A wide swath of the Midwest and Plains states is under a tornado watch and severe weather conditions are forecast to persist into next week, the National Weather service said Thursday. Organizers delayed the start of a concert by the pop star Beyonce as threatening weather loomed over Soldier Field in Chicago,

A busy stretch of severe thunderstorms is underway due to record heat and now the threats are ramping up, putting major metro areas from Chicago to Nashville under threat as the country hits the peak of tornado season.

Cities like Chicago, Minneapolis and Milwaukee are at risk for a severe weather outbreak on May 15, forecasters said.