The Tempestarii are a race of beings who control the weather from their magical land of Magonia. Because they live in the clouds, naturally they can’t grow crops. So, they cause magical storms–the crops ruined by these storms are in fact taken back to Magonia on great sky-ships.
In Medieval Europe, fake wizards would pretend to be able to control the Tempestarii, and charge the population a certain portion of the crops to keep these weather pirates away.
In 815, in Lyons, France, such a storm occurred. The local population discovered three strangers just after it, and immediately realizing they were Tempestarii who had fallen from their ship, threw them in prison. The local Roman Catholic bishop, Agobard, argued them out of jail before the livid population stoned them to death.
Henry Charles Lea, A History of the Inquisition of the Middle Ages, Harper & brothers, 1887
http://en.wikipedia.org/wiki/Tempestarii (Please note that–at the time of writing–the Wikipedia article confuses the Tempestarii and the fake wizards who took money to keep them away. But I used it as a source, so I’m referencing it here.)