Tornadoes are extremely complex wind events that cause damage ranging from minimal or minor to absolute devastation. In a simplified tornado model, there are three regions of wind: (1) Near the surface, close to the core or vortex of the tornado. In this region, the winds are complicated and include the peak low level wind speeds, but are dominated by the tornado's strong rotation. It is in this region that strong upward motions occur that carry debris upward, as well as around the tornado. (2) Near the surface, away from the tornado's core or vortex. In this region, the flow is dominated by inflow to the tornado. The inflow can be complicated and is often concentrated into relatively narrow swaths of strong inflow rather than a uniform flow into the tornado's core circulation. (3) Above the surface, typically above the tops of most structures, the flow tends to become very nearly circular. In an actual tornado, the diameter of the core or vortex circulation can change with time, so it is impossible to say precisely where one region of the tornado's flow ends and another begins. Also, the visible funnel cloud associated with and typically labeled the vortex of a tornado is not always the edge of the strong extreme winds. Rather, the visible funnel cloud boundary is determined by the temperature and moisture content of the tornado's inflowing air. The highest wind speeds in a tornado occur at a radius measured from the tornado core that can be larger than the visible funnel cloud's radius. It is important to remember that a tornado's wind speeds cannot be determined just by looking at the tornado. (FEMA, Building Performance Assessment Report: Midwest Tornadoes of May 3, 1999, July 13, 1999, p. 2-4)