Over the last couple of decades, the ski industry has waged a public relations campaign aimed at “the back yard syndrome.’’ The message: if you don’t see snow at home, you’ll find it on the slopes, despite the lack of natural snowfall. The only constant is cold weather. A week or so of snowmaking temperatures in the mountains can turn the toughest snow droughts into winter wonderlands. But after a hopeful sweeping storm around Halloween turned much of New England white, the winter wimped out and the Christmas vacation period found many ski resorts with only marginal terrain open, and business slower than usual for what traditionally is the kick off to winter.