Ben from NightHawkInLight shared a video of his beautifully crafted indoor tornado machine. The machine creates a continuous swirling vortex from what appears to be dry ice in water. Ben mentioned in the video that he will be posting a full tutorial video about the build in the next few weeks.
This was a big project but the result is awesome. I love having this machine in my living room and it will be great for science demonstrations I teach throughout the year.