During the storm cold air and warm air combine in a set pattern: the cold air drops as the warm air rises. The warm air eventually twists into a spiral and forms the funnel cloud that we all associate with a tornado. From both cold air and warm air traveling at different speeds , this causes a wind shear.

The Great Tri-State Tornado of Wednesday, March 18, 1925, is the deadliest tornado in U.S. history. Inflicting 695 fatalities,[2] the tornado killed more than twice as many as the second deadliest, the 1840 Great Natchez Tornado. The continuous ≥219 miletrack left by the tornado was the longest ever recorded in the world as it crossed from southeastern Missouri, through southern Illinois, then into southwestern Indiana. Although not officially rated by NOAA, it is recognized by most experts (such as Tom Grazulis) as an F5 tornado, the maximum damage rating issued on the Fujita scale.