Although tornadoes occur in many parts of the world, these destructive forces of nature are found most frequently in the United States east of the Rocky Mountains during the spring and summer months.
Thunderstorms develop in warm, moist air in advance of eastward-moving cold fronts.
These thunderstorms often produce large hail, strong winds, and tornadoes. Tornadoes in the winter and early spring are often associated with strong, frontal systems that form in the Central States and move east. Occasionally, large outbreaks of tornadoes occur with this type of weather pattern. Tornado-producing thunderstorms may form as the dryline moves east during the afternoon hours. If other favorable conditions exist, these thunderstorms can produce tornadoes.