https://www.washingtonpost.com/weather/2018/12/13/tornadoes-spawn-cloud-ground-right-probably-not-says-this-new-study/?utm_term=.effa756c6d3a

The study, presented Thursday at the American Geophysical Union
annual meeting in Washington, expands on previously published work that
investigated the massive El Reno tornado in 2013. It had winds up to 300 mph,
and was the widest tornado ever observed. It killed several storm chasers. And
it is one of the most-studied tornadoes of the past five years.

When Jana Houser and her colleagues looked back at the data, they noticed
something they hadn’t observed before — instead of starting in the clouds and
dropping to the ground, the tornadoes they examined appeared to have started at
the ground and worked their way up. The 2013 El Reno tornado was among these. In
all, they found five cases in which their radars detected that signature. It’s a
small sample size, but it could prove invaluable to the severe-weather research
community.