A severe thunderstorm warning means there is significant danger for the warned area. In rare instances, severe thunderstorms can and do produce a tornado without warning. Frequently, a severe thunderstorm will produce serious wind damage as severe as a tornado. Some storms, especially in the Great Plains, may produce massive hailstones the size of baseballs or even grapefruit, falling fast enough to kill a person by repeated blunt trauma. Everyone in the path of such a storm should take cover immediately, as it is a very dangerous and posibly life-threatening.
A warning must not be confused with a severe thunderstorm watch.