Major Federal Aviation Administration (FAA) planning documents (e.g., the FAA Flight Plan 2005-2008, the FAA Air Traffic Organization Fiscal Year 2005 Business Plan, and the Operational Evolution Plan) stress the importance of: Improving National Airspace System operations efficiency by increasing safety and capacity (e.g., reducing delays) and Providing FAA services more efficiently, such that operations costs can be reduced while improving safety and capacity. Continued improvements in air traffic delay mitigation in the NAS are imperative, given expectations for significant increases in near-term air traffic demand. The latest FAA aerospace growth forecast projects a 30% increase in Air Route Traffic Control Center (ARTCC) operations by 2015 (FAA Office of Aviation Policy and Plans, 2005). Improving Air Traffic Control (ATC) productivity during convective weather impact events is particularly important. Air traffic demand is escalating in an airspace network near capacity even in clear-weather. This will limit the ability to exploit advancements made in mitigating en route convective weather delays, unless fielded decision support systems are able to improve traffic management efficiency. Moreover, it is also essential that ATC productivity (e.g., as measured by the number of employees and overtime) be improved, given the reduction in Aviation Trust funding from the passenger ticket tax and overall federal funding constraints. We have previously described how a contemporary convective weather decision support system - the Corridor Integrated Weather System (CIWS) - can facilitate significantly improved capacity enhancing decisions, such as keeping routes open longer and proactive rerouting (e.g., Evans et al. 2005; Robinson et al. 2004). These CIWS-enabled capacity enhancements were shown to result in significant reductions in air traffic delays, airline operating costs, and delay-incurred passenger costs (Robinson et al. 2004). A study of the CIWS contributions to ATC productivity enhancements began in 2005. As part of this effort, real-time observations of CIWS product usage and the time to accomplish weather impact mitigation planning decisions during multiday thunderstorm events were carried out at 8 U.S. ARTCCs. A description of the design (and methodological challenges) of this experiment are presented in Section 2 of this paper. Improved ATC productivity was found to have two components: (1) Reduced workload and increased operational efficiency, as characterized by the amount of time required to develop and implement convective weather mitigation plans and the ability to enhance staffing decisions (2) Increased frequency of capacity enhancing decisions. Results demonstrating how CIWS helped traffic managers reduce workload and increase operational efficiency through time-savings and improved decision-making are presented in Section 3. Important factors such as the variation in performance from ARTCC to ARTCC are discussed in some detail. We show that a very important factor in this performance is whether the Area Supervisors at an ARTCC have direct access to CIWS products. The paper concludes by discussing future plans for CIWS ATC productivity enhancement investigations.