Ski resort operators in northern New England are looking past their zip lines and water parks to the winter ahead and like what they see: The pent-up demand for skiing after last year’s snow drought is producing brisk sales of early-bird season passes. New Hampshire’s Loon Mountain reports sales up 20 percent over last year. Maine’s Sunday River reports season pass sales are up 10 percent from last year. Vermont’s Magic Mountain in the month of April sold half of last year’s total season pass sales. But winter revenues are no longer the make-it-or-break-it barometer for New England resorts, which pioneered summer attractions like zip lines, water parks and mountain coasters. Moose tours at Maine ski areas are in the mix as well.