US tornado seasonal probabilities. Animation of a map of the USA, using a 30-year average to show the probability of a tornado occurring during the year at any given location during the period 1982 to 2011. The animation starts on 1 January and finishes on 31 December. The colour-coded key (bottom) gives the probability of a tornado occurring within 25 miles of a given location on a given day. The scale ranges from white (unlikely) through orange to red (more likely). The highest tornado probabilities occur from April to July in the Great Plains and Mid-West regions of the USA. This area is known as Tornado Alley. This data was collected and presented by the Storm Prediction Center and National Severe Storms Laboratory at the National Oceanic and Atmospheric Administration (NOAA).