Nocturnal thunderstorms in Poland: Environments, synoptic patterns and comparison to diurnal thunderstorms

Abstract

Forecasting nocturnal thunderstorms, due to (among others) their development from higher atmospheric layers compared to daytime thunderstorms, is a significant challenge. To address this issue, we analyzed more than 2 mln nocturnal cloud-to-ground (CG) lightning flashes and performed synoptic analysis for more than 1000 nights with thunderstorms. That allowed us to inspect synoptic and environmental conditions of nocturnal thunderstorms in Poland, which are relatively frequent (~50% of all CG lightning flashes), especially in the western part, considering even the whole of Europe. The analysis yielded that CG lightning flashes are the most frequent during convergence line and waving front, however, due to the highest medians of MUWMAXSHEAR reaching 600 m2 s−2, waving and the warm front seem to have the highest potential for severe nocturnal thunderstorms. Lower atmospheric instability compared to daytime thunderstorms is compensated by increased wind shear, and thus this environment is favorable for thunderstorms. The threshold of 200 J kg−1 of MUCAPE and 190 m2 s−2 of MUWMAXSHEAR may be applied in distinguishing between lightning and non-lightning situations. Significant overlap between multiple parameters for diurnal and nocturnal convection initiation (CI) demonstrates how difficult is forecasting nocturnal thunderstorms.