Short-term risk forecasts of heavy rainfall

Methodologies for risk forecasts of severe weather hardly exist on the scale of nowcasting (0-3 hours), Here we discuss short-term risk forecasts of heavy precipitation associated with local thunderstorms, We use COTREC/RainCast: a procedure to extrapolate radar images into the near future, An error density function is defined using the estimated error of location of the extrapolated radar patterns. The radar forecast is folded (''smeared'') with the density function, leading to a probability distribution of radar intensities. An algorithm to convert the radar intensities into values of precipitation intensity provides the desired probability (or risk) of heavy rainfall at any position within the considered window in space and time. We discuss, as an example, a flood event from summer 2000.