29th April 2011 - Deadliest tornadoes since 1974 rip apart towns and lives in six US states

An article in the Guardian website yesterday states the following:

Death toll close to 300 after severe storm batters south, with authorities warning of more to come

The national weather service said the storms were the most ferocious some of their forecasters had ever seen; the deadliest since tornadoes in 1974 killed 315 people.

The tornado in 1974 is referred to as the Super Outbreak.

A worse outbreak was experienced by North America in 1925 with the Tri-State Tornado event that killed 695.

But are tornado events becoming more severe or frequent? According to a 2010 study in the The Open Atmospheric Science Journal, 2011 entitled Detection of Tornado Frequency Trend Over Ontario, Canada one of the conclusions was that "It is found for the first time that over the last six decades the tornado frequency exhibits an increasing trend but also that "More research work needs to be carried out in the future in order to detail the physical processes responsible for the detected tornado frequency trend."