As agencies progress toward mechanistic-empirical flexible design procedures, it is critical to quantify the relationships between climate factors and the resulting seasonal variations in pavement layer moduli for a given region. This was investigated for flexible pavement structures and climate conditions specific to Minnesota. The objective of this study was to quantify the relationships between climate factors, subsurface conditions, and pavement material properties for use in a mechanistic-empirical design procedure that reflect conditions specific to Minnesota. The approach used to establish these relationships may suggest possible directions for similar studies in other regions. The data used in this study were obtained from the Minnesota Road Research Project, located on Interstate 94 in central Minnesota. The extensive instrumentation, on-site weather station, and deflection testing performed at this facility provide valuable environmental and pavement response data. The results show that the maximum stiffness for the pavement layers occurs in the winter, and the minimum stiffness occurs at different periods in a typical year for the different layers. The asphalt concrete modulus is at a minimum in the summer when temperatures are high. The base layer modulus is at a minimum in the spring thaw period, and the subgrade layer modulus is at a minimum in the late spring and summer months. The seasonal variations in pavement layer moduli are used to establish seasonal factors for each layer which describe the modulus cycling in a typical year. These factors may be applied to a mechanistic-empirical design procedure specific to Minnesota.