Here's why the US experiences more tornadoes than any other country.
Editor’s Note: The CNN Original Series “Violent Earth with Liev Schreiber” delves into the increasingly frequent and severe weather events driven by our changing climate. The premiere episode, focusing on tornadoes, airs on Sunday, June 2 at 9pm ET/PT.
The US averages over 1,150 tornadoes annually, surpassing any other country. In fact, this figure exceeds the combined total of tornadoes in Canada, Australia, and all European countries.
Every state in the US has experienced at least one tornado, with some states encountering dozens each year. The US stands out in producing a significant number of tornadoes, especially the more violent ones.
On average, tornadoes cause 73 fatalities per year in the US. In contrast, Europe, where tornadoes tend to be weaker, experiences an estimated 10 to 15 fatalities annually.
Some states are particularly prone to deadly tornadoes. Texas leads with an average of 140 tornadoes each year, followed by Kansas, Florida, Oklahoma, and Nebraska. However, the sheer number of tornadoes doesn't always correlate with the death toll. For instance, Alabama averages 42 tornadoes per year—far fewer than Texas—yet it tops the list for tornado fatalities, with an average of 14 deaths annually, nearly double that of Missouri, which has eight deaths per year.
The time of day and the topography where a tornado occurs significantly impact the fatality rate.
In Alabama and other Southern states, the landscape often includes rolling hills, plateaus, and a higher density of trees compared to the Plains states like Kansas, Texas, and Nebraska, where tornadoes can often be seen from miles away. The greater visibility in the Plains allows for faster reporting of tornadoes, providing more time for people to be warned and seek shelter.
Southern states such as Tennessee, Kentucky, and Arkansas experience more tornadoes overnight than other states. This leads to higher fatalities since many people are asleep and unaware of an approaching tornado.
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“Tornadoes in the Southeast tend to be more dangerous than their Great Plains counterparts,” says Brandon Miller, CNN Meteorologist. “There are several reasons for this, both meteorological and geographic. Southeastern tornadoes often travel faster, driven by a swifter jet stream.”
All these factors contribute to a higher fatality rate in Southern states compared to the Plains. However, these regions share a common feature: ideal atmospheric conditions for tornado formation.
“The basic ingredients for severe thunderstorms that can produce tornadoes include warm, moist air near the ground, relatively dry, cool air aloft (about 10,000 to 30,000 feet), and horizontal winds in the storm environment that increase with height and change direction, blowing from the equator near the ground and from the west aloft,” explains Dr. Harold Brooks, senior scientist with the NOAA National Severe Storms Laboratory.
In the US, low-pressure systems pull warm, moist air from the Gulf of Mexico and cool, dry air from the Rocky Mountains or the High Desert in the southwest. The states situated between these regions are in an ideal location for severe weather to develop.
“No other place in the world has the combination of large warm water to the south and a wide, high range of mountains extending north to south to the west,” says Dr. Brooks. “All other tornado-prone regions have at least one suboptimal feature.”
The US leads the world in the number of tornadoes. While other countries, such as Germany, Australia, South Africa, eastern China, Japan, Bangladesh, and Argentina, also experience tornadoes, the disparity in numbers and fatalities is striking.
Despite Europe being comparable in size to the US, the frequency and fatality rates of tornadoes are significantly lower. From 2011 to 2020, the US averaged 1,173 tornadoes per year, whereas Europe averaged around 256. However, Dr. Pieter Groenemeijer, Director of the European Severe Storms Laboratory (ESSL), notes that the European figure may be underreported, particularly for weaker tornadoes in countries like France and the UK.
European Russia, west of 58 degrees East longitude, has the highest number of tornadoes annually in Europe, averaging 86. Germany follows with an average of 28 tornadoes per year.
A study on severe storms in Europe, published in December 2020, highlights that the peak density of tornado reports aligns with high population areas in Belgium, the Netherlands, and northern Germany. The study also reveals that thunderstorms are twice as frequent in the US, with up to four times more storm reports compared to Europe.
One commonality among most countries is the time of day when tornadoes occur, typically in the afternoon and early evening. However, the peak tornado season varies by region. In the US, spring is the peak season for tornado activity. In central and northern Europe, tornadoes are most common in the summer. The western and central Mediterranean regions see the most tornadoes in autumn, while the eastern Mediterranean experiences peak activity in winter.
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Outside the US, Canada ranks second in the number of tornadoes, averaging about 100 per year.
Tornadoes are not exclusive to the Northern Hemisphere. Australia experiences dozens of tornadoes annually, and South Africa also reports tornado occurrences each year. In South America, there is a tornado hotspot known as the "pasillo de los tornados," which includes Argentina, Uruguay, Paraguay, and parts of Brazil.
In New Zealand, tornadoes are relatively rare, with the National Institute of Water and Atmospheric Research reporting an average of seven to ten moderate to strong tornado events annually.
Notably, tornadoes in the Southern Hemisphere typically rotate clockwise, opposite to the counterclockwise rotation of tornadoes in the Northern Hemisphere.