5月底6月初是最Popular Season

因這時，大部分都化了，瀑布最大，最壯觀. If you go around May 25 this year, you may see moonbow in Yosemite Falls.

In the early April, Tioga pass will not be open. You have to drive 150 miles more to go Death valley from Yosemite. You have to go through ugly, dirty country road 99 instead of scenery roads 120 & 395 and miss Mono lake and many beautiful scenes in high elevation Yosemite Park.  

http://www.nps.gov/yose/planyourvisit/tiogaopen.htm