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 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 ...

activity consisting of a series of

tornado outbreak __NOTOC__ A tornado outbreak is the occurrence of multiple tornadoes 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 l ...

s over multiple days with no or very few days lacking tornado outbreaks. Major tornado outbreak sequences occurred in the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...

in May

1917 Events Below, the events of World War I have the "WWI" prefix. January * January 9 – WWI – Battle of Rafa: The last substantial Ottoman Army garrison on the Sinai Peninsula is captured by the Egyptian Expeditionary Fo ...

, 1930, 1949, 1965, 1974, 2003, and 2011. Another exceptional outbreak sequence apparently occurred during mid to late May 1896. Although some days lacked tornado outbreaks, the period from mid to late April 2011 and late May 2019Scientists forecasted late May tornado outbreak nearly four weeks before it ripped through U.S.
/ref> also were periods of especially high tornado activity. Tornado outbreak sequences tend to dominate the tornado statistics for a year and often cause a spike in tornado numbers for the entire year. Not all periods of active tornado occurrences are outbreak sequences, there must be no break in the activity to satisfy the definition. Active periods occur ranging from every year to every several years whereas continuously active periods are less common and can be rare depending on the parameters applied to define a sequence. By the late 2010s, medium to long range

forecasting Forecasting is the process of making predictions based on past and present data. Later these can be compared (resolved) against what happens. For example, a company might estimate their revenue in the next year, then compare it against the actual ...

advanced sufficiently that some periods of high tornado activity can be somewhat reliably predicted several days to several weeks in advance.

See also

References

Further reading