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.

Severe thunderstorm and tornado warnings in Europe

“…The SPC provides forecasts of severe weather for the 48 continental United States (excluding Alaska and Hawaii). The history of the SPC is described in Galway (1989), Ostby (1992Ostby ( , 1999, Corfidi (1999) and Doswell (2007). In producing an outlook, forecasters primarily use guidance from numerical weather prediction models, looking for evidence of environments favourable for severe weather.…”

Tornadoes in Germany 1950–2003 and their relation to particular weather conditions

“…Due to the development in meteorological research, computer and other technical facilities, and more than 50-yr experience in severe storm forecasting, a number of observational tools (e.g. Doppler radar) and model output parameters are available today for operational nowcasting and short-range prediction (Ostby, 1999). This is not the case for long-range and climate forecasts.…”

Articles

“…First issued by the Severe Local Storms Unit [SELS, now the Storm Prediction Center (SPC)] in 17 March 1952 (Galway 1975), the tornado watch is a manually generated product, based upon NWP output and observations, and may be issued up to several hours in advance of initial convective initiation. The skill level of the tornado watch has continued to improve over the years with increased observations, refined conceptual models, and more accurate and higher-resolution NWP (Pearson and Weiss 1979;Ostby 1999). Two additional, increasingly popular products issued by the SPC are the convective outlooks and mesoscale convective discussions (MCDs; Stough et al 2012).…”