Nancy, there is no reasonable way to make any predictions as to how heavy or light the snow will be by April. Right now, we're pretty close to the average. But that can all change in the next 3 months.
Mid-June is the marginal time. Right now, I would assume you will encounter icy spots coming down the 99 switchbacks. You will have to watch the trail conditions reports just before you start the hike. If the switchbacks aren't in use by that time, you should bring an ice axe and know how to use it, so you can get down the chute.
