In addition to providing aviation weather products developed at its own facilities, the National Weather Service (NWS) also provides on-site staff at each of the Federal Aviation Admin. (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. This report: (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. Charts and tables.