Rain-wind induced vibration of stay cables is a great concern for the designers of cable stayed bridges. Despite numerous experimental investigations, an accurate quantitative prediction of this effect in the design stage is not feasible without extensive experiments. This paper presents a model to predict the possible rain-wind induced vibrations of inclined stay cables. This model is based on the results of earlier research and observations in practice. It is a design model, based on a worst-case scenario. The loading of the cable is im-plemented as a modified galloping equation. With this model, the critical velocity at which the aerodynamic instabilities may occur and the amplitudes of the cables are determined. The results depend on cable diameter, damping, stiffness, mass and the variation of lift coefficient with wind angle. For the lift coefficient, data from earlier experiments were used to implement into the design model. A comparison of the results of this model and an analysis of the observed vibrations on a bridge in full scale shows that this model represents the ob-served phenomena well, and the model has been used in the design stage of a second cable stayed bridge.