An Observing System Simulation Experiment (OSSE) system has been implemented at the National Oceanographic and Atmospheric Administration Earth Systems Research Laboratory in the US as part of an international Joint OSSE effort. The setup of the OSSE consists of a Nature Run from a 13-month free run of the European Center for Medium-Range Weather Forecasts operational model, synthetic observations developed at the National Centers for Environmental Prediction (NCEP) and the National Aeronautics and Space Administration Global Modelling and Assimilation Office, and an operational version of the NCEP Gridpoint Statistical Interpolation data assimilation and Global Forecast System numerical weather prediction model. Synthetic observations included both conventional observations and the following radiance observations: AIRS, AMSU-A, AMSU-B, HIRS2, HIRS3, MSU, GOES radiance and OSBUV. Calibration was performed by modifying the error added to the conventional synthetic observations to achieve a match between data denial impacts on the analysis state in the OSSE system and in the real data system. Following calibration, the performance of the OSSE system was evaluated in terms of forecast skill scores and impact of observations on forecast fields.