Watch how crowdsourced citizen data demonstrated how tornadoes form

The deadly 2013 El Reno tornado was 2.5 miles (4 km) wide and killed a team of tornado experts. But as Anton Seimon explains, his colleagues turned that tragedy into an opportunity to confirm a key element of tornado formation.

Through crowdsourcing, his team was able to demonstrate that this kind of tornado forms from the ground up, not from the clouds downward.

Image: YouTube / National Geographic