“An Assessment of Thunderstorm Probability Forecasting Skill” Revisited: Progress from 1983–1993 to 2009–2022

Abstract A probabilistic thunderstorm forecast contest has been hosted by the Department of Atmospheric and Environmental Sciences at the University at Albany since 1979. The contest involves issuing forecasts of the 24-h probability of thunder at 10 locations in the contiguous United States during the summer. A previous study by Bosart and Landin in 1994 used consensus forecasts from this contest to assess probabilistic thunder forecast skill during the 1983–93 period. Given the research advances and improvements in observation and modeling systems that have occurred since 1993, a renewed analysis of thunderstorm forecast skill in the contest is warranted. This study revisits the conclusions of the previous study and provides an updated assessment of the state of human and model thunderstorm forecast skill for the period from 2009 to 2022. Through the lens of this contest, probabilistic thunderstorm forecast skill has increased substantially in the past two decades. The 14-yr average skill from 2009 to 2022 was 34.2% (standard deviation of 5.7%) relative to climatology, an increase from 21.8% during the 1983–93 period. This increase in forecast skill is found to largely be a result of improved forecast confidence with continued forecast reliability. In the 2009–22 period, contest participants tended to forecast at the extreme ends of the probability distribution more often than in 1983–93, evidence of greater forecast confidence due to improved nowcasting and short-term forecasting tools. Significance Statement The purpose of this study is to examine how the ability of forecasters to predict the probability of thunderstorms has improved over time. To examine thunderstorm forecast skill, we analyze entries in a thunderstorm forecast contest. Our results demonstrate that probabilistic thunderstorm forecast skill has improved greatly in the past few decades. This skill increase occurred as forecasters have become more confident in issuing forecasts of either very high or very low thunder probabilities, although participants continue to overforecast the probability of thunder at low probabilities and underforecast the probability of thunder at high probabilities. These results demonstrate that research advances and improvements in technology are resulting in more skillful forecasts of hazardous weather such as thunderstorms.