Flash floods are rare events (in Europe, one ore two flash flood per year have dramatic consequences) and they are ill documented (each country has its own investigation and archiving rules frequently separating the meteorological and hydrological aspects). Flash floods result from the concatenation of meteorological and hydrological conditions. Recognition of the coupled meteorological/hydrological nature of flash floods is now evident in interpretative studies and in the development of predictive models. There is a real need for research that will improve the understanding of the major atmospheric and hydrologic factors leading to extreme flood event, especially those affecting small medium ungauged basins. This paper proposes few advances in our understanding of the hydrometeorological processes and their associated modeling requirements that may be useful to introduce within operational forecasting chain.