The primary purpose of this research program is to confirm the spontaneous planning behavior in post-disaster operations while at the same time contribute to the development of the concept in a tornado type disaster. An additional goal also includes examining how the process takes place in resolving unanticipated problems as a disaster unfolds. This study uses qualitative methodology which is case study to probe the concept of spontaneous planning behavior to solve unexpected challenges as a disaster develops. Specifically, semi-structured, open-ended questions were utilized to collect data from stakeholders in eleven functional organizations in three impacted cities during the North Texas April 3, 2012, tornadoes. Findings indicate that debris removal and ensuring public safety, search and rescue, securing damaged neighborhoods, activation of emergency operations centers, damage assessment, restoration of communication system, public relations and media, and volunteer and donation management activities appear to have benefited from spontaneous planning behavior. Further findings suggest that the driving forces behind the phenomenon were gathering valuable new information, learning opportunity within the disaster, relative freedom and significant high degree of discretion, response was innovative with flexibility, and solutions waiting for problems features proposed in the integrated decision-making model (IDMM). However, it was uncovered that interview respondents’ answers tend to indicate that mixed organizational structures helped in problem resolutions rather than just flat organizational structure as some decision making literature may suggest. Analysis of this decision-making model expanded the understanding of how spontaneous planning behavior took place in resolving unforeseen problems in post-disaster operations. This research project confirmed the concept of spontaneous planning in the North Texas tornadoes as well as suggesting how it occurred. The research program validates spontaneous planning behavior in tornadoes; advances and develops the concept of spontaneous planning; increases understanding, description, and management of post-disaster operations; improves emergency management operations; promotes spontaneous planning as a key principle among responders and others involved in emergency management; and proposes IDMM as a useful model that explains decision-making behavior during a disaster.