Why the United States Ranks Number One in Tornado Frequency in the World
There is no other country in the world that has more tornadoes per year than in the United States of America. There is a huge supply of cool, dry air that comes down from Canada, warm moist air is readily available to come up from the south, and dry air is sometimes another ingredient that is almost always present in the southwestern states and in Mexico. That is what makes the U.S. the leader in tornado activity. There is nowhere else in the world that you have better conditions more conducive to tornado development than in the heartland of the U.S. The lack of any mountain ranges running west to east allows the cold air from Canada and the Arctic region to flow south and the warm air is free to flow north unobstructed from the Gulf of Mexico. The way the continent extends all the way into the Arctic allows the cold air masses to build and to extend southward, without being modified quickly by large bodies of water. The Gulf of Mexico provides the warmth and the moisture for these storms. The dry air from the southwestern states and Mexico is needed to produce the so-called dry-line, which causes numerous tornadoes and severe thunderstorms. Strangely enough, the dry air that infiltrates the low pressure center actually makes tornadoes more likely in certain situations. Upper level winds are very often favorable in ėtornado alleyî during the late winter and spring. Winds that blow from different directions at different altitudes can cause the spin necessary to produce a tornado. Note that tornadoes can form (and usually do) during any month of the year.