Ah, the tri-state tornado. So large is was said to resemble a boiling mass of clouds at ground level. The roar it produced was so loud that it made people become disoriented and vomit.
I’d also recommend checking out the Super Outbreak (http://en.wikipedia.org/wiki/Super_Outbreak) A devastating outbreak of tornadoes on april 3–4 of 1974. At one point during this outbreak, there were more F5 tornadoes in a day than there were in any other year.
There’s also the Daultipur-Salturia tornado (http://en.wikipedia.org/wiki/Daultipur-Salturia_Tornado) which is the deadliest single tornado in the history of the world.