Sydney 2000 Forecast Demonstration Project: Convective storm nowcasting

Five of the nowcasting systems that were available during the Sydney 2000 Forecast Demonstration Project (FDP) were selected for evaluation. These systems, from the United States, the United Kingdom, and Australia, had the capability to nowcast the location and, with one exception, the intensity of convective storms. Six of the most significant convective storm cases from the 3-month FDP were selected for evaluating the performance of these state-of-the-art nowcasting systems, which extrapolated storms using a variety of methods, including cell and area tracking, model winds, and sounding winds. Three of the systems had the ability to forecast the initiation and growth of storms. Nowcasts for 30 and 60 min were evaluated, and it was found that even for such short time periods the skill of the extrapolation-only systems was often very low. Extrapolation techniques that allowed for differential motion performed slightly better, since high-impact storms often have motions different than surrounding storms. The ability to forecast initiation, growth, and dissipation is in its infancy. However, it was demonstrated that significant improvement in forecast accuracy was obtained for several of these cases when the locations of boundary layer convergence lines (sea breeze and gust fronts) were used in the nowcasts. Based on the experiences during the FDP, and in forecast offices in the United States, a discussion is provided of the overall status of nowcasting convective storms. In addition, proposed future directions are discussed concerning the specificity of nowcast products, experimental test beds, and additional observations and research required.