Tornado Alley
It has also been asserted that there are numerous Tornado Alleys. In addition to the Texas/Oklahoma/Kansas core, such areas include the Upper Midwest, the lower Ohio Valley, the Tennessee Valley and the lower Mississippi valley. Some studies suggest that there are also smaller tornado alleys located across the United States.
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.