Where Did Groundhog Day Come From?

image credit: StephenZacharias cc
Today is Groundhog Day. According to folklore, if it's cloudy when a groundhog emerges from its burrow on this day, then spring will come early; if it's sunny, the groundhog will supposedly see its shadow and retreat back into its burrow, and the winter weather will continue for six more weeks. But just who decided we should trust a Pennsylvania rodent with weather prognostication?
(via Miss Cellania)