In May 2012, there were no tornado deaths in the United States. How unusual was that?
We can look at the record of tornado deaths, discussed here, dating back to 1875. The last time there were no deaths in the month of May was in 2005. Prior to that, it was 1994. Overall, there have been 15 years in the 138 years of the record (1875-2012) with no deaths in the month of May, so we’d expect that to happen about once every decade.
May 2012 stands in dramatic contrast to May 2011, when 178 people died in tornadoes, 158 of them in the Joplin, Missouri tornado of 22 May. 178 deaths is the fifth highest death toll in the period 1875-2012, and the largest since 211 people died in 1933. The deadliest May on record was 1896, when 502 people were killed, including 255 in the Saint Louis, MO-East Saint Louis, MO tornado of 27 May. Adjusted for wealth of the country, that tornado was the costliest in US history, with damage adjusted to 2011 dollars of over $6 billion.