With as much as 6 feet of new snow expected at the upper elevations of the Lake Tahoe region by Monday, skiers and snowboarders will likely receive the gift of fully open ski resorts this Christmas.Kirkwood Mountain Resort has been 100 percent open for several weeks, while Heavenly Mountain Resort and Sierra-at-Tahoe Ski Resort were just more than 90 percent open Friday, according to resort representatives.Heavenly was able to open the Boulder Lodge base area, the Boulder chairlift, Galaxy chairlift and North Bowl chairlift Friday, as well as the Groove Terrain Park, said Heavenly Mountain Resort spokesman Russ Pecoraro.He said …