Is it too soon to be prepping for winter trips?

My summer season is coming to an end with going back to school for my senior year of university. I'm thinking of beginning to buy gear for the month of December I have off. I'm set as far as 3 season goes but what should be at the top of the list for beginning to go below freezing/light snow. I'll be buying a new tent soon to switch out my tarp. Thinking Bowfin 2 for free standing purpose. Basically, what do I need to extend from 3 seasons to 4

Location: Yosemite in December

Not asking for a pack shakedown I am asking what gear needs to be added for snow to remain safe. https://lighterpack.com/r/329a0p