A testbed provides a physical environment for researchers, partners, and users to work side-by-side in order to evaluate research results and predictive tools. The key goal for the Testbed Activity is to translate what was learned in the research activities and workshops into tangible outcomes, products, and tools for decision makers. For example, we may learn in the Research Priorities Workshop that water managers see the impacts of a dam break on a reservoir as their worst-case scenario from an S2S extreme precipitation event. We also may learn in the Product Definition Meeting that water managers need predictions for a range of decision thresholds (e.g., 6 inches of precipitation over 14 days, 12 inches over 30 days) at least two weeks in advance to release excess water from reservoirs. But until researchers and stakeholders sit side-by-side and discuss what information is critical, we likely will not complete our databases, analyses, and predictive models sufficiently to enable future development of tools that enhance societal preparedness and resilience against extreme precipitation impacts.