Scientists say the tornado that flattened Moore OK was a rare and extraordinarily powerful EF5, capable of lifting reinforced buildings off the ground, hurling cars like missiles and stripping trees free of bark. Wind speeds are estimated to have reached 200 to 210 mph.

It's not the first EF5 to hit the U.S. In 2011 another tore through Hackleburg AL. It killed 18 people and caused massive destruction over a long path of 25  miles. The National Weather Service does extensive research on storms like this.

In some cases areas prone to tornadoes like this are eligible for government assistance in building storm shelters. In Moore OK Several people took advantage of that after a tornado that tore through the area in 1999. They said those shelters saved their lives this time.