Observations -- Yes, they generally mean "closed"
Even in severe drought conditions, it is extremely unlikely that Tioga Pass (eastern edge of Yosemite would be open in mid-April). We have been in truly wild snow conditions in the mountains around Yosemite in April. On the other hand, the Dogwood Trees are often in bloom in April and they are a sight to behold -- looks like snow -- but isn't. Most of the park will remain open throughout the winter and early spring -- but you need to confirm road conditions daily.
US-50 is often subject to avalanche closures in April, but they are short-lived and the views around Tahoe are awesome.
Highway to the Sun in Glacier will not be open. Most of the routes you identified will be extremely "iffy" about being open that early in the spring.
Snowfall in the Cascades looks to be as heavy as normal this winter -- so I would bet you will find plenty of snow in those areas.
Mark