We examine the dynamics of the outer plasmasphere during a 3-day interval in February, 1992 by comparing observations from three widely-spaced geosynchronous satellites with the predictions of the Magnetospheric Specification and Forecast Model (MSFM). For this study the MSFM was modified to include a cold, plasmaspheric population subject to the effects of corotation, convection, and ionospheric refilling. The model does a very good job of reproducing the observations; in particular, it clearly shows the formation and westward transport of duskside plasmaspheric plumes, accounting for the progressively earlier local time observations of cold ions following periods of enhanced convection. The MSFM's ability to model dynamically the evolution of the outer plasmasphere under varying solar wind conditions improves upon previous plasmaspheric models and has aided our understanding of spatially and temporally separated observations of plasmaspheric ions at geosynchronous orbit.¿ 1997 American Geophysical Union