"Twister"

I have a friend that can be called somewhat of a tornado chaser. While we were discussing his work, I began to think about tornado formations.  There are certain conditions that favor the formation of a tornado. The "normal" pressure is about 29.92 inches Hg.  When a tornado occurs, the pressure drops significantly. The lowest recorded pressure during a tornado was 25.17 in Hg on June, 24, 2003 in Manchester, South Dakota. Wind shear is key in tornadoes, especially a clockwise change in direction with increasing speed. The change in direction makes warm and unstable air flow in, and the change in speed starts the air rotation that characterizes tornado movement. The most favorable conditions for a tornado are high humidity, instability (moist air rising quickly) and a cold front.