Tornado climatology
Tornadoes have been recorded on all continents except Antarctica and are most common in the middle latitudes where conditions are often favorable for convective storm development. The United States has the most tornadoes of any country, as well as the strongest and most violent tornadoes. A large portion of these tornadoes form in an area of the central United States popularly known as Tornado Alley. Other areas of the world that have frequent tornadoes include significant portions of Europe, South Africa, Philippines, Bangladesh, parts of Argentina, Uruguay, and southern and southeast Brazil, northern Mexico, New Zealand, and far eastern Asia.
Tornado climatology
Some people mistakenly believe that tornadoes only occur in the countryside. This is hardly the case. While it is true that the plains states are the most tornado-prone places in the nation, it should be noted that tornadoes have been reported in every U.S state, including Alaska and Hawaii. One likely reason tornadoes are so common in the central U.S is because this is where Arctic air, cold fronts that have not been "weakened" yet first collide with warm tropical air from the Gulf of Mexico. As these fronts head further east, they sometimes lose their strength as they travel over more warm air. For this reason, tornadoes are not as common on the East Coast as they are in the Midwest. However, they have happened on rare occasion, such as the F3 twister that struck Limerick Township, Pennsylvania near Philadelphia on 27 July 1994, the F2 twister that struck the northern suburbs of New York City on 12 July 2006, the EF2 twister in the borough of Brooklyn on 8 August 2007, or the F4 twister that struck La Plata, Maryland on 28 April 2002.