Regional trends of severe convective weather from high-resolution WRF simulations

Historical trends in hazardous convective weather such as tornadoes and damaging winds have been difficult to assess with confidence due to the fact that the hazard observations are derived largely from eyewitness reports and/or damage. Such reports are convolved with the growth of population, changes in report procedure, development of education and awareness programs, etc. Thus, we explore the use of high-resolution dynamical downscaling for trend correction or reconstruction. Our basic approach involves a multi-decadal sequence of daily integrations of the Weather Research and Forecasting model in a convective-storm permitting setup, with global reanalysis data as initial and boundary conditions. Our current focus is on different quantitative measures such as storm-scale updraft rotation to discriminate between severe and non-severe thunderstorm events. The relative skill of these proxies in representing the spatial distribution of severe-thunderstorm occurrences over different geographical areas is also examined. The best representative proxy is chosen for each geographical region, and the connection of these proxies to regional dynamics is considered. Consistency in changes in storm occurrence with modes of internal climate variability is also found. Lastly, the implications of this study on identifying severe-thunderstorm trends in an anthropogenically enhanced climate are discussed.