Where did Groundhog's Day come from?

Seeing as yesterday was Groundhog's Day, maybe a little history lesson is in order. It seems this holiday has been around for a whole lot longer than the 200 years we in the US have been calling it Groundhog's Day. It was originally named Imbolg, and was one of the pre-christian Gaelic holidays. It is tied to the Irish goddess Brigid, and the whole point to it was to celebrate the lengthening of the daylight and first stirrings of Spring in the deep of winter from the Sun having been born on Yule. After the Christianisation of Ireland, and the beatification of Brigid into St. Brigid, the Holiday became St. Brigid's Day or Candlemas (the return of the light). The day was changed to the first, of course, because a good Christian could not celebrate on the same day as his pagan neighbors. Then he would be just like them, and most likely revert back to his old ways.

The origin of the Groundhog remains a bit of a mystery. It is said that the German immigrants to the US had a belief that the Groundhog would come out on this day to see the weather. If he saw his shadow, he would go back in for a six week snooze and we would have more winter weather. Where this came from, no one knows, but it sounds very Amish.

There is an older belief that comes from the Irish, which is sort of similar. This has to do with the Hag Goddess Cailleach. According to the Irish legend, she gathers her firewood during winter. If the winter is to last longer, she makes certain she has a bright sunny day to gather her wood. If the winter is to end soon, she sleeps through Imbolg because she needs no more firewood. Likewise, the day is cloudy because she does not need the sun to gather her wood.

I guess somewhere along the way someone mistook a Groundhog for a Hag?