A more than 1,000-mile stretch across parts of the Plains and the Midwest is at risk of severe thunderstorms as moisture from Hurricane Simon, which is churning off the coast of western Mexico, is being funneled north and will enhance storms Tuesday from Texas to Illinois. In addition to damaging wind gusts, large hail and a low-end tornado risk on Tuesday, these tropically-enhanced storms will also dump heavy rain across the region for most of the workweek, fueling a flash flood threat that will last at least through Thursday.