On February 2, 1887, Groundhog Day, featuring a rodent meteorologist,
was celebrated for the first time at Gobbler’s Knob in Punxsutawney,
Pennsylvania. According to tradition, if a groundhog comes out of its
hole on this day and sees its shadow, it gets scared and runs back into
its burrow, predicting six more weeks of winter weather; no shadow
means an early spring.

Groundhog Day has its roots in the ancient Christian tradition called
Candlemas, when clergy would bless and distribute candles needed
for winter. The candles represented how long and cold the winter
would be. Germans expanded on this concept by selecting an animal–
the hedgehog–as a means of predicting weather. Once they came to
America, German settlers in Pennsylvania continued the tradition,
although they switched from hedgehogs to groundhogs, which were
plentiful in the Keystone State.

Groundhog Day is a popular tradition celebrated in Canada and the United
States on February 2. It derives from the Pennsylvania Dutch superstition
that if a groundhog (Marmota monax), also called "woodchuck";  emerging
from its burrow on this day sees a shadow due to clear weather, it will
retreat to its den and winter will persist for six more weeks, and if it does
not see its shadow because of cloudiness, spring will arrive early.