A severe thunderstorm is a thunderstorm with winds 56 mph (90 km/h) or greater, 3/4 inch (2 cm) or larger hail, or tornadoes. These storms also can contain deadly cloud-to-ground lightning, heavy downpours which can lead to localized flooding, gusty winds, and possible tornadoes.
Severe thunderstorms may occur as a Supercell_thunderstorm or in a line with other non-severe storms.
See also: Severe thunderstorm watch, Severe thunderstorm warning, Tornado watch, Tornado warning.