The development and use of nowcasting systems should inevitably be accompanied by the development and application of suitable verification methods. A thorough verification strategy is needed to adequately assess the quality of the system and consequently to lead to improvements. Different verification methods for thunderstorms and its attributes are discussed along with the importance of observational data sets. They are applied to two radar-based nowcasting algorithms for a convective season using various observation data sets. The results show, that the combination of the two algorithms outperforms a single algorithm.