Physical activity is a key health behavior that reduces disease risk, and yet most older adults are not very active. This study examined time-varying associations between physical activity and a recognized barrier, namely, precipitation. And it examined the moderating role of physical activity intentions and functional mobility on precipitation-physical activity associations.One hundred and twenty-six older adults (M age = 72 years; 64% women) from Metro Vancouver provided health and background information and wore triaxial accelerometers for up to 10 consecutive days. Daily weather information was collected from local weather stations.Multilevel models corroborate previous research by showing that older adults engaged in less physical activity on days with increased precipitation across four indices: activity counts, step counts, minutes of moderate to vigorous physical activity (MVPA), and bout-corrected minutes of MVPA. Older adults with strong physical activity intentions engaged in more physical activity overall. Physical activity intentions also modified the association between time-varying precipitation and activity counts and step counts, whereas functional mobility moderated the negative association between precipitation and activity counts and minutes of MVPA.Findings highlight the important role of time-varying influences on physical activity and how these associations are moderated by psychological and biological factors.