Lows can get rather chilly. The valley is at the 4,000 ft. elevation, and can get quite cold at night, about 45 to 50 degrees. During the spring, there is no telling what might happen. It can be rainy and cold one day, and then have cobalt-blue skies and 80 degrees the next. Winter is the exact opposite.
Storms come from out of nowhere, and it can rain and blow for a few days.
Yes, Yosemite is beautiful in winter, but be prepared. DO NOT go far into the backcountry after October 1st.