The Groundhog Day celebration is rooted in a Celtic tradition that says if a hibernating animal casts a shadow on February 2, the Pagan holiday of Imbolc, winter will last another six weeks. If no shadow was seen, legend says spring would come early.
The ties in Pennsylvania may actually come from Germans, when clear skies on Candlemas Day, February 2, were said to herald cold weather ahead. In Germany, the tradition morphed into a myth that if the sun came out on Candlemas, a hedgehog would cast its shadow, predicting snow all the way into May. When German immigrants settled in Pennsylvania, they transferred the tradition onto local fauna, replacing hedgehogs with groundhogs.
In reality, the Inner Circle makes the determination as to whether or not Phil supposedly sees his shadow several days in advance of the ceremony and does not make its criteria public; this discontinuity was made obvious in the 2016 ceremonies, in which Phil “saw his shadow” and thus predicted six more weeks of winter despite overcast skies and a significant snowstorm bearing down on the town that day.