Everything you need to know about a flash flood

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Everything you need to know about a flash flood

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JOHN SPINK / AJC
Homes were evacuated and a campground monitored by officials in Pickens and Gilmer Wednesday, Aug. 7, 2013 after up to 10 inches of rain inundated the same area of the state hit by flooding less than a week ago. JOHN SPINK/JSPINK@AJC.COM

When the weather gets bad it can be a challenge to know which weather alerts require action and which ones are just minor warnings. During rainy seasons, flash floods are one of the most common warnings that Metro Atlanta residents are likely to see crossing their television screens. Here's a brief explanation of this kind of flood.

What exactly is a flash flood?

The National Weather Service defines a flash flood as any flood that develops in less than six hours. They can occur almost anywhere, but are most commonly found in low-altitude areas with poor drainage systems.

What causes flash floods?

Heavy rains can cause flash floods in many areas, but other factors like dam failures, ice jams and snow melts can cause water to rise quickly, too.

What areas are most at risk for flash floods?

According to the National Severe Storm Laboratory, densely populated areas create a high risk for flash floods in and of themselves. An increase in construction and the vast presence of paved surfaces like parking lots, roads, highways, driveways and buildings can reduce the amount of surface area available to absorb rainwater. Runoff from these paved surfaces vastly heightens the chances of a flash flood.

The NSSL also notes that high-risk areas for flash floods can also include recent burn areas and low water crossings.

What is a flash flood watch?

According to the National Weather Service, issuing a flash flood watch indicates that the conditions are favorable for a flash flood. It does not guarantee that the area under the watch will endure a flash flood, but provides a heads up for area residents or visitors.

What is a flash flood warning?

A flash flood warning can mean that a flash flood is currently occurring or that a flash flood is imminent in the area under the advisory.

What should I do if a flash flood warning is issued in my area?

If possible, try to head to higher ground for the duration of the warning. The Red Cross warns citizens to stay away from floodwaters altogether, keeping children out of the water entirely and moving in the opposite direction if you encounter water that reaches your ankles. It only takes six inches of standing water to knock over an adult.

What if the water doesn't seem to be that deep?

Flash floods can sweep away vehicles, knock over trees and provide dangerous electrical conditions, and according to weather.com, the "most frightening" part of this weather phenomenon is how quickly the water is capable of rising. When a flash flood warning is issued for your area, conditions can change quickly and an area that looks safe at first glance may not stay that way. Always use caution when dealing with a flash flood warning.

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