Groundhog Day!

You may not know this, but Groundhog Day is an ancient tradition predating even Roman times. Groundhog day was actually referred to as Candlemas Day. Candlemas Day was the day priests blessed Candles, or said a Mass for them. Candles were used for light at the time and you would want it to last so you could conserve them. As this is the half-point in winter, this makes sense. Longer nights in winter, you need more candles.
So where oh where did our own Punxsutawney Phil come in?

Well, consider the song Old English recited:
If Candlemas be fair and bright,
Come, Winter, have another flight;
If Candlemas brings clouds and rain,
Go Winter, and come not again.

Scottish had their own version and then it passed to Romans who conquered northern lands and this thought/tradition/way to predict nature landed in Early Germany. These Germans predicted that if the sun was shining on Candlemas Day, then an early animal leaving its hibernation, like say... a hedgehog (and then a groundhog) would see its shadow. They believed this animal was smart enough to know this light meant a second winter.
You may know, Pennsylvania had a huge influx of German immigrants settle here. They carried their traditions, language and culture to this area and thanks to the Punxsutawney Groundhog Club ... our tradition of checking in with Punxsutawney Phil began.
Also, farmers knew if they were only half way through their hay they were ok... since this is the half way mark of Winter. 

Just in case you were wondering. So bless your candles, check your hay and just so you know, Phil saw his shadow today.
That's right, students. Six. more. weeks.

Thanks for the info
http://www.groundhog.org/groundhog-day/history/