What allows this tornado to form in a frying pan? I have just seen this video here where a mini tornado has formed in a frying pan:
https://www.youtube.com/watch?v=6CJ-8ze2FjE
Does anyone know how this happens or where I can find an explanation?
 A: The window on one side is open providing an asymmetric air supply, and you can hear what sounds like a loud overhead extractor fan running. With the hot pan providing a source of rising smokey hot air, these are great conditions for producing an indoor tornado.
The window appears to be cracked open, forming a vertical slit (off-camera to the left) letting air into the kitchen very close to the pan. As Mike Dunleavy noted in his answer to a Whirlpools and Tornados question, "Tornadoes happen when angular momentum of air is concentrated sufficiently in a vortex vertical to the ground." The window slit here provides a slightly off-center air supply that has non-zero angular momentum relative to the hot air rising from the pan. Just like a figure skater spinning faster as they draw in their arms and leg, angular momentum conservation makes the air spin faster as it is drawn into the vortex core.
For examples of how simply having an asymmetric vertical-slit air supply can turn hot rising air into a tornado, check out Best Fire Tornado - DIY - no moving parts! and How to build a DIY Dry ice tornado! - Fluid dynamics in a vortex!.  An overhead fan also helps to increase and concentrate the vertical air flow, as shown in How To Make An Indoor Tornado In 3 Easy Steps!.
