| http://www.w3.org/ns/prov#value | - Some tornadoes may also contain secondary vortices (also referred to as suction vortices, subvortices, multiple, and satellite vortices).Tornadoes have been observed on all continents except Antarctica but are most common in the United States, where the average number of reported tornadoes is roughly 1000 per year, with the majority of them on the central plains and in the southeastern states (see
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