The invention relates to a meteorological modelling method for calculating an aircraft flight plan, the aircraft comprising a communication means and a navigation management system.The method comprises at least the following steps: the communication means carries out the acquisition of meteorological prediction data related to waypoints in proximity to the nominal route in addition to the waypoints belonging to the nominal route, the navigation management system allocates by projection onto the current route of the aircraft the prediction data for the said waypoints not belonging to the current route, the navigation management system calculates the meteorological prediction data for the waypoints of the current route of the flight plan according to the prediction data allocated by projection onto the current route of the aircraft.The invention is a modelling method for aircraft navigation management systems.