Did you know fast moving water just above your ankles can knock you off your feet? Most people do not! That’s why each year, more deaths occur due to flooding than from any other thunderstorm related hazard. Many of the deaths occur in automobiles as they are swept downstream. Of these drownings, many are preventable, but too many people continue to drive around the barriers that warn you the road is flooded. You will not know the depth of the water nor will you know the condition of the road under the water. Whether you are driving or walking, if you come to a flooded road, Turn Around Don't Drown!
Most flash floods are caused by slow moving thunderstorms, thunderstorms that move repeatedly over the same area, or heavy rains from tropical storms and hurricanes. These floods can develop within minutes or hours depending on the intensity and duration of the rain, the topography, soil conditions, and ground cover.
High resolution (Credit: USGS)
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. Flash flood-producing rains also can trigger catastrophic mud slides.
Occasionally, floating debris or ice can accumulate at a natural or man-made obstruction and restrict the flow of water. Water held back by the ice jam or debris dam can cause flooding upstream. Subsequent flash flooding can occur downstream if the obstruction should suddenly release.
What kinds of flooding alerts does NOAA issue?
FLASH FLOOD or FLOOD WATCH: Flash flooding or flooding is possible within the designated watch area — be alert.
FLASH FLOOD or FLOOD WARNING: Flash flooding or flooding has been reported or is imminent — take necessary precautions at once!
URBAN and SMALL STREAM ADVISORY: Flooding of small streams, streets and low-lying areas, such as railroad underpasses and urban storm drains is occurring.
FLASH FLOOD or FLOOD STATEMENT: Follow-up information regarding a flash flood/flood event.
What is NOAA doing about the flood and flash flood problem?
Researchers are figuring out ways to blend data from radar, satellite, lightning, and rain gauges to improve flash flood monitoring and prediction. This will help overcome significant challenges in estimating precipitation type and amount. These ideas are being tested in projects around the U.S. including California and North Carolina.
Forecasters and researchers are creating a debris flow or mudslide warning system for southern California where homes are frequently destroyed and major highways have been washed out. They are focusing on burn areas that are especially susceptible to flash floods and debris flows during rainstorms because rainfall that is normally absorbed by vegetation can run off almost instantly.
NOAA Research is working hard to improve warnings and forecasts of floods and flash floods. By investigating the meteorological causes of flash flooding and working on flash flood and river flood warning decision making tools, we hope to see more lives saved and less property destroyed.
For more information about flood watches and warnings in your area, visit the NOAAWatch Flood Warning Web site.