In order to implement a Flood Warning System, a methodology for the establishment of an operational hydrological model is presented here. The model is fed with real-time precipitation estimates from weather radar data. The Mixcoac River experimental watershed, located west of Mexico City and, Cerro Catedral weather radar for the implementation of the model was used. Such models are needed in basin where the topography is very rugged and cause flash floods affecting populations, to several economic and transport and telecommunications infrastructure. Owning a warning system of this kind helps stakeholders, in areas such as Civil Protection and institutions responsible, to activate the security measures protocols to mitigate the effects caused by the floods.