February 2 - Groundhog Day, a time when an animal, also known as a woodchuck, should emerge from his burrow after a long winter sleep to look for his shadow. If he sees his shadow, he regards it as an omen of six more weeks of bad weather and returns to his hole. If the day is cloudy and, hence, shadowless, he takes it as a sign of warm weather and stays above ground.
     February 2 has been recognized for centuries as a time when climatic changes are most pronounced.  The story begins with astronomers analyzing the skies, and it proceeds to our analyzing the behavior of a lowly creature that spends much of its time underground. The cross-quarter day should actually be called the beginning of spring. Daylight hours are noticeably longer. The Celts called it Imbolg or the feast of St. Brigit, who was born at sunrise on a threshold, representing the transition to spring. Brigit was god of fire and fertility for the Celts. Later, Christians dedicated the day to St. Brigit. Legend has it that she was born at sunrise on the threshold, neither inside or outside, thus representing the transition to spring. She had milk from a supernatural cow, dried her dresses on sunbeams, and everything around her glowed. In Scotland the cross-quarter date was celebrated as Candlemas, the legendary day when Christ was first presented in the temple. It was said that on Candlemas, the weather pattern for the year was apparent, as signified by their well-known rhyme which says that if “Candlemas is fair and clear, there will be two winters in the year”. 
     All weather watchers hoped for a cloudy day so the weather would improve. Weather prophets suggest a basis for this. Clear weather in early February usually results from cold, clear, stable air masses that are likely to persist, and there will be sustained cold temperatures. This theory of weather predicting became associated with hibernating animals, such as bears and hedgehogs, coming out of the ground to see if they cast shadows. 
       The first settlers in the area known today as Punxsutawney Pennsylvania, about 80 miles northeast of Pittsburgh, are responible for transforming  Imbolg, St. Brigit's Day, and Candlemas into what we refer to as Groundhog Day. The editor of a local paper publicized the custom back in 1886. The next year he formed the Punxsutawney Groundhog Club to observe the Punxsutawney groundhog. For many years the exact location of this teller of weather was kept a secret. In wasn’t until 1966 that Gobbler's Knob, a hill just outside of town, was disclosed as the groundhog's home. Since then there has been a great following of print, radio and television reporters present to flash the world about Punxsutawney Phil's prediction. Hordes of people travel to this little town to join the celebration during the first two days of February.
      More recently, Sun Prairie, Wisc., a town that is rich in G-hogs, declared itself to be the official "Groundhog Capital of the World" in 1950. Sun Prairie Jimmy and his predecessors have been on the job for over fifty years.
     If you are inclined to believe the prediction of a groundhog, you'll do better on February 2nd than believers did 20 years ago and before.  Whether you check a local critter, or rely on one of the more famous prognosticators like Punxsutawney Phil and Sun Prairie Jimmy, you have a 59 percent chance that the little guy will be right. 
    The National Climactic Data Center concludes that the animals' predictions since 1887 had an overall accuracy rate of just 39 percent. Over the last 20 years, however, they have become more skillful and have raised their average correctness by 20 percent. Nice going Phil and Jimmy!
Facts about the prognosticating rodent
According to the School of Veterinary Medicine, Cornell University:
* Groundhog and woodchuck are names of the same animal. Related to squirrels, 
they can climb trees, and  they can swim.
* The groundhog's internal clock is believed to be affected by changes in the amount of daylight. Hormonal responses change the production of melatonin and are thought to be the signal to wake up.

How much wood could a woodchuck chuck if a woodchuck could chuck wood? 
Answer to the classic question: About 700 pounds. A wildlife biologist measured the inside volume of a typical woodchuck burrow; he estimated that if the burrow were filled with wood instead of dirt, the industrious animal would have chucked about 700 pounds' worth. Of course, the woodchuck doesn't chuck wood. They will chew on wood, but they are not adept at moving timber, especially when compared to beavers.

The official site of Punxsutawney groundhog club

STORMFAX weather Almanac