Though the trail up to the rock can be clear of snow by early May, in years past the granite top would still be covered because it faces north, said park spokeswoman Kari Cobb.
The trail traditionally opens on May 23, but because of the low snowpack this year, park visitors can begin scaling Half Dome's steel cables and wood planks on Sunday.
Though the regular season's allotment of 300 hiking permits were already awarded in March, an additional 50 permits per day will be issued two days in advance for park visitors who enter a lottery at recreation.gov. Visitors can apply for a permit between midnight and 1 p.m. the same day. Results are posted the next day at 6 a.m.
Half Dome is one of the Yosemite's most iconic features and the hike can be an all-day experience if started from the beginning of the 17-mile trail in Yosemite Valley. Hikers ascend 4,800 feet, including a final steep climb for which steel cables and wooden planks hammered into the rockside support the ascent to the 8,800-foot-high summit.
In another sign of the state's parched times, Yosemite also opened Glacier Point Road in March -- the first time it's opened before the traditional May date in 20 years.