Left- and right-moving supercell dynamics, environments and hazards – today and in future

Abstract. Supercell thunderstorms are among the most hazardous and damaging weather phenomena in Europe. However, little information is available on the relationship between supercell morphology and environmental conditions in Europe. We dissect supercell morphology, the changes in environmental conditions, and the subsequent changes in associated hazardous weather using numerical simulations of the current and a warmer (+3 °C) climate at 2 km grid resolution. Comparing right- (RM) and left-moving (LM) storms, we find that RMs have a more coherent storm structure and larger high-intensity areas, and their motion deviates stronger from the mean flow compared to LMs. LMs occur in a narrower range of environmental conditions, namely in hotter and less stable environments compared to RMs. Overall, in the warmer climate the pre-storm environment becomes less stable, and deep-layer shear increases. Accordingly, hazards associated with supercells such as lightning, wind gusts, intense precipitation, and hail size all increase. RMs and LMs reach similar hazard intensities, while RMs tend to have larger high-hazard areas than LMs. The relative increase in hazard severity in the warmer climate is more pronounced for LMs, particularly for hail area and lightning intensity. A regional decomposition across Europe indicates LMs tend to occur in warmer, more unstable conditions than RMs, and that these regional differences are generally greater than the differences in storm environments between LMs and RMs.