A downdraft is a volume of sinking air that originates from a convective storm. The air sinks due to negative buoyancy (being colder and thus denser than the surrounding air). A downburst is common from convective storms and when intense evaporative cooling aloft produces negative buoyancy. An analogy to a downburst is a water balloon thrown to the concrete. The water will splash in all directions but the splash will be more directed in the angle that the balloon hit the concrete. The diagram below shows the pattern produced from a downdraft. The damage pattern will show a downdraft center with wind directions originating radially out of the contact center. The wind speed and thus damage can be more in a particular direction. This is because the forward motion of the storm and the downdraft approaching the surface at an angle will produce a stronger wind due to the forward motion of the downdraft as it sinks toward the ground. Longer vectors are drawn where the winds are stronger at the surface. The damage tends to fall in the direction the wind is moving toward. From example, a strong wind from the west will cause most trees to fall down toward an easterly direction. A tornado damage pattern will tend to produce a streak across the surface. The damage can be much more in one direction that another. For example, a ¼ mile wide tornado that moves along the surface for 2 miles will have a damage pattern that is 8 times greater in one direction than another. The tornado damage pattern is also much more chaotic. There is a 360 degree variation in wind direction in the vicinity of the tornado. This produces a wind from all directions over the locations the tornado moves over. The diagram below shows a damage pattern from a tornado but it is more disorganized than what is shown in the diagram. Places that the tornado just misses will tend to have a wind direction that does not vary near as much as the locations that are directly struck by the tornado. The damage is chaotic in the path of the tornado and tends to occur in a band of damage. When damage surveys are done, the pattern of the damage helps the surveyor determine if a tornado occurred or if a downdraft occurred.  |