Tornadoes can wreak havoc any time of the year, touching down in every continent except Antarctica, but are most common during the spring months, especially in the United States.
Tornadoes can occur wherever dry polar air sits atop moist, warm air in the troposphere, and the unstable air rises rapidly, forming a tunnel. They are considered the most powerful, unpredictable and destructive weather systems on earth and are usually associated with a severe thunderstorm. An average tornado has maximum wind speeds of 112 miles per hour, a 250-foot width and travels one mile before dispersing.
Tornadoes are ranked on severity using the Fujita Scale (see below) with numbers from zero to six, based in the degree of observed damage.
According to livescience.com, the United Kingdom reports the most tornadoes by land area. However, a 2013 Lloyd’s of London report points out that the U.S. experiences more tornadoes that any other country in the world.
Approximately 75 percent of the world’s known tornadoes occur in the United States because of its tornado climatology in terms of frequency, intensity and destructive outbreak events. An article published on ustornadoes.com claims that the U.S. is the uncontested heavyweight tornado champion of the world.
Tornado Alley, in fact, is a term that refers to a wide tornado-prone area between the Rocky Mountains and Appalachian Mountains that experience tornadoes frequently. The borders, although not clearly defined, start in central Texas and head north through Oklahoma, Kansas, Nebraska and eastern South Dakota, and head east through Iowa, Missouri, Illinois, Indiana and Ohio. Other reports say that Florida has its own Tornado Alley because it has numerous tornadoes each year, many of which are considered mild.
Already this year, Wikipedia reports 202 U.S. tornadoes, of which at least 141 have been confirmed (as of March 21, 2016).
Following is a brief look at where the remaining 25 percent of the world’s tornadoes normally strike.
Canada. Canada receives 5 percent of world’s tornadoes, although its tornadoes are more likely to occur in the summer. Canada experiences an average 60 to 100 confirmed tornadoes a year. The Canadian plains and prairies that include southern Alberta, Saskatchewan and Manitoba have flat, open terrain, similar to that of the U.S. Great Plains, which is prone to clashes of Gulf of Mexico air and colder arctic air.
Bangladesh. Right behind Canada in the most reported tornadoes is Bangladesh, which is known for both its violent tornado outbreaks and high tornado fatality rate. Bangladesh is densely populated with a high poverty rate. Since many of its structures are not build to withstand tornadoes, fatality rates are 30 or more per tornado on average.
Europe. The United Kingdom has about 30 annual tornadoes and Germany around 10. Russia, part of which is in Europe, receives the most tornadoes in this region, although most are weak and are not reported.
Australia. Between 20 and 25 tornadoes, on average, are reported in this country each year. Meteorologists believe that more occur in desolate or low-populated areas but are not registered. Most of Australia’s tornadoes are caused by land-falling tropical cyclones, particularly in the country’s southeastern areas.
South Africa. Most of this country’s tornadoes are mild and occur between October and February—its spring and summer months.
Argentina. Although Argentina does not have a high frequency of tornadoes, it does experience the strongest ones in the southern hemisphere.
For information about preparing for a tornado from the Red Cross, click here.
Note: Most of the information in this blog post was gathered from the 2013 usatornadoes.com report entitled, “From domestic to international: Tornadoes around the world.”