They found that as a supercell evolves, the mesocyclone would form and mature, then begin to weaken. During this weakening, a new mesocylclone would form, in similar fashion to the formation of an area of low pressure on a stationary front . Tornadoes might spin up beneath each intensifying mesocyclone. Beyond these observations, however, there is not a lot understood about how exactly tornadoes form, grow and die. But, as you can see when you take an airplane trip anywhere in the U.S., built-up areas make up only a small part of the country.
Tornadoes are small compared with other kinds of storms and are really pretty rare.
The odds are that they will hit open land more often than cities because there is a lot of open land. Also, some of the most built-up parts of the U.S. such as the Northeast Coast and along the California Coast are places where strong tornadoes are rare because the general weather conditions aren't as favorable as they are in the Southeast, on the Plains and in the Midwest. The most violent tornadoes , F4s and F5s on the Fujita tornado intensity scale , often spawn multiple vortices while spiraling around a central axis of the parent tornado's vortex. Multiple vortices are very rare in F1-F3 tornadoes. The individual vortices in a multiple vortex tornado are indeed called suction vortices.