There is currently great interest in improving the ability to quantitatively assess how well U.S. Air Traffic Control (ATC) services are being provided as new weather-air traffic management (ATM) decision support capabilities are added. One of the three proposed metrics currently under study by the Federal Aviation Administration (FAA) and airlines is resource utilization, which has been defined as "the safe and efficient use of available airport or airspace capacity." Measurement of capacity utilization is particularly difficult during convective weather since storms cause capacity reductions in both en route and terminal airspace. In particular, en route capacity loss results in network congestion that cannot be readily characterized by scalar metrics. This paper proposes the use of (i) models for translating 3-D weather radar data into time-varying estimates of the capacity reductions in affected en route sectors, terminal airspace, and airports, together with (ii) automatically-generated, broad-area ATM strategies that utilize the time-varying estimates of airspace capacity and demand to determine optimal reroute strategies or, when necessary, minimally disruptive ground or airborne delay programs to assess how the available capacity could best been utilized. By comparing actual vs. optimal capacity utilization, one can assess how effective the actual weather-ATM system was at utilizing the available capacity. Examples of applying this methodology to severe convective weather events from 2005 and 2006 will be presented.