I live in Colorado and Breck and Key have a great park during April with mainly bluebird days. You might even catch a huge dump and shred some pow. I assume Mammoth, Whistler, and the Utah Mountains are sick as well.
Timberline on mt hood in oregon. park is real fun, can still snow a good amount, and no crowds really there until summer hits. and if you hit it right you can buy their spring pass for $100.
Mammoth for sure. The snowpack is really solid in April and everything is dialed in. Also, don't trip about lines, there won't be any, even on weekends and holidays.
I can say that in general utah can have some of its best skiing in april. Hell 2 years ago it was still snowing hard on closing day at brighton (probably like may 20th or so). If you want park its there, but really I don't understand why anyone would travel just to ski park