Onion snow comes far deeper from history than pennsylvania. Most likely Germany or Bavaria as it once was. France also has the legend. It was refered to as the Three Ice Men. The legend originated around three Catholic Saints. Research it if you like.
Anther neat local legend, Kunigund day. March 3rd when the frost will go no deeper. And instead will turn around and start coming out of the ground. My grandfather said you don’t plant onions until after Kunigund day.