Flash Flooding is an often-overlooked, but seriously deadly type of weather. We got a serious dose of flash flooding in the DC Metro area on Wednesday night and Thursday morning, when a powerful cold front swept through. This moisture-laden system dumped between 1.5" and 4" of rain in a span of less than 8 hours, prompting Flood Warnings on many of our local creeks and streams. Flash Flood Warnings were issued on Wednesday night for much of the eastern slope of the Appalachians, as rainfall rates approached 1" per hour in some spots.
Some DC Metro residents, perhaps unprepared for this type of event, inadvertently drove into flood waters on our area roadways on Wednesday night and early Thursday morning. At least 8 high-water rescues were reported as a result. These folks were lucky that emergency personnel were able to save them-- in the United States, the average yearly death toll from flooding is 92 people. That is way more than the number of Americans who die due to lightning (55 people), tornadoes (56), and hurricanes (47).
This article on wusa9.com shows just how deadly flash flooding can be. Your car can quickly become a death trap if you drive into high water. It only takes about 18 inches of water to make a typical vehicle float; in some cases, even less water can cause the engine to stop working. The car will start to fill with water shortly after floating, making the situation even more dire.
On the surface, this situation might seem ridiculous. "How didn't these people know they were driving into a flood?", you might think. The problem is that when you're driving and you encounter a roadway that is completely covered in water, you have no way of knowing how deep that water is. Notice in the one picture above that the water is muddy, and in the other picture it is dark outside. Both of these are classic examples of why it's impossible to judge the water's depth before you try to drive into it. If you can't see the lines on the roadway (either the yellow line down the center or the white line on the side), DO NOT attempt to drive through!
Another important thing to keep in mind is that water can erode the dirt underneath a road. This is especially true on roadways near bridges and overpasses. If the water is flowing, it's even more likely that the road underneath has been compromised! The pavement might not be strong enough to support your vehicle, causing the road to cave in, and your car to plunge into the water underneath.
So, the important thing to keep in mind is that you can never tell how deep the water is in front of you, and it's way too risky to attempt. As per the National Weather Service motto, "Turn Around, Don't Drown"!