Timing of Spring trip to Sequoia NP

We plan to make a trip out West this spring. We would like to go in early spring like late April. Some of the places that we plan to tour are Sequoia NP, Kings Canyon NP, Yosemite NP, Lassen Volcanic NP and Redwood NP in CA. We will then take in the Oregon Coast. We want to go as early as we can but we want to be sure that we can get in without being blocked by snow to see the Sequoias and Redwoods. Will this time of year work? Thanks for your help.