Although Convective Available Potential Energy (CAPE) is a well-established factor in supercell development in the United States, its role in European tornadogenesis—particularly under low CAPE conditions—remains poorly documented. This study examines tornado occurrences in western Europe between 1940 and 2022, using a dataset of 1,675 tornadoes recorded in Portugal, Spain, France, Belgium, and the Netherlands, of which 255 were classified as intense (≥EF2). Using ERA5 reanalysis data, the thundeR package, and convective diagnostics, we find that 58% (n = 148) of these intense tornadoes occurred with Most Unstable CAPE (MUCAPE) values ≤ 500 J/kg. The spatial and seasonal distribution of these low-CAPE, high-intensity events highlights a marked autumn and winter signal. Autumn tornadoes were consistently associated with the left-exit region of 300 hPa jet streaks, strong vertical wind shear, and enhanced low-level storm-relative helicity (SRH). While also frequently occurring near jet streak exit regions, winter events showed a less systematic relationship suggesting the contribution of additional factors such as weaker upper-level forcing and colder low-level environments. Five distinct synoptic patterns were identified, modulated in part by the North Atlantic Oscillation (NAO). Positive NAO phases favoured tornado activity in northern France and western Spain during autumn, whereas negative phases were linked to winter tornadoes across the Iberian Peninsula. The overall findings underscore the importance of dynamic forcing—particularly low-level shear and helicity—in driving intense tornadogenesis in low-CAPE environments across western Europe, with clear seasonal and synoptic-scale variability partly driven by jet stream behaviour.
Lacroix et al. (Fri,) studied this question.