We camped in Sequoia back in 1993, at the end of May and half the camp ground was closed due to snow.
That was when the kids were little and we were camping in a tent.
It was quite cold and spectacular, I will definitely go back, just would plan for later in the year.
It was dark as we were going up the switch-backs to get to the park, my son was up from with me, the "girls" were in the back of the van sleeping and we woke them up with all the "wows" we were exclaiming as we lit up trees that were wider than the stuff around home are tall
-Brian