Infiltration-induced landslides are among the most common natural disasters threatening modern civilization, but conventional methods for studying the triggering mechanisms and predicting the occurrence of these slides are limited by incomplete consideration of underlying physical processes and the lack of precision inherent in limit-equilibrium analyses. To address this problem the spatial-temporal evolution of failure is investigated in a seasonally unstable section of interstate highway embankment, known as the Straight Creek landslide, Colorado. The study includes multi-year site investigation, monitoring, and numerical simulation using a rigorous hydromechanical framework along with a field of local factor of safety method. The sensitivity of episodic landslide reactivation to infiltration characteristics is evaluated. Results indicate that annual cumulative snowmelt infiltration, which typically accounts for approximately 75% of total annual cumulative infiltration and occurs over a short period in the spring, has the most substantial impact on slide activation. The rate of snowmelt infiltration varies independently of annual cumulative snowmelt infiltration and cumulative infiltration in the previous year, but still affects antecedent soil moisture conditions at the onset of snowmelt infiltration and therefore also the level of slide activation. These findings are used to establish specific thresholds for exacerbated slide movement using annual snowpack accumulation, forecasted snowmelt rate, and the previous year’s snowmelt, an approach which may be applied for predicting movement at this and other recurring or potential slide sites.