Reliability and predictability of the timing behavior have shown to be major issues for wireless sensor network deployments. Real-time requirements presented by several applications can be fulfilled by implementing communication schemes that lower possible sources of non-determinism of the timing behavior, assuming that the nodes are synchronized. The predictability of current synchronization protocols, however, cannot be verified, due to potential interferences with other activities. In this paper we propose Secondis, a dissemination protocol that periodically synchronizes and orchestrates activities in the network, providing three main benefits. (1) The synchronization task is performed in short time windows, where no interferences can occur, independently of any available communication structure. (2) The synchronization is energy-efficient, and (3) robust against link and node failures. Secondis provides probabilistic bounds on its predictability using probabilistic model checking a...