Friday's Oklahoma tornado was one for the record books.
The National Weather Service says the twister was 2.6 miles wide- making it the widest U.S. tornado ever. It was a rare EF5; the highest level of tornado intensity.
Bill Nye and Tom Foreman explain why the tornado was so large.
Erin Burnett talks to Storm Chaser Dave Holder about the death of his colleague veteran storm chaser Tim Samaras.
NEW: Warnings expire in Oklahoma City
Parts of the nation are already being hammered by tornadoes and golf ball-sized hail
Areas from Texas to Wisconsin and parts of the Northeast are now under tornado and severe thunderstorm warnings.
There were reports of at least one tornado touching down in Southern Nebraska and this system is threatening to get even worse as we enter the hours of peak danger.
Our Chad Myers is on the ground with a group of storm chasers.
According to the Discovery Channel, the U.S. is hit by more severe storms than any other nation in the world.
Erin Burnett reports.