What is a flash flood watch or warning? Here's what to know about this deadly weather hazard
Flash floods are among the nation's most deadly weather hazards. But what are they?
Flash floods are the most dangerous kind of floods because they combine the destructive power of a flood with incredible speed, according to the National Severe Storms Laboratory.
Flash floods occur when heavy rainfall exceeds the ability of the ground to absorb it, or when enough water accumulates for streams to overtop their banks, causing rapid rises of water in a short amount of time, the NSSL said.
They can happen within minutes of the rainfall that caused it, limiting the time available to warn and protect the public.
Although flash floods are usually caused by heavy rainfall, they can also be caused by dam or levee breaks and other factors, according to Ed Clark, director of the National Oceanic and Atmospheric Administration's National Water Center.
“After heavy rains, they can rip through riverbeds or urban streets,” Clark said, “really just destroying everything that the waters encounter.”
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The floods can occur in various terrains, but urban areas are more prone. Such environments have more paved areas, preventing water from filtering into the ground.
Clark called flash flooding “an extremely hazardous event,” noting that 6 inches of moving water can knock a person off his or her feet, and 12 inches can move smaller vehicles.
Flood watch vs. flood warning. What's the difference?
These terms may sound similar, but they have very different meanings: A flood watch is issued when conditions are favorable for flooding to occur, the National Weather Service said. It does not mean flooding will happen, but it is possible.
A flash-flood warning is issued when a flash flood is imminent or occurring, the Weather Service said. If you are in a flood-prone area during a flash-flood warning, move immediately to high ground. It is even possible to experience a flash flood in areas that aren't receiving rain, according to the Weather Service.
Turn around, don't drown
It is never safe to drive or walk into floodwaters, the National Weather Service said.
“Particularly when faced with moving water, with flash flood situations, it's imperative that folks do not drive into those waterways,” Clark said. “We don’t know how fast that water’s moving. We don’t know how deep that water is.”
Each year, more deaths in the U.S. occur from flooding than from any other thunderstorm-related hazard, the Weather Service said. In fact, in the U.S., floods kill more people each year than tornadoes, hurricanes or lightning.
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And over half of all flood-related drownings occur when a vehicle is driven into hazardous floodwater.
Water may be deeper than it appears and can hide hazards such as sharp objects, washed-out road surfaces, electrical wires and chemicals. A vehicle caught in swiftly moving water can be swept away in seconds, the Weather Service warned.
Jenelle Eli, Red Cross spokesperson, told USA TODAY that people should stay off the road during flash flood warnings, and if a roadway is flooded, they should “turn around and go another way.”
“The adage ‘Turn around, don’t drown’ is really prescient advice,” Eli said.
Other types of flooding
In addition to flash flooding, the U.S. also endures other types of floods, including slow-motion river flooding and coastal flooding during big storms, hurricanes and sometimes during times of high tide.
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Contributing: Marina Pitofsky, USA TODAY
This article originally appeared on USA TODAY: Flash flood warning: Weather hazards among most deadly in the nation
