Mild aside: As a native New Yorker, I kind of cringe to see it lumped into the Mid-Atlantic. There really isn't any part of New York, other than the city and LI, that's not as far north as CT (in New England). And the most mountainous part (think Gore, Whiteface) is at the same latitudes as VT / NH.
NY is an odd one. Northeastern NY hills have more in common with their New England Neighbors than PA, VA etc. But the south eastern ones are more like mid-atlantic. Think tuxedo Ridge.
And the western NY resorts (Holliday Valley etc) are more like the Midwest.
If I were dividing it up, I'd say:
Northeast ( New England, northeast NY, Quebec & the maritime provinces)
Mid-atlantic( southeast NY, NJ, PA, MD, VA)
Great Lakes (any resort that's in the great lakes drainage basin. Lake Champlain is not a great lake for this purpose (c: )
Southern Apalachia (WV, NC, AL,GA)
Bottom line is that state and provincal borders make lousy dividing lines. For instance, interior BC has much more in common with Rockies than PNW.