1.   Figures on powerful tornadoes are fairly reliable over the decades because they often leave widespread damage.

2.   It was also, in terms of the combination of the area it covered and the damage wrought, possibly the most powerful tornado ever recorded.

3.   Robert Chartuk, a spokesman for the National Weather Service, called such a powerful tornado extremely rare in Maryland.

4.   The three engineers concede that all bets are off for tornadoes as powerful as the ones in Oklahoma.

5.   A powerful tornado blew through downtown just after rush hour Tuesday night, shattering windows in high-rise buildings, overturning cars and uprooting trees.

6.   Scientists see link between La Nina and powerful tornadoes.