This paper describes a flood warning system that increases the mitigation time before the onset of a flood. This flood warning system consists of “hardware, software, plans and procedures, and personnel.” A longer mitigation time is possible through “a reduction in the time required to collect data, to evaluate and identify the flood threat, to notify emergency personnel and the public, and to make decisions about the appropriate response.” This article evaluates damage reduction via expected damage computation procedures. This system is demonstrated using a case study from the Sacramento River basin in California. The benefit of such a warning system is that there is a substantial decrease in damage. It is suggested that this flood warning system can be used for various floods.