The tornadoes that hit the southeastern US in April 2011 were…

The tornadoes that hit the southeastern US in April 2011 were…

The tornadoes that hit the southeastern US in April 2011 were devastating

in terms of loss of human lives and destruction of infrastructure. Tornadoes are not uncommon in parts of the US, especially from April through June, but why was the system of tornadoes that hit the southeast so powerful that it has been called the “perfect storm” by some meteorologists?  What factors do you think combined to make the recent southeastern tornadoes a “perfect storm” of destruction (hint:  more than the usual suite of factors occurred)? Was this an unusual event or do tornadoes of this extent and intensity occur more often than we realize?