It has its roots in an ancient Celtic celebration called Imbolog. The date is one of the four quarter days of the year, the midpoints between the spring and fall equinoxes and the summer and winter solstice.  The day is known as Groundhog Day in North America. It is related to Candlemas and Imbolc.
Tradition states that one must observe a groundhog's burrow on this day. If the groundhog emerges and fails to see its shadow because the weather is cloudy, winter will soon end; however, if the groundhog sees its shadow because the weather is bright and clear, it will be frightened and run back into its hole, and the winter will continue for six more weeks. Certain small towns have celebrated meteorological groundhogs, such as Punxsutawney Phil and Wiarton Willie.
The U.S. tradition derived from a Scottish couplet:
There is also a romantic comedy called Groundhog Day.