Do tornadoes only occur in North America?

Dear Cecil: I have never heard of a tornado occurring outside North America. Is this weather phenomenon unique to North America? Is this because only North America has mobile home parks which attract tornadoes? The straight dope, please. Dean, Dallas

Cecil replies:

Silly boy. Tornadoes occur throughout the world. I have reports here of tornadoes from Moscow, Peshawar (Pakistan), even Vienna. But they do occur most frequently in North America, and in particular in the central plains of the U.S. Something like 700 tornadoes a year occur in the U.S.; Australia, with 200, is a distant second.

Roughly 90 percent of U.S. twisters occur in a 300-mile wide corridor extending from West Texas to Canada. That’s because conditions there are ideal for tornado formation. First you get warm, moist surface winds blowing up from the Gulf of Mexico, while cool high-altitude winds blow over the tops of the Rockies. This situation is inherently unstable because cool air wants to sink while warm air wants to rise. However, for reasons we need not delve into here, the mountain air causes a temperature inversion, which prevents the warm surface air from rising. It’s like clamping the lid on a pressure cooker. The surface weather systems build up a big head of steam until they break through the inversion, whereupon they shoot up to towering heights. This sets in motion the violent up- and downdrafts that lead, through circumstances still imperfectly understood, to the formation of more tornadoes than anywhere else in the world.

Cecil Adams

Send questions to Cecil via cecil@straightdope.com.