This paper addresses parameter drift in stochastic models. We define a notion of context that represents invariant,stable-over-time behavior and we then propose an algorithm for detecting context changes in processing a stream of data. A context change is seen as model failure,when a probabilistic model representing current behavior is no longer able to fit newly encountered data. We specify our stochastic models using a first-order logic-based probabilistic modeling language called Generalized Loopy Logic (GLL). An important component of GLL is its leing mechanism that can identify context drift. We demonstrate how our algorithm can be incorporated into a failure-driven context-switching probabilistic modeling framework and offer several examples of its application.