Severe drought and other extreme climate events create opportunity windows for invasion, for example by aiding dispersal or reducing biotic resistance. Pairing local environmental and resource monitoring data is instructive for understanding past invasion events. We used analyses for dynamic systems to identify climatic and biotic drivers of plant community change in a grassland monitored over a 30-year period that included decadal drought and historic flood. Short-lived non-native forbs increased following hot, dry summers and autumns, while milder springs and flood facilitated non-native grass invasion. Identifying lagged effects of seasonal climate informs which species to watch, when, for proactive management.