“Has ANYBODY ever heard that term before (besides it being Spanish for “right”)?”
This storm is the first time I ever heard of “derecho” but according to NOAA it goes back to 1888:
Origin of the term “derecho”
The word “derecho” was coined by Dr. Gustavus Hinrichs, a physics professor at the University of Iowa, in a paper published in the American Meteorological Journal in 1888. A defining excerpt from the paper can be seen in this figure showing a derecho crossing Iowa on July 31, 1877. Hinrichs chose this terminology for thunderstorm-induced straight-line winds as an analog to the word tornado. “Derecho” is a Spanish word that can be defined as “direct” or “straight ahead.” In contrast, the word “tornado” is thought by some, including Hinrichs, to have been derived from the Spanish word “tornar,” which means “to turn”. A web page about Gustavus Hinrichs has been created by National Weather Service Science and Operations Officer Ray Wolf. The page provides information on Hinrichs’ background and on his development of the term “derecho” in the late 1800s. Wolf’s page also briefly discusses how the term “derecho” came into more common use in the late 1900s.
Facts About Derechos:
http://www.spc.noaa.gov/misc/AbtDerechos/derechofacts.htm
Obviously this change in our language is Iowas’s fault because of all the cars they were driving there in 1877! ;^)