornadoes and killing at least one person, knocking down power lines and trees and ripping roofs off homes. Dozens of tornado and severe thunderstorm warnings were posted in several states as violent storms hit the region Wednesday. At least one tornado emergency was issued in Arkansas. Forecasters say it is the opening act for a week of wild weather as daytime heating combines with an unstable atmosphere, strong wind shear and abundant moisture streaming in from the Gulf.