Most flood deaths occur at night and when people become trapped in automobiles that stall in areas that are flooded. Flash floods occur within a few minutes or hours after excessive rainfall, a dam or levee failure, or a sudden release of water held by an ice jam or mud slide.
Flash floods can tear out trees and destroy buildings and bridges.
Because flash floods happen in a short period of time, generally less than six hours, they are more life threatening than general floods or river flooding. Areas most susceptible to flash flooding are mountainous streams and rivers, urban areas, low-lying areas, storm drains, and culverts. The mountain regions of middle and east Tennessee have potentially more flash flood problems than west Tennessee but all parts of the state are susceptible. The National Weather Service issues a Flood or Flash Flood Watch when conditions are detected that can result in flash flooding within a designated area, but the occurrence is neither certain nor imminent. Persons in the watch area are advised to check flood action plans, keep informed, and be ready to take action if a warning is issued or flooding is observed.