A Climatology of High Shear-Low CAPE Tornadic Events in the Ohio Valley

This presentation investigates the short-term climatology of High Shear-Low CAPE (HSLC) tornadoes in the Ohio Valley from 2003-2021. While traditional tornadoes occur in warm-season environments of high instability, HSLC tornadoes take place during the cool season and are more wind-shear driven. Specifically, this study quantifies the spatio-temporal variations in HSLC tornadoes in Illinois, Indiana, Kentucky, and Ohio, and characterizes the synoptic conditions associated with their occurrence. HSLC tornadoes are defined use two different sets of criteria: 1) Surface-Based Convective Available Potential Energy (SBCAPE) ≤ 500 J kg^-1 and 0-6 km Bulk Wind Shear ≥ 18 m s^-1 (HSLC1), and 2) SBCAPE ≤ 500 J kg^-1 and 0-6 km Bulk Wind Shear ≥ 18 m s^-1 and MUCAPE ≤ 1000 J kg^-1 (HSLC2). This study found that HSLC tornadoes account for > 22% (28.9% for HSLC1 and 22.5% for HSLC2) of all the tornadoes that occur in the study region. For high-CAPE tornadoes, the number of tornadoes categorized by the Enhanced Fujita (EF) Scale decreases with intensity. However, when observing HSLC tornadoes, the number of EF-1 tornadoes is higher than that of EF-0, then decreases from EF-2 to EF-5. HSLC tornadoes in the Ohio Valley are most prevalent during the cool season and they are the dominant tornado type in October through February. Also, 59.8% of HSLC1 tornadoes and 55.5% of HSLC2 tornadoes take place during the overnight and early-morning hours. Not surprisingly, the majority of HSLC tornadoes occur in non-supercell environments and they are associated with thunderstorms that are strongly influenced by linear forcing features like frontal boundaries instead of being influenced primarily by warm sectors near a synoptic low-pressure system. This study has implications for operational forecasting and public safety. Since many HSLC tornadoes occur during the overnight hours in the cool season, and are associated with non-supercell environments, they may catch both the general public and operational forecasters off-guard. This highlights the importance of increasing public awareness of the potential for HSLC tornadic activity. With an increased knowledge in the timing and storm mode in which HSLC tornadoes take place, operational meteorologists can use this information to help improve the accuracy of non-supercell HSLC tornado forecasting, as well as the real-time monitoring of tornadoes during severe weather events that present atypical tornado environments.