Orographic and lake effects on the evolution of thunderstorms in the region of Lake Balaton, Hungary

Lake Balaton is the largest lake in Central Europe. The Hungarian Meteorological Service operates a lake storm warning system by the lake to ensure the safety of sailors, fishermen and the thousands of tourists who visit the area. Thunderstorms are the most dangerous phenomena following windstorms caused by cold fronts due to wind gusts and lightning. Thunderstorms have a frequent occurrence in the region from May to August, occurring every three days on average.Observations indicate that the 600 km² lake can significantly influence the evolution of these thunderstorms. It affects instability conditions and the moisture content, as well as the location of convergent and divergent areas. In calmer weather situations, when synoptic-scale processes allow local effects to dominate, significant lake circulation develops. Convection is therefore inhibited over the lake during the daytime, while it is promoted along the convergence lines over the shores. Additionally, circulation above the lake generates wind shear and vortices, which can intensify the evolution of thunderstorms.To the northwest of Lake Balaton lies the Bakony Mountains, whose highest peak is around 700 m high. The orographic lifting mechanism can also initiate the formation of daytime thunderstorms. These thunderstorms can affect the weather over the lake by generating gust fronts, lightning and showers. The lake circulation and the most frequent prevailing flow can further enhance orographic lifting. In the convective season these additional effects often result in the first daily formation of thunderstorms over the Bakony Mountains. If the direction of the main flow is northwest, the sinking of air on the lee side may weaken or even dissipate cumulonimbus clouds.This study used radar data, lightning and surface measurements to examine the development of thunderstorms in the region of the lake. Statistical analyses of the data and case studies are also provided, examining the various local effects. The WRF (Weather Research and Forecasting) numerical model was applied to simulate the impact of these local effects on thunderstorm evolution.