Feb. 2, when, according to tradition, the groundhog comes out of hibernation: if it sees its shadow, it supposedly returns to its hole for six more weeks of winter weather
See Groundhog Day in American Heritage Dictionary 4
(groundˈhôgˌ, -hŏgˌ)
noun
February 2, on which according to popular legend the groundhog emerges from its burrow, prompting the prediction of an early spring if it does not see its shadow or six more weeks of winter if it does.