On average , most recorded tornadoes , including the vast majority of significant -- F2 or stronger -- tornadoes , form in the U.S. , although as many as 500 may take place internationally .
Consequently , available documentation in 1973 mainly covered the United States .
On average , most recorded tornadoes , including the vast majority of significant -- F2 or stronger -- tornadoes , form in the United States , although as many as 500 may take place internationally .
Consequently , available documentation in 1973 mainly covered the United States .