The main objective of a meteorological nowcasting system is to analyse and predict in ultra-short range those weather phenomena, which might be dangerous for life and property. The Hungarian Meteorological Service developed a nowcasting system (MEANDER), and its most computational intensive calculations have been parallelised by means of P-GRADE graphical programming environment. In this paper the application of P-GRADE environment is demonstrated in a real-size meteorological problem. We give an overview on the parallelisation of MEANDER system applying P-GRADE environment at the different stages of parallel program development cycle; specification, design, debugging and performance analysis. However, the paper focuses on a novel approach of parallel debugging, which combines ideas from the field of formal methods and model checking techniques with advanced parallel debugging methods in a user-friendly way.