In the Northern Hemisphere, it always occurs around December 21 or 22. (In the Southern Hemisphere, it is around June 20 or 21.) This date is considered to be the first day of Winter. Here’s a chart that shows what day of the week the First Day of Winter is celebrated in Northern Hemisphere from 2012 – 2022:

http://www.primarygames.com/seasons/winter/when_is_winter.php