Estimates of regional snow water equivalent (SWE) are essential for hydrological prediction, climatological analysis, and meteorological forecasting. Passive microwave-derived estimates of snow cover have unique benefits such as all-weather imaging, rapid scene revisit capabilities, and the ability to provide these quantitative SWE data. For this study the available time series of special sensor microwave/imager (SSM/I) brightness temperatures in the equal area SSM/I Earth grid projection were processed with the Canadian Atmospheric Environment Service dual-channel SWE algorithm for a ground-validated North American prairie region. Seven winter seasons (December, January, and February) of SWE imagery spanning 1988--1995 and averaged for 5 day intervals were subjected to a rotated principal components analysis (PCA) performed individually for each season. A final PCA considering all 7 winter seasons was performed in order to investigate the degree to which snow cover patterns reappear from one season to the next. Results indicate that modes of snow cover in the North American prairies are most persistent during the late winter (February) and exhibit a greater degree of variability during December than the other winter months. Two snow cover regimes are identified for the study region, with the winters of 1988/1989--1991/1992 characterized in a manner that is unique in both temporal and spatial aspects from the winters of 1992/1993--1994/1995. ¿ 2000 American Geophysical Union