Tornado season hits an historically dangerous peak this week

The anniversaries of four of the 10 deadliest tornadoes in United States history all occur within the next 22 days starting Friday. Those include the May 22, 2011, EF-5 tornado that hit Joplin, Missouri, through to the June 12, 1899, EF-5 twister that struck New Richmond, Wisconsin.

The other two were the Great St. Louis Tornado on May 27, 1896, considered now to be an EF-4, and the EF-5 tornado that hit Flint, Michigan, on June 8, 1953.

May and June are the peak months for tornadoes in the United States, with an average of 269 occurring in May and an average of 229 in June, according to National Oceanic and Atmospheric Administration (NOAA) data from 1991-2015.

Improved forecasting, the use of Doppler radar and better early warning systems have led to a significant drop in the death toll from tornadoes, despite increasing populations in tornado-prone areas. The Joplin, Missouri, event is the only one of America's 10 deadliest tornadoes to have occurred in the last 67 years.

Worldwide, tornado record-keeping is spotty because twisters often strike in unpopulated or unobserved areas and the technology in some places is not as robust. But it's estimated that the U.S. experiences roughly three to four times the annual number of tornadoes of the rest of the world combined.

An average of between 1,253 and 1,297 tornadoes occur annually in the U.S., while other countries combined get roughly between 300 and 400 a year. Canada, Russia, the United Kingdom and Bangladesh would round out the world's top five hot spots.

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In fact, Bangladesh is widely considered to have experienced the world's deadliest recorded tornado on April 26, 1989, which leveled a path of destruction from Daultipur to Saturia and was responsible for more than 1,300 deaths and more than 12,000 injuries.

Although tornadoes can occur at any time, the U.S. tornado season typically runs from March through November or sometimes into early December. Tornadoes cause an average of 80 U.S. fatalities annually, and tornadoes and their destruction killed a total of 41 people in 2019. A total of 73 tornado-related fatalities have occurred so far in 2020, the most by this time of year since the devastating 2011 season when there were 366 by May 18.

The current average number of U.S. tornadoes per year based on long-term data is lower than what actually occurs each year. That's because the number of tornadoes reported annually has been rising over the past few decades mainly because more are reported as the U.S. population has risen and more people have access to mobile devices and cameras. Many tornadoes of the past were not seen or recorded; this change may amount for an increase of reported tornadoes of up to 20 percent over the last 40 years and 10 percent over the past 20 years.

Here are the 10 deadliest documented tornadoes in U.S. history.

1. Tri-State Tornado, March 18, 1925: 695 deaths
2. Nachez, Mississippi, May 6, 1840: 317 deaths
3. The Great St. Louis Tornado, May 27, 1896: 255 deaths
4. Tupelo, Mississippi, April 5, 1936: 216 deaths
5. Gainesville, Georgia, April 6, 1936: 203 deaths
6. Texas/Kansas/Oklahoma tornado: April 9, 1947: 181 deaths
7. Joplin, Missouri, May 22, 2011: 158 deaths
8. Amite, Louisiana/Purvis, Mississippi, April 24, 1908: 143 deaths
9. New Richmond, Wisconsin, June 12, 1899: 117 deaths
10. Flint, Michigan, June 8, 1953: 116 deaths.