A tornado is a rapidly rotating column of air that extends from a thunderstorm to the ground. It forms when warm, moist air near the surface meets cooler, dry air above, creating instability in the atmosphere. Tornadoes can vary in size and intensity, with the strongest ones classified as EF5 on the Enhanced Fujita scale, capable of causing severe damage. Tornadoes are most common in the United States, particularly in an area known as "Tornado Alley." They can occur in any season but are most frequent in spring and early summer. Safety measures, such as seeking shelter in a sturdy building, are crucial during tornado warnings.