Dear Tom,

What percentage of the world's tornadoes occurs in the U.S.?

David Plebanski, Mokena

Dear David,

Tornado researcher Tom Grazulis estimates that about 75 percent of the world's tornadoes occur in the United States. Many of the twisters that develop outside of this country are small and weak, but at least 40 countries have been hit by significant tornadoes that produced severe damage and numerous fatalities. Tornado-prone areas around the world include Canada, Japan, Australia, western Europe, Russia, Argentina, and most notably Bangladesh, where over the years tornadoes have killed thousands. In 1989, what may be the world's deadliest tornado killed more than 1,300 people there. And just last month, a series of twisters struck Bangladesh, killing at least 78 people, injuring more than 700 and leaving thousands more homeless.

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Tom Skilling is chief meteorologist at WGN-TV. His weather forecasts can be seen Monday through Friday on WGN News at noon and 9 p.m.

Write to: ASK TOM WHY, 2501 Bradley Place, Chicago, IL 60618 or asktomwhy@wgntv.com (Mail volume precludes personal response.)