In June/July 2009 the weather in the Czech Republic was influenced by a 12 days lasting baric low located over Mediterranean, which resulted in a sequence of many flash foods. The total damage was estimated to be about 200 mil. EUR and 15 people died. Although the flash flood is considered as hardly predictable phenomena, first efforts in flash floods forecasting have been already done [1]. Some flash floods can be predicted several tens of minutes in advance. Nowadays, new methods of nowcasting are being developed and they promise a new progress in predicting of these events. The paper shows a detail case study of a flash flood - from the point of view of flash flood forecasting. Based on the results, the prediction system consisting of several nowcasting tools (COTREC, CELLTRACK, etc.) combined with the HYDROG rainfall-runoff model will be set up for testing in operation.