Some summary statistics are below the graph.
It is a climatological standard to use a 30-year data period for the averages or normals. 1950-2000 Average is 39 tornadoes per year. 1953-2000 Average is 41 tornadoes per year. 1961-1990 Average is 36 tornadoes per year. 1971-2000 Average is 43 tornadoes per year.