Two Summit County ski areas, Arapahoe Basin and Copper Mountain, began snowmaking operations in the wee hours of Tuesday morning. Arapahoe Basin, which was the first Colorado ski area to open the past three seasons, began making snow on the High Noon run, which is always the first to open there. Copper Mountain began making snow on a trail that will be used by the U.S. Ski Team for early season race training when snowmaking on that run is complete. Arapahoe Basin is usually the first in Colorado to welcome skiers and has failed to open in October only once in the past 21 seasons. It opened Oct. 17 in 2021, Oct. 23 in 2022  and Oct. 29 in 2023. Related Articles Outdoors | When every Colorado ski resort plans to open for the 2024-25 season Snowmakers monitor “wet bulb temperature,” a formula which takes into account humidity in relation to temperature, to determine when they can make snow. “Dry air, or low humidity, helps us get a lower wet bulb temperature,” Keystone spokeswoman Shayna Silverman said. “Humidity isn’t helpful for us to make snow, it’s too wet. We get better quality, longer-lasting flakes when air is drier. This morning around 4 a.m., we saw ambient temperatures in the mid-30s and low humidity. This yielded a 25-27 degrees wet bulb, which is exactly what we’re looking for.” Keystone had conditions that would have allowed for snowmaking but elected to hold off. “We could have made snow,” said Keystone spokesman Max Winter. “Temperatures dropped low enough, but we were looking at the highs (temperatures) over the next few days. From a sustainability standpoint, it didn’t feel like that snow would stick around.” Arapahoe Basin, Keystone and Loveland plan to open as soon as conditions allow. Copper Mountain plans to open on Nov. 8. Subscribe to our weekly newsletter, The Adventurist, to get outdoors news sent straight to your inbox.