How were the 13 states affected by the tornado of 1974?

No single tornado affected 13 states. What you are referring to was the Super Outbreak of 1974, in which 148 tornadoes touched down in 15 hours. Alabama, Indiana, Kentucky, Tennessee, and Ohio were devastated. Extensive damage also occurred in Georgia, North Carolina, Illinois, Virginia, West Virginia, Michigan and the Canadian province of Ontario.

There was also some lesser damage in Mississippi and New York.