strong land-tornadoes have hit Florida and reports show Florida has a very high number of overall tornadoes, the tornadoes in the state seldom reach the velocity of those that may occur in the Southern Plains. In the United States, tornadoes typically occur in late spring and early summer during the changing season patterns as a warm air mass typically collides with a cold air mass resulting in tornadoes. Another criterion for the location of Tornado Alley can be where the strongest tornadoes occur more frequently. Tornado Alley can also be defined as an area reaching from central Texas to the Canadian Prairies and from eastern Colorado to western Ohio. Some researchers argue that there are several Tornado Alleys. In addition to the Texas/Oklahoma/Kansas core, such other areas include the Upper Midwest, the lower Ohio Valley, the Tennessee Valley, and the lower Mississippi valley, which may have respective distinguishing characteristics. A coherent conception considers that there is a single Tornado Alley in the United States and Canada, and that this can simply be subdivided into smaller areas based on regional attributes. The extension of the North American tornadically active in the southeastern U.S., notably the lower Mississippi Valley and the upper Tennessee Valley, are sometimes called by the nickname "Dixie Alley", coined in 1971 by Allen Pearson, former director of the National Severe Storms Forecast Center (NSSFC). A 2018 study found in the U.S., over the study period 1979-2017, an overall eastward shift of tornado frequency and impacts - toward Dixie Alley. The study found, since 1979, relatively-lower tornado frequency and impacts in parts of the traditional Tornado Alley, especially areas from north-central Texas toward the Houston, TX area, and relatively-higher tornado frequency and impacts in parts of the Mid-South, especially eastern Arkansas, the greater Memphis, TN area and northern Mississippi - all areas near the heart of Dixie Alley - see especially Figure 4. In Tornado Alley, warm, humid air from the equator meets cool to cold, dry air from Canada and the Rocky Mountains. This creates an ideal environment for tornadoes to form within developed thunderstorms and supercells. Origin of the term The term "tornado alley" was first used in 1952 by U.S. Air Force meteorologists Major Ernest J. Fawbush (1915–1982) and Captain Robert C. Miller (1920–1998), as the title of a research project to study severe weather in parts of Texas and Oklahoma. Impact Despite the elevated frequency