Possible causes for American tornadoes

Answer 1

Current, scientists believe most tornadoes form by the following, rather complicated process:

First, a condition called wind shear, in which the speed or direction of the wind changes with altitude. If the shear is strong enough it can essentially tilt a thunderstorm, this separates the updraft and downdraft of the thunderstorm, preventing them from interfering with one another. This allows the storm to become stronger and last longer.

Additionally, if the wind shear is strong enough it can start the air rolling in what is called horizontal vorticity. This horizontal vorticity can then be turned vertical by a thunderstorm's updraft. When this happens, the thunderstorm may start rotating. The rotation is especially strong in an updraft called a mesocyclone. If the storm intensifies rapidly enough, a relatively warm downdraft called a rear-flank downdraft or RFD can wrap around the bottom part of the mesocyclone. This can then tighten and intensify its rotation and bring it down to the ground to produce a tornado.

Answer 2

American tornadoes are primarily caused by the collision of cold, dry air from Canada with warm, moist air from the Gulf of Mexico. Other contributing factors include the presence of a strong jet stream, atmospheric instability, and topographical features that can create wind patterns conducive to tornado formation. Climate change is also thought to play a role in the increasing frequency and intensity of tornadoes in the United States.