MM5-based regional climate model (CMM5) simulations of the diurnal cycle of U.S. summer precipitation are found to be sensitive to the choice of cumulus parameterization schemes, whose skills are highly regime selective. The Grell scheme realistically simulates the nocturnal precipitation maxima and their associated eastward propagation of convective systems over the Great Plains where the diurnal timing of convection is controlled by the large-scale tropospheric forcing; whereas the Kain-Fritsch scheme is more accurate for the late afternoon peaks in the southeast U.S. where moist convection is governed by the near-surface forcing. In radar rainfall data and the simulation with the Grell scheme, another weaker eastward propagating diurnal signal is evident from the Appalachians to the east coast. The result demonstrates the importance of cumulus schemes and provides a realistic simulation of the central U.S. nocturnal precipitation maxima.