Terrain affects connectivity in mobile ad hoc networks (MANET). Both average pairwise link closure and the rate at which the link-state changes when nodes move depend on the characteristics of the intervening terrain. However, these key parameters depend only mildly on internode distances in common real-world terrains, which suggests that network performance in real terrains can be usefully modeled using simple time and location-invariant average link-state probability and rate of change. We use this fact to predict the number of disconnected subnets at a random instant in a given terrain, and we compare these predictions against Monte Carlo sampling of node positions.