- ''For the book by William S. Burroughs, see Tornado Alley (book).
Tornado Alley is a colloquial term most often used in reference to the area of the United States in which tornadoes are most frequent. Although an official location is not defined, the areas in between the Rocky Mountains and Appalachian Mountains are the areas usually associated with it.
Although no state
is entirely free of tornadoes
, they are most frequent in the Plains
area between the Rocky and Appalachian Mountains and in the state of Florida
. The state where twisters most commonly occur is Oklahoma
(notably due to its nature and the area where tornadoes can occur). When land area is taken into account, however, Florida
has the highest density of tornado occurrence in the country. However nearly all of Florida's tornadoes are weak, short lived and not produced by supercell
thunderstorms that originate from cumulonimbus clouds; Oklahoma
has the highest occurrence of such "classic" supercellular tornadoes. In contrast, the Northeast
tend to be the least tornado-prone regions in the United States.
Although Tornado Alley is generally considered to be in the areas of the Central United States
, no official definition of the term has actually been produced by the National Weather Service
. According to the National Severe Storms Laboratory FAQ, "Tornado Alley" is a term created by the media to refer to areas that have greater numbers of tornadoes. There are several ideas of what Tornado Alley is, but those ideas are the result of the different criteria used to refer to it.
Significant Tornado Alley
Perhaps the most common definition of tornado alley is the location of where the strongest tornadoes occur most frequently. In the United States that location is from Texas
, northward through Oklahoma
, and into South Dakota
. States to the east of this region do experience strong tornadoes, however they do not occur with the frequency as they do in states to the west.
Another criterion for determining Tornado Alley is to not focus on just the strongest tornadoes, but the location of where tornadoes happen more frequently relative to other places in the country. When using this method tornado alley has a much wider reaching grasp. In addition to Significant Tornado Alley, this area can include the great lowland areas of the Mississippi
and lower Missouri River
valleys, as well as the Southeast
Time of year
Also to be considered is the time of year. The highest frequency of tornadoes, commonly (but incorrectly) called "tornado season", shifts geographically depending on the season. During the winter
months the Southeastern United States
receives the highest number of tornadoes. During the months of March - May the threat shifts into the central United States. Then during the summer months the highest concentration of tornadoes tends to shift farther north as the weather warms across the U.S. Technically speaking, however, the central plains
may be considered part of the tornado alley almost all-year-round, since this is where "temperature swings" between warm and cold air are most common.
The nickname "Dixie Alley
" is sometimes used for the areas in the southeastern U.S.–notably the lower Mississippi Valley
and the upper Tennessee Valley
–which are particularly vulnerable to strong tornadoes. More people have been killed by tornadoes in this particular region than those of the Great Plains because of the higher population density in the southeastern United States. The term Dixie Alley is used extensively by The Weather Channel
In the heart of tornado alley, building codes
are often stricter than those for other parts of the U.S., requiring strengthened roofs and more secure connections between the building and its foundation
. Other common precautionary measures include the construction of storm cellars
, and the installation of tornado sirens
. Tornado awareness and media
weather coverage are also high.
Some studies suggest that there are also smaller tornado alleys located across the United States.