By mid to late April Spring is in full swing in Yosemite. The entire park is vibrant with color and that fresh Spring smell.
The Upper and Lower Yosemite Falls will be flowing strong, and Bridalveil Falls will be super powerful as well.
In April, your chance of seeing a rainbow waterfall is actually quite high, because the water volume from the waterfalls is intense.
During the week you will likely have lots of room and will be able to really slow down and enjoy the views.