Improved Accuracy in Severe Storm Forecasting by the Severe Local Storms Unit during the Last 25 Years: Then versus Now

Abstract

The purpose of this paper is to review the large strides made in tornado and severe thunderstorm forecasting by the Severe Local Storms Unit (SELS) of the National Severe Storms Forecast Center during the last 25 years or so of its existence. The author compares and illustrates the tools available to the SELS forecasters in the early 1970s versus those of the 1990s. Also discussed is the transition over the years from a largely empirical forecast approach to an approach based strongly on physical reasoning. The evolution of the computer systems employed at SELS and their impact on the forecast operation are traced. With the advent of interactive computer processing capability, SELS forecasters were able to assess the potential for severe convection with much greater precision than ever before. Noteworthy was the improvement brought about by the automation of largely clerical tasks, allowing the forecasters more time to focus on the forecast problem at hand. In addition, the forecast staff was able to devote more time to relevant research projects and benefit from the significant advances taking place in improved understanding of mesoscale processes. Verification results are shown to validate the notion that these advances led to better predictions. For example, the watch accuracy in terms of percent of severe weather watches verified rose from 63% in 1975 to 90% in 1996. Finally, information is given showing important milestones in the history of SELS and a list of the lead forecasters whose experience, judgment, and forecast skill brought about these improvements.