We examine the dynamics of the outer plasmasphere during 10 post-ssc events by comparing observations of cold, dense ions from Los Alamos magnetospheric plasma analyzers on board three widely spaced geosynchronous satellites with output from the Magnetospheric Specification and Forecast Model (MSFM). The MSFM is a data-driven, operational space weather specification and forecast code originally designed to facilitate U.S. Air Force spacecraft operations. For this study we modified the MSFM to include a cold plasmaspheric ion population that was subject to the effects of ionospheric refilling. We utilized the electron density model of Carpenter and Anderson [1992> and the assumption of charge neutrality to initialize the plasmaspheric proton density within a specified plasmapause. This configuration was then allowed to evolve under the effects of E¿B drift and refilling. The modified MSFM clearly shows the development and westward transport of duskside plasmaspheric plumes/tails during periods of enhanced convection and the eastward transport of these structures during decreasing activity. We present a detailed comparison between the data and the model output for one case and a statistical analysis of the comparison for all 10 cases. We also compare the model results with previously published observations of plasmaspheric ions and models of plasmaspheric dynamics. The MSFM was able to systematically reproduce the geosynchronous observations with good accuracy in both local time placement and density level. We find the modified MSFM to be an improvement upon previous plasmaspheric models and a useful tool in the interpretation of spatially and temporally separated geosynchronous observations. ¿ 1997 American Geophysical Union