An obnoxious TV weatherman (Murray) is trapped in a time loop, living the same day (Groundhog Day) over and over again in the small town of Punxsutawney, Pennsylvania (which, both in the movie and in real life, holds a major celebration for Groundhog Day). He rapidly takes advantage of this knowledge of the same external events which repeat from day to day to fancy an extravagant life of pleasures, money, and seduced women. But when he attempts to seduce in this way his colleague (MacDowell) he meets with repeated failures and realize that his "powers" enable him only to mere futilities and that he can construct nothing out of it. After useless attempts to kill himself out of his frustration, he gradually finds a goal to his trapped life as a benefactor to others. He cannot, in a single day, bring others to fulfill his needs but he can learn and educate himself as a better man on a daily basis. He then develops many talents and knowledge of others which, in return, serve him as an appreciated and loved man and eventually allow him to escape the magic spell and awaken a reciprocal love with his beloved one.
The movie is a deep tale on the value of what one's knowledge and qualities are worth to others, as compared to their use for selfish and egocentric satisfaction.
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From the reviews
"An example of an exceptional work of moral fiction is the apparently minor comedy, Groundhog Day, which shows us a character who has to be exiled from normal life so he can discover that he is in exile from himself." 
"If I had to nominate one movie as my favourite I think it would be Groundhog Day. It is a comedy, a fantasy, a romance and a moral tale of a cynical man's redemption." 
Development of the movieThe original script started in the middle. They were worried that the audience would feel cheated without seeing how he got there. In the original script the author envisioned the character going through the same day for thousands of years. "It's about doing what you can do in the moment to make things better." The love story was less developed in the original script than in the final movie.
The location for most of the shooting was not actually in Punxsutawney. In Punxsutawney the celebration takes place outside of town. While scouting they pulled into Woodstock, Illinois. "It just seemed right."
Some of the filming was done when it was quite cold. The town folk brought out heaters to help the crew. They started filming in winter and ended in spring.