Guide Note:Tornadoes are violently rotating columns of air that touch the Earth. Oklahoma ranks second in the United States for number of tornadoes, and spring is the season that tornadoes are most likely to form. Although May is the month when tornadoes are most apt to occur, tornadoes that occur earlier in the spring are usually stronger. Currently, its impossible to predict tornadoes more than a few days in advance.

Fast Facts:

1. Deadliest: May 3, 1999 (36 killed)
2. Second deadliest:June 12, 1942 (35 killed)
3. Costliest: May 3, 1999 ($1 billion)
4. Second costliest: March 20, 1948
5. Most tornadoes in one day: 5, on June 8, 1974.