derecho (n.): a large cluster of thunderstorms that produces widespread wind damage.
Here we are again. About a year ago, a historic derecho tore across the Mid-Atlantic U.S., producing the highest wind gusts ever recorded in the months of June or July. Some 5 million people lost power and 22 lost their lives. The storm also hit major metropolitan areas—meaning that it got a lot more attention from the media and general public than derechos in years past. This week, weather reports indicated that another derecho could be upon us. So what, exactly, does that word mean and where does it come from?
First, it’s pronounced deh-REY-choh. The word means straight in Spanish, a reference to the long lines of wind damage the storms can leave behind. By definition, if the wind damage is at least 240 miles long and gusts are at least 58 mph, the storm is a derecho. But the summer squalls can be even more severe than that, with winds topping 100 mph; a derecho that hit Michigan in 1998 had winds blowing at 130 mph.
For the weather geeks out there, the government’s Storm Prediction Center goes into greater meteorological detail. (If you don’t want to read phrases like “convective downdraft,” skip this part):
Derechos are associated with bands of showers or thunderstorms … that assume a curved or bowed shape. The bow-shaped storms are called bow echoes. … Derecho winds are the product of what meteorologists call downbursts. A downburst is a concentrated area of strong wind produced by a convective downdraft [i.e. areas of downward moving wind that are smaller and more intense than other types of downdrafts].
As of Thursday morning, no derecho had materialized, but there were still severe thunderstorm warnings for the Mid-Atlantic and beyond. And as a Washington Post writer argued, the bottom line is that a big storm is brewing; people should try to be prepared, regardless of what it’s called.
Spanish words are at the root of other weather phenomena. There is the tornado, which likely comes from tronada, meaning thunderstorm, and tornar, meaning to turn. And hurricane looks an awful lot like the Spanish huracan. But other languages have made their mark in our weather talk, too. Cyclone, according to the Oxford English Dictionary, may come from a greek word meaning “coiled serpent.” And the credit for tsunami, obviously, goes to the Japanese.