A program was designed to search for reports of thunder with snow from a CD-ROM archive of surface data. For 223 surface stations across the United States, the period of 1961-1990 reveals that over 350 thundersnow events have occurred in that time span. A normalized distribution shows that convective snow is most likely to occur over the central Rocky Mountain, Central Plains, and Great Lakes states, with a distinct temporal peak in the frequency of events evident during March. Surface analyses were generated so that each event could be classified according to the location of the thundersnow-reporting station relative to a cyclone center, or into one of six other categories discussed below. The results show that 73 percent of the events were associated with surface cyclones, 79 percent of which were located in either the northwestern or northeastern quadrant of the system, and at a mean distance of 456 kilometers from a cyclone center. Of the remaining events, 5 percent were classified as lake-effect, 12 percent as orographically driven, 5 percent as being associated with an off-shore cyclone with an undetermined position, 3 percent as Canadian, Mexican, or Gulf of Mexico cyclones, and 2 percent as miscellaneous.