LAST FEBRUARY, Italian alpinist Simone Moro led a team to the top of Nanga Parbat, in the western Himalayas, leaving K2 as the only 8,000- meter peak without a winter ascent. “There’s a reason for that,” says Garrett Madison, who operates Madison Mountaineering and has climbed K2 once. “It’s by far the most challenging.” Only 386 people have made it to thetop of the 28,251- foot mountain, compared with 7,604 on Mount Everest; one person dies for every four who summit. So far, three winter attempts have failed, felled by biting temperatures, minimal daylight, erratic storms, and teetering seracs. Moro would be a good bet to finally succeed—he’s notched four first winter ascents of 8,000-meter peaks—were itnot for one thing: in 2011, his wife dreamed he died on K2, and…