ARAPAHOE BASIN — The fanatic Breckenridge snowboarder known in these parts as Nate Dogggg claimed the first chair for the 23rd consecutive year Friday when Arapahoe Basin opened for the season, but he wasn’t any more stoked about his annual ritual than a woman who rode up on the second chair behind him and his posse. When Gretchen Pleshaw arrived 12 hours earlier, on Thursday night, to get in line, it was snowing heavily at “The Legend” and an impromptu dance party was in progress on the deck at the lodge, complete with a disco ball and champagne.