Healthcare costs are driven by a surprisingly small number of patients. Predicting who is likely to require care in the near future could help reduce costs by pre-empting use of expensive health care resources such as emergency departments and hospitals. We describe the design of an architecture for a joint hospital-primary care data warehouse (JDW) that can monitor the effectiveness of in-hospital interventions in reducing readmissions and predict which patients are most likely to be admitted to hospital in the near future. The design identifies the key governance elements, the architectural principles, the business case, the privacy architecture, future work flows, the IT infrastructure, the data analytics and the high level implementation plan for realization of the JDW. This architecture fills a gap in bridging data from two separate hospital and primary care organizations, not a single managed care entity with multiple locations. The JDW architecture design was well received by the stakeholders engaged and by senior leadership at the hospital and the primary care organization. Future plans include creating a demonstration system and conducting a pilot study.