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A tornado outbreak is the occurrence of multiple

tornado A tornado is a violently rotating column of air that is in contact with both the surface of the Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. It is often referred to as a twister, whirlwind or cyclone, altho ...

es spawned by the same synoptic scale weather system. The number of tornadoes required to qualify as an outbreak typically are at least six to ten, with at least two rotational locations (if squall line) or at least two supercells producing multiple tornadoes. The tornadoes usually occur within the same day or continue into the early morning hours of the succeeding day, and within the same region. Most definitions allow for a break in tornado activity (time elapsed from the end of the last tornado to the beginning of the next tornado) of six hours. If tornado activity indeed resumes after such a lull, many definitions consider the event to be a new outbreak. A series of continuous or nearly continuous tornado outbreak days is a

tornado outbreak sequence A tornado outbreak sequence, or tornado outbreak day sequence, sometimes referred to as an extended tornado outbreak, is a period of continuous or nearly continuous high tornado activity consisting of a series of tornado outbreaks over multiple days ...

. In the United States and Canada, tornado outbreaks usually occur from March through June in the

Great Plains The Great Plains (french: Grandes Plaines), sometimes simply "the Plains", is a broad expanse of flatland in North America. It is located west of the Mississippi River and east of the Rocky Mountains, much of it covered in prairie, steppe, an ...

, the

Midwestern United States The Midwestern United States, also referred to as the Midwest or the American Midwest, is one of four census regions of the United States Census Bureau (also known as "Region 2"). It occupies the northern central part of the United States. I ...

, and the Southeastern United States in an area colloquially referred to as

Tornado Alley Tornado Alley is a loosely defined area of the central United States where tornadoes are most frequent. The term was first used in 1952 as the title of a research project to study severe weather in areas of Texas, Louisiana, Oklahoma, Kansas, So ...

. Tornado outbreaks can also occur during other times of the year and in other parts of the world. A secondary less active and annually inconsistent tornado "season" in the U.S. occurs in late autumn. Very large tornado outbreaks are known as super outbreaks. The largest tornado outbreak on record was the

2011 Super Outbreak The 2011 Super Outbreak was the largest, costliest, and one of the deadliest tornado outbreaks ever recorded, taking place in the Southern, Midwestern, and Northeastern United States from April 25–28, 2011, leaving catastrophic destruction ...

, with 362 tornadoes and about $10 billion in direct damages. It surpasses the

1974 Super Outbreak The 1974 Super Outbreak was the second-largest tornado outbreak on record for a single 24-hour period, just behind the 2011 Super Outbreak. It was also the most violent tornado outbreak ever recorded, with 30 F4/F5 tornadoes confirmed. From Apri ...

, in which 148 tornadoes were counted. Both occurred within the United States and Canada. The total number of tornadoes is a problematic method of comparing outbreaks from different periods, however, as many weaker tornadoes, but not stronger tornadoes, are reported in the US in recent decades than in previous ones due to improvements in tornado detection.

References

External links

US Violent Tornado Outbreak Statistics
( SPC) {{DEFAULTSORT:Tornado Outbreak Tornado * Natural disasters

See also

References

Further reading

External links