On Saturday, 21 athletes died during the fourth annual Yellow River Stone Forest Park 100K, a race held in Gansu, China. The weather turned bad about 15 miles in and more than 6,000 feet above sea level, after the leading runners left the second checkpoint and started an exposed 3,000-foot climb. Suddenly, the route was hammered with a mess of freezing rain and hail, and temperatures plummeted to near freezing at higher elevations. “At the bottom of the mountain there was already wind and rain, and the higher you climbed the bigger the rain and wind got,” blogged Zhang Xiaotao, a racer who survived the storm. “Halfway up, the rain started to mix with hail and kept smashing into my face, and my eyes started getting obscured and blurry. A few places, you couldn’t make out the route clearly.” Another racer he came across on the trail, he wrote, “had begun to shake all over his body.”