Very large tornado can often consist of multiple small tornadoes that are circling around the parent tornado. In the case of the El Reno, Oklahoma tornado, numerous multivortex funnels occurred and caught many storm chasers off guard.
The entire tornadic wind field can be much larger than the condensation funnel; in this case many storm chaser drove right into the circulation without evening knowing it.
-Garrett
(Our thanks to KFOR, our sister station, for supplying some of the video and content)