The graph below shows the monthly distribution of “killer” tornadoes in the US from 1950-2011. Statistics show that the least likely month for a tornado dangerous enough to take lives is July, and the most likely is April. Note that this distribution is different than the monthly distribution for ALL tornadoes. On that graph, which is below, May is the month that has the most tornadoes. You might think that the month that has the MOST tornadoes would also be the month that has the most tornado deaths, but that is not so. There are a number of factors that affect this difference.
graph showing the months that have had the most killer tornadoes from 1950 to 2011
  1. The tornadoes that occur earlier in the year are more intense and violent than those that occur later.
  2. Since darkness falls earlier in March and April than it does in May or June, the tornadoes often strike after dark, and sometimes very late at night, when tornadoes are more difficult to spot visually, and are more likely to catch people unawares.
  3. Tornadoes that occur earlier in the year tend to be in the southern states of the US. They are often rain wrapped. Since the weather in the southern states is more temperate, the homes are built to different specifications than those in states that experience colder weather. Many homes are set on blocks rather than on a slab foundation or over a basement. They may be built of unreinforced cement or cinder blocks. A high water table in some states precludes construction of a basement. Rural poverty is prevalent in some areas. These factors make the homes and their occupants in the Southern states more vulnerable.

Take a look at our first Top Ten page, and you will notice the preponderance of southern states in the categories that mention “deaths.” The state of Massachusetts sticks out as an exception because of a single tornado that killed 94 people in 1953, and Indiana and Ohio stand out because of the many deaths in the April 11, 1965 Palm Sunday tornado and the April 3, 1974 SuperOutbreak.



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