What Makes Something a Flash Flood?

7/16/2021 (Permalink)

The weather report often gets a bad rap for being unreliable and imprecise. The meteorologists on TV might call for rain and get sunshine, or vice versa, and all of a sudden people start to discount everything that they say.

While the science of predicting the weather can sometimes be a probabilistic guessing game, the language that we use to describe particular weather events is usually very, very precise.

Take the difference between a “flood” and a “flash flood.” You probably have a vague grasp of what separates the two, but could you put it into writing?

A flood is defined by the National Weather Service as “an overflow of water onto normally dry land.” Water levels rise in existing waterways because of precipitation, and floods spill out and cause trouble.

Flash floods, meanwhile, are tied to a timeline: six hours. If the rainfall that caused the flooding occurred in a six-hour timespan, and the flooding was nearly immediate, then it’s a flash flood. Actually, flash floods can be declared even if no rain has fallen so long as there’s an influx of water, as in a dam or a levee breaking.