It would turn out to be lucky for us that we all knew the signs of flooding.Īs we sat, feet kicking the green clear water, I noticed a few cypress branches floating by our group. We had all grown up on the river or had spent summers at this beautiful site. There had been no rain for over a week and never thought about the chance for flash flooding. We had been sitting on some large white rock ledges and chatting with one another. On a hot sunny Texas day I was enjoying the river along with 5 other family members. Have you ever experienced a flash flood? Tell us about it in the comments below! A 19-foot wall of water killed 139 people, as it swept away boulders, cars, bridges, even a restaurant with the diners still inside. Twelve inches of rain fell in five hours, making the river rise with astonishing speed. One For the Recordsįact: Thousands of campers in Colorado’s narrow Big Thompson Canyon ignored warnings of flooding on July 31, 1976, with tragic results. The most difficult challenge is how to measure how much moisture the ground can soak up: NASA has begun exploring the use of satellites to measure soil moisture over much larger areas than those currently monitored by rain gauges. To address this, land surface characteristics such as terrain are now included in computer models along with data from radar and gauges, resulting in better predictions about how a certain location will handle a given amount of water. In addition, the farther away you get from the radar, the less accurate the information.Īnother big unknown: How will the water behave once it’s on the ground? “Flash floods don’t always happen in the natural stream channel,” says Kelsch. However, radar is limited in its ability to detect rain in mountainous areas. “That way, the forecaster can receive as the rain is falling,” says Matthew Kelsch, a meteorologist for NOAA, which is based in Boulder, Colorado. Radar and stream gauges automatically convey this information via phone lines, radio waves, or satellites. To have any chance of predicting a flash flood, forecasters need to know where the “bullseye” of intense rain is-that is: Flood Warning: A flood warning is issued when flooding is imminent or occurring.It does not necessarily mean that flooding will occur, but that it is possible. Flood Watch: A flood watch is issued when conditions are favorable for flooding.Be aware of a “flood watch” or “flood warning” from the National Weather Service.During flood watches, do not park your car near a river or on a street that you know floods. As land turns from fields or woodlands into roads and parking lots, it loses its ability to absorb rainfall.If you see water is collecting in pools, this is a sign the ground is oversaturated with water and that flooding can occur.Hurricanes are another big source of intense rain.Watch for slow-moving storms that repeatedly move over the same area.Listen for news of dam or levee failures.Flash floods occur within six hours of a rain event.It’s difficult to predict flash floods, so you should always be aware of the conditions that lead can to them: Tip: Stay out of flowing water! A mere six inches of moving water can knock you off your feet, while two feet of water will carry away most cars. Predicting Tornadoes: Off the Radar Screen
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