A method for providing a fleet of aircraft with weather data during flight, the method comprising: generating at least one weather model using a source of weather data, wherein the weather model incorporates flight operations information and performance requirements from the fleet of aircraft, taking into account operator preferences and air traffic control objectives; and generating weather messages from the weather model to provide consistent weather data across flights from different operators, each weather message being generated in a format that is compatible with the aircraft to which the weather message is being sent; wherein generating a weather message from the weather model comprises: receiving a weather service request for a plurality of aircraft; verifying a subscription status of the plurality of aircraft; if the subscription status is effective for at least a subset of the plurality of aircraft, generating the weather message using the weather model; verifying the subscription status of each of the plurality of aircraft; if the subscription status is effective for one or more individual aircraft of the plurality of aircraft, transmitting the weather message comprises transmitting the weather message, during flight of the aircraft, at least one of directly to the one or more individual aircraft or to one or more aircraft operator entities that control operation of the one or more individual aircraft; and if the subscription status is effective for one or more individual aircraft of the plurality of aircraft using forecast winds, such that changes in winds may be compensated by at least one of autopilot, auto-throttle and by pilot manual control inputs; wherein generating a weather message from the weather model further comprises: generating an intermediate weather file by reducing the weather model to a subset of weather data, the reducing the weather model to a subset of weather data comprising compressing the weather model from a four dimensional weather grid into a single three dimensional grid which is valid for a given period of time during which the discrepancy between forecast weather and actual weather is estimated to be acceptable; and using the intermediate weather file to formulate the weather message according to one or more weather message encoding rules of the aircraft. generating at least one weather model using a source of weather data, wherein the weather model incorporates flight operations information and performance requirements from the fleet of aircraft, taking into account operator preferences and air traffic control objectives; and generating weather messages from the weather model to provide consistent weather data across flights from different operators, each weather message being generated in a format that is compatible with the aircraft to which the weather message is being sent; receiving a weather service request for a plurality of aircraft; verifying a subscription status of the plurality of aircraft; if the subscription status is effective for at least a subset of the plurality of aircraft, generating the weather message using the weather model; verifying the subscription status of each of the plurality of aircraft; if the subscription status is effective for one or more individual aircraft of the plurality of aircraft, transmitting the weather message comprises transmitting the weather message, during flight of the aircraft, at least one of directly to the one or more individual aircraft or to one or more aircraft operator entities that control operation of the one or more individual aircraft; and if the subscription status is effective for one or more individual aircraft of the plurality of aircraft using forecast winds, such that changes in winds may be compensated by at least one of autopilot, auto-throttle and by pilot manual control inputs; generating an intermediate weather file by reducing the weather model to a subset of weather data, the reducing the weather model to a subset of weather data comprising compressing the weather model from a four dimensional weather grid into a single three dimensional grid which is valid for a given period of time during which the discrepancy between forecast weather and actual weather is estimated to be acceptable; and using the intermediate weather file to formulate the weather message according to one or more weather message encoding rules of the aircraft.