This turned out to be an especially interesting question, and one that made me wish that I had become an anthropologist. (Only briefly, of course. I have no desire to spend my life mucking about in grubby old jungles, miles from the nearest decent pizzeria.)

In any case, I had never heard the phrase "The devil is beating his wife" before, although I have experienced that unusual mix of rain and sunshine, usually called a "sunshower," on several occasions. And when I went looking for the precise origin, logic or history of the term, the cupboards were bare. But while poking around on the internet, I came across a query about folk terms for "sunshowers" posted by a Harvard linguist to a linguistics e-mail discussion group last year. The dozens of responses to his question proved that folks around the world have come up with some very weird words and phrases for this meteorological phenomenon.

"The devil is beating his wife," for instance, occurs not only in English, but Dutch and Hungarian as well. Other such phrases include "The devil is getting married" (Hungarian), "The devil is kissing his wife" (Tennessee), and "The devil is having a parish fair" (German).

The other main category of phrases used to explain sunshowers involves, I kid you not, animal weddings. "The rats are getting married," one would say in Arabic, while the Bulgarians say it's "the bear" that's getting hitched. Other betrothed parties include jackals (Hindi), tigers (Korea), witches (Spain), the poor (Greece), and leopards (various African languages). One animal, the fox, crops up all over the world, from Japan to Armenia, in such phrases.

The question raised by all of this is, of course, why? Well, all of these phrases were probably serious myths at some point, concocted to explain an unusual weather event. They live on today as colorful folk sayings, for which we should be grateful
http://www.word-detective.com/072999.html#sunshower