In this study, thunderstorm activity during the cold part of the year was analyzed based on Thunderstorm Intensity Index data on a pre-defined grid with a mesh of 3 km × 3 km in Croatia. The study covered a five-year period from 2016 to 2020, focusing on the months from October to March. The goal of the research was to conduct a spatial and temporal analysis of thunderstorm activity and determine the synoptic and thermodynamic conditions under which it occurs. The analysis aims to provide an overview of the fundamental characteristics, thereby improving the understanding of deep moist convection in the cold part of the year, which poses a significant challenge in operational weather forecasting due to its lower frequency and more difficult intensity assessment. The occurrence of surface frontal disturbances is detected based on surface synoptic charts and the flow regime at the 500 hPa level is determined using upper-level synoptic charts. Thermodynamic and kinematic parameters are calculated from radiosonde profiles from stations in San Pietro Capofiume, Brindisi, Pratica di Mare (Italy), Zagreb, and Zadar (Croatia), using the thundeR free software package. A total of 290 convective days were selected for analysis from the observed period. The results indicate that synoptic forcing plays a significantly greater role in the development of convection during the cold part of the year compared to the warm part, while the dominant upper-level flow regime is southwest. The obtained values of Convective Available Potential Energy (CAPE) in the cold part of the year are much lower than those in the warm part, with a significant contribution from the considerably lower amount of solar surface heating. Additionally, most thunderstorms develop under conditions of strong vertical wind shear, indicating that the atmospheric environment conducive to winter thunderstorms is predominantly a high shear – low CAPE environment.