On Feb. 2 a woodchuck (groundhog) emerges or is hauled out into the light. If it sees its shadow there will be 6 weeks of winter; otherwise, an early spring. This amazing
prediction depends entirely on whether it is cloudy (no shadow), or sunny (shadow).
No groundhog is needed! With our own human eyes and brains we can detect whether we sense sunshine and see shadows. Then we alone make the meteorological forecast (which is also nonsense but that's another story).
Sorry, Punxsutawney, it is just SHADOW OR NO SHADOW DAY.