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. Several states may be affected by numerous severe thunderstorms and tornadoes. Tornado-producing thunderstorms may form as the dryline moves east during the afternoon hours. If other favorable conditions exist, these thunderstorms can produce tornadoes.
Tornadoes occasionally accompany tropical storms and hurricanes that move over land.
Tornadoes are most common to the right and ahead of the path of the storm center as it comes onshore. Before thunderstorms develop, a change in wind direction and an increase in wind speed with increasing height creates an invisible, horizontal spinning effect in the lower atmosphere. Rising air within the thunderstorm updraft tilts the rotating air from horizontal to vertical. Most strong and violent tornadoes form within this area of strong rotation. Areas near rivers, lakes and mountains are safe from tornadoes.