Short-term risk forecasts of severe weather

Methodologies for risk forecasts of severe weather hardly exist on the scal e of nowcasting (0-3 hours). In this contribution we discuss short-term ris k forecasts of hail by using COTREC/RainCast: a procedure to extrapolate ra dar images into the near future. An error density function is defined using the error of location of the extrapolated radar patterns. The radar foreca st is folded ("smeared") with the density function, leading to a probabilit y distribution of radar intensities. An algorithm to convert the radar data into signatures of hail provides the desired probability (or risk) of hail at any position within the considered window in space and time. This metho dology is considered to be useful for risk forecasts of floods, heavy wind and snowfall or freezing rain as well. We will discuss the design of approp riate forecast models. (C) 2000 Elsevier Science Ltd. All rights reserved.