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.
Geography of Oklahoma
Oklahoma sits at a frequent crossroads between three different air masses: warm, humid air from the Gulf of Mexico; warm to hot, dry air from Mexico and the Southwestern U.S.; and cold, dry air from Canada. Especially from fall to spring, Oklahoma sees frequent air mass changes, which can produce drastic swings in both temperature and humidity. Much of the state is often subjected to extremes in temperature, wind, drought, and rainfall. Most of the state lies in an area known as Tornado Alley characterized by frequent interaction between cold and warm air masses, producing severe weather, with the highest-risk months from April to June. An average of 62 tornadoes strike the state per year, making that one of the highest rates in the world. Due to its position between zones of differing prevailing temperature and winds, weather patterns within the state can vary widely between relatively short distances. Precipitation occurs year-round, but average monthly precipitation is generally lowest in the winter months, rises dramatically to a peak in May (the year's wettest month virtually statewide, owing to frequent, and not uncommonly severe, thunderstorm activity), and decreases again by mid-summer, when long stretches of hot, dry weather are common in July and August many years. Early to mid fall (September and October) often sees a secondary precipitation maximum. From late October to December, precipitation generally decreases again.