Why are flash floods so deadly? How to stay safe from their shocking power.
Flooding in Texas appeared swiftly and soon turned deadly, showing how deceptively powerful a flash flood can be.
Amazingly, it only takes 6 inches of rapidly moving water to knock you off your feet. And according to Weather.com, water flowing at just 6 mph exerts the same force per unit area as air blowing at EF5 tornado wind speeds.
Water moving at 25 mph has the pressure equivalent of wind blowing at 790 mph, faster than the speed of sound.
Here's what to know about these incredible forces of nature ‒ and how you can prepare:
What is a flash flood?
A flash flood is a rapid rise of water along a stream or in a low-lying urban area, the National Weather Service said. Flash flooding can result from slow-moving thunderstorms, from numerous thunderstorms that develop repeatedly over the same area, or from heavy rains associated with tropical cyclones.
"These floods may develop within minutes, depending on the intensity of the rainfall, the topography, soil conditions, and ground cover," the weather service said.
In the July 4 flooding disaster, extreme flooding began in the Texas Hill Country around 4 a.m. as thunderstorms dumped more than 10 inches of rain on parts of the region. The relentless rain overwhelmed the Guadalupe River, causing it to surge over 26 feet in less than an hour, Texas Lt. Gov. Dan Patrick said.
Be careful in your car
In general, most U.S. flash flood deaths occur in vehicles when people try to drive through flooded water and eventually drown. This has prompted the well-known slogan "Turn around, don't drown" from the weather service.
The national 30-year average for flood deaths is around 127 people per year, and weather service data indicates that nearly half of all flash flood fatalities are vehicle-related. The majority of victims are males, and flood deaths affect all age groups.
"Once your vehicle is floating, the floodwaters become your steering wheel. If that water is moving, your vehicle could be swept away, tipped on its side, or flipped," Weather.com meteorologist Jonathan Belles said in an online report.
And according to the Federal Emergency Management Agency:
◾6 inches of water will reach the bottom of most passenger cars, causing loss of control and potential stalling.
◾1 foot of water will float many vehicles.
◾2 feet of rushing water will carry away most vehicles, including SUVs and pickups.
Stay informed about the weather
Cell phones or weather radios are a key part of staying informed of incoming severe weather.
"Awareness of the weather can save your life in a flash flood," Belles said in an online report.
In addition to apps from your favorite weather provider, such as the Weather Channel or AccuWeather, be sure you pay attention to wireless emergency alerts (WEA) on your phone, which are emergency messages sent by authorized government alerting authorities through your mobile carrier. "Government partners include local and state public safety agencies, FEMA, the FCC, the Department of Homeland Security, and the National Weather Service," the weather service said.
Other flash flood safety tips
A few important tips to help you stay safe during a flash flood:
◾If you're caught in a flood, immediately head to higher ground.
◾Avoid walking or driving through floodwaters.
◾If you encounter rising water, "Turn around, don't drown."