Friday is the first day of winter — but are we counting wrong?

So what makes this the first day of winter, anyway?
It’s not the coldest or snowiest day. It’s not the first cold day. In weather terms, Dec. 21 is an in-between day — pretty cold on average, somewhat snowy too, but without any real reason to feel as though it’s the start of anything.
It’s not the day when you start needing winter tires or when you start wearing a winter coat.
Lakes are freezing over but are not yet safe to walk on; skiing is still iffy; outdoor ska