Abstract The Southern Great Plains experience fluctuating precipitation extremes that significantly impact agriculture and water management. Despite ongoing efforts to enhance forecast accuracy, the underlying causes of these climatic phenomena remain inadequately understood. This study elucidates the relative influence of the tropical Pacific and Atlantic basins on April-May-June precipitation variability in this region. Our partial ocean assimilation experiments using the Community Earth System Model unveil the prominent role of inter-basin interaction, with the Pacific and Atlantic contributing approximately 70% and 30%, respectively, to these inter-basin contrasts. Our statistical analyses suggest that these tropical inter-basin contrasts could serve as a more reliable indicator for late-spring precipitation anomalies than the El Niño Southern Oscillation. The conclusions are reinforced by analyses of seven climate forecasting systems within the North American Multi-Model Ensemble, offering an optimistic outlook for enhancing real-time forecasting of late-spring precipitation in the Southern Plains. However, the current predictive skills of the inter-basin contrasts across the prediction systems are hindered by the lower predictability of the tropical Atlantic Ocean, pointing to the need for future research to refine climate prediction models further.