Relativistic electrons appear in the geosynchronous environment following some, but not all, geomagnetic storms. The ability to identify which storms produce these electrons would bring us much closer to explaining the mechanism responsible for their appearance, and it would provide the space weather community with a means to anticipate the electron hazard to geosynchronous spacecraft. We apply a recently developed statistical technique to produce an hourly time series of relativistic electron conditions at local noon along geosynchronous orbit using several geosynchronous monitors. We use a cross-correlation analysis to determine what parameters in the solar wind and magnetosphere might influence the flux of relativistic electrons. We then perform a superposed epoch analysis to compare storms with and storms without the appearance of these electrons. We investigate a number of solar wind and magnetospheric parameters for these two sets of storms at 1-hour resolution. In particular, sustained solar wind velocity in excess of 450 km s-1 is a strong external indicator of the subsequent appearance of relativistic electrons. In the magnetosphere, long-duration elevated Pc 5 ULF wave power during the recovery phase of magnetic storms appears to discriminate best between those storms that do and do not produce relativistic electrons. ¿ 2001 American Geophysical Union