Question: When does winter occur in the northern hemisphere?
Disambiguated questions and answers: question: What is the name of the day that winter occurs in the northern hemisphere?
On what date does winter occur in the northern hemisphere?
For what range of dates does Winter occur in the northern hemisphere?
answer: Winter Solstice
December 21st
December 21 - March 20
Natural Questions answer: December , January and February (from the Wikipedia article "Winter")