Tornadoes are complex and tough to predict but this short documentary from NASA is a good introduction to how they work. Researcher Tim Samaras explains how different weather systems collide across the central U.S. to create tornadoes. Satellite imagery and a "turtle probe" that Samaras designed help researchers identify where storms might occur.
Alexis Madrigal's "Tornadoes in America: The Oklahoma Disaster in Context" has more on the science of the storm that hit Moore, Oklahoma.
For more videos from NASA, visit http://www.nasa.gov/.