Those conditions—which stretched across Mississippi, Alabama, and Georgia—included warm, moist air rising and mixing with colder, dry air at higher altitudes.

Unfortunately for those living in the tornadoes' path, "weather conditions came together perfectly," said Tim Samaras, a Denver, Colorado-based tornado expert and producer of the tornado-research website TWISTEX.

"Mississippi, Alabama, and Georgia had that down to a T. It was a very, very rare day for everything to come together for this type of event," said Samaras, also a National Geographic Society Emerging Explorer. (The Society owns National Geographic News.)

Upper-level winds known as the jet stream also caused the storm system to rotate, according to meteorologist