Tornado climatology
The United States averaged 1,274 tornadoes per year in the last decade. April 2011 saw the most tornadoes ever recorded for any month in the US National Weather Service's history, 875; the previous record was 542 in one month. It has more tornadoes yearly than any other country and reports more violent (F4 and F5) tornadoes than anywhere else.
Tornado Alley
The average tornado usually only stays on ground for 5 minutes but these figures, reported by the National Climatic Data Center for the period between 1991 and 2010, show the seventeen U.S. states with the highest average number of tornadoes per per year.
After the U.S., Canada gets the most tornadoes in the world. The average number of tornadoes per is highest in the southern parts of Alberta, Saskatchewan, and Manitoba, as well as Southern Ontario. Northern Ontario between the Manitoba border and the Lake Superior lakehead is also prone to severe tornadoes, but tornadoes in this area are believed to be underestimated due to the extremely low population in this region.