Karina -- thanks for the tip. I'll check out the Clannad album. I learned this song from Triona post-Bothy Band, when she was playing in a group called Touchstone from North Carolina, about 15 years ago. She wrote down the lyrics for me.
I'm also pretty familiar with Pentangle's version, which also includes the line, "lay the bent to the bonny broom," that Kiwi mentioned from the Old Blind Dogs version. It's much more melancholy than Triona's/Clannad's version.
As far as the Wind and Rain--I've seen that in a couple of different songs; one entitled "The Cruel Mother" who drowns her two babes, and the other The Cruel Sister or the Twa Sisters.
Pentangle's version of The Cruel Sister doesn't use the refrain "Oh the wind and rain," but nonetheless, the eldest sister's crime is revealed when some musicians happen upon the younger sister's corpse and make a harp from her hair and bones. They then scamper on to the wedding of the eldest sister and Johnny, where the harp sings out the grisly details of the murder.
Lindahl -- I suspect the tune is medieval or at least pretty old, just judging from the number of versions there are, as well as the more oblique rreferences/crossovers (i.e. The Wind and Rain).