The Fujita scale for damaging winds uses only the first digit of the Fujita-Pearson scale. The greatest incidence of tornadoes is generally assumed to be North America, and especially in the Mississippi Valley. On an equal area basis, however, other countries, such as Italy, New Zealand, and the United Kingdom, exceed or at least challenge the incidence rate of the united States. In actual numbers observed, Australia ranks second to the United States. The United States is notable for the incidence of severe tornadoes of scale 4 or 5.
Tornadoes occurring in the tropics are usually extremely weak and often begin as waterspouts.
The Stockholm, Sweden and Saint Petersburg, Russia areas appear to be the northernmost regions that experience tornadoes.