Flash Flood Warning: What Is It and What to Do

A flash flood warning has been issued in parts of Massachusetts, including much of the Greater Boston and Area and all of Essex County.

The warning is in effect until midnight Saturday.

The warning is for the red area in the photo above. It stretches from about Norwood to Scituate and up to the New Hampshire border.

The NWS says nearly 3 million people are under "potential exposure."

• ALSO: 2 Workers Die as Water Main Break Floods Boston Trench

What is it and how can you stay safe?

The National Weather Service says a flash flood warning is issued when a flash flood is imminent or occurring. If you are in a flood-prone area move immediately to high ground. A flash flood is a sudden violent flood that can develop in just minutes, or it can take hours to develop. It is even possible to experience a flash flood in areas not immediately receiving rain.

Flash flooding is a “very dangerous situation,” according to the National Weather Service.

More deaths occur due to flooding than any other thunderstorm-related hazard, according to the National Weather Service. More than half of all flood-related drownings occur when a vehicle is driven into flood waters, according to a report by the Centers for Disease Control cited by the weather service.

“People underestimate the force and power of water,” the weather service says on its website. “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.”

Six inches of fast-moving flood water can knock over an adult, and 12 inches of rushing water is enough to carry away a small car, while 2 feet of rushing water can carry away most vehicles, the service says.
“It is NEVER safe to drive or walk into flood water,” the weather service notes in its ”Turn Around, Don’t Drown” campaign.

Keep these items in mind:

• Flash flooding is very dangerous and can move quickly.
• Be aware of low-lying roads, streams, creeks and other areas known to flood suddenly.
• Do not walk through moving water. Six inches of moving water can make you fall. If you have to walk in water, walk where the water is not moving.
• Do not drive into flooded areas. If floodwaters rise around your car, abandon the car and move to higher ground if you can do so safely. You and the vehicle can be swept away quickly.

This National Weather Service video demonstrates what can happen:

Karen Wall, Patch Staff, contributed to this report