Analysis of the high-end derecho in Corsica in 2022

On August 18, 2022, Europe experienced the most severe storm of the year. In the early morning, a derecho formed, causing significant damage along a path of over 1000 km as it travelled at an exceptional speed of up to 40 m/s, with wind gusts reaching a maximum of 62.2 m/s. The storm had a widespread impact, affecting Spain, France, Italy, Slovenia, Austria, and the Czech Republic. The severe weather caused fatalities in several countries, with the highest death tolls reported on Corsica and in the Alps. The focus of this analysis is to understand the factors that led to the derecho's exceptional intensity. We examine the storm's chronological development, and the intensification phases it underwent. We also investigate how external and internal forcing contributed to the rapid upscale growth of the storm.

From the perspective of external factors, we show the importance of a mid-level front and warm air advection at the lower levels and their relation to the distribution of CIN in the vicinity of the event. We show that the development and movement of convective cells were influenced by the mid-level front. The system was also strongly influenced by the internal forcing as it formed in an environment of high CAPE values and strong low-level vertical wind shear, and intense storm-relative inflow. The combination of internal and external forcing factors eventually resulted in the extreme forward speed of the derecho. Due to the interaction with complex topography, the derecho underwent several weakening and strengthening phases, which we associate with the changes to the internal and external forcing. Finally, we compare the environment of the derecho to typical environments of severe convective wind gusts in Europe and compare the event to similar Mediterranean derecho cases from the past.