Not planned
This site answers one question: when does it get cold enough to blow snow, and how long after that do resorts open? That matters where resorts make their own winter. Where it snows for real, the answer is probably just that the resort opens when it snows. I do not know whether this is worth having for the Rockies, the East or anywhere else.
We need somebody to find opening and closing dates, and to tell the pre-season opening apart from the full one where the two differ. That mostly means digging through Facebook feeds by hand. Sometimes the website has it. Minnesota shows what a region looks like once it is filled in.
If you want this for your mountains, say so and say what would make it useful. Email eazydp@gmail.com. Dates for resorts already listed are just as welcome.