Several factors contribute to flash flooding. The two key elements are rainfall intensity and duration. Intensity is the rate of rainfall, and the duration is how long the rain lasts. Topography, soil conditions, and ground cover also play an important role.
Flash Floods Occur within a few minutes or hours of excessive rainfall, a dam or levee failure, or sudden release of water held by an ice jam. Flash floods can roll boulders, tear out trees, destroy buildings and bridges, and scour out new channels. Rapidly rising water can reach heights of 30 feet or more.
Furthermore, flash flood-producing rains can trigger catastrophic mud slides. You will not always have a warning that these deadly, sudden floods are coming.
Most Flash Flooding is caused by slow-moving Thunderstorms, Thunderstorms repeatedly moving over the same area, or heavy rains from Hurricanes or Tropical Storms.
What is the difference between Flooding and Flash Flooding? The answer is that Flash Flooding occurs within six hours of the rain event, whereas Flooding is a longer term event and may last a week or more.
It is important to know your areas flood risk.
Who is most at risk from flooding? Those in automobiles when Flash Flooding occurs near them.
Watches and Warnings
Flash Flood Watch
Flooding or Flash Flooding is possible within the designated watch area. Remain alert to changing weather conditions. When your area is under a Flash Flood Watch
Flash Flooding or Flooding has been reported or is immanent. Take necessary precautions at once.