 When this happens, catastrophic flooding is possible.In Rapid City, South Dakota, in 1972, an unusual alignment of winds at various levels of the atmosphere combined to produce a continuously training set of cells that dropped an enormous quantity of rain upon the same area, resulting in devastating flash flooding.A similar event occurred in Boscastle, England, on 16 August 2004, and over Chennai on 1 December 2015 

Each year, many people are killed or seriously injured by severe thunderstorms despite the advance warning.