Move somewhere drier and warmer. Nothing improved my warmth on the hill like moving to Colorado...
In all seriousness, on those never-coming-in days in NE, if you ask 100 coaches, you're going to find 95 different answers. It's especially bad if you are going to haul gates/set a course/ski intensively for a portion of the day and stand around not really moving for another portion of the day ... just brutal.
If you're just skiing all day, it's a bit easier. I'd make sure you have a base layer, and at least 2 midlayers, and ski with/stash a pack with different midlayer options as weather changes. Optimize versatility, with pit zips and leg zips as much as possible.
Or, you can invest in electronic heat, including for your core. I haven't used skiing, but if it works for people doing manual labor outside in the winter, it'll work for skiing too. We had a few for our field crews in New England; I forget brand, but they'd last 6-8 hours in the field pretty easily. Even some crusty academy coaches are moving in this direction (though they pretend they're still hard guys).