Is there added value of convection-permitting regional climate model simulations for storms over the German Bight and Northern Germany?

This study tackles the question: Do very high-resolution convective-permitting regional climate model (RCM) simulations add value compared to coarser RCM runs for certain extreme weather conditions, namely strong wind and storm situations? Ten strong storm cases of the last two decades were selected and dynamically downscaled with the RCM COSMO-CLM (24 and 2.8 km grid point distance). These cyclones crossed the high-resolution model domain, which encompasses the German Bight, Northern Germany, and parts of the Baltic Sea. One storm case study (storm Christian of October 2013) is discussed in more detail in order to analyze the small-scale storm features and the associated potential added value of the high-resolution simulation. The results indicate an added value for atmospheric dynamical processes such as convective precipitation or post-frontal cloud cover. The multiple storm analysis revealed added value for the high-resolution regional climate simulation for 10 m wind speed, mean sea level pressure, and total cloud cover for most storms which were examined, but the improvements are small. Wind direction and precipitation were already well simulated by the coarser RCM and the higher resolution could often not add any value for these variables. The analysis showed that the added value is more distinct for the synoptic comparisons than for the multiple storm study analyzed with statistical measures like the Brier Skill Score.