Tornado Outbreak: Destruction in the Heartland

The Midwest has suffered from three straight days of tornado activity.
3:42 | 05/21/13

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Transcript for Tornado Outbreak: Destruction in the Heartland
They know something about killer wind speeds in Moore Oklahoma in fact may third is a shorthand in that part of tornado Alley. From the 1999 storm that took over forty lives -- municipal website even has a page. Pointing out just how remote the chances are that more could ever have another. May third type event but this. The may twentieth monster that followed that same stores path with -- position already. Has a higher body count President Obama has declared a state of emergency in Oklahoma tonight and ABC's Sam Champion -- -- to put this rash of deadly twisters. And -- broader perspectives. -- -- -- -- -- -- The destruction is widespread. And devastating. Preliminarily classified as an EF four tornado the second most powerful level of twister. Cutting -- -- -- miles wide at least twelve miles long. -- National Weather Service says it may have been on the ground -- longest forty minutes. The tornado in these Oklahoma City suburbs just the latest assault to a region already reeling from a weekend of severe storms. Needed just portrait like a -- just run right does senator Evan. A local television helicopter capturing the pictures from up in the sky the severe weather and action below. Look closely and you can see the flashes as the power lines and transformers. Are ripped apart. Well there's a huge avalanche. -- various it is just rip it up everything -- -- -- it's the latest in a three day outbreak that has brought more than fifty tornadoes from Oklahoma. All the way to Nebraska. -- -- -- 6:30 PM. Just a violent tornadoes in this outbreak the massive twisters came one after another stop on the ground for miles. Dozens of Storm Chasers in pursuit -- I get -- -- we got to -- out -- and if you -- that good in America. This was Sunday night in Shawnee Oklahoma. Listen as the sirens -- A warning to residents to take cover immediately. -- -- -- -- -- -- -- -- There was also advanced warning for the massive twister from -- Baltimore yeah. The National Weather Service says it was issued at 2:40 PM a full sixteen minutes before the storm actually touch the ground. A warning that no doubt help save lives. This part of Oklahoma is no stranger to deadly tornadoes. Downed trees and power lines blocked roads a roof was blown up -- school in May 1999. The town was hit. By twister that reach speeds of over 300 miles an hour the top scale and EF five some of the fastest winds ever recorded on earth. 36 people were killed. And the storm still ranks as one of the costliest in American history how long do you think you'll stay on the scene here in -- like. And this new round of deadly storms comes almost two years -- the day that a 158. People were killed. In Joplin Missouri. And -- they'll help suction this polling. Wednesday marks the two year anniversary of the storm that also left more than 1000 people injured. It's still ranks as the deadliest in modern US history. America's heartland there will be more severe storms on Tuesday but in Oklahoma tonight they're hoping they seen the worst of this year's outbreaks. In everything -- happened. Then you kill the pleasure. Of the tornado. And everything. Going everywhere. For Nightline I'm Sam Champion in Shawnee Oklahoma.

This transcript has been automatically generated and may not be 100% accurate.

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