IIRC, January, February, and March are the best times to go. End of January or early February is good. For me to bring the family, the week in Feb. that has President's Day in it is great because the kids get that week off of school for "mid-winter break". The weekend of MLK Jr's birthday is good too, since that's when my and Troy's birthdays (the 14th) are...
However, I don't know that the conditions are the same there as they were the last I went there. We've been having weird weather in the northwest for the last few years. It's been snowing earlier than normal, and then it gets much warmer than normal, then goes back to snow again... don't know if it's doing that in the Sierra's as well.
