The date falls halfway between the winter solstice and spring equinox, a period of significance in European festivals and religious celebrations, experts explain.
German immigrants brought the custom to the U.S. in the 18th and 19th centuries. In Europe, animals like hedgehogs and badgers were used to predict spring weather.
In Pennsylvania, folks chose the groundhog.
Groundhog day explained: Why this furry forecaster still matters
Hidden meanings in simple things.