This video focuses on the 2011 tornado season in the U.S., considered extreme - killing over 550 people. The material covers efforts to improve warning systems, as well as construction. (The latter seems improbable, given the fact the DVD also reported that the Joplin hospital was moved 4" off its foundation by the tornado that hit in 2011.)
However, I still don't understand how tornadoes are formed, nor whether their incidence is increasing or not. Would like to have seen more video shot from within tornadoes - the DVD had a few such clips but didn't explain their origin or other wise comment on them.