This paper proposes a scenario-based ambulance location model which explicitly computes the availability of ambulances with stochastic call arrivals under a dispatching policy. The model utilizes two-stage stochastic programming to represent the temporal variations in call arrivals as a set of call arrival sequences. Constraints are embedded in the model to ensure that available ambulances are assigned to incoming calls following a dispatching policy. A logic-based Benders decomposition algorithm is presented to solve the model. The advantage of using our algorithm is demonstrated by comparing its performance with those of other location models.