Sounding‐derived parameters associated with tornadic storms in Catalonia

Abstract

ABSTRACTCatalonia, a southern Europe coastal region in the western Mediterranean basin, is regularly affected by severe local storms which every year produce an average of 5 tornadoes and 12 waterspouts, based on data recorded from 2000 to 2016. Despite these tornadoes mostly being weak – not exceeding EF1 on the enhanced Fujita (EF) damage intensity scale – they occasionally reach stronger intensities, posing an evident threat to population and socio‐economic activity, particularly in densely populated coastal conurbations such as Tarragona or Barcelona. This study provides analysis of upper air conditions that favour the formation of tornadic storms in the region, considering five different stations in Spain and France to build a database of 333 soundings which included 49 tornadic soundings, 104 waterspout soundings (WAT) as well as non‐tornadic thunderstorms and dry period soundings. For each one, 12 different parameters were calculated and analysed to test their potential capacity to discriminate non‐tornadic from tornadic environments and also to assess the feasibility of stratifying tornado intensity (EF0, and EF1 or stronger, on the EF scale). The results indicate that storm‐relative helicity for the layer 0–3 km, with a threshold value of 150 m2 s−2, wind shear for the same layer, with a threshold of 15 m s−1, and composite parameters such as the supercell composite parameter with a threshold of 1.2 and universal tornadic index with a threshold of 0.3 are all useful to distinguish between non‐tornadic thunderstorms and EF1 or stronger tornadic events. These results contribute to a better description of the climatology of upper air conditions that favour tornadic storms in the region and can also help operational weather forecasting and surveillance tasks, thus increasing situational awareness in severe convective weather events.