Rainfall-induced highway slope failure is a common geotechnical hazard for Texas transportation infrastructures, especially for highway slopes. Differential rainfall events, along with the type of soil of the slopes, have been identified as one of the major causes of highway slope stability problems. Depending on the soil type, its behavior differs in response to the variable rainfall pattern. Hence, for the stable earthen highway infrastructure design, both soil behavior and environmental conditions play a critical role. In this study, rainfall characteristics were developed based on the weather radar network, and subsequently, critical rainfall events were identified. The critical rainfall events were then used as input to numerically evaluate the highway slope’s stability using the finite element method (FEM) for seepage analysis and the limit equilibrium method for slope stability analysis. The numerical analysis indicated the significant variation of the factor of safety of the slopes under the differential rainfall events. The lowest factor of safety achieved in the analysis was approximately 1.2. It also revealed that the lowest factor of safety could be attained within 3 to 5 days during rainfall events.