According to the National Oceanographic and Atmospheric Administration, tornadoes form when wind shear creates a rotation in an active storm system, and rising moisture-laden air shifts that rotation from a horizontal spin to a vertically spinning column. This rotation intensifies, creating a potentially devastating funnel cloud in the lower part of the storm.
Tornadoes can form quickly and without warning, so when conditions are favorable for tornado development, the National Weather Service issues watches to ensure that citizens in affected areas remain vigilant and prepared for potential dangers. Doppler radar systems provide detailed information about wind speeds and directions, so these systems can identify areas in a thunderstorm cell that may be developing the rotation that precedes a tornado's development. Identification of one of these distinctive "hook echoes" may be the only warning a community receives before the funnel cloud forms, and meteorologists often issue warnings based entirely off radar data without waiting for visual confirmation. Once a tornado forms, it usually only lasts for a few minutes, due to the incredible forces involved. However, the rotation that spawned the tornado may continue higher up in the cloud system, allowing a tornado to dissipate and re-form further along as the storm system moves through a region.