Environmental Discriminators for Significant Tornadoes and Hail in the Midwestern United States

Identifying regional environmental characteristics which are associated with severe weather can help operational meteorologists improve forecast and warning issuance accuracy. Previous work (Rasmussen and Blanchard 1998, Thompson et al 2003, Craven and Brooks 2004) has identified statistically significant ingredients associated with severe thunderstorms, but has not offered a multi-year climatology of pre-convective environmental discriminators for a specific geographic region. For this study, data from 0Z, 12Z and special upper air soundings originating from 18 different locations in a geographic domain representing the Midwestern United States were collected from 1999 - 2017. Severe hail (1-2” in diameter), significant severe hail (greater than 2” in diameter), tornado (EF0-EF1), and significant tornado (EF2 or greater) reports gathered by local NWS offices were then examined to see if they occurred within 150 km and +/- 3 hours of the radiosonde launch. For the soundings which have at least one of these severe reports occurring in this spatial and temporal domain, 16 different atmospheric parameters (which are measured by the radiosonde data and are significant to the development of severe thunderstorms) are quantitatively examined. A multinomial logistical regression test was then run on the dataset to examine the possibility of statistically significant atmospheric parameters. Preliminary results have indicated that 850mb Wind Speed and 0-0.5km Storm Relative Helicity are discriminators of tornado and significant tornado occurrence, while Convective Available Potential Energy and 700-500 mb Lapse Rate are discriminators of severe hail and significant severe hail occurrence.