Groundhog Day is an annual holiday celebrated on February 2^[1] in the United States and Canada on which folklore tells if a groundhog emerges from its burrow and fails to see its shadow because the weather is cloudy, winter will soon end.
If on the other hand, it is sunny and the groundhog sees its shadow, the groundhog will supposedly retreat into its burrow, and winter will continue for six more weeks.^[2]

The holiday, which began as a Pennsylvania German custom in southeastern and central Pennsylvania in the 18th and 19th centuries, has its origins in ancient European weather lore, wherein a badger or sacred bear is the prognosticator as opposed to a groundhog.^[1]
The holiday also bears some similarities to the medieval Catholic holiday of Candlemas^[3]
It also bears similarities to the Pagan festival of Imbolc, the seasonal turning point of the Celtic year, which is celebrated on February 1 and also involves weather prognostication.

Wikipedia

1. υ π ά ρ χ ε ι μέρα της μαρμότας!
2. υπάρχει κι από παλιά...
3. πόση καταχνιά έχει φάει στη μάπα όποιος ψάχνει σε μαρμοτοχρησμούς
να βρει ελπίδα για άνοιξη?
4. σήμερα πάντως είδα μια ανθισμένη αμυγδαλιά...