The National Weather Service's (NWS) weather products are a vital component of the Federal Aviation Administration's (FAA) air traffic control system. In addition to providing aviation weather products developed at its own facilities, NWS also provides staff onsite at each of FAA's en route centers-the facilities that control high-altitude flight outside the airport tower and terminal areas. Over the last few years, FAA and NWS have been exploring options for enhancing the efficiency of the aviation weather services provided at en route centers. GAO was asked to summarize its draft report that (1) determines the status and plans of efforts to restructure the center weather service units, (2) evaluates efforts to establish a baseline of the current performance provided by these units, and (3) evaluates challenges to restructuring them. In preparing the draft report on which this testimony is based, GAO evaluated agency plans for the restructuring and for establishing performance measures. GAO also compared agency efforts to leading practices and interviewed agency officials.