During May 1998, the Center for Analysis and Prediction of Storms (CAPS) at the University of Oklahoma coordinated a multi-institution numerical forecast project known as the Storm and Mesoscale Ensemble Experiment (SAMEX). SAMEX involved, for the first time, the real-time operation of four different ensembles of mesoscale models over the same region of the United States. The main purpose of this paper is the evaluation of the ensemble forecasts, performed at a relatively coarse resolution of 30 km. An additional SAMEX goal not discussed here is to compare the value of the ensemble forecasts against single forecasts made over smaller subregions of the Great Plains at both intermediate (10 km) and high (3 km) resolution. The SAMEX ’98 ensembles consisted of a single 36-h control forecast from the ARPS (at CAPS), the Penn State–NCAR fifth-generation Mesoscale Model (at NSSL), and the Eta Model and Regional Spectral Model (at NCEP), all with horizontal resolutions of approximately 30 km, and perturb... Abstract During May 1998, the Center for Analysis and Prediction of Storms (CAPS) at the University of Oklahoma coordinated a multi-institution numerical forecast project known as the Storm and Mesoscale Ensemble Experiment (SAMEX). SAMEX involved, for the first time, the real-time operation of four different ensembles of mesoscale models over the same region of the United States. The main purpose of this paper is the evaluation of the ensemble forecasts, performed at a relatively coarse resolution of 30 km. An additional SAMEX goal not discussed here is to compare the value of the ensemble forecasts against single forecasts made over smaller subregions of the Great Plains at both intermediate (10 km) and high (3 km) resolution. The SAMEX ’98 ensembles consisted of a single 36-h control forecast from the ARPS (at CAPS), the Penn State–NCAR fifth-generation Mesoscale Model (at NSSL), and the Eta Model and Regional Spectral Model (at NCEP), all with horizontal resolutions of approximately 30 km, and perturb...