Thunderstorm Strike Probability Nowcasting, a New Algorithm

Thunderstorm nowcasting is an important function for the severe weather forecaster. The usual method is for radar to detect thunderstorms, and for downstream systems to generate ’threat areas’ for issuing warnings. However, these threat areas are difficult for other systems to work with as they are not mathematically well defined. In this paper we develop an algorithm, THESPA (THunderstorm Environment Strike Probability Algorithm), to translate a radar thunderstorm detection into a ’strike probability’, a new concept for thunderstorm nowcasting. This represents the probability a given point will be affected by a thunderstorm in a given period. Being well defined, this can be combined with other strike probabilities or can be utilized by other systems or forecasters to produce a more valuable warning product. The paper includes studies that justify assumptions made about the statistics of thunderstorm motion, and results demonstrating how effective the algorithm is at thunderstorm nowcasting.