Apparently, some people like to chase tornadoes - why, I don't know...
From the website:
The cone shape is generally part of the life cycle the tornado goes through on its way to another form, block, wedge or tube. This tornado kept the cone shape for about 5 minutes then changed to a dusty block of clouds on the ground. Shortly after this image was taken the tornado hit a small tank farm in open country igniting one of the tanks.