Tornado Alley
Although the official boundaries of Tornado Alley are not clearly defined, its core extends from northern Texas, Oklahoma, Kansas, Nebraska, into South Dakota. States such as Missouri, Iowa, Minnesota, Wisconsin, Illinois, Indiana, and western Ohio are sometimes included in Tornado Alley. Some research suggests that tornadoes are becoming more frequent in the northern parts of Tornado Alley where it reaches the Canadian prairies.
Climate of Oklahoma City
Oklahoma City has a very active severe weather season from March through June, especially during April and May. Located in the center of a region colloquially known as Tornado Alley, Oklahoma City is prone to especially frequent and severe tornadoes, as well as very severe hailstorms and occasional derechoes. Tornadoes have occurred in every month of the year in Oklahoma City, and a secondary smaller peak also occurs during the early autumn, especially in mid-September to late-October. The Oklahoma City metropolitan area is one of the most tornado-prone major cities in the world, with about 150 tornadoes striking within the city limits since 1890. Since the time weather records have been kept, Oklahoma City has been struck by thirteen violent tornadoes, eleven F/EF4's and two F/EF5's. On May 3, 1999 parts of southern Oklahoma City and nearby suburbs suffered one of the most powerful tornadoes on record, an F5 on the Fujita scale, with wind speeds estimated by radar at . On May 20, 2013, far southwest Oklahoma City, along with Newcastle and Moore, was hit again by another EF5 tornado; that one was wide and killed 23 people. On May 31 of that same year, another outbreak affected the Oklahoma City area, including an EF1 and an EF0 within the city and a tornado several miles west of the city that was in width, the widest tornado ever recorded, and it, as was the May 3, 1999 F5, was one of the most powerful tornadoes on record.