In the winter I start turning all verbs ending in "-ow" into irregular Old Englishy sort of past participles. I think it's because of the snow. It makes me want to say, "Look! It has snown."
I don't think it's too wrong to think of these verbs with the "-own" or "-ewn" ending. Many of the "-ow" verbs still retain what I'm assuming really is an OE ending. Here are some of the ones that really end that way in Modern English:
Some of these have two possible endings, like "mown" is most often just "mowed." In fact, proper Modern English lovers probably would not let you get away with "mown" even though it is perfectly proper. It just sounds archaic. But I like that. So here's how we should say the following verbs as past participles when the mood strikes us, and again, grammarians be damned!
"It has snown for fourteen days."
"Yes, the snow has not slown down one bit."
"I might have known -- that is why your brow has been furrown."
"Indeed. It is so dark and cold the cock has not crown."
So there. What else do we have to amuse ourselves with when it has snown a fortnight and the cock has not crown?
"Words, English words." -- Virginia Woolf, Craftsmanship