What is a mesocyclone?
A mesocyclone is an entire column of circulation within a thunderstorm cell. Instead of a concentrated circulation (like a tornado) the entire cloud formation swirls around a central point underneath a supercell. This is one of the most dangerous points of a thunderstorm and can lead to a very volatile tornado. A mesocyclone is often found in the right rear flank of a supercell (or often on the eastern, or front, flank of a High-Precipitation storm).
