This study examines the characteristics of the diurnal cycle in NASA's MERRA reanalysis data. The study focuses specifically on the warm-season hydrological cycle, including the diurnal variation of precipitation, low-level jets, and associated moisture transport over the North American continental region. The results are compared with other reanalysis products, and are validated against a number of satellite and ground-based observations, for the purpose of assessing the limitations and potential benefits of the data for climate studies.