groundhog day † DCHP-1 (pre-1967)
February 2, the day on which the groundhog (def. 1) is supposed to come out of his burrow to determine the length of time remaining till spring; the legend being that he will anticipate an additional six weeks of hard winter if he should see his shadow and a relatively mild period if he should not.
See also: groundhog (def. 1)