During a 4-day period from April 25-28, 2011, more than 200 tornadoes occurred in five southeastern states. The deadliest part of the outbreak was the afternoon and evening of April 27, when a total of 122 tornadoes resulted in 313 deaths across central and northern Mississippi, central and northern Alabama, eastern Tennessee, southwestern Virginia, and northern Georgia. Three additional lives were claimed by tornadoes in the pre-dawn hours ofApril 27 bringing the daily total to 316. There were 15 violent (Enhanced Fujita Scale 4 or 5) tornadoes reported. Eight of the tornadoes had path lengths in excess of 50 miles. Two of the tornadoes-one in northern Alabama and another that struck the Tuscaloosa and Birmingham areas in Alabama-each claimed more than 60 lives.The magnitude of this event resulted in the formation of a multi-agency Service Assessment Team to evaluate the warning and forecast services provided to key decision makers and the public. In keeping with the National Oceanic and Atmospheric Administration's vision for a Weather-Ready Nation and the goals of supporting the development of hazard-awarecommunities, the team was also tasked to identify the societal impacts of NWS products and services. The team investigated possible reasons for the large loss of life during this event.Significant tornado events impacted portions of the southeast United States on April 15, and the St. Louis metropolitan area on April22. A devastating tornado struck Joplin, Moon May 22. The National Weather Service conducted service reviews following each of these events. The NWS regional reviews of the North Carolina/South Carolina/Virginia U.S. Tornado Outbreak, led by Mickey Brown (NWS Eastern Region Deputy Director), and the St. Louis Metropolitan Area Tornado Event, led by Rick Shanklin (Warning Coordination Meteorologist, NWS WFO Paducah, KY), are included in this service assessment as appendices. The regional review forthe Joplin, Missouri, Tornado- May 22, 2011, led by Richard Wagenmaker (Meteorologist in Charge, NWS WFO Detroit, Ml), was publicly released in September 2011 and not included in this document.The facts, findings, recommendations, and best practices from this assessment are offered with the goals of 1) improving the quality of warning and forecast products and services; 2) enhancing collaboration with local, state, and federal preparedness partners; and 3) increasing public education and awareness regarding issues associated with tornado safety. The ultimate goal is to help the National Weather Service meet its mission to protect lives and property and enhance the national economy.