<P> Tornadoes are most common in spring and least common in winter . The seasonal transition during autumn and spring promotes the development of extratropical cyclones and frontal systems that support strong convective storms . Tornadoes are also common in landfalling tropical cyclones, where they are focused in the right poleward section of the cyclone . Tornadoes can also be spawned as a result of eyewall mesovortices, which persist until landfall . However, favorable conditions for tornado development can occur any time of the year . </P> <P> Tornado occurrence is highly dependent on the time of day, because of solar heating . Worldwide, most tornadoes occur in the late afternoon, between 3 pm and 7 pm local time, with a peak near 5 pm . Destructive tornadoes can occur at any time of day, as evidenced by the Gainesville Tornado of 1936 (one of the deadliest tornadoes in history) that occurred at 8: 30 am local time . </P> <P> The United States has the most tornadoes of any country . Many of these form in an area of the central (with some definitions including Southern) United States known as Tornado Alley . This area extends into Canada, particularly the Prairie Provinces and Ontario; however, activity in Canada is less frequent and intense than that of the US . The high frequency of tornadoes in North America is largely due to geography, as moisture from the Gulf of Mexico is easily advected into the midcontinent with few topographic barriers in the way . The Rocky Mountains block Pacific - sourced moisture and buckle the atmospheric flow, forcing drier air at mid-levels of the troposphere due to downsloping winds and causing cyclogenesis downstream to the east of the mountains . Downsloping winds off the Rockies force the formation of a dry line when the flow aloft is strong, while the Gulf of Mexico fuels abundant low - level moisture . This unique topography allows for frequent collisions of warm and cold air, the conditions that breed strong, long - lived storms throughout the year . This area extends into Canada, particularly Ontario and the Prairie Provinces, and strong tornadoes can also occur in northern Mexico . </P> <P> A large region of South America is characterized by storms that reach the level of supercells and produce intense hailstorms, floods, and tornadoes during the spring, summer, and early fall . The region recently appointed as the Tornado Corridor (South America) is considered as the second largest in the world in terms of the formation of extreme weather events . It covers most of central Argentina, southern Paraguay, southeastern Brazil, and Uruguay . </P>

Which continent experiences the highest number of tornadoes per year