Supercells in Europe modelled by a Convection-Permitting Climate Model: Climatological features and future change

Supercells are the rarest type of thunderstorms, well known because of their multi-hazard characteristics in the Great Plains region of the US. These hazards include tornadoes, very large hail, lightning, damaging wind gusts, and/or excessive precipitation resulting in flash floods. However, their spatial footprints are not limited to there, with the whole of the midlatitudes, including Europe, having their share. Little is known about the spatial and temporal distribution of supercells outside the US. In Europe for instance, there are only a few short-term observational studies addressing the topic.

Supercells are characterized by the presence of a mesocyclone, which is a rotating updraft. Using an updraft helicity metric, which aims to extract such mesocyclonic features within a convection-permitting climate model (CPM), we present a supercell climatology for Europe and an assessment of their future changes based on RCP8.5. The climatology is based on a 20-y long hindcast, and  we also assess three further 10-y long simulations: 1) control, 2) mid-century future, and 3) end-of-century future.

Our results show that supercells are more frequent in southern Europe, compared to the north, and predominantly occur in summer. Left-movers, which are conventionally overlooked, but observations suggest can produce as much hazards in Europe (e.g. very large hail), consist of 15% of all supercells. With warming, the frequency increases in the south and to a lesser extent in the north, whilst there are decreases in Central Europe. Finally, we claim that changes in favourable environmental conditions of severe thunderstorms might not directly translate into the changes in severe thunderstorms themselves, highlighting the need for CPMs for assessing hazardous weather extremes at small spatial scales.