Tornadoes are one of the most dramatic types of weather we experience in SE Minnesota and NE Iowa. The way they develop is also extremely complex.
Lets walk through how tornadoes form. The process of how a thunderstorm becomes capable of producing something so violent. When the sun heats the ground during the day, that warm air rises. When the atmosphere is unstable, that warm air will continue to rise and eventually can form cumulonimbus clouds (thunderstorm clouds).
Now that we have a warm and unstable atmosphere...how do we get the right conditions to form a tornado? We need several other factors to be present in order to get a tornado to form.
We need something called "wind shear" in the atmosphere. Wind shear is the change in wind speed and direction with height. When the winds begin to back (change direction) in the upper levels of the atmosphere that will form a rotating column of air. Power warm updrafts within the thunderstorm will help move the rotating column of air vertically. However, if you have too much wind shear, it could eliminate any potential the thunderstorm had in producing a tornado.
These types of thunderstorms that have a rotating updraft are called supercells. These thunderstorms produce most of the tornadoes each year in the U.S. Not only do these thunderstorms have a strong updraft, but they also have a strong downdraft. The cold air within the supercell will sink extremely fast helping create a downward motion.
This downward motion can lead to the development of a wall cloud. If the supercell is strong enough, the wall cloud will reach the ground and a tornado is born!