The history of Groundhog Day is linked to winter's midpoint.
We are about halfway between the winter solstice, which came Dec. 21, and the vernal equinox, which comes March 20 this year, a point known as a cross-quarter day. (Halloween is another cross-quarter day we still celebrate.)
Well before Punxsutawney Phil became America’s foremost groundhog meteorologist in 1887, superstition held that the weather on Feb. 2 was a hint of what was to come as spring approached.
Ancient Celts called the holiday Imbolc or Brigantia, according to the Old Farmer's Almanac. It became known as Candlemas "from the candles lit that day in churches to celebrate the presentation of the Christ Child in the temple of Jerusalem."
Superstition held that sunshine that day indicated a stormy and cold second half of winter was ahead, while cloudy skies foretold an early spring. On Groundhog Day, the superstition is the same -- a Pennsylvania groundhog named Punxsutawney Phil is just the one who does the interpreting.
Phil became famous thanks to Clymer H. Freas, city editor of the Punxsutawney Spirit newspaper, who began boasting of the groundhog's forecasting prowess in 1887, according to the National Centers for Environmental Information.
According to the Punxsutawney Groundhog Club, it is rare that Phil does not see his shadow -- it has happened only 18 times since 1887. That indicates a more than 85 percent chance Phil will predict six more weeks of winter on Thursday.
According to the human forecasters at NCEI, Phil "shows no predictive skill" when comparing average temperatures in February and March and whether the groundhog sees his shadow.