Nowcasting thunderstorms in the Alpine region using a radar based adaptive thresholding scheme

In this paper we present a new automated, radar based tool for thunderstorms nowcasting called TRT (Thunderstorms Radar Tracking). The goal of this real-time tool is the automated detection, tracking and characterization of intense convective precipitation systems. TRT uses the reflectivity data of the composite image of the Swiss radar network. The algorithm is based on an adaptive thresholding scheme, which allows the detection of convective cells at individual thresholds, depending on their development phase. In this way, thunderstorms can be tracked very early during their growing phase (cells as small as a few 2×2 km pixels) as well as in the mature stage, and trajectories are created from a sequence of radar images. The tracking is based on the method of the geographical overlapping of cells. Splits and merges are also taken into account. TRT forecasts storm movement by extrapolating the motion of individual cells up to 1 h, using the weighted cell displacement velocity. TRT is used as a nowcasting tool in a pre-operational mode at MeteoSwiss since May 2003.